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")]
109#[ferrocene::prevalidated]
110pub const fn from_fn<T: [const] Destruct, const N: usize, F>(f: F) -> [T; N]
111where
112 F: [const] FnMut(usize) -> T + [const] Destruct,
113{
114 try_from_fn(NeverShortCircuit::wrap_mut_1(f)).0
115}
116
117/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
118/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error
119/// if any element creation was unsuccessful.
120///
121/// The return type of this function depends on the return type of the closure.
122/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
123/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
124///
125/// # Arguments
126///
127/// * `cb`: Callback where the passed argument is the current array index.
128///
129/// # Example
130///
131/// ```rust
132/// #![feature(array_try_from_fn)]
133///
134/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
135/// assert_eq!(array, Ok([0, 1, 2, 3, 4]));
136///
137/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
138/// assert!(array.is_err());
139///
140/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
141/// assert_eq!(array, Some([100, 101, 102, 103]));
142///
143/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
144/// assert_eq!(array, None);
145/// ```
146#[inline]
147#[unstable(feature = "array_try_from_fn", issue = "89379")]
148#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
149#[ferrocene::prevalidated]
150pub const fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]>
151where
152 R: [const] Try<Residual: [const] Residual<[R::Output; N]>, Output: [const] Destruct>,
153 F: [const] FnMut(usize) -> R + [const] Destruct,
154{
155 let mut array = [const { MaybeUninit::uninit() }; N];
156 match try_from_fn_erased(&mut array, cb) {
157 ControlFlow::Break(r) => FromResidual::from_residual(r),
158 ControlFlow::Continue(()) => {
159 // SAFETY: All elements of the array were populated.
160 try { unsafe { MaybeUninit::array_assume_init(array) } }
161 }
162 }
163}
164
165/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
166#[stable(feature = "array_from_ref", since = "1.53.0")]
167#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
168#[ferrocene::prevalidated]
169pub const fn from_ref<T>(s: &T) -> &[T; 1] {
170 // SAFETY: Converting `&T` to `&[T; 1]` is sound.
171 unsafe { &*(s as *const T).cast::<[T; 1]>() }
172}
173
174/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
175#[stable(feature = "array_from_ref", since = "1.53.0")]
176#[rustc_const_stable(feature = "const_array_from_ref", since = "1.83.0")]
177#[ferrocene::prevalidated]
178pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
179 // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
180 unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
181}
182
183/// The error type returned when a conversion from a slice to an array fails.
184#[stable(feature = "try_from", since = "1.34.0")]
185#[derive(Debug, Copy, Clone)]
186#[ferrocene::prevalidated]
187pub struct TryFromSliceError(());
188
189#[stable(feature = "core_array", since = "1.35.0")]
190impl fmt::Display for TryFromSliceError {
191 #[inline]
192 #[ferrocene::prevalidated]
193 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
194 "could not convert slice to array".fmt(f)
195 }
196}
197
198#[stable(feature = "try_from", since = "1.34.0")]
199impl Error for TryFromSliceError {}
200
201#[stable(feature = "try_from_slice_error", since = "1.36.0")]
202#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
203impl const From<Infallible> for TryFromSliceError {
204 fn from(x: Infallible) -> TryFromSliceError {
205 match x {}
206 }
207}
208
209#[stable(feature = "rust1", since = "1.0.0")]
210#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
211impl<T, const N: usize> const AsRef<[T]> for [T; N] {
212 #[inline]
213 #[ferrocene::prevalidated]
214 fn as_ref(&self) -> &[T] {
215 &self[..]
216 }
217}
218
219#[stable(feature = "rust1", since = "1.0.0")]
220#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
221impl<T, const N: usize> const AsMut<[T]> for [T; N] {
222 #[inline]
223 fn as_mut(&mut self) -> &mut [T] {
224 &mut self[..]
