1//! Slice management and manipulation.
2//!
3//! For more details see [`std::slice`].
4//!
5//! [`std::slice`]: ../../std/slice/index.html
6
7#![stable(feature = "rust1", since = "1.0.0")]
8
9use crate::clone::TrivialClone;
10use crate::cmp::Ordering::{self, Equal, Greater, Less};
11use crate::intrinsics::{exact_div, unchecked_sub};
12use crate::mem::{self, MaybeUninit, SizedTypeProperties};
13use crate::num::NonZero;
14use crate::ops::{OneSidedRange, OneSidedRangeBound, Range, RangeBounds, RangeInclusive};
15use crate::panic::const_panic;
16use crate::simd::{self, Simd};
17use crate::ub_checks::assert_unsafe_precondition;
18use crate::{fmt, hint, ptr, range, slice};
19
20#[unstable(
21 feature = "slice_internals",
22 issue = "none",
23 reason = "exposed from core to be reused in std; use the memchr crate"
24)]
25#[doc(hidden)]
26/// Pure Rust memchr implementation, taken from rust-memchr
27pub mod memchr;
28
29#[unstable(
30 feature = "slice_internals",
31 issue = "none",
32 reason = "exposed from core to be reused in std;"
33)]
34#[doc(hidden)]
35pub mod sort;
36
37mod ascii;
38mod cmp;
39pub(crate) mod index;
40mod iter;
41mod raw;
42mod rotate;
43mod specialize;
44
45#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
46pub use ascii::EscapeAscii;
47#[unstable(feature = "str_internals", issue = "none")]
48#[doc(hidden)]
49pub use ascii::is_ascii_simple;
50#[stable(feature = "slice_get_slice", since = "1.28.0")]
51pub use index::SliceIndex;
52#[unstable(feature = "slice_range", issue = "76393")]
53pub use index::{range, try_range};
54#[unstable(feature = "array_windows", issue = "75027")]
55pub use iter::ArrayWindows;
56#[stable(feature = "slice_group_by", since = "1.77.0")]
57pub use iter::{ChunkBy, ChunkByMut};
58#[stable(feature = "rust1", since = "1.0.0")]
59pub use iter::{Chunks, ChunksMut, Windows};
60#[stable(feature = "chunks_exact", since = "1.31.0")]
61pub use iter::{ChunksExact, ChunksExactMut};
62#[stable(feature = "rust1", since = "1.0.0")]
63pub use iter::{Iter, IterMut};
64#[stable(feature = "rchunks", since = "1.31.0")]
65pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
66#[stable(feature = "slice_rsplit", since = "1.27.0")]
67pub use iter::{RSplit, RSplitMut};
68#[stable(feature = "rust1", since = "1.0.0")]
69pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
70#[stable(feature = "split_inclusive", since = "1.51.0")]
71pub use iter::{SplitInclusive, SplitInclusiveMut};
72#[stable(feature = "from_ref", since = "1.28.0")]
73pub use raw::{from_mut, from_ref};
74#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
75pub use raw::{from_mut_ptr_range, from_ptr_range};
76#[stable(feature = "rust1", since = "1.0.0")]
77pub use raw::{from_raw_parts, from_raw_parts_mut};
78
79/// Calculates the direction and split point of a one-sided range.
80///
81/// This is a helper function for `split_off` and `split_off_mut` that returns
82/// the direction of the split (front or back) as well as the index at
83/// which to split. Returns `None` if the split index would overflow.
84#[inline]
85fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
86 use OneSidedRangeBound::{End, EndInclusive, StartInclusive};
87
88 Some(match range.bound() {
89 (StartInclusive, i: usize) => (Direction::Back, i),
90 (End, i: usize) => (Direction::Front, i),
91 (EndInclusive, i: usize) => (Direction::Front, i.checked_add(1)?),
92 })
93}
94
95enum Direction {
96 Front,
97 Back,
98}
99
100impl<T> [T] {
101 /// Returns the number of elements in the slice.
102 ///
103 /// # Examples
104 ///
105 /// ```
106 /// let a = [1, 2, 3];
107 /// assert_eq!(a.len(), 3);
108 /// ```
109 #[lang = "slice_len_fn"]
110 #[stable(feature = "rust1", since = "1.0.0")]
111 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
112 #[rustc_no_implicit_autorefs]
113 #[inline]
114 #[must_use]
115 pub const fn len(&self) -> usize {
116 ptr::metadata(self)
117 }
118
119 /// Returns `true` if the slice has a length of 0.
120 ///
121 /// # Examples
122 ///
123 /// ```
124 /// let a = [1, 2, 3];
125 /// assert!(!a.is_empty());
126 ///
127 /// let b: &[i32] = &[];
128 /// assert!(b.is_empty());
129 /// ```
130 #[stable(feature = "rust1", since = "1.0.0")]
131 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
132 #[rustc_no_implicit_autorefs]
133 #[inline]
134 #[must_use]
135 pub const fn is_empty(&self) -> bool {
136 self.len() == 0
137 }
138
139 /// Returns the first element of the slice, or `None` if it is empty.
140 ///
141 /// # Examples
142 ///
143 /// ```
144 /// let v = [10, 40, 30];
145 /// assert_eq!(Some(&10), v.first());
146 ///
147 /// let w: &[i32] = &[];
148 /// assert_eq!(None, w.first());
149 /// ```
150 #[stable(feature = "rust1", since = "1.0.0")]
151 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
152 #[inline]
153 #[must_use]
154 pub const fn first(&self) -> Option<&T> {
155 if let [first, ..] = self { Some(first) } else { None }
156 }
157
158 /// Returns a mutable reference to the first element of the slice, or `None` if it is empty.
159 ///
160 /// # Examples
161 ///
162 /// ```
163 /// let x = &mut [0, 1, 2];
164 ///
165 /// if let Some(first) = x.first_mut() {
166 /// *first = 5;
167 /// }
168 /// assert_eq!(x, &[5, 1, 2]);
169 ///
170 /// let y: &mut [i32] = &mut [];
171 /// assert_eq!(None, y.first_mut());
172 /// ```
173 #[stable(feature = "rust1", since = "1.0.0")]
174 #[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
175 #[inline]
176 #[must_use]
177 pub const fn first_mut(&mut self) -> Option<&mut T> {
178 if let [first, ..] = self { Some(first) } else { None }
179 }
180
181 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
182 ///
183 /// # Examples
184 ///
185 /// ```
186 /// let x = &[0, 1, 2];
187 ///
188 /// if let Some((first, elements)) = x.split_first() {
189 /// assert_eq!(first, &0);
190 /// assert_eq!(elements, &[1, 2]);
191 /// }
192 /// ```
193 #[stable(feature = "slice_splits", since = "1.5.0")]
194 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
195 #[inline]
196 #[must_use]
197 pub const fn split_first(&self) -> Option<(&T, &[T])> {
198 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
199 }
200
201 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
202 ///
203 /// # Examples
204 ///
205 /// ```
206 /// let x = &mut [0, 1, 2];
207 ///
208 /// if let Some((first, elements)) = x.split_first_mut() {
209 /// *first = 3;
210 /// elements[0] = 4;
211 /// elements[1] = 5;
212 /// }
213 /// assert_eq!(x, &[3, 4, 5]);
214 /// ```
215 #[stable(feature = "slice_splits", since = "1.5.0")]
216 #[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
217 #[inline]
218 #[must_use]
219 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
220 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
221 }
222
223 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
224 ///
225 /// # Examples
226 ///
227 /// ```
228 /// let x = &[0, 1, 2];
229 ///
230 /// if let Some((last, elements)) = x.split_last() {
231 /// assert_eq!(last, &2);
232 /// assert_eq!(elements, &[0, 1]);
233 /// }
234 /// ```
235 #[stable(feature = "slice_splits", since = "1.5.0")]
236 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
237 #[inline]
238 #[must_use]
239 pub const fn split_last(&self) -> Option<(&T, &[T])> {
240 if let [init @ .., last] = self { Some((last, init)) } else { None }
241 }
242
243 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
244 ///
245 /// # Examples
246 ///
247 /// ```
248 /// let x = &mut [0, 1, 2];
249 ///
250 /// if let Some((last, elements)) = x.split_last_mut() {
251 /// *last = 3;
252 /// elements[0] = 4;
253 /// elements[1] = 5;
254 /// }
255 /// assert_eq!(x, &[4, 5, 3]);
256 /// ```
257 #[stable(feature = "slice_splits", since = "1.5.0")]
258 #[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
259 #[inline]
260 #[must_use]
261 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
262 if let [init @ .., last] = self { Some((last, init)) } else { None }
263 }
264
265 /// Returns the last element of the slice, or `None` if it is empty.
266 ///
267 /// # Examples
268 ///
269 /// ```
270 /// let v = [10, 40, 30];
271 /// assert_eq!(Some(&30), v.last());
272 ///
273 /// let w: &[i32] = &[];
274 /// assert_eq!(None, w.last());
275 /// ```
276 #[stable(feature = "rust1", since = "1.0.0")]
277 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
278 #[inline]
279 #[must_use]
280 pub const fn last(&self) -> Option<&T> {
281 if let [.., last] = self { Some(last) } else { None }
282 }
283
284 /// Returns a mutable reference to the last item in the slice, or `None` if it is empty.
285 ///
286 /// # Examples
287 ///
288 /// ```
289 /// let x = &mut [0, 1, 2];
290 ///
291 /// if let Some(last) = x.last_mut() {
292 /// *last = 10;
293 /// }
294 /// assert_eq!(x, &[0, 1, 10]);
295 ///
296 /// let y: &mut [i32] = &mut [];
297 /// assert_eq!(None, y.last_mut());
298 /// ```
299 #[stable(feature = "rust1", since = "1.0.0")]
300 #[rustc_const_stable(feature = "const_slice_first_last", since = "1.83.0")]
301 #[inline]
302 #[must_use]
303 pub const fn last_mut(&mut self) -> Option<&mut T> {
304 if let [.., last] = self { Some(last) } else { None }
305 }
306
307 /// Returns an array reference to the first `N` items in the slice.
308 ///
309 /// If the slice is not at least `N` in length, this will return `None`.
310 ///
311 /// # Examples
312 ///
313 /// ```
314 /// let u = [10, 40, 30];
315 /// assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());
316 ///
317 /// let v: &[i32] = &[10];
318 /// assert_eq!(None, v.first_chunk::<2>());
319 ///
320 /// let w: &[i32] = &[];
321 /// assert_eq!(Some(&[]), w.first_chunk::<0>());
322 /// ```
323 #[inline]
324 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
325 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
326 pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]> {
327 if self.len() < N {
328 None
329 } else {
330 // SAFETY: We explicitly check for the correct number of elements,
331 // and do not let the reference outlive the slice.
332 Some(unsafe { &*(self.as_ptr().cast_array()) })
333 }
334 }
335
336 /// Returns a mutable array reference to the first `N` items in the slice.
337 ///
338 /// If the slice is not at least `N` in length, this will return `None`.
339 ///
340 /// # Examples
341 ///
342 /// ```
343 /// let x = &mut [0, 1, 2];
344 ///
345 /// if let Some(first) = x.first_chunk_mut::<2>() {
346 /// first[0] = 5;
347 /// first[1] = 4;
348 /// }
349 /// assert_eq!(x, &[5, 4, 2]);
350 ///
351 /// assert_eq!(None, x.first_chunk_mut::<4>());
352 /// ```
353 #[inline]
354 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
355 #[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
356 pub const fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
357 if self.len() < N {
358 None
359 } else {
360 // SAFETY: We explicitly check for the correct number of elements,
361 // do not let the reference outlive the slice,
362 // and require exclusive access to the entire slice to mutate the chunk.
363 Some(unsafe { &mut *(self.as_mut_ptr().cast_array()) })
364 }
365 }
366
367 /// Returns an array reference to the first `N` items in the slice and the remaining slice.
368 ///
369 /// If the slice is not at least `N` in length, this will return `None`.
370 ///
371 /// # Examples
372 ///
373 /// ```
374 /// let x = &[0, 1, 2];
375 ///
376 /// if let Some((first, elements)) = x.split_first_chunk::<2>() {
377 /// assert_eq!(first, &[0, 1]);
378 /// assert_eq!(elements, &[2]);
379 /// }
380 ///
381 /// assert_eq!(None, x.split_first_chunk::<4>());
382 /// ```
383 #[inline]
384 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
385 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
386 pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
387 let Some((first, tail)) = self.split_at_checked(N) else { return None };
388
389 // SAFETY: We explicitly check for the correct number of elements,
390 // and do not let the references outlive the slice.
391 Some((unsafe { &*(first.as_ptr().cast_array()) }, tail))
392 }
393
394 /// Returns a mutable array reference to the first `N` items in the slice and the remaining
395 /// slice.
396 ///
397 /// If the slice is not at least `N` in length, this will return `None`.
398 ///
399 /// # Examples
400 ///
401 /// ```
402 /// let x = &mut [0, 1, 2];
403 ///
404 /// if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
405 /// first[0] = 3;
406 /// first[1] = 4;
407 /// elements[0] = 5;
408 /// }
409 /// assert_eq!(x, &[3, 4, 5]);
410 ///
411 /// assert_eq!(None, x.split_first_chunk_mut::<4>());
412 /// ```
413 #[inline]
414 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
415 #[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
416 pub const fn split_first_chunk_mut<const N: usize>(
417 &mut self,
418 ) -> Option<(&mut [T; N], &mut [T])> {
419 let Some((first, tail)) = self.split_at_mut_checked(N) else { return None };
420
421 // SAFETY: We explicitly check for the correct number of elements,
422 // do not let the reference outlive the slice,
423 // and enforce exclusive mutability of the chunk by the split.
424 Some((unsafe { &mut *(first.as_mut_ptr().cast_array()) }, tail))
425 }
426
427 /// Returns an array reference to the last `N` items in the slice and the remaining slice.
428 ///
429 /// If the slice is not at least `N` in length, this will return `None`.
430 ///
431 /// # Examples
432 ///
433 /// ```
434 /// let x = &[0, 1, 2];
435 ///
436 /// if let Some((elements, last)) = x.split_last_chunk::<2>() {
437 /// assert_eq!(elements, &[0]);
438 /// assert_eq!(last, &[1, 2]);
439 /// }
440 ///
441 /// assert_eq!(None, x.split_last_chunk::<4>());
442 /// ```
443 #[inline]
444 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
445 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
446 pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])> {
447 let Some(index) = self.len().checked_sub(N) else { return None };
448 let (init, last) = self.split_at(index);
449
450 // SAFETY: We explicitly check for the correct number of elements,
451 // and do not let the references outlive the slice.
452 Some((init, unsafe { &*(last.as_ptr().cast_array()) }))
453 }
454
455 /// Returns a mutable array reference to the last `N` items in the slice and the remaining
456 /// slice.
457 ///
458 /// If the slice is not at least `N` in length, this will return `None`.
459 ///
460 /// # Examples
461 ///
462 /// ```
463 /// let x = &mut [0, 1, 2];
464 ///
465 /// if let Some((elements, last)) = x.split_last_chunk_mut::<2>() {
466 /// last[0] = 3;
467 /// last[1] = 4;
468 /// elements[0] = 5;
469 /// }
470 /// assert_eq!(x, &[5, 3, 4]);
471 ///
472 /// assert_eq!(None, x.split_last_chunk_mut::<4>());
473 /// ```
474 #[inline]
475 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
476 #[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
477 pub const fn split_last_chunk_mut<const N: usize>(
478 &mut self,
479 ) -> Option<(&mut [T], &mut [T; N])> {
480 let Some(index) = self.len().checked_sub(N) else { return None };
481 let (init, last) = self.split_at_mut(index);
482
483 // SAFETY: We explicitly check for the correct number of elements,
484 // do not let the reference outlive the slice,
485 // and enforce exclusive mutability of the chunk by the split.
486 Some((init, unsafe { &mut *(last.as_mut_ptr().cast_array()) }))
487 }
488
489 /// Returns an array reference to the last `N` items in the slice.
490 ///
491 /// If the slice is not at least `N` in length, this will return `None`.
492 ///
493 /// # Examples
494 ///
495 /// ```
496 /// let u = [10, 40, 30];
497 /// assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());
498 ///
499 /// let v: &[i32] = &[10];
500 /// assert_eq!(None, v.last_chunk::<2>());
501 ///
502 /// let w: &[i32] = &[];
503 /// assert_eq!(Some(&[]), w.last_chunk::<0>());
504 /// ```
505 #[inline]
506 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
507 #[rustc_const_stable(feature = "const_slice_last_chunk", since = "1.80.0")]
508 pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]> {
509 // FIXME(const-hack): Without const traits, we need this instead of `get`.
510 let Some(index) = self.len().checked_sub(N) else { return None };
511 let (_, last) = self.split_at(index);
512
513 // SAFETY: We explicitly check for the correct number of elements,
514 // and do not let the references outlive the slice.
515 Some(unsafe { &*(last.as_ptr().cast_array()) })
516 }
517
518 /// Returns a mutable array reference to the last `N` items in the slice.
519 ///
520 /// If the slice is not at least `N` in length, this will return `None`.
521 ///
522 /// # Examples
523 ///
524 /// ```
525 /// let x = &mut [0, 1, 2];
526 ///
527 /// if let Some(last) = x.last_chunk_mut::<2>() {
528 /// last[0] = 10;
529 /// last[1] = 20;
530 /// }
531 /// assert_eq!(x, &[0, 10, 20]);
532 ///
533 /// assert_eq!(None, x.last_chunk_mut::<4>());
534 /// ```
535 #[inline]
536 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
537 #[rustc_const_stable(feature = "const_slice_first_last_chunk", since = "1.83.0")]
538 pub const fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
539 // FIXME(const-hack): Without const traits, we need this instead of `get`.
540 let Some(index) = self.len().checked_sub(N) else { return None };
541 let (_, last) = self.split_at_mut(index);
542
543 // SAFETY: We explicitly check for the correct number of elements,
544 // do not let the reference outlive the slice,
545 // and require exclusive access to the entire slice to mutate the chunk.
546 Some(unsafe { &mut *(last.as_mut_ptr().cast_array()) })
547 }
548
549 /// Returns a reference to an element or subslice depending on the type of
550 /// index.
551 ///
552 /// - If given a position, returns a reference to the element at that
553 /// position or `None` if out of bounds.
554 /// - If given a range, returns the subslice corresponding to that range,
555 /// or `None` if out of bounds.
556 ///
557 /// # Examples
558 ///
559 /// ```
560 /// let v = [10, 40, 30];
561 /// assert_eq!(Some(&40), v.get(1));
562 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
563 /// assert_eq!(None, v.get(3));
564 /// assert_eq!(None, v.get(0..4));
565 /// ```
566 #[stable(feature = "rust1", since = "1.0.0")]
567 #[rustc_no_implicit_autorefs]
568 #[inline]
569 #[must_use]
570 #[rustc_const_unstable(feature = "const_index", issue = "143775")]
571 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
572 where
573 I: [const] SliceIndex<Self>,
574 {
575 index.get(self)
576 }
577
578 /// Returns a mutable reference to an element or subslice depending on the
579 /// type of index (see [`get`]) or `None` if the index is out of bounds.
580 ///
581 /// [`get`]: slice::get
582 ///
583 /// # Examples
584 ///
585 /// ```
586 /// let x = &mut [0, 1, 2];
587 ///
588 /// if let Some(elem) = x.get_mut(1) {
589 /// *elem = 42;
590 /// }
591 /// assert_eq!(x, &[0, 42, 2]);
592 /// ```
593 #[stable(feature = "rust1", since = "1.0.0")]
594 #[rustc_no_implicit_autorefs]
595 #[inline]
596 #[must_use]
597 #[rustc_const_unstable(feature = "const_index", issue = "143775")]
598 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
599 where
600 I: [const] SliceIndex<Self>,
601 {
602 index.get_mut(self)
603 }
604
605 /// Returns a reference to an element or subslice, without doing bounds
606 /// checking.
607 ///
608 /// For a safe alternative see [`get`].
609 ///
610 /// # Safety
611 ///
612 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
613 /// even if the resulting reference is not used.
614 ///
615 /// You can think of this like `.get(index).unwrap_unchecked()`. It's UB
616 /// to call `.get_unchecked(len)`, even if you immediately convert to a
617 /// pointer. And it's UB to call `.get_unchecked(..len + 1)`,
618 /// `.get_unchecked(..=len)`, or similar.
619 ///
620 /// [`get`]: slice::get
621 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
622 ///
623 /// # Examples
624 ///
625 /// ```
626 /// let x = &[1, 2, 4];
627 ///
628 /// unsafe {
629 /// assert_eq!(x.get_unchecked(1), &2);
630 /// }
631 /// ```
632 #[stable(feature = "rust1", since = "1.0.0")]
633 #[rustc_no_implicit_autorefs]
634 #[inline]
635 #[must_use]
636 #[track_caller]
637 #[rustc_const_unstable(feature = "const_index", issue = "143775")]
638 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
639 where
640 I: [const] SliceIndex<Self>,
641 {
642 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
643 // the slice is dereferenceable because `self` is a safe reference.
644 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
645 unsafe { &*index.get_unchecked(self) }
646 }
647
648 /// Returns a mutable reference to an element or subslice, without doing
649 /// bounds checking.
650 ///
651 /// For a safe alternative see [`get_mut`].
652 ///
653 /// # Safety
654 ///
655 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
656 /// even if the resulting reference is not used.
657 ///
658 /// You can think of this like `.get_mut(index).unwrap_unchecked()`. It's
659 /// UB to call `.get_unchecked_mut(len)`, even if you immediately convert
660 /// to a pointer. And it's UB to call `.get_unchecked_mut(..len + 1)`,
661 /// `.get_unchecked_mut(..=len)`, or similar.
662 ///
663 /// [`get_mut`]: slice::get_mut
664 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
665 ///
666 /// # Examples
667 ///
668 /// ```
669 /// let x = &mut [1, 2, 4];
670 ///
671 /// unsafe {
672 /// let elem = x.get_unchecked_mut(1);
673 /// *elem = 13;
674 /// }
675 /// assert_eq!(x, &[1, 13, 4]);
676 /// ```
677 #[stable(feature = "rust1", since = "1.0.0")]
678 #[rustc_no_implicit_autorefs]
679 #[inline]
680 #[must_use]
681 #[track_caller]
682 #[rustc_const_unstable(feature = "const_index", issue = "143775")]
683 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
684 where
685 I: [const] SliceIndex<Self>,
686 {
687 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
688 // the slice is dereferenceable because `self` is a safe reference.
689 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
690 unsafe { &mut *index.get_unchecked_mut(self) }
691 }
692
693 /// Returns a raw pointer to the slice's buffer.
694 ///
695 /// The caller must ensure that the slice outlives the pointer this
696 /// function returns, or else it will end up dangling.
697 ///
698 /// The caller must also ensure that the memory the pointer (non-transitively) points to
699 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
700 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
701 ///
702 /// Modifying the container referenced by this slice may cause its buffer
703 /// to be reallocated, which would also make any pointers to it invalid.
