1//! Utilities for the array primitive type.
2//!
3//! *[See also the array primitive type](array).*
4
5#![stable(feature = "core_array", since = "1.35.0")]
6
7use crate::borrow::{Borrow, BorrowMut};
8use crate::cmp::Ordering;
9use crate::convert::Infallible;
10use crate::error::Error;
11use crate::fmt;
12use crate::hash::{self, Hash};
13use crate::intrinsics::transmute_unchecked;
14use crate::iter::{UncheckedIterator, repeat_n};
15use crate::mem::{self, MaybeUninit};
16use crate::ops::{
17 ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
18};
19use crate::ptr::{null, null_mut};
20use crate::slice::{Iter, IterMut};
21
22mod ascii;
23mod drain;
24mod equality;
25mod iter;
26
27pub(crate) use drain::drain_array_with;
28#[stable(feature = "array_value_iter", since = "1.51.0")]
29pub use iter::IntoIter;
30
31/// Creates an array of type `[T; N]` by repeatedly cloning a value.
32///
33/// This is the same as `[val; N]`, but it also works for types that do not
34/// implement [`Copy`].
35///
36/// The provided value will be used as an element of the resulting array and
37/// will be cloned N - 1 times to fill up the rest. If N is zero, the value
38/// will be dropped.
39///
40/// # Example
41///
42/// Creating multiple copies of a `String`:
43/// ```rust
44/// #![feature(array_repeat)]
45///
46/// use std::array;
47///
48/// let string = "Hello there!".to_string();
49/// let strings = array::repeat(string);
50/// assert_eq!(strings, ["Hello there!", "Hello there!"]);
51/// ```
52#[inline]
53#[unstable(feature = "array_repeat", issue = "126695")]
54pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {
55 from_trusted_iterator(iter:repeat_n(element:val, N))
56}
57
58/// Creates an array where each element is produced by calling `f` with
59/// that element's index while walking forward through the array.
60///
61/// This is essentially the same as writing
62/// ```text
63/// [f(0), f(1), f(2), …, f(N - 2), f(N - 1)]
64/// ```
65/// and is similar to `(0..i).map(f)`, just for arrays not iterators.
66///
67/// If `N == 0`, this produces an empty array without ever calling `f`.
68///
69/// # Example
70///
71/// ```rust
72/// // type inference is helping us here, the way `from_fn` knows how many
73/// // elements to produce is the length of array down there: only arrays of
74/// // equal lengths can be compared, so the const generic parameter `N` is
75/// // inferred to be 5, thus creating array of 5 elements.
76///
77/// let array = core::array::from_fn(|i| i);
78/// // indexes are: 0 1 2 3 4
79/// assert_eq!(array, [0, 1, 2, 3, 4]);
80///
81/// let array2: [usize; 8] = core::array::from_fn(|i| i * 2);
82/// // indexes are: 0 1 2 3 4 5 6 7
83/// assert_eq!(array2, [0, 2, 4, 6, 8, 10, 12, 14]);
84///
85/// let bool_arr = core::array::from_fn::<_, 5, _>(|i| i % 2 == 0);
86/// // indexes are: 0 1 2 3 4
87/// assert_eq!(bool_arr, [true, false, true, false, true]);
88/// ```
89///
90/// You can also capture things, for example to create an array full of clones
91/// where you can't just use `[item; N]` because it's not `Copy`:
92/// ```
93/// # // TBH `array::repeat` would be better for this, but it's not stable yet.
94/// let my_string = String::from("Hello");
95/// let clones: [String; 42] = std::array::from_fn(|_| my_string.clone());
96/// assert!(clones.iter().all(|x| *x == my_string));
97/// ```
98///
99/// The array is generated in ascending index order, starting from the front
100/// and going towards the back, so you can use closures with mutable state:
101/// ```
102/// let mut state = 1;
103/// let a = std::array::from_fn(|_| { let x = state; state *= 2; x });
104/// assert_eq!(a, [1, 2, 4, 8, 16, 32]);
105/// ```
106#[inline]
107#[stable(feature = "array_from_fn", since = "1.63.0")]
108pub fn from_fn<T, const N: usize, F>(f: F) -> [T; N]
109where
110 F: FnMut(usize) -> T,
111{
112 try_from_fn(cb:NeverShortCircuit::wrap_mut_1(f)).0
113}
114
115/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
116/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error
117/// if any element creation was unsuccessful.
