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#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
425impl<T: [const] PartialOrd, const N: usize> const 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")]
450#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
451impl<T: [const] Ord, const N: usize> const Ord for [T; N] {
452 #[inline]
453 fn cmp(&self, other: &[T; N]) -> Ordering {
454 Ord::cmp(&&self[..], &&other[..])
455 }
456}
457
458#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
459impl<T: Copy, const N: usize> Copy for [T; N] {}
460
461#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
462impl<T: Clone, const N: usize> Clone for [T; N] {
463 #[inline]
464 #[ferrocene::prevalidated]
465 fn clone(&self) -> Self {
466 SpecArrayClone::clone(self)
467 }
468
469 #[inline]
470 fn clone_from(&mut self, other: &Self) {
471 self.clone_from_slice(other);
472 }
473}
474
475#[doc(hidden)]
476#[unstable(feature = "trivial_clone", issue = "none")]
477unsafe impl<T: TrivialClone, const N: usize> TrivialClone for [T; N] {}
478
479trait SpecArrayClone: Clone {
480 fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
481}
482
483impl<T: Clone> SpecArrayClone for T {
484 #[inline]
485 #[ferrocene::prevalidated]
486 default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
487 from_trusted_iterator(array.iter().cloned())
488 }
489}
490
491impl<T: TrivialClone> SpecArrayClone for T {
492 #[inline]
493 #[ferrocene::prevalidated]
494 fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
495 // SAFETY: `TrivialClone` implies that this is equivalent to calling
496 // `Clone` on every element.
497 unsafe { ptr::read(array) }
498 }
499}
500
501// The Default impls cannot be done with const generics because `[T; 0]` doesn't
502// require Default to be implemented, and having different impl blocks for
503// different numbers isn't supported yet.
504//
505// Trying to improve the `[T; 0]` situation has proven to be difficult.
506// Please see these issues for more context on past attempts and crater runs:
507// - https://github.com/rust-lang/rust/issues/61415
508// - https://github.com/rust-lang/rust/pull/145457
509
510macro_rules! array_impl_default {
511 {$n:expr, $t:ident $($ts:ident)*} => {
512 #[stable(since = "1.4.0", feature = "array_default")]
513 impl<T> Default for [T; $n] where T: Default {
514 fn default() -> [T; $n] {
515 [$t::default(), $($ts::default()),*]
516 }
517 }
518 array_impl_default!{($n - 1), $($ts)*}
519 };
520 {$n:expr,} => {
521 #[stable(since = "1.4.0", feature = "array_default")]
522 impl<T> Default for [T; $n] {
523 fn default() -> [T; $n] { [] }
524 }
525 };
526}
527
528array_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}
529
530impl<T, const N: usize> [T; N] {
531 /// Returns an array of the same size as `self`, with function `f` applied to each element
532 /// in order.
533 ///
534 /// If you don't necessarily need a new fixed-size array, consider using
535 /// [`Iterator::map`] instead.
536 ///
537 ///
538 /// # Note on performance and stack usage
539 ///
540 /// Note that this method is *eager*. It evaluates `f` all `N` times before
541 /// returning the new array.
542 ///
543 /// That means that `arr.map(f).map(g)` is, in general, *not* equivalent to
544 /// `array.map(|x| g(f(x)))`, as the former calls `f` 4 times then `g` 4 times,
545 /// whereas the latter interleaves the calls (`fgfgfgfg`).
546 ///
547 /// A consequence of this is that it can have fairly-high stack usage, especially
548 /// in debug mode or for long arrays. The backend may be able to optimize it
549 /// away, but especially for complicated mappings it might not be able to.
550 ///
551 /// If you're doing a one-step `map` and really want an array as the result,
552 /// then absolutely use this method. Its implementation uses a bunch of tricks
553 /// to help the optimizer handle it well. Particularly for simple arrays,
554 /// like `[u8; 3]` or `[f32; 4]`, there's nothing to be concerned about.
555 ///
556 /// However, if you don't actually need an *array* of the results specifically,
557 /// just to process them, then you likely want [`Iterator::map`] instead.
558 ///
559 /// For example, rather than doing an array-to-array map of all the elements
560 /// in the array up-front and only iterating after that completes,
561 ///
562 /// ```
563 /// # let my_array = [1, 2, 3];
564 /// # let f = |x: i32| x + 1;
565 /// for x in my_array.map(f) {
566 /// // ...