704 ///
705 /// # Examples
706 ///
707 /// ```
708 /// let x = &[1, 2, 4];
709 /// let x_ptr = x.as_ptr();
710 ///
711 /// unsafe {
712 /// for i in 0..x.len() {
713 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
714 /// }
715 /// }
716 /// ```
717 ///
718 /// [`as_mut_ptr`]: slice::as_mut_ptr
719 #[stable(feature = "rust1", since = "1.0.0")]
720 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
721 #[rustc_never_returns_null_ptr]
722 #[rustc_as_ptr]
723 #[inline(always)]
724 #[must_use]
725 pub const fn as_ptr(&self) -> *const T {
726 self as *const [T] as *const T
727 }
728
729 /// Returns an unsafe mutable pointer to the slice's buffer.
730 ///
731 /// The caller must ensure that the slice outlives the pointer this
732 /// function returns, or else it will end up dangling.
733 ///
734 /// Modifying the container referenced by this slice may cause its buffer
735 /// to be reallocated, which would also make any pointers to it invalid.
736 ///
737 /// # Examples
738 ///
739 /// ```
740 /// let x = &mut [1, 2, 4];
741 /// let x_ptr = x.as_mut_ptr();
742 ///
743 /// unsafe {
744 /// for i in 0..x.len() {
745 /// *x_ptr.add(i) += 2;
746 /// }
747 /// }
748 /// assert_eq!(x, &[3, 4, 6]);
749 /// ```
750 #[stable(feature = "rust1", since = "1.0.0")]
751 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
752 #[rustc_never_returns_null_ptr]
753 #[rustc_as_ptr]
754 #[inline(always)]
755 #[must_use]
756 pub const fn as_mut_ptr(&mut self) -> *mut T {
757 self as *mut [T] as *mut T
758 }
759
760 /// Returns the two raw pointers spanning the slice.
761 ///
762 /// The returned range is half-open, which means that the end pointer
763 /// points *one past* the last element of the slice. This way, an empty
764 /// slice is represented by two equal pointers, and the difference between
765 /// the two pointers represents the size of the slice.
766 ///
767 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
768 /// requires extra caution, as it does not point to a valid element in the
769 /// slice.
770 ///
771 /// This function is useful for interacting with foreign interfaces which
772 /// use two pointers to refer to a range of elements in memory, as is
773 /// common in C++.
774 ///
775 /// It can also be useful to check if a pointer to an element refers to an
776 /// element of this slice:
777 ///
778 /// ```
779 /// let a = [1, 2, 3];
780 /// let x = &a[1] as *const _;
781 /// let y = &5 as *const _;
782 ///
783 /// assert!(a.as_ptr_range().contains(&x));
784 /// assert!(!a.as_ptr_range().contains(&y));
785 /// ```
786 ///
787 /// [`as_ptr`]: slice::as_ptr
788 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
789 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
790 #[inline]
791 #[must_use]
792 pub const fn as_ptr_range(&self) -> Range<*const T> {
793 let start = self.as_ptr();
794 // SAFETY: The `add` here is safe, because:
795 //
796 // - Both pointers are part of the same object, as pointing directly
797 // past the object also counts.
798 //
799 // - The size of the slice is never larger than `isize::MAX` bytes, as
800 // noted here:
801 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
802 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
803 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
804 // (This doesn't seem normative yet, but the very same assumption is
805 // made in many places, including the Index implementation of slices.)
806 //
807 // - There is no wrapping around involved, as slices do not wrap past
808 // the end of the address space.
809 //
810 // See the documentation of [`pointer::add`].
811 let end = unsafe { start.add(self.len()) };
812 start..end
813 }
814
815 /// Returns the two unsafe mutable pointers spanning the slice.
816 ///
817 /// The returned range is half-open, which means that the end pointer
818 /// points *one past* the last element of the slice. This way, an empty
819 /// slice is represented by two equal pointers, and the difference between
820 /// the two pointers represents the size of the slice.
821 ///
822 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
823 /// pointer requires extra caution, as it does not point to a valid element
824 /// in the slice.
825 ///
826 /// This function is useful for interacting with foreign interfaces which
827 /// use two pointers to refer to a range of elements in memory, as is
828 /// common in C++.
829 ///
830 /// [`as_mut_ptr`]: slice::as_mut_ptr
831 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
832 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
833 #[inline]
834 #[must_use]
835 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
836 let start = self.as_mut_ptr();
837 // SAFETY: See as_ptr_range() above for why `add` here is safe.
838 let end = unsafe { start.add(self.len()) };
839 start..end
840 }
841
842 /// Gets a reference to the underlying array.
843 ///
844 /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
845 #[stable(feature = "core_slice_as_array", since = "1.93.0")]
846 #[rustc_const_stable(feature = "core_slice_as_array", since = "1.93.0")]
847 #[inline]
848 #[must_use]
849 pub const fn as_array<const N: usize>(&self) -> Option<&[T; N]> {
850 if self.len() == N {
851 let ptr = self.as_ptr().cast_array();
852
853 // SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
854 let me = unsafe { &*ptr };
855 Some(me)
856 } else {
857 None
858 }
859 }
860
861 /// Gets a mutable reference to the slice's underlying array.
862 ///
863 /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
864 #[stable(feature = "core_slice_as_array", since = "1.93.0")]
865 #[rustc_const_stable(feature = "core_slice_as_array", since = "1.93.0")]
866 #[inline]
867 #[must_use]
868 pub const fn as_mut_array<const N: usize>(&mut self) -> Option<&mut [T; N]> {
869 if self.len() == N {
870 let ptr = self.as_mut_ptr().cast_array();
871
872 // SAFETY: The underlying array of a slice can be reinterpreted as an actual array `[T; N]` if `N` is not greater than the slice's length.
873 let me = unsafe { &mut *ptr };
874 Some(me)
875 } else {
876 None
877 }
878 }
879
880 /// Swaps two elements in the slice.
881 ///
882 /// If `a` equals to `b`, it's guaranteed that elements won't change value.
883 ///
884 /// # Arguments
885 ///
886 /// * a - The index of the first element
887 /// * b - The index of the second element
888 ///
889 /// # Panics
890 ///
891 /// Panics if `a` or `b` are out of bounds.
892 ///
893 /// # Examples
894 ///
895 /// ```
896 /// let mut v = ["a", "b", "c", "d", "e"];
897 /// v.swap(2, 4);
898 /// assert!(v == ["a", "b", "e", "d", "c"]);
899 /// ```
900 #[stable(feature = "rust1", since = "1.0.0")]
901 #[rustc_const_stable(feature = "const_swap", since = "1.85.0")]
902 #[inline]
903 #[track_caller]
904 pub const fn swap(&mut self, a: usize, b: usize) {
905 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
906 // Can't take two mutable loans from one vector, so instead use raw pointers.
907 let pa = &raw mut self[a];
908 let pb = &raw mut self[b];
909 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
910 // to elements in the slice and therefore are guaranteed to be valid and aligned.
911 // Note that accessing the elements behind `a` and `b` is checked and will
912 // panic when out of bounds.
913 unsafe {
914 ptr::swap(pa, pb);
915 }
916 }
917
918 /// Swaps two elements in the slice, without doing bounds checking.
919 ///
920 /// For a safe alternative see [`swap`].
921 ///
922 /// # Arguments
923 ///
924 /// * a - The index of the first element
925 /// * b - The index of the second element
926 ///
927 /// # Safety
928 ///
929 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
930 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
931 ///
932 /// # Examples
933 ///
934 /// ```
935 /// #![feature(slice_swap_unchecked)]
936 ///
937 /// let mut v = ["a", "b", "c", "d"];
938 /// // SAFETY: we know that 1 and 3 are both indices of the slice
939 /// unsafe { v.swap_unchecked(1, 3) };
940 /// assert!(v == ["a", "d", "c", "b"]);
941 /// ```
942 ///
943 /// [`swap`]: slice::swap
944 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
945 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
946 #[track_caller]
947 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
948 assert_unsafe_precondition!(
949 check_library_ub,
950 "slice::swap_unchecked requires that the indices are within the slice",
951 (
952 len: usize = self.len(),
953 a: usize = a,
954 b: usize = b,
955 ) => a < len && b < len,
956 );
957
958 let ptr = self.as_mut_ptr();
959 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
960 unsafe {
961 ptr::swap(ptr.add(a), ptr.add(b));
962 }
963 }
964
965 /// Reverses the order of elements in the slice, in place.
966 ///
967 /// # Examples
968 ///
969 /// ```
970 /// let mut v = [1, 2, 3];
971 /// v.reverse();
972 /// assert!(v == [3, 2, 1]);
973 /// ```
974 #[stable(feature = "rust1", since = "1.0.0")]
975 #[rustc_const_stable(feature = "const_slice_reverse", since = "1.90.0")]
976 #[inline]
977 pub const fn reverse(&mut self) {
978 let half_len = self.len() / 2;
979 let Range { start, end } = self.as_mut_ptr_range();
980
981 // These slices will skip the middle item for an odd length,
982 // since that one doesn't need to move.
983 let (front_half, back_half) =
984 // SAFETY: Both are subparts of the original slice, so the memory
985 // range is valid, and they don't overlap because they're each only
986 // half (or less) of the original slice.
987 unsafe {
988 (
989 slice::from_raw_parts_mut(start, half_len),
990 slice::from_raw_parts_mut(end.sub(half_len), half_len),
991 )
992 };
993
994 // Introducing a function boundary here means that the two halves
995 // get `noalias` markers, allowing better optimization as LLVM
996 // knows that they're disjoint, unlike in the original slice.
997 revswap(front_half, back_half, half_len);
998
999 #[inline]
1000 const fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
1001 debug_assert!(a.len() == n);
1002 debug_assert!(b.len() == n);
1003
1004 // Because this function is first compiled in isolation,
1005 // this check tells LLVM that the indexing below is
1006 // in-bounds. Then after inlining -- once the actual
1007 // lengths of the slices are known -- it's removed.
1008 // FIXME(const_trait_impl) replace with let (a, b) = (&mut a[..n], &mut b[..n]);
1009 let (a, _) = a.split_at_mut(n);
1010 let (b, _) = b.split_at_mut(n);
1011
1012 let mut i = 0;
1013 while i < n {
1014 mem::swap(&mut a[i], &mut b[n - 1 - i]);
1015 i += 1;
1016 }
1017 }
1018 }
1019
1020 /// Returns an iterator over the slice.
1021 ///
1022 /// The iterator yields all items from start to end.
1023 ///
1024 /// # Examples
1025 ///
1026 /// ```
1027 /// let x = &[1, 2, 4];
1028 /// let mut iterator = x.iter();
1029 ///
1030 /// assert_eq!(iterator.next(), Some(&1));
1031 /// assert_eq!(iterator.next(), Some(&2));
1032 /// assert_eq!(iterator.next(), Some(&4));
1033 /// assert_eq!(iterator.next(), None);
1034 /// ```
1035 #[stable(feature = "rust1", since = "1.0.0")]
1036 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1037 #[inline]
1038 #[rustc_diagnostic_item = "slice_iter"]
1039 pub const fn iter(&self) -> Iter<'_, T> {
1040 Iter::new(self)
1041 }
1042
1043 /// Returns an iterator that allows modifying each value.
1044 ///
1045 /// The iterator yields all items from start to end.
1046 ///
1047 /// # Examples
1048 ///
1049 /// ```
1050 /// let x = &mut [1, 2, 4];
1051 /// for elem in x.iter_mut() {
1052 /// *elem += 2;
1053 /// }
1054 /// assert_eq!(x, &[3, 4, 6]);
1055 /// ```
1056 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1057 #[stable(feature = "rust1", since = "1.0.0")]
1058 #[inline]
1059 pub const fn iter_mut(&mut self) -> IterMut<'_, T> {
1060 IterMut::new(self)
1061 }
1062
1063 /// Returns an iterator over all contiguous windows of length
1064 /// `size`. The windows overlap. If the slice is shorter than
1065 /// `size`, the iterator returns no values.
1066 ///
1067 /// # Panics
1068 ///
1069 /// Panics if `size` is zero.
1070 ///
1071 /// # Examples
1072 ///
1073 /// ```
1074 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1075 /// let mut iter = slice.windows(3);
1076 /// assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
1077 /// assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
1078 /// assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
1079 /// assert!(iter.next().is_none());
1080 /// ```
1081 ///
1082 /// If the slice is shorter than `size`:
1083 ///
1084 /// ```
1085 /// let slice = ['f', 'o', 'o'];
1086 /// let mut iter = slice.windows(4);
1087 /// assert!(iter.next().is_none());
1088 /// ```
1089 ///
1090 /// Because the [Iterator] trait cannot represent the required lifetimes,
1091 /// there is no `windows_mut` analog to `windows`;
1092 /// `[0,1,2].windows_mut(2).collect()` would violate [the rules of references]
1093 /// (though a [LendingIterator] analog is possible). You can sometimes use
1094 /// [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
1095 /// conjunction with `windows` instead:
1096 ///
1097 /// [the rules of references]: https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#the-rules-of-references
1098 /// [LendingIterator]: https://blog.rust-lang.org/2022/10/28/gats-stabilization.html
1099 /// ```
1100 /// use std::cell::Cell;
1101 ///
1102 /// let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
1103 /// let slice = &mut array[..];
1104 /// let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
1105 /// for w in slice_of_cells.windows(3) {
1106 /// Cell::swap(&w[0], &w[2]);
1107 /// }
1108 /// assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);
1109 /// ```
1110 #[stable(feature = "rust1", since = "1.0.0")]
1111 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1112 #[inline]
1113 #[track_caller]
1114 pub const fn windows(&self, size: usize) -> Windows<'_, T> {
1115 let size = NonZero::new(size).expect("window size must be non-zero");
1116 Windows::new(self, size)
1117 }
1118
1119 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1120 /// beginning of the slice.
1121 ///
1122 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1123 /// slice, then the last chunk will not have length `chunk_size`.
1124 ///
1125 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
1126 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
1127 /// slice.
1128 ///
1129 /// If your `chunk_size` is a constant, consider using [`as_chunks`] instead, which will
1130 /// give references to arrays of exactly that length, rather than slices.
1131 ///
1132 /// # Panics
1133 ///
1134 /// Panics if `chunk_size` is zero.
1135 ///
1136 /// # Examples
1137 ///
1138 /// ```
1139 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1140 /// let mut iter = slice.chunks(2);
1141 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1142 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1143 /// assert_eq!(iter.next().unwrap(), &['m']);
1144 /// assert!(iter.next().is_none());
1145 /// ```
1146 ///
1147 /// [`chunks_exact`]: slice::chunks_exact
1148 /// [`rchunks`]: slice::rchunks
1149 /// [`as_chunks`]: slice::as_chunks
1150 #[stable(feature = "rust1", since = "1.0.0")]
1151 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1152 #[inline]
1153 #[track_caller]
1154 pub const fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
1155 assert!(chunk_size != 0, "chunk size must be non-zero");
1156 Chunks::new(self, chunk_size)
1157 }
1158
1159 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1160 /// beginning of the slice.
1161 ///
1162 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1163 /// length of the slice, then the last chunk will not have length `chunk_size`.
1164 ///
1165 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
1166 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
1167 /// the end of the slice.
1168 ///
1169 /// If your `chunk_size` is a constant, consider using [`as_chunks_mut`] instead, which will
1170 /// give references to arrays of exactly that length, rather than slices.
1171 ///
1172 /// # Panics
1173 ///
1174 /// Panics if `chunk_size` is zero.
1175 ///
1176 /// # Examples
1177 ///
1178 /// ```
1179 /// let v = &mut [0, 0, 0, 0, 0];
1180 /// let mut count = 1;
1181 ///
1182 /// for chunk in v.chunks_mut(2) {
1183 /// for elem in chunk.iter_mut() {
1184 /// *elem += count;
1185 /// }
1186 /// count += 1;
1187 /// }
1188 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
1189 /// ```
1190 ///
1191 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1192 /// [`rchunks_mut`]: slice::rchunks_mut
1193 /// [`as_chunks_mut`]: slice::as_chunks_mut
1194 #[stable(feature = "rust1", since = "1.0.0")]
1195 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1196 #[inline]
1197 #[track_caller]
1198 pub const fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
1199 assert!(chunk_size != 0, "chunk size must be non-zero");
1200 ChunksMut::new(self, chunk_size)
1201 }
1202
1203 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1204 /// beginning of the slice.
1205 ///
1206 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1207 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1208 /// from the `remainder` function of the iterator.
1209 ///
1210 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1211 /// resulting code better than in the case of [`chunks`].
1212 ///
1213 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
1214 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
1215 ///
1216 /// If your `chunk_size` is a constant, consider using [`as_chunks`] instead, which will
1217 /// give references to arrays of exactly that length, rather than slices.
1218 ///
1219 /// # Panics
1220 ///
1221 /// Panics if `chunk_size` is zero.
1222 ///
1223 /// # Examples
1224 ///
1225 /// ```
1226 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1227 /// let mut iter = slice.chunks_exact(2);
1228 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1229 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1230 /// assert!(iter.next().is_none());
1231 /// assert_eq!(iter.remainder(), &['m']);
1232 /// ```
1233 ///
1234 /// [`chunks`]: slice::chunks
1235 /// [`rchunks_exact`]: slice::rchunks_exact
1236 /// [`as_chunks`]: slice::as_chunks
1237 #[stable(feature = "chunks_exact", since = "1.31.0")]
1238 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1239 #[inline]
1240 #[track_caller]
1241 pub const fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
1242 assert!(chunk_size != 0, "chunk size must be non-zero");
1243 ChunksExact::new(self, chunk_size)
1244 }
1245
1246 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1247 /// beginning of the slice.
1248 ///
1249 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1250 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1251 /// retrieved from the `into_remainder` function of the iterator.
1252 ///
1253 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1254 /// resulting code better than in the case of [`chunks_mut`].
1255 ///
1256 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
1257 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
1258 /// the slice.
1259 ///
1260 /// If your `chunk_size` is a constant, consider using [`as_chunks_mut`] instead, which will
1261 /// give references to arrays of exactly that length, rather than slices.
1262 ///
1263 /// # Panics
1264 ///
1265 /// Panics if `chunk_size` is zero.
1266 ///
1267 /// # Examples
1268 ///
1269 /// ```
1270 /// let v = &mut [0, 0, 0, 0, 0];
1271 /// let mut count = 1;
1272 ///
1273 /// for chunk in v.chunks_exact_mut(2) {
1274 /// for elem in chunk.iter_mut() {
1275 /// *elem += count;
1276 /// }
1277 /// count += 1;
1278 /// }
1279 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1280 /// ```
1281 ///
1282 /// [`chunks_mut`]: slice::chunks_mut
1283 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1284 /// [`as_chunks_mut`]: slice::as_chunks_mut
1285 #[stable(feature = "chunks_exact", since = "1.31.0")]
1286 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1287 #[inline]
1288 #[track_caller]
1289 pub const fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
1290 assert!(chunk_size != 0, "chunk size must be non-zero");
1291 ChunksExactMut::new(self, chunk_size)
1292 }
1293
1294 /// Splits the slice into a slice of `N`-element arrays,
1295 /// assuming that there's no remainder.
1296 ///
1297 /// This is the inverse operation to [`as_flattened`].
1298 ///
1299 /// [`as_flattened`]: slice::as_flattened
1300 ///
1301 /// As this is `unsafe`, consider whether you could use [`as_chunks`] or
1302 /// [`as_rchunks`] instead, perhaps via something like
1303 /// `if let (chunks, []) = slice.as_chunks()` or
1304 /// `let (chunks, []) = slice.as_chunks() else { unreachable!() };`.
1305 ///
1306 /// [`as_chunks`]: slice::as_chunks
1307 /// [`as_rchunks`]: slice::as_rchunks
1308 ///
1309 /// # Safety
1310 ///
1311 /// This may only be called when
1312 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1313 /// - `N != 0`.
1314 ///
1315 /// # Examples
1316 ///
1317 /// ```
1318 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
1319 /// let chunks: &[[char; 1]] =
1320 /// // SAFETY: 1-element chunks never have remainder
1321 /// unsafe { slice.as_chunks_unchecked() };
1322 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1323 /// let chunks: &[[char; 3]] =
1324 /// // SAFETY: The slice length (6) is a multiple of 3
1325 /// unsafe { slice.as_chunks_unchecked() };
1326 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
1327 ///
1328 /// // These would be unsound:
1329 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
1330 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
1331 /// ```
1332 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1333 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1334 #[inline]
1335 #[must_use]
1336 #[track_caller]
1337 pub const unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
1338 assert_unsafe_precondition!(
1339 check_language_ub,
1340 "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
1341 (n: usize = N, len: usize = self.len()) => n != 0 && len.is_multiple_of(n),
1342 );
1343 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1344 let new_len = unsafe { exact_div(self.len(), N) };
1345 // SAFETY: We cast a slice of `new_len * N` elements into
1346 // a slice of `new_len` many `N` elements chunks.
1347 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
1348 }
1349
1350 /// Splits the slice into a slice of `N`-element arrays,
1351 /// starting at the beginning of the slice,
1352 /// and a remainder slice with length strictly less than `N`.
1353 ///
1354 /// The remainder is meaningful in the division sense. Given
1355 /// `let (chunks, remainder) = slice.as_chunks()`, then:
1356 /// - `chunks.len()` equals `slice.len() / N`,
1357 /// - `remainder.len()` equals `slice.len() % N`, and
1358 /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
1359 ///
1360 /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
1361 ///
1362 /// [`as_flattened`]: slice::as_flattened
1363 ///
1364 /// # Panics
1365 ///
1366 /// Panics if `N` is zero.
1367 ///
1368 /// Note that this check is against a const generic parameter, not a runtime
1369 /// value, and thus a particular monomorphization will either always panic
1370 /// or it will never panic.
1371 ///
1372 /// # Examples
1373 ///
1374 /// ```
1375 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1376 /// let (chunks, remainder) = slice.as_chunks();
1377 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
1378 /// assert_eq!(remainder, &['m']);
1379 /// ```
1380 ///
1381 /// If you expect the slice to be an exact multiple, you can combine
1382 /// `let`-`else` with an empty slice pattern:
1383 /// ```
1384 /// let slice = ['R', 'u', 's', 't'];
1385 /// let (chunks, []) = slice.as_chunks::<2>() else {
1386 /// panic!("slice didn't have even length")
1387 /// };
1388 /// assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);
1389 /// ```
1390 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1391 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1392 #[inline]
1393 #[track_caller]
1394 #[must_use]
1395 pub const fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1396 assert!(N != 0, "chunk size must be non-zero");
1397 let len_rounded_down = self.len() / N * N;
1398 // SAFETY: The rounded-down value is always the same or smaller than the
1399 // original length, and thus must be in-bounds of the slice.
1400 let (multiple_of_n, remainder) = unsafe { self.split_at_unchecked(len_rounded_down) };
1401 // SAFETY: We already panicked for zero, and ensured by construction
1402 // that the length of the subslice is a multiple of N.
1403 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1404 (array_slice, remainder)
1405 }
1406
1407 /// Splits the slice into a slice of `N`-element arrays,
1408 /// starting at the end of the slice,
1409 /// and a remainder slice with length strictly less than `N`.
1410 ///
1411 /// The remainder is meaningful in the division sense. Given
1412 /// `let (remainder, chunks) = slice.as_rchunks()`, then:
1413 /// - `remainder.len()` equals `slice.len() % N`,
1414 /// - `chunks.len()` equals `slice.len() / N`, and
1415 /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
1416 ///
1417 /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
1418 ///
1419 /// [`as_flattened`]: slice::as_flattened
1420 ///
1421 /// # Panics
1422 ///
1423 /// Panics if `N` is zero.