118///
119/// The return type of this function depends on the return type of the closure.
120/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
121/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
122///
123/// # Arguments
124///
125/// * `cb`: Callback where the passed argument is the current array index.
126///
127/// # Example
128///
129/// ```rust
130/// #![feature(array_try_from_fn)]
131///
132/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
133/// assert_eq!(array, Ok([0, 1, 2, 3, 4]));
134///
135/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
136/// assert!(array.is_err());
137///
138/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
139/// assert_eq!(array, Some([100, 101, 102, 103]));
140///
141/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
142/// assert_eq!(array, None);
143/// ```
144#[inline]
145#[unstable(feature = "array_try_from_fn", issue = "89379")]
146pub fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]>
147where
148 F: FnMut(usize) -> R,
149 R: Try,
150 R::Residual: Residual<[R::Output; N]>,
151{
152 let mut array: [MaybeUninit>; N] = [const { MaybeUninit::uninit() }; N];
153 match try_from_fn_erased(&mut array, generator:cb) {
154 ControlFlow::Break(r: impl Residual<[impl Residual<…>; N]>) => FromResidual::from_residual(r),
155 ControlFlow::Continue(()) => {
156 // SAFETY: All elements of the array were populated.
157 try { unsafe { MaybeUninit::array_assume_init(array) } }
158 }
159 }
160}
161
162/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
163#[stable(feature = "array_from_ref", since = "1.53.0")]
164#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
165pub const fn from_ref<T>(s: &T) -> &[T; 1] {
166 // SAFETY: Converting `&T` to `&[T; 1]` is sound.
167 unsafe { &*(s as *const T).cast::<[T; 1]>() }
168}
169
170/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
171#[stable(feature = "array_from_ref", since = "1.53.0")]
172#[rustc_const_stable(feature = "const_array_from_ref", since = "1.83.0")]
173pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
174 // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
175 unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
176}
177
178/// The error type returned when a conversion from a slice to an array fails.
179#[stable(feature = "try_from", since = "1.34.0")]
180#[derive(Debug, Copy, Clone)]
181pub struct TryFromSliceError(());
182
183#[stable(feature = "core_array", since = "1.35.0")]
184impl fmt::Display for TryFromSliceError {
185 #[inline]
186 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
187 #[allow(deprecated)]
188 self.description().fmt(f)
189 }
190}
191
192#[stable(feature = "try_from", since = "1.34.0")]
193impl Error for TryFromSliceError {
194 #[allow(deprecated)]
195 fn description(&self) -> &str {
196 "could not convert slice to array"
197 }
198}
199
200#[stable(feature = "try_from_slice_error", since = "1.36.0")]
201impl From<Infallible> for TryFromSliceError {
202 fn from(x: Infallible) -> TryFromSliceError {
203 match x {}
204 }
205}
206
207#[stable(feature = "rust1", since = "1.0.0")]
208impl<T, const N: usize> AsRef<[T]> for [T; N] {
209 #[inline]
210 fn as_ref(&self) -> &[T] {
211 &self[..]
212 }
213}
214
215#[stable(feature = "rust1", since = "1.0.0")]
216impl<T, const N: usize> AsMut<[T]> for [T; N] {
217 #[inline]
218 fn as_mut(&mut self) -> &mut [T] {
219 &mut self[..]
220 }
221}
222
223#[stable(feature = "array_borrow", since = "1.4.0")]
224impl<T, const N: usize> Borrow<[T]> for [T; N] {
225 fn borrow(&self) -> &[T] {
226 self
227 }
228}
229
230#[stable(feature = "array_borrow", since = "1.4.0")]
231impl<T, const N: usize> BorrowMut<[T]> for [T; N] {
232 fn borrow_mut(&mut self) -> &mut [T] {
233 self
234 }
235}
236
237/// Tries to create an array `[T; N]` by copying from a slice `&[T]`.
