core/array/mod.rs
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::clone::TrivialClone;
9use crate::cmp::Ordering;
10use crate::convert::Infallible;
11use crate::error::Error;
12use crate::hash::{self, Hash};
13use crate::intrinsics::transmute_unchecked;
14use crate::iter::{UncheckedIterator, repeat_n};
15use crate::marker::Destruct;
16use crate::mem::{self, ManuallyDrop, MaybeUninit};
17use crate::ops::{
18 ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
19};
20use crate::ptr::{null, null_mut};
21use crate::slice::{Iter, IterMut};
22use crate::{fmt, ptr};
23
24mod ascii;
25mod drain;
26mod equality;
27mod iter;
28
29#[stable(feature = "array_value_iter", since = "1.51.0")]
30pub use iter::IntoIter;
31
32/// Creates an array of type `[T; N]` by repeatedly cloning a value.
33///
34/// This is the same as `[val; N]`, but it also works for types that do not
35/// implement [`Copy`].
36///
37/// The provided value will be used as an element of the resulting array and
38/// will be cloned N - 1 times to fill up the rest. If N is zero, the value
39/// will be dropped.
40///
41/// # Example
42///
43/// Creating multiple copies of a `String`:
44/// ```rust
45/// use std::array;
46///
47/// let string = "Hello there!".to_string();
48/// let strings = array::repeat(string);
49/// assert_eq!(strings, ["Hello there!", "Hello there!"]);
50/// ```
51#[inline]
52#[must_use = "cloning is often expensive and is not expected to have side effects"]
53#[stable(feature = "array_repeat", since = "1.91.0")]
54pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {
55 from_trusted_iterator(repeat_n(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")]
108#[rustc_const_unstable(feature = "const_array", issue = "147606")]
109pub const fn from_fn<T: [const] Destruct, const N: usize, F>(f: F) -> [T; N]
110where
111 F: [const] FnMut(usize) -> T + [const] Destruct,
112{
113 try_from_fn(NeverShortCircuit::wrap_mut_1(f)).0
114}
115
116/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
117/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error
118/// if any element creation was unsuccessful.
119///
120/// The return type of this function depends on the return type of the closure.
121/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
122/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
123///
124/// # Arguments
125///
126/// * `cb`: Callback where the passed argument is the current array index.
127///
128/// # Example
129///
130/// ```rust
131/// #![feature(array_try_from_fn)]
132///
133/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
134/// assert_eq!(array, Ok([0, 1, 2, 3, 4]));
135///
136/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
137/// assert!(array.is_err());
138///
139/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
140/// assert_eq!(array, Some([100, 101, 102, 103]));
141///
142/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
143/// assert_eq!(array, None);
144/// ```
145#[inline]
146#[unstable(feature = "array_try_from_fn", issue = "89379")]
147#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
148pub const fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]>
149where
150 R: [const] Try<Residual: [const] Residual<[R::Output; N]>, Output: [const] Destruct>,
151 F: [const] FnMut(usize) -> R + [const] Destruct,
152{
153 let mut array = [const { MaybeUninit::uninit() }; N];
154 match try_from_fn_erased(&mut array, cb) {
155 ControlFlow::Break(r) => FromResidual::from_residual(r),
156 ControlFlow::Continue(()) => {
157 // SAFETY: All elements of the array were populated.
158 try { unsafe { MaybeUninit::array_assume_init(array) } }
159 }
160 }
161}
162
163/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
164#[stable(feature = "array_from_ref", since = "1.53.0")]
165#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
166pub const fn from_ref<T>(s: &T) -> &[T; 1] {
167 // SAFETY: Converting `&T` to `&[T; 1]` is sound.
168 unsafe { &*(s as *const T).cast::<[T; 1]>() }
169}
170
171/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
172#[stable(feature = "array_from_ref", since = "1.53.0")]
173#[rustc_const_stable(feature = "const_array_from_ref", since = "1.83.0")]
174pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
175 // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
176 unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
177}
178
179/// The error type returned when a conversion from a slice to an array fails.