567 /// }
568 /// ```
569 ///
570 /// It's often better to use an iterator along the lines of
571 ///
572 /// ```
573 /// # let my_array = [1, 2, 3];
574 /// # let f = |x: i32| x + 1;
575 /// for x in my_array.into_iter().map(f) {
576 /// // ...
577 /// }
578 /// ```
579 ///
580 /// as that's more likely to avoid large temporaries.
581 ///
582 ///
583 /// # Examples
584 ///
585 /// ```
586 /// let x = [1, 2, 3];
587 /// let y = x.map(|v| v + 1);
588 /// assert_eq!(y, [2, 3, 4]);
589 ///
590 /// let x = [1, 2, 3];
591 /// let mut temp = 0;
592 /// let y = x.map(|v| { temp += 1; v * temp });
593 /// assert_eq!(y, [1, 4, 9]);
594 ///
595 /// let x = ["Ferris", "Bueller's", "Day", "Off"];
596 /// let y = x.map(|v| v.len());
597 /// assert_eq!(y, [6, 9, 3, 3]);
598 /// ```
599 #[must_use]
600 #[stable(feature = "array_map", since = "1.55.0")]
601 #[rustc_const_unstable(feature = "const_array", issue = "147606")]
602 #[ferrocene::prevalidated]
603 pub const fn map<F, U>(self, f: F) -> [U; N]
604 where
605 F: [const] FnMut(T) -> U + [const] Destruct,
606 U: [const] Destruct,
607 T: [const] Destruct,
608 {
609 self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
610 }
611
612 /// A fallible function `f` applied to each element on array `self` in order to
613 /// return an array the same size as `self` or the first error encountered.
614 ///
615 /// The return type of this function depends on the return type of the closure.
616 /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
617 /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
618 ///
619 /// # Examples
620 ///
621 /// ```
622 /// #![feature(array_try_map)]
623 ///
624 /// let a = ["1", "2", "3"];
625 /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
626 /// assert_eq!(b, [2, 3, 4]);
627 ///
628 /// let a = ["1", "2a", "3"];
629 /// let b = a.try_map(|v| v.parse::<u32>());
630 /// assert!(b.is_err());
631 ///
632 /// use std::num::NonZero;
633 ///
634 /// let z = [1, 2, 0, 3, 4];
635 /// assert_eq!(z.try_map(NonZero::new), None);
636 ///
637 /// let a = [1, 2, 3];
638 /// let b = a.try_map(NonZero::new);
639 /// let c = b.map(|x| x.map(NonZero::get));
640 /// assert_eq!(c, Some(a));
641 /// ```
642 #[unstable(feature = "array_try_map", issue = "79711")]
643 #[rustc_const_unstable(feature = "array_try_map", issue = "79711")]
644 #[ferrocene::prevalidated]
645 pub const fn try_map<R>(
646 self,
647 mut f: impl [const] FnMut(T) -> R + [const] Destruct,
648 ) -> ChangeOutputType<R, [R::Output; N]>
649 where
650 R: [const] Try<Residual: [const] Residual<[R::Output; N]>, Output: [const] Destruct>,
651 T: [const] Destruct,
652 {
653 let mut me = ManuallyDrop::new(self);
654 // SAFETY: try_from_fn calls `f` N times.
655 let mut f = unsafe { drain::Drain::new(&mut me, &mut f) };
656 try_from_fn(&mut f)
657 }
658
659 /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
660 #[stable(feature = "array_as_slice", since = "1.57.0")]
661 #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
662 #[ferrocene::prevalidated]
663 pub const fn as_slice(&self) -> &[T] {
664 self
665 }
666
667 /// Returns a mutable slice containing the entire array. Equivalent to
668 /// `&mut s[..]`.
669 #[stable(feature = "array_as_slice", since = "1.57.0")]
670 #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "1.89.0")]
671 #[ferrocene::prevalidated]
672 pub const fn as_mut_slice(&mut self) -> &mut [T] {
673 self
674 }
675
676 /// Borrows each element and returns an array of references with the same
677 /// size as `self`.
678 ///
679 ///
680 /// # Example
681 ///
682 /// ```
683 /// let floats = [3.1, 2.7, -1.0];
684 /// let float_refs: [&f64; 3] = floats.each_ref();
685 /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
686 /// ```
687 ///
688 /// This method is particularly useful if combined with other methods, like
689 /// [`map`](#method.map). This way, you can avoid moving the original
690 /// array if its elements are not [`Copy`].