238/// Succeeds if `slice.len() == N`.
239///
240/// ```
241/// let bytes: [u8; 3] = [1, 0, 2];
242///
243/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
244/// assert_eq!(1, u16::from_le_bytes(bytes_head));
245///
246/// let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
247/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
248/// ```
249#[stable(feature = "try_from", since = "1.34.0")]
250impl<T, const N: usize> TryFrom<&[T]> for [T; N]
251where
252 T: Copy,
253{
254 type Error = TryFromSliceError;
255
256 #[inline]
257 fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
258 <&Self>::try_from(slice).copied()
259 }
260}
261
262/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
263/// Succeeds if `slice.len() == N`.
264///
265/// ```
266/// let mut bytes: [u8; 3] = [1, 0, 2];
267///
268/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
269/// assert_eq!(1, u16::from_le_bytes(bytes_head));
270///
271/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
272/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
273/// ```
274#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
275impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]
276where
277 T: Copy,
278{
279 type Error = TryFromSliceError;
280
281 #[inline]
282 fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
283 <Self>::try_from(&*slice)
284 }
285}
286
287/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
288/// `slice.len() == N`.
289///
290/// ```
291/// let bytes: [u8; 3] = [1, 0, 2];
292///
293/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
294/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
295///
296/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
297/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
298/// ```
299#[stable(feature = "try_from", since = "1.34.0")]
300impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
301 type Error = TryFromSliceError;
302
303 #[inline]
304 fn try_from(slice: &'a [T]) -> Result<&'a [T; N], TryFromSliceError> {
305 slice.as_array().ok_or(err:TryFromSliceError(()))
306 }
307}
308
309/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
310/// `&mut [T]`. Succeeds if `slice.len() == N`.
311///
312/// ```
313/// let mut bytes: [u8; 3] = [1, 0, 2];
314///
315/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
316/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
317///
318/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
319/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
320/// ```
321#[stable(feature = "try_from", since = "1.34.0")]
322impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] {
323 type Error = TryFromSliceError;
324
325 #[inline]
326 fn try_from(slice: &'a mut [T]) -> Result<&'a mut [T; N], TryFromSliceError> {
327 slice.as_mut_array().ok_or(err:TryFromSliceError(()))
328 }
329}
330
331/// The hash of an array is the same as that of the corresponding slice,
332/// as required by the `Borrow` implementation.
333///
334/// ```
335/// use std::hash::BuildHasher;
336///
337/// let b = std::hash::RandomState::new();
338/// let a: [u8; 3] = [0xa8, 0x3c, 0x09];
339/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
340/// assert_eq!(b.hash_one(a), b.hash_one(s));
341/// ```
342#[stable(feature = "rust1", since = "1.0.0")]
343impl<T: Hash, const N: usize> Hash for [T; N] {
344 fn hash<H: hash::Hasher>(&self, state: &mut H) {
345 Hash::hash(&self[..], state)
346 }
347}
348
349#[stable(feature = "rust1", since = "1.0.0")]
350impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] {
351 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
352 fmt::Debug::fmt(&&self[..], f)
353 }
354}
355
356#[stable(feature = "rust1", since = "1.0.0")]
357impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
358 type Item = &'a T;
359 type IntoIter = Iter<'a, T>;
360
361 fn into_iter(self) -> Iter<'a, T> {
362 self.iter()
363 }
364}
365
366#[stable(feature = "rust1", since = "1.0.0")]
367impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
368 type Item = &'a mut T;
369 type IntoIter = IterMut<'a, T>;
370
371 fn into_iter(self) -> IterMut<'a, T> {
372 self.iter_mut()
373 }
374}
375
376#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
377impl<T, I, const N: usize> Index<I> for [T; N]
378where
379 [T]: Index<I>,
380{
381 type Output = <[T] as Index<I>>::Output;
382
383 #[inline]
384 fn index(&self, index: I) -> &Self::Output {
385 Index::index(self as &[T], index)
386 }
387}
388
389#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
390impl<T, I, const N: usize> IndexMut<I> for [T; N]
391where
392 [T]: IndexMut<I>,
393{
394 #[inline]
395 fn index_mut(&mut self, index: I) -> &mut Self::Output {
396 IndexMut::index_mut(self as &mut [T], index)
397 }
398}
399
400/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
401#[stable(feature = "rust1", since = "1.0.0")]
402impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] {
403 #[inline]