180#[stable(feature = "try_from", since = "1.34.0")]
181#[derive(Debug, Copy, Clone)]
182pub struct TryFromSliceError(());
183
184#[stable(feature = "core_array", since = "1.35.0")]
185impl fmt::Display for TryFromSliceError {
186 #[inline]
187 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
188 "could not convert slice to array".fmt(f)
189 }
190}
191
192#[stable(feature = "try_from", since = "1.34.0")]
193impl Error for TryFromSliceError {}
194
195#[stable(feature = "try_from_slice_error", since = "1.36.0")]
196#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
197impl const From<Infallible> for TryFromSliceError {
198 fn from(x: Infallible) -> TryFromSliceError {
199 match x {}
200 }
201}
202
203#[stable(feature = "rust1", since = "1.0.0")]
204#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
205impl<T, const N: usize> const AsRef<[T]> for [T; N] {
206 #[inline]
207 fn as_ref(&self) -> &[T] {
208 &self[..]
209 }
210}
211
212#[stable(feature = "rust1", since = "1.0.0")]
213#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
214impl<T, const N: usize> const AsMut<[T]> for [T; N] {
215 #[inline]
216 fn as_mut(&mut self) -> &mut [T] {
217 &mut self[..]
218 }
219}
220
221#[stable(feature = "array_borrow", since = "1.4.0")]
222#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
223impl<T, const N: usize> const Borrow<[T]> for [T; N] {
224 fn borrow(&self) -> &[T] {
225 self
226 }
227}
228
229#[stable(feature = "array_borrow", since = "1.4.0")]
230#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
231impl<T, const N: usize> const 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")]
250#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
251impl<T, const N: usize> const TryFrom<&[T]> for [T; N]
252where
253 T: Copy,
254{
255 type Error = TryFromSliceError;
256
257 #[inline]
258 fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
259 <&Self>::try_from(slice).copied()
260 }
261}
262
263/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
264/// Succeeds if `slice.len() == N`.
265///
266/// ```
267/// let mut bytes: [u8; 3] = [1, 0, 2];
268///
269/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
270/// assert_eq!(1, u16::from_le_bytes(bytes_head));
271///
272/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
273/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
274/// ```
275#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
276#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
277impl<T, const N: usize> const TryFrom<&mut [T]> for [T; N]
278where
279 T: Copy,
280{
281 type Error = TryFromSliceError;
282
283 #[inline]
284 fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
285 <Self>::try_from(&*slice)
286 }
287}
288
289/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
290/// `slice.len() == N`.
291///
292/// ```
293/// let bytes: [u8; 3] = [1, 0, 2];
294///
295/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
296/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
297///
298/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
299/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
300/// ```
301#[stable(feature = "try_from", since = "1.34.0")]
302#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
303impl<'a, T, const N: usize> const TryFrom<&'a [T]> for &'a [T; N] {
304 type Error = TryFromSliceError;
305
306 #[inline]
307 fn try_from(slice: &'a [T]) -> Result<&'a [T; N], TryFromSliceError> {
308 slice.as_array().ok_or(TryFromSliceError(()))
309 }
310}
311
312/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
313/// `&mut [T]`. Succeeds if `slice.len() == N`.
314///
315/// ```
316/// let mut bytes: [u8; 3] = [1, 0, 2];
317///
318/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
319/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
320///
321/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
322/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
323/// ```
324#[stable(feature = "try_from", since = "1.34.0")]
325#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
326impl<'a, T, const N: usize> const TryFrom<&'a mut [T]> for &'a mut [T; N] {
327 type Error = TryFromSliceError;
328
329 #[inline]
330 fn try_from(slice: &'a mut [T]) -> Result<&'a mut [T; N], TryFromSliceError> {
331 slice.as_mut_array().ok_or(TryFromSliceError(()))
332 }
333}
334
335/// The hash of an array is the same as that of the corresponding slice,
336/// as required by the `Borrow` implementation.