225 }
226}
227
228#[stable(feature = "array_borrow", since = "1.4.0")]
229#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
230impl<T, const N: usize> const Borrow<[T]> for [T; N] {
231 fn borrow(&self) -> &[T] {
232 self
233 }
234}
235
236#[stable(feature = "array_borrow", since = "1.4.0")]
237#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
238impl<T, const N: usize> const BorrowMut<[T]> for [T; N] {
239 fn borrow_mut(&mut self) -> &mut [T] {
240 self
241 }
242}
243
244/// Tries to create an array `[T; N]` by copying from a slice `&[T]`.
245/// Succeeds if `slice.len() == N`.
246///
247/// ```
248/// let bytes: [u8; 3] = [1, 0, 2];
249///
250/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
251/// assert_eq!(1, u16::from_le_bytes(bytes_head));
252///
253/// let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
254/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
255/// ```
256#[stable(feature = "try_from", since = "1.34.0")]
257#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
258impl<T, const N: usize> const TryFrom<&[T]> for [T; N]
259where
260 T: Copy,
261{
262 type Error = TryFromSliceError;
263
264 #[inline]
265 #[ferrocene::prevalidated]
266 fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
267 <&Self>::try_from(slice).copied()
268 }
269}
270
271/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
272/// Succeeds if `slice.len() == N`.
273///
274/// ```
275/// let mut bytes: [u8; 3] = [1, 0, 2];
276///
277/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
278/// assert_eq!(1, u16::from_le_bytes(bytes_head));
279///
280/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
281/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
282/// ```
283#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
284#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
285impl<T, const N: usize> const TryFrom<&mut [T]> for [T; N]
286where
287 T: Copy,
288{
289 type Error = TryFromSliceError;
290
291 #[inline]
292 #[ferrocene::prevalidated]
293 fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
294 <Self>::try_from(&*slice)
295 }
296}
297
298/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
299/// `slice.len() == N`.
300///
301/// ```
302/// let bytes: [u8; 3] = [1, 0, 2];
303///
304/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
305/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
306///
307/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
308/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
309/// ```
310#[stable(feature = "try_from", since = "1.34.0")]
311#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
312impl<'a, T, const N: usize> const TryFrom<&'a [T]> for &'a [T; N] {
313 type Error = TryFromSliceError;
314
315 #[inline]
316 #[ferrocene::prevalidated]
317 fn try_from(slice: &'a [T]) -> Result<&'a [T; N], TryFromSliceError> {
318 slice.as_array().ok_or(TryFromSliceError(()))
319 }
320}
321
322/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
323/// `&mut [T]`. Succeeds if `slice.len() == N`.
324///
325/// ```
326/// let mut bytes: [u8; 3] = [1, 0, 2];
327///
328/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
329/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
330///
331/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
332/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
333/// ```
334#[stable(feature = "try_from", since = "1.34.0")]
335#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
336impl<'a, T, const N: usize> const TryFrom<&'a mut [T]> for &'a mut [T; N] {
337 type Error = TryFromSliceError;
338
339 #[inline]
340 #[ferrocene::prevalidated]
341 fn try_from(slice: &'a mut [T]) -> Result<&'a mut [T; N], TryFromSliceError> {
342 slice.as_mut_array().ok_or(TryFromSliceError(()))
343 }
344}
345
346/// The hash of an array is the same as that of the corresponding slice,
347/// as required by the `Borrow` implementation.