404 fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> {
405 PartialOrd::partial_cmp(&&self[..], &&other[..])
406 }
407 #[inline]
408 fn lt(&self, other: &[T; N]) -> bool {
409 PartialOrd::lt(&&self[..], &&other[..])
410 }
411 #[inline]
412 fn le(&self, other: &[T; N]) -> bool {
413 PartialOrd::le(&&self[..], &&other[..])
414 }
415 #[inline]
416 fn ge(&self, other: &[T; N]) -> bool {
417 PartialOrd::ge(&&self[..], &&other[..])
418 }
419 #[inline]
420 fn gt(&self, other: &[T; N]) -> bool {
421 PartialOrd::gt(&&self[..], &&other[..])
422 }
423}
424
425/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
426#[stable(feature = "rust1", since = "1.0.0")]
427impl<T: Ord, const N: usize> Ord for [T; N] {
428 #[inline]
429 fn cmp(&self, other: &[T; N]) -> Ordering {
430 Ord::cmp(&&self[..], &&other[..])
431 }
432}
433
434#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
435impl<T: Copy, const N: usize> Copy for [T; N] {}
436
437#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
438impl<T: Clone, const N: usize> Clone for [T; N] {
439 #[inline]
440 fn clone(&self) -> Self {
441 SpecArrayClone::clone(self)
442 }
443
444 #[inline]
445 fn clone_from(&mut self, other: &Self) {
446 self.clone_from_slice(src:other);
447 }
448}
449
450trait SpecArrayClone: Clone {
451 fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
452}
453
454impl<T: Clone> SpecArrayClone for T {
455 #[inline]
456 default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
457 from_trusted_iterator(iter:array.iter().cloned())
458 }
459}
460
461impl<T: Copy> SpecArrayClone for T {
462 #[inline]
463 fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
464 *array
465 }
466}
467
468// The Default impls cannot be done with const generics because `[T; 0]` doesn't
469// require Default to be implemented, and having different impl blocks for
470// different numbers isn't supported yet.
471
472macro_rules! array_impl_default {
473 {$n:expr, $t:ident $($ts:ident)*} => {
474 #[stable(since = "1.4.0", feature = "array_default")]
475 impl<T> Default for [T; $n] where T: Default {
476 fn default() -> [T; $n] {
477 [$t::default(), $($ts::default()),*]
478 }
479 }
480 array_impl_default!{($n - 1), $($ts)*}
481 };
482 {$n:expr,} => {
483 #[stable(since = "1.4.0", feature = "array_default")]
484 impl<T> Default for [T; $n] {
485 fn default() -> [T; $n] { [] }
486 }
487 };
488}
489
490array_impl_default! {32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T}
491
492impl<T, const N: usize> [T; N] {
493 /// Returns an array of the same size as `self`, with function `f` applied to each element
494 /// in order.
495 ///
496 /// If you don't necessarily need a new fixed-size array, consider using
497 /// [`Iterator::map`] instead.
498 ///
499 ///
500 /// # Note on performance and stack usage
501 ///
502 /// Unfortunately, usages of this method are currently not always optimized
503 /// as well as they could be. This mainly concerns large arrays, as mapping
504 /// over small arrays seem to be optimized just fine. Also note that in
505 /// debug mode (i.e. without any optimizations), this method can use a lot
506 /// of stack space (a few times the size of the array or more).
507 ///
508 /// Therefore, in performance-critical code, try to avoid using this method
509 /// on large arrays or check the emitted code. Also try to avoid chained
510 /// maps (e.g. `arr.map(...).map(...)`).
511 ///
512 /// In many cases, you can instead use [`Iterator::map`] by calling `.iter()`
513 /// or `.into_iter()` on your array. `[T; N]::map` is only necessary if you
514 /// really need a new array of the same size as the result. Rust's lazy
515 /// iterators tend to get optimized very well.
