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::cmp::Ordering::{self, Equal, Greater, Less};
10use crate::fmt;
11use crate::hint;
12use crate::intrinsics::exact_div;
13use crate::mem::{self, SizedTypeProperties};
14use crate::num::NonZero;
15use crate::ops::{Bound, OneSidedRange, Range, RangeBounds};
16use crate::ptr;
17use crate::simd::{self, Simd};
18use crate::slice;
19use crate::ub_checks::assert_unsafe_precondition;
20
21#[unstable(
22 feature = "slice_internals",
23 issue = "none",
24 reason = "exposed from core to be reused in std; use the memchr crate"
25)]
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)]
34pub mod sort;
35
36mod ascii;
37mod cmp;
38pub(crate) mod index;
39mod iter;
40mod raw;
41mod rotate;
42mod select;
43mod specialize;
44
45#[unstable(feature = "str_internals", issue = "none")]
46#[doc(hidden)]
47pub use ascii::is_ascii_simple;
48
49#[stable(feature = "rust1", since = "1.0.0")]
50pub use iter::{Chunks, ChunksMut, Windows};
51#[stable(feature = "rust1", since = "1.0.0")]
52pub use iter::{Iter, IterMut};
53#[stable(feature = "rust1", since = "1.0.0")]
54pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
55
56#[stable(feature = "slice_rsplit", since = "1.27.0")]
57pub use iter::{RSplit, RSplitMut};
58
59#[stable(feature = "chunks_exact", since = "1.31.0")]
60pub use iter::{ChunksExact, ChunksExactMut};
61
62#[stable(feature = "rchunks", since = "1.31.0")]
63pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
64
65#[unstable(feature = "array_chunks", issue = "74985")]
66pub use iter::{ArrayChunks, ArrayChunksMut};
67
68#[unstable(feature = "array_windows", issue = "75027")]
69pub use iter::ArrayWindows;
70
71#[stable(feature = "slice_group_by", since = "1.77.0")]
72pub use iter::{ChunkBy, ChunkByMut};
73
74#[stable(feature = "split_inclusive", since = "1.51.0")]
75pub use iter::{SplitInclusive, SplitInclusiveMut};
76
77#[stable(feature = "rust1", since = "1.0.0")]
78pub use raw::{from_raw_parts, from_raw_parts_mut};
79
80#[stable(feature = "from_ref", since = "1.28.0")]
81pub use raw::{from_mut, from_ref};
82
83#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
84pub use raw::{from_mut_ptr_range, from_ptr_range};
85
86// This function is public only because there is no other way to unit test heapsort.
87#[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
88pub use sort::heapsort;
89
90#[stable(feature = "slice_get_slice", since = "1.28.0")]
91pub use index::SliceIndex;
92
93#[unstable(feature = "slice_range", issue = "76393")]
94pub use index::{range, try_range};
95
96#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
97pub use ascii::EscapeAscii;
98
99/// Calculates the direction and split point of a one-sided range.
100///
101/// This is a helper function for `take` and `take_mut` that returns
102/// the direction of the split (front or back) as well as the index at
103/// which to split. Returns `None` if the split index would overflow.
104#[inline]
105fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
106 use Bound::*;
107
108 Some(match (range.start_bound(), range.end_bound()) {
109 (Unbounded, Excluded(i: &usize)) => (Direction::Front, *i),
110 (Unbounded, Included(i: &usize)) => (Direction::Front, i.checked_add(1)?),
111 (Excluded(i: &usize), Unbounded) => (Direction::Back, i.checked_add(1)?),
112 (Included(i: &usize), Unbounded) => (Direction::Back, *i),
113 _ => unreachable!(),
114 })
115}
116
117enum Direction {
118 Front,
119 Back,
120}
121
122#[cfg(not(test))]
123impl<T> [T] {
124 /// Returns the number of elements in the slice.
125 ///
126 /// # Examples
127 ///
128 /// ```
129 /// let a = [1, 2, 3];
130 /// assert_eq!(a.len(), 3);
131 /// ```
132 #[lang = "slice_len_fn"]
133 #[stable(feature = "rust1", since = "1.0.0")]
134 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
135 #[rustc_allow_const_fn_unstable(ptr_metadata)]
136 #[inline]
137 #[must_use]
138 pub const fn len(&self) -> usize {
139 ptr::metadata(self)
140 }
141
142 /// Returns `true` if the slice has a length of 0.
143 ///
144 /// # Examples
145 ///
146 /// ```
147 /// let a = [1, 2, 3];
148 /// assert!(!a.is_empty());
149 ///
150 /// let b: &[i32] = &[];
151 /// assert!(b.is_empty());
152 /// ```
153 #[stable(feature = "rust1", since = "1.0.0")]
154 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
155 #[inline]
156 #[must_use]
157 pub const fn is_empty(&self) -> bool {
158 self.len() == 0
159 }
160
161 /// Returns the first element of the slice, or `None` if it is empty.
162 ///
163 /// # Examples
164 ///
165 /// ```
166 /// let v = [10, 40, 30];
167 /// assert_eq!(Some(&10), v.first());
168 ///
169 /// let w: &[i32] = &[];
170 /// assert_eq!(None, w.first());
171 /// ```
172 #[stable(feature = "rust1", since = "1.0.0")]
173 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
174 #[inline]
175 #[must_use]
176 pub const fn first(&self) -> Option<&T> {
177 if let [first, ..] = self { Some(first) } else { None }
178 }
179
180 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
181 ///
182 /// # Examples
183 ///
184 /// ```
185 /// let x = &mut [0, 1, 2];
186 ///
187 /// if let Some(first) = x.first_mut() {
188 /// *first = 5;
189 /// }
190 /// assert_eq!(x, &[5, 1, 2]);
191 ///
192 /// let y: &mut [i32] = &mut [];
193 /// assert_eq!(None, y.first_mut());
194 /// ```
195 #[stable(feature = "rust1", since = "1.0.0")]
196 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
197 #[inline]
198 #[must_use]
199 pub const fn first_mut(&mut self) -> Option<&mut T> {
200 if let [first, ..] = self { Some(first) } else { None }
201 }
202
203 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
204 ///
205 /// # Examples
206 ///
207 /// ```
208 /// let x = &[0, 1, 2];
209 ///
210 /// if let Some((first, elements)) = x.split_first() {
211 /// assert_eq!(first, &0);
212 /// assert_eq!(elements, &[1, 2]);
213 /// }
214 /// ```
215 #[stable(feature = "slice_splits", since = "1.5.0")]
216 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
217 #[inline]
218 #[must_use]
219 pub const fn split_first(&self) -> Option<(&T, &[T])> {
220 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
221 }
222
223 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
224 ///
225 /// # Examples
226 ///
227 /// ```
228 /// let x = &mut [0, 1, 2];
229 ///
230 /// if let Some((first, elements)) = x.split_first_mut() {
231 /// *first = 3;
232 /// elements[0] = 4;
233 /// elements[1] = 5;
234 /// }
235 /// assert_eq!(x, &[3, 4, 5]);
236 /// ```
237 #[stable(feature = "slice_splits", since = "1.5.0")]
238 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
239 #[inline]
240 #[must_use]
241 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
242 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
243 }
244
245 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
246 ///
247 /// # Examples
248 ///
249 /// ```
250 /// let x = &[0, 1, 2];
251 ///
252 /// if let Some((last, elements)) = x.split_last() {
253 /// assert_eq!(last, &2);
254 /// assert_eq!(elements, &[0, 1]);
255 /// }
256 /// ```
257 #[stable(feature = "slice_splits", since = "1.5.0")]
258 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
259 #[inline]
260 #[must_use]
261 pub const fn split_last(&self) -> Option<(&T, &[T])> {
262 if let [init @ .., last] = self { Some((last, init)) } else { None }
263 }
264
265 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
266 ///
267 /// # Examples
268 ///
269 /// ```
270 /// let x = &mut [0, 1, 2];
271 ///
272 /// if let Some((last, elements)) = x.split_last_mut() {
273 /// *last = 3;
274 /// elements[0] = 4;
275 /// elements[1] = 5;
276 /// }
277 /// assert_eq!(x, &[4, 5, 3]);
278 /// ```
279 #[stable(feature = "slice_splits", since = "1.5.0")]
280 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
281 #[inline]
282 #[must_use]
283 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
284 if let [init @ .., last] = self { Some((last, init)) } else { None }
285 }
286
287 /// Returns the last element of the slice, or `None` if it is empty.
288 ///
289 /// # Examples
290 ///
291 /// ```
292 /// let v = [10, 40, 30];
293 /// assert_eq!(Some(&30), v.last());
294 ///
295 /// let w: &[i32] = &[];
296 /// assert_eq!(None, w.last());
297 /// ```
298 #[stable(feature = "rust1", since = "1.0.0")]
299 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
300 #[inline]
301 #[must_use]
302 pub const fn last(&self) -> Option<&T> {
303 if let [.., last] = self { Some(last) } else { None }
304 }
305
306 /// Returns a mutable reference to the last item in the slice, or `None` if it is empty.
307 ///
308 /// # Examples
309 ///
310 /// ```
311 /// let x = &mut [0, 1, 2];
312 ///
313 /// if let Some(last) = x.last_mut() {
314 /// *last = 10;
315 /// }
316 /// assert_eq!(x, &[0, 1, 10]);
317 ///
318 /// let y: &mut [i32] = &mut [];
319 /// assert_eq!(None, y.last_mut());
320 /// ```
321 #[stable(feature = "rust1", since = "1.0.0")]
322 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
323 #[inline]
324 #[must_use]
325 pub const fn last_mut(&mut self) -> Option<&mut T> {
326 if let [.., last] = self { Some(last) } else { None }
327 }
328
329 /// Return an array reference to the first `N` items in the slice.
330 ///
331 /// If the slice is not at least `N` in length, this will return `None`.
332 ///
333 /// # Examples
334 ///
335 /// ```
336 /// let u = [10, 40, 30];
337 /// assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());
338 ///
339 /// let v: &[i32] = &[10];
340 /// assert_eq!(None, v.first_chunk::<2>());
341 ///
342 /// let w: &[i32] = &[];
343 /// assert_eq!(Some(&[]), w.first_chunk::<0>());
344 /// ```
345 #[inline]
346 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
347 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
348 pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]> {
349 if self.len() < N {
350 None
351 } else {
352 // SAFETY: We explicitly check for the correct number of elements,
353 // and do not let the reference outlive the slice.
354 Some(unsafe { &*(self.as_ptr().cast::<[T; N]>()) })
355 }
356 }
357
358 /// Return a mutable array reference to the first `N` items in the slice.
359 ///
360 /// If the slice is not at least `N` in length, this will return `None`.
361 ///
362 /// # Examples
363 ///
364 /// ```
365 /// let x = &mut [0, 1, 2];
366 ///
367 /// if let Some(first) = x.first_chunk_mut::<2>() {
368 /// first[0] = 5;
369 /// first[1] = 4;
370 /// }
371 /// assert_eq!(x, &[5, 4, 2]);
372 ///
373 /// assert_eq!(None, x.first_chunk_mut::<4>());
374 /// ```
375 #[inline]
376 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
377 #[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
378 pub const fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
379 if self.len() < N {
380 None
381 } else {
382 // SAFETY: We explicitly check for the correct number of elements,
383 // do not let the reference outlive the slice,
384 // and require exclusive access to the entire slice to mutate the chunk.
385 Some(unsafe { &mut *(self.as_mut_ptr().cast::<[T; N]>()) })
386 }
387 }
388
389 /// Return an array reference to the first `N` items in the slice and the remaining slice.
390 ///
391 /// If the slice is not at least `N` in length, this will return `None`.
392 ///
393 /// # Examples
394 ///
395 /// ```
396 /// let x = &[0, 1, 2];
397 ///
398 /// if let Some((first, elements)) = x.split_first_chunk::<2>() {
399 /// assert_eq!(first, &[0, 1]);
400 /// assert_eq!(elements, &[2]);
401 /// }
402 ///
403 /// assert_eq!(None, x.split_first_chunk::<4>());
404 /// ```
405 #[inline]
406 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
407 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
408 pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
409 if self.len() < N {
410 None
411 } else {
412 // SAFETY: We manually verified the bounds of the split.
413 let (first, tail) = unsafe { self.split_at_unchecked(N) };
414
415 // SAFETY: We explicitly check for the correct number of elements,
416 // and do not let the references outlive the slice.
417 Some((unsafe { &*(first.as_ptr().cast::<[T; N]>()) }, tail))
418 }
419 }
420
421 /// Return a mutable array reference to the first `N` items in the slice and the remaining
422 /// slice.
423 ///
424 /// If the slice is not at least `N` in length, this will return `None`.
425 ///
426 /// # Examples
427 ///
428 /// ```
429 /// let x = &mut [0, 1, 2];
430 ///
431 /// if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
432 /// first[0] = 3;
433 /// first[1] = 4;
434 /// elements[0] = 5;
435 /// }
436 /// assert_eq!(x, &[3, 4, 5]);
437 ///
438 /// assert_eq!(None, x.split_first_chunk_mut::<4>());
439 /// ```
440 #[inline]
441 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
442 #[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
443 pub const fn split_first_chunk_mut<const N: usize>(
444 &mut self,
445 ) -> Option<(&mut [T; N], &mut [T])> {
446 if self.len() < N {
447 None
448 } else {
449 // SAFETY: We manually verified the bounds of the split.
450 let (first, tail) = unsafe { self.split_at_mut_unchecked(N) };
451
452 // SAFETY: We explicitly check for the correct number of elements,
453 // do not let the reference outlive the slice,
454 // and enforce exclusive mutability of the chunk by the split.
455 Some((unsafe { &mut *(first.as_mut_ptr().cast::<[T; N]>()) }, tail))
456 }
457 }
458
459 /// Return an array reference to the last `N` items in the slice and the remaining slice.
460 ///
461 /// If the slice is not at least `N` in length, this will return `None`.
462 ///
463 /// # Examples
464 ///
465 /// ```
466 /// let x = &[0, 1, 2];
467 ///
468 /// if let Some((elements, last)) = x.split_last_chunk::<2>() {
469 /// assert_eq!(elements, &[0]);
470 /// assert_eq!(last, &[1, 2]);
471 /// }
472 ///
473 /// assert_eq!(None, x.split_last_chunk::<4>());
474 /// ```
475 #[inline]
476 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
477 #[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
478 pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])> {
479 if self.len() < N {
480 None
481 } else {
482 // SAFETY: We manually verified the bounds of the split.
483 let (init, last) = unsafe { self.split_at_unchecked(self.len() - N) };
484
485 // SAFETY: We explicitly check for the correct number of elements,
486 // and do not let the references outlive the slice.
487 Some((init, unsafe { &*(last.as_ptr().cast::<[T; N]>()) }))
488 }
489 }
490
491 /// Return a mutable array reference to the last `N` items in the slice and the remaining
492 /// slice.
493 ///
494 /// If the slice is not at least `N` in length, this will return `None`.
495 ///
496 /// # Examples
497 ///
498 /// ```
499 /// let x = &mut [0, 1, 2];
500 ///
501 /// if let Some((elements, last)) = x.split_last_chunk_mut::<2>() {
502 /// last[0] = 3;
503 /// last[1] = 4;
504 /// elements[0] = 5;
505 /// }
506 /// assert_eq!(x, &[5, 3, 4]);
507 ///
508 /// assert_eq!(None, x.split_last_chunk_mut::<4>());
509 /// ```
510 #[inline]
511 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
512 #[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
513 pub const fn split_last_chunk_mut<const N: usize>(
514 &mut self,
515 ) -> Option<(&mut [T], &mut [T; N])> {
516 if self.len() < N {
517 None
518 } else {
519 // SAFETY: We manually verified the bounds of the split.
520 let (init, last) = unsafe { self.split_at_mut_unchecked(self.len() - N) };
521
522 // SAFETY: We explicitly check for the correct number of elements,
523 // do not let the reference outlive the slice,
524 // and enforce exclusive mutability of the chunk by the split.
525 Some((init, unsafe { &mut *(last.as_mut_ptr().cast::<[T; N]>()) }))
526 }
527 }
528
529 /// Return an array reference to the last `N` items in the slice.
530 ///
531 /// If the slice is not at least `N` in length, this will return `None`.
532 ///
533 /// # Examples
534 ///
535 /// ```
536 /// let u = [10, 40, 30];
537 /// assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());
538 ///
539 /// let v: &[i32] = &[10];
540 /// assert_eq!(None, v.last_chunk::<2>());
541 ///
542 /// let w: &[i32] = &[];
543 /// assert_eq!(Some(&[]), w.last_chunk::<0>());
544 /// ```
545 #[inline]
546 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
547 #[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
548 pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]> {
549 if self.len() < N {
550 None
551 } else {
552 // SAFETY: We manually verified the bounds of the slice.
553 // FIXME: Without const traits, we need this instead of `get_unchecked`.
554 let last = unsafe { self.split_at_unchecked(self.len() - N).1 };
555
556 // SAFETY: We explicitly check for the correct number of elements,
557 // and do not let the references outlive the slice.
558 Some(unsafe { &*(last.as_ptr().cast::<[T; N]>()) })
559 }
560 }
561
562 /// Return a mutable array reference to the last `N` items in the slice.
563 ///
564 /// If the slice is not at least `N` in length, this will return `None`.
565 ///
566 /// # Examples
567 ///
568 /// ```
569 /// let x = &mut [0, 1, 2];
570 ///
571 /// if let Some(last) = x.last_chunk_mut::<2>() {
572 /// last[0] = 10;
573 /// last[1] = 20;
574 /// }
575 /// assert_eq!(x, &[0, 10, 20]);
576 ///
577 /// assert_eq!(None, x.last_chunk_mut::<4>());
578 /// ```
579 #[inline]
580 #[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
581 #[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
582 pub const fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
583 if self.len() < N {
584 None
585 } else {
586 // SAFETY: We manually verified the bounds of the slice.
587 // FIXME: Without const traits, we need this instead of `get_unchecked`.
588 let last = unsafe { self.split_at_mut_unchecked(self.len() - N).1 };
589
590 // SAFETY: We explicitly check for the correct number of elements,
591 // do not let the reference outlive the slice,
592 // and require exclusive access to the entire slice to mutate the chunk.
593 Some(unsafe { &mut *(last.as_mut_ptr().cast::<[T; N]>()) })
594 }
595 }
596
597 /// Returns a reference to an element or subslice depending on the type of
598 /// index.
599 ///
600 /// - If given a position, returns a reference to the element at that
601 /// position or `None` if out of bounds.
602 /// - If given a range, returns the subslice corresponding to that range,
603 /// or `None` if out of bounds.