337///
338/// ```
339/// use std::hash::BuildHasher;
340///
341/// let b = std::hash::RandomState::new();
342/// let a: [u8; 3] = [0xa8, 0x3c, 0x09];
343/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
344/// assert_eq!(b.hash_one(a), b.hash_one(s));
345/// ```
346#[stable(feature = "rust1", since = "1.0.0")]
347impl<T: Hash, const N: usize> Hash for [T; N] {
348 fn hash<H: hash::Hasher>(&self, state: &mut H) {
349 Hash::hash(&self[..], state)
350 }
351}
352
353#[stable(feature = "rust1", since = "1.0.0")]
354impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] {
355 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
356 fmt::Debug::fmt(&&self[..], f)
357 }
358}
359
360#[stable(feature = "rust1", since = "1.0.0")]
361impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
362 type Item = &'a T;
363 type IntoIter = Iter<'a, T>;
364
365 fn into_iter(self) -> Iter<'a, T> {
366 self.iter()
367 }
368}
369
370#[stable(feature = "rust1", since = "1.0.0")]
371impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
372 type Item = &'a mut T;
373 type IntoIter = IterMut<'a, T>;
374
375 fn into_iter(self) -> IterMut<'a, T> {
376 self.iter_mut()
377 }
378}
379
380#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
381#[rustc_const_unstable(feature = "const_index", issue = "143775")]
382impl<T, I, const N: usize> const Index<I> for [T; N]
383where
384 [T]: [const] Index<I>,
385{
386 type Output = <[T] as Index<I>>::Output;
387
388 #[inline]
389 fn index(&self, index: I) -> &Self::Output {
390 Index::index(self as &[T], index)
391 }
392}
393
394#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
395#[rustc_const_unstable(feature = "const_index", issue = "143775")]
396impl<T, I, const N: usize> const IndexMut<I> for [T; N]
397where
398 [T]: [const] IndexMut<I>,
399{
400 #[inline]
401 fn index_mut(&mut self, index: I) -> &mut Self::Output {
402 IndexMut::index_mut(self as &mut [T], index)
403 }
404}
405
406/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
407#[stable(feature = "rust1", since = "1.0.0")]
408impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] {
409 #[inline]
410 fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> {
411 PartialOrd::partial_cmp(&&self[..], &&other[..])
412 }
413 #[inline]
414 fn lt(&self, other: &[T; N]) -> bool {
415 PartialOrd::lt(&&self[..], &&other[..])
416 }
417 #[inline]
418 fn le(&self, other: &[T; N]) -> bool {
419 PartialOrd::le(&&self[..], &&other[..])
420 }
421 #[inline]
422 fn ge(&self, other: &[T; N]) -> bool {
423 PartialOrd::ge(&&self[..], &&other[..])
424 }
425 #[inline]
426 fn gt(&self, other: &[T; N]) -> bool {
427 PartialOrd::gt(&&self[..], &&other[..])
428 }
429}
430
431/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
432#[stable(feature = "rust1", since = "1.0.0")]
433impl<T: Ord, const N: usize> Ord for [T; N] {
434 #[inline]