516 ///
517 ///
518 /// # Examples
519 ///
520 /// ```
521 /// let x = [1, 2, 3];
522 /// let y = x.map(|v| v + 1);
523 /// assert_eq!(y, [2, 3, 4]);
524 ///
525 /// let x = [1, 2, 3];
526 /// let mut temp = 0;
527 /// let y = x.map(|v| { temp += 1; v * temp });
528 /// assert_eq!(y, [1, 4, 9]);
529 ///
530 /// let x = ["Ferris", "Bueller's", "Day", "Off"];
531 /// let y = x.map(|v| v.len());
532 /// assert_eq!(y, [6, 9, 3, 3]);
533 /// ```
534 #[must_use]
535 #[stable(feature = "array_map", since = "1.55.0")]
536 pub fn map<F, U>(self, f: F) -> [U; N]
537 where
538 F: FnMut(T) -> U,
539 {
540 self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
541 }
542
543 /// A fallible function `f` applied to each element on array `self` in order to
544 /// return an array the same size as `self` or the first error encountered.
545 ///
546 /// The return type of this function depends on the return type of the closure.
547 /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
548 /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
549 ///
550 /// # Examples
551 ///
552 /// ```
553 /// #![feature(array_try_map)]
554 ///
555 /// let a = ["1", "2", "3"];
556 /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
557 /// assert_eq!(b, [2, 3, 4]);
558 ///
559 /// let a = ["1", "2a", "3"];
560 /// let b = a.try_map(|v| v.parse::<u32>());
561 /// assert!(b.is_err());
562 ///
563 /// use std::num::NonZero;
564 ///
565 /// let z = [1, 2, 0, 3, 4];
566 /// assert_eq!(z.try_map(NonZero::new), None);
567 ///
568 /// let a = [1, 2, 3];
569 /// let b = a.try_map(NonZero::new);
570 /// let c = b.map(|x| x.map(NonZero::get));
571 /// assert_eq!(c, Some(a));
572 /// ```
573 #[unstable(feature = "array_try_map", issue = "79711")]
574 pub fn try_map<R>(self, f: impl FnMut(T) -> R) -> ChangeOutputType<R, [R::Output; N]>
575 where
576 R: Try<Residual: Residual<[R::Output; N]>>,
577 {
578 drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f)))
579 }
580
581 /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
582 #[stable(feature = "array_as_slice", since = "1.57.0")]
583 #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
584 pub const fn as_slice(&self) -> &[T] {
585 self
586 }
587
588 /// Returns a mutable slice containing the entire array. Equivalent to
589 /// `&mut s[..]`.
590 #[stable(feature = "array_as_slice", since = "1.57.0")]
591 #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "CURRENT_RUSTC_VERSION")]
592 pub const fn as_mut_slice(&mut self) -> &mut [T] {
593 self
594 }
595
596 /// Borrows each element and returns an array of references with the same
597 /// size as `self`.
598 ///
599 ///
600 /// # Example
601 ///
602 /// ```
603 /// let floats = [3.1, 2.7, -1.0];
604 /// let float_refs: [&f64; 3] = floats.each_ref();
605 /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
606 /// ```
607 ///
608 /// This method is particularly useful if combined with other methods, like
609 /// [`map`](#method.map). This way, you can avoid moving the original
610 /// array if its elements are not [`Copy`].
611 ///
612 /// ```
613 /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
614 /// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
615 /// assert_eq!(is_ascii, [true, false, true]);
616 ///
617 /// // We can still access the original array: it has not been moved.
618 /// assert_eq!(strings.len(), 3);
619 /// ```
620 #[stable(feature = "array_methods", since = "1.77.0")]
621 #[rustc_const_unstable(feature = "const_array_each_ref", issue = "133289")]
622 pub const fn each_ref(&self) -> [&T; N] {
623 let mut buf = [null::<T>(); N];
624
625 // FIXME(const-hack): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.