348///
349/// ```
350/// use std::hash::BuildHasher;
351///
352/// let b = std::hash::RandomState::new();
353/// let a: [u8; 3] = [0xa8, 0x3c, 0x09];
354/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
355/// assert_eq!(b.hash_one(a), b.hash_one(s));
356/// ```
357#[stable(feature = "rust1", since = "1.0.0")]
358impl<T: Hash, const N: usize> Hash for [T; N] {
359 fn hash<H: hash::Hasher>(&self, state: &mut H) {
360 Hash::hash(&self[..], state)
361 }
362}
363
364#[stable(feature = "rust1", since = "1.0.0")]
365impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] {
366 #[ferrocene::prevalidated]
367 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
368 fmt::Debug::fmt(&&self[..], f)
369 }
370}
371
372#[stable(feature = "rust1", since = "1.0.0")]
373impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
374 type Item = &'a T;
375 type IntoIter = Iter<'a, T>;
376
377 #[ferrocene::prevalidated]
378 fn into_iter(self) -> Iter<'a, T> {
379 self.iter()
380 }
381}
382
383#[stable(feature = "rust1", since = "1.0.0")]
384impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
385 type Item = &'a mut T;
386 type IntoIter = IterMut<'a, T>;
387
388 #[ferrocene::prevalidated]
389 fn into_iter(self) -> IterMut<'a, T> {
390 self.iter_mut()
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 Index<I> for [T; N]
397where
398 [T]: [const] Index<I>,
399{
400 type Output = <[T] as Index<I>>::Output;
401
402 #[inline]
403 #[ferrocene::prevalidated]
404 fn index(&self, index: I) -> &Self::Output {
405 Index::index(self as &[T], index)
406 }
407}
408
409#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
410#[rustc_const_unstable(feature = "const_index", issue = "143775")]
411impl<T, I, const N: usize> const IndexMut<I> for [T; N]
412where
413 [T]: [const] IndexMut<I>,
414{
415 #[inline]
416 #[ferrocene::prevalidated]
417 fn index_mut(&mut self, index: I) -> &mut Self::Output {
418 IndexMut::index_mut(self as &mut [T], index)
419 }
420}
421
422/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
423#[stable(feature = "rust1", since = "1.0.0")]
424// blocked by PartialOrd
425impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] {
426 #[inline]
427 fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> {
428 PartialOrd::partial_cmp(&&self[..], &&other[..])
429 }
430 #[inline]
431 fn lt(&self, other: &[T; N]) -> bool {
432 PartialOrd::lt(&&self[..], &&other[..])
433 }
434 #[inline]
435 fn le(&self, other: &[T; N]) -> bool {
436 PartialOrd::le(&&self[..], &&other[..])
437 }
438 #[inline]
439 fn ge(&self, other: &[T; N]) -> bool {
440 PartialOrd::ge(&&self[..], &&other[..])
441 }
442 #[inline]
443 fn gt(&self, other: &[T; N]) -> bool {
444 PartialOrd::gt(&&self[..], &&other[..])
445 }
446}
447
448/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
449#[stable(feature = "rust1", since = "1.0.0")]
450impl<T: Ord, const N: usize> Ord for [T; N] {
451 #[inline]
452 fn cmp(&self, other: &[T; N]) -> Ordering {
453 Ord::cmp(&&self[..], &&other[..])
454 }
455}
456
457#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
458impl<T: Copy, const N: usize> Copy for [T; N] {}
459
460#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
461impl<T: Clone, const N: usize> Clone for [T; N] {
462 #[inline]
463 #[ferrocene::prevalidated]
464 fn clone(&self) -> Self {
465 SpecArrayClone::clone(self)
466 }
467
468 #[inline]
469 fn clone_from(&mut self, other: &Self) {
470 self.clone_from_slice(other);
471 }
472}
473
474#[doc(hidden)]
475#[unstable(feature = "trivial_clone", issue = "none")]
476unsafe impl<T: TrivialClone, const N: usize> TrivialClone for [T; N] {}
477
478trait SpecArrayClone: Clone {
479 fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
480}
481
482impl<T: Clone> SpecArrayClone for T {
483 #[inline]
484 #[ferrocene::prevalidated]
485 default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
486 from_trusted_iterator(array.iter().cloned())
487 }
488}
489
490impl<T: TrivialClone> SpecArrayClone for T {
491 #[inline]
492 #[ferrocene::prevalidated]
493 fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
494 // SAFETY: `TrivialClone` implies that this is equivalent to calling
495 // `Clone` on every element.
496 unsafe { ptr::read(array) }
497 }
498}
499
500// The Default impls cannot be done with const generics because `[T; 0]` doesn't
501// require Default to be implemented, and having different impl blocks for
502// different numbers isn't supported yet.
503//
504// Trying to improve the `[T; 0]` situation has proven to be difficult.