435 fn cmp(&self, other: &[T; N]) -> Ordering {
436 Ord::cmp(&&self[..], &&other[..])
437 }
438}
439
440#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
441impl<T: Copy, const N: usize> Copy for [T; N] {}
442
443#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
444impl<T: Clone, const N: usize> Clone for [T; N] {
445 #[inline]
446 fn clone(&self) -> Self {
447 SpecArrayClone::clone(self)
448 }
449
450 #[inline]
451 fn clone_from(&mut self, other: &Self) {
452 self.clone_from_slice(other);
453 }
454}
455
456#[doc(hidden)]
457#[unstable(feature = "trivial_clone", issue = "none")]
458unsafe impl<T: TrivialClone, const N: usize> TrivialClone for [T; N] {}
459
460trait SpecArrayClone: Clone {
461 fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
462}
463
464impl<T: Clone> SpecArrayClone for T {
465 #[inline]
466 default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
467 from_trusted_iterator(array.iter().cloned())
468 }
469}
470
471impl<T: TrivialClone> SpecArrayClone for T {
472 #[inline]
473 fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
474 // SAFETY: `TrivialClone` implies that this is equivalent to calling
475 // `Clone` on every element.
476 unsafe { ptr::read(array) }
477 }
478}
479
480// The Default impls cannot be done with const generics because `[T; 0]` doesn't
481// require Default to be implemented, and having different impl blocks for
482// different numbers isn't supported yet.
483//
484// Trying to improve the `[T; 0]` situation has proven to be difficult.
485// Please see these issues for more context on past attempts and crater runs:
486// - https://github.com/rust-lang/rust/issues/61415
487// - https://github.com/rust-lang/rust/pull/145457
488
489macro_rules! array_impl_default {
490 {$n:expr, $t:ident $($ts:ident)*} => {
491 #[stable(since = "1.4.0", feature = "array_default")]
492 impl<T> Default for [T; $n] where T: Default {
493 fn default() -> [T; $n] {
494 [$t::default(), $($ts::default()),*]
495 }
496 }
497 array_impl_default!{($n - 1), $($ts)*}
498 };
499 {$n:expr,} => {
500 #[stable(since = "1.4.0", feature = "array_default")]
501 impl<T> Default for [T; $n] {
502 fn default() -> [T; $n] { [] }
503 }
504 };
505}
506
507array_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}
508
509impl<T, const N: usize> [T; N] {
510 /// Returns an array of the same size as `self`, with function `f` applied to each element
511 /// in order.
512 ///
513 /// If you don't necessarily need a new fixed-size array, consider using
514 /// [`Iterator::map`] instead.
515 ///
516 ///
517 /// # Note on performance and stack usage
518 ///
519 /// Unfortunately, usages of this method are currently not always optimized
520 /// as well as they could be. This mainly concerns large arrays, as mapping
521 /// over small arrays seem to be optimized just fine. Also note that in
522 /// debug mode (i.e. without any optimizations), this method can use a lot
523 /// of stack space (a few times the size of the array or more).
524 ///
525 /// Therefore, in performance-critical code, try to avoid using this method
526 /// on large arrays or check the emitted code. Also try to avoid chained
527 /// maps (e.g. `arr.map(...).map(...)`).
528 ///
529 /// In many cases, you can instead use [`Iterator::map`] by calling `.iter()`
530 /// or `.into_iter()` on your array. `[T; N]::map` is only necessary if you
531 /// really need a new array of the same size as the result. Rust's lazy
532 /// iterators tend to get optimized very well.
533 ///
534 ///
535 /// # Examples
536 ///
537 /// ```
538 /// let x = [1, 2, 3];
539 /// let y = x.map(|v| v + 1);
540 /// assert_eq!(y, [2, 3, 4]);
541 ///
542 /// let x = [1, 2, 3];
543 /// let mut temp = 0;
544 /// let y = x.map(|v| { temp += 1; v * temp });
545 /// assert_eq!(y, [1, 4, 9]);
546 ///
547 /// let x = ["Ferris", "Bueller's", "Day", "Off"];
548 /// let y = x.map(|v| v.len());
549 /// assert_eq!(y, [6, 9, 3, 3]);
550 /// ```
551 #[must_use]
552 #[stable(feature = "array_map", since = "1.55.0")]
553 #[rustc_const_unstable(feature = "const_array", issue = "147606")]
554 pub const fn map<F, U>(self, f: F) -> [U; N]
555 where
556 F: [const] FnMut(T) -> U + [const] Destruct,
557 U: [const] Destruct,
558 T: [const] Destruct,
559 {
560 self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
561 }
562
563 /// A fallible function `f` applied to each element on array `self` in order to
564 /// return an array the same size as `self` or the first error encountered.