604 ///
605 /// # Examples
606 ///
607 /// ```
608 /// let v = [10, 40, 30];
609 /// assert_eq!(Some(&40), v.get(1));
610 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
611 /// assert_eq!(None, v.get(3));
612 /// assert_eq!(None, v.get(0..4));
613 /// ```
614 #[stable(feature = "rust1", since = "1.0.0")]
615 #[inline]
616 #[must_use]
617 pub fn get<I>(&self, index: I) -> Option<&I::Output>
618 where
619 I: SliceIndex<Self>,
620 {
621 index.get(self)
622 }
623
624 /// Returns a mutable reference to an element or subslice depending on the
625 /// type of index (see [`get`]) or `None` if the index is out of bounds.
626 ///
627 /// [`get`]: slice::get
628 ///
629 /// # Examples
630 ///
631 /// ```
632 /// let x = &mut [0, 1, 2];
633 ///
634 /// if let Some(elem) = x.get_mut(1) {
635 /// *elem = 42;
636 /// }
637 /// assert_eq!(x, &[0, 42, 2]);
638 /// ```
639 #[stable(feature = "rust1", since = "1.0.0")]
640 #[inline]
641 #[must_use]
642 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
643 where
644 I: SliceIndex<Self>,
645 {
646 index.get_mut(self)
647 }
648
649 /// Returns a reference to an element or subslice, without doing bounds
650 /// checking.
651 ///
652 /// For a safe alternative see [`get`].
653 ///
654 /// # Safety
655 ///
656 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
657 /// even if the resulting reference is not used.
658 ///
659 /// You can think of this like `.get(index).unwrap_unchecked()`. It's UB
660 /// to call `.get_unchecked(len)`, even if you immediately convert to a
661 /// pointer. And it's UB to call `.get_unchecked(..len + 1)`,
662 /// `.get_unchecked(..=len)`, or similar.
663 ///
664 /// [`get`]: slice::get
665 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
666 ///
667 /// # Examples
668 ///
669 /// ```
670 /// let x = &[1, 2, 4];
671 ///
672 /// unsafe {
673 /// assert_eq!(x.get_unchecked(1), &2);
674 /// }
675 /// ```
676 #[stable(feature = "rust1", since = "1.0.0")]
677 #[inline]
678 #[must_use]
679 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
680 where
681 I: SliceIndex<Self>,
682 {
683 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
684 // the slice is dereferenceable because `self` is a safe reference.
685 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
686 unsafe { &*index.get_unchecked(self) }
687 }
688
689 /// Returns a mutable reference to an element or subslice, without doing
690 /// bounds checking.
691 ///
692 /// For a safe alternative see [`get_mut`].
693 ///
694 /// # Safety
695 ///
696 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
697 /// even if the resulting reference is not used.
698 ///
699 /// You can think of this like `.get_mut(index).unwrap_unchecked()`. It's
700 /// UB to call `.get_unchecked_mut(len)`, even if you immediately convert
701 /// to a pointer. And it's UB to call `.get_unchecked_mut(..len + 1)`,
702 /// `.get_unchecked_mut(..=len)`, or similar.
703 ///
704 /// [`get_mut`]: slice::get_mut
705 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
706 ///
707 /// # Examples
708 ///
709 /// ```
710 /// let x = &mut [1, 2, 4];
711 ///
712 /// unsafe {
713 /// let elem = x.get_unchecked_mut(1);
714 /// *elem = 13;
715 /// }
716 /// assert_eq!(x, &[1, 13, 4]);
717 /// ```
718 #[stable(feature = "rust1", since = "1.0.0")]
719 #[inline]
720 #[must_use]
721 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
722 where
723 I: SliceIndex<Self>,
724 {
725 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
726 // the slice is dereferenceable because `self` is a safe reference.
727 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
728 unsafe { &mut *index.get_unchecked_mut(self) }
729 }
730
731 /// Returns a raw pointer to the slice's buffer.
732 ///
733 /// The caller must ensure that the slice outlives the pointer this
734 /// function returns, or else it will end up pointing to garbage.
735 ///
736 /// The caller must also ensure that the memory the pointer (non-transitively) points to
737 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
738 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
739 ///
740 /// Modifying the container referenced by this slice may cause its buffer
741 /// to be reallocated, which would also make any pointers to it invalid.
742 ///
743 /// # Examples
744 ///
745 /// ```
746 /// let x = &[1, 2, 4];
747 /// let x_ptr = x.as_ptr();
748 ///
749 /// unsafe {
750 /// for i in 0..x.len() {
751 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
752 /// }
753 /// }
754 /// ```
755 ///
756 /// [`as_mut_ptr`]: slice::as_mut_ptr
757 #[stable(feature = "rust1", since = "1.0.0")]
758 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
759 #[rustc_never_returns_null_ptr]
760 #[inline(always)]
761 #[must_use]
762 pub const fn as_ptr(&self) -> *const T {
763 self as *const [T] as *const T
764 }
765
766 /// Returns an unsafe mutable pointer to the slice's buffer.
767 ///
768 /// The caller must ensure that the slice outlives the pointer this
769 /// function returns, or else it will end up pointing to garbage.
770 ///
771 /// Modifying the container referenced by this slice may cause its buffer
772 /// to be reallocated, which would also make any pointers to it invalid.
773 ///
774 /// # Examples
775 ///
776 /// ```
777 /// let x = &mut [1, 2, 4];
778 /// let x_ptr = x.as_mut_ptr();
779 ///
780 /// unsafe {
781 /// for i in 0..x.len() {
782 /// *x_ptr.add(i) += 2;
783 /// }
784 /// }
785 /// assert_eq!(x, &[3, 4, 6]);
786 /// ```
787 #[stable(feature = "rust1", since = "1.0.0")]
788 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
789 #[rustc_allow_const_fn_unstable(const_mut_refs)]
790 #[rustc_never_returns_null_ptr]
791 #[inline(always)]
792 #[must_use]
793 pub const fn as_mut_ptr(&mut self) -> *mut T {
794 self as *mut [T] as *mut T
795 }
796
797 /// Returns the two raw pointers spanning the slice.
798 ///
799 /// The returned range is half-open, which means that the end pointer
800 /// points *one past* the last element of the slice. This way, an empty
801 /// slice is represented by two equal pointers, and the difference between
802 /// the two pointers represents the size of the slice.
803 ///
804 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
805 /// requires extra caution, as it does not point to a valid element in the
806 /// slice.
807 ///
808 /// This function is useful for interacting with foreign interfaces which
809 /// use two pointers to refer to a range of elements in memory, as is
810 /// common in C++.
811 ///
812 /// It can also be useful to check if a pointer to an element refers to an
813 /// element of this slice:
814 ///
815 /// ```
816 /// let a = [1, 2, 3];
817 /// let x = &a[1] as *const _;
818 /// let y = &5 as *const _;
819 ///
820 /// assert!(a.as_ptr_range().contains(&x));
821 /// assert!(!a.as_ptr_range().contains(&y));
822 /// ```
823 ///
824 /// [`as_ptr`]: slice::as_ptr
825 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
826 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
827 #[inline]
828 #[must_use]
829 pub const fn as_ptr_range(&self) -> Range<*const T> {
830 let start = self.as_ptr();
831 // SAFETY: The `add` here is safe, because:
832 //
833 // - Both pointers are part of the same object, as pointing directly
834 // past the object also counts.
835 //
836 // - The size of the slice is never larger than isize::MAX bytes, as
837 // noted here:
838 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
839 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
840 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
841 // (This doesn't seem normative yet, but the very same assumption is
842 // made in many places, including the Index implementation of slices.)
843 //
844 // - There is no wrapping around involved, as slices do not wrap past
845 // the end of the address space.
846 //
847 // See the documentation of pointer::add.
848 let end = unsafe { start.add(self.len()) };
849 start..end
850 }
851
852 /// Returns the two unsafe mutable pointers spanning the slice.
853 ///
854 /// The returned range is half-open, which means that the end pointer
855 /// points *one past* the last element of the slice. This way, an empty
856 /// slice is represented by two equal pointers, and the difference between
857 /// the two pointers represents the size of the slice.
858 ///
859 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
860 /// pointer requires extra caution, as it does not point to a valid element
861 /// in the slice.
862 ///
863 /// This function is useful for interacting with foreign interfaces which
864 /// use two pointers to refer to a range of elements in memory, as is
865 /// common in C++.
866 ///
867 /// [`as_mut_ptr`]: slice::as_mut_ptr
868 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
869 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
870 #[rustc_allow_const_fn_unstable(const_mut_refs)]
871 #[inline]
872 #[must_use]
873 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
874 let start = self.as_mut_ptr();
875 // SAFETY: See as_ptr_range() above for why `add` here is safe.
876 let end = unsafe { start.add(self.len()) };
877 start..end
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_unstable(feature = "const_swap", issue = "83163")]
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 = ptr::addr_of_mut!(self[a]);
908 let pb = ptr::addr_of_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 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
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 #[inline]
976 pub fn reverse(&mut self) {
977 let half_len = self.len() / 2;
978 let Range { start, end } = self.as_mut_ptr_range();
979
980 // These slices will skip the middle item for an odd length,
981 // since that one doesn't need to move.
982 let (front_half, back_half) =
983 // SAFETY: Both are subparts of the original slice, so the memory
984 // range is valid, and they don't overlap because they're each only
985 // half (or less) of the original slice.
986 unsafe {
987 (
988 slice::from_raw_parts_mut(start, half_len),
989 slice::from_raw_parts_mut(end.sub(half_len), half_len),
990 )
991 };
992
993 // Introducing a function boundary here means that the two halves
994 // get `noalias` markers, allowing better optimization as LLVM
995 // knows that they're disjoint, unlike in the original slice.
996 revswap(front_half, back_half, half_len);
997
998 #[inline]
999 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
1000 debug_assert!(a.len() == n);
1001 debug_assert!(b.len() == n);
1002
1003 // Because this function is first compiled in isolation,
1004 // this check tells LLVM that the indexing below is
1005 // in-bounds. Then after inlining -- once the actual
1006 // lengths of the slices are known -- it's removed.
1007 let (a, b) = (&mut a[..n], &mut b[..n]);
1008
1009 let mut i = 0;
1010 while i < n {
1011 mem::swap(&mut a[i], &mut b[n - 1 - i]);
1012 i += 1;
1013 }
1014 }
1015 }
1016
1017 /// Returns an iterator over the slice.
1018 ///
1019 /// The iterator yields all items from start to end.
1020 ///
1021 /// # Examples
1022 ///
1023 /// ```
1024 /// let x = &[1, 2, 4];
1025 /// let mut iterator = x.iter();
1026 ///
1027 /// assert_eq!(iterator.next(), Some(&1));
1028 /// assert_eq!(iterator.next(), Some(&2));
1029 /// assert_eq!(iterator.next(), Some(&4));
1030 /// assert_eq!(iterator.next(), None);
1031 /// ```
1032 #[stable(feature = "rust1", since = "1.0.0")]
1033 #[inline]
1034 pub fn iter(&self) -> Iter<'_, T> {
1035 Iter::new(self)
1036 }
1037
1038 /// Returns an iterator that allows modifying each value.
1039 ///
1040 /// The iterator yields all items from start to end.
1041 ///
1042 /// # Examples
1043 ///
1044 /// ```
1045 /// let x = &mut [1, 2, 4];
1046 /// for elem in x.iter_mut() {
1047 /// *elem += 2;
1048 /// }
1049 /// assert_eq!(x, &[3, 4, 6]);
1050 /// ```
1051 #[stable(feature = "rust1", since = "1.0.0")]
1052 #[inline]
1053 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
1054 IterMut::new(self)
1055 }
1056
1057 /// Returns an iterator over all contiguous windows of length
1058 /// `size`. The windows overlap. If the slice is shorter than
1059 /// `size`, the iterator returns no values.
1060 ///
1061 /// # Panics
1062 ///
1063 /// Panics if `size` is 0.
1064 ///
1065 /// # Examples
1066 ///
1067 /// ```
1068 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1069 /// let mut iter = slice.windows(3);
1070 /// assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
1071 /// assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
1072 /// assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
1073 /// assert!(iter.next().is_none());
1074 /// ```
1075 ///
1076 /// If the slice is shorter than `size`:
1077 ///
1078 /// ```
1079 /// let slice = ['f', 'o', 'o'];
1080 /// let mut iter = slice.windows(4);
1081 /// assert!(iter.next().is_none());
1082 /// ```
1083 ///
1084 /// There's no `windows_mut`, as that existing would let safe code violate the
1085 /// "only one `&mut` at a time to the same thing" rule. However, you can sometimes
1086 /// use [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
1087 /// conjunction with `windows` to accomplish something similar:
1088 /// ```
1089 /// use std::cell::Cell;
1090 ///
1091 /// let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
1092 /// let slice = &mut array[..];
1093 /// let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
1094 /// for w in slice_of_cells.windows(3) {
1095 /// Cell::swap(&w[0], &w[2]);
1096 /// }
1097 /// assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);
1098 /// ```
1099 #[stable(feature = "rust1", since = "1.0.0")]
1100 #[inline]
1101 #[track_caller]
1102 pub fn windows(&self, size: usize) -> Windows<'_, T> {
1103 let size = NonZero::new(size).expect("window size must be non-zero");
1104 Windows::new(self, size)
1105 }
1106
1107 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1108 /// beginning of the slice.
1109 ///
1110 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1111 /// slice, then the last chunk will not have length `chunk_size`.
1112 ///
1113 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
1114 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
1115 /// slice.
1116 ///
1117 /// # Panics
1118 ///
1119 /// Panics if `chunk_size` is 0.
1120 ///
1121 /// # Examples
1122 ///
1123 /// ```
1124 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1125 /// let mut iter = slice.chunks(2);
1126 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1127 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1128 /// assert_eq!(iter.next().unwrap(), &['m']);
1129 /// assert!(iter.next().is_none());
1130 /// ```
1131 ///
1132 /// [`chunks_exact`]: slice::chunks_exact
1133 /// [`rchunks`]: slice::rchunks
1134 #[stable(feature = "rust1", since = "1.0.0")]
1135 #[inline]
1136 #[track_caller]
1137 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
1138 assert!(chunk_size != 0, "chunk size must be non-zero");
1139 Chunks::new(self, chunk_size)
1140 }
1141
1142 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1143 /// beginning of the slice.
1144 ///
1145 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1146 /// length of the slice, then the last chunk will not have length `chunk_size`.
1147 ///
1148 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
1149 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
1150 /// the end of the slice.
1151 ///
1152 /// # Panics
1153 ///
1154 /// Panics if `chunk_size` is 0.
1155 ///
1156 /// # Examples
1157 ///
1158 /// ```
1159 /// let v = &mut [0, 0, 0, 0, 0];
1160 /// let mut count = 1;
1161 ///
1162 /// for chunk in v.chunks_mut(2) {
1163 /// for elem in chunk.iter_mut() {
1164 /// *elem += count;
1165 /// }
1166 /// count += 1;
1167 /// }
1168 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
1169 /// ```
1170 ///
1171 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1172 /// [`rchunks_mut`]: slice::rchunks_mut
1173 #[stable(feature = "rust1", since = "1.0.0")]
1174 #[inline]
1175 #[track_caller]
1176 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
1177 assert!(chunk_size != 0, "chunk size must be non-zero");
1178 ChunksMut::new(self, chunk_size)
1179 }
1180
1181 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1182 /// beginning of the slice.
1183 ///
1184 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1185 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1186 /// from the `remainder` function of the iterator.
1187 ///
1188 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1189 /// resulting code better than in the case of [`chunks`].
1190 ///
1191 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
1192 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
1193 ///
1194 /// # Panics
1195 ///
1196 /// Panics if `chunk_size` is 0.
1197 ///
1198 /// # Examples
1199 ///
1200 /// ```
1201 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1202 /// let mut iter = slice.chunks_exact(2);
1203 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1204 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1205 /// assert!(iter.next().is_none());
1206 /// assert_eq!(iter.remainder(), &['m']);
1207 /// ```
1208 ///
1209 /// [`chunks`]: slice::chunks
1210 /// [`rchunks_exact`]: slice::rchunks_exact
1211 #[stable(feature = "chunks_exact", since = "1.31.0")]
1212 #[inline]
1213 #[track_caller]
1214 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
1215 assert!(chunk_size != 0, "chunk size must be non-zero");
1216 ChunksExact::new(self, chunk_size)
1217 }
1218
1219 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1220 /// beginning of the slice.
1221 ///
1222 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1223 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1224 /// retrieved from the `into_remainder` function of the iterator.
1225 ///
1226 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1227 /// resulting code better than in the case of [`chunks_mut`].
1228 ///
1229 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
1230 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
1231 /// the slice.
1232 ///
1233 /// # Panics
1234 ///
1235 /// Panics if `chunk_size` is 0.
1236 ///
1237 /// # Examples
1238 ///
1239 /// ```
1240 /// let v = &mut [0, 0, 0, 0, 0];
1241 /// let mut count = 1;
1242 ///
1243 /// for chunk in v.chunks_exact_mut(2) {
1244 /// for elem in chunk.iter_mut() {
1245 /// *elem += count;
1246 /// }
1247 /// count += 1;
1248 /// }
1249 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1250 /// ```
1251 ///
1252 /// [`chunks_mut`]: slice::chunks_mut
1253 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1254 #[stable(feature = "chunks_exact", since = "1.31.0")]
1255 #[inline]
1256 #[track_caller]
1257 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
1258 assert!(chunk_size != 0, "chunk size must be non-zero");
1259 ChunksExactMut::new(self, chunk_size)
1260 }
1261
1262 /// Splits the slice into a slice of `N`-element arrays,
1263 /// assuming that there's no remainder.
1264 ///
1265 /// # Safety
1266 ///
1267 /// This may only be called when
1268 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1269 /// - `N != 0`.
1270 ///
1271 /// # Examples
1272 ///
1273 /// ```
1274 /// #![feature(slice_as_chunks)]
1275 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
1276 /// let chunks: &[[char; 1]] =
1277 /// // SAFETY: 1-element chunks never have remainder
1278 /// unsafe { slice.as_chunks_unchecked() };
1279 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1280 /// let chunks: &[[char; 3]] =
1281 /// // SAFETY: The slice length (6) is a multiple of 3
1282 /// unsafe { slice.as_chunks_unchecked() };
1283 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
1284 ///
1285 /// // These would be unsound:
1286 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
1287 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
1288 /// ```
1289 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1290 #[inline]
1291 #[must_use]
1292 pub const unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
1293 assert_unsafe_precondition!(
1294 check_language_ub,
1295 "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
1296 (n: usize = N, len: usize = self.len()) => n != 0 && len % n == 0,
1297 );
1298 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1299 let new_len = unsafe { exact_div(self.len(), N) };
1300 // SAFETY: We cast a slice of `new_len * N` elements into
1301 // a slice of `new_len` many `N` elements chunks.
1302 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
1303 }
1304
1305 /// Splits the slice into a slice of `N`-element arrays,
1306 /// starting at the beginning of the slice,
1307 /// and a remainder slice with length strictly less than `N`.
1308 ///
1309 /// # Panics
1310 ///
1311 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1312 /// error before this method gets stabilized.