505// Please see these issues for more context on past attempts and crater runs:
506// - https://github.com/rust-lang/rust/issues/61415
507// - https://github.com/rust-lang/rust/pull/145457
508
509macro_rules! array_impl_default {
510 {$n:expr, $t:ident $($ts:ident)*} => {
511 #[stable(since = "1.4.0", feature = "array_default")]
512 impl<T> Default for [T; $n] where T: Default {
513 fn default() -> [T; $n] {
514 [$t::default(), $($ts::default()),*]
515 }
516 }
517 array_impl_default!{($n - 1), $($ts)*}
518 };
519 {$n:expr,} => {
520 #[stable(since = "1.4.0", feature = "array_default")]
521 impl<T> Default for [T; $n] {
522 fn default() -> [T; $n] { [] }
523 }
524 };
525}
526
527array_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}
528
529impl<T, const N: usize> [T; N] {
530 /// Returns an array of the same size as `self`, with function `f` applied to each element
531 /// in order.
532 ///
533 /// If you don't necessarily need a new fixed-size array, consider using
534 /// [`Iterator::map`] instead.
535 ///
536 ///
537 /// # Note on performance and stack usage
538 ///
539 /// Note that this method is *eager*. It evaluates `f` all `N` times before
540 /// returning the new array.
541 ///
542 /// That means that `arr.map(f).map(g)` is, in general, *not* equivalent to
543 /// `array.map(|x| g(f(x)))`, as the former calls `f` 4 times then `g` 4 times,
544 /// whereas the latter interleaves the calls (`fgfgfgfg`).
545 ///
546 /// A consequence of this is that it can have fairly-high stack usage, especially
547 /// in debug mode or for long arrays. The backend may be able to optimize it
548 /// away, but especially for complicated mappings it might not be able to.
549 ///
550 /// If you're doing a one-step `map` and really want an array as the result,
551 /// then absolutely use this method. Its implementation uses a bunch of tricks
552 /// to help the optimizer handle it well. Particularly for simple arrays,
553 /// like `[u8; 3]` or `[f32; 4]`, there's nothing to be concerned about.
554 ///
555 /// However, if you don't actually need an *array* of the results specifically,
556 /// just to process them, then you likely want [`Iterator::map`] instead.
557 ///
558 /// For example, rather than doing an array-to-array map of all the elements
559 /// in the array up-front and only iterating after that completes,
560 ///
561 /// ```
562 /// # let my_array = [1, 2, 3];
563 /// # let f = |x: i32| x + 1;
564 /// for x in my_array.map(f) {
565 /// // ...
566 /// }
567 /// ```
568 ///
569 /// It's often better to use an iterator along the lines of
570 ///
571 /// ```
572 /// # let my_array = [1, 2, 3];
573 /// # let f = |x: i32| x + 1;
574 /// for x in my_array.into_iter().map(f) {
575 /// // ...
576 /// }
577 /// ```
578 ///
579 /// as that's more likely to avoid large temporaries.
580 ///
581 ///
582 /// # Examples
583 ///
584 /// ```
585 /// let x = [1, 2, 3];
586 /// let y = x.map(|v| v + 1);
587 /// assert_eq!(y, [2, 3, 4]);
588 ///
589 /// let x = [1, 2, 3];
590 /// let mut temp = 0;
591 /// let y = x.map(|v| { temp += 1; v * temp });
592 /// assert_eq!(y, [1, 4, 9]);
593 ///
594 /// let x = ["Ferris", "Bueller's", "Day", "Off"];
595 /// let y = x.map(|v| v.len());
596 /// assert_eq!(y, [6, 9, 3, 3]);
597 /// ```
598 #[must_use]
599 #[stable(feature = "array_map", since = "1.55.0")]
600 #[rustc_const_unstable(feature = "const_array", issue = "147606")]
601 #[ferrocene::prevalidated]
602 pub const fn map<F, U>(self, f: F) -> [U; N]
603 where
604 F: [const] FnMut(T) -> U + [const] Destruct,
605 U: [const] Destruct,
606 T: [const] Destruct,
607 {
608 self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
609 }
610
611 /// A fallible function `f` applied to each element on array `self` in order to
612 /// return an array the same size as `self` or the first error encountered.