1424 ///
1425 /// Note that this check is against a const generic parameter, not a runtime
1426 /// value, and thus a particular monomorphization will either always panic
1427 /// or it will never panic.
1428 ///
1429 /// # Examples
1430 ///
1431 /// ```
1432 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1433 /// let (remainder, chunks) = slice.as_rchunks();
1434 /// assert_eq!(remainder, &['l']);
1435 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1436 /// ```
1437 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1438 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1439 #[inline]
1440 #[track_caller]
1441 #[must_use]
1442 pub const fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1443 assert!(N != 0, "chunk size must be non-zero");
1444 let len = self.len() / N;
1445 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1446 // SAFETY: We already panicked for zero, and ensured by construction
1447 // that the length of the subslice is a multiple of N.
1448 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1449 (remainder, array_slice)
1450 }
1451
1452 /// Splits the slice into a slice of `N`-element arrays,
1453 /// assuming that there's no remainder.
1454 ///
1455 /// This is the inverse operation to [`as_flattened_mut`].
1456 ///
1457 /// [`as_flattened_mut`]: slice::as_flattened_mut
1458 ///
1459 /// As this is `unsafe`, consider whether you could use [`as_chunks_mut`] or
1460 /// [`as_rchunks_mut`] instead, perhaps via something like
1461 /// `if let (chunks, []) = slice.as_chunks_mut()` or
1462 /// `let (chunks, []) = slice.as_chunks_mut() else { unreachable!() };`.
1463 ///
1464 /// [`as_chunks_mut`]: slice::as_chunks_mut
1465 /// [`as_rchunks_mut`]: slice::as_rchunks_mut
1466 ///
1467 /// # Safety
1468 ///
1469 /// This may only be called when
1470 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1471 /// - `N != 0`.
1472 ///
1473 /// # Examples
1474 ///
1475 /// ```
1476 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1477 /// let chunks: &mut [[char; 1]] =
1478 /// // SAFETY: 1-element chunks never have remainder
1479 /// unsafe { slice.as_chunks_unchecked_mut() };
1480 /// chunks[0] = ['L'];
1481 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1482 /// let chunks: &mut [[char; 3]] =
1483 /// // SAFETY: The slice length (6) is a multiple of 3
1484 /// unsafe { slice.as_chunks_unchecked_mut() };
1485 /// chunks[1] = ['a', 'x', '?'];
1486 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1487 ///
1488 /// // These would be unsound:
1489 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1490 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1491 /// ```
1492 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1493 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1494 #[inline]
1495 #[must_use]
1496 #[track_caller]
1497 pub const unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1498 assert_unsafe_precondition!(
1499 check_language_ub,
1500 "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
1501 (n: usize = N, len: usize = self.len()) => n != 0 && len.is_multiple_of(n)
1502 );
1503 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1504 let new_len = unsafe { exact_div(self.len(), N) };
1505 // SAFETY: We cast a slice of `new_len * N` elements into
1506 // a slice of `new_len` many `N` elements chunks.
1507 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1508 }
1509
1510 /// Splits the slice into a slice of `N`-element arrays,
1511 /// starting at the beginning of the slice,
1512 /// and a remainder slice with length strictly less than `N`.
1513 ///
1514 /// The remainder is meaningful in the division sense. Given
1515 /// `let (chunks, remainder) = slice.as_chunks_mut()`, then:
1516 /// - `chunks.len()` equals `slice.len() / N`,
1517 /// - `remainder.len()` equals `slice.len() % N`, and
1518 /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
1519 ///
1520 /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
1521 ///
1522 /// [`as_flattened_mut`]: slice::as_flattened_mut
1523 ///
1524 /// # Panics
1525 ///
1526 /// Panics if `N` is zero.
1527 ///
1528 /// Note that this check is against a const generic parameter, not a runtime
1529 /// value, and thus a particular monomorphization will either always panic
1530 /// or it will never panic.
1531 ///
1532 /// # Examples
1533 ///
1534 /// ```
1535 /// let v = &mut [0, 0, 0, 0, 0];
1536 /// let mut count = 1;
1537 ///
1538 /// let (chunks, remainder) = v.as_chunks_mut();
1539 /// remainder[0] = 9;
1540 /// for chunk in chunks {
1541 /// *chunk = [count; 2];
1542 /// count += 1;
1543 /// }
1544 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1545 /// ```
1546 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1547 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1548 #[inline]
1549 #[track_caller]
1550 #[must_use]
1551 pub const fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1552 assert!(N != 0, "chunk size must be non-zero");
1553 let len_rounded_down = self.len() / N * N;
1554 // SAFETY: The rounded-down value is always the same or smaller than the
1555 // original length, and thus must be in-bounds of the slice.
1556 let (multiple_of_n, remainder) = unsafe { self.split_at_mut_unchecked(len_rounded_down) };
1557 // SAFETY: We already panicked for zero, and ensured by construction
1558 // that the length of the subslice is a multiple of N.
1559 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1560 (array_slice, remainder)
1561 }
1562
1563 /// Splits the slice into a slice of `N`-element arrays,
1564 /// starting at the end of the slice,
1565 /// and a remainder slice with length strictly less than `N`.
1566 ///
1567 /// The remainder is meaningful in the division sense. Given
1568 /// `let (remainder, chunks) = slice.as_rchunks_mut()`, then:
1569 /// - `remainder.len()` equals `slice.len() % N`,
1570 /// - `chunks.len()` equals `slice.len() / N`, and
1571 /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
1572 ///
1573 /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
1574 ///
1575 /// [`as_flattened_mut`]: slice::as_flattened_mut
1576 ///
1577 /// # Panics
1578 ///
1579 /// Panics if `N` is zero.
1580 ///
1581 /// Note that this check is against a const generic parameter, not a runtime
1582 /// value, and thus a particular monomorphization will either always panic
1583 /// or it will never panic.
1584 ///
1585 /// # Examples
1586 ///
1587 /// ```
1588 /// let v = &mut [0, 0, 0, 0, 0];
1589 /// let mut count = 1;
1590 ///
1591 /// let (remainder, chunks) = v.as_rchunks_mut();
1592 /// remainder[0] = 9;
1593 /// for chunk in chunks {
1594 /// *chunk = [count; 2];
1595 /// count += 1;
1596 /// }
1597 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1598 /// ```
1599 #[stable(feature = "slice_as_chunks", since = "1.88.0")]
1600 #[rustc_const_stable(feature = "slice_as_chunks", since = "1.88.0")]
1601 #[inline]
1602 #[track_caller]
1603 #[must_use]
1604 pub const fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1605 assert!(N != 0, "chunk size must be non-zero");
1606 let len = self.len() / N;
1607 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1608 // SAFETY: We already panicked for zero, and ensured by construction
1609 // that the length of the subslice is a multiple of N.
1610 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1611 (remainder, array_slice)
1612 }
1613
1614 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1615 /// starting at the beginning of the slice.
1616 ///
1617 /// This is the const generic equivalent of [`windows`].
1618 ///
1619 /// If `N` is greater than the size of the slice, it will return no windows.
1620 ///
1621 /// # Panics
1622 ///
1623 /// Panics if `N` is zero. This check will most probably get changed to a compile time
1624 /// error before this method gets stabilized.
1625 ///
1626 /// # Examples
1627 ///
1628 /// ```
1629 /// #![feature(array_windows)]
1630 /// let slice = [0, 1, 2, 3];
1631 /// let mut iter = slice.array_windows();
1632 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1633 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1634 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1635 /// assert!(iter.next().is_none());
1636 /// ```
1637 ///
1638 /// [`windows`]: slice::windows
1639 #[unstable(feature = "array_windows", issue = "75027")]
1640 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1641 #[inline]
1642 #[track_caller]
1643 pub const fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1644 assert!(N != 0, "window size must be non-zero");
1645 ArrayWindows::new(self)
1646 }
1647
1648 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1649 /// of the slice.
1650 ///
1651 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1652 /// slice, then the last chunk will not have length `chunk_size`.
1653 ///
1654 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1655 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1656 /// of the slice.
1657 ///
1658 /// If your `chunk_size` is a constant, consider using [`as_rchunks`] instead, which will
1659 /// give references to arrays of exactly that length, rather than slices.
1660 ///
1661 /// # Panics
1662 ///
1663 /// Panics if `chunk_size` is zero.
1664 ///
1665 /// # Examples
1666 ///
1667 /// ```
1668 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1669 /// let mut iter = slice.rchunks(2);
1670 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1671 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1672 /// assert_eq!(iter.next().unwrap(), &['l']);
1673 /// assert!(iter.next().is_none());
1674 /// ```
1675 ///
1676 /// [`rchunks_exact`]: slice::rchunks_exact
1677 /// [`chunks`]: slice::chunks
1678 /// [`as_rchunks`]: slice::as_rchunks
1679 #[stable(feature = "rchunks", since = "1.31.0")]
1680 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1681 #[inline]
1682 #[track_caller]
1683 pub const fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1684 assert!(chunk_size != 0, "chunk size must be non-zero");
1685 RChunks::new(self, chunk_size)
1686 }
1687
1688 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1689 /// of the slice.
1690 ///
1691 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1692 /// length of the slice, then the last chunk will not have length `chunk_size`.
1693 ///
1694 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1695 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1696 /// beginning of the slice.
1697 ///
1698 /// If your `chunk_size` is a constant, consider using [`as_rchunks_mut`] instead, which will
1699 /// give references to arrays of exactly that length, rather than slices.
1700 ///
1701 /// # Panics
1702 ///
1703 /// Panics if `chunk_size` is zero.
1704 ///
1705 /// # Examples
1706 ///
1707 /// ```
1708 /// let v = &mut [0, 0, 0, 0, 0];
1709 /// let mut count = 1;
1710 ///
1711 /// for chunk in v.rchunks_mut(2) {
1712 /// for elem in chunk.iter_mut() {
1713 /// *elem += count;
1714 /// }
1715 /// count += 1;
1716 /// }
1717 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1718 /// ```
1719 ///
1720 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1721 /// [`chunks_mut`]: slice::chunks_mut
1722 /// [`as_rchunks_mut`]: slice::as_rchunks_mut
1723 #[stable(feature = "rchunks", since = "1.31.0")]
1724 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1725 #[inline]
1726 #[track_caller]
1727 pub const fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1728 assert!(chunk_size != 0, "chunk size must be non-zero");
1729 RChunksMut::new(self, chunk_size)
1730 }
1731
1732 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1733 /// end of the slice.
1734 ///
1735 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1736 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1737 /// from the `remainder` function of the iterator.
1738 ///
1739 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1740 /// resulting code better than in the case of [`rchunks`].
1741 ///
1742 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1743 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1744 /// slice.
1745 ///
1746 /// If your `chunk_size` is a constant, consider using [`as_rchunks`] instead, which will
1747 /// give references to arrays of exactly that length, rather than slices.
1748 ///
1749 /// # Panics
1750 ///
1751 /// Panics if `chunk_size` is zero.
1752 ///
1753 /// # Examples
1754 ///
1755 /// ```
1756 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1757 /// let mut iter = slice.rchunks_exact(2);
1758 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1759 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1760 /// assert!(iter.next().is_none());
1761 /// assert_eq!(iter.remainder(), &['l']);
1762 /// ```
1763 ///
1764 /// [`chunks`]: slice::chunks
1765 /// [`rchunks`]: slice::rchunks
1766 /// [`chunks_exact`]: slice::chunks_exact
1767 /// [`as_rchunks`]: slice::as_rchunks
1768 #[stable(feature = "rchunks", since = "1.31.0")]
1769 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1770 #[inline]
1771 #[track_caller]
1772 pub const fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1773 assert!(chunk_size != 0, "chunk size must be non-zero");
1774 RChunksExact::new(self, chunk_size)
1775 }
1776
1777 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1778 /// of the slice.
1779 ///
1780 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1781 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1782 /// retrieved from the `into_remainder` function of the iterator.
1783 ///
1784 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1785 /// resulting code better than in the case of [`chunks_mut`].
1786 ///
1787 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1788 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1789 /// of the slice.
1790 ///
1791 /// If your `chunk_size` is a constant, consider using [`as_rchunks_mut`] instead, which will
1792 /// give references to arrays of exactly that length, rather than slices.
1793 ///
1794 /// # Panics
1795 ///
1796 /// Panics if `chunk_size` is zero.
1797 ///
1798 /// # Examples
1799 ///
1800 /// ```
1801 /// let v = &mut [0, 0, 0, 0, 0];
1802 /// let mut count = 1;
1803 ///
1804 /// for chunk in v.rchunks_exact_mut(2) {
1805 /// for elem in chunk.iter_mut() {
1806 /// *elem += count;
1807 /// }
1808 /// count += 1;
1809 /// }
1810 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1811 /// ```
1812 ///
1813 /// [`chunks_mut`]: slice::chunks_mut
1814 /// [`rchunks_mut`]: slice::rchunks_mut
1815 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1816 /// [`as_rchunks_mut`]: slice::as_rchunks_mut
1817 #[stable(feature = "rchunks", since = "1.31.0")]
1818 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1819 #[inline]
1820 #[track_caller]
1821 pub const fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1822 assert!(chunk_size != 0, "chunk size must be non-zero");
1823 RChunksExactMut::new(self, chunk_size)
1824 }
1825
1826 /// Returns an iterator over the slice producing non-overlapping runs
1827 /// of elements using the predicate to separate them.
1828 ///
1829 /// The predicate is called for every pair of consecutive elements,
1830 /// meaning that it is called on `slice[0]` and `slice[1]`,
1831 /// followed by `slice[1]` and `slice[2]`, and so on.
1832 ///
1833 /// # Examples
1834 ///
1835 /// ```
1836 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1837 ///
1838 /// let mut iter = slice.chunk_by(|a, b| a == b);
1839 ///
1840 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1841 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1842 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1843 /// assert_eq!(iter.next(), None);
1844 /// ```
1845 ///
1846 /// This method can be used to extract the sorted subslices:
1847 ///
1848 /// ```
1849 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1850 ///
1851 /// let mut iter = slice.chunk_by(|a, b| a <= b);
1852 ///
1853 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1854 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1855 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1856 /// assert_eq!(iter.next(), None);
1857 /// ```
1858 #[stable(feature = "slice_group_by", since = "1.77.0")]
1859 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1860 #[inline]
1861 pub const fn chunk_by<F>(&self, pred: F) -> ChunkBy<'_, T, F>
1862 where
1863 F: FnMut(&T, &T) -> bool,
1864 {
1865 ChunkBy::new(self, pred)
1866 }
1867
1868 /// Returns an iterator over the slice producing non-overlapping mutable
1869 /// runs of elements using the predicate to separate them.
1870 ///
1871 /// The predicate is called for every pair of consecutive elements,
1872 /// meaning that it is called on `slice[0]` and `slice[1]`,
1873 /// followed by `slice[1]` and `slice[2]`, and so on.
1874 ///
1875 /// # Examples
1876 ///
1877 /// ```
1878 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1879 ///
1880 /// let mut iter = slice.chunk_by_mut(|a, b| a == b);
1881 ///
1882 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1883 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1884 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1885 /// assert_eq!(iter.next(), None);
1886 /// ```
1887 ///
1888 /// This method can be used to extract the sorted subslices:
1889 ///
1890 /// ```
1891 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1892 ///
1893 /// let mut iter = slice.chunk_by_mut(|a, b| a <= b);
1894 ///
1895 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1896 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1897 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1898 /// assert_eq!(iter.next(), None);
1899 /// ```
1900 #[stable(feature = "slice_group_by", since = "1.77.0")]
1901 #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
1902 #[inline]
1903 pub const fn chunk_by_mut<F>(&mut self, pred: F) -> ChunkByMut<'_, T, F>
1904 where
1905 F: FnMut(&T, &T) -> bool,
1906 {
1907 ChunkByMut::new(self, pred)
1908 }
1909
1910 /// Divides one slice into two at an index.
1911 ///
1912 /// The first will contain all indices from `[0, mid)` (excluding
1913 /// the index `mid` itself) and the second will contain all
1914 /// indices from `[mid, len)` (excluding the index `len` itself).
1915 ///
1916 /// # Panics
1917 ///
1918 /// Panics if `mid > len`. For a non-panicking alternative see
1919 /// [`split_at_checked`](slice::split_at_checked).
1920 ///
1921 /// # Examples
1922 ///
1923 /// ```
1924 /// let v = ['a', 'b', 'c'];
1925 ///
1926 /// {
1927 /// let (left, right) = v.split_at(0);
1928 /// assert_eq!(left, []);
1929 /// assert_eq!(right, ['a', 'b', 'c']);
1930 /// }
1931 ///
1932 /// {
1933 /// let (left, right) = v.split_at(2);
1934 /// assert_eq!(left, ['a', 'b']);
1935 /// assert_eq!(right, ['c']);
1936 /// }
1937 ///
1938 /// {
1939 /// let (left, right) = v.split_at(3);
1940 /// assert_eq!(left, ['a', 'b', 'c']);
1941 /// assert_eq!(right, []);
1942 /// }
1943 /// ```
1944 #[stable(feature = "rust1", since = "1.0.0")]
1945 #[rustc_const_stable(feature = "const_slice_split_at_not_mut", since = "1.71.0")]
1946 #[inline]
1947 #[track_caller]
1948 #[must_use]
1949 pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1950 match self.split_at_checked(mid) {
1951 Some(pair) => pair,
1952 None => panic!("mid > len"),
1953 }
1954 }
1955
1956 /// Divides one mutable slice into two at an index.
1957 ///
1958 /// The first will contain all indices from `[0, mid)` (excluding
1959 /// the index `mid` itself) and the second will contain all
1960 /// indices from `[mid, len)` (excluding the index `len` itself).
1961 ///
1962 /// # Panics
1963 ///
1964 /// Panics if `mid > len`. For a non-panicking alternative see
1965 /// [`split_at_mut_checked`](slice::split_at_mut_checked).
1966 ///
1967 /// # Examples
1968 ///
1969 /// ```
1970 /// let mut v = [1, 0, 3, 0, 5, 6];
1971 /// let (left, right) = v.split_at_mut(2);
1972 /// assert_eq!(left, [1, 0]);
1973 /// assert_eq!(right, [3, 0, 5, 6]);
1974 /// left[1] = 2;
1975 /// right[1] = 4;
1976 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1977 /// ```
1978 #[stable(feature = "rust1", since = "1.0.0")]
1979 #[inline]
1980 #[track_caller]
1981 #[must_use]
1982 #[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
1983 pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1984 match self.split_at_mut_checked(mid) {
1985 Some(pair) => pair,
1986 None => panic!("mid > len"),
1987 }
1988 }
1989
1990 /// Divides one slice into two at an index, without doing bounds checking.
1991 ///
1992 /// The first will contain all indices from `[0, mid)` (excluding
1993 /// the index `mid` itself) and the second will contain all
1994 /// indices from `[mid, len)` (excluding the index `len` itself).
1995 ///
1996 /// For a safe alternative see [`split_at`].
1997 ///
1998 /// # Safety
1999 ///
2000 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
2001 /// even if the resulting reference is not used. The caller has to ensure that
2002 /// `0 <= mid <= self.len()`.
2003 ///
2004 /// [`split_at`]: slice::split_at
2005 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2006 ///
2007 /// # Examples
2008 ///
2009 /// ```
2010 /// let v = ['a', 'b', 'c'];
2011 ///
2012 /// unsafe {
2013 /// let (left, right) = v.split_at_unchecked(0);
2014 /// assert_eq!(left, []);
2015 /// assert_eq!(right, ['a', 'b', 'c']);
2016 /// }
2017 ///
2018 /// unsafe {
2019 /// let (left, right) = v.split_at_unchecked(2);
2020 /// assert_eq!(left, ['a', 'b']);
2021 /// assert_eq!(right, ['c']);
2022 /// }
2023 ///
2024 /// unsafe {
2025 /// let (left, right) = v.split_at_unchecked(3);
2026 /// assert_eq!(left, ['a', 'b', 'c']);
2027 /// assert_eq!(right, []);
2028 /// }
2029 /// ```
2030 #[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
2031 #[rustc_const_stable(feature = "const_slice_split_at_unchecked", since = "1.77.0")]
2032 #[inline]
2033 #[must_use]
2034 #[track_caller]
2035 pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
2036 // FIXME(const-hack): the const function `from_raw_parts` is used to make this
2037 // function const; previously the implementation used
2038 // `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
2039
2040 let len = self.len();
2041 let ptr = self.as_ptr();
2042
2043 assert_unsafe_precondition!(
2044 check_library_ub,
2045 "slice::split_at_unchecked requires the index to be within the slice",
2046 (mid: usize = mid, len: usize = len) => mid <= len,
2047 );
2048
2049 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
2050 unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), unchecked_sub(len, mid))) }
2051 }
2052
2053 /// Divides one mutable slice into two at an index, without doing bounds checking.
2054 ///
2055 /// The first will contain all indices from `[0, mid)` (excluding
2056 /// the index `mid` itself) and the second will contain all
2057 /// indices from `[mid, len)` (excluding the index `len` itself).
2058 ///
2059 /// For a safe alternative see [`split_at_mut`].
2060 ///
2061 /// # Safety
2062 ///
2063 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
2064 /// even if the resulting reference is not used. The caller has to ensure that
2065 /// `0 <= mid <= self.len()`.
2066 ///
2067 /// [`split_at_mut`]: slice::split_at_mut
2068 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2069 ///
2070 /// # Examples
2071 ///
2072 /// ```
2073 /// let mut v = [1, 0, 3, 0, 5, 6];
2074 /// // scoped to restrict the lifetime of the borrows
2075 /// unsafe {
2076 /// let (left, right) = v.split_at_mut_unchecked(2);
2077 /// assert_eq!(left, [1, 0]);
2078 /// assert_eq!(right, [3, 0, 5, 6]);
2079 /// left[1] = 2;
2080 /// right[1] = 4;
2081 /// }
2082 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
2083 /// ```
2084 #[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
2085 #[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
2086 #[inline]
2087 #[must_use]
2088 #[track_caller]
2089 pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
2090 let len = self.len();
2091 let ptr = self.as_mut_ptr();
2092
2093 assert_unsafe_precondition!(
2094 check_library_ub,
2095 "slice::split_at_mut_unchecked requires the index to be within the slice",
2096 (mid: usize = mid, len: usize = len) => mid <= len,
2097 );
2098
2099 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
2100 //
2101 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
2102 // is fine.
2103 unsafe {
2104 (
2105 from_raw_parts_mut(ptr, mid),
2106 from_raw_parts_mut(ptr.add(mid), unchecked_sub(len, mid)),
2107 )
2108 }
2109 }
2110
2111 /// Divides one slice into two at an index, returning `None` if the slice is
2112 /// too short.
2113 ///
2114 /// If `mid ≤ len` returns a pair of slices where the first will contain all
2115 /// indices from `[0, mid)` (excluding the index `mid` itself) and the
2116 /// second will contain all indices from `[mid, len)` (excluding the index
2117 /// `len` itself).
2118 ///
2119 /// Otherwise, if `mid > len`, returns `None`.