626 let mut i = 0;
627 while i < N {
628 buf[i] = &raw const self[i];
629
630 i += 1;
631 }
632
633 // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.
634 unsafe { transmute_unchecked(buf) }
635 }
636
637 /// Borrows each element mutably and returns an array of mutable references
638 /// with the same size as `self`.
639 ///
640 ///
641 /// # Example
642 ///
643 /// ```
644 ///
645 /// let mut floats = [3.1, 2.7, -1.0];
646 /// let float_refs: [&mut f64; 3] = floats.each_mut();
647 /// *float_refs[0] = 0.0;
648 /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
649 /// assert_eq!(floats, [0.0, 2.7, -1.0]);
650 /// ```
651 #[stable(feature = "array_methods", since = "1.77.0")]
652 #[rustc_const_unstable(feature = "const_array_each_ref", issue = "133289")]
653 pub const fn each_mut(&mut self) -> [&mut T; N] {
654 let mut buf = [null_mut::<T>(); N];
655
656 // FIXME(const-hack): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.
657 let mut i = 0;
658 while i < N {
659 buf[i] = &raw mut self[i];
660
661 i += 1;
662 }
663
664 // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.
665 unsafe { transmute_unchecked(buf) }
666 }
667
668 /// Divides one array reference into two at an index.
669 ///
670 /// The first will contain all indices from `[0, M)` (excluding
671 /// the index `M` itself) and the second will contain all
672 /// indices from `[M, N)` (excluding the index `N` itself).
673 ///
674 /// # Panics
675 ///
676 /// Panics if `M > N`.
677 ///
678 /// # Examples
679 ///
680 /// ```
681 /// #![feature(split_array)]
682 ///
683 /// let v = [1, 2, 3, 4, 5, 6];
684 ///
685 /// {
686 /// let (left, right) = v.split_array_ref::<0>();
687 /// assert_eq!(left, &[]);
688 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
689 /// }
690 ///
691 /// {
692 /// let (left, right) = v.split_array_ref::<2>();
693 /// assert_eq!(left, &[1, 2]);
694 /// assert_eq!(right, &[3, 4, 5, 6]);
695 /// }
696 ///
697 /// {
698 /// let (left, right) = v.split_array_ref::<6>();
699 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
700 /// assert_eq!(right, &[]);
701 /// }
702 /// ```
703 #[unstable(
704 feature = "split_array",
705 reason = "return type should have array as 2nd element",
706 issue = "90091"
707 )]
708 #[inline]
709 pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
710 (&self[..]).split_first_chunk::<M>().unwrap()
711 }
712
713 /// Divides one mutable array reference into two at an index.
714 ///
715 /// The first will contain all indices from `[0, M)` (excluding
716 /// the index `M` itself) and the second will contain all
717 /// indices from `[M, N)` (excluding the index `N` itself).
718 ///
719 /// # Panics
720 ///
721 /// Panics if `M > N`.
722 ///
723 /// # Examples
724 ///
725 /// ```
726 /// #![feature(split_array)]
727 ///
728 /// let mut v = [1, 0, 3, 0, 5, 6];
729 /// let (left, right) = v.split_array_mut::<2>();
730 /// assert_eq!(left, &mut [1, 0][..]);
731 /// assert_eq!(right, &mut [3, 0, 5, 6]);
732 /// left[1] = 2;
733 /// right[1] = 4;
734 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
735 /// ```
736 #[unstable(
737 feature = "split_array",
738 reason = "return type should have array as 2nd element",
739 issue = "90091"
740 )]
741 #[inline]
742 pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
743 (&mut self[..]).split_first_chunk_mut::<M>().unwrap()
744 }
745
746 /// Divides one array reference into two at an index from the end.
747 ///
748 /// The first will contain all indices from `[0, N - M)` (excluding
749 /// the index `N - M` itself) and the second will contain all
750 /// indices from `[N - M, N)` (excluding the index `N` itself).
751 ///
752 /// # Panics
753 ///
754 /// Panics if `M > N`.