613 ///
614 /// The return type of this function depends on the return type of the closure.
615 /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
616 /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
617 ///
618 /// # Examples
619 ///
620 /// ```
621 /// #![feature(array_try_map)]
622 ///
623 /// let a = ["1", "2", "3"];
624 /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
625 /// assert_eq!(b, [2, 3, 4]);
626 ///
627 /// let a = ["1", "2a", "3"];
628 /// let b = a.try_map(|v| v.parse::<u32>());
629 /// assert!(b.is_err());
630 ///
631 /// use std::num::NonZero;
632 ///
633 /// let z = [1, 2, 0, 3, 4];
634 /// assert_eq!(z.try_map(NonZero::new), None);
635 ///
636 /// let a = [1, 2, 3];
637 /// let b = a.try_map(NonZero::new);
638 /// let c = b.map(|x| x.map(NonZero::get));
639 /// assert_eq!(c, Some(a));
640 /// ```
641 #[unstable(feature = "array_try_map", issue = "79711")]
642 #[rustc_const_unstable(feature = "array_try_map", issue = "79711")]
643 #[ferrocene::prevalidated]
644 pub const fn try_map<R>(
645 self,
646 mut f: impl [const] FnMut(T) -> R + [const] Destruct,
647 ) -> ChangeOutputType<R, [R::Output; N]>
648 where
649 R: [const] Try<Residual: [const] Residual<[R::Output; N]>, Output: [const] Destruct>,
650 T: [const] Destruct,
651 {
652 let mut me = ManuallyDrop::new(self);
653 // SAFETY: try_from_fn calls `f` N times.
654 let mut f = unsafe { drain::Drain::new(&mut me, &mut f) };
655 try_from_fn(&mut f)
656 }
657
658 /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
659 #[stable(feature = "array_as_slice", since = "1.57.0")]
660 #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
661 #[ferrocene::prevalidated]
662 pub const fn as_slice(&self) -> &[T] {
663 self
664 }
665
666 /// Returns a mutable slice containing the entire array. Equivalent to
667 /// `&mut s[..]`.
668 #[stable(feature = "array_as_slice", since = "1.57.0")]
669 #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "1.89.0")]
670 #[ferrocene::prevalidated]
671 pub const fn as_mut_slice(&mut self) -> &mut [T] {
672 self
673 }
674
675 /// Borrows each element and returns an array of references with the same
676 /// size as `self`.
677 ///
678 ///
679 /// # Example
680 ///
681 /// ```
682 /// let floats = [3.1, 2.7, -1.0];
683 /// let float_refs: [&f64; 3] = floats.each_ref();
684 /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
685 /// ```
686 ///
687 /// This method is particularly useful if combined with other methods, like
688 /// [`map`](#method.map). This way, you can avoid moving the original
689 /// array if its elements are not [`Copy`].
690 ///
691 /// ```
692 /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
693 /// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
694 /// assert_eq!(is_ascii, [true, false, true]);
695 ///
696 /// // We can still access the original array: it has not been moved.
697 /// assert_eq!(strings.len(), 3);
698 /// ```
699 #[stable(feature = "array_methods", since = "1.77.0")]
700 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
701 pub const fn each_ref(&self) -> [&T; N] {
702 let mut buf = [null::<T>(); N];
703
704 // 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.
705 let mut i = 0;
706 while i < N {
707 buf[i] = &raw const self[i];
708
709 i += 1;
710 }
711
712 // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.
713 unsafe { transmute_unchecked(buf) }
714 }
715
716 /// Borrows each element mutably and returns an array of mutable references
717 /// with the same size as `self`.
718 ///
719 ///
720 /// # Example
721 ///
722 /// ```
723 ///
724 /// let mut floats = [3.1, 2.7, -1.0];
725 /// let float_refs: [&mut f64; 3] = floats.each_mut();
726 /// *float_refs[0] = 0.0;
727 /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
728 /// assert_eq!(floats, [0.0, 2.7, -1.0]);
729 /// ```
730 #[stable(feature = "array_methods", since = "1.77.0")]
731 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
732 pub const fn each_mut(&mut self) -> [&mut T; N] {
733 let mut buf = [null_mut::<T>(); N];
734
735 // 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.