565 ///
566 /// The return type of this function depends on the return type of the closure.
567 /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
568 /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
569 ///
570 /// # Examples
571 ///
572 /// ```
573 /// #![feature(array_try_map)]
574 ///
575 /// let a = ["1", "2", "3"];
576 /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
577 /// assert_eq!(b, [2, 3, 4]);
578 ///
579 /// let a = ["1", "2a", "3"];
580 /// let b = a.try_map(|v| v.parse::<u32>());
581 /// assert!(b.is_err());
582 ///
583 /// use std::num::NonZero;
584 ///
585 /// let z = [1, 2, 0, 3, 4];
586 /// assert_eq!(z.try_map(NonZero::new), None);
587 ///
588 /// let a = [1, 2, 3];
589 /// let b = a.try_map(NonZero::new);
590 /// let c = b.map(|x| x.map(NonZero::get));
591 /// assert_eq!(c, Some(a));
592 /// ```
593 #[unstable(feature = "array_try_map", issue = "79711")]
594 #[rustc_const_unstable(feature = "array_try_map", issue = "79711")]
595 pub const fn try_map<R>(
596 self,
597 mut f: impl [const] FnMut(T) -> R + [const] Destruct,
598 ) -> ChangeOutputType<R, [R::Output; N]>
599 where
600 R: [const] Try<Residual: [const] Residual<[R::Output; N]>, Output: [const] Destruct>,
601 T: [const] Destruct,
602 {
603 let mut me = ManuallyDrop::new(self);
604 // SAFETY: try_from_fn calls `f` N times.
605 let mut f = unsafe { drain::Drain::new(&mut me, &mut f) };
606 try_from_fn(&mut f)
607 }
608
609 /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
610 #[stable(feature = "array_as_slice", since = "1.57.0")]
611 #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
612 pub const fn as_slice(&self) -> &[T] {
613 self
614 }
615
616 /// Returns a mutable slice containing the entire array. Equivalent to
617 /// `&mut s[..]`.
618 #[stable(feature = "array_as_slice", since = "1.57.0")]
619 #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "1.89.0")]
620 pub const fn as_mut_slice(&mut self) -> &mut [T] {
621 self
622 }
623
624 /// Borrows each element and returns an array of references with the same
625 /// size as `self`.
626 ///
627 ///
628 /// # Example
629 ///
630 /// ```
631 /// let floats = [3.1, 2.7, -1.0];
632 /// let float_refs: [&f64; 3] = floats.each_ref();
633 /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
634 /// ```
635 ///
636 /// This method is particularly useful if combined with other methods, like
637 /// [`map`](#method.map). This way, you can avoid moving the original
638 /// array if its elements are not [`Copy`].
639 ///
640 /// ```
641 /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
642 /// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
643 /// assert_eq!(is_ascii, [true, false, true]);
644 ///
645 /// // We can still access the original array: it has not been moved.
646 /// assert_eq!(strings.len(), 3);
647 /// ```
648 #[stable(feature = "array_methods", since = "1.77.0")]
649 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
650 pub const fn each_ref(&self) -> [&T; N] {
651 let mut buf = [null::<T>(); N];
652
653 // FIXME(const_trait_impl): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.
654 let mut i = 0;
655 while i < N {
656 buf[i] = &raw const self[i];
657
658 i += 1;
659 }
660
661 // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.
662 unsafe { transmute_unchecked(buf) }
663 }
664
665 /// Borrows each element mutably and returns an array of mutable references
666 /// with the same size as `self`.