691 ///
692 /// ```
693 /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
694 /// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
695 /// assert_eq!(is_ascii, [true, false, true]);
696 ///
697 /// // We can still access the original array: it has not been moved.
698 /// assert_eq!(strings.len(), 3);
699 /// ```
700 #[stable(feature = "array_methods", since = "1.77.0")]
701 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
702 pub const fn each_ref(&self) -> [&T; N] {
703 let mut buf = [null::<T>(); N];
704
705 // 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.
706 let mut i = 0;
707 while i < N {
708 buf[i] = &raw const self[i];
709
710 i += 1;
711 }
712
713 // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.
714 unsafe { transmute_unchecked(buf) }
715 }
716
717 /// Borrows each element mutably and returns an array of mutable references
718 /// with the same size as `self`.
719 ///
720 ///
721 /// # Example
722 ///
723 /// ```
724 ///
725 /// let mut floats = [3.1, 2.7, -1.0];
726 /// let float_refs: [&mut f64; 3] = floats.each_mut();
727 /// *float_refs[0] = 0.0;
728 /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
729 /// assert_eq!(floats, [0.0, 2.7, -1.0]);
730 /// ```
731 #[stable(feature = "array_methods", since = "1.77.0")]
732 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
733 pub const fn each_mut(&mut self) -> [&mut T; N] {
734 let mut buf = [null_mut::<T>(); N];
735
736 // 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.
737 let mut i = 0;
738 while i < N {
739 buf[i] = &raw mut self[i];
740
741 i += 1;
742 }
743
744 // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.
745 unsafe { transmute_unchecked(buf) }
746 }
747
748 /// Divides one array reference into two at an index.
749 ///
750 /// The first will contain all indices from `[0, M)` (excluding
751 /// the index `M` itself) and the second will contain all
752 /// indices from `[M, N)` (excluding the index `N` itself).
753 ///
754 /// # Panics
755 ///
756 /// Panics if `M > N`.
757 ///
758 /// # Examples
759 ///
760 /// ```
761 /// #![feature(split_array)]
762 ///
763 /// let v = [1, 2, 3, 4, 5, 6];
764 ///
765 /// {
766 /// let (left, right) = v.split_array_ref::<0>();
767 /// assert_eq!(left, &[]);
768 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
769 /// }
770 ///
771 /// {
772 /// let (left, right) = v.split_array_ref::<2>();
773 /// assert_eq!(left, &[1, 2]);
774 /// assert_eq!(right, &[3, 4, 5, 6]);
775 /// }
776 ///
777 /// {
778 /// let (left, right) = v.split_array_ref::<6>();
779 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
780 /// assert_eq!(right, &[]);
781 /// }
782 /// ```
783 #[unstable(
784 feature = "split_array",
785 reason = "return type should have array as 2nd element",
786 issue = "90091"
787 )]
788 #[inline]
789 pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
790 self.split_first_chunk::<M>().unwrap()
791 }
792
793 /// Divides one mutable array reference into two at an index.
794 ///
795 /// The first will contain all indices from `[0, M)` (excluding
796 /// the index `M` itself) and the second will contain all
797 /// indices from `[M, N)` (excluding the index `N` itself).
798 ///
799 /// # Panics
800 ///
801 /// Panics if `M > N`.
802 ///
803 /// # Examples
804 ///
805 /// ```
806 /// #![feature(split_array)]
807 ///
808 /// let mut v = [1, 0, 3, 0, 5, 6];
809 /// let (left, right) = v.split_array_mut::<2>();
810 /// assert_eq!(left, &mut [1, 0][..]);
811 /// assert_eq!(right, &mut [3, 0, 5, 6]);
812 /// left[1] = 2;
813 /// right[1] = 4;
814 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
815 /// ```
816 #[unstable(
817 feature = "split_array",
818 reason = "return type should have array as 2nd element",
819 issue = "90091"
820 )]
821 #[inline]
822 pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
823 self.split_first_chunk_mut::<M>().unwrap()
824 }
825
826 /// Divides one array reference into two at an index from the end.
827 ///
828 /// The first will contain all indices from `[0, N - M)` (excluding
829 /// the index `N - M` itself) and the second will contain all
830 /// indices from `[N - M, N)` (excluding the index `N` itself).
831 ///
832 /// # Panics
833 ///
834 /// Panics if `M > N`.