736 let mut i = 0;
737 while i < N {
738 buf[i] = &raw mut self[i];
739
740 i += 1;
741 }
742
743 // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.
744 unsafe { transmute_unchecked(buf) }
745 }
746
747 /// Divides one array reference into two at an index.
748 ///
749 /// The first will contain all indices from `[0, M)` (excluding
750 /// the index `M` itself) and the second will contain all
751 /// indices from `[M, N)` (excluding the index `N` itself).
752 ///
753 /// # Panics
754 ///
755 /// Panics if `M > N`.
756 ///
757 /// # Examples
758 ///
759 /// ```
760 /// #![feature(split_array)]
761 ///
762 /// let v = [1, 2, 3, 4, 5, 6];
763 ///
764 /// {
765 /// let (left, right) = v.split_array_ref::<0>();
766 /// assert_eq!(left, &[]);
767 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
768 /// }
769 ///
770 /// {
771 /// let (left, right) = v.split_array_ref::<2>();
772 /// assert_eq!(left, &[1, 2]);
773 /// assert_eq!(right, &[3, 4, 5, 6]);
774 /// }
775 ///
776 /// {
777 /// let (left, right) = v.split_array_ref::<6>();
778 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
779 /// assert_eq!(right, &[]);
780 /// }
781 /// ```
782 #[unstable(
783 feature = "split_array",
784 reason = "return type should have array as 2nd element",
785 issue = "90091"
786 )]
787 #[inline]
788 pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
789 self.split_first_chunk::<M>().unwrap()
790 }
791
792 /// Divides one mutable array reference into two at an index.
793 ///
794 /// The first will contain all indices from `[0, M)` (excluding
795 /// the index `M` itself) and the second will contain all
796 /// indices from `[M, N)` (excluding the index `N` itself).
797 ///
798 /// # Panics
799 ///
800 /// Panics if `M > N`.
801 ///
802 /// # Examples
803 ///
804 /// ```
805 /// #![feature(split_array)]
806 ///
807 /// let mut v = [1, 0, 3, 0, 5, 6];
808 /// let (left, right) = v.split_array_mut::<2>();
809 /// assert_eq!(left, &mut [1, 0][..]);
810 /// assert_eq!(right, &mut [3, 0, 5, 6]);
811 /// left[1] = 2;
812 /// right[1] = 4;
813 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
814 /// ```
815 #[unstable(
816 feature = "split_array",
817 reason = "return type should have array as 2nd element",
818 issue = "90091"
819 )]
820 #[inline]
821 pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
822 self.split_first_chunk_mut::<M>().unwrap()
823 }
824
825 /// Divides one array reference into two at an index from the end.
826 ///
827 /// The first will contain all indices from `[0, N - M)` (excluding
828 /// the index `N - M` itself) and the second will contain all
829 /// indices from `[N - M, N)` (excluding the index `N` itself).
830 ///
831 /// # Panics
832 ///
833 /// Panics if `M > N`.
834 ///
835 /// # Examples
836 ///
837 /// ```
838 /// #![feature(split_array)]
839 ///
840 /// let v = [1, 2, 3, 4, 5, 6];
841 ///
842 /// {
843 /// let (left, right) = v.rsplit_array_ref::<0>();
844 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
845 /// assert_eq!(right, &[]);
846 /// }
847 ///
848 /// {
849 /// let (left, right) = v.rsplit_array_ref::<2>();
850 /// assert_eq!(left, &[1, 2, 3, 4]);
851 /// assert_eq!(right, &[5, 6]);
852 /// }
853 ///
854 /// {
855 /// let (left, right) = v.rsplit_array_ref::<6>();
856 /// assert_eq!(left, &[]);
857 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
858 /// }
859 /// ```
860 #[unstable(
861 feature = "split_array",
862 reason = "return type should have array as 2nd element",
863 issue = "90091"
864 )]
865 #[inline]
866 pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
867 self.split_last_chunk::<M>().unwrap()
868 }
869
870 /// Divides one mutable array reference into two at an index from the end.