2120 ///
2121 /// # Examples
2122 ///
2123 /// ```
2124 /// let v = [1, -2, 3, -4, 5, -6];
2125 ///
2126 /// {
2127 /// let (left, right) = v.split_at_checked(0).unwrap();
2128 /// assert_eq!(left, []);
2129 /// assert_eq!(right, [1, -2, 3, -4, 5, -6]);
2130 /// }
2131 ///
2132 /// {
2133 /// let (left, right) = v.split_at_checked(2).unwrap();
2134 /// assert_eq!(left, [1, -2]);
2135 /// assert_eq!(right, [3, -4, 5, -6]);
2136 /// }
2137 ///
2138 /// {
2139 /// let (left, right) = v.split_at_checked(6).unwrap();
2140 /// assert_eq!(left, [1, -2, 3, -4, 5, -6]);
2141 /// assert_eq!(right, []);
2142 /// }
2143 ///
2144 /// assert_eq!(None, v.split_at_checked(7));
2145 /// ```
2146 #[stable(feature = "split_at_checked", since = "1.80.0")]
2147 #[rustc_const_stable(feature = "split_at_checked", since = "1.80.0")]
2148 #[inline]
2149 #[must_use]
2150 pub const fn split_at_checked(&self, mid: usize) -> Option<(&[T], &[T])> {
2151 if mid <= self.len() {
2152 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
2153 // fulfills the requirements of `split_at_unchecked`.
2154 Some(unsafe { self.split_at_unchecked(mid) })
2155 } else {
2156 None
2157 }
2158 }
2159
2160 /// Divides one mutable slice into two at an index, returning `None` if the
2161 /// slice is too short.
2162 ///
2163 /// If `mid ≤ len` returns a pair of slices where the first will contain all
2164 /// indices from `[0, mid)` (excluding the index `mid` itself) and the
2165 /// second will contain all indices from `[mid, len)` (excluding the index
2166 /// `len` itself).
2167 ///
2168 /// Otherwise, if `mid > len`, returns `None`.
2169 ///
2170 /// # Examples
2171 ///
2172 /// ```
2173 /// let mut v = [1, 0, 3, 0, 5, 6];
2174 ///
2175 /// if let Some((left, right)) = v.split_at_mut_checked(2) {
2176 /// assert_eq!(left, [1, 0]);
2177 /// assert_eq!(right, [3, 0, 5, 6]);
2178 /// left[1] = 2;
2179 /// right[1] = 4;
2180 /// }
2181 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
2182 ///
2183 /// assert_eq!(None, v.split_at_mut_checked(7));
2184 /// ```
2185 #[stable(feature = "split_at_checked", since = "1.80.0")]
2186 #[rustc_const_stable(feature = "const_slice_split_at_mut", since = "1.83.0")]
2187 #[inline]
2188 #[must_use]
2189 pub const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut [T], &mut [T])> {
2190 if mid <= self.len() {
2191 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
2192 // fulfills the requirements of `split_at_unchecked`.
2193 Some(unsafe { self.split_at_mut_unchecked(mid) })
2194 } else {
2195 None
2196 }
2197 }
2198
2199 /// Returns an iterator over subslices separated by elements that match
2200 /// `pred`. The matched element is not contained in the subslices.
2201 ///
2202 /// # Examples
2203 ///
2204 /// ```
2205 /// let slice = [10, 40, 33, 20];
2206 /// let mut iter = slice.split(|num| num % 3 == 0);
2207 ///
2208 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
2209 /// assert_eq!(iter.next().unwrap(), &[20]);
2210 /// assert!(iter.next().is_none());
2211 /// ```
2212 ///
2213 /// If the first element is matched, an empty slice will be the first item
2214 /// returned by the iterator. Similarly, if the last element in the slice
2215 /// is matched, an empty slice will be the last item returned by the
2216 /// iterator:
2217 ///
2218 /// ```
2219 /// let slice = [10, 40, 33];
2220 /// let mut iter = slice.split(|num| num % 3 == 0);
2221 ///
2222 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
2223 /// assert_eq!(iter.next().unwrap(), &[]);
2224 /// assert!(iter.next().is_none());
2225 /// ```
2226 ///
2227 /// If two matched elements are directly adjacent, an empty slice will be
2228 /// present between them:
2229 ///
2230 /// ```
2231 /// let slice = [10, 6, 33, 20];
2232 /// let mut iter = slice.split(|num| num % 3 == 0);
2233 ///
2234 /// assert_eq!(iter.next().unwrap(), &[10]);
2235 /// assert_eq!(iter.next().unwrap(), &[]);
2236 /// assert_eq!(iter.next().unwrap(), &[20]);
2237 /// assert!(iter.next().is_none());
2238 /// ```
2239 #[stable(feature = "rust1", since = "1.0.0")]
2240 #[inline]
2241 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
2242 where
2243 F: FnMut(&T) -> bool,
2244 {
2245 Split::new(self, pred)
2246 }
2247
2248 /// Returns an iterator over mutable subslices separated by elements that
2249 /// match `pred`. The matched element is not contained in the subslices.
2250 ///
2251 /// # Examples
2252 ///
2253 /// ```
2254 /// let mut v = [10, 40, 30, 20, 60, 50];
2255 ///
2256 /// for group in v.split_mut(|num| *num % 3 == 0) {
2257 /// group[0] = 1;
2258 /// }
2259 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
2260 /// ```
2261 #[stable(feature = "rust1", since = "1.0.0")]
2262 #[inline]
2263 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
2264 where
2265 F: FnMut(&T) -> bool,
2266 {
2267 SplitMut::new(self, pred)
2268 }
2269
2270 /// Returns an iterator over subslices separated by elements that match
2271 /// `pred`. The matched element is contained in the end of the previous
2272 /// subslice as a terminator.
2273 ///
2274 /// # Examples
2275 ///
2276 /// ```
2277 /// let slice = [10, 40, 33, 20];
2278 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
2279 ///
2280 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
2281 /// assert_eq!(iter.next().unwrap(), &[20]);
2282 /// assert!(iter.next().is_none());
2283 /// ```
2284 ///
2285 /// If the last element of the slice is matched,
2286 /// that element will be considered the terminator of the preceding slice.
2287 /// That slice will be the last item returned by the iterator.
2288 ///
2289 /// ```
2290 /// let slice = [3, 10, 40, 33];
2291 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
2292 ///
2293 /// assert_eq!(iter.next().unwrap(), &[3]);
2294 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
2295 /// assert!(iter.next().is_none());
2296 /// ```
2297 #[stable(feature = "split_inclusive", since = "1.51.0")]
2298 #[inline]
2299 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
2300 where
2301 F: FnMut(&T) -> bool,
2302 {
2303 SplitInclusive::new(self, pred)
2304 }
2305
2306 /// Returns an iterator over mutable subslices separated by elements that
2307 /// match `pred`. The matched element is contained in the previous
2308 /// subslice as a terminator.
2309 ///
2310 /// # Examples
2311 ///
2312 /// ```
2313 /// let mut v = [10, 40, 30, 20, 60, 50];
2314 ///
2315 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
2316 /// let terminator_idx = group.len()-1;
2317 /// group[terminator_idx] = 1;
2318 /// }
2319 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
2320 /// ```
2321 #[stable(feature = "split_inclusive", since = "1.51.0")]
2322 #[inline]
2323 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
2324 where
2325 F: FnMut(&T) -> bool,
2326 {
2327 SplitInclusiveMut::new(self, pred)
2328 }
2329
2330 /// Returns an iterator over subslices separated by elements that match
2331 /// `pred`, starting at the end of the slice and working backwards.
2332 /// The matched element is not contained in the subslices.
2333 ///
2334 /// # Examples
2335 ///
2336 /// ```
2337 /// let slice = [11, 22, 33, 0, 44, 55];
2338 /// let mut iter = slice.rsplit(|num| *num == 0);
2339 ///
2340 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
2341 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
2342 /// assert_eq!(iter.next(), None);
2343 /// ```
2344 ///
2345 /// As with `split()`, if the first or last element is matched, an empty
2346 /// slice will be the first (or last) item returned by the iterator.
2347 ///
2348 /// ```
2349 /// let v = &[0, 1, 1, 2, 3, 5, 8];
2350 /// let mut it = v.rsplit(|n| *n % 2 == 0);
2351 /// assert_eq!(it.next().unwrap(), &[]);
2352 /// assert_eq!(it.next().unwrap(), &[3, 5]);
2353 /// assert_eq!(it.next().unwrap(), &[1, 1]);
2354 /// assert_eq!(it.next().unwrap(), &[]);
2355 /// assert_eq!(it.next(), None);
2356 /// ```
2357 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2358 #[inline]
2359 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
2360 where
2361 F: FnMut(&T) -> bool,
2362 {
2363 RSplit::new(self, pred)
2364 }
2365
2366 /// Returns an iterator over mutable subslices separated by elements that
2367 /// match `pred`, starting at the end of the slice and working
2368 /// backwards. The matched element is not contained in the subslices.
2369 ///
2370 /// # Examples
2371 ///
2372 /// ```
2373 /// let mut v = [100, 400, 300, 200, 600, 500];
2374 ///
2375 /// let mut count = 0;
2376 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
2377 /// count += 1;
2378 /// group[0] = count;
2379 /// }
2380 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
2381 /// ```
2382 ///
2383 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2384 #[inline]
2385 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
2386 where
2387 F: FnMut(&T) -> bool,
2388 {
2389 RSplitMut::new(self, pred)
2390 }
2391
2392 /// Returns an iterator over subslices separated by elements that match
2393 /// `pred`, limited to returning at most `n` items. The matched element is
2394 /// not contained in the subslices.
2395 ///
2396 /// The last element returned, if any, will contain the remainder of the
2397 /// slice.
2398 ///
2399 /// # Examples
2400 ///
2401 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2402 /// `[20, 60, 50]`):
2403 ///
2404 /// ```
2405 /// let v = [10, 40, 30, 20, 60, 50];
2406 ///
2407 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2408 /// println!("{group:?}");
2409 /// }
2410 /// ```
2411 #[stable(feature = "rust1", since = "1.0.0")]
2412 #[inline]
2413 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2414 where
2415 F: FnMut(&T) -> bool,
2416 {
2417 SplitN::new(self.split(pred), n)
2418 }
2419
2420 /// Returns an iterator over mutable subslices separated by elements that match
2421 /// `pred`, limited to returning at most `n` items. The matched element is
2422 /// not contained in the subslices.
2423 ///
2424 /// The last element returned, if any, will contain the remainder of the
2425 /// slice.
2426 ///
2427 /// # Examples
2428 ///
2429 /// ```
2430 /// let mut v = [10, 40, 30, 20, 60, 50];
2431 ///
2432 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2433 /// group[0] = 1;
2434 /// }
2435 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2436 /// ```
2437 #[stable(feature = "rust1", since = "1.0.0")]
2438 #[inline]
2439 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2440 where
2441 F: FnMut(&T) -> bool,
2442 {
2443 SplitNMut::new(self.split_mut(pred), n)
2444 }
2445
2446 /// Returns an iterator over subslices separated by elements that match
2447 /// `pred` limited to returning at most `n` items. This starts at the end of
2448 /// the slice and works backwards. The matched element is not contained in
2449 /// the subslices.
2450 ///
2451 /// The last element returned, if any, will contain the remainder of the
2452 /// slice.
2453 ///
2454 /// # Examples
2455 ///
2456 /// Print the slice split once, starting from the end, by numbers divisible
2457 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2458 ///
2459 /// ```
2460 /// let v = [10, 40, 30, 20, 60, 50];
2461 ///
2462 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2463 /// println!("{group:?}");
2464 /// }
2465 /// ```
2466 #[stable(feature = "rust1", since = "1.0.0")]
2467 #[inline]
2468 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2469 where
2470 F: FnMut(&T) -> bool,
2471 {
2472 RSplitN::new(self.rsplit(pred), n)
2473 }
2474
2475 /// Returns an iterator over subslices separated by elements that match
2476 /// `pred` limited to returning at most `n` items. This starts at the end of
2477 /// the slice and works backwards. The matched element is not contained in
2478 /// the subslices.
2479 ///
2480 /// The last element returned, if any, will contain the remainder of the
2481 /// slice.
2482 ///
2483 /// # Examples
2484 ///
2485 /// ```
2486 /// let mut s = [10, 40, 30, 20, 60, 50];
2487 ///
2488 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2489 /// group[0] = 1;
2490 /// }
2491 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2492 /// ```
2493 #[stable(feature = "rust1", since = "1.0.0")]
2494 #[inline]
2495 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2496 where
2497 F: FnMut(&T) -> bool,
2498 {
2499 RSplitNMut::new(self.rsplit_mut(pred), n)
2500 }
2501
2502 /// Splits the slice on the first element that matches the specified
2503 /// predicate.
2504 ///
2505 /// If any matching elements are present in the slice, returns the prefix
2506 /// before the match and suffix after. The matching element itself is not
2507 /// included. If no elements match, returns `None`.
2508 ///
2509 /// # Examples
2510 ///
2511 /// ```
2512 /// #![feature(slice_split_once)]
2513 /// let s = [1, 2, 3, 2, 4];
2514 /// assert_eq!(s.split_once(|&x| x == 2), Some((
2515 /// &[1][..],
2516 /// &[3, 2, 4][..]
2517 /// )));
2518 /// assert_eq!(s.split_once(|&x| x == 0), None);
2519 /// ```
2520 #[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
2521 #[inline]
2522 pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
2523 where
2524 F: FnMut(&T) -> bool,
2525 {
2526 let index = self.iter().position(pred)?;
2527 Some((&self[..index], &self[index + 1..]))
2528 }
2529
2530 /// Splits the slice on the last element that matches the specified
2531 /// predicate.
2532 ///
2533 /// If any matching elements are present in the slice, returns the prefix
2534 /// before the match and suffix after. The matching element itself is not
2535 /// included. If no elements match, returns `None`.
2536 ///
2537 /// # Examples
2538 ///
2539 /// ```
2540 /// #![feature(slice_split_once)]
2541 /// let s = [1, 2, 3, 2, 4];
2542 /// assert_eq!(s.rsplit_once(|&x| x == 2), Some((
2543 /// &[1, 2, 3][..],
2544 /// &[4][..]
2545 /// )));
2546 /// assert_eq!(s.rsplit_once(|&x| x == 0), None);
2547 /// ```
2548 #[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
2549 #[inline]
2550 pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
2551 where
2552 F: FnMut(&T) -> bool,
2553 {
2554 let index = self.iter().rposition(pred)?;
2555 Some((&self[..index], &self[index + 1..]))
2556 }
2557
2558 /// Returns `true` if the slice contains an element with the given value.
2559 ///
2560 /// This operation is *O*(*n*).
2561 ///
2562 /// Note that if you have a sorted slice, [`binary_search`] may be faster.
2563 ///
2564 /// [`binary_search`]: slice::binary_search
2565 ///
2566 /// # Examples
2567 ///
2568 /// ```
2569 /// let v = [10, 40, 30];
2570 /// assert!(v.contains(&30));
2571 /// assert!(!v.contains(&50));
2572 /// ```
2573 ///
2574 /// If you do not have a `&T`, but some other value that you can compare
2575 /// with one (for example, `String` implements `PartialEq<str>`), you can
2576 /// use `iter().any`:
2577 ///
2578 /// ```
2579 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2580 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2581 /// assert!(!v.iter().any(|e| e == "hi"));
2582 /// ```
2583 #[stable(feature = "rust1", since = "1.0.0")]
2584 #[inline]
2585 #[must_use]
2586 pub fn contains(&self, x: &T) -> bool
2587 where
2588 T: PartialEq,
2589 {
2590 cmp::SliceContains::slice_contains(x, self)
2591 }
2592
2593 /// Returns `true` if `needle` is a prefix of the slice or equal to the slice.
2594 ///
2595 /// # Examples
2596 ///
2597 /// ```
2598 /// let v = [10, 40, 30];
2599 /// assert!(v.starts_with(&[10]));
2600 /// assert!(v.starts_with(&[10, 40]));
2601 /// assert!(v.starts_with(&v));
2602 /// assert!(!v.starts_with(&[50]));
2603 /// assert!(!v.starts_with(&[10, 50]));
2604 /// ```
2605 ///
2606 /// Always returns `true` if `needle` is an empty slice:
2607 ///
2608 /// ```
2609 /// let v = &[10, 40, 30];
2610 /// assert!(v.starts_with(&[]));
2611 /// let v: &[u8] = &[];
2612 /// assert!(v.starts_with(&[]));
2613 /// ```
2614 #[stable(feature = "rust1", since = "1.0.0")]
2615 #[must_use]
2616 pub fn starts_with(&self, needle: &[T]) -> bool
2617 where
2618 T: PartialEq,
2619 {
2620 let n = needle.len();
2621 self.len() >= n && needle == &self[..n]
2622 }
2623
2624 /// Returns `true` if `needle` is a suffix of the slice or equal to the slice.
2625 ///
2626 /// # Examples
2627 ///
2628 /// ```
2629 /// let v = [10, 40, 30];
2630 /// assert!(v.ends_with(&[30]));
2631 /// assert!(v.ends_with(&[40, 30]));
2632 /// assert!(v.ends_with(&v));
2633 /// assert!(!v.ends_with(&[50]));
2634 /// assert!(!v.ends_with(&[50, 30]));
2635 /// ```
2636 ///
2637 /// Always returns `true` if `needle` is an empty slice:
2638 ///
2639 /// ```
2640 /// let v = &[10, 40, 30];
2641 /// assert!(v.ends_with(&[]));
2642 /// let v: &[u8] = &[];
2643 /// assert!(v.ends_with(&[]));
2644 /// ```
2645 #[stable(feature = "rust1", since = "1.0.0")]
2646 #[must_use]
2647 pub fn ends_with(&self, needle: &[T]) -> bool
2648 where
2649 T: PartialEq,
2650 {
2651 let (m, n) = (self.len(), needle.len());
2652 m >= n && needle == &self[m - n..]
2653 }
2654
2655 /// Returns a subslice with the prefix removed.
2656 ///
2657 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2658 /// If `prefix` is empty, simply returns the original slice. If `prefix` is equal to the
2659 /// original slice, returns an empty slice.
2660 ///
2661 /// If the slice does not start with `prefix`, returns `None`.
2662 ///
2663 /// # Examples
2664 ///
2665 /// ```
2666 /// let v = &[10, 40, 30];
2667 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2668 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2669 /// assert_eq!(v.strip_prefix(&[10, 40, 30]), Some(&[][..]));
2670 /// assert_eq!(v.strip_prefix(&[50]), None);
2671 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2672 ///
2673 /// let prefix : &str = "he";
2674 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2675 /// Some(b"llo".as_ref()));
2676 /// ```
2677 #[must_use = "returns the subslice without modifying the original"]
2678 #[stable(feature = "slice_strip", since = "1.51.0")]
2679 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2680 where
2681 T: PartialEq,
2682 {
2683 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2684 let prefix = prefix.as_slice();
2685 let n = prefix.len();
2686 if n <= self.len() {
2687 let (head, tail) = self.split_at(n);
2688 if head == prefix {
2689 return Some(tail);
2690 }
2691 }
2692 None
2693 }
2694
2695 /// Returns a subslice with the suffix removed.
2696 ///
2697 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2698 /// If `suffix` is empty, simply returns the original slice. If `suffix` is equal to the
2699 /// original slice, returns an empty slice.
2700 ///
2701 /// If the slice does not end with `suffix`, returns `None`.
2702 ///
2703 /// # Examples
2704 ///
2705 /// ```
2706 /// let v = &[10, 40, 30];
2707 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2708 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2709 /// assert_eq!(v.strip_suffix(&[10, 40, 30]), Some(&[][..]));
2710 /// assert_eq!(v.strip_suffix(&[50]), None);
2711 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2712 /// ```
2713 #[must_use = "returns the subslice without modifying the original"]
2714 #[stable(feature = "slice_strip", since = "1.51.0")]
2715 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2716 where
2717 T: PartialEq,
2718 {
2719 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2720 let suffix = suffix.as_slice();
2721 let (len, n) = (self.len(), suffix.len());
2722 if n <= len {
2723 let (head, tail) = self.split_at(len - n);
2724 if tail == suffix {
2725 return Some(head);
2726 }
2727 }
2728 None
2729 }
2730
2731 /// Returns a subslice with the prefix and suffix removed.
2732 ///
2733 /// If the slice starts with `prefix` and ends with `suffix`, returns the subslice after the
2734 /// prefix and before the suffix, wrapped in `Some`.
2735 ///
2736 /// If the slice does not start with `prefix` or does not end with `suffix`, returns `None`.
2737 ///
2738 /// # Examples
2739 ///
2740 /// ```
2741 /// #![feature(strip_circumfix)]
2742 ///
2743 /// let v = &[10, 50, 40, 30];
2744 /// assert_eq!(v.strip_circumfix(&[10], &[30]), Some(&[50, 40][..]));
2745 /// assert_eq!(v.strip_circumfix(&[10], &[40, 30]), Some(&[50][..]));
2746 /// assert_eq!(v.strip_circumfix(&[10, 50], &[40, 30]), Some(&[][..]));
2747 /// assert_eq!(v.strip_circumfix(&[50], &[30]), None);
2748 /// assert_eq!(v.strip_circumfix(&[10], &[40]), None);
2749 /// assert_eq!(v.strip_circumfix(&[], &[40, 30]), Some(&[10, 50][..]));
2750 /// assert_eq!(v.strip_circumfix(&[10, 50], &[]), Some(&[40, 30][..]));
2751 /// ```
2752 #[must_use = "returns the subslice without modifying the original"]
2753 #[unstable(feature = "strip_circumfix", issue = "147946")]
2754 pub fn strip_circumfix<S, P>(&self, prefix: &P, suffix: &S) -> Option<&[T]>
2755 where
2756 T: PartialEq,
2757 S: SlicePattern<Item = T> + ?Sized,
2758 P: SlicePattern<Item = T> + ?Sized,
2759 {
2760 self.strip_prefix(prefix)?.strip_suffix(suffix)
2761 }
2762
2763 /// Returns a subslice with the optional prefix removed.
2764 ///
2765 /// If the slice starts with `prefix`, returns the subslice after the prefix. If `prefix`
2766 /// is empty or the slice does not start with `prefix`, simply returns the original slice.
2767 /// If `prefix` is equal to the original slice, returns an empty slice.
2768 ///
2769 /// # Examples
2770 ///
2771 /// ```
2772 /// #![feature(trim_prefix_suffix)]
2773 ///
2774 /// let v = &[10, 40, 30];
2775 ///
2776 /// // Prefix present - removes it
2777 /// assert_eq!(v.trim_prefix(&[10]), &[40, 30][..]);
2778 /// assert_eq!(v.trim_prefix(&[10, 40]), &[30][..]);
2779 /// assert_eq!(v.trim_prefix(&[10, 40, 30]), &[][..]);
2780 ///
2781 /// // Prefix absent - returns original slice
2782 /// assert_eq!(v.trim_prefix(&[50]), &[10, 40, 30][..]);
2783 /// assert_eq!(v.trim_prefix(&[10, 50]), &[10, 40, 30][..]);
2784 ///
2785 /// let prefix : &str = "he";
2786 /// assert_eq!(b"hello".trim_prefix(prefix.as_bytes()), b"llo".as_ref());
2787 /// ```
2788 #[must_use = "returns the subslice without modifying the original"]
2789 #[unstable(feature = "trim_prefix_suffix", issue = "142312")]
2790 pub fn trim_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> &[T]
2791 where
2792 T: PartialEq,
2793 {
2794 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2795 let prefix = prefix.as_slice();
2796 let n = prefix.len();
2797 if n <= self.len() {
2798 let (head, tail) = self.split_at(n);
2799 if head == prefix {
2800 return tail;
2801 }
2802 }
2803 self
2804 }
2805
2806 /// Returns a subslice with the optional suffix removed.