755 ///
756 /// # Examples
757 ///
758 /// ```
759 /// #![feature(split_array)]
760 ///
761 /// let v = [1, 2, 3, 4, 5, 6];
762 ///
763 /// {
764 /// let (left, right) = v.rsplit_array_ref::<0>();
765 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
766 /// assert_eq!(right, &[]);
767 /// }
768 ///
769 /// {
770 /// let (left, right) = v.rsplit_array_ref::<2>();
771 /// assert_eq!(left, &[1, 2, 3, 4]);
772 /// assert_eq!(right, &[5, 6]);
773 /// }
774 ///
775 /// {
776 /// let (left, right) = v.rsplit_array_ref::<6>();
777 /// assert_eq!(left, &[]);
778 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
779 /// }
780 /// ```
781 #[unstable(
782 feature = "split_array",
783 reason = "return type should have array as 2nd element",
784 issue = "90091"
785 )]
786 #[inline]
787 pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
788 (&self[..]).split_last_chunk::<M>().unwrap()
789 }
790
791 /// Divides one mutable array reference into two at an index from the end.
792 ///
793 /// The first will contain all indices from `[0, N - M)` (excluding
794 /// the index `N - M` itself) and the second will contain all
795 /// indices from `[N - M, N)` (excluding the index `N` itself).
796 ///
797 /// # Panics
798 ///
799 /// Panics if `M > N`.
800 ///
801 /// # Examples
802 ///
803 /// ```
804 /// #![feature(split_array)]
805 ///
806 /// let mut v = [1, 0, 3, 0, 5, 6];
807 /// let (left, right) = v.rsplit_array_mut::<4>();
808 /// assert_eq!(left, &mut [1, 0]);
809 /// assert_eq!(right, &mut [3, 0, 5, 6][..]);
810 /// left[1] = 2;
811 /// right[1] = 4;
812 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
813 /// ```
814 #[unstable(
815 feature = "split_array",
816 reason = "return type should have array as 2nd element",
817 issue = "90091"
818 )]
819 #[inline]
820 pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
821 (&mut self[..]).split_last_chunk_mut::<M>().unwrap()
822 }
823}
824
825/// Populate an array from the first `N` elements of `iter`
826///
827/// # Panics
828///
829/// If the iterator doesn't actually have enough items.
830///
831/// By depending on `TrustedLen`, however, we can do that check up-front (where
832/// it easily optimizes away) so it doesn't impact the loop that fills the array.
833#[inline]
834fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
835 try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
836}
837
838#[inline]
839fn try_from_trusted_iterator<T, R, const N: usize>(
840 iter: impl UncheckedIterator<Item = R>,
841) -> ChangeOutputType<R, [T; N]>
842where
843 R: Try<Output = T>,
844 R::Residual: Residual<[T; N]>,
845{
846 assert!(iter.size_hint().0 >= N);
847 fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
848 move |_| {
849 // SAFETY: We know that `from_fn` will call this at most N times,
850 // and we checked to ensure that we have at least that many items.
851 unsafe { iter.next_unchecked() }
852 }
853 }
854
855 try_from_fn(cb:next(iter))
856}
857
858/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
859/// needing to monomorphize for every array length.
860///
861/// This takes a generator rather than an iterator so that *at the type level*
862/// it never needs to worry about running out of items. When combined with
863/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
864/// it to optimize well.
865///
866/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
867/// function that does the union of both things, but last time it was that way
868/// it resulted in poor codegen from the "are there enough source items?" checks
869/// not optimizing away. So if you give it a shot, make sure to watch what
870/// happens in the codegen tests.
871#[inline]
872fn try_from_fn_erased<T, R>(
873 buffer: &mut [MaybeUninit<T>],
874 mut generator: impl FnMut(usize) -> R,
875) -> ControlFlow<R::Residual>
876where
877 R: Try<Output = T>,
878{
879 let mut guard: Guard<'_, T> = Guard { array_mut: buffer, initialized: 0 };
880
881 while guard.initialized < guard.array_mut.len() {
882 let item: T = generator(guard.initialized).branch()?;
883
884 // SAFETY: The loop condition ensures we have space to push the item
885 unsafe { guard.push_unchecked(item) };
886 }
887
888 mem::forget(guard);
889 ControlFlow::Continue(())
890}
891
892/// Panic guard for incremental initialization of arrays.