871 ///
872 /// The first will contain all indices from `[0, N - M)` (excluding
873 /// the index `N - M` itself) and the second will contain all
874 /// indices from `[N - M, N)` (excluding the index `N` itself).
875 ///
876 /// # Panics
877 ///
878 /// Panics if `M > N`.
879 ///
880 /// # Examples
881 ///
882 /// ```
883 /// #![feature(split_array)]
884 ///
885 /// let mut v = [1, 0, 3, 0, 5, 6];
886 /// let (left, right) = v.rsplit_array_mut::<4>();
887 /// assert_eq!(left, &mut [1, 0]);
888 /// assert_eq!(right, &mut [3, 0, 5, 6][..]);
889 /// left[1] = 2;
890 /// right[1] = 4;
891 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
892 /// ```
893 #[unstable(
894 feature = "split_array",
895 reason = "return type should have array as 2nd element",
896 issue = "90091"
897 )]
898 #[inline]
899 pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
900 self.split_last_chunk_mut::<M>().unwrap()
901 }
902}
903
904/// Populate an array from the first `N` elements of `iter`
905///
906/// # Panics
907///
908/// If the iterator doesn't actually have enough items.
909///
910/// By depending on `TrustedLen`, however, we can do that check up-front (where
911/// it easily optimizes away) so it doesn't impact the loop that fills the array.
912#[inline]
913#[ferrocene::prevalidated]
914fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
915 try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
916}
917
918#[inline]
919#[ferrocene::prevalidated]
920fn try_from_trusted_iterator<T, R, const N: usize>(
921 iter: impl UncheckedIterator<Item = R>,
922) -> ChangeOutputType<R, [T; N]>
923where
924 R: Try<Output = T>,
925 R::Residual: Residual<[T; N]>,
926{
927 assert!(iter.size_hint().0 >= N);
928 #[ferrocene::prevalidated]
929 fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
930 move |_| {
931 // SAFETY: We know that `from_fn` will call this at most N times,
932 // and we checked to ensure that we have at least that many items.
933 unsafe { iter.next_unchecked() }
934 }
935 }
936
937 try_from_fn(next(iter))
938}
939
940/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
941/// needing to monomorphize for every array length.
942///
943/// This takes a generator rather than an iterator so that *at the type level*
944/// it never needs to worry about running out of items. When combined with
945/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
946/// it to optimize well.
947///
948/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
949/// function that does the union of both things, but last time it was that way
950/// it resulted in poor codegen from the "are there enough source items?" checks
951/// not optimizing away. So if you give it a shot, make sure to watch what
952/// happens in the codegen tests.
953#[inline]
954#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
955#[ferrocene::prevalidated]
956const fn try_from_fn_erased<R: [const] Try<Output: [const] Destruct>>(
957 buffer: &mut [MaybeUninit<R::Output>],
958 mut generator: impl [const] FnMut(usize) -> R + [const] Destruct,
959) -> ControlFlow<R::Residual> {
960 let mut guard = Guard { array_mut: buffer, initialized: 0 };
961
962 while guard.initialized < guard.array_mut.len() {
963 let item = generator(guard.initialized).branch()?;
964
965 // SAFETY: The loop condition ensures we have space to push the item
966 unsafe { guard.push_unchecked(item) };
967 }
968
969 mem::forget(guard);
970 ControlFlow::Continue(())
971}
972
973/// Panic guard for incremental initialization of arrays.
974///
975/// Disarm the guard with `mem::forget` once the array has been initialized.
976///
977/// # Safety
978///
979/// All write accesses to this structure are unsafe and must maintain a correct
980/// count of `initialized` elements.
981///
982/// To minimize indirection, fields are still pub but callers should at least use
983/// `push_unchecked` to signal that something unsafe is going on.