1313 ///
1314 /// # Examples
1315 ///
1316 /// ```
1317 /// #![feature(slice_as_chunks)]
1318 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1319 /// let (chunks, remainder) = slice.as_chunks();
1320 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
1321 /// assert_eq!(remainder, &['m']);
1322 /// ```
1323 ///
1324 /// If you expect the slice to be an exact multiple, you can combine
1325 /// `let`-`else` with an empty slice pattern:
1326 /// ```
1327 /// #![feature(slice_as_chunks)]
1328 /// let slice = ['R', 'u', 's', 't'];
1329 /// let (chunks, []) = slice.as_chunks::<2>() else {
1330 /// panic!("slice didn't have even length")
1331 /// };
1332 /// assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);
1333 /// ```
1334 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1335 #[inline]
1336 #[track_caller]
1337 #[must_use]
1338 pub const fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1339 assert!(N != 0, "chunk size must be non-zero");
1340 let len = self.len() / N;
1341 let (multiple_of_n, remainder) = self.split_at(len * N);
1342 // SAFETY: We already panicked for zero, and ensured by construction
1343 // that the length of the subslice is a multiple of N.
1344 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1345 (array_slice, remainder)
1346 }
1347
1348 /// Splits the slice into a slice of `N`-element arrays,
1349 /// starting at the end of the slice,
1350 /// and a remainder slice with length strictly less than `N`.
1351 ///
1352 /// # Panics
1353 ///
1354 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1355 /// error before this method gets stabilized.
1356 ///
1357 /// # Examples
1358 ///
1359 /// ```
1360 /// #![feature(slice_as_chunks)]
1361 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1362 /// let (remainder, chunks) = slice.as_rchunks();
1363 /// assert_eq!(remainder, &['l']);
1364 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1365 /// ```
1366 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1367 #[inline]
1368 #[track_caller]
1369 #[must_use]
1370 pub const fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1371 assert!(N != 0, "chunk size must be non-zero");
1372 let len = self.len() / N;
1373 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1374 // SAFETY: We already panicked for zero, and ensured by construction
1375 // that the length of the subslice is a multiple of N.
1376 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1377 (remainder, array_slice)
1378 }
1379
1380 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1381 /// beginning of the slice.
1382 ///
1383 /// The chunks are array references and do not overlap. If `N` does not divide the
1384 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1385 /// retrieved from the `remainder` function of the iterator.
1386 ///
1387 /// This method is the const generic equivalent of [`chunks_exact`].
1388 ///
1389 /// # Panics
1390 ///
1391 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1392 /// error before this method gets stabilized.
1393 ///
1394 /// # Examples
1395 ///
1396 /// ```
1397 /// #![feature(array_chunks)]
1398 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1399 /// let mut iter = slice.array_chunks();
1400 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1401 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1402 /// assert!(iter.next().is_none());
1403 /// assert_eq!(iter.remainder(), &['m']);
1404 /// ```
1405 ///
1406 /// [`chunks_exact`]: slice::chunks_exact
1407 #[unstable(feature = "array_chunks", issue = "74985")]
1408 #[inline]
1409 #[track_caller]
1410 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1411 assert!(N != 0, "chunk size must be non-zero");
1412 ArrayChunks::new(self)
1413 }
1414
1415 /// Splits the slice into a slice of `N`-element arrays,
1416 /// assuming that there's no remainder.
1417 ///
1418 /// # Safety
1419 ///
1420 /// This may only be called when
1421 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1422 /// - `N != 0`.
1423 ///
1424 /// # Examples
1425 ///
1426 /// ```
1427 /// #![feature(slice_as_chunks)]
1428 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1429 /// let chunks: &mut [[char; 1]] =
1430 /// // SAFETY: 1-element chunks never have remainder
1431 /// unsafe { slice.as_chunks_unchecked_mut() };
1432 /// chunks[0] = ['L'];
1433 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1434 /// let chunks: &mut [[char; 3]] =
1435 /// // SAFETY: The slice length (6) is a multiple of 3
1436 /// unsafe { slice.as_chunks_unchecked_mut() };
1437 /// chunks[1] = ['a', 'x', '?'];
1438 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1439 ///
1440 /// // These would be unsound:
1441 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1442 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1443 /// ```
1444 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1445 #[inline]
1446 #[must_use]
1447 pub const unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1448 assert_unsafe_precondition!(
1449 check_language_ub,
1450 "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
1451 (n: usize = N, len: usize = self.len()) => n != 0 && len % n == 0
1452 );
1453 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1454 let new_len = unsafe { exact_div(self.len(), N) };
1455 // SAFETY: We cast a slice of `new_len * N` elements into
1456 // a slice of `new_len` many `N` elements chunks.
1457 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1458 }
1459
1460 /// Splits the slice into a slice of `N`-element arrays,
1461 /// starting at the beginning of the slice,
1462 /// and a remainder slice with length strictly less than `N`.
1463 ///
1464 /// # Panics
1465 ///
1466 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1467 /// error before this method gets stabilized.
1468 ///
1469 /// # Examples
1470 ///
1471 /// ```
1472 /// #![feature(slice_as_chunks)]
1473 /// let v = &mut [0, 0, 0, 0, 0];
1474 /// let mut count = 1;
1475 ///
1476 /// let (chunks, remainder) = v.as_chunks_mut();
1477 /// remainder[0] = 9;
1478 /// for chunk in chunks {
1479 /// *chunk = [count; 2];
1480 /// count += 1;
1481 /// }
1482 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1483 /// ```
1484 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1485 #[inline]
1486 #[track_caller]
1487 #[must_use]
1488 pub const fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1489 assert!(N != 0, "chunk size must be non-zero");
1490 let len = self.len() / N;
1491 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1492 // SAFETY: We already panicked for zero, and ensured by construction
1493 // that the length of the subslice is a multiple of N.
1494 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1495 (array_slice, remainder)
1496 }
1497
1498 /// Splits the slice into a slice of `N`-element arrays,
1499 /// starting at the end of the slice,
1500 /// and a remainder slice with length strictly less than `N`.
1501 ///
1502 /// # Panics
1503 ///
1504 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1505 /// error before this method gets stabilized.
1506 ///
1507 /// # Examples
1508 ///
1509 /// ```
1510 /// #![feature(slice_as_chunks)]
1511 /// let v = &mut [0, 0, 0, 0, 0];
1512 /// let mut count = 1;
1513 ///
1514 /// let (remainder, chunks) = v.as_rchunks_mut();
1515 /// remainder[0] = 9;
1516 /// for chunk in chunks {
1517 /// *chunk = [count; 2];
1518 /// count += 1;
1519 /// }
1520 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1521 /// ```
1522 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1523 #[inline]
1524 #[track_caller]
1525 #[must_use]
1526 pub const fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1527 assert!(N != 0, "chunk size must be non-zero");
1528 let len = self.len() / N;
1529 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1530 // SAFETY: We already panicked for zero, and ensured by construction
1531 // that the length of the subslice is a multiple of N.
1532 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1533 (remainder, array_slice)
1534 }
1535
1536 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1537 /// beginning of the slice.
1538 ///
1539 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1540 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1541 /// can be retrieved from the `into_remainder` function of the iterator.
1542 ///
1543 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1544 ///
1545 /// # Panics
1546 ///
1547 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1548 /// error before this method gets stabilized.
1549 ///
1550 /// # Examples
1551 ///
1552 /// ```
1553 /// #![feature(array_chunks)]
1554 /// let v = &mut [0, 0, 0, 0, 0];
1555 /// let mut count = 1;
1556 ///
1557 /// for chunk in v.array_chunks_mut() {
1558 /// *chunk = [count; 2];
1559 /// count += 1;
1560 /// }
1561 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1562 /// ```
1563 ///
1564 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1565 #[unstable(feature = "array_chunks", issue = "74985")]
1566 #[inline]
1567 #[track_caller]
1568 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1569 assert!(N != 0, "chunk size must be non-zero");
1570 ArrayChunksMut::new(self)
1571 }
1572
1573 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1574 /// starting at the beginning of the slice.
1575 ///
1576 /// This is the const generic equivalent of [`windows`].
1577 ///
1578 /// If `N` is greater than the size of the slice, it will return no windows.
1579 ///
1580 /// # Panics
1581 ///
1582 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1583 /// error before this method gets stabilized.
1584 ///
1585 /// # Examples
1586 ///
1587 /// ```
1588 /// #![feature(array_windows)]
1589 /// let slice = [0, 1, 2, 3];
1590 /// let mut iter = slice.array_windows();
1591 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1592 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1593 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1594 /// assert!(iter.next().is_none());
1595 /// ```
1596 ///
1597 /// [`windows`]: slice::windows
1598 #[unstable(feature = "array_windows", issue = "75027")]
1599 #[inline]
1600 #[track_caller]
1601 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1602 assert!(N != 0, "window size must be non-zero");
1603 ArrayWindows::new(self)
1604 }
1605
1606 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1607 /// of the slice.
1608 ///
1609 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1610 /// slice, then the last chunk will not have length `chunk_size`.
1611 ///
1612 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1613 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1614 /// of the slice.
1615 ///
1616 /// # Panics
1617 ///
1618 /// Panics if `chunk_size` is 0.
1619 ///
1620 /// # Examples
1621 ///
1622 /// ```
1623 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1624 /// let mut iter = slice.rchunks(2);
1625 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1626 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1627 /// assert_eq!(iter.next().unwrap(), &['l']);
1628 /// assert!(iter.next().is_none());
1629 /// ```
1630 ///
1631 /// [`rchunks_exact`]: slice::rchunks_exact
1632 /// [`chunks`]: slice::chunks
1633 #[stable(feature = "rchunks", since = "1.31.0")]
1634 #[inline]
1635 #[track_caller]
1636 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1637 assert!(chunk_size != 0, "chunk size must be non-zero");
1638 RChunks::new(self, chunk_size)
1639 }
1640
1641 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1642 /// of the slice.
1643 ///
1644 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1645 /// length of the slice, then the last chunk will not have length `chunk_size`.
1646 ///
1647 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1648 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1649 /// beginning of the slice.
1650 ///
1651 /// # Panics
1652 ///
1653 /// Panics if `chunk_size` is 0.
1654 ///
1655 /// # Examples
1656 ///
1657 /// ```
1658 /// let v = &mut [0, 0, 0, 0, 0];
1659 /// let mut count = 1;
1660 ///
1661 /// for chunk in v.rchunks_mut(2) {
1662 /// for elem in chunk.iter_mut() {
1663 /// *elem += count;
1664 /// }
1665 /// count += 1;
1666 /// }
1667 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1668 /// ```
1669 ///
1670 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1671 /// [`chunks_mut`]: slice::chunks_mut
1672 #[stable(feature = "rchunks", since = "1.31.0")]
1673 #[inline]
1674 #[track_caller]
1675 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1676 assert!(chunk_size != 0, "chunk size must be non-zero");
1677 RChunksMut::new(self, chunk_size)
1678 }
1679
1680 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1681 /// end of the slice.
1682 ///
1683 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1684 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1685 /// from the `remainder` function of the iterator.
1686 ///
1687 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1688 /// resulting code better than in the case of [`rchunks`].
1689 ///
1690 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1691 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1692 /// slice.
1693 ///
1694 /// # Panics
1695 ///
1696 /// Panics if `chunk_size` is 0.
1697 ///
1698 /// # Examples
1699 ///
1700 /// ```
1701 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1702 /// let mut iter = slice.rchunks_exact(2);
1703 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1704 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1705 /// assert!(iter.next().is_none());
1706 /// assert_eq!(iter.remainder(), &['l']);
1707 /// ```
1708 ///
1709 /// [`chunks`]: slice::chunks
1710 /// [`rchunks`]: slice::rchunks
1711 /// [`chunks_exact`]: slice::chunks_exact
1712 #[stable(feature = "rchunks", since = "1.31.0")]
1713 #[inline]
1714 #[track_caller]
1715 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1716 assert!(chunk_size != 0, "chunk size must be non-zero");
1717 RChunksExact::new(self, chunk_size)
1718 }
1719
1720 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1721 /// of the slice.
1722 ///
1723 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1724 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1725 /// retrieved from the `into_remainder` function of the iterator.
1726 ///
1727 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1728 /// resulting code better than in the case of [`chunks_mut`].
1729 ///
1730 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1731 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1732 /// of the slice.
1733 ///
1734 /// # Panics
1735 ///
1736 /// Panics if `chunk_size` is 0.
1737 ///
1738 /// # Examples
1739 ///
1740 /// ```
1741 /// let v = &mut [0, 0, 0, 0, 0];
1742 /// let mut count = 1;
1743 ///
1744 /// for chunk in v.rchunks_exact_mut(2) {
1745 /// for elem in chunk.iter_mut() {
1746 /// *elem += count;
1747 /// }
1748 /// count += 1;
1749 /// }
1750 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1751 /// ```
1752 ///
1753 /// [`chunks_mut`]: slice::chunks_mut
1754 /// [`rchunks_mut`]: slice::rchunks_mut
1755 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1756 #[stable(feature = "rchunks", since = "1.31.0")]
1757 #[inline]
1758 #[track_caller]
1759 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1760 assert!(chunk_size != 0, "chunk size must be non-zero");
1761 RChunksExactMut::new(self, chunk_size)
1762 }
1763
1764 /// Returns an iterator over the slice producing non-overlapping runs
1765 /// of elements using the predicate to separate them.
1766 ///
1767 /// The predicate is called for every pair of consecutive elements,
1768 /// meaning that it is called on `slice[0]` and `slice[1]`,
1769 /// followed by `slice[1]` and `slice[2]`, and so on.
1770 ///
1771 /// # Examples
1772 ///
1773 /// ```
1774 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1775 ///
1776 /// let mut iter = slice.chunk_by(|a, b| a == b);
1777 ///
1778 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1779 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1780 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1781 /// assert_eq!(iter.next(), None);
1782 /// ```
1783 ///
1784 /// This method can be used to extract the sorted subslices:
1785 ///
1786 /// ```
1787 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1788 ///
1789 /// let mut iter = slice.chunk_by(|a, b| a <= b);
1790 ///
1791 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1792 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1793 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1794 /// assert_eq!(iter.next(), None);
1795 /// ```
1796 #[stable(feature = "slice_group_by", since = "1.77.0")]
1797 #[inline]
1798 pub fn chunk_by<F>(&self, pred: F) -> ChunkBy<'_, T, F>
1799 where
1800 F: FnMut(&T, &T) -> bool,
1801 {
1802 ChunkBy::new(self, pred)
1803 }
1804
1805 /// Returns an iterator over the slice producing non-overlapping mutable
1806 /// runs of elements using the predicate to separate them.
1807 ///
1808 /// The predicate is called for every pair of consecutive elements,
1809 /// meaning that it is called on `slice[0]` and `slice[1]`,
1810 /// followed by `slice[1]` and `slice[2]`, and so on.
1811 ///
1812 /// # Examples
1813 ///
1814 /// ```
1815 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1816 ///
1817 /// let mut iter = slice.chunk_by_mut(|a, b| a == b);
1818 ///
1819 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1820 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1821 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1822 /// assert_eq!(iter.next(), None);
1823 /// ```
1824 ///
1825 /// This method can be used to extract the sorted subslices:
1826 ///
1827 /// ```
1828 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1829 ///
1830 /// let mut iter = slice.chunk_by_mut(|a, b| a <= b);
1831 ///
1832 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1833 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1834 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1835 /// assert_eq!(iter.next(), None);
1836 /// ```
1837 #[stable(feature = "slice_group_by", since = "1.77.0")]
1838 #[inline]
1839 pub fn chunk_by_mut<F>(&mut self, pred: F) -> ChunkByMut<'_, T, F>
1840 where
1841 F: FnMut(&T, &T) -> bool,
1842 {
1843 ChunkByMut::new(self, pred)
1844 }
1845
1846 /// Divides one slice into two at an index.
1847 ///
1848 /// The first will contain all indices from `[0, mid)` (excluding
1849 /// the index `mid` itself) and the second will contain all
1850 /// indices from `[mid, len)` (excluding the index `len` itself).
1851 ///
1852 /// # Panics
1853 ///
1854 /// Panics if `mid > len`. For a non-panicking alternative see
1855 /// [`split_at_checked`](slice::split_at_checked).
1856 ///
1857 /// # Examples
1858 ///
1859 /// ```
1860 /// let v = [1, 2, 3, 4, 5, 6];
1861 ///
1862 /// {
1863 /// let (left, right) = v.split_at(0);
1864 /// assert_eq!(left, []);
1865 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1866 /// }
1867 ///
1868 /// {
1869 /// let (left, right) = v.split_at(2);
1870 /// assert_eq!(left, [1, 2]);
1871 /// assert_eq!(right, [3, 4, 5, 6]);
1872 /// }
1873 ///
1874 /// {
1875 /// let (left, right) = v.split_at(6);
1876 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1877 /// assert_eq!(right, []);
1878 /// }
1879 /// ```
1880 #[stable(feature = "rust1", since = "1.0.0")]
1881 #[rustc_const_stable(feature = "const_slice_split_at_not_mut", since = "1.71.0")]
1882 #[rustc_allow_const_fn_unstable(split_at_checked)]
1883 #[inline]
1884 #[track_caller]
1885 #[must_use]
1886 pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1887 match self.split_at_checked(mid) {
1888 Some(pair) => pair,
1889 None => panic!("mid > len"),
1890 }
1891 }
1892
1893 /// Divides one mutable slice into two at an index.
1894 ///
1895 /// The first will contain all indices from `[0, mid)` (excluding
1896 /// the index `mid` itself) and the second will contain all
1897 /// indices from `[mid, len)` (excluding the index `len` itself).
1898 ///
1899 /// # Panics
1900 ///
1901 /// Panics if `mid > len`. For a non-panicking alternative see
1902 /// [`split_at_mut_checked`](slice::split_at_mut_checked).
1903 ///
1904 /// # Examples
1905 ///
1906 /// ```
1907 /// let mut v = [1, 0, 3, 0, 5, 6];
1908 /// let (left, right) = v.split_at_mut(2);
1909 /// assert_eq!(left, [1, 0]);
1910 /// assert_eq!(right, [3, 0, 5, 6]);
1911 /// left[1] = 2;
1912 /// right[1] = 4;
1913 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1914 /// ```
1915 #[stable(feature = "rust1", since = "1.0.0")]
1916 #[inline]
1917 #[track_caller]
1918 #[must_use]
1919 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
1920 pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1921 match self.split_at_mut_checked(mid) {
1922 Some(pair) => pair,
1923 None => panic!("mid > len"),
1924 }
1925 }
1926
1927 /// Divides one slice into two at an index, without doing bounds checking.
1928 ///
1929 /// The first will contain all indices from `[0, mid)` (excluding
1930 /// the index `mid` itself) and the second will contain all
1931 /// indices from `[mid, len)` (excluding the index `len` itself).
1932 ///
1933 /// For a safe alternative see [`split_at`].
1934 ///
1935 /// # Safety
1936 ///
1937 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1938 /// even if the resulting reference is not used. The caller has to ensure that
1939 /// `0 <= mid <= self.len()`.