835 ///
836 /// # Examples
837 ///
838 /// ```
839 /// #![feature(split_array)]
840 ///
841 /// let v = [1, 2, 3, 4, 5, 6];
842 ///
843 /// {
844 /// let (left, right) = v.rsplit_array_ref::<0>();
845 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
846 /// assert_eq!(right, &[]);
847 /// }
848 ///
849 /// {
850 /// let (left, right) = v.rsplit_array_ref::<2>();
851 /// assert_eq!(left, &[1, 2, 3, 4]);
852 /// assert_eq!(right, &[5, 6]);
853 /// }
854 ///
855 /// {
856 /// let (left, right) = v.rsplit_array_ref::<6>();
857 /// assert_eq!(left, &[]);
858 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
859 /// }
860 /// ```
861 #[unstable(
862 feature = "split_array",
863 reason = "return type should have array as 2nd element",
864 issue = "90091"
865 )]
866 #[inline]
867 pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
868 self.split_last_chunk::<M>().unwrap()
869 }
870
871 /// Divides one mutable array reference into two at an index from the end.
872 ///
873 /// The first will contain all indices from `[0, N - M)` (excluding
874 /// the index `N - M` itself) and the second will contain all
875 /// indices from `[N - M, N)` (excluding the index `N` itself).
876 ///
877 /// # Panics
878 ///
879 /// Panics if `M > N`.
880 ///
881 /// # Examples
882 ///
883 /// ```
884 /// #![feature(split_array)]
885 ///
886 /// let mut v = [1, 0, 3, 0, 5, 6];
887 /// let (left, right) = v.rsplit_array_mut::<4>();
888 /// assert_eq!(left, &mut [1, 0]);
889 /// assert_eq!(right, &mut [3, 0, 5, 6][..]);
890 /// left[1] = 2;
891 /// right[1] = 4;
892 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
893 /// ```
894 #[unstable(
895 feature = "split_array",
896 reason = "return type should have array as 2nd element",
897 issue = "90091"
898 )]
899 #[inline]
900 pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
901 self.split_last_chunk_mut::<M>().unwrap()
902 }
903}
904
905/// Populate an array from the first `N` elements of `iter`
906///
907/// # Panics
908///
909/// If the iterator doesn't actually have enough items.
910///
911/// By depending on `TrustedLen`, however, we can do that check up-front (where
912/// it easily optimizes away) so it doesn't impact the loop that fills the array.
913#[inline]
914#[ferrocene::prevalidated]
915fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
916 try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
917}
918
919#[inline]
920#[ferrocene::prevalidated]
921fn try_from_trusted_iterator<T, R, const N: usize>(
922 iter: impl UncheckedIterator<Item = R>,
923) -> ChangeOutputType<R, [T; N]>
924where
925 R: Try<Output = T>,
926 R::Residual: Residual<[T; N]>,
927{
928 assert!(iter.size_hint().0 >= N);
929 #[ferrocene::prevalidated]
930 fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
931 move |_| {
932 // SAFETY: We know that `from_fn` will call this at most N times,
933 // and we checked to ensure that we have at least that many items.
934 unsafe { iter.next_unchecked() }
935 }
936 }
937
938 try_from_fn(next(iter))
939}
940
941/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
942/// needing to monomorphize for every array length.
943///
944/// This takes a generator rather than an iterator so that *at the type level*
945/// it never needs to worry about running out of items. When combined with
946/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
947/// it to optimize well.
948///
949/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
950/// function that does the union of both things, but last time it was that way
951/// it resulted in poor codegen from the "are there enough source items?" checks
952/// not optimizing away. So if you give it a shot, make sure to watch what
953/// happens in the codegen tests.
954#[inline]
955#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
956#[ferrocene::prevalidated]
957const fn try_from_fn_erased<R: [const] Try<Output: [const] Destruct>>(
958 buffer: &mut [MaybeUninit<R::Output>],
959 mut generator: impl [const] FnMut(usize) -> R + [const] Destruct,
960) -> ControlFlow<R::Residual> {
961 let mut guard = Guard { array_mut: buffer, initialized: 0 };
962
963 while guard.initialized < guard.array_mut.len() {
964 let item = generator(guard.initialized).branch()?;
965
966 // SAFETY: The loop condition ensures we have space to push the item
967 unsafe { guard.push_unchecked(item) };
968 }
969
970 mem::forget(guard);
971 ControlFlow::Continue(())
972}
973
974/// Panic guard for incremental initialization of arrays.
975///
976/// Disarm the guard with `mem::forget` once the array has been initialized.