984#[ferrocene::prevalidated]
985struct Guard<'a, T> {
986 /// The array to be initialized.
987 pub array_mut: &'a mut [MaybeUninit<T>],
988 /// The number of items that have been initialized so far.
989 pub initialized: usize,
990}
991
992impl<T> Guard<'_, T> {
993 /// Adds an item to the array and updates the initialized item counter.
994 ///
995 /// # Safety
996 ///
997 /// No more than N elements must be initialized.
998 #[inline]
999 #[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
1000 #[ferrocene::prevalidated]
1001 pub(crate) const unsafe fn push_unchecked(&mut self, item: T) {
1002 // SAFETY: If `initialized` was correct before and the caller does not
1003 // invoke this method more than N times, then writes will be in-bounds
1004 // and slots will not be initialized more than once.
1005 unsafe {
1006 self.array_mut.get_unchecked_mut(self.initialized).write(item);
1007 self.initialized = self.initialized.unchecked_add(1);
1008 }
1009 }
1010}
1011
1012#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
1013impl<T: [const] Destruct> const Drop for Guard<'_, T> {
1014 #[inline]
1015 #[ferrocene::prevalidated]
1016 fn drop(&mut self) {
1017 debug_assert!(self.initialized <= self.array_mut.len());
1018 // SAFETY: this slice will contain only initialized objects.
1019 unsafe {
1020 self.array_mut.get_unchecked_mut(..self.initialized).assume_init_drop();
1021 }
1022 }
1023}
1024
1025/// Pulls `N` items from `iter` and returns them as an array. If the iterator
1026/// yields fewer than `N` items, `Err` is returned containing an iterator over
1027/// the already yielded items.
1028///
1029/// Since the iterator is passed as a mutable reference and this function calls
1030/// `next` at most `N` times, the iterator can still be used afterwards to
1031/// retrieve the remaining items.
1032///
1033/// If `iter.next()` panics, all items already yielded by the iterator are
1034/// dropped.
1035///
1036/// Used for [`Iterator::next_chunk`].
1037#[inline]
1038pub(crate) fn iter_next_chunk<T, const N: usize>(
1039 iter: &mut impl Iterator<Item = T>,
1040) -> Result<[T; N], IntoIter<T, N>> {
1041 let mut array = [const { MaybeUninit::uninit() }; N];
1042 let r = iter_next_chunk_erased(&mut array, iter);
1043 match r {
1044 Ok(()) => {
1045 // SAFETY: All elements of `array` were populated.
1046 Ok(unsafe { MaybeUninit::array_assume_init(array) })
1047 }
1048 Err(initialized) => {
1049 // SAFETY: Only the first `initialized` elements were populated
1050 Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
1051 }
1052 }
1053}
1054
1055/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
1056/// needing to monomorphize for every array length.
1057///
1058/// Unfortunately this loop has two exit conditions, the buffer filling up
1059/// or the iterator running out of items, making it tend to optimize poorly.
1060#[inline]
1061fn iter_next_chunk_erased<T>(
1062 buffer: &mut [MaybeUninit<T>],
1063 iter: &mut impl Iterator<Item = T>,
1064) -> Result<(), usize> {
1065 // if `Iterator::next` panics, this guard will drop already initialized items
1066 let mut guard = Guard { array_mut: buffer, initialized: 0 };
1067 while guard.initialized < guard.array_mut.len() {
1068 let Some(item) = iter.next() else {
1069 // Unlike `try_from_fn_erased`, we want to keep the partial results,
1070 // so we need to defuse the guard instead of using `?`.
1071 let initialized = guard.initialized;
1072 mem::forget(guard);
1073 return Err(initialized);
1074 };
1075
1076 // SAFETY: The loop condition ensures we have space to push the item
1077 unsafe { guard.push_unchecked(item) };
1078 }
1079
1080 mem::forget(guard);
1081 Ok(())
1082}
1083
1084/// Ferrocene addition: Hidden module to test crate-internal functionality
1085#[doc(hidden)]
1086#[unstable(feature = "ferrocene_test", issue = "none")]
1087pub mod ferrocene_test;