1940 ///
1941 /// [`split_at`]: slice::split_at
1942 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1943 ///
1944 /// # Examples
1945 ///
1946 /// ```
1947 /// let v = [1, 2, 3, 4, 5, 6];
1948 ///
1949 /// unsafe {
1950 /// let (left, right) = v.split_at_unchecked(0);
1951 /// assert_eq!(left, []);
1952 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1953 /// }
1954 ///
1955 /// unsafe {
1956 /// let (left, right) = v.split_at_unchecked(2);
1957 /// assert_eq!(left, [1, 2]);
1958 /// assert_eq!(right, [3, 4, 5, 6]);
1959 /// }
1960 ///
1961 /// unsafe {
1962 /// let (left, right) = v.split_at_unchecked(6);
1963 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1964 /// assert_eq!(right, []);
1965 /// }
1966 /// ```
1967 #[stable(feature = "slice_split_at_unchecked", since = "CURRENT_RUSTC_VERSION")]
1968 #[rustc_const_stable(feature = "const_slice_split_at_unchecked", since = "1.77.0")]
1969 #[inline]
1970 #[must_use]
1971 pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1972 // HACK: the const function `from_raw_parts` is used to make this
1973 // function const; previously the implementation used
1974 // `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
1975
1976 let len = self.len();
1977 let ptr = self.as_ptr();
1978
1979 assert_unsafe_precondition!(
1980 check_library_ub,
1981 "slice::split_at_unchecked requires the index to be within the slice",
1982 (mid: usize = mid, len: usize = len) => mid <= len,
1983 );
1984
1985 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1986 unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), len - mid)) }
1987 }
1988
1989 /// Divides one mutable slice into two at an index, without doing bounds checking.
1990 ///
1991 /// The first will contain all indices from `[0, mid)` (excluding
1992 /// the index `mid` itself) and the second will contain all
1993 /// indices from `[mid, len)` (excluding the index `len` itself).
1994 ///
1995 /// For a safe alternative see [`split_at_mut`].
1996 ///
1997 /// # Safety
1998 ///
1999 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
2000 /// even if the resulting reference is not used. The caller has to ensure that
2001 /// `0 <= mid <= self.len()`.
2002 ///
2003 /// [`split_at_mut`]: slice::split_at_mut
2004 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
2005 ///
2006 /// # Examples
2007 ///
2008 /// ```
2009 /// let mut v = [1, 0, 3, 0, 5, 6];
2010 /// // scoped to restrict the lifetime of the borrows
2011 /// unsafe {
2012 /// let (left, right) = v.split_at_mut_unchecked(2);
2013 /// assert_eq!(left, [1, 0]);
2014 /// assert_eq!(right, [3, 0, 5, 6]);
2015 /// left[1] = 2;
2016 /// right[1] = 4;
2017 /// }
2018 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
2019 /// ```
2020 #[stable(feature = "slice_split_at_unchecked", since = "CURRENT_RUSTC_VERSION")]
2021 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
2022 #[inline]
2023 #[must_use]
2024 pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
2025 let len = self.len();
2026 let ptr = self.as_mut_ptr();
2027
2028 assert_unsafe_precondition!(
2029 check_library_ub,
2030 "slice::split_at_mut_unchecked requires the index to be within the slice",
2031 (mid: usize = mid, len: usize = len) => mid <= len,
2032 );
2033
2034 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
2035 //
2036 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
2037 // is fine.
2038 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
2039 }
2040
2041 /// Divides one slice into two at an index, returning `None` if the slice is
2042 /// too short.
2043 ///
2044 /// If `mid ≤ len` returns a pair of slices where the first will contain all
2045 /// indices from `[0, mid)` (excluding the index `mid` itself) and the
2046 /// second will contain all indices from `[mid, len)` (excluding the index
2047 /// `len` itself).
2048 ///
2049 /// Otherwise, if `mid > len`, returns `None`.
2050 ///
2051 /// # Examples
2052 ///
2053 /// ```
2054 /// #![feature(split_at_checked)]
2055 ///
2056 /// let v = [1, -2, 3, -4, 5, -6];
2057 ///
2058 /// {
2059 /// let (left, right) = v.split_at_checked(0).unwrap();
2060 /// assert_eq!(left, []);
2061 /// assert_eq!(right, [1, -2, 3, -4, 5, -6]);
2062 /// }
2063 ///
2064 /// {
2065 /// let (left, right) = v.split_at_checked(2).unwrap();
2066 /// assert_eq!(left, [1, -2]);
2067 /// assert_eq!(right, [3, -4, 5, -6]);
2068 /// }
2069 ///
2070 /// {
2071 /// let (left, right) = v.split_at_checked(6).unwrap();
2072 /// assert_eq!(left, [1, -2, 3, -4, 5, -6]);
2073 /// assert_eq!(right, []);
2074 /// }
2075 ///
2076 /// assert_eq!(None, v.split_at_checked(7));
2077 /// ```
2078 #[unstable(feature = "split_at_checked", reason = "new API", issue = "119128")]
2079 #[rustc_const_unstable(feature = "split_at_checked", issue = "119128")]
2080 #[inline]
2081 #[must_use]
2082 pub const fn split_at_checked(&self, mid: usize) -> Option<(&[T], &[T])> {
2083 if mid <= self.len() {
2084 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
2085 // fulfills the requirements of `split_at_unchecked`.
2086 Some(unsafe { self.split_at_unchecked(mid) })
2087 } else {
2088 None
2089 }
2090 }
2091
2092 /// Divides one mutable slice into two at an index, returning `None` if the
2093 /// slice is too short.
2094 ///
2095 /// If `mid ≤ len` returns a pair of slices where the first will contain all
2096 /// indices from `[0, mid)` (excluding the index `mid` itself) and the
2097 /// second will contain all indices from `[mid, len)` (excluding the index
2098 /// `len` itself).
2099 ///
2100 /// Otherwise, if `mid > len`, returns `None`.
2101 ///
2102 /// # Examples
2103 ///
2104 /// ```
2105 /// #![feature(split_at_checked)]
2106 ///
2107 /// let mut v = [1, 0, 3, 0, 5, 6];
2108 ///
2109 /// if let Some((left, right)) = v.split_at_mut_checked(2) {
2110 /// assert_eq!(left, [1, 0]);
2111 /// assert_eq!(right, [3, 0, 5, 6]);
2112 /// left[1] = 2;
2113 /// right[1] = 4;
2114 /// }
2115 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
2116 ///
2117 /// assert_eq!(None, v.split_at_mut_checked(7));
2118 /// ```
2119 #[unstable(feature = "split_at_checked", reason = "new API", issue = "119128")]
2120 #[rustc_const_unstable(feature = "split_at_checked", issue = "119128")]
2121 #[inline]
2122 #[must_use]
2123 pub const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut [T], &mut [T])> {
2124 if mid <= self.len() {
2125 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
2126 // fulfills the requirements of `split_at_unchecked`.
2127 Some(unsafe { self.split_at_mut_unchecked(mid) })
2128 } else {
2129 None
2130 }
2131 }
2132
2133 /// Returns an iterator over subslices separated by elements that match
2134 /// `pred`. The matched element is not contained in the subslices.
2135 ///
2136 /// # Examples
2137 ///
2138 /// ```
2139 /// let slice = [10, 40, 33, 20];
2140 /// let mut iter = slice.split(|num| num % 3 == 0);
2141 ///
2142 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
2143 /// assert_eq!(iter.next().unwrap(), &[20]);
2144 /// assert!(iter.next().is_none());
2145 /// ```
2146 ///
2147 /// If the first element is matched, an empty slice will be the first item
2148 /// returned by the iterator. Similarly, if the last element in the slice
2149 /// is matched, an empty slice will be the last item returned by the
2150 /// iterator:
2151 ///
2152 /// ```
2153 /// let slice = [10, 40, 33];
2154 /// let mut iter = slice.split(|num| num % 3 == 0);
2155 ///
2156 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
2157 /// assert_eq!(iter.next().unwrap(), &[]);
2158 /// assert!(iter.next().is_none());
2159 /// ```
2160 ///
2161 /// If two matched elements are directly adjacent, an empty slice will be
2162 /// present between them:
2163 ///
2164 /// ```
2165 /// let slice = [10, 6, 33, 20];
2166 /// let mut iter = slice.split(|num| num % 3 == 0);
2167 ///
2168 /// assert_eq!(iter.next().unwrap(), &[10]);
2169 /// assert_eq!(iter.next().unwrap(), &[]);
2170 /// assert_eq!(iter.next().unwrap(), &[20]);
2171 /// assert!(iter.next().is_none());
2172 /// ```
2173 #[stable(feature = "rust1", since = "1.0.0")]
2174 #[inline]
2175 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
2176 where
2177 F: FnMut(&T) -> bool,
2178 {
2179 Split::new(self, pred)
2180 }
2181
2182 /// Returns an iterator over mutable subslices separated by elements that
2183 /// match `pred`. The matched element is not contained in the subslices.
2184 ///
2185 /// # Examples
2186 ///
2187 /// ```
2188 /// let mut v = [10, 40, 30, 20, 60, 50];
2189 ///
2190 /// for group in v.split_mut(|num| *num % 3 == 0) {
2191 /// group[0] = 1;
2192 /// }
2193 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
2194 /// ```
2195 #[stable(feature = "rust1", since = "1.0.0")]
2196 #[inline]
2197 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
2198 where
2199 F: FnMut(&T) -> bool,
2200 {
2201 SplitMut::new(self, pred)
2202 }
2203
2204 /// Returns an iterator over subslices separated by elements that match
2205 /// `pred`. The matched element is contained in the end of the previous
2206 /// subslice as a terminator.
2207 ///
2208 /// # Examples
2209 ///
2210 /// ```
2211 /// let slice = [10, 40, 33, 20];
2212 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
2213 ///
2214 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
2215 /// assert_eq!(iter.next().unwrap(), &[20]);
2216 /// assert!(iter.next().is_none());
2217 /// ```
2218 ///
2219 /// If the last element of the slice is matched,
2220 /// that element will be considered the terminator of the preceding slice.
2221 /// That slice will be the last item returned by the iterator.
2222 ///
2223 /// ```
2224 /// let slice = [3, 10, 40, 33];
2225 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
2226 ///
2227 /// assert_eq!(iter.next().unwrap(), &[3]);
2228 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
2229 /// assert!(iter.next().is_none());
2230 /// ```
2231 #[stable(feature = "split_inclusive", since = "1.51.0")]
2232 #[inline]
2233 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
2234 where
2235 F: FnMut(&T) -> bool,
2236 {
2237 SplitInclusive::new(self, pred)
2238 }
2239
2240 /// Returns an iterator over mutable subslices separated by elements that
2241 /// match `pred`. The matched element is contained in the previous
2242 /// subslice as a terminator.
2243 ///
2244 /// # Examples
2245 ///
2246 /// ```
2247 /// let mut v = [10, 40, 30, 20, 60, 50];
2248 ///
2249 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
2250 /// let terminator_idx = group.len()-1;
2251 /// group[terminator_idx] = 1;
2252 /// }
2253 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
2254 /// ```
2255 #[stable(feature = "split_inclusive", since = "1.51.0")]
2256 #[inline]
2257 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
2258 where
2259 F: FnMut(&T) -> bool,
2260 {
2261 SplitInclusiveMut::new(self, pred)
2262 }
2263
2264 /// Returns an iterator over subslices separated by elements that match
2265 /// `pred`, starting at the end of the slice and working backwards.
2266 /// The matched element is not contained in the subslices.
2267 ///
2268 /// # Examples
2269 ///
2270 /// ```
2271 /// let slice = [11, 22, 33, 0, 44, 55];
2272 /// let mut iter = slice.rsplit(|num| *num == 0);
2273 ///
2274 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
2275 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
2276 /// assert_eq!(iter.next(), None);
2277 /// ```
2278 ///
2279 /// As with `split()`, if the first or last element is matched, an empty
2280 /// slice will be the first (or last) item returned by the iterator.
2281 ///
2282 /// ```
2283 /// let v = &[0, 1, 1, 2, 3, 5, 8];
2284 /// let mut it = v.rsplit(|n| *n % 2 == 0);
2285 /// assert_eq!(it.next().unwrap(), &[]);
2286 /// assert_eq!(it.next().unwrap(), &[3, 5]);
2287 /// assert_eq!(it.next().unwrap(), &[1, 1]);
2288 /// assert_eq!(it.next().unwrap(), &[]);
2289 /// assert_eq!(it.next(), None);
2290 /// ```
2291 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2292 #[inline]
2293 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
2294 where
2295 F: FnMut(&T) -> bool,
2296 {
2297 RSplit::new(self, pred)
2298 }
2299
2300 /// Returns an iterator over mutable subslices separated by elements that
2301 /// match `pred`, starting at the end of the slice and working
2302 /// backwards. The matched element is not contained in the subslices.
2303 ///
2304 /// # Examples
2305 ///
2306 /// ```
2307 /// let mut v = [100, 400, 300, 200, 600, 500];
2308 ///
2309 /// let mut count = 0;
2310 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
2311 /// count += 1;
2312 /// group[0] = count;
2313 /// }
2314 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
2315 /// ```
2316 ///
2317 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2318 #[inline]
2319 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
2320 where
2321 F: FnMut(&T) -> bool,
2322 {
2323 RSplitMut::new(self, pred)
2324 }
2325
2326 /// Returns an iterator over subslices separated by elements that match
2327 /// `pred`, limited to returning at most `n` items. The matched element is
2328 /// not contained in the subslices.
2329 ///
2330 /// The last element returned, if any, will contain the remainder of the
2331 /// slice.
2332 ///
2333 /// # Examples
2334 ///
2335 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2336 /// `[20, 60, 50]`):
2337 ///
2338 /// ```
2339 /// let v = [10, 40, 30, 20, 60, 50];
2340 ///
2341 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2342 /// println!("{group:?}");
2343 /// }
2344 /// ```
2345 #[stable(feature = "rust1", since = "1.0.0")]
2346 #[inline]
2347 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2348 where
2349 F: FnMut(&T) -> bool,
2350 {
2351 SplitN::new(self.split(pred), n)
2352 }
2353
2354 /// Returns an iterator over mutable subslices separated by elements that match
2355 /// `pred`, limited to returning at most `n` items. The matched element is
2356 /// not contained in the subslices.
2357 ///
2358 /// The last element returned, if any, will contain the remainder of the
2359 /// slice.
2360 ///
2361 /// # Examples
2362 ///
2363 /// ```
2364 /// let mut v = [10, 40, 30, 20, 60, 50];
2365 ///
2366 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2367 /// group[0] = 1;
2368 /// }
2369 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2370 /// ```
2371 #[stable(feature = "rust1", since = "1.0.0")]
2372 #[inline]
2373 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2374 where
2375 F: FnMut(&T) -> bool,
2376 {
2377 SplitNMut::new(self.split_mut(pred), n)
2378 }
2379
2380 /// Returns an iterator over subslices separated by elements that match
2381 /// `pred` limited to returning at most `n` items. This starts at the end of
2382 /// the slice and works backwards. The matched element is not contained in
2383 /// the subslices.
2384 ///
2385 /// The last element returned, if any, will contain the remainder of the
2386 /// slice.
2387 ///
2388 /// # Examples
2389 ///
2390 /// Print the slice split once, starting from the end, by numbers divisible
2391 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2392 ///
2393 /// ```
2394 /// let v = [10, 40, 30, 20, 60, 50];
2395 ///
2396 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2397 /// println!("{group:?}");
2398 /// }
2399 /// ```
2400 #[stable(feature = "rust1", since = "1.0.0")]
2401 #[inline]
2402 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2403 where
2404 F: FnMut(&T) -> bool,
2405 {
2406 RSplitN::new(self.rsplit(pred), n)
2407 }
2408
2409 /// Returns an iterator over subslices separated by elements that match
2410 /// `pred` limited to returning at most `n` items. This starts at the end of
2411 /// the slice and works backwards. The matched element is not contained in
2412 /// the subslices.
2413 ///
2414 /// The last element returned, if any, will contain the remainder of the
2415 /// slice.
2416 ///
2417 /// # Examples
2418 ///
2419 /// ```
2420 /// let mut s = [10, 40, 30, 20, 60, 50];
2421 ///
2422 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2423 /// group[0] = 1;
2424 /// }
2425 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2426 /// ```
2427 #[stable(feature = "rust1", since = "1.0.0")]
2428 #[inline]
2429 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2430 where
2431 F: FnMut(&T) -> bool,
2432 {
2433 RSplitNMut::new(self.rsplit_mut(pred), n)
2434 }
2435
2436 /// Splits the slice on the first element that matches the specified
2437 /// predicate.
2438 ///
2439 /// If any matching elements are present in the slice, returns the prefix
2440 /// before the match and suffix after. The matching element itself is not
2441 /// included. If no elements match, returns `None`.
2442 ///
2443 /// # Examples
2444 ///
2445 /// ```
2446 /// #![feature(slice_split_once)]
2447 /// let s = [1, 2, 3, 2, 4];
2448 /// assert_eq!(s.split_once(|&x| x == 2), Some((
2449 /// &[1][..],
2450 /// &[3, 2, 4][..]
2451 /// )));
2452 /// assert_eq!(s.split_once(|&x| x == 0), None);
2453 /// ```
2454 #[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
2455 #[inline]
2456 pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
2457 where
2458 F: FnMut(&T) -> bool,
2459 {
2460 let index = self.iter().position(pred)?;
2461 Some((&self[..index], &self[index + 1..]))
2462 }
2463
2464 /// Splits the slice on the last element that matches the specified
2465 /// predicate.
2466 ///
2467 /// If any matching elements are present in the slice, returns the prefix
2468 /// before the match and suffix after. The matching element itself is not
2469 /// included. If no elements match, returns `None`.
2470 ///
2471 /// # Examples
2472 ///
2473 /// ```
2474 /// #![feature(slice_split_once)]
2475 /// let s = [1, 2, 3, 2, 4];
2476 /// assert_eq!(s.rsplit_once(|&x| x == 2), Some((
2477 /// &[1, 2, 3][..],
2478 /// &[4][..]
2479 /// )));
2480 /// assert_eq!(s.rsplit_once(|&x| x == 0), None);
2481 /// ```
2482 #[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
2483 #[inline]
2484 pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
2485 where
2486 F: FnMut(&T) -> bool,
2487 {
2488 let index = self.iter().rposition(pred)?;
2489 Some((&self[..index], &self[index + 1..]))
2490 }
2491
2492 /// Returns `true` if the slice contains an element with the given value.
2493 ///
2494 /// This operation is *O*(*n*).
2495 ///
2496 /// Note that if you have a sorted slice, [`binary_search`] may be faster.