667 ///
668 ///
669 /// # Example
670 ///
671 /// ```
672 ///
673 /// let mut floats = [3.1, 2.7, -1.0];
674 /// let float_refs: [&mut f64; 3] = floats.each_mut();
675 /// *float_refs[0] = 0.0;
676 /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
677 /// assert_eq!(floats, [0.0, 2.7, -1.0]);
678 /// ```
679 #[stable(feature = "array_methods", since = "1.77.0")]
680 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
681 pub const fn each_mut(&mut self) -> [&mut T; N] {
682 let mut buf = [null_mut::<T>(); N];
683
684 // FIXME(const_trait_impl): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.
685 let mut i = 0;
686 while i < N {
687 buf[i] = &raw mut self[i];
688
689 i += 1;
690 }
691
692 // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.
693 unsafe { transmute_unchecked(buf) }
694 }
695
696 /// Divides one array reference into two at an index.
697 ///
698 /// The first will contain all indices from `[0, M)` (excluding
699 /// the index `M` itself) and the second will contain all
700 /// indices from `[M, N)` (excluding the index `N` itself).
701 ///
702 /// # Panics
703 ///
704 /// Panics if `M > N`.
705 ///
706 /// # Examples
707 ///
708 /// ```
709 /// #![feature(split_array)]
710 ///
711 /// let v = [1, 2, 3, 4, 5, 6];
712 ///
713 /// {
714 /// let (left, right) = v.split_array_ref::<0>();
715 /// assert_eq!(left, &[]);
716 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
717 /// }
718 ///
719 /// {
720 /// let (left, right) = v.split_array_ref::<2>();
721 /// assert_eq!(left, &[1, 2]);
722 /// assert_eq!(right, &[3, 4, 5, 6]);
723 /// }
724 ///
725 /// {
726 /// let (left, right) = v.split_array_ref::<6>();
727 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
728 /// assert_eq!(right, &[]);
729 /// }
730 /// ```
731 #[unstable(
732 feature = "split_array",
733 reason = "return type should have array as 2nd element",
734 issue = "90091"
735 )]
736 #[inline]
737 pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
738 self.split_first_chunk::<M>().unwrap()
739 }
740
741 /// Divides one mutable array reference into two at an index.
742 ///
743 /// The first will contain all indices from `[0, M)` (excluding
744 /// the index `M` itself) and the second will contain all
745 /// indices from `[M, N)` (excluding the index `N` itself).
746 ///
747 /// # Panics
748 ///
749 /// Panics if `M > N`.
750 ///
751 /// # Examples
752 ///
753 /// ```
754 /// #![feature(split_array)]
755 ///
756 /// let mut v = [1, 0, 3, 0, 5, 6];
757 /// let (left, right) = v.split_array_mut::<2>();
758 /// assert_eq!(left, &mut [1, 0][..]);
759 /// assert_eq!(right, &mut [3, 0, 5, 6]);
760 /// left[1] = 2;
761 /// right[1] = 4;
762 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
763 /// ```
764 #[unstable(
765 feature = "split_array",
766 reason = "return type should have array as 2nd element",
767 issue = "90091"
768 )]
769 #[inline]
770 pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
771 self.split_first_chunk_mut::<M>().unwrap()
772 }
773
774 /// Divides one array reference into two at an index from the end.
775 ///
776 /// The first will contain all indices from `[0, N - M)` (excluding
777 /// the index `N - M` itself) and the second will contain all
778 /// indices from `[N - M, N)` (excluding the index `N` itself).
779 ///
780 /// # Panics
781 ///
782 /// Panics if `M > N`.