2807 ///
2808 /// If the slice ends with `suffix`, returns the subslice before the suffix. If `suffix`
2809 /// is empty or the slice does not end with `suffix`, simply returns the original slice.
2810 /// If `suffix` is equal to the original slice, returns an empty slice.
2811 ///
2812 /// # Examples
2813 ///
2814 /// ```
2815 /// #![feature(trim_prefix_suffix)]
2816 ///
2817 /// let v = &[10, 40, 30];
2818 ///
2819 /// // Suffix present - removes it
2820 /// assert_eq!(v.trim_suffix(&[30]), &[10, 40][..]);
2821 /// assert_eq!(v.trim_suffix(&[40, 30]), &[10][..]);
2822 /// assert_eq!(v.trim_suffix(&[10, 40, 30]), &[][..]);
2823 ///
2824 /// // Suffix absent - returns original slice
2825 /// assert_eq!(v.trim_suffix(&[50]), &[10, 40, 30][..]);
2826 /// assert_eq!(v.trim_suffix(&[50, 30]), &[10, 40, 30][..]);
2827 /// ```
2828 #[must_use = "returns the subslice without modifying the original"]
2829 #[unstable(feature = "trim_prefix_suffix", issue = "142312")]
2830 pub fn trim_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> &[T]
2831 where
2832 T: PartialEq,
2833 {
2834 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2835 let suffix = suffix.as_slice();
2836 let (len, n) = (self.len(), suffix.len());
2837 if n <= len {
2838 let (head, tail) = self.split_at(len - n);
2839 if tail == suffix {
2840 return head;
2841 }
2842 }
2843 self
2844 }
2845
2846 /// Binary searches this slice for a given element.
2847 /// If the slice is not sorted, the returned result is unspecified and
2848 /// meaningless.
2849 ///
2850 /// If the value is found then [`Result::Ok`] is returned, containing the
2851 /// index of the matching element. If there are multiple matches, then any
2852 /// one of the matches could be returned. The index is chosen
2853 /// deterministically, but is subject to change in future versions of Rust.
2854 /// If the value is not found then [`Result::Err`] is returned, containing
2855 /// the index where a matching element could be inserted while maintaining
2856 /// sorted order.
2857 ///
2858 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2859 ///
2860 /// [`binary_search_by`]: slice::binary_search_by
2861 /// [`binary_search_by_key`]: slice::binary_search_by_key
2862 /// [`partition_point`]: slice::partition_point
2863 ///
2864 /// # Examples
2865 ///
2866 /// Looks up a series of four elements. The first is found, with a
2867 /// uniquely determined position; the second and third are not
2868 /// found; the fourth could match any position in `[1, 4]`.
2869 ///
2870 /// ```
2871 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2872 ///
2873 /// assert_eq!(s.binary_search(&13), Ok(9));
2874 /// assert_eq!(s.binary_search(&4), Err(7));
2875 /// assert_eq!(s.binary_search(&100), Err(13));
2876 /// let r = s.binary_search(&1);
2877 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2878 /// ```
2879 ///
2880 /// If you want to find that whole *range* of matching items, rather than
2881 /// an arbitrary matching one, that can be done using [`partition_point`]:
2882 /// ```
2883 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2884 ///
2885 /// let low = s.partition_point(|x| x < &1);
2886 /// assert_eq!(low, 1);
2887 /// let high = s.partition_point(|x| x <= &1);
2888 /// assert_eq!(high, 5);
2889 /// let r = s.binary_search(&1);
2890 /// assert!((low..high).contains(&r.unwrap()));
2891 ///
2892 /// assert!(s[..low].iter().all(|&x| x < 1));
2893 /// assert!(s[low..high].iter().all(|&x| x == 1));
2894 /// assert!(s[high..].iter().all(|&x| x > 1));
2895 ///
2896 /// // For something not found, the "range" of equal items is empty
2897 /// assert_eq!(s.partition_point(|x| x < &11), 9);
2898 /// assert_eq!(s.partition_point(|x| x <= &11), 9);
2899 /// assert_eq!(s.binary_search(&11), Err(9));
2900 /// ```
2901 ///
2902 /// If you want to insert an item to a sorted vector, while maintaining
2903 /// sort order, consider using [`partition_point`]:
2904 ///
2905 /// ```
2906 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2907 /// let num = 42;
2908 /// let idx = s.partition_point(|&x| x <= num);
2909 /// // If `num` is unique, `s.partition_point(|&x| x < num)` (with `<`) is equivalent to
2910 /// // `s.binary_search(&num).unwrap_or_else(|x| x)`, but using `<=` will allow `insert`
2911 /// // to shift less elements.
2912 /// s.insert(idx, num);
2913 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2914 /// ```
2915 #[stable(feature = "rust1", since = "1.0.0")]
2916 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2917 where
2918 T: Ord,
2919 {
2920 self.binary_search_by(|p| p.cmp(x))
2921 }
2922
2923 /// Binary searches this slice with a comparator function.
2924 ///
2925 /// The comparator function should return an order code that indicates
2926 /// whether its argument is `Less`, `Equal` or `Greater` the desired
2927 /// target.
2928 /// If the slice is not sorted or if the comparator function does not
2929 /// implement an order consistent with the sort order of the underlying
2930 /// slice, the returned result is unspecified and meaningless.
2931 ///
2932 /// If the value is found then [`Result::Ok`] is returned, containing the
2933 /// index of the matching element. If there are multiple matches, then any
2934 /// one of the matches could be returned. The index is chosen
2935 /// deterministically, but is subject to change in future versions of Rust.
2936 /// If the value is not found then [`Result::Err`] is returned, containing
2937 /// the index where a matching element could be inserted while maintaining
2938 /// sorted order.
2939 ///
2940 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2941 ///
2942 /// [`binary_search`]: slice::binary_search
2943 /// [`binary_search_by_key`]: slice::binary_search_by_key
2944 /// [`partition_point`]: slice::partition_point
2945 ///
2946 /// # Examples
2947 ///
2948 /// Looks up a series of four elements. The first is found, with a
2949 /// uniquely determined position; the second and third are not
2950 /// found; the fourth could match any position in `[1, 4]`.
2951 ///
2952 /// ```
2953 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2954 ///
2955 /// let seek = 13;
2956 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2957 /// let seek = 4;
2958 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2959 /// let seek = 100;
2960 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2961 /// let seek = 1;
2962 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2963 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2964 /// ```
2965 #[stable(feature = "rust1", since = "1.0.0")]
2966 #[inline]
2967 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2968 where
2969 F: FnMut(&'a T) -> Ordering,
2970 {
2971 let mut size = self.len();
2972 if size == 0 {
2973 return Err(0);
2974 }
2975 let mut base = 0usize;
2976
2977 // This loop intentionally doesn't have an early exit if the comparison
2978 // returns Equal. We want the number of loop iterations to depend *only*
2979 // on the size of the input slice so that the CPU can reliably predict
2980 // the loop count.
2981 while size > 1 {
2982 let half = size / 2;
2983 let mid = base + half;
2984
2985 // SAFETY: the call is made safe by the following invariants:
2986 // - `mid >= 0`: by definition
2987 // - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
2988 let cmp = f(unsafe { self.get_unchecked(mid) });
2989
2990 // Binary search interacts poorly with branch prediction, so force
2991 // the compiler to use conditional moves if supported by the target
2992 // architecture.
2993 base = hint::select_unpredictable(cmp == Greater, base, mid);
2994
2995 // This is imprecise in the case where `size` is odd and the
2996 // comparison returns Greater: the mid element still gets included
2997 // by `size` even though it's known to be larger than the element
2998 // being searched for.
2999 //
3000 // This is fine though: we gain more performance by keeping the
3001 // loop iteration count invariant (and thus predictable) than we
3002 // lose from considering one additional element.
3003 size -= half;
3004 }
3005
3006 // SAFETY: base is always in [0, size) because base <= mid.
3007 let cmp = f(unsafe { self.get_unchecked(base) });
3008 if cmp == Equal {
3009 // SAFETY: same as the `get_unchecked` above.
3010 unsafe { hint::assert_unchecked(base < self.len()) };
3011 Ok(base)
3012 } else {
3013 let result = base + (cmp == Less) as usize;
3014 // SAFETY: same as the `get_unchecked` above.
3015 // Note that this is `<=`, unlike the assume in the `Ok` path.
3016 unsafe { hint::assert_unchecked(result <= self.len()) };
3017 Err(result)
3018 }
3019 }
3020
3021 /// Binary searches this slice with a key extraction function.
3022 ///
3023 /// Assumes that the slice is sorted by the key, for instance with
3024 /// [`sort_by_key`] using the same key extraction function.
3025 /// If the slice is not sorted by the key, the returned result is
3026 /// unspecified and meaningless.
3027 ///
3028 /// If the value is found then [`Result::Ok`] is returned, containing the
3029 /// index of the matching element. If there are multiple matches, then any
3030 /// one of the matches could be returned. The index is chosen
3031 /// deterministically, but is subject to change in future versions of Rust.
3032 /// If the value is not found then [`Result::Err`] is returned, containing
3033 /// the index where a matching element could be inserted while maintaining
3034 /// sorted order.
3035 ///
3036 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
3037 ///
3038 /// [`sort_by_key`]: slice::sort_by_key
3039 /// [`binary_search`]: slice::binary_search
3040 /// [`binary_search_by`]: slice::binary_search_by
3041 /// [`partition_point`]: slice::partition_point
3042 ///
3043 /// # Examples
3044 ///
3045 /// Looks up a series of four elements in a slice of pairs sorted by
3046 /// their second elements. The first is found, with a uniquely
3047 /// determined position; the second and third are not found; the
3048 /// fourth could match any position in `[1, 4]`.
3049 ///
3050 /// ```
3051 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
3052 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
3053 /// (1, 21), (2, 34), (4, 55)];
3054 ///
3055 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
3056 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
3057 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
3058 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
3059 /// assert!(match r { Ok(1..=4) => true, _ => false, });
3060 /// ```
3061 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
3062 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
3063 // This breaks links when slice is displayed in core, but changing it to use relative links
3064 // would break when the item is re-exported. So allow the core links to be broken for now.
3065 #[allow(rustdoc::broken_intra_doc_links)]
3066 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
3067 #[inline]
3068 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
3069 where
3070 F: FnMut(&'a T) -> B,
3071 B: Ord,
3072 {
3073 self.binary_search_by(|k| f(k).cmp(b))
3074 }
3075
3076 /// Sorts the slice in ascending order **without** preserving the initial order of equal elements.
3077 ///
3078 /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
3079 /// allocate), and *O*(*n* \* log(*n*)) worst-case.
3080 ///
3081 /// If the implementation of [`Ord`] for `T` does not implement a [total order], the function
3082 /// may panic; even if the function exits normally, the resulting order of elements in the slice
3083 /// is unspecified. See also the note on panicking below.
3084 ///
3085 /// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
3086 /// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
3087 /// examples see the [`Ord`] documentation.
3088 ///
3089 ///
3090 /// All original elements will remain in the slice and any possible modifications via interior
3091 /// mutability are observed in the input. Same is true if the implementation of [`Ord`] for `T` panics.
3092 ///
3093 /// Sorting types that only implement [`PartialOrd`] such as [`f32`] and [`f64`] require
3094 /// additional precautions. For example, `f32::NAN != f32::NAN`, which doesn't fulfill the
3095 /// reflexivity requirement of [`Ord`]. By using an alternative comparison function with
3096 /// `slice::sort_unstable_by` such as [`f32::total_cmp`] or [`f64::total_cmp`] that defines a
3097 /// [total order] users can sort slices containing floating-point values. Alternatively, if all
3098 /// values in the slice are guaranteed to be in a subset for which [`PartialOrd::partial_cmp`]
3099 /// forms a [total order], it's possible to sort the slice with `sort_unstable_by(|a, b|
3100 /// a.partial_cmp(b).unwrap())`.
3101 ///
3102 /// # Current implementation
3103 ///
3104 /// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
3105 /// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
3106 /// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
3107 /// expected time to sort the data is *O*(*n* \* log(*k*)).
3108 ///
3109 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
3110 /// slice is partially sorted.
3111 ///
3112 /// # Panics
3113 ///
3114 /// May panic if the implementation of [`Ord`] for `T` does not implement a [total order], or if
3115 /// the [`Ord`] implementation panics.
3116 ///
3117 /// # Examples
3118 ///
3119 /// ```
3120 /// let mut v = [4, -5, 1, -3, 2];
3121 ///
3122 /// v.sort_unstable();
3123 /// assert_eq!(v, [-5, -3, 1, 2, 4]);
3124 /// ```
3125 ///
3126 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3127 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3128 #[stable(feature = "sort_unstable", since = "1.20.0")]
3129 #[inline]
3130 pub fn sort_unstable(&mut self)
3131 where
3132 T: Ord,
3133 {
3134 sort::unstable::sort(self, &mut T::lt);
3135 }
3136
3137 /// Sorts the slice in ascending order with a comparison function, **without** preserving the
3138 /// initial order of equal elements.
3139 ///
3140 /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
3141 /// allocate), and *O*(*n* \* log(*n*)) worst-case.
3142 ///
3143 /// If the comparison function `compare` does not implement a [total order], the function
3144 /// may panic; even if the function exits normally, the resulting order of elements in the slice
3145 /// is unspecified. See also the note on panicking below.
3146 ///
3147 /// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
3148 /// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
3149 /// examples see the [`Ord`] documentation.
3150 ///
3151 /// All original elements will remain in the slice and any possible modifications via interior
3152 /// mutability are observed in the input. Same is true if `compare` panics.
3153 ///
3154 /// # Current implementation
3155 ///
3156 /// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
3157 /// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
3158 /// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
3159 /// expected time to sort the data is *O*(*n* \* log(*k*)).
3160 ///
3161 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
3162 /// slice is partially sorted.
3163 ///
3164 /// # Panics
3165 ///
3166 /// May panic if the `compare` does not implement a [total order], or if
3167 /// the `compare` itself panics.
3168 ///
3169 /// # Examples
3170 ///
3171 /// ```
3172 /// let mut v = [4, -5, 1, -3, 2];
3173 /// v.sort_unstable_by(|a, b| a.cmp(b));
3174 /// assert_eq!(v, [-5, -3, 1, 2, 4]);
3175 ///
3176 /// // reverse sorting
3177 /// v.sort_unstable_by(|a, b| b.cmp(a));
3178 /// assert_eq!(v, [4, 2, 1, -3, -5]);
3179 /// ```
3180 ///
3181 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3182 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3183 #[stable(feature = "sort_unstable", since = "1.20.0")]
3184 #[inline]
3185 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
3186 where
3187 F: FnMut(&T, &T) -> Ordering,
3188 {
3189 sort::unstable::sort(self, &mut |a, b| compare(a, b) == Ordering::Less);
3190 }
3191
3192 /// Sorts the slice in ascending order with a key extraction function, **without** preserving
3193 /// the initial order of equal elements.
3194 ///
3195 /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
3196 /// allocate), and *O*(*n* \* log(*n*)) worst-case.
3197 ///
3198 /// If the implementation of [`Ord`] for `K` does not implement a [total order], the function
3199 /// may panic; even if the function exits normally, the resulting order of elements in the slice
3200 /// is unspecified. See also the note on panicking below.
3201 ///
3202 /// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
3203 /// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
3204 /// examples see the [`Ord`] documentation.
3205 ///
3206 /// All original elements will remain in the slice and any possible modifications via interior
3207 /// mutability are observed in the input. Same is true if the implementation of [`Ord`] for `K` panics.
3208 ///
3209 /// # Current implementation
3210 ///
3211 /// The current implementation is based on [ipnsort] by Lukas Bergdoll and Orson Peters, which
3212 /// combines the fast average case of quicksort with the fast worst case of heapsort, achieving
3213 /// linear time on fully sorted and reversed inputs. On inputs with k distinct elements, the
3214 /// expected time to sort the data is *O*(*n* \* log(*k*)).
3215 ///
3216 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
3217 /// slice is partially sorted.
3218 ///
3219 /// # Panics
3220 ///
3221 /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order], or if
3222 /// the [`Ord`] implementation panics.
3223 ///
3224 /// # Examples
3225 ///
3226 /// ```
3227 /// let mut v = [4i32, -5, 1, -3, 2];
3228 ///
3229 /// v.sort_unstable_by_key(|k| k.abs());
3230 /// assert_eq!(v, [1, 2, -3, 4, -5]);
3231 /// ```
3232 ///
3233 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3234 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3235 #[stable(feature = "sort_unstable", since = "1.20.0")]
3236 #[inline]
3237 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
3238 where
3239 F: FnMut(&T) -> K,
3240 K: Ord,
3241 {
3242 sort::unstable::sort(self, &mut |a, b| f(a).lt(&f(b)));
3243 }
3244
3245 /// Reorders the slice such that the element at `index` is at a sort-order position. All
3246 /// elements before `index` will be `<=` to this value, and all elements after will be `>=` to
3247 /// it.
3248 ///
3249 /// This reordering is unstable (i.e. any element that compares equal to the nth element may end
3250 /// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
3251 /// function is also known as "kth element" in other libraries.
3252 ///
3253 /// Returns a triple that partitions the reordered slice:
3254 ///
3255 /// * The unsorted subslice before `index`, whose elements all satisfy `x <= self[index]`.
3256 ///
3257 /// * The element at `index`.
3258 ///
3259 /// * The unsorted subslice after `index`, whose elements all satisfy `x >= self[index]`.
3260 ///
3261 /// # Current implementation
3262 ///
3263 /// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
3264 /// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
3265 /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
3266 /// for all inputs.
3267 ///
3268 /// [`sort_unstable`]: slice::sort_unstable
3269 ///
3270 /// # Panics
3271 ///
3272 /// Panics when `index >= len()`, and so always panics on empty slices.
3273 ///
3274 /// May panic if the implementation of [`Ord`] for `T` does not implement a [total order].
3275 ///
3276 /// # Examples
3277 ///
3278 /// ```
3279 /// let mut v = [-5i32, 4, 2, -3, 1];
3280 ///
3281 /// // Find the items `<=` to the median, the median itself, and the items `>=` to it.
3282 /// let (lesser, median, greater) = v.select_nth_unstable(2);
3283 ///
3284 /// assert!(lesser == [-3, -5] || lesser == [-5, -3]);
3285 /// assert_eq!(median, &mut 1);
3286 /// assert!(greater == [4, 2] || greater == [2, 4]);
3287 ///
3288 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3289 /// // about the specified index.
3290 /// assert!(v == [-3, -5, 1, 2, 4] ||
3291 /// v == [-5, -3, 1, 2, 4] ||
3292 /// v == [-3, -5, 1, 4, 2] ||
3293 /// v == [-5, -3, 1, 4, 2]);
3294 /// ```
3295 ///
3296 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3297 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3298 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3299 #[inline]
3300 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
3301 where
3302 T: Ord,
3303 {
3304 sort::select::partition_at_index(self, index, T::lt)
3305 }
3306
3307 /// Reorders the slice with a comparator function such that the element at `index` is at a
3308 /// sort-order position. All elements before `index` will be `<=` to this value, and all
3309 /// elements after will be `>=` to it, according to the comparator function.
3310 ///
3311 /// This reordering is unstable (i.e. any element that compares equal to the nth element may end
3312 /// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
3313 /// function is also known as "kth element" in other libraries.
3314 ///
3315 /// Returns a triple partitioning the reordered slice:
3316 ///
3317 /// * The unsorted subslice before `index`, whose elements all satisfy
3318 /// `compare(x, self[index]).is_le()`.
3319 ///
3320 /// * The element at `index`.
3321 ///
3322 /// * The unsorted subslice after `index`, whose elements all satisfy
3323 /// `compare(x, self[index]).is_ge()`.
3324 ///
3325 /// # Current implementation
3326 ///
3327 /// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
3328 /// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
3329 /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
3330 /// for all inputs.
3331 ///
3332 /// [`sort_unstable`]: slice::sort_unstable
3333 ///
3334 /// # Panics
3335 ///
3336 /// Panics when `index >= len()`, and so always panics on empty slices.
3337 ///
3338 /// May panic if `compare` does not implement a [total order].
3339 ///
3340 /// # Examples
3341 ///
3342 /// ```
3343 /// let mut v = [-5i32, 4, 2, -3, 1];
3344 ///
3345 /// // Find the items `>=` to the median, the median itself, and the items `<=` to it, by using
3346 /// // a reversed comparator.
3347 /// let (before, median, after) = v.select_nth_unstable_by(2, |a, b| b.cmp(a));
3348 ///
3349 /// assert!(before == [4, 2] || before == [2, 4]);
3350 /// assert_eq!(median, &mut 1);
3351 /// assert!(after == [-3, -5] || after == [-5, -3]);
3352 ///
3353 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3354 /// // about the specified index.
3355 /// assert!(v == [2, 4, 1, -5, -3] ||
3356 /// v == [2, 4, 1, -3, -5] ||
3357 /// v == [4, 2, 1, -5, -3] ||
3358 /// v == [4, 2, 1, -3, -5]);
3359 /// ```
3360 ///
3361 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3362 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3363 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3364 #[inline]
3365 pub fn select_nth_unstable_by<F>(
3366 &mut self,
3367 index: usize,
3368 mut compare: F,
3369 ) -> (&mut [T], &mut T, &mut [T])
3370 where
3371 F: FnMut(&T, &T) -> Ordering,
3372 {
3373 sort::select::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
3374 }
3375
3376 /// Reorders the slice with a key extraction function such that the element at `index` is at a
3377 /// sort-order position. All elements before `index` will have keys `<=` to the key at `index`,
3378 /// and all elements after will have keys `>=` to it.
3379 ///
3380 /// This reordering is unstable (i.e. any element that compares equal to the nth element may end
3381 /// up at that position), in-place (i.e. does not allocate), and runs in *O*(*n*) time. This
3382 /// function is also known as "kth element" in other libraries.
3383 ///
3384 /// Returns a triple partitioning the reordered slice:
3385 ///
3386 /// * The unsorted subslice before `index`, whose elements all satisfy `f(x) <= f(self[index])`.
3387 ///
3388 /// * The element at `index`.
3389 ///
3390 /// * The unsorted subslice after `index`, whose elements all satisfy `f(x) >= f(self[index])`.
3391 ///
3392 /// # Current implementation
3393 ///
3394 /// The current algorithm is an introselect implementation based on [ipnsort] by Lukas Bergdoll
3395 /// and Orson Peters, which is also the basis for [`sort_unstable`]. The fallback algorithm is
3396 /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
3397 /// for all inputs.
3398 ///
3399 /// [`sort_unstable`]: slice::sort_unstable
3400 ///
3401 /// # Panics
3402 ///
3403 /// Panics when `index >= len()`, meaning it always panics on empty slices.
3404 ///
3405 /// May panic if `K: Ord` does not implement a total order.
3406 ///
3407 /// # Examples
3408 ///
3409 /// ```
3410 /// let mut v = [-5i32, 4, 1, -3, 2];
3411 ///
3412 /// // Find the items `<=` to the absolute median, the absolute median itself, and the items
3413 /// // `>=` to it.
3414 /// let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs());
3415 ///
3416 /// assert!(lesser == [1, 2] || lesser == [2, 1]);
3417 /// assert_eq!(median, &mut -3);
3418 /// assert!(greater == [4, -5] || greater == [-5, 4]);
3419 ///
3420 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3421 /// // about the specified index.