2497 ///
2498 /// [`binary_search`]: slice::binary_search
2499 ///
2500 /// # Examples
2501 ///
2502 /// ```
2503 /// let v = [10, 40, 30];
2504 /// assert!(v.contains(&30));
2505 /// assert!(!v.contains(&50));
2506 /// ```
2507 ///
2508 /// If you do not have a `&T`, but some other value that you can compare
2509 /// with one (for example, `String` implements `PartialEq<str>`), you can
2510 /// use `iter().any`:
2511 ///
2512 /// ```
2513 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2514 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2515 /// assert!(!v.iter().any(|e| e == "hi"));
2516 /// ```
2517 #[stable(feature = "rust1", since = "1.0.0")]
2518 #[inline]
2519 #[must_use]
2520 pub fn contains(&self, x: &T) -> bool
2521 where
2522 T: PartialEq,
2523 {
2524 cmp::SliceContains::slice_contains(x, self)
2525 }
2526
2527 /// Returns `true` if `needle` is a prefix of the slice or equal to the slice.
2528 ///
2529 /// # Examples
2530 ///
2531 /// ```
2532 /// let v = [10, 40, 30];
2533 /// assert!(v.starts_with(&[10]));
2534 /// assert!(v.starts_with(&[10, 40]));
2535 /// assert!(v.starts_with(&v));
2536 /// assert!(!v.starts_with(&[50]));
2537 /// assert!(!v.starts_with(&[10, 50]));
2538 /// ```
2539 ///
2540 /// Always returns `true` if `needle` is an empty slice:
2541 ///
2542 /// ```
2543 /// let v = &[10, 40, 30];
2544 /// assert!(v.starts_with(&[]));
2545 /// let v: &[u8] = &[];
2546 /// assert!(v.starts_with(&[]));
2547 /// ```
2548 #[stable(feature = "rust1", since = "1.0.0")]
2549 #[must_use]
2550 pub fn starts_with(&self, needle: &[T]) -> bool
2551 where
2552 T: PartialEq,
2553 {
2554 let n = needle.len();
2555 self.len() >= n && needle == &self[..n]
2556 }
2557
2558 /// Returns `true` if `needle` is a suffix of the slice or equal to the slice.
2559 ///
2560 /// # Examples
2561 ///
2562 /// ```
2563 /// let v = [10, 40, 30];
2564 /// assert!(v.ends_with(&[30]));
2565 /// assert!(v.ends_with(&[40, 30]));
2566 /// assert!(v.ends_with(&v));
2567 /// assert!(!v.ends_with(&[50]));
2568 /// assert!(!v.ends_with(&[50, 30]));
2569 /// ```
2570 ///
2571 /// Always returns `true` if `needle` is an empty slice:
2572 ///
2573 /// ```
2574 /// let v = &[10, 40, 30];
2575 /// assert!(v.ends_with(&[]));
2576 /// let v: &[u8] = &[];
2577 /// assert!(v.ends_with(&[]));
2578 /// ```
2579 #[stable(feature = "rust1", since = "1.0.0")]
2580 #[must_use]
2581 pub fn ends_with(&self, needle: &[T]) -> bool
2582 where
2583 T: PartialEq,
2584 {
2585 let (m, n) = (self.len(), needle.len());
2586 m >= n && needle == &self[m - n..]
2587 }
2588
2589 /// Returns a subslice with the prefix removed.
2590 ///
2591 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2592 /// If `prefix` is empty, simply returns the original slice. If `prefix` is equal to the
2593 /// original slice, returns an empty slice.
2594 ///
2595 /// If the slice does not start with `prefix`, returns `None`.
2596 ///
2597 /// # Examples
2598 ///
2599 /// ```
2600 /// let v = &[10, 40, 30];
2601 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2602 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2603 /// assert_eq!(v.strip_prefix(&[10, 40, 30]), Some(&[][..]));
2604 /// assert_eq!(v.strip_prefix(&[50]), None);
2605 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2606 ///
2607 /// let prefix : &str = "he";
2608 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2609 /// Some(b"llo".as_ref()));
2610 /// ```
2611 #[must_use = "returns the subslice without modifying the original"]
2612 #[stable(feature = "slice_strip", since = "1.51.0")]
2613 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2614 where
2615 T: PartialEq,
2616 {
2617 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2618 let prefix = prefix.as_slice();
2619 let n = prefix.len();
2620 if n <= self.len() {
2621 let (head, tail) = self.split_at(n);
2622 if head == prefix {
2623 return Some(tail);
2624 }
2625 }
2626 None
2627 }
2628
2629 /// Returns a subslice with the suffix removed.
2630 ///
2631 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2632 /// If `suffix` is empty, simply returns the original slice. If `suffix` is equal to the
2633 /// original slice, returns an empty slice.
2634 ///
2635 /// If the slice does not end with `suffix`, returns `None`.
2636 ///
2637 /// # Examples
2638 ///
2639 /// ```
2640 /// let v = &[10, 40, 30];
2641 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2642 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2643 /// assert_eq!(v.strip_suffix(&[10, 40, 30]), Some(&[][..]));
2644 /// assert_eq!(v.strip_suffix(&[50]), None);
2645 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2646 /// ```
2647 #[must_use = "returns the subslice without modifying the original"]
2648 #[stable(feature = "slice_strip", since = "1.51.0")]
2649 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2650 where
2651 T: PartialEq,
2652 {
2653 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2654 let suffix = suffix.as_slice();
2655 let (len, n) = (self.len(), suffix.len());
2656 if n <= len {
2657 let (head, tail) = self.split_at(len - n);
2658 if tail == suffix {
2659 return Some(head);
2660 }
2661 }
2662 None
2663 }
2664
2665 /// Binary searches this slice for a given element.
2666 /// If the slice is not sorted, the returned result is unspecified and
2667 /// meaningless.
2668 ///
2669 /// If the value is found then [`Result::Ok`] is returned, containing the
2670 /// index of the matching element. If there are multiple matches, then any
2671 /// one of the matches could be returned. The index is chosen
2672 /// deterministically, but is subject to change in future versions of Rust.
2673 /// If the value is not found then [`Result::Err`] is returned, containing
2674 /// the index where a matching element could be inserted while maintaining
2675 /// sorted order.
2676 ///
2677 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2678 ///
2679 /// [`binary_search_by`]: slice::binary_search_by
2680 /// [`binary_search_by_key`]: slice::binary_search_by_key
2681 /// [`partition_point`]: slice::partition_point
2682 ///
2683 /// # Examples
2684 ///
2685 /// Looks up a series of four elements. The first is found, with a
2686 /// uniquely determined position; the second and third are not
2687 /// found; the fourth could match any position in `[1, 4]`.
2688 ///
2689 /// ```
2690 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2691 ///
2692 /// assert_eq!(s.binary_search(&13), Ok(9));
2693 /// assert_eq!(s.binary_search(&4), Err(7));
2694 /// assert_eq!(s.binary_search(&100), Err(13));
2695 /// let r = s.binary_search(&1);
2696 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2697 /// ```
2698 ///
2699 /// If you want to find that whole *range* of matching items, rather than
2700 /// an arbitrary matching one, that can be done using [`partition_point`]:
2701 /// ```
2702 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2703 ///
2704 /// let low = s.partition_point(|x| x < &1);
2705 /// assert_eq!(low, 1);
2706 /// let high = s.partition_point(|x| x <= &1);
2707 /// assert_eq!(high, 5);
2708 /// let r = s.binary_search(&1);
2709 /// assert!((low..high).contains(&r.unwrap()));
2710 ///
2711 /// assert!(s[..low].iter().all(|&x| x < 1));
2712 /// assert!(s[low..high].iter().all(|&x| x == 1));
2713 /// assert!(s[high..].iter().all(|&x| x > 1));
2714 ///
2715 /// // For something not found, the "range" of equal items is empty
2716 /// assert_eq!(s.partition_point(|x| x < &11), 9);
2717 /// assert_eq!(s.partition_point(|x| x <= &11), 9);
2718 /// assert_eq!(s.binary_search(&11), Err(9));
2719 /// ```
2720 ///
2721 /// If you want to insert an item to a sorted vector, while maintaining
2722 /// sort order, consider using [`partition_point`]:
2723 ///
2724 /// ```
2725 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2726 /// let num = 42;
2727 /// let idx = s.partition_point(|&x| x <= num);
2728 /// // If `num` is unique, `s.partition_point(|&x| x < num)` (with `<`) is equivalent to
2729 /// // `s.binary_search(&num).unwrap_or_else(|x| x)`, but using `<=` will allow `insert`
2730 /// // to shift less elements.
2731 /// s.insert(idx, num);
2732 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2733 /// ```
2734 #[stable(feature = "rust1", since = "1.0.0")]
2735 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2736 where
2737 T: Ord,
2738 {
2739 self.binary_search_by(|p| p.cmp(x))
2740 }
2741
2742 /// Binary searches this slice with a comparator function.
2743 ///
2744 /// The comparator function should return an order code that indicates
2745 /// whether its argument is `Less`, `Equal` or `Greater` the desired
2746 /// target.
2747 /// If the slice is not sorted or if the comparator function does not
2748 /// implement an order consistent with the sort order of the underlying
2749 /// slice, the returned result is unspecified and meaningless.
2750 ///
2751 /// If the value is found then [`Result::Ok`] is returned, containing the
2752 /// index of the matching element. If there are multiple matches, then any
2753 /// one of the matches could be returned. The index is chosen
2754 /// deterministically, but is subject to change in future versions of Rust.
2755 /// If the value is not found then [`Result::Err`] is returned, containing
2756 /// the index where a matching element could be inserted while maintaining
2757 /// sorted order.
2758 ///
2759 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2760 ///
2761 /// [`binary_search`]: slice::binary_search
2762 /// [`binary_search_by_key`]: slice::binary_search_by_key
2763 /// [`partition_point`]: slice::partition_point
2764 ///
2765 /// # Examples
2766 ///
2767 /// Looks up a series of four elements. The first is found, with a
2768 /// uniquely determined position; the second and third are not
2769 /// found; the fourth could match any position in `[1, 4]`.
2770 ///
2771 /// ```
2772 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2773 ///
2774 /// let seek = 13;
2775 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2776 /// let seek = 4;
2777 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2778 /// let seek = 100;
2779 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2780 /// let seek = 1;
2781 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2782 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2783 /// ```
2784 #[stable(feature = "rust1", since = "1.0.0")]
2785 #[inline]
2786 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2787 where
2788 F: FnMut(&'a T) -> Ordering,
2789 {
2790 // INVARIANTS:
2791 // - 0 <= left <= left + size = right <= self.len()
2792 // - f returns Less for everything in self[..left]
2793 // - f returns Greater for everything in self[right..]
2794 let mut size = self.len();
2795 let mut left = 0;
2796 let mut right = size;
2797 while left < right {
2798 let mid = left + size / 2;
2799
2800 // SAFETY: the while condition means `size` is strictly positive, so
2801 // `size/2 < size`. Thus `left + size/2 < left + size`, which
2802 // coupled with the `left + size <= self.len()` invariant means
2803 // we have `left + size/2 < self.len()`, and this is in-bounds.
2804 let cmp = f(unsafe { self.get_unchecked(mid) });
2805
2806 // This control flow produces conditional moves, which results in
2807 // fewer branches and instructions than if/else or matching on
2808 // cmp::Ordering.
2809 // This is x86 asm for u8: https://rust.godbolt.org/z/698eYffTx.
2810 left = if cmp == Less { mid + 1 } else { left };
2811 right = if cmp == Greater { mid } else { right };
2812 if cmp == Equal {
2813 // SAFETY: same as the `get_unchecked` above
2814 unsafe { hint::assert_unchecked(mid < self.len()) };
2815 return Ok(mid);
2816 }
2817
2818 size = right - left;
2819 }
2820
2821 // SAFETY: directly true from the overall invariant.
2822 // Note that this is `<=`, unlike the assume in the `Ok` path.
2823 unsafe { hint::assert_unchecked(left <= self.len()) };
2824 Err(left)
2825 }
2826
2827 /// Binary searches this slice with a key extraction function.
2828 ///
2829 /// Assumes that the slice is sorted by the key, for instance with
2830 /// [`sort_by_key`] using the same key extraction function.
2831 /// If the slice is not sorted by the key, the returned result is
2832 /// unspecified and meaningless.
2833 ///
2834 /// If the value is found then [`Result::Ok`] is returned, containing the
2835 /// index of the matching element. If there are multiple matches, then any
2836 /// one of the matches could be returned. The index is chosen
2837 /// deterministically, but is subject to change in future versions of Rust.
2838 /// If the value is not found then [`Result::Err`] is returned, containing
2839 /// the index where a matching element could be inserted while maintaining
2840 /// sorted order.
2841 ///
2842 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2843 ///
2844 /// [`sort_by_key`]: slice::sort_by_key
2845 /// [`binary_search`]: slice::binary_search
2846 /// [`binary_search_by`]: slice::binary_search_by
2847 /// [`partition_point`]: slice::partition_point
2848 ///
2849 /// # Examples
2850 ///
2851 /// Looks up a series of four elements in a slice of pairs sorted by
2852 /// their second elements. The first is found, with a uniquely
2853 /// determined position; the second and third are not found; the
2854 /// fourth could match any position in `[1, 4]`.
2855 ///
2856 /// ```
2857 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2858 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2859 /// (1, 21), (2, 34), (4, 55)];
2860 ///
2861 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2862 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2863 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2864 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2865 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2866 /// ```
2867 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2868 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2869 // This breaks links when slice is displayed in core, but changing it to use relative links
2870 // would break when the item is re-exported. So allow the core links to be broken for now.
2871 #[allow(rustdoc::broken_intra_doc_links)]
2872 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2873 #[inline]
2874 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2875 where
2876 F: FnMut(&'a T) -> B,
2877 B: Ord,
2878 {
2879 self.binary_search_by(|k| f(k).cmp(b))
2880 }
2881
2882 /// Sorts the slice, but might not preserve the order of equal elements.
2883 ///
2884 /// This sort is unstable (i.e., may reorder equal elements), in-place
2885 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2886 ///
2887 /// # Current implementation
2888 ///
2889 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2890 /// which combines the fast average case of randomized quicksort with the fast worst case of
2891 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2892 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2893 /// deterministic behavior.
2894 ///
2895 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2896 /// slice consists of several concatenated sorted sequences.
2897 ///
2898 /// # Examples
2899 ///
2900 /// ```
2901 /// let mut v = [-5, 4, 1, -3, 2];
2902 ///
2903 /// v.sort_unstable();
2904 /// assert!(v == [-5, -3, 1, 2, 4]);
2905 /// ```
2906 ///
2907 /// [pdqsort]: https://github.com/orlp/pdqsort
2908 #[stable(feature = "sort_unstable", since = "1.20.0")]
2909 #[inline]
2910 pub fn sort_unstable(&mut self)
2911 where
2912 T: Ord,
2913 {
2914 sort::quicksort(self, T::lt);
2915 }
2916
2917 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2918 /// elements.
2919 ///
2920 /// This sort is unstable (i.e., may reorder equal elements), in-place
2921 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2922 ///
2923 /// The comparator function must define a total ordering for the elements in the slice. If
2924 /// the ordering is not total, the order of the elements is unspecified. An order is a
2925 /// total order if it is (for all `a`, `b` and `c`):
2926 ///
2927 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2928 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2929 ///
2930 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2931 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2932 ///
2933 /// ```
2934 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2935 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2936 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2937 /// ```
2938 ///
2939 /// # Current implementation
2940 ///
2941 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2942 /// which combines the fast average case of randomized quicksort with the fast worst case of
2943 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2944 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2945 /// deterministic behavior.
2946 ///
2947 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2948 /// slice consists of several concatenated sorted sequences.
2949 ///
2950 /// # Examples
2951 ///
2952 /// ```
2953 /// let mut v = [5, 4, 1, 3, 2];
2954 /// v.sort_unstable_by(|a, b| a.cmp(b));
2955 /// assert!(v == [1, 2, 3, 4, 5]);
2956 ///
2957 /// // reverse sorting
2958 /// v.sort_unstable_by(|a, b| b.cmp(a));
2959 /// assert!(v == [5, 4, 3, 2, 1]);
2960 /// ```
2961 ///
2962 /// [pdqsort]: https://github.com/orlp/pdqsort
2963 #[stable(feature = "sort_unstable", since = "1.20.0")]
2964 #[inline]
2965 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2966 where
2967 F: FnMut(&T, &T) -> Ordering,
2968 {
2969 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2970 }
2971
2972 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2973 /// elements.
2974 ///
2975 /// This sort is unstable (i.e., may reorder equal elements), in-place
2976 /// (i.e., does not allocate), and *O*(*m* \* *n* \* log(*n*)) worst-case, where the key function is
2977 /// *O*(*m*).
2978 ///
2979 /// # Current implementation
2980 ///
2981 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2982 /// which combines the fast average case of randomized quicksort with the fast worst case of
2983 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2984 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2985 /// deterministic behavior.
2986 ///
2987 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2988 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2989 /// cases where the key function is expensive.
2990 ///
2991 /// # Examples
2992 ///
2993 /// ```
2994 /// let mut v = [-5i32, 4, 1, -3, 2];
2995 ///
2996 /// v.sort_unstable_by_key(|k| k.abs());
2997 /// assert!(v == [1, 2, -3, 4, -5]);
2998 /// ```
2999 ///
3000 /// [pdqsort]: https://github.com/orlp/pdqsort
3001 #[stable(feature = "sort_unstable", since = "1.20.0")]
3002 #[inline]
3003 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
3004 where
3005 F: FnMut(&T) -> K,
3006 K: Ord,
3007 {
3008 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
3009 }
3010
3011 /// Reorder the slice such that the element at `index` after the reordering is at its final sorted position.
3012 ///
3013 /// This reordering has the additional property that any value at position `i < index` will be
3014 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
3015 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
3016 /// (i.e. does not allocate), and runs in *O*(*n*) time.
3017 /// This function is also known as "kth element" in other libraries.
3018 ///
3019 /// It returns a triplet of the following from the reordered slice:
3020 /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
3021 /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
3022 /// and greater-than-or-equal-to the value of the element at `index`.
3023 ///
3024 /// # Current implementation
3025 ///
3026 /// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
3027 /// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
3028 /// pivot selection, which guarantees linear runtime for all inputs.
3029 ///
3030 /// [`sort_unstable`]: slice::sort_unstable
3031 ///
3032 /// # Panics
3033 ///
3034 /// Panics when `index >= len()`, meaning it always panics on empty slices.
3035 ///
3036 /// # Examples
3037 ///
3038 /// ```
3039 /// let mut v = [-5i32, 4, 2, -3, 1];
3040 ///
3041 /// // Find the items less than or equal to the median, the median, and greater than or equal to
3042 /// // the median.
3043 /// let (lesser, median, greater) = v.select_nth_unstable(2);
3044 ///
3045 /// assert!(lesser == [-3, -5] || lesser == [-5, -3]);
3046 /// assert_eq!(median, &mut 1);
3047 /// assert!(greater == [4, 2] || greater == [2, 4]);
3048 ///
3049 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3050 /// // about the specified index.