893///
894/// Disarm the guard with `mem::forget` once the array has been initialized.
895///
896/// # Safety
897///
898/// All write accesses to this structure are unsafe and must maintain a correct
899/// count of `initialized` elements.
900///
901/// To minimize indirection fields are still pub but callers should at least use
902/// `push_unchecked` to signal that something unsafe is going on.
903struct Guard<'a, T> {
904 /// The array to be initialized.
905 pub array_mut: &'a mut [MaybeUninit<T>],
906 /// The number of items that have been initialized so far.
907 pub initialized: usize,
908}
909
910impl<T> Guard<'_, T> {
911 /// Adds an item to the array and updates the initialized item counter.
912 ///
913 /// # Safety
914 ///
915 /// No more than N elements must be initialized.
916 #[inline]
917 pub(crate) unsafe fn push_unchecked(&mut self, item: T) {
918 // SAFETY: If `initialized` was correct before and the caller does not
919 // invoke this method more than N times then writes will be in-bounds
920 // and slots will not be initialized more than once.
921 unsafe {
922 self.array_mut.get_unchecked_mut(self.initialized).write(val:item);
923 self.initialized = self.initialized.unchecked_add(1);
924 }
925 }
926}
927
928impl<T> Drop for Guard<'_, T> {
929 #[inline]
930 fn drop(&mut self) {
931 debug_assert!(self.initialized <= self.array_mut.len());
932
933 // SAFETY: this slice will contain only initialized objects.
934 unsafe {
935 self.array_mut.get_unchecked_mut(..self.initialized).assume_init_drop();
936 }
937 }
938}
939
940/// Pulls `N` items from `iter` and returns them as an array. If the iterator
941/// yields fewer than `N` items, `Err` is returned containing an iterator over
942/// the already yielded items.
943///
944/// Since the iterator is passed as a mutable reference and this function calls
945/// `next` at most `N` times, the iterator can still be used afterwards to
946/// retrieve the remaining items.
947///
948/// If `iter.next()` panicks, all items already yielded by the iterator are
949/// dropped.
950///
951/// Used for [`Iterator::next_chunk`].
952#[inline]
953pub(crate) fn iter_next_chunk<T, const N: usize>(
954 iter: &mut impl Iterator<Item = T>,
955) -> Result<[T; N], IntoIter<T, N>> {
956 let mut array: [MaybeUninit; N] = [const { MaybeUninit::uninit() }; N];
957 let r: Result<(), usize> = iter_next_chunk_erased(&mut array, iter);
958 match r {
959 Ok(()) => {
960 // SAFETY: All elements of `array` were populated.
961 Ok(unsafe { MaybeUninit::array_assume_init(array) })
962 }
963 Err(initialized: usize) => {
964 // SAFETY: Only the first `initialized` elements were populated
965 Err(unsafe { IntoIter::new_unchecked(buffer:array, initialized:0..initialized) })
966 }
967 }
968}
969
970/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
971/// needing to monomorphize for every array length.
972///
973/// Unfortunately this loop has two exit conditions, the buffer filling up
974/// or the iterator running out of items, making it tend to optimize poorly.
975#[inline]
976fn iter_next_chunk_erased<T>(
977 buffer: &mut [MaybeUninit<T>],
978 iter: &mut impl Iterator<Item = T>,
979) -> Result<(), usize> {
980 let mut guard: Guard<'_, T> = Guard { array_mut: buffer, initialized: 0 };
981 while guard.initialized < guard.array_mut.len() {
982 let Some(item: T) = iter.next() else {
983 // Unlike `try_from_fn_erased`, we want to keep the partial results,
984 // so we need to defuse the guard instead of using `?`.
985 let initialized: usize = guard.initialized;
986 mem::forget(guard);
987 return Err(initialized);
988 };
989
990 // SAFETY: The loop condition ensures we have space to push the item
991 unsafe { guard.push_unchecked(item) };
992 }
993
994 mem::forget(guard);
995 Ok(())
996}
997