3422 /// assert!(v == [1, 2, -3, 4, -5] ||
3423 /// v == [1, 2, -3, -5, 4] ||
3424 /// v == [2, 1, -3, 4, -5] ||
3425 /// v == [2, 1, -3, -5, 4]);
3426 /// ```
3427 ///
3428 /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort
3429 /// [total order]: https://en.wikipedia.org/wiki/Total_order
3430 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3431 #[inline]
3432 pub fn select_nth_unstable_by_key<K, F>(
3433 &mut self,
3434 index: usize,
3435 mut f: F,
3436 ) -> (&mut [T], &mut T, &mut [T])
3437 where
3438 F: FnMut(&T) -> K,
3439 K: Ord,
3440 {
3441 sort::select::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
3442 }
3443
3444 /// Moves all consecutive repeated elements to the end of the slice according to the
3445 /// [`PartialEq`] trait implementation.
3446 ///
3447 /// Returns two slices. The first contains no consecutive repeated elements.
3448 /// The second contains all the duplicates in no specified order.
3449 ///
3450 /// If the slice is sorted, the first returned slice contains no duplicates.
3451 ///
3452 /// # Examples
3453 ///
3454 /// ```
3455 /// #![feature(slice_partition_dedup)]
3456 ///
3457 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
3458 ///
3459 /// let (dedup, duplicates) = slice.partition_dedup();
3460 ///
3461 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
3462 /// assert_eq!(duplicates, [2, 3, 1]);
3463 /// ```
3464 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3465 #[inline]
3466 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
3467 where
3468 T: PartialEq,
3469 {
3470 self.partition_dedup_by(|a, b| a == b)
3471 }
3472
3473 /// Moves all but the first of consecutive elements to the end of the slice satisfying
3474 /// a given equality relation.
3475 ///
3476 /// Returns two slices. The first contains no consecutive repeated elements.
3477 /// The second contains all the duplicates in no specified order.
3478 ///
3479 /// The `same_bucket` function is passed references to two elements from the slice and
3480 /// must determine if the elements compare equal. The elements are passed in opposite order
3481 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
3482 /// at the end of the slice.
3483 ///
3484 /// If the slice is sorted, the first returned slice contains no duplicates.
3485 ///
3486 /// # Examples
3487 ///
3488 /// ```
3489 /// #![feature(slice_partition_dedup)]
3490 ///
3491 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
3492 ///
3493 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
3494 ///
3495 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
3496 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
3497 /// ```
3498 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3499 #[inline]
3500 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
3501 where
3502 F: FnMut(&mut T, &mut T) -> bool,
3503 {
3504 // Although we have a mutable reference to `self`, we cannot make
3505 // *arbitrary* changes. The `same_bucket` calls could panic, so we
3506 // must ensure that the slice is in a valid state at all times.
3507 //
3508 // The way that we handle this is by using swaps; we iterate
3509 // over all the elements, swapping as we go so that at the end
3510 // the elements we wish to keep are in the front, and those we
3511 // wish to reject are at the back. We can then split the slice.
3512 // This operation is still `O(n)`.
3513 //
3514 // Example: We start in this state, where `r` represents "next
3515 // read" and `w` represents "next_write".
3516 //
3517 // r
3518 // +---+---+---+---+---+---+
3519 // | 0 | 1 | 1 | 2 | 3 | 3 |
3520 // +---+---+---+---+---+---+
3521 // w
3522 //
3523 // Comparing self[r] against self[w-1], this is not a duplicate, so
3524 // we swap self[r] and self[w] (no effect as r==w) and then increment both
3525 // r and w, leaving us with:
3526 //
3527 // r
3528 // +---+---+---+---+---+---+
3529 // | 0 | 1 | 1 | 2 | 3 | 3 |
3530 // +---+---+---+---+---+---+
3531 // w
3532 //
3533 // Comparing self[r] against self[w-1], this value is a duplicate,
3534 // so we increment `r` but leave everything else unchanged:
3535 //
3536 // r
3537 // +---+---+---+---+---+---+
3538 // | 0 | 1 | 1 | 2 | 3 | 3 |
3539 // +---+---+---+---+---+---+
3540 // w
3541 //
3542 // Comparing self[r] against self[w-1], this is not a duplicate,
3543 // so swap self[r] and self[w] and advance r and w:
3544 //
3545 // r
3546 // +---+---+---+---+---+---+
3547 // | 0 | 1 | 2 | 1 | 3 | 3 |
3548 // +---+---+---+---+---+---+
3549 // w
3550 //
3551 // Not a duplicate, repeat:
3552 //
3553 // r
3554 // +---+---+---+---+---+---+
3555 // | 0 | 1 | 2 | 3 | 1 | 3 |
3556 // +---+---+---+---+---+---+
3557 // w
3558 //
3559 // Duplicate, advance r. End of slice. Split at w.
3560
3561 let len = self.len();
3562 if len <= 1 {
3563 return (self, &mut []);
3564 }
3565
3566 let ptr = self.as_mut_ptr();
3567 let mut next_read: usize = 1;
3568 let mut next_write: usize = 1;
3569
3570 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
3571 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
3572 // one element before `ptr_write`, but `next_write` starts at 1, so
3573 // `prev_ptr_write` is never less than 0 and is inside the slice.
3574 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
3575 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
3576 // and `prev_ptr_write.offset(1)`.
3577 //
3578 // `next_write` is also incremented at most once per loop at most meaning
3579 // no element is skipped when it may need to be swapped.
3580 //
3581 // `ptr_read` and `prev_ptr_write` never point to the same element. This
3582 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
3583 // The explanation is simply that `next_read >= next_write` is always true,
3584 // thus `next_read > next_write - 1` is too.
3585 unsafe {
3586 // Avoid bounds checks by using raw pointers.
3587 while next_read < len {
3588 let ptr_read = ptr.add(next_read);
3589 let prev_ptr_write = ptr.add(next_write - 1);
3590 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
3591 if next_read != next_write {
3592 let ptr_write = prev_ptr_write.add(1);
3593 mem::swap(&mut *ptr_read, &mut *ptr_write);
3594 }
3595 next_write += 1;
3596 }
3597 next_read += 1;
3598 }
3599 }
3600
3601 self.split_at_mut(next_write)
3602 }
3603
3604 /// Moves all but the first of consecutive elements to the end of the slice that resolve
3605 /// to the same key.
3606 ///
3607 /// Returns two slices. The first contains no consecutive repeated elements.
3608 /// The second contains all the duplicates in no specified order.
3609 ///
3610 /// If the slice is sorted, the first returned slice contains no duplicates.
3611 ///
3612 /// # Examples
3613 ///
3614 /// ```
3615 /// #![feature(slice_partition_dedup)]
3616 ///
3617 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
3618 ///
3619 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
3620 ///
3621 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
3622 /// assert_eq!(duplicates, [21, 30, 13]);
3623 /// ```
3624 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3625 #[inline]
3626 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
3627 where
3628 F: FnMut(&mut T) -> K,
3629 K: PartialEq,
3630 {
3631 self.partition_dedup_by(|a, b| key(a) == key(b))
3632 }
3633
3634 /// Rotates the slice in-place such that the first `mid` elements of the
3635 /// slice move to the end while the last `self.len() - mid` elements move to
3636 /// the front.
3637 ///
3638 /// After calling `rotate_left`, the element previously at index `mid` will
3639 /// become the first element in the slice.
3640 ///
3641 /// # Panics
3642 ///
3643 /// This function will panic if `mid` is greater than the length of the
3644 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
3645 /// rotation.
3646 ///
3647 /// # Complexity
3648 ///
3649 /// Takes linear (in `self.len()`) time.
3650 ///
3651 /// # Examples
3652 ///
3653 /// ```
3654 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3655 /// a.rotate_left(2);
3656 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
3657 /// ```
3658 ///
3659 /// Rotating a subslice:
3660 ///
3661 /// ```
3662 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3663 /// a[1..5].rotate_left(1);
3664 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
3665 /// ```
3666 #[stable(feature = "slice_rotate", since = "1.26.0")]
3667 #[rustc_const_stable(feature = "const_slice_rotate", since = "1.92.0")]
3668 pub const fn rotate_left(&mut self, mid: usize) {
3669 assert!(mid <= self.len());
3670 let k = self.len() - mid;
3671 let p = self.as_mut_ptr();
3672
3673 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3674 // valid for reading and writing, as required by `ptr_rotate`.
3675 unsafe {
3676 rotate::ptr_rotate(mid, p.add(mid), k);
3677 }
3678 }
3679
3680 /// Rotates the slice in-place such that the first `self.len() - k`
3681 /// elements of the slice move to the end while the last `k` elements move
3682 /// to the front.
3683 ///
3684 /// After calling `rotate_right`, the element previously at index
3685 /// `self.len() - k` will become the first element in the slice.
3686 ///
3687 /// # Panics
3688 ///
3689 /// This function will panic if `k` is greater than the length of the
3690 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
3691 /// rotation.
3692 ///
3693 /// # Complexity
3694 ///
3695 /// Takes linear (in `self.len()`) time.
3696 ///
3697 /// # Examples
3698 ///
3699 /// ```
3700 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3701 /// a.rotate_right(2);
3702 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
3703 /// ```
3704 ///
3705 /// Rotating a subslice:
3706 ///
3707 /// ```
3708 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3709 /// a[1..5].rotate_right(1);
3710 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
3711 /// ```
3712 #[stable(feature = "slice_rotate", since = "1.26.0")]
3713 #[rustc_const_stable(feature = "const_slice_rotate", since = "1.92.0")]
3714 pub const fn rotate_right(&mut self, k: usize) {
3715 assert!(k <= self.len());
3716 let mid = self.len() - k;
3717 let p = self.as_mut_ptr();
3718
3719 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3720 // valid for reading and writing, as required by `ptr_rotate`.
3721 unsafe {
3722 rotate::ptr_rotate(mid, p.add(mid), k);
3723 }
3724 }
3725
3726 /// Fills `self` with elements by cloning `value`.
3727 ///
3728 /// # Examples
3729 ///
3730 /// ```
3731 /// let mut buf = vec![0; 10];
3732 /// buf.fill(1);
3733 /// assert_eq!(buf, vec![1; 10]);
3734 /// ```
3735 #[doc(alias = "memset")]
3736 #[stable(feature = "slice_fill", since = "1.50.0")]
3737 pub fn fill(&mut self, value: T)
3738 where
3739 T: Clone,
3740 {
3741 specialize::SpecFill::spec_fill(self, value);
3742 }
3743
3744 /// Fills `self` with elements returned by calling a closure repeatedly.
3745 ///
3746 /// This method uses a closure to create new values. If you'd rather
3747 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3748 /// trait to generate values, you can pass [`Default::default`] as the
3749 /// argument.
3750 ///
3751 /// [`fill`]: slice::fill
3752 ///
3753 /// # Examples
3754 ///
3755 /// ```
3756 /// let mut buf = vec![1; 10];
3757 /// buf.fill_with(Default::default);
3758 /// assert_eq!(buf, vec![0; 10]);
3759 /// ```
3760 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3761 pub fn fill_with<F>(&mut self, mut f: F)
3762 where
3763 F: FnMut() -> T,
3764 {
3765 for el in self {
3766 *el = f();
3767 }
3768 }
3769
3770 /// Copies the elements from `src` into `self`.
3771 ///
3772 /// The length of `src` must be the same as `self`.
3773 ///
3774 /// # Panics
3775 ///
3776 /// This function will panic if the two slices have different lengths.
3777 ///
3778 /// # Examples
3779 ///
3780 /// Cloning two elements from a slice into another:
3781 ///
3782 /// ```
3783 /// let src = [1, 2, 3, 4];
3784 /// let mut dst = [0, 0];
3785 ///
3786 /// // Because the slices have to be the same length,
3787 /// // we slice the source slice from four elements
3788 /// // to two. It will panic if we don't do this.
3789 /// dst.clone_from_slice(&src[2..]);
3790 ///
3791 /// assert_eq!(src, [1, 2, 3, 4]);
3792 /// assert_eq!(dst, [3, 4]);
3793 /// ```
3794 ///
3795 /// Rust enforces that there can only be one mutable reference with no
3796 /// immutable references to a particular piece of data in a particular
3797 /// scope. Because of this, attempting to use `clone_from_slice` on a
3798 /// single slice will result in a compile failure:
3799 ///
3800 /// ```compile_fail
3801 /// let mut slice = [1, 2, 3, 4, 5];
3802 ///
3803 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3804 /// ```
3805 ///
3806 /// To work around this, we can use [`split_at_mut`] to create two distinct
3807 /// sub-slices from a slice:
3808 ///
3809 /// ```
3810 /// let mut slice = [1, 2, 3, 4, 5];
3811 ///
3812 /// {
3813 /// let (left, right) = slice.split_at_mut(2);
3814 /// left.clone_from_slice(&right[1..]);
3815 /// }
3816 ///
3817 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3818 /// ```
3819 ///
3820 /// [`copy_from_slice`]: slice::copy_from_slice
3821 /// [`split_at_mut`]: slice::split_at_mut
3822 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3823 #[track_caller]
3824 pub fn clone_from_slice(&mut self, src: &[T])
3825 where
3826 T: Clone,
3827 {
3828 self.spec_clone_from(src);
3829 }
3830
3831 /// Copies all elements from `src` into `self`, using a memcpy.
3832 ///
3833 /// The length of `src` must be the same as `self`.
3834 ///
3835 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3836 ///
3837 /// # Panics
3838 ///
3839 /// This function will panic if the two slices have different lengths.
3840 ///
3841 /// # Examples
3842 ///
3843 /// Copying two elements from a slice into another:
3844 ///
3845 /// ```
3846 /// let src = [1, 2, 3, 4];
3847 /// let mut dst = [0, 0];
3848 ///
3849 /// // Because the slices have to be the same length,
3850 /// // we slice the source slice from four elements
3851 /// // to two. It will panic if we don't do this.
3852 /// dst.copy_from_slice(&src[2..]);
3853 ///
3854 /// assert_eq!(src, [1, 2, 3, 4]);
3855 /// assert_eq!(dst, [3, 4]);
3856 /// ```
3857 ///
3858 /// Rust enforces that there can only be one mutable reference with no
3859 /// immutable references to a particular piece of data in a particular
3860 /// scope. Because of this, attempting to use `copy_from_slice` on a
3861 /// single slice will result in a compile failure:
3862 ///
3863 /// ```compile_fail
3864 /// let mut slice = [1, 2, 3, 4, 5];
3865 ///
3866 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3867 /// ```
3868 ///
3869 /// To work around this, we can use [`split_at_mut`] to create two distinct
3870 /// sub-slices from a slice:
3871 ///
3872 /// ```
3873 /// let mut slice = [1, 2, 3, 4, 5];
3874 ///
3875 /// {
3876 /// let (left, right) = slice.split_at_mut(2);
3877 /// left.copy_from_slice(&right[1..]);
3878 /// }
3879 ///
3880 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3881 /// ```
3882 ///
3883 /// [`clone_from_slice`]: slice::clone_from_slice
3884 /// [`split_at_mut`]: slice::split_at_mut
3885 #[doc(alias = "memcpy")]
3886 #[inline]
3887 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3888 #[rustc_const_stable(feature = "const_copy_from_slice", since = "1.87.0")]
3889 #[track_caller]
3890 pub const fn copy_from_slice(&mut self, src: &[T])
3891 where
3892 T: Copy,
3893 {
3894 // SAFETY: `T` implements `Copy`.
3895 unsafe { copy_from_slice_impl(self, src) }
3896 }
3897
3898 /// Copies elements from one part of the slice to another part of itself,
3899 /// using a memmove.
3900 ///
3901 /// `src` is the range within `self` to copy from. `dest` is the starting
3902 /// index of the range within `self` to copy to, which will have the same
3903 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3904 /// must be less than or equal to `self.len()`.
3905 ///
3906 /// # Panics
3907 ///
3908 /// This function will panic if either range exceeds the end of the slice,
3909 /// or if the end of `src` is before the start.
3910 ///
3911 /// # Examples
3912 ///
3913 /// Copying four bytes within a slice:
3914 ///
3915 /// ```
3916 /// let mut bytes = *b"Hello, World!";
3917 ///
3918 /// bytes.copy_within(1..5, 8);
3919 ///
3920 /// assert_eq!(&bytes, b"Hello, Wello!");
3921 /// ```
3922 #[stable(feature = "copy_within", since = "1.37.0")]
3923 #[track_caller]
3924 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3925 where
3926 T: Copy,
3927 {
3928 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3929 let count = src_end - src_start;
3930 assert!(dest <= self.len() - count, "dest is out of bounds");
3931 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3932 // as have those for `ptr::add`.
3933 unsafe {
3934 // Derive both `src_ptr` and `dest_ptr` from the same loan
3935 let ptr = self.as_mut_ptr();
3936 let src_ptr = ptr.add(src_start);
3937 let dest_ptr = ptr.add(dest);
3938 ptr::copy(src_ptr, dest_ptr, count);
3939 }
3940 }
3941
3942 /// Swaps all elements in `self` with those in `other`.
3943 ///
3944 /// The length of `other` must be the same as `self`.
3945 ///
3946 /// # Panics
3947 ///
3948 /// This function will panic if the two slices have different lengths.
3949 ///
3950 /// # Example
3951 ///
3952 /// Swapping two elements across slices:
3953 ///
3954 /// ```
3955 /// let mut slice1 = [0, 0];
3956 /// let mut slice2 = [1, 2, 3, 4];
3957 ///
3958 /// slice1.swap_with_slice(&mut slice2[2..]);
3959 ///
3960 /// assert_eq!(slice1, [3, 4]);
3961 /// assert_eq!(slice2, [1, 2, 0, 0]);
3962 /// ```
3963 ///
3964 /// Rust enforces that there can only be one mutable reference to a
3965 /// particular piece of data in a particular scope. Because of this,
3966 /// attempting to use `swap_with_slice` on a single slice will result in
3967 /// a compile failure:
3968 ///
3969 /// ```compile_fail
3970 /// let mut slice = [1, 2, 3, 4, 5];
3971 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3972 /// ```
3973 ///
3974 /// To work around this, we can use [`split_at_mut`] to create two distinct
3975 /// mutable sub-slices from a slice:
3976 ///
3977 /// ```
3978 /// let mut slice = [1, 2, 3, 4, 5];
3979 ///
3980 /// {
3981 /// let (left, right) = slice.split_at_mut(2);
3982 /// left.swap_with_slice(&mut right[1..]);
3983 /// }
3984 ///
3985 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3986 /// ```
3987 ///
3988 /// [`split_at_mut`]: slice::split_at_mut
3989 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3990 #[rustc_const_unstable(feature = "const_swap_with_slice", issue = "142204")]
3991 #[track_caller]
3992 pub const fn swap_with_slice(&mut self, other: &mut [T]) {
3993 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3994 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3995 // checked to have the same length. The slices cannot overlap because
3996 // mutable references are exclusive.
3997 unsafe {
3998 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3999 }
4000 }
4001
4002 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
4003 fn align_to_offsets<U>(&self) -> (usize, usize) {
4004 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
4005 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
4006 //
4007 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
4008 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
4009 // place of every 3 Ts in the `rest` slice. A bit more complicated.
4010 //
4011 // Formula to calculate this is:
4012 //
4013 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
4014 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
4015 //
4016 // Expanded and simplified:
4017 //
4018 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
4019 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
4020 //
4021 // Luckily since all this is constant-evaluated... performance here matters not!
4022 const fn gcd(a: usize, b: usize) -> usize {
4023 if b == 0 { a } else { gcd(b, a % b) }
4024 }
4025
4026 // Explicitly wrap the function call in a const block so it gets
4027 // constant-evaluated even in debug mode.
4028 let gcd: usize = const { gcd(size_of::<T>(), size_of::<U>()) };
4029 let ts: usize = size_of::<U>() / gcd;
4030 let us: usize = size_of::<T>() / gcd;
4031
4032 // Armed with this knowledge, we can find how many `U`s we can fit!
4033 let us_len = self.len() / ts * us;
4034 // And how many `T`s will be in the trailing slice!
4035 let ts_len = self.len() % ts;
4036 (us_len, ts_len)
4037 }
4038
4039 /// Transmutes the slice to a slice of another type, ensuring alignment of the types is
4040 /// maintained.
4041 ///
4042 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
4043 /// slice of a new type, and the suffix slice. The middle part will be as big as possible under
4044 /// the given alignment constraint and element size.
4045 ///
4046 /// This method has no purpose when either input element `T` or output element `U` are
4047 /// zero-sized and will return the original slice without splitting anything.
4048 ///
4049 /// # Safety
4050 ///
4051 /// This method is essentially a `transmute` with respect to the elements in the returned
4052 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
4053 ///
4054 /// # Examples
4055 ///
4056 /// Basic usage:
4057 ///
4058 /// ```
4059 /// unsafe {
4060 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
4061 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
4062 /// // less_efficient_algorithm_for_bytes(prefix);
4063 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
4064 /// // less_efficient_algorithm_for_bytes(suffix);
4065 /// }
4066 /// ```
4067 #[stable(feature = "slice_align_to", since = "1.30.0")]
4068 #[must_use]
4069 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
4070 // Note that most of this function will be constant-evaluated,
4071 if U::IS_ZST || T::IS_ZST {
4072 // handle ZSTs specially, which is – don't handle them at all.
4073 return (self, &[], &[]);
4074 }
4075
4076 // First, find at what point do we split between the first and 2nd slice. Easy with
4077 // ptr.align_offset.
4078 let ptr = self.as_ptr();
4079 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
4080 let offset = unsafe { crate::ptr::align_offset(ptr, align_of::<U>()) };
4081 if offset > self.len() {
4082 (self, &[], &[])
4083 } else {
4084 let (left, rest) = self.split_at(offset);
4085 let (us_len, ts_len) = rest.align_to_offsets::<U>();
4086 // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
4087 #[cfg(miri)]
4088 crate::intrinsics::miri_promise_symbolic_alignment(
4089 rest.as_ptr().cast(),
4090 align_of::<U>(),
4091 );
4092 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
4093 // since the caller guarantees that we can transmute `T` to `U` safely.
4094 unsafe {
4095 (
4096 left,
4097 from_raw_parts(rest.as_ptr() as *const U, us_len),
4098 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
4099 )
4100 }
4101 }
4102 }
4103
4104 /// Transmutes the mutable slice to a mutable slice of another type, ensuring alignment of the
4105 /// types is maintained.
4106 ///
4107 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
4108 /// slice of a new type, and the suffix slice. The middle part will be as big as possible under
4109 /// the given alignment constraint and element size.
4110 ///
4111 /// This method has no purpose when either input element `T` or output element `U` are
4112 /// zero-sized and will return the original slice without splitting anything.
4113 ///
4114 /// # Safety
4115 ///
4116 /// This method is essentially a `transmute` with respect to the elements in the returned
4117 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
4118 ///
4119 /// # Examples
4120 ///
4121 /// Basic usage:
4122 ///
4123 /// ```
4124 /// unsafe {
4125 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
4126 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
4127 /// // less_efficient_algorithm_for_bytes(prefix);
4128 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
4129 /// // less_efficient_algorithm_for_bytes(suffix);
4130 /// }
4131 /// ```
4132 #[stable(feature = "slice_align_to", since = "1.30.0")]
4133 #[must_use]
4134 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
4135 // Note that most of this function will be constant-evaluated,
4136 if U::IS_ZST || T::IS_ZST {
4137 // handle ZSTs specially, which is – don't handle them at all.