3051 /// assert!(v == [-3, -5, 1, 2, 4] ||
3052 /// v == [-5, -3, 1, 2, 4] ||
3053 /// v == [-3, -5, 1, 4, 2] ||
3054 /// v == [-5, -3, 1, 4, 2]);
3055 /// ```
3056 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3057 #[inline]
3058 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
3059 where
3060 T: Ord,
3061 {
3062 select::partition_at_index(self, index, T::lt)
3063 }
3064
3065 /// Reorder the slice with a comparator function such that the element at `index` after the reordering is at
3066 /// its final sorted position.
3067 ///
3068 /// This reordering has the additional property that any value at position `i < index` will be
3069 /// less than or equal to any value at a position `j > index` using the comparator function.
3070 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
3071 /// position `index`), in-place (i.e. does not allocate), and runs in *O*(*n*) time.
3072 /// This function is also known as "kth element" in other libraries.
3073 ///
3074 /// It returns a triplet of the following from
3075 /// the slice reordered according to the provided comparator function: the subslice prior to
3076 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
3077 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
3078 /// the value of the element at `index`.
3079 ///
3080 /// # Current implementation
3081 ///
3082 /// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
3083 /// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
3084 /// pivot selection, which guarantees linear runtime for all inputs.
3085 ///
3086 /// [`sort_unstable`]: slice::sort_unstable
3087 ///
3088 /// # Panics
3089 ///
3090 /// Panics when `index >= len()`, meaning it always panics on empty slices.
3091 ///
3092 /// # Examples
3093 ///
3094 /// ```
3095 /// let mut v = [-5i32, 4, 2, -3, 1];
3096 ///
3097 /// // Find the items less than or equal to the median, the median, and greater than or equal to
3098 /// // the median as if the slice were sorted in descending order.
3099 /// let (lesser, median, greater) = v.select_nth_unstable_by(2, |a, b| b.cmp(a));
3100 ///
3101 /// assert!(lesser == [4, 2] || lesser == [2, 4]);
3102 /// assert_eq!(median, &mut 1);
3103 /// assert!(greater == [-3, -5] || greater == [-5, -3]);
3104 ///
3105 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3106 /// // about the specified index.
3107 /// assert!(v == [2, 4, 1, -5, -3] ||
3108 /// v == [2, 4, 1, -3, -5] ||
3109 /// v == [4, 2, 1, -5, -3] ||
3110 /// v == [4, 2, 1, -3, -5]);
3111 /// ```
3112 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3113 #[inline]
3114 pub fn select_nth_unstable_by<F>(
3115 &mut self,
3116 index: usize,
3117 mut compare: F,
3118 ) -> (&mut [T], &mut T, &mut [T])
3119 where
3120 F: FnMut(&T, &T) -> Ordering,
3121 {
3122 select::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
3123 }
3124
3125 /// Reorder the slice with a key extraction function such that the element at `index` after the reordering is
3126 /// at its final sorted position.
3127 ///
3128 /// This reordering has the additional property that any value at position `i < index` will be
3129 /// less than or equal to any value at a position `j > index` using the key extraction function.
3130 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
3131 /// position `index`), in-place (i.e. does not allocate), and runs in *O*(*n*) time.
3132 /// This function is also known as "kth element" in other libraries.
3133 ///
3134 /// It returns a triplet of the following from
3135 /// the slice reordered according to the provided key extraction function: the subslice prior to
3136 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
3137 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
3138 /// the value of the element at `index`.
3139 ///
3140 /// # Current implementation
3141 ///
3142 /// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
3143 /// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
3144 /// pivot selection, which guarantees linear runtime for all inputs.
3145 ///
3146 /// [`sort_unstable`]: slice::sort_unstable
3147 ///
3148 /// # Panics
3149 ///
3150 /// Panics when `index >= len()`, meaning it always panics on empty slices.
3151 ///
3152 /// # Examples
3153 ///
3154 /// ```
3155 /// let mut v = [-5i32, 4, 1, -3, 2];
3156 ///
3157 /// // Find the items less than or equal to the median, the median, and greater than or equal to
3158 /// // the median as if the slice were sorted according to absolute value.
3159 /// let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs());
3160 ///
3161 /// assert!(lesser == [1, 2] || lesser == [2, 1]);
3162 /// assert_eq!(median, &mut -3);
3163 /// assert!(greater == [4, -5] || greater == [-5, 4]);
3164 ///
3165 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
3166 /// // about the specified index.
3167 /// assert!(v == [1, 2, -3, 4, -5] ||
3168 /// v == [1, 2, -3, -5, 4] ||
3169 /// v == [2, 1, -3, 4, -5] ||
3170 /// v == [2, 1, -3, -5, 4]);
3171 /// ```
3172 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
3173 #[inline]
3174 pub fn select_nth_unstable_by_key<K, F>(
3175 &mut self,
3176 index: usize,
3177 mut f: F,
3178 ) -> (&mut [T], &mut T, &mut [T])
3179 where
3180 F: FnMut(&T) -> K,
3181 K: Ord,
3182 {
3183 select::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
3184 }
3185
3186 /// Moves all consecutive repeated elements to the end of the slice according to the
3187 /// [`PartialEq`] trait implementation.
3188 ///
3189 /// Returns two slices. The first contains no consecutive repeated elements.
3190 /// The second contains all the duplicates in no specified order.
3191 ///
3192 /// If the slice is sorted, the first returned slice contains no duplicates.
3193 ///
3194 /// # Examples
3195 ///
3196 /// ```
3197 /// #![feature(slice_partition_dedup)]
3198 ///
3199 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
3200 ///
3201 /// let (dedup, duplicates) = slice.partition_dedup();
3202 ///
3203 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
3204 /// assert_eq!(duplicates, [2, 3, 1]);
3205 /// ```
3206 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3207 #[inline]
3208 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
3209 where
3210 T: PartialEq,
3211 {
3212 self.partition_dedup_by(|a, b| a == b)
3213 }
3214
3215 /// Moves all but the first of consecutive elements to the end of the slice satisfying
3216 /// a given equality relation.
3217 ///
3218 /// Returns two slices. The first contains no consecutive repeated elements.
3219 /// The second contains all the duplicates in no specified order.
3220 ///
3221 /// The `same_bucket` function is passed references to two elements from the slice and
3222 /// must determine if the elements compare equal. The elements are passed in opposite order
3223 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
3224 /// at the end of the slice.
3225 ///
3226 /// If the slice is sorted, the first returned slice contains no duplicates.
3227 ///
3228 /// # Examples
3229 ///
3230 /// ```
3231 /// #![feature(slice_partition_dedup)]
3232 ///
3233 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
3234 ///
3235 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
3236 ///
3237 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
3238 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
3239 /// ```
3240 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3241 #[inline]
3242 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
3243 where
3244 F: FnMut(&mut T, &mut T) -> bool,
3245 {
3246 // Although we have a mutable reference to `self`, we cannot make
3247 // *arbitrary* changes. The `same_bucket` calls could panic, so we
3248 // must ensure that the slice is in a valid state at all times.
3249 //
3250 // The way that we handle this is by using swaps; we iterate
3251 // over all the elements, swapping as we go so that at the end
3252 // the elements we wish to keep are in the front, and those we
3253 // wish to reject are at the back. We can then split the slice.
3254 // This operation is still `O(n)`.
3255 //
3256 // Example: We start in this state, where `r` represents "next
3257 // read" and `w` represents "next_write".
3258 //
3259 // r
3260 // +---+---+---+---+---+---+
3261 // | 0 | 1 | 1 | 2 | 3 | 3 |
3262 // +---+---+---+---+---+---+
3263 // w
3264 //
3265 // Comparing self[r] against self[w-1], this is not a duplicate, so
3266 // we swap self[r] and self[w] (no effect as r==w) and then increment both
3267 // r and w, leaving us with:
3268 //
3269 // r
3270 // +---+---+---+---+---+---+
3271 // | 0 | 1 | 1 | 2 | 3 | 3 |
3272 // +---+---+---+---+---+---+
3273 // w
3274 //
3275 // Comparing self[r] against self[w-1], this value is a duplicate,
3276 // so we increment `r` but leave everything else unchanged:
3277 //
3278 // r
3279 // +---+---+---+---+---+---+
3280 // | 0 | 1 | 1 | 2 | 3 | 3 |
3281 // +---+---+---+---+---+---+
3282 // w
3283 //
3284 // Comparing self[r] against self[w-1], this is not a duplicate,
3285 // so swap self[r] and self[w] and advance r and w:
3286 //
3287 // r
3288 // +---+---+---+---+---+---+
3289 // | 0 | 1 | 2 | 1 | 3 | 3 |
3290 // +---+---+---+---+---+---+
3291 // w
3292 //
3293 // Not a duplicate, repeat:
3294 //
3295 // r
3296 // +---+---+---+---+---+---+
3297 // | 0 | 1 | 2 | 3 | 1 | 3 |
3298 // +---+---+---+---+---+---+
3299 // w
3300 //
3301 // Duplicate, advance r. End of slice. Split at w.
3302
3303 let len = self.len();
3304 if len <= 1 {
3305 return (self, &mut []);
3306 }
3307
3308 let ptr = self.as_mut_ptr();
3309 let mut next_read: usize = 1;
3310 let mut next_write: usize = 1;
3311
3312 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
3313 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
3314 // one element before `ptr_write`, but `next_write` starts at 1, so
3315 // `prev_ptr_write` is never less than 0 and is inside the slice.
3316 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
3317 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
3318 // and `prev_ptr_write.offset(1)`.
3319 //
3320 // `next_write` is also incremented at most once per loop at most meaning
3321 // no element is skipped when it may need to be swapped.
3322 //
3323 // `ptr_read` and `prev_ptr_write` never point to the same element. This
3324 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
3325 // The explanation is simply that `next_read >= next_write` is always true,
3326 // thus `next_read > next_write - 1` is too.
3327 unsafe {
3328 // Avoid bounds checks by using raw pointers.
3329 while next_read < len {
3330 let ptr_read = ptr.add(next_read);
3331 let prev_ptr_write = ptr.add(next_write - 1);
3332 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
3333 if next_read != next_write {
3334 let ptr_write = prev_ptr_write.add(1);
3335 mem::swap(&mut *ptr_read, &mut *ptr_write);
3336 }
3337 next_write += 1;
3338 }
3339 next_read += 1;
3340 }
3341 }
3342
3343 self.split_at_mut(next_write)
3344 }
3345
3346 /// Moves all but the first of consecutive elements to the end of the slice that resolve
3347 /// to the same key.
3348 ///
3349 /// Returns two slices. The first contains no consecutive repeated elements.
3350 /// The second contains all the duplicates in no specified order.
3351 ///
3352 /// If the slice is sorted, the first returned slice contains no duplicates.
3353 ///
3354 /// # Examples
3355 ///
3356 /// ```
3357 /// #![feature(slice_partition_dedup)]
3358 ///
3359 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
3360 ///
3361 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
3362 ///
3363 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
3364 /// assert_eq!(duplicates, [21, 30, 13]);
3365 /// ```
3366 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3367 #[inline]
3368 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
3369 where
3370 F: FnMut(&mut T) -> K,
3371 K: PartialEq,
3372 {
3373 self.partition_dedup_by(|a, b| key(a) == key(b))
3374 }
3375
3376 /// Rotates the slice in-place such that the first `mid` elements of the
3377 /// slice move to the end while the last `self.len() - mid` elements move to
3378 /// the front. After calling `rotate_left`, the element previously at index
3379 /// `mid` will become the first element in the slice.
3380 ///
3381 /// # Panics
3382 ///
3383 /// This function will panic if `mid` is greater than the length of the
3384 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
3385 /// rotation.
3386 ///
3387 /// # Complexity
3388 ///
3389 /// Takes linear (in `self.len()`) time.
3390 ///
3391 /// # Examples
3392 ///
3393 /// ```
3394 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3395 /// a.rotate_left(2);
3396 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
3397 /// ```
3398 ///
3399 /// Rotating a subslice:
3400 ///
3401 /// ```
3402 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3403 /// a[1..5].rotate_left(1);
3404 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
3405 /// ```
3406 #[stable(feature = "slice_rotate", since = "1.26.0")]
3407 pub fn rotate_left(&mut self, mid: usize) {
3408 assert!(mid <= self.len());
3409 let k = self.len() - mid;
3410 let p = self.as_mut_ptr();
3411
3412 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3413 // valid for reading and writing, as required by `ptr_rotate`.
3414 unsafe {
3415 rotate::ptr_rotate(mid, p.add(mid), k);
3416 }
3417 }
3418
3419 /// Rotates the slice in-place such that the first `self.len() - k`
3420 /// elements of the slice move to the end while the last `k` elements move
3421 /// to the front. After calling `rotate_right`, the element previously at
3422 /// index `self.len() - k` will become the first element in the slice.
3423 ///
3424 /// # Panics
3425 ///
3426 /// This function will panic if `k` is greater than the length of the
3427 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
3428 /// rotation.
3429 ///
3430 /// # Complexity
3431 ///
3432 /// Takes linear (in `self.len()`) time.
3433 ///
3434 /// # Examples
3435 ///
3436 /// ```
3437 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3438 /// a.rotate_right(2);
3439 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
3440 /// ```
3441 ///
3442 /// Rotating a subslice:
3443 ///
3444 /// ```
3445 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3446 /// a[1..5].rotate_right(1);
3447 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
3448 /// ```
3449 #[stable(feature = "slice_rotate", since = "1.26.0")]
3450 pub fn rotate_right(&mut self, k: usize) {
3451 assert!(k <= self.len());
3452 let mid = self.len() - k;
3453 let p = self.as_mut_ptr();
3454
3455 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3456 // valid for reading and writing, as required by `ptr_rotate`.
3457 unsafe {
3458 rotate::ptr_rotate(mid, p.add(mid), k);
3459 }
3460 }
3461
3462 /// Fills `self` with elements by cloning `value`.
3463 ///
3464 /// # Examples
3465 ///
3466 /// ```
3467 /// let mut buf = vec![0; 10];
3468 /// buf.fill(1);
3469 /// assert_eq!(buf, vec![1; 10]);
3470 /// ```
3471 #[doc(alias = "memset")]
3472 #[stable(feature = "slice_fill", since = "1.50.0")]
3473 pub fn fill(&mut self, value: T)
3474 where
3475 T: Clone,
3476 {
3477 specialize::SpecFill::spec_fill(self, value);
3478 }
3479
3480 /// Fills `self` with elements returned by calling a closure repeatedly.
3481 ///
3482 /// This method uses a closure to create new values. If you'd rather
3483 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3484 /// trait to generate values, you can pass [`Default::default`] as the
3485 /// argument.
3486 ///
3487 /// [`fill`]: slice::fill
3488 ///
3489 /// # Examples
3490 ///
3491 /// ```
3492 /// let mut buf = vec![1; 10];
3493 /// buf.fill_with(Default::default);
3494 /// assert_eq!(buf, vec![0; 10]);
3495 /// ```
3496 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3497 pub fn fill_with<F>(&mut self, mut f: F)
3498 where
3499 F: FnMut() -> T,
3500 {
3501 for el in self {
3502 *el = f();
3503 }
3504 }
3505
3506 /// Copies the elements from `src` into `self`.
3507 ///
3508 /// The length of `src` must be the same as `self`.
3509 ///
3510 /// # Panics
3511 ///
3512 /// This function will panic if the two slices have different lengths.
3513 ///
3514 /// # Examples
3515 ///
3516 /// Cloning two elements from a slice into another:
3517 ///
3518 /// ```
3519 /// let src = [1, 2, 3, 4];
3520 /// let mut dst = [0, 0];
3521 ///
3522 /// // Because the slices have to be the same length,
3523 /// // we slice the source slice from four elements
3524 /// // to two. It will panic if we don't do this.
3525 /// dst.clone_from_slice(&src[2..]);
3526 ///
3527 /// assert_eq!(src, [1, 2, 3, 4]);
3528 /// assert_eq!(dst, [3, 4]);
3529 /// ```
3530 ///
3531 /// Rust enforces that there can only be one mutable reference with no
3532 /// immutable references to a particular piece of data in a particular
3533 /// scope. Because of this, attempting to use `clone_from_slice` on a
3534 /// single slice will result in a compile failure:
3535 ///
3536 /// ```compile_fail
3537 /// let mut slice = [1, 2, 3, 4, 5];
3538 ///
3539 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3540 /// ```
3541 ///
3542 /// To work around this, we can use [`split_at_mut`] to create two distinct
3543 /// sub-slices from a slice:
3544 ///
3545 /// ```
3546 /// let mut slice = [1, 2, 3, 4, 5];
3547 ///
3548 /// {
3549 /// let (left, right) = slice.split_at_mut(2);
3550 /// left.clone_from_slice(&right[1..]);
3551 /// }
3552 ///
3553 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3554 /// ```
3555 ///
3556 /// [`copy_from_slice`]: slice::copy_from_slice
3557 /// [`split_at_mut`]: slice::split_at_mut
3558 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3559 #[track_caller]
3560 pub fn clone_from_slice(&mut self, src: &[T])
3561 where
3562 T: Clone,
3563 {
3564 self.spec_clone_from(src);
3565 }
3566
3567 /// Copies all elements from `src` into `self`, using a memcpy.
3568 ///
3569 /// The length of `src` must be the same as `self`.
3570 ///
3571 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3572 ///
3573 /// # Panics
3574 ///
3575 /// This function will panic if the two slices have different lengths.
3576 ///
3577 /// # Examples
3578 ///
3579 /// Copying two elements from a slice into another:
3580 ///
3581 /// ```
3582 /// let src = [1, 2, 3, 4];
3583 /// let mut dst = [0, 0];
3584 ///
3585 /// // Because the slices have to be the same length,
3586 /// // we slice the source slice from four elements
3587 /// // to two. It will panic if we don't do this.
3588 /// dst.copy_from_slice(&src[2..]);
3589 ///
3590 /// assert_eq!(src, [1, 2, 3, 4]);
3591 /// assert_eq!(dst, [3, 4]);
3592 /// ```
3593 ///
3594 /// Rust enforces that there can only be one mutable reference with no
3595 /// immutable references to a particular piece of data in a particular
3596 /// scope. Because of this, attempting to use `copy_from_slice` on a
3597 /// single slice will result in a compile failure:
3598 ///
3599 /// ```compile_fail
3600 /// let mut slice = [1, 2, 3, 4, 5];
3601 ///
3602 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3603 /// ```
3604 ///
3605 /// To work around this, we can use [`split_at_mut`] to create two distinct
3606 /// sub-slices from a slice:
3607 ///
3608 /// ```
3609 /// let mut slice = [1, 2, 3, 4, 5];
3610 ///
3611 /// {
3612 /// let (left, right) = slice.split_at_mut(2);
3613 /// left.copy_from_slice(&right[1..]);
3614 /// }
3615 ///
3616 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3617 /// ```
3618 ///
3619 /// [`clone_from_slice`]: slice::clone_from_slice
3620 /// [`split_at_mut`]: slice::split_at_mut
3621 #[doc(alias = "memcpy")]
3622 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3623 #[track_caller]
3624 pub fn copy_from_slice(&mut self, src: &[T])
3625 where
3626 T: Copy,
3627 {
3628 // The panic code path was put into a cold function to not bloat the
3629 // call site.