783 ///
784 /// # Examples
785 ///
786 /// ```
787 /// #![feature(split_array)]
788 ///
789 /// let v = [1, 2, 3, 4, 5, 6];
790 ///
791 /// {
792 /// let (left, right) = v.rsplit_array_ref::<0>();
793 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
794 /// assert_eq!(right, &[]);
795 /// }
796 ///
797 /// {
798 /// let (left, right) = v.rsplit_array_ref::<2>();
799 /// assert_eq!(left, &[1, 2, 3, 4]);
800 /// assert_eq!(right, &[5, 6]);
801 /// }
802 ///
803 /// {
804 /// let (left, right) = v.rsplit_array_ref::<6>();
805 /// assert_eq!(left, &[]);
806 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
807 /// }
808 /// ```
809 #[unstable(
810 feature = "split_array",
811 reason = "return type should have array as 2nd element",
812 issue = "90091"
813 )]
814 #[inline]
815 pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
816 self.split_last_chunk::<M>().unwrap()
817 }
818
819 /// Divides one mutable array reference into two at an index from the end.
820 ///
821 /// The first will contain all indices from `[0, N - M)` (excluding
822 /// the index `N - M` itself) and the second will contain all
823 /// indices from `[N - M, N)` (excluding the index `N` itself).
824 ///
825 /// # Panics
826 ///
827 /// Panics if `M > N`.
828 ///
829 /// # Examples
830 ///
831 /// ```
832 /// #![feature(split_array)]
833 ///
834 /// let mut v = [1, 0, 3, 0, 5, 6];
835 /// let (left, right) = v.rsplit_array_mut::<4>();
836 /// assert_eq!(left, &mut [1, 0]);
837 /// assert_eq!(right, &mut [3, 0, 5, 6][..]);
838 /// left[1] = 2;
839 /// right[1] = 4;
840 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
841 /// ```
842 #[unstable(
843 feature = "split_array",
844 reason = "return type should have array as 2nd element",
845 issue = "90091"
846 )]
847 #[inline]
848 pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
849 self.split_last_chunk_mut::<M>().unwrap()
850 }
851}
852
853/// Populate an array from the first `N` elements of `iter`
854///
855/// # Panics
856///
857/// If the iterator doesn't actually have enough items.
858///
859/// By depending on `TrustedLen`, however, we can do that check up-front (where
860/// it easily optimizes away) so it doesn't impact the loop that fills the array.
861#[inline]
862fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
863 try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
864}
865
866#[inline]
867fn try_from_trusted_iterator<T, R, const N: usize>(
868 iter: impl UncheckedIterator<Item = R>,
869) -> ChangeOutputType<R, [T; N]>
870where
871 R: Try<Output = T>,
872 R::Residual: Residual<[T; N]>,
873{
874 assert!(iter.size_hint().0 >= N);
875 fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
876 move |_| {
877 // SAFETY: We know that `from_fn` will call this at most N times,
878 // and we checked to ensure that we have at least that many items.
879 unsafe { iter.next_unchecked() }
880 }
881 }
882
883 try_from_fn(next(iter))
884}
885
886/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
887/// needing to monomorphize for every array length.
888///
889/// This takes a generator rather than an iterator so that *at the type level*
890/// it never needs to worry about running out of items. When combined with
891/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
892/// it to optimize well.
893///
894/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
895/// function that does the union of both things, but last time it was that way
896/// it resulted in poor codegen from the "are there enough source items?" checks
897/// not optimizing away. So if you give it a shot, make sure to watch what
898/// happens in the codegen tests.
899#[inline]
900#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
901const fn try_from_fn_erased<R: [const] Try<Output: [const] Destruct>>(
902 buffer: &mut [MaybeUninit<R::Output>],
903 mut generator: impl [const] FnMut(usize) -> R + [const] Destruct,
904) -> ControlFlow<R::Residual> {
905 let mut guard = Guard { array_mut: buffer, initialized: 0 };
906
907 while guard.initialized < guard.array_mut.len() {
908 let item = generator(guard.initialized).branch()?;
909
910 // SAFETY: The loop condition ensures we have space to push the item
911 unsafe { guard.push_unchecked(item) };
912 }
913
914 mem::forget(guard);
915 ControlFlow::Continue(())
916}
917
918/// Panic guard for incremental initialization of arrays.