4138 return (self, &mut [], &mut []);
4139 }
4140
4141 // First, find at what point do we split between the first and 2nd slice. Easy with
4142 // ptr.align_offset.
4143 let ptr = self.as_ptr();
4144 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
4145 // rest of the method. This is done by passing a pointer to &[T] with an
4146 // alignment targeted for U.
4147 // `crate::ptr::align_offset` is called with a correctly aligned and
4148 // valid pointer `ptr` (it comes from a reference to `self`) and with
4149 // a size that is a power of two (since it comes from the alignment for U),
4150 // satisfying its safety constraints.
4151 let offset = unsafe { crate::ptr::align_offset(ptr, align_of::<U>()) };
4152 if offset > self.len() {
4153 (self, &mut [], &mut [])
4154 } else {
4155 let (left, rest) = self.split_at_mut(offset);
4156 let (us_len, ts_len) = rest.align_to_offsets::<U>();
4157 let rest_len = rest.len();
4158 let mut_ptr = rest.as_mut_ptr();
4159 // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
4160 #[cfg(miri)]
4161 crate::intrinsics::miri_promise_symbolic_alignment(
4162 mut_ptr.cast() as *const (),
4163 align_of::<U>(),
4164 );
4165 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
4166 // SAFETY: see comments for `align_to`.
4167 unsafe {
4168 (
4169 left,
4170 from_raw_parts_mut(mut_ptr as *mut U, us_len),
4171 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
4172 )
4173 }
4174 }
4175 }
4176
4177 /// Splits a slice into a prefix, a middle of aligned SIMD types, and a suffix.
4178 ///
4179 /// This is a safe wrapper around [`slice::align_to`], so inherits the same
4180 /// guarantees as that method.
4181 ///
4182 /// # Panics
4183 ///
4184 /// This will panic if the size of the SIMD type is different from
4185 /// `LANES` times that of the scalar.
4186 ///
4187 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
4188 /// that from ever happening, as only power-of-two numbers of lanes are
4189 /// supported. It's possible that, in the future, those restrictions might
4190 /// be lifted in a way that would make it possible to see panics from this
4191 /// method for something like `LANES == 3`.
4192 ///
4193 /// # Examples
4194 ///
4195 /// ```
4196 /// #![feature(portable_simd)]
4197 /// use core::simd::prelude::*;
4198 ///
4199 /// let short = &[1, 2, 3];
4200 /// let (prefix, middle, suffix) = short.as_simd::<4>();
4201 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
4202 ///
4203 /// // They might be split in any possible way between prefix and suffix
4204 /// let it = prefix.iter().chain(suffix).copied();
4205 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
4206 ///
4207 /// fn basic_simd_sum(x: &[f32]) -> f32 {
4208 /// use std::ops::Add;
4209 /// let (prefix, middle, suffix) = x.as_simd();
4210 /// let sums = f32x4::from_array([
4211 /// prefix.iter().copied().sum(),
4212 /// 0.0,
4213 /// 0.0,
4214 /// suffix.iter().copied().sum(),
4215 /// ]);
4216 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
4217 /// sums.reduce_sum()
4218 /// }
4219 ///
4220 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
4221 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
4222 /// ```
4223 #[unstable(feature = "portable_simd", issue = "86656")]
4224 #[must_use]
4225 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
4226 where
4227 Simd<T, LANES>: AsRef<[T; LANES]>,
4228 T: simd::SimdElement,
4229 simd::LaneCount<LANES>: simd::SupportedLaneCount,
4230 {
4231 // These are expected to always match, as vector types are laid out like
4232 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
4233 // might as well double-check since it'll optimize away anyhow.
4234 assert_eq!(size_of::<Simd<T, LANES>>(), size_of::<[T; LANES]>());
4235
4236 // SAFETY: The simd types have the same layout as arrays, just with
4237 // potentially-higher alignment, so the de-facto transmutes are sound.
4238 unsafe { self.align_to() }
4239 }
4240
4241 /// Splits a mutable slice into a mutable prefix, a middle of aligned SIMD types,
4242 /// and a mutable suffix.
4243 ///
4244 /// This is a safe wrapper around [`slice::align_to_mut`], so inherits the same
4245 /// guarantees as that method.
4246 ///
4247 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
4248 ///
4249 /// # Panics
4250 ///
4251 /// This will panic if the size of the SIMD type is different from
4252 /// `LANES` times that of the scalar.
4253 ///
4254 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
4255 /// that from ever happening, as only power-of-two numbers of lanes are
4256 /// supported. It's possible that, in the future, those restrictions might
4257 /// be lifted in a way that would make it possible to see panics from this
4258 /// method for something like `LANES == 3`.
4259 #[unstable(feature = "portable_simd", issue = "86656")]
4260 #[must_use]
4261 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
4262 where
4263 Simd<T, LANES>: AsMut<[T; LANES]>,
4264 T: simd::SimdElement,
4265 simd::LaneCount<LANES>: simd::SupportedLaneCount,
4266 {
4267 // These are expected to always match, as vector types are laid out like
4268 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
4269 // might as well double-check since it'll optimize away anyhow.
4270 assert_eq!(size_of::<Simd<T, LANES>>(), size_of::<[T; LANES]>());
4271
4272 // SAFETY: The simd types have the same layout as arrays, just with
4273 // potentially-higher alignment, so the de-facto transmutes are sound.
4274 unsafe { self.align_to_mut() }
4275 }
4276
4277 /// Checks if the elements of this slice are sorted.
4278 ///
4279 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
4280 /// slice yields exactly zero or one element, `true` is returned.
4281 ///
4282 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
4283 /// implies that this function returns `false` if any two consecutive items are not
4284 /// comparable.
4285 ///
4286 /// # Examples
4287 ///
4288 /// ```
4289 /// let empty: [i32; 0] = [];
4290 ///
4291 /// assert!([1, 2, 2, 9].is_sorted());
4292 /// assert!(![1, 3, 2, 4].is_sorted());
4293 /// assert!([0].is_sorted());
4294 /// assert!(empty.is_sorted());
4295 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
4296 /// ```
4297 #[inline]
4298 #[stable(feature = "is_sorted", since = "1.82.0")]
4299 #[must_use]
4300 pub fn is_sorted(&self) -> bool
4301 where
4302 T: PartialOrd,
4303 {
4304 // This odd number works the best. 32 + 1 extra due to overlapping chunk boundaries.
4305 const CHUNK_SIZE: usize = 33;
4306 if self.len() < CHUNK_SIZE {
4307 return self.windows(2).all(|w| w[0] <= w[1]);
4308 }
4309 let mut i = 0;
4310 // Check in chunks for autovectorization.
4311 while i < self.len() - CHUNK_SIZE {
4312 let chunk = &self[i..i + CHUNK_SIZE];
4313 if !chunk.windows(2).fold(true, |acc, w| acc & (w[0] <= w[1])) {
4314 return false;
4315 }
4316 // We need to ensure that chunk boundaries are also sorted.
4317 // Overlap the next chunk with the last element of our last chunk.
4318 i += CHUNK_SIZE - 1;
4319 }
4320 self[i..].windows(2).all(|w| w[0] <= w[1])
4321 }
4322
4323 /// Checks if the elements of this slice are sorted using the given comparator function.
4324 ///
4325 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
4326 /// function to determine whether two elements are to be considered in sorted order.
4327 ///
4328 /// # Examples
4329 ///
4330 /// ```
4331 /// assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
4332 /// assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b));
4333 ///
4334 /// assert!([0].is_sorted_by(|a, b| true));
4335 /// assert!([0].is_sorted_by(|a, b| false));
4336 ///
4337 /// let empty: [i32; 0] = [];
4338 /// assert!(empty.is_sorted_by(|a, b| false));
4339 /// assert!(empty.is_sorted_by(|a, b| true));
4340 /// ```
4341 #[stable(feature = "is_sorted", since = "1.82.0")]
4342 #[must_use]
4343 pub fn is_sorted_by<'a, F>(&'a self, mut compare: F) -> bool
4344 where
4345 F: FnMut(&'a T, &'a T) -> bool,
4346 {
4347 self.array_windows().all(|[a, b]| compare(a, b))
4348 }
4349
4350 /// Checks if the elements of this slice are sorted using the given key extraction function.
4351 ///
4352 /// Instead of comparing the slice's elements directly, this function compares the keys of the
4353 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
4354 /// documentation for more information.
4355 ///
4356 /// [`is_sorted`]: slice::is_sorted
4357 ///
4358 /// # Examples
4359 ///
4360 /// ```
4361 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
4362 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
4363 /// ```
4364 #[inline]
4365 #[stable(feature = "is_sorted", since = "1.82.0")]
4366 #[must_use]
4367 pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool
4368 where
4369 F: FnMut(&'a T) -> K,
4370 K: PartialOrd,
4371 {
4372 self.iter().is_sorted_by_key(f)
4373 }
4374
4375 /// Returns the index of the partition point according to the given predicate
4376 /// (the index of the first element of the second partition).
4377 ///
4378 /// The slice is assumed to be partitioned according to the given predicate.
4379 /// This means that all elements for which the predicate returns true are at the start of the slice
4380 /// and all elements for which the predicate returns false are at the end.
4381 /// For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0`
4382 /// (all odd numbers are at the start, all even at the end).
4383 ///
4384 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
4385 /// as this method performs a kind of binary search.
4386 ///
4387 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
4388 ///
4389 /// [`binary_search`]: slice::binary_search
4390 /// [`binary_search_by`]: slice::binary_search_by
4391 /// [`binary_search_by_key`]: slice::binary_search_by_key
4392 ///
4393 /// # Examples
4394 ///
4395 /// ```
4396 /// let v = [1, 2, 3, 3, 5, 6, 7];
4397 /// let i = v.partition_point(|&x| x < 5);
4398 ///
4399 /// assert_eq!(i, 4);
4400 /// assert!(v[..i].iter().all(|&x| x < 5));
4401 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
4402 /// ```
4403 ///
4404 /// If all elements of the slice match the predicate, including if the slice
4405 /// is empty, then the length of the slice will be returned:
4406 ///
4407 /// ```
4408 /// let a = [2, 4, 8];
4409 /// assert_eq!(a.partition_point(|x| x < &100), a.len());
4410 /// let a: [i32; 0] = [];
4411 /// assert_eq!(a.partition_point(|x| x < &100), 0);
4412 /// ```
4413 ///
4414 /// If you want to insert an item to a sorted vector, while maintaining
4415 /// sort order:
4416 ///
4417 /// ```
4418 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
4419 /// let num = 42;
4420 /// let idx = s.partition_point(|&x| x <= num);
4421 /// s.insert(idx, num);
4422 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
4423 /// ```
4424 #[stable(feature = "partition_point", since = "1.52.0")]
4425 #[must_use]
4426 pub fn partition_point<P>(&self, mut pred: P) -> usize
4427 where
4428 P: FnMut(&T) -> bool,
4429 {
4430 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
4431 }
4432
4433 /// Removes the subslice corresponding to the given range
4434 /// and returns a reference to it.
4435 ///
4436 /// Returns `None` and does not modify the slice if the given
4437 /// range is out of bounds.
4438 ///
4439 /// Note that this method only accepts one-sided ranges such as
4440 /// `2..` or `..6`, but not `2..6`.
4441 ///
4442 /// # Examples
4443 ///
4444 /// Splitting off the first three elements of a slice:
4445 ///
4446 /// ```
4447 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4448 /// let mut first_three = slice.split_off(..3).unwrap();
4449 ///
4450 /// assert_eq!(slice, &['d']);
4451 /// assert_eq!(first_three, &['a', 'b', 'c']);
4452 /// ```
4453 ///
4454 /// Splitting off a slice starting with the third element:
4455 ///
4456 /// ```
4457 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4458 /// let mut tail = slice.split_off(2..).unwrap();
4459 ///
4460 /// assert_eq!(slice, &['a', 'b']);
4461 /// assert_eq!(tail, &['c', 'd']);
4462 /// ```
4463 ///
4464 /// Getting `None` when `range` is out of bounds:
4465 ///
4466 /// ```
4467 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4468 ///
4469 /// assert_eq!(None, slice.split_off(5..));
4470 /// assert_eq!(None, slice.split_off(..5));
4471 /// assert_eq!(None, slice.split_off(..=4));
4472 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
4473 /// assert_eq!(Some(expected), slice.split_off(..4));
4474 /// ```
4475 #[inline]
4476 #[must_use = "method does not modify the slice if the range is out of bounds"]
4477 #[stable(feature = "slice_take", since = "1.87.0")]
4478 pub fn split_off<'a, R: OneSidedRange<usize>>(
4479 self: &mut &'a Self,
4480 range: R,
4481 ) -> Option<&'a Self> {
4482 let (direction, split_index) = split_point_of(range)?;
4483 if split_index > self.len() {
4484 return None;
4485 }
4486 let (front, back) = self.split_at(split_index);
4487 match direction {
4488 Direction::Front => {
4489 *self = back;
4490 Some(front)
4491 }
4492 Direction::Back => {
4493 *self = front;
4494 Some(back)
4495 }
4496 }
4497 }
4498
4499 /// Removes the subslice corresponding to the given range
4500 /// and returns a mutable reference to it.
4501 ///
4502 /// Returns `None` and does not modify the slice if the given
4503 /// range is out of bounds.
4504 ///
4505 /// Note that this method only accepts one-sided ranges such as
4506 /// `2..` or `..6`, but not `2..6`.
4507 ///
4508 /// # Examples
4509 ///
4510 /// Splitting off the first three elements of a slice:
4511 ///
4512 /// ```
4513 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4514 /// let mut first_three = slice.split_off_mut(..3).unwrap();
4515 ///
4516 /// assert_eq!(slice, &mut ['d']);
4517 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
4518 /// ```
4519 ///
4520 /// Splitting off a slice starting with the third element:
4521 ///
4522 /// ```
4523 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4524 /// let mut tail = slice.split_off_mut(2..).unwrap();
4525 ///
4526 /// assert_eq!(slice, &mut ['a', 'b']);
4527 /// assert_eq!(tail, &mut ['c', 'd']);
4528 /// ```
4529 ///
4530 /// Getting `None` when `range` is out of bounds:
4531 ///
4532 /// ```
4533 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4534 ///
4535 /// assert_eq!(None, slice.split_off_mut(5..));
4536 /// assert_eq!(None, slice.split_off_mut(..5));
4537 /// assert_eq!(None, slice.split_off_mut(..=4));
4538 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4539 /// assert_eq!(Some(expected), slice.split_off_mut(..4));
4540 /// ```
4541 #[inline]
4542 #[must_use = "method does not modify the slice if the range is out of bounds"]
4543 #[stable(feature = "slice_take", since = "1.87.0")]
4544 pub fn split_off_mut<'a, R: OneSidedRange<usize>>(
4545 self: &mut &'a mut Self,
4546 range: R,
4547 ) -> Option<&'a mut Self> {
4548 let (direction, split_index) = split_point_of(range)?;
4549 if split_index > self.len() {
4550 return None;
4551 }
4552 let (front, back) = mem::take(self).split_at_mut(split_index);
4553 match direction {
4554 Direction::Front => {
4555 *self = back;
4556 Some(front)
4557 }
4558 Direction::Back => {
4559 *self = front;
4560 Some(back)
4561 }
4562 }
4563 }
4564
4565 /// Removes the first element of the slice and returns a reference
4566 /// to it.
4567 ///
4568 /// Returns `None` if the slice is empty.
4569 ///
4570 /// # Examples
4571 ///
4572 /// ```
4573 /// let mut slice: &[_] = &['a', 'b', 'c'];
4574 /// let first = slice.split_off_first().unwrap();
4575 ///
4576 /// assert_eq!(slice, &['b', 'c']);
4577 /// assert_eq!(first, &'a');
4578 /// ```
4579 #[inline]
4580 #[stable(feature = "slice_take", since = "1.87.0")]
4581 #[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
4582 pub const fn split_off_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
4583 // FIXME(const-hack): Use `?` when available in const instead of `let-else`.
4584 let Some((first, rem)) = self.split_first() else { return None };
4585 *self = rem;
4586 Some(first)
4587 }
4588
4589 /// Removes the first element of the slice and returns a mutable
4590 /// reference to it.
4591 ///
4592 /// Returns `None` if the slice is empty.
4593 ///
4594 /// # Examples
4595 ///
4596 /// ```
4597 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4598 /// let first = slice.split_off_first_mut().unwrap();
4599 /// *first = 'd';
4600 ///
4601 /// assert_eq!(slice, &['b', 'c']);
4602 /// assert_eq!(first, &'d');
4603 /// ```
4604 #[inline]
4605 #[stable(feature = "slice_take", since = "1.87.0")]
4606 #[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
4607 pub const fn split_off_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4608 // FIXME(const-hack): Use `mem::take` and `?` when available in const.
4609 // Original: `mem::take(self).split_first_mut()?`
4610 let Some((first, rem)) = mem::replace(self, &mut []).split_first_mut() else { return None };
4611 *self = rem;
4612 Some(first)
4613 }
4614
4615 /// Removes the last element of the slice and returns a reference
4616 /// to it.
4617 ///
4618 /// Returns `None` if the slice is empty.
4619 ///
4620 /// # Examples
4621 ///
4622 /// ```
4623 /// let mut slice: &[_] = &['a', 'b', 'c'];
4624 /// let last = slice.split_off_last().unwrap();
4625 ///
4626 /// assert_eq!(slice, &['a', 'b']);
4627 /// assert_eq!(last, &'c');
4628 /// ```
4629 #[inline]
4630 #[stable(feature = "slice_take", since = "1.87.0")]
4631 #[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
4632 pub const fn split_off_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
4633 // FIXME(const-hack): Use `?` when available in const instead of `let-else`.
4634 let Some((last, rem)) = self.split_last() else { return None };
4635 *self = rem;
4636 Some(last)
4637 }
4638
4639 /// Removes the last element of the slice and returns a mutable
4640 /// reference to it.
4641 ///
4642 /// Returns `None` if the slice is empty.
4643 ///
4644 /// # Examples
4645 ///
4646 /// ```
4647 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4648 /// let last = slice.split_off_last_mut().unwrap();
4649 /// *last = 'd';
4650 ///
4651 /// assert_eq!(slice, &['a', 'b']);
4652 /// assert_eq!(last, &'d');
4653 /// ```
4654 #[inline]
4655 #[stable(feature = "slice_take", since = "1.87.0")]
4656 #[rustc_const_unstable(feature = "const_split_off_first_last", issue = "138539")]
4657 pub const fn split_off_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4658 // FIXME(const-hack): Use `mem::take` and `?` when available in const.
4659 // Original: `mem::take(self).split_last_mut()?`
4660 let Some((last, rem)) = mem::replace(self, &mut []).split_last_mut() else { return None };
4661 *self = rem;
4662 Some(last)
4663 }
4664
4665 /// Returns mutable references to many indices at once, without doing any checks.
4666 ///
4667 /// An index can be either a `usize`, a [`Range`] or a [`RangeInclusive`]. Note
4668 /// that this method takes an array, so all indices must be of the same type.
4669 /// If passed an array of `usize`s this method gives back an array of mutable references
4670 /// to single elements, while if passed an array of ranges it gives back an array of
4671 /// mutable references to slices.
4672 ///
4673 /// For a safe alternative see [`get_disjoint_mut`].
4674 ///
4675 /// # Safety
4676 ///
4677 /// Calling this method with overlapping or out-of-bounds indices is *[undefined behavior]*
4678 /// even if the resulting references are not used.
4679 ///
4680 /// # Examples
4681 ///
4682 /// ```
4683 /// let x = &mut [1, 2, 4];
4684 ///
4685 /// unsafe {
4686 /// let [a, b] = x.get_disjoint_unchecked_mut([0, 2]);
4687 /// *a *= 10;
4688 /// *b *= 100;
4689 /// }
4690 /// assert_eq!(x, &[10, 2, 400]);
4691 ///
4692 /// unsafe {
4693 /// let [a, b] = x.get_disjoint_unchecked_mut([0..1, 1..3]);
4694 /// a[0] = 8;
4695 /// b[0] = 88;
4696 /// b[1] = 888;
4697 /// }
4698 /// assert_eq!(x, &[8, 88, 888]);
4699 ///
4700 /// unsafe {
4701 /// let [a, b] = x.get_disjoint_unchecked_mut([1..=2, 0..=0]);
4702 /// a[0] = 11;
4703 /// a[1] = 111;
4704 /// b[0] = 1;
4705 /// }
4706 /// assert_eq!(x, &[1, 11, 111]);
4707 /// ```
4708 ///
4709 /// [`get_disjoint_mut`]: slice::get_disjoint_mut
4710 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
4711 #[stable(feature = "get_many_mut", since = "1.86.0")]
4712 #[inline]
4713 #[track_caller]
4714 pub unsafe fn get_disjoint_unchecked_mut<I, const N: usize>(
4715 &mut self,
4716 indices: [I; N],
4717 ) -> [&mut I::Output; N]
4718 where
4719 I: GetDisjointMutIndex + SliceIndex<Self>,
4720 {
4721 // NB: This implementation is written as it is because any variation of
4722 // `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
4723 // or generate worse code otherwise. This is also why we need to go
4724 // through a raw pointer here.
4725 let slice: *mut [T] = self;
4726 let mut arr: MaybeUninit<[&mut I::Output; N]> = MaybeUninit::uninit();
4727 let arr_ptr = arr.as_mut_ptr();
4728
4729 // SAFETY: We expect `indices` to contain disjunct values that are
4730 // in bounds of `self`.
4731 unsafe {
4732 for i in 0..N {
4733 let idx = indices.get_unchecked(i).clone();
4734 arr_ptr.cast::<&mut I::Output>().add(i).write(&mut *slice.get_unchecked_mut(idx));
4735 }
4736 arr.assume_init()
4737 }
4738 }
4739
4740 /// Returns mutable references to many indices at once.
4741 ///
4742 /// An index can be either a `usize`, a [`Range`] or a [`RangeInclusive`]. Note
4743 /// that this method takes an array, so all indices must be of the same type.
4744 /// If passed an array of `usize`s this method gives back an array of mutable references
4745 /// to single elements, while if passed an array of ranges it gives back an array of
4746 /// mutable references to slices.
4747 ///
4748 /// Returns an error if any index is out-of-bounds, or if there are overlapping indices.
4749 /// An empty range is not considered to overlap if it is located at the beginning or at
4750 /// the end of another range, but is considered to overlap if it is located in the middle.
4751 ///
4752 /// This method does a O(n^2) check to check that there are no overlapping indices, so be careful
4753 /// when passing many indices.