3630 #[inline(never)]
3631 #[cold]
3632 #[track_caller]
3633 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3634 panic!(
3635 "source slice length ({}) does not match destination slice length ({})",
3636 src_len, dst_len,
3637 );
3638 }
3639
3640 if self.len() != src.len() {
3641 len_mismatch_fail(self.len(), src.len());
3642 }
3643
3644 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3645 // checked to have the same length. The slices cannot overlap because
3646 // mutable references are exclusive.
3647 unsafe {
3648 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3649 }
3650 }
3651
3652 /// Copies elements from one part of the slice to another part of itself,
3653 /// using a memmove.
3654 ///
3655 /// `src` is the range within `self` to copy from. `dest` is the starting
3656 /// index of the range within `self` to copy to, which will have the same
3657 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3658 /// must be less than or equal to `self.len()`.
3659 ///
3660 /// # Panics
3661 ///
3662 /// This function will panic if either range exceeds the end of the slice,
3663 /// or if the end of `src` is before the start.
3664 ///
3665 /// # Examples
3666 ///
3667 /// Copying four bytes within a slice:
3668 ///
3669 /// ```
3670 /// let mut bytes = *b"Hello, World!";
3671 ///
3672 /// bytes.copy_within(1..5, 8);
3673 ///
3674 /// assert_eq!(&bytes, b"Hello, Wello!");
3675 /// ```
3676 #[stable(feature = "copy_within", since = "1.37.0")]
3677 #[track_caller]
3678 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3679 where
3680 T: Copy,
3681 {
3682 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3683 let count = src_end - src_start;
3684 assert!(dest <= self.len() - count, "dest is out of bounds");
3685 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3686 // as have those for `ptr::add`.
3687 unsafe {
3688 // Derive both `src_ptr` and `dest_ptr` from the same loan
3689 let ptr = self.as_mut_ptr();
3690 let src_ptr = ptr.add(src_start);
3691 let dest_ptr = ptr.add(dest);
3692 ptr::copy(src_ptr, dest_ptr, count);
3693 }
3694 }
3695
3696 /// Swaps all elements in `self` with those in `other`.
3697 ///
3698 /// The length of `other` must be the same as `self`.
3699 ///
3700 /// # Panics
3701 ///
3702 /// This function will panic if the two slices have different lengths.
3703 ///
3704 /// # Example
3705 ///
3706 /// Swapping two elements across slices:
3707 ///
3708 /// ```
3709 /// let mut slice1 = [0, 0];
3710 /// let mut slice2 = [1, 2, 3, 4];
3711 ///
3712 /// slice1.swap_with_slice(&mut slice2[2..]);
3713 ///
3714 /// assert_eq!(slice1, [3, 4]);
3715 /// assert_eq!(slice2, [1, 2, 0, 0]);
3716 /// ```
3717 ///
3718 /// Rust enforces that there can only be one mutable reference to a
3719 /// particular piece of data in a particular scope. Because of this,
3720 /// attempting to use `swap_with_slice` on a single slice will result in
3721 /// a compile failure:
3722 ///
3723 /// ```compile_fail
3724 /// let mut slice = [1, 2, 3, 4, 5];
3725 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3726 /// ```
3727 ///
3728 /// To work around this, we can use [`split_at_mut`] to create two distinct
3729 /// mutable sub-slices from a slice:
3730 ///
3731 /// ```
3732 /// let mut slice = [1, 2, 3, 4, 5];
3733 ///
3734 /// {
3735 /// let (left, right) = slice.split_at_mut(2);
3736 /// left.swap_with_slice(&mut right[1..]);
3737 /// }
3738 ///
3739 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3740 /// ```
3741 ///
3742 /// [`split_at_mut`]: slice::split_at_mut
3743 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3744 #[track_caller]
3745 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3746 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3747 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3748 // checked to have the same length. The slices cannot overlap because
3749 // mutable references are exclusive.
3750 unsafe {
3751 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3752 }
3753 }
3754
3755 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3756 fn align_to_offsets<U>(&self) -> (usize, usize) {
3757 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3758 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3759 //
3760 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3761 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3762 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3763 //
3764 // Formula to calculate this is:
3765 //
3766 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3767 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3768 //
3769 // Expanded and simplified:
3770 //
3771 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3772 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3773 //
3774 // Luckily since all this is constant-evaluated... performance here matters not!
3775 const fn gcd(a: usize, b: usize) -> usize {
3776 if b == 0 { a } else { gcd(b, a % b) }
3777 }
3778
3779 // Explicitly wrap the function call in a const block so it gets
3780 // constant-evaluated even in debug mode.
3781 let gcd: usize = const { gcd(mem::size_of::<T>(), mem::size_of::<U>()) };
3782 let ts: usize = mem::size_of::<U>() / gcd;
3783 let us: usize = mem::size_of::<T>() / gcd;
3784
3785 // Armed with this knowledge, we can find how many `U`s we can fit!
3786 let us_len = self.len() / ts * us;
3787 // And how many `T`s will be in the trailing slice!
3788 let ts_len = self.len() % ts;
3789 (us_len, ts_len)
3790 }
3791
3792 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3793 /// maintained.
3794 ///
3795 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3796 /// slice of a new type, and the suffix slice. The middle part will be as big as possible under
3797 /// the given alignment constraint and element size.
3798 ///
3799 /// This method has no purpose when either input element `T` or output element `U` are
3800 /// zero-sized and will return the original slice without splitting anything.
3801 ///
3802 /// # Safety
3803 ///
3804 /// This method is essentially a `transmute` with respect to the elements in the returned
3805 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3806 ///
3807 /// # Examples
3808 ///
3809 /// Basic usage:
3810 ///
3811 /// ```
3812 /// unsafe {
3813 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3814 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3815 /// // less_efficient_algorithm_for_bytes(prefix);
3816 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3817 /// // less_efficient_algorithm_for_bytes(suffix);
3818 /// }
3819 /// ```
3820 #[stable(feature = "slice_align_to", since = "1.30.0")]
3821 #[must_use]
3822 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3823 // Note that most of this function will be constant-evaluated,
3824 if U::IS_ZST || T::IS_ZST {
3825 // handle ZSTs specially, which is – don't handle them at all.
3826 return (self, &[], &[]);
3827 }
3828
3829 // First, find at what point do we split between the first and 2nd slice. Easy with
3830 // ptr.align_offset.
3831 let ptr = self.as_ptr();
3832 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3833 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3834 if offset > self.len() {
3835 (self, &[], &[])
3836 } else {
3837 let (left, rest) = self.split_at(offset);
3838 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3839 // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
3840 #[cfg(miri)]
3841 crate::intrinsics::miri_promise_symbolic_alignment(
3842 rest.as_ptr().cast(),
3843 mem::align_of::<U>(),
3844 );
3845 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3846 // since the caller guarantees that we can transmute `T` to `U` safely.
3847 unsafe {
3848 (
3849 left,
3850 from_raw_parts(rest.as_ptr() as *const U, us_len),
3851 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3852 )
3853 }
3854 }
3855 }
3856
3857 /// Transmute the mutable slice to a mutable slice of another type, ensuring alignment of the
3858 /// types is maintained.
3859 ///
3860 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3861 /// slice of a new type, and the suffix slice. The middle part will be as big as possible under
3862 /// the given alignment constraint and element size.
3863 ///
3864 /// This method has no purpose when either input element `T` or output element `U` are
3865 /// zero-sized and will return the original slice without splitting anything.
3866 ///
3867 /// # Safety
3868 ///
3869 /// This method is essentially a `transmute` with respect to the elements in the returned
3870 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3871 ///
3872 /// # Examples
3873 ///
3874 /// Basic usage:
3875 ///
3876 /// ```
3877 /// unsafe {
3878 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3879 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3880 /// // less_efficient_algorithm_for_bytes(prefix);
3881 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3882 /// // less_efficient_algorithm_for_bytes(suffix);
3883 /// }
3884 /// ```
3885 #[stable(feature = "slice_align_to", since = "1.30.0")]
3886 #[must_use]
3887 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3888 // Note that most of this function will be constant-evaluated,
3889 if U::IS_ZST || T::IS_ZST {
3890 // handle ZSTs specially, which is – don't handle them at all.
3891 return (self, &mut [], &mut []);
3892 }
3893
3894 // First, find at what point do we split between the first and 2nd slice. Easy with
3895 // ptr.align_offset.
3896 let ptr = self.as_ptr();
3897 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3898 // rest of the method. This is done by passing a pointer to &[T] with an
3899 // alignment targeted for U.
3900 // `crate::ptr::align_offset` is called with a correctly aligned and
3901 // valid pointer `ptr` (it comes from a reference to `self`) and with
3902 // a size that is a power of two (since it comes from the alignment for U),
3903 // satisfying its safety constraints.
3904 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3905 if offset > self.len() {
3906 (self, &mut [], &mut [])
3907 } else {
3908 let (left, rest) = self.split_at_mut(offset);
3909 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3910 let rest_len = rest.len();
3911 let mut_ptr = rest.as_mut_ptr();
3912 // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
3913 #[cfg(miri)]
3914 crate::intrinsics::miri_promise_symbolic_alignment(
3915 mut_ptr.cast() as *const (),
3916 mem::align_of::<U>(),
3917 );
3918 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3919 // SAFETY: see comments for `align_to`.
3920 unsafe {
3921 (
3922 left,
3923 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3924 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3925 )
3926 }
3927 }
3928 }
3929
3930 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3931 ///
3932 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3933 /// postconditions as that method. You're only assured that
3934 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3935 ///
3936 /// Notably, all of the following are possible:
3937 /// - `prefix.len() >= LANES`.
3938 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3939 /// - `suffix.len() >= LANES`.
3940 ///
3941 /// That said, this is a safe method, so if you're only writing safe code,
3942 /// then this can at most cause incorrect logic, not unsoundness.
3943 ///
3944 /// # Panics
3945 ///
3946 /// This will panic if the size of the SIMD type is different from
3947 /// `LANES` times that of the scalar.
3948 ///
3949 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3950 /// that from ever happening, as only power-of-two numbers of lanes are
3951 /// supported. It's possible that, in the future, those restrictions might
3952 /// be lifted in a way that would make it possible to see panics from this
3953 /// method for something like `LANES == 3`.
3954 ///
3955 /// # Examples
3956 ///
3957 /// ```
3958 /// #![feature(portable_simd)]
3959 /// use core::simd::prelude::*;
3960 ///
3961 /// let short = &[1, 2, 3];
3962 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3963 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3964 ///
3965 /// // They might be split in any possible way between prefix and suffix
3966 /// let it = prefix.iter().chain(suffix).copied();
3967 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3968 ///
3969 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3970 /// use std::ops::Add;
3971 /// let (prefix, middle, suffix) = x.as_simd();
3972 /// let sums = f32x4::from_array([
3973 /// prefix.iter().copied().sum(),
3974 /// 0.0,
3975 /// 0.0,
3976 /// suffix.iter().copied().sum(),
3977 /// ]);
3978 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3979 /// sums.reduce_sum()
3980 /// }
3981 ///
3982 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3983 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3984 /// ```
3985 #[unstable(feature = "portable_simd", issue = "86656")]
3986 #[must_use]
3987 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3988 where
3989 Simd<T, LANES>: AsRef<[T; LANES]>,
3990 T: simd::SimdElement,
3991 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3992 {
3993 // These are expected to always match, as vector types are laid out like
3994 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3995 // might as well double-check since it'll optimize away anyhow.
3996 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3997
3998 // SAFETY: The simd types have the same layout as arrays, just with
3999 // potentially-higher alignment, so the de-facto transmutes are sound.
4000 unsafe { self.align_to() }
4001 }
4002
4003 /// Split a mutable slice into a mutable prefix, a middle of aligned SIMD types,
4004 /// and a mutable suffix.
4005 ///
4006 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
4007 /// postconditions as that method. You're only assured that
4008 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
4009 ///
4010 /// Notably, all of the following are possible:
4011 /// - `prefix.len() >= LANES`.
4012 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
4013 /// - `suffix.len() >= LANES`.
4014 ///
4015 /// That said, this is a safe method, so if you're only writing safe code,
4016 /// then this can at most cause incorrect logic, not unsoundness.
4017 ///
4018 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
4019 ///
4020 /// # Panics
4021 ///
4022 /// This will panic if the size of the SIMD type is different from
4023 /// `LANES` times that of the scalar.
4024 ///
4025 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
4026 /// that from ever happening, as only power-of-two numbers of lanes are
4027 /// supported. It's possible that, in the future, those restrictions might
4028 /// be lifted in a way that would make it possible to see panics from this
4029 /// method for something like `LANES == 3`.
4030 #[unstable(feature = "portable_simd", issue = "86656")]
4031 #[must_use]
4032 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
4033 where
4034 Simd<T, LANES>: AsMut<[T; LANES]>,
4035 T: simd::SimdElement,
4036 simd::LaneCount<LANES>: simd::SupportedLaneCount,
4037 {
4038 // These are expected to always match, as vector types are laid out like
4039 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
4040 // might as well double-check since it'll optimize away anyhow.
4041 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
4042
4043 // SAFETY: The simd types have the same layout as arrays, just with
4044 // potentially-higher alignment, so the de-facto transmutes are sound.
4045 unsafe { self.align_to_mut() }
4046 }
4047
4048 /// Checks if the elements of this slice are sorted.
4049 ///
4050 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
4051 /// slice yields exactly zero or one element, `true` is returned.
4052 ///
4053 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
4054 /// implies that this function returns `false` if any two consecutive items are not
4055 /// comparable.
4056 ///
4057 /// # Examples
4058 ///
4059 /// ```
4060 /// #![feature(is_sorted)]
4061 /// let empty: [i32; 0] = [];
4062 ///
4063 /// assert!([1, 2, 2, 9].is_sorted());
4064 /// assert!(![1, 3, 2, 4].is_sorted());
4065 /// assert!([0].is_sorted());
4066 /// assert!(empty.is_sorted());
4067 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
4068 /// ```
4069 #[inline]
4070 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
4071 #[must_use]
4072 pub fn is_sorted(&self) -> bool
4073 where
4074 T: PartialOrd,
4075 {
4076 self.is_sorted_by(|a, b| a <= b)
4077 }
4078
4079 /// Checks if the elements of this slice are sorted using the given comparator function.
4080 ///
4081 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
4082 /// function to determine whether two elements are to be considered in sorted order.
4083 ///
4084 /// # Examples
4085 ///
4086 /// ```
4087 /// #![feature(is_sorted)]
4088 ///
4089 /// assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
4090 /// assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b));
4091 ///
4092 /// assert!([0].is_sorted_by(|a, b| true));
4093 /// assert!([0].is_sorted_by(|a, b| false));
4094 ///
4095 /// let empty: [i32; 0] = [];
4096 /// assert!(empty.is_sorted_by(|a, b| false));
4097 /// assert!(empty.is_sorted_by(|a, b| true));
4098 /// ```
4099 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
4100 #[must_use]
4101 pub fn is_sorted_by<'a, F>(&'a self, mut compare: F) -> bool
4102 where
4103 F: FnMut(&'a T, &'a T) -> bool,
4104 {
4105 self.array_windows().all(|[a, b]| compare(a, b))
4106 }
4107
4108 /// Checks if the elements of this slice are sorted using the given key extraction function.
4109 ///
4110 /// Instead of comparing the slice's elements directly, this function compares the keys of the
4111 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
4112 /// documentation for more information.
4113 ///
4114 /// [`is_sorted`]: slice::is_sorted
4115 ///
4116 /// # Examples
4117 ///
4118 /// ```
4119 /// #![feature(is_sorted)]
4120 ///
4121 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
4122 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
4123 /// ```
4124 #[inline]
4125 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
4126 #[must_use]
4127 pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool
4128 where
4129 F: FnMut(&'a T) -> K,
4130 K: PartialOrd,
4131 {
4132 self.iter().is_sorted_by_key(f)
4133 }
4134
4135 /// Returns the index of the partition point according to the given predicate
4136 /// (the index of the first element of the second partition).
4137 ///
4138 /// The slice is assumed to be partitioned according to the given predicate.
4139 /// This means that all elements for which the predicate returns true are at the start of the slice
4140 /// and all elements for which the predicate returns false are at the end.
4141 /// For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0`
4142 /// (all odd numbers are at the start, all even at the end).
4143 ///
4144 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
4145 /// as this method performs a kind of binary search.
4146 ///
4147 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
4148 ///
4149 /// [`binary_search`]: slice::binary_search
4150 /// [`binary_search_by`]: slice::binary_search_by
4151 /// [`binary_search_by_key`]: slice::binary_search_by_key
4152 ///
4153 /// # Examples
4154 ///
4155 /// ```
4156 /// let v = [1, 2, 3, 3, 5, 6, 7];
4157 /// let i = v.partition_point(|&x| x < 5);
4158 ///
4159 /// assert_eq!(i, 4);
4160 /// assert!(v[..i].iter().all(|&x| x < 5));
4161 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
4162 /// ```
4163 ///
4164 /// If all elements of the slice match the predicate, including if the slice
4165 /// is empty, then the length of the slice will be returned:
4166 ///
4167 /// ```
4168 /// let a = [2, 4, 8];
4169 /// assert_eq!(a.partition_point(|x| x < &100), a.len());
4170 /// let a: [i32; 0] = [];
4171 /// assert_eq!(a.partition_point(|x| x < &100), 0);
4172 /// ```
4173 ///
4174 /// If you want to insert an item to a sorted vector, while maintaining
4175 /// sort order:
4176 ///
4177 /// ```
4178 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
4179 /// let num = 42;
4180 /// let idx = s.partition_point(|&x| x <= num);
4181 /// s.insert(idx, num);
4182 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
4183 /// ```
4184 #[stable(feature = "partition_point", since = "1.52.0")]
4185 #[must_use]
4186 pub fn partition_point<P>(&self, mut pred: P) -> usize
4187 where
4188 P: FnMut(&T) -> bool,
4189 {
4190 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
4191 }
4192
4193 /// Removes the subslice corresponding to the given range
4194 /// and returns a reference to it.
4195 ///
4196 /// Returns `None` and does not modify the slice if the given
4197 /// range is out of bounds.
4198 ///
4199 /// Note that this method only accepts one-sided ranges such as
4200 /// `2..` or `..6`, but not `2..6`.