977///
978/// # Safety
979///
980/// All write accesses to this structure are unsafe and must maintain a correct
981/// count of `initialized` elements.
982///
983/// To minimize indirection, fields are still pub but callers should at least use
984/// `push_unchecked` to signal that something unsafe is going on.
985#[ferrocene::prevalidated]
986struct Guard<'a, T> {
987 /// The array to be initialized.
988 pub array_mut: &'a mut [MaybeUninit<T>],
989 /// The number of items that have been initialized so far.
990 pub initialized: usize,
991}
992
993impl<T> Guard<'_, T> {
994 /// Adds an item to the array and updates the initialized item counter.
995 ///
996 /// # Safety
997 ///
998 /// No more than N elements must be initialized.
999 #[inline]
1000 #[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
1001 #[ferrocene::prevalidated]
1002 pub(crate) const unsafe fn push_unchecked(&mut self, item: T) {
1003 // SAFETY: If `initialized` was correct before and the caller does not
1004 // invoke this method more than N times, then writes will be in-bounds
1005 // and slots will not be initialized more than once.
1006 unsafe {
1007 self.array_mut.get_unchecked_mut(self.initialized).write(item);
1008 self.initialized = self.initialized.unchecked_add(1);
1009 }
1010 }
1011}
1012
1013#[rustc_const_unstable(feature = "array_try_from_fn", issue = "89379")]
1014impl<T: [const] Destruct> const Drop for Guard<'_, T> {
1015 #[inline]
1016 #[ferrocene::prevalidated]
1017 fn drop(&mut self) {
1018 debug_assert!(self.initialized <= self.array_mut.len());
1019 // SAFETY: this slice will contain only initialized objects.
1020 unsafe {
1021 self.array_mut.get_unchecked_mut(..self.initialized).assume_init_drop();
1022 }
1023 }
1024}
1025
1026/// Pulls `N` items from `iter` and returns them as an array. If the iterator
1027/// yields fewer than `N` items, `Err` is returned containing an iterator over
1028/// the already yielded items.
1029///
1030/// Since the iterator is passed as a mutable reference and this function calls
1031/// `next` at most `N` times, the iterator can still be used afterwards to
1032/// retrieve the remaining items.
1033///
1034/// If `iter.next()` panics, all items already yielded by the iterator are
1035/// dropped.
1036///
1037/// Used for [`Iterator::next_chunk`].
1038#[inline]
1039pub(crate) fn iter_next_chunk<T, const N: usize>(
1040 iter: &mut impl Iterator<Item = T>,
1041) -> Result<[T; N], IntoIter<T, N>> {
1042 let mut array = [const { MaybeUninit::uninit() }; N];
1043 let r = iter_next_chunk_erased(&mut array, iter);
1044 match r {
1045 Ok(()) => {
1046 // SAFETY: All elements of `array` were populated.
1047 Ok(unsafe { MaybeUninit::array_assume_init(array) })
1048 }
1049 Err(initialized) => {
1050 // SAFETY: Only the first `initialized` elements were populated
1051 Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
1052 }
1053 }
1054}
1055
1056/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
1057/// needing to monomorphize for every array length.
1058///
1059/// Unfortunately this loop has two exit conditions, the buffer filling up
1060/// or the iterator running out of items, making it tend to optimize poorly.
1061#[inline]
1062fn iter_next_chunk_erased<T>(
1063 buffer: &mut [MaybeUninit<T>],
1064 iter: &mut impl Iterator<Item = T>,
1065) -> Result<(), usize> {
1066 // if `Iterator::next` panics, this guard will drop already initialized items
1067 let mut guard = Guard { array_mut: buffer, initialized: 0 };
1068 while guard.initialized < guard.array_mut.len() {
1069 let Some(item) = iter.next() else {
1070 // Unlike `try_from_fn_erased`, we want to keep the partial results,
1071 // so we need to defuse the guard instead of using `?`.
1072 let initialized = guard.initialized;
1073 mem::forget(guard);
1074 return Err(initialized);
1075 };
1076
1077 // SAFETY: The loop condition ensures we have space to push the item
1078 unsafe { guard.push_unchecked(item) };
1079 }
1080
1081 mem::forget(guard);
1082 Ok(())
1083}
1084
1085/// Ferrocene addition: Hidden module to test crate-internal functionality
1086#[doc(hidden)]
1087#[unstable(feature = "ferrocene_test", issue = "none")]
1088pub mod ferrocene_test;