4754 ///
4755 /// # Examples
4756 ///
4757 /// ```
4758 /// let v = &mut [1, 2, 3];
4759 /// if let Ok([a, b]) = v.get_disjoint_mut([0, 2]) {
4760 /// *a = 413;
4761 /// *b = 612;
4762 /// }
4763 /// assert_eq!(v, &[413, 2, 612]);
4764 ///
4765 /// if let Ok([a, b]) = v.get_disjoint_mut([0..1, 1..3]) {
4766 /// a[0] = 8;
4767 /// b[0] = 88;
4768 /// b[1] = 888;
4769 /// }
4770 /// assert_eq!(v, &[8, 88, 888]);
4771 ///
4772 /// if let Ok([a, b]) = v.get_disjoint_mut([1..=2, 0..=0]) {
4773 /// a[0] = 11;
4774 /// a[1] = 111;
4775 /// b[0] = 1;
4776 /// }
4777 /// assert_eq!(v, &[1, 11, 111]);
4778 /// ```
4779 #[stable(feature = "get_many_mut", since = "1.86.0")]
4780 #[inline]
4781 pub fn get_disjoint_mut<I, const N: usize>(
4782 &mut self,
4783 indices: [I; N],
4784 ) -> Result<[&mut I::Output; N], GetDisjointMutError>
4785 where
4786 I: GetDisjointMutIndex + SliceIndex<Self>,
4787 {
4788 get_disjoint_check_valid(&indices, self.len())?;
4789 // SAFETY: The `get_disjoint_check_valid()` call checked that all indices
4790 // are disjunct and in bounds.
4791 unsafe { Ok(self.get_disjoint_unchecked_mut(indices)) }
4792 }
4793
4794 /// Returns the index that an element reference points to.
4795 ///
4796 /// Returns `None` if `element` does not point to the start of an element within the slice.
4797 ///
4798 /// This method is useful for extending slice iterators like [`slice::split`].
4799 ///
4800 /// Note that this uses pointer arithmetic and **does not compare elements**.
4801 /// To find the index of an element via comparison, use
4802 /// [`.iter().position()`](crate::iter::Iterator::position) instead.
4803 ///
4804 /// # Panics
4805 /// Panics if `T` is zero-sized.
4806 ///
4807 /// # Examples
4808 /// Basic usage:
4809 /// ```
4810 /// #![feature(substr_range)]
4811 ///
4812 /// let nums: &[u32] = &[1, 7, 1, 1];
4813 /// let num = &nums[2];
4814 ///
4815 /// assert_eq!(num, &1);
4816 /// assert_eq!(nums.element_offset(num), Some(2));
4817 /// ```
4818 /// Returning `None` with an unaligned element:
4819 /// ```
4820 /// #![feature(substr_range)]
4821 ///
4822 /// let arr: &[[u32; 2]] = &[[0, 1], [2, 3]];
4823 /// let flat_arr: &[u32] = arr.as_flattened();
4824 ///
4825 /// let ok_elm: &[u32; 2] = flat_arr[0..2].try_into().unwrap();
4826 /// let weird_elm: &[u32; 2] = flat_arr[1..3].try_into().unwrap();
4827 ///
4828 /// assert_eq!(ok_elm, &[0, 1]);
4829 /// assert_eq!(weird_elm, &[1, 2]);
4830 ///
4831 /// assert_eq!(arr.element_offset(ok_elm), Some(0)); // Points to element 0
4832 /// assert_eq!(arr.element_offset(weird_elm), None); // Points between element 0 and 1
4833 /// ```
4834 #[must_use]
4835 #[unstable(feature = "substr_range", issue = "126769")]
4836 pub fn element_offset(&self, element: &T) -> Option<usize> {
4837 if T::IS_ZST {
4838 panic!("elements are zero-sized");
4839 }
4840
4841 let self_start = self.as_ptr().addr();
4842 let elem_start = ptr::from_ref(element).addr();
4843
4844 let byte_offset = elem_start.wrapping_sub(self_start);
4845
4846 if !byte_offset.is_multiple_of(size_of::<T>()) {
4847 return None;
4848 }
4849
4850 let offset = byte_offset / size_of::<T>();
4851
4852 if offset < self.len() { Some(offset) } else { None }
4853 }
4854
4855 /// Returns the range of indices that a subslice points to.
4856 ///
4857 /// Returns `None` if `subslice` does not point within the slice or if it is not aligned with the
4858 /// elements in the slice.
4859 ///
4860 /// This method **does not compare elements**. Instead, this method finds the location in the slice that
4861 /// `subslice` was obtained from. To find the index of a subslice via comparison, instead use
4862 /// [`.windows()`](slice::windows)[`.position()`](crate::iter::Iterator::position).
4863 ///
4864 /// This method is useful for extending slice iterators like [`slice::split`].
4865 ///
4866 /// Note that this may return a false positive (either `Some(0..0)` or `Some(self.len()..self.len())`)
4867 /// if `subslice` has a length of zero and points to the beginning or end of another, separate, slice.
4868 ///
4869 /// # Panics
4870 /// Panics if `T` is zero-sized.
4871 ///
4872 /// # Examples
4873 /// Basic usage:
4874 /// ```
4875 /// #![feature(substr_range)]
4876 ///
4877 /// let nums = &[0, 5, 10, 0, 0, 5];
4878 ///
4879 /// let mut iter = nums
4880 /// .split(|t| *t == 0)
4881 /// .map(|n| nums.subslice_range(n).unwrap());
4882 ///
4883 /// assert_eq!(iter.next(), Some(0..0));
4884 /// assert_eq!(iter.next(), Some(1..3));
4885 /// assert_eq!(iter.next(), Some(4..4));
4886 /// assert_eq!(iter.next(), Some(5..6));
4887 /// ```
4888 #[must_use]
4889 #[unstable(feature = "substr_range", issue = "126769")]
4890 pub fn subslice_range(&self, subslice: &[T]) -> Option<Range<usize>> {
4891 if T::IS_ZST {
4892 panic!("elements are zero-sized");
4893 }
4894
4895 let self_start = self.as_ptr().addr();
4896 let subslice_start = subslice.as_ptr().addr();
4897
4898 let byte_start = subslice_start.wrapping_sub(self_start);
4899
4900 if !byte_start.is_multiple_of(size_of::<T>()) {
4901 return None;
4902 }
4903
4904 let start = byte_start / size_of::<T>();
4905 let end = start.wrapping_add(subslice.len());
4906
4907 if start <= self.len() && end <= self.len() { Some(start..end) } else { None }
4908 }
4909}
4910
4911impl<T> [MaybeUninit<T>] {
4912 /// Transmutes the mutable uninitialized slice to a mutable uninitialized slice of
4913 /// another type, ensuring alignment of the types is maintained.
4914 ///
4915 /// This is a safe wrapper around [`slice::align_to_mut`], so inherits the same
4916 /// guarantees as that method.
4917 ///
4918 /// # Examples
4919 ///
4920 /// ```
4921 /// #![feature(align_to_uninit_mut)]
4922 /// use std::mem::MaybeUninit;
4923 ///
4924 /// pub struct BumpAllocator<'scope> {
4925 /// memory: &'scope mut [MaybeUninit<u8>],
4926 /// }
4927 ///
4928 /// impl<'scope> BumpAllocator<'scope> {
4929 /// pub fn new(memory: &'scope mut [MaybeUninit<u8>]) -> Self {
4930 /// Self { memory }
4931 /// }
4932 /// pub fn try_alloc_uninit<T>(&mut self) -> Option<&'scope mut MaybeUninit<T>> {
4933 /// let first_end = self.memory.as_ptr().align_offset(align_of::<T>()) + size_of::<T>();
4934 /// let prefix = self.memory.split_off_mut(..first_end)?;
4935 /// Some(&mut prefix.align_to_uninit_mut::<T>().1[0])
4936 /// }
4937 /// pub fn try_alloc_u32(&mut self, value: u32) -> Option<&'scope mut u32> {
4938 /// let uninit = self.try_alloc_uninit()?;
4939 /// Some(uninit.write(value))
4940 /// }
4941 /// }
4942 ///
4943 /// let mut memory = [MaybeUninit::<u8>::uninit(); 10];
4944 /// let mut allocator = BumpAllocator::new(&mut memory);
4945 /// let v = allocator.try_alloc_u32(42);
4946 /// assert_eq!(v, Some(&mut 42));
4947 /// ```
4948 #[unstable(feature = "align_to_uninit_mut", issue = "139062")]
4949 #[inline]
4950 #[must_use]
4951 pub fn align_to_uninit_mut<U>(&mut self) -> (&mut Self, &mut [MaybeUninit<U>], &mut Self) {
4952 // SAFETY: `MaybeUninit` is transparent. Correct size and alignment are guaranteed by
4953 // `align_to_mut` itself. Therefore the only thing that we have to ensure for a safe
4954 // `transmute` is that the values are valid for the types involved. But for `MaybeUninit`
4955 // any values are valid, so this operation is safe.
4956 unsafe { self.align_to_mut() }
4957 }
4958}
4959
4960impl<T, const N: usize> [[T; N]] {
4961 /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
4962 ///
4963 /// For the opposite operation, see [`as_chunks`] and [`as_rchunks`].
4964 ///
4965 /// [`as_chunks`]: slice::as_chunks
4966 /// [`as_rchunks`]: slice::as_rchunks
4967 ///
4968 /// # Panics
4969 ///
4970 /// This panics if the length of the resulting slice would overflow a `usize`.
4971 ///
4972 /// This is only possible when flattening a slice of arrays of zero-sized
4973 /// types, and thus tends to be irrelevant in practice. If
4974 /// `size_of::<T>() > 0`, this will never panic.
4975 ///
4976 /// # Examples
4977 ///
4978 /// ```
4979 /// assert_eq!([[1, 2, 3], [4, 5, 6]].as_flattened(), &[1, 2, 3, 4, 5, 6]);
4980 ///
4981 /// assert_eq!(
4982 /// [[1, 2, 3], [4, 5, 6]].as_flattened(),
4983 /// [[1, 2], [3, 4], [5, 6]].as_flattened(),
4984 /// );
4985 ///
4986 /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
4987 /// assert!(slice_of_empty_arrays.as_flattened().is_empty());
4988 ///
4989 /// let empty_slice_of_arrays: &[[u32; 10]] = &[];
4990 /// assert!(empty_slice_of_arrays.as_flattened().is_empty());
4991 /// ```
4992 #[stable(feature = "slice_flatten", since = "1.80.0")]
4993 #[rustc_const_stable(feature = "const_slice_flatten", since = "1.87.0")]
4994 pub const fn as_flattened(&self) -> &[T] {
4995 let len = if T::IS_ZST {
4996 self.len().checked_mul(N).expect("slice len overflow")
4997 } else {
4998 // SAFETY: `self.len() * N` cannot overflow because `self` is
4999 // already in the address space.
5000 unsafe { self.len().unchecked_mul(N) }
5001 };
5002 // SAFETY: `[T]` is layout-identical to `[T; N]`
5003 unsafe { from_raw_parts(self.as_ptr().cast(), len) }
5004 }
5005
5006 /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
5007 ///
5008 /// For the opposite operation, see [`as_chunks_mut`] and [`as_rchunks_mut`].
5009 ///
5010 /// [`as_chunks_mut`]: slice::as_chunks_mut
5011 /// [`as_rchunks_mut`]: slice::as_rchunks_mut
5012 ///
5013 /// # Panics
5014 ///
5015 /// This panics if the length of the resulting slice would overflow a `usize`.
5016 ///
5017 /// This is only possible when flattening a slice of arrays of zero-sized
5018 /// types, and thus tends to be irrelevant in practice. If
5019 /// `size_of::<T>() > 0`, this will never panic.
5020 ///
5021 /// # Examples
5022 ///
5023 /// ```
5024 /// fn add_5_to_all(slice: &mut [i32]) {
5025 /// for i in slice {
5026 /// *i += 5;
5027 /// }
5028 /// }
5029 ///
5030 /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
5031 /// add_5_to_all(array.as_flattened_mut());
5032 /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
5033 /// ```
5034 #[stable(feature = "slice_flatten", since = "1.80.0")]
5035 #[rustc_const_stable(feature = "const_slice_flatten", since = "1.87.0")]
5036 pub const fn as_flattened_mut(&mut self) -> &mut [T] {
5037 let len = if T::IS_ZST {
5038 self.len().checked_mul(N).expect("slice len overflow")
5039 } else {
5040 // SAFETY: `self.len() * N` cannot overflow because `self` is
5041 // already in the address space.
5042 unsafe { self.len().unchecked_mul(N) }
5043 };
5044 // SAFETY: `[T]` is layout-identical to `[T; N]`
5045 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
5046 }
5047}
5048
5049impl [f32] {
5050 /// Sorts the slice of floats.
5051 ///
5052 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
5053 /// the ordering defined by [`f32::total_cmp`].
5054 ///
5055 /// # Current implementation
5056 ///
5057 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
5058 ///
5059 /// # Examples
5060 ///
5061 /// ```
5062 /// #![feature(sort_floats)]
5063 /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
5064 ///
5065 /// v.sort_floats();
5066 /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
5067 /// assert_eq!(&v[..8], &sorted[..8]);
5068 /// assert!(v[8].is_nan());
5069 /// ```
5070 #[unstable(feature = "sort_floats", issue = "93396")]
5071 #[inline]
5072 pub fn sort_floats(&mut self) {
5073 self.sort_unstable_by(f32::total_cmp);
5074 }
5075}
5076
5077impl [f64] {
5078 /// Sorts the slice of floats.
5079 ///
5080 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
5081 /// the ordering defined by [`f64::total_cmp`].
5082 ///
5083 /// # Current implementation
5084 ///
5085 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
5086 ///
5087 /// # Examples
5088 ///
5089 /// ```
5090 /// #![feature(sort_floats)]
5091 /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
5092 ///
5093 /// v.sort_floats();
5094 /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
5095 /// assert_eq!(&v[..8], &sorted[..8]);
5096 /// assert!(v[8].is_nan());
5097 /// ```
5098 #[unstable(feature = "sort_floats", issue = "93396")]
5099 #[inline]
5100 pub fn sort_floats(&mut self) {
5101 self.sort_unstable_by(f64::total_cmp);
5102 }
5103}
5104
5105/// Copies `src` to `dest`.
5106///
5107/// # Safety
5108/// `T` must implement one of `Copy` or `TrivialClone`.
5109#[track_caller]
5110const unsafe fn copy_from_slice_impl<T: Clone>(dest: &mut [T], src: &[T]) {
5111 // The panic code path was put into a cold function to not bloat the
5112 // call site.
5113 #[cfg_attr(not(panic = "immediate-abort"), inline(never), cold)]
5114 #[cfg_attr(panic = "immediate-abort", inline)]
5115 #[track_caller]
5116 const fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
5117 const_panic!(
5118 "copy_from_slice: source slice length does not match destination slice length",
5119 "copy_from_slice: source slice length ({src_len}) does not match destination slice length ({dst_len})",
5120 src_len: usize,
5121 dst_len: usize,
5122 )
5123 }
5124
5125 if dest.len() != src.len() {
5126 len_mismatch_fail(dest.len(), src.len());
5127 }
5128
5129 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
5130 // checked to have the same length. The slices cannot overlap because
5131 // mutable references are exclusive.
5132 unsafe {
5133 ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(), dest.len());
5134 }
5135}
5136
5137trait CloneFromSpec<T> {
5138 fn spec_clone_from(&mut self, src: &[T]);
5139}
5140
5141impl<T> CloneFromSpec<T> for [T]
5142where
5143 T: Clone,
5144{
5145 #[track_caller]
5146 default fn spec_clone_from(&mut self, src: &[T]) {
5147 assert!(self.len() == src.len(), "destination and source slices have different lengths");
5148 // NOTE: We need to explicitly slice them to the same length
5149 // to make it easier for the optimizer to elide bounds checking.
5150 // But since it can't be relied on we also have an explicit specialization for T: Copy.
5151 let len: usize = self.len();
5152 let src: &[T] = &src[..len];
5153 for i: usize in 0..len {
5154 self[i].clone_from(&src[i]);
5155 }
5156 }
5157}
5158
5159impl<T> CloneFromSpec<T> for [T]
5160where
5161 T: TrivialClone,
5162{
5163 #[track_caller]
5164 fn spec_clone_from(&mut self, src: &[T]) {
5165 // SAFETY: `T` implements `TrivialClone`.
5166 unsafe {
5167 copy_from_slice_impl(self, src);
5168 }
5169 }
5170}
5171
5172#[stable(feature = "rust1", since = "1.0.0")]
5173#[rustc_const_unstable(feature = "const_default", issue = "143894")]
5174impl<T> const Default for &[T] {
5175 /// Creates an empty slice.
5176 fn default() -> Self {
5177 &[]
5178 }
5179}
5180
5181#[stable(feature = "mut_slice_default", since = "1.5.0")]
5182#[rustc_const_unstable(feature = "const_default", issue = "143894")]
5183impl<T> const Default for &mut [T] {
5184 /// Creates a mutable empty slice.
5185 fn default() -> Self {
5186 &mut []
5187 }
5188}
5189
5190#[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
5191/// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
5192/// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
5193/// `str`) to slices, and then this trait will be replaced or abolished.
5194pub trait SlicePattern {
5195 /// The element type of the slice being matched on.
5196 type Item;
5197
5198 /// Currently, the consumers of `SlicePattern` need a slice.
5199 fn as_slice(&self) -> &[Self::Item];
5200}
5201
5202#[stable(feature = "slice_strip", since = "1.51.0")]
5203impl<T> SlicePattern for [T] {
5204 type Item = T;
5205
5206 #[inline]
5207 fn as_slice(&self) -> &[Self::Item] {
5208 self
5209 }
5210}
5211
5212#[stable(feature = "slice_strip", since = "1.51.0")]
5213impl<T, const N: usize> SlicePattern for [T; N] {
5214 type Item = T;
5215
5216 #[inline]
5217 fn as_slice(&self) -> &[Self::Item] {
5218 self
5219 }
5220}
5221
5222/// This checks every index against each other, and against `len`.
5223///
5224/// This will do `binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, ..`
5225/// comparison operations.
5226#[inline]
5227fn get_disjoint_check_valid<I: GetDisjointMutIndex, const N: usize>(
5228 indices: &[I; N],
5229 len: usize,
5230) -> Result<(), GetDisjointMutError> {
5231 // NB: The optimizer should inline the loops into a sequence
5232 // of instructions without additional branching.
5233 for (i: usize, idx: &I) in indices.iter().enumerate() {
5234 if !idx.is_in_bounds(len) {
5235 return Err(GetDisjointMutError::IndexOutOfBounds);
5236 }
5237 for idx2: &I in &indices[..i] {
5238 if idx.is_overlapping(idx2) {
5239 return Err(GetDisjointMutError::OverlappingIndices);
5240 }
5241 }
5242 }
5243 Ok(())
5244}
5245
5246/// The error type returned by [`get_disjoint_mut`][`slice::get_disjoint_mut`].
5247///
5248/// It indicates one of two possible errors:
5249/// - An index is out-of-bounds.
5250/// - The same index appeared multiple times in the array
5251/// (or different but overlapping indices when ranges are provided).
5252///
5253/// # Examples
5254///
5255/// ```
5256/// use std::slice::GetDisjointMutError;
5257///
5258/// let v = &mut [1, 2, 3];
5259/// assert_eq!(v.get_disjoint_mut([0, 999]), Err(GetDisjointMutError::IndexOutOfBounds));
5260/// assert_eq!(v.get_disjoint_mut([1, 1]), Err(GetDisjointMutError::OverlappingIndices));
5261/// ```
5262#[stable(feature = "get_many_mut", since = "1.86.0")]
5263#[derive(Debug, Clone, PartialEq, Eq)]
5264pub enum GetDisjointMutError {
5265 /// An index provided was out-of-bounds for the slice.
5266 IndexOutOfBounds,
5267 /// Two indices provided were overlapping.
5268 OverlappingIndices,
5269}
5270
5271#[stable(feature = "get_many_mut", since = "1.86.0")]
5272impl fmt::Display for GetDisjointMutError {
5273 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
5274 let msg: &'static str = match self {
5275 GetDisjointMutError::IndexOutOfBounds => "an index is out of bounds",
5276 GetDisjointMutError::OverlappingIndices => "there were overlapping indices",
5277 };
5278 fmt::Display::fmt(self:msg, f)
5279 }
5280}
5281
5282mod private_get_disjoint_mut_index {
5283 use super::{Range, RangeInclusive, range};
5284
5285 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5286 pub trait Sealed {}
5287
5288 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5289 impl Sealed for usize {}
5290 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5291 impl Sealed for Range<usize> {}
5292 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5293 impl Sealed for RangeInclusive<usize> {}
5294 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5295 impl Sealed for range::Range<usize> {}
5296 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5297 impl Sealed for range::RangeInclusive<usize> {}
5298}
5299
5300/// A helper trait for `<[T]>::get_disjoint_mut()`.
5301///
5302/// # Safety
5303///
5304/// If `is_in_bounds()` returns `true` and `is_overlapping()` returns `false`,
5305/// it must be safe to index the slice with the indices.
5306#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5307pub unsafe trait GetDisjointMutIndex:
5308 Clone + private_get_disjoint_mut_index::Sealed
5309{
5310 /// Returns `true` if `self` is in bounds for `len` slice elements.
5311 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5312 fn is_in_bounds(&self, len: usize) -> bool;
5313
5314 /// Returns `true` if `self` overlaps with `other`.
5315 ///
5316 /// Note that we don't consider zero-length ranges to overlap at the beginning or the end,
5317 /// but do consider them to overlap in the middle.
5318 #[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5319 fn is_overlapping(&self, other: &Self) -> bool;
5320}
5321
5322#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5323// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
5324unsafe impl GetDisjointMutIndex for usize {
5325 #[inline]
5326 fn is_in_bounds(&self, len: usize) -> bool {
5327 *self < len
5328 }
5329
5330 #[inline]
5331 fn is_overlapping(&self, other: &Self) -> bool {
5332 *self == *other
5333 }
5334}
5335
5336#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5337// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
5338unsafe impl GetDisjointMutIndex for Range<usize> {
5339 #[inline]
5340 fn is_in_bounds(&self, len: usize) -> bool {
5341 (self.start <= self.end) & (self.end <= len)
5342 }
5343
5344 #[inline]
5345 fn is_overlapping(&self, other: &Self) -> bool {
5346 (self.start < other.end) & (other.start < self.end)
5347 }
5348}
5349
5350#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5351// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
5352unsafe impl GetDisjointMutIndex for RangeInclusive<usize> {
5353 #[inline]
5354 fn is_in_bounds(&self, len: usize) -> bool {
5355 (self.start <= self.end) & (self.end < len)
5356 }
5357
5358 #[inline]
5359 fn is_overlapping(&self, other: &Self) -> bool {
5360 (self.start <= other.end) & (other.start <= self.end)
5361 }
5362}
5363
5364#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5365// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
5366unsafe impl GetDisjointMutIndex for range::Range<usize> {
5367 #[inline]
5368 fn is_in_bounds(&self, len: usize) -> bool {
5369 Range::from(*self).is_in_bounds(len)
5370 }
5371
5372 #[inline]
5373 fn is_overlapping(&self, other: &Self) -> bool {
5374 Range::from(*self).is_overlapping(&Range::from(*other))
5375 }
5376}
5377
5378#[unstable(feature = "get_disjoint_mut_helpers", issue = "none")]
5379// SAFETY: We implement `is_in_bounds()` and `is_overlapping()` correctly.
5380unsafe impl GetDisjointMutIndex for range::RangeInclusive<usize> {
5381 #[inline]
5382 fn is_in_bounds(&self, len: usize) -> bool {
5383 RangeInclusive::from(*self).is_in_bounds(len)
5384 }
5385
5386 #[inline]
5387 fn is_overlapping(&self, other: &Self) -> bool {
5388 RangeInclusive::from(*self).is_overlapping(&RangeInclusive::from(*other))
5389 }
5390}
5391