919///
920/// Disarm the guard with `mem::forget` once the array has been initialized.
921///
922/// # Safety
923///
924/// All write accesses to this structure are unsafe and must maintain a correct
925/// count of `initialized` elements.
926///
927/// To minimize indirection fields are still pub but callers should at least use
928/// `push_unchecked` to signal that something unsafe is going on.
929struct Guard<'a, T> {
930 /// The array to be initialized.
931 pub array_mut: &'a mut [MaybeUninit<T>],
932 /// The number of items that have been initialized so far.
933 pub initialized: usize,
934}
935
936impl<T> Guard<'_, T> {
937 /// Adds an item to the array and updates the initialized item counter.
938 ///
939 /// # Safety
940 ///
941 /// No more than N elements must be initialized.
942 #[inline]
943 #[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
944 pub(crate) const unsafe fn push_unchecked(&mut self, item: T) {
945 // SAFETY: If `initialized` was correct before and the caller does not
946 // invoke this method more than N times then writes will be in-bounds
947 // and slots will not be initialized more than once.
948 unsafe {
949 self.array_mut.get_unchecked_mut(self.initialized).write(item);
950 self.initialized = self.initialized.unchecked_add(1);
951 }
952 }
953}
954
955#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
956impl<T: [const] Destruct> const Drop for Guard<'_, T> {
957 #[inline]
958 fn drop(&mut self) {
959 debug_assert!(self.initialized <= self.array_mut.len());
960 // SAFETY: this slice will contain only initialized objects.
961 unsafe {
962 self.array_mut.get_unchecked_mut(..self.initialized).assume_init_drop();
963 }
964 }
965}
966
967/// Pulls `N` items from `iter` and returns them as an array. If the iterator
968/// yields fewer than `N` items, `Err` is returned containing an iterator over
969/// the already yielded items.
970///
971/// Since the iterator is passed as a mutable reference and this function calls
972/// `next` at most `N` times, the iterator can still be used afterwards to
973/// retrieve the remaining items.
974///
975/// If `iter.next()` panicks, all items already yielded by the iterator are
976/// dropped.
977///
978/// Used for [`Iterator::next_chunk`].
979#[inline]
980pub(crate) fn iter_next_chunk<T, const N: usize>(
981 iter: &mut impl Iterator<Item = T>,
982) -> Result<[T; N], IntoIter<T, N>> {
983 let mut array = [const { MaybeUninit::uninit() }; N];
984 let r = iter_next_chunk_erased(&mut array, iter);
985 match r {
986 Ok(()) => {
987 // SAFETY: All elements of `array` were populated.
988 Ok(unsafe { MaybeUninit::array_assume_init(array) })
989 }
990 Err(initialized) => {
991 // SAFETY: Only the first `initialized` elements were populated
992 Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
993 }
994 }
995}
996
997/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
998/// needing to monomorphize for every array length.
999///
1000/// Unfortunately this loop has two exit conditions, the buffer filling up
1001/// or the iterator running out of items, making it tend to optimize poorly.
1002#[inline]
1003fn iter_next_chunk_erased<T>(
1004 buffer: &mut [MaybeUninit<T>],
1005 iter: &mut impl Iterator<Item = T>,
1006) -> Result<(), usize> {
1007 let mut guard = Guard { array_mut: buffer, initialized: 0 };
1008 while guard.initialized < guard.array_mut.len() {
1009 let Some(item) = iter.next() else {
1010 // Unlike `try_from_fn_erased`, we want to keep the partial results,
1011 // so we need to defuse the guard instead of using `?`.
1012 let initialized = guard.initialized;
1013 mem::forget(guard);
1014 return Err(initialized);
1015 };
1016
1017 // SAFETY: The loop condition ensures we have space to push the item
1018 unsafe { guard.push_unchecked(item) };
1019 }
1020
1021 mem::forget(guard);
1022 Ok(())
1023}