4201 ///
4202 /// # Examples
4203 ///
4204 /// Taking the first three elements of a slice:
4205 ///
4206 /// ```
4207 /// #![feature(slice_take)]
4208 ///
4209 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4210 /// let mut first_three = slice.take(..3).unwrap();
4211 ///
4212 /// assert_eq!(slice, &['d']);
4213 /// assert_eq!(first_three, &['a', 'b', 'c']);
4214 /// ```
4215 ///
4216 /// Taking the last two elements of a slice:
4217 ///
4218 /// ```
4219 /// #![feature(slice_take)]
4220 ///
4221 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4222 /// let mut tail = slice.take(2..).unwrap();
4223 ///
4224 /// assert_eq!(slice, &['a', 'b']);
4225 /// assert_eq!(tail, &['c', 'd']);
4226 /// ```
4227 ///
4228 /// Getting `None` when `range` is out of bounds:
4229 ///
4230 /// ```
4231 /// #![feature(slice_take)]
4232 ///
4233 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
4234 ///
4235 /// assert_eq!(None, slice.take(5..));
4236 /// assert_eq!(None, slice.take(..5));
4237 /// assert_eq!(None, slice.take(..=4));
4238 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
4239 /// assert_eq!(Some(expected), slice.take(..4));
4240 /// ```
4241 #[inline]
4242 #[must_use = "method does not modify the slice if the range is out of bounds"]
4243 #[unstable(feature = "slice_take", issue = "62280")]
4244 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
4245 let (direction, split_index) = split_point_of(range)?;
4246 if split_index > self.len() {
4247 return None;
4248 }
4249 let (front, back) = self.split_at(split_index);
4250 match direction {
4251 Direction::Front => {
4252 *self = back;
4253 Some(front)
4254 }
4255 Direction::Back => {
4256 *self = front;
4257 Some(back)
4258 }
4259 }
4260 }
4261
4262 /// Removes the subslice corresponding to the given range
4263 /// and returns a mutable reference to it.
4264 ///
4265 /// Returns `None` and does not modify the slice if the given
4266 /// range is out of bounds.
4267 ///
4268 /// Note that this method only accepts one-sided ranges such as
4269 /// `2..` or `..6`, but not `2..6`.
4270 ///
4271 /// # Examples
4272 ///
4273 /// Taking the first three elements of a slice:
4274 ///
4275 /// ```
4276 /// #![feature(slice_take)]
4277 ///
4278 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4279 /// let mut first_three = slice.take_mut(..3).unwrap();
4280 ///
4281 /// assert_eq!(slice, &mut ['d']);
4282 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
4283 /// ```
4284 ///
4285 /// Taking the last two elements of a slice:
4286 ///
4287 /// ```
4288 /// #![feature(slice_take)]
4289 ///
4290 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4291 /// let mut tail = slice.take_mut(2..).unwrap();
4292 ///
4293 /// assert_eq!(slice, &mut ['a', 'b']);
4294 /// assert_eq!(tail, &mut ['c', 'd']);
4295 /// ```
4296 ///
4297 /// Getting `None` when `range` is out of bounds:
4298 ///
4299 /// ```
4300 /// #![feature(slice_take)]
4301 ///
4302 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4303 ///
4304 /// assert_eq!(None, slice.take_mut(5..));
4305 /// assert_eq!(None, slice.take_mut(..5));
4306 /// assert_eq!(None, slice.take_mut(..=4));
4307 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
4308 /// assert_eq!(Some(expected), slice.take_mut(..4));
4309 /// ```
4310 #[inline]
4311 #[must_use = "method does not modify the slice if the range is out of bounds"]
4312 #[unstable(feature = "slice_take", issue = "62280")]
4313 pub fn take_mut<'a, R: OneSidedRange<usize>>(
4314 self: &mut &'a mut Self,
4315 range: R,
4316 ) -> Option<&'a mut Self> {
4317 let (direction, split_index) = split_point_of(range)?;
4318 if split_index > self.len() {
4319 return None;
4320 }
4321 let (front, back) = mem::take(self).split_at_mut(split_index);
4322 match direction {
4323 Direction::Front => {
4324 *self = back;
4325 Some(front)
4326 }
4327 Direction::Back => {
4328 *self = front;
4329 Some(back)
4330 }
4331 }
4332 }
4333
4334 /// Removes the first element of the slice and returns a reference
4335 /// to it.
4336 ///
4337 /// Returns `None` if the slice is empty.
4338 ///
4339 /// # Examples
4340 ///
4341 /// ```
4342 /// #![feature(slice_take)]
4343 ///
4344 /// let mut slice: &[_] = &['a', 'b', 'c'];
4345 /// let first = slice.take_first().unwrap();
4346 ///
4347 /// assert_eq!(slice, &['b', 'c']);
4348 /// assert_eq!(first, &'a');
4349 /// ```
4350 #[inline]
4351 #[unstable(feature = "slice_take", issue = "62280")]
4352 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
4353 let (first, rem) = self.split_first()?;
4354 *self = rem;
4355 Some(first)
4356 }
4357
4358 /// Removes the first element of the slice and returns a mutable
4359 /// reference to it.
4360 ///
4361 /// Returns `None` if the slice is empty.
4362 ///
4363 /// # Examples
4364 ///
4365 /// ```
4366 /// #![feature(slice_take)]
4367 ///
4368 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4369 /// let first = slice.take_first_mut().unwrap();
4370 /// *first = 'd';
4371 ///
4372 /// assert_eq!(slice, &['b', 'c']);
4373 /// assert_eq!(first, &'d');
4374 /// ```
4375 #[inline]
4376 #[unstable(feature = "slice_take", issue = "62280")]
4377 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4378 let (first, rem) = mem::take(self).split_first_mut()?;
4379 *self = rem;
4380 Some(first)
4381 }
4382
4383 /// Removes the last element of the slice and returns a reference
4384 /// to it.
4385 ///
4386 /// Returns `None` if the slice is empty.
4387 ///
4388 /// # Examples
4389 ///
4390 /// ```
4391 /// #![feature(slice_take)]
4392 ///
4393 /// let mut slice: &[_] = &['a', 'b', 'c'];
4394 /// let last = slice.take_last().unwrap();
4395 ///
4396 /// assert_eq!(slice, &['a', 'b']);
4397 /// assert_eq!(last, &'c');
4398 /// ```
4399 #[inline]
4400 #[unstable(feature = "slice_take", issue = "62280")]
4401 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
4402 let (last, rem) = self.split_last()?;
4403 *self = rem;
4404 Some(last)
4405 }
4406
4407 /// Removes the last element of the slice and returns a mutable
4408 /// reference to it.
4409 ///
4410 /// Returns `None` if the slice is empty.
4411 ///
4412 /// # Examples
4413 ///
4414 /// ```
4415 /// #![feature(slice_take)]
4416 ///
4417 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4418 /// let last = slice.take_last_mut().unwrap();
4419 /// *last = 'd';
4420 ///
4421 /// assert_eq!(slice, &['a', 'b']);
4422 /// assert_eq!(last, &'d');
4423 /// ```
4424 #[inline]
4425 #[unstable(feature = "slice_take", issue = "62280")]
4426 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4427 let (last, rem) = mem::take(self).split_last_mut()?;
4428 *self = rem;
4429 Some(last)
4430 }
4431
4432 /// Returns mutable references to many indices at once, without doing any checks.
4433 ///
4434 /// For a safe alternative see [`get_many_mut`].
4435 ///
4436 /// # Safety
4437 ///
4438 /// Calling this method with overlapping or out-of-bounds indices is *[undefined behavior]*
4439 /// even if the resulting references are not used.
4440 ///
4441 /// # Examples
4442 ///
4443 /// ```
4444 /// #![feature(get_many_mut)]
4445 ///
4446 /// let x = &mut [1, 2, 4];
4447 ///
4448 /// unsafe {
4449 /// let [a, b] = x.get_many_unchecked_mut([0, 2]);
4450 /// *a *= 10;
4451 /// *b *= 100;
4452 /// }
4453 /// assert_eq!(x, &[10, 2, 400]);
4454 /// ```
4455 ///
4456 /// [`get_many_mut`]: slice::get_many_mut
4457 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
4458 #[unstable(feature = "get_many_mut", issue = "104642")]
4459 #[inline]
4460 pub unsafe fn get_many_unchecked_mut<const N: usize>(
4461 &mut self,
4462 indices: [usize; N],
4463 ) -> [&mut T; N] {
4464 // NB: This implementation is written as it is because any variation of
4465 // `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
4466 // or generate worse code otherwise. This is also why we need to go
4467 // through a raw pointer here.
4468 let slice: *mut [T] = self;
4469 let mut arr: mem::MaybeUninit<[&mut T; N]> = mem::MaybeUninit::uninit();
4470 let arr_ptr = arr.as_mut_ptr();
4471
4472 // SAFETY: We expect `indices` to contain disjunct values that are
4473 // in bounds of `self`.
4474 unsafe {
4475 for i in 0..N {
4476 let idx = *indices.get_unchecked(i);
4477 *(*arr_ptr).get_unchecked_mut(i) = &mut *slice.get_unchecked_mut(idx);
4478 }
4479 arr.assume_init()
4480 }
4481 }
4482
4483 /// Returns mutable references to many indices at once.
4484 ///
4485 /// Returns an error if any index is out-of-bounds, or if the same index was
4486 /// passed more than once.
4487 ///
4488 /// # Examples
4489 ///
4490 /// ```
4491 /// #![feature(get_many_mut)]
4492 ///
4493 /// let v = &mut [1, 2, 3];
4494 /// if let Ok([a, b]) = v.get_many_mut([0, 2]) {
4495 /// *a = 413;
4496 /// *b = 612;
4497 /// }
4498 /// assert_eq!(v, &[413, 2, 612]);
4499 /// ```
4500 #[unstable(feature = "get_many_mut", issue = "104642")]
4501 #[inline]
4502 pub fn get_many_mut<const N: usize>(
4503 &mut self,
4504 indices: [usize; N],
4505 ) -> Result<[&mut T; N], GetManyMutError<N>> {
4506 if !get_many_check_valid(&indices, self.len()) {
4507 return Err(GetManyMutError { _private: () });
4508 }
4509 // SAFETY: The `get_many_check_valid()` call checked that all indices
4510 // are disjunct and in bounds.
4511 unsafe { Ok(self.get_many_unchecked_mut(indices)) }
4512 }
4513}
4514
4515impl<T, const N: usize> [[T; N]] {
4516 /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
4517 ///
4518 /// # Panics
4519 ///
4520 /// This panics if the length of the resulting slice would overflow a `usize`.
4521 ///
4522 /// This is only possible when flattening a slice of arrays of zero-sized
4523 /// types, and thus tends to be irrelevant in practice. If
4524 /// `size_of::<T>() > 0`, this will never panic.
4525 ///
4526 /// # Examples
4527 ///
4528 /// ```
4529 /// #![feature(slice_flatten)]
4530 ///
4531 /// assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);
4532 ///
4533 /// assert_eq!(
4534 /// [[1, 2, 3], [4, 5, 6]].flatten(),
4535 /// [[1, 2], [3, 4], [5, 6]].flatten(),
4536 /// );
4537 ///
4538 /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
4539 /// assert!(slice_of_empty_arrays.flatten().is_empty());
4540 ///
4541 /// let empty_slice_of_arrays: &[[u32; 10]] = &[];
4542 /// assert!(empty_slice_of_arrays.flatten().is_empty());
4543 /// ```
4544 #[unstable(feature = "slice_flatten", issue = "95629")]
4545 pub const fn flatten(&self) -> &[T] {
4546 let len = if T::IS_ZST {
4547 self.len().checked_mul(N).expect("slice len overflow")
4548 } else {
4549 // SAFETY: `self.len() * N` cannot overflow because `self` is
4550 // already in the address space.
4551 unsafe { self.len().unchecked_mul(N) }
4552 };
4553 // SAFETY: `[T]` is layout-identical to `[T; N]`
4554 unsafe { from_raw_parts(self.as_ptr().cast(), len) }
4555 }
4556
4557 /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
4558 ///
4559 /// # Panics
4560 ///
4561 /// This panics if the length of the resulting slice would overflow a `usize`.
4562 ///
4563 /// This is only possible when flattening a slice of arrays of zero-sized
4564 /// types, and thus tends to be irrelevant in practice. If
4565 /// `size_of::<T>() > 0`, this will never panic.
4566 ///
4567 /// # Examples
4568 ///
4569 /// ```
4570 /// #![feature(slice_flatten)]
4571 ///
4572 /// fn add_5_to_all(slice: &mut [i32]) {
4573 /// for i in slice {
4574 /// *i += 5;
4575 /// }
4576 /// }
4577 ///
4578 /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
4579 /// add_5_to_all(array.flatten_mut());
4580 /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
4581 /// ```
4582 #[unstable(feature = "slice_flatten", issue = "95629")]
4583 pub fn flatten_mut(&mut self) -> &mut [T] {
4584 let len = if T::IS_ZST {
4585 self.len().checked_mul(N).expect("slice len overflow")
4586 } else {
4587 // SAFETY: `self.len() * N` cannot overflow because `self` is
4588 // already in the address space.
4589 unsafe { self.len().unchecked_mul(N) }
4590 };
4591 // SAFETY: `[T]` is layout-identical to `[T; N]`
4592 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
4593 }
4594}
4595
4596#[cfg(not(test))]
4597impl [f32] {
4598 /// Sorts the slice of floats.
4599 ///
4600 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4601 /// the ordering defined by [`f32::total_cmp`].
4602 ///
4603 /// # Current implementation
4604 ///
4605 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4606 ///
4607 /// # Examples
4608 ///
4609 /// ```
4610 /// #![feature(sort_floats)]
4611 /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
4612 ///
4613 /// v.sort_floats();
4614 /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
4615 /// assert_eq!(&v[..8], &sorted[..8]);
4616 /// assert!(v[8].is_nan());
4617 /// ```
4618 #[unstable(feature = "sort_floats", issue = "93396")]
4619 #[inline]
4620 pub fn sort_floats(&mut self) {
4621 self.sort_unstable_by(f32::total_cmp);
4622 }
4623}
4624
4625#[cfg(not(test))]
4626impl [f64] {
4627 /// Sorts the slice of floats.
4628 ///
4629 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4630 /// the ordering defined by [`f64::total_cmp`].
4631 ///
4632 /// # Current implementation
4633 ///
4634 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4635 ///
4636 /// # Examples
4637 ///
4638 /// ```
4639 /// #![feature(sort_floats)]
4640 /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
4641 ///
4642 /// v.sort_floats();
4643 /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
4644 /// assert_eq!(&v[..8], &sorted[..8]);
4645 /// assert!(v[8].is_nan());
4646 /// ```
4647 #[unstable(feature = "sort_floats", issue = "93396")]
4648 #[inline]
4649 pub fn sort_floats(&mut self) {
4650 self.sort_unstable_by(f64::total_cmp);
4651 }
4652}
4653
4654trait CloneFromSpec<T> {
4655 fn spec_clone_from(&mut self, src: &[T]);
4656}
4657
4658impl<T> CloneFromSpec<T> for [T]
4659where
4660 T: Clone,
4661{
4662 #[track_caller]
4663 default fn spec_clone_from(&mut self, src: &[T]) {
4664 assert!(self.len() == src.len(), "destination and source slices have different lengths");
4665 // NOTE: We need to explicitly slice them to the same length
4666 // to make it easier for the optimizer to elide bounds checking.
4667 // But since it can't be relied on we also have an explicit specialization for T: Copy.
4668 let len: usize = self.len();
4669 let src: &[T] = &src[..len];
4670 for i: usize in 0..len {
4671 self[i].clone_from(&src[i]);
4672 }
4673 }
4674}
4675
4676impl<T> CloneFromSpec<T> for [T]
4677where
4678 T: Copy,
4679{
4680 #[track_caller]
4681 fn spec_clone_from(&mut self, src: &[T]) {
4682 self.copy_from_slice(src);
4683 }
4684}
4685
4686#[stable(feature = "rust1", since = "1.0.0")]
4687impl<T> Default for &[T] {
4688 /// Creates an empty slice.
4689 fn default() -> Self {
4690 &[]
4691 }
4692}
4693
4694#[stable(feature = "mut_slice_default", since = "1.5.0")]
4695impl<T> Default for &mut [T] {
4696 /// Creates a mutable empty slice.
4697 fn default() -> Self {
4698 &mut []
4699 }
4700}
4701
4702#[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4703/// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4704/// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4705/// `str`) to slices, and then this trait will be replaced or abolished.
4706pub trait SlicePattern {
4707 /// The element type of the slice being matched on.
4708 type Item;
4709
4710 /// Currently, the consumers of `SlicePattern` need a slice.
4711 fn as_slice(&self) -> &[Self::Item];
4712}
4713
4714#[stable(feature = "slice_strip", since = "1.51.0")]
4715impl<T> SlicePattern for [T] {
4716 type Item = T;
4717
4718 #[inline]
4719 fn as_slice(&self) -> &[Self::Item] {
4720 self
4721 }
4722}
4723
4724#[stable(feature = "slice_strip", since = "1.51.0")]
4725impl<T, const N: usize> SlicePattern for [T; N] {
4726 type Item = T;
4727
4728 #[inline]
4729 fn as_slice(&self) -> &[Self::Item] {
4730 self
4731 }
4732}
4733
4734/// This checks every index against each other, and against `len`.
4735///
4736/// This will do `binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, ..`
4737/// comparison operations.
4738fn get_many_check_valid<const N: usize>(indices: &[usize; N], len: usize) -> bool {
4739 // NB: The optimizer should inline the loops into a sequence
4740 // of instructions without additional branching.
4741 let mut valid: bool = true;
4742 for (i: usize, &idx: usize) in indices.iter().enumerate() {
4743 valid &= idx < len;
4744 for &idx2: usize in &indices[..i] {
4745 valid &= idx != idx2;
4746 }
4747 }
4748 valid
4749}
4750
4751/// The error type returned by [`get_many_mut<N>`][`slice::get_many_mut`].
4752///
4753/// It indicates one of two possible errors:
4754/// - An index is out-of-bounds.
4755/// - The same index appeared multiple times in the array.
4756///
4757/// # Examples
4758///
4759/// ```
4760/// #![feature(get_many_mut)]
4761///
4762/// let v = &mut [1, 2, 3];
4763/// assert!(v.get_many_mut([0, 999]).is_err());
4764/// assert!(v.get_many_mut([1, 1]).is_err());
4765/// ```
4766#[unstable(feature = "get_many_mut", issue = "104642")]
4767// NB: The N here is there to be forward-compatible with adding more details
4768// to the error type at a later point
4769pub struct GetManyMutError<const N: usize> {
4770 _private: (),
4771}
4772
4773#[unstable(feature = "get_many_mut", issue = "104642")]
4774impl<const N: usize> fmt::Debug for GetManyMutError<N> {
4775 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
4776 f.debug_struct(name:"GetManyMutError").finish_non_exhaustive()
4777 }
4778}
4779
4780#[unstable(feature = "get_many_mut", issue = "104642")]
4781impl<const N: usize> fmt::Display for GetManyMutError<N> {
4782 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
4783 fmt::Display::fmt(self:"an index is out of bounds or appeared multiple times in the array", f)
4784 }
4785}
4786