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
7#[cfg(not(feature = "ferrocene_certified"))]
8use crate::borrow::{Borrow, BorrowMut};
9#[cfg(not(feature = "ferrocene_certified"))]
10use crate::cmp::Ordering;
11#[cfg(not(feature = "ferrocene_certified"))]
12use crate::convert::Infallible;
13#[cfg(not(feature = "ferrocene_certified"))]
14use crate::error::Error;
15#[cfg(not(feature = "ferrocene_certified"))]
16use crate::fmt;
17#[cfg(not(feature = "ferrocene_certified"))]
18use crate::hash::{self, Hash};
19#[cfg(not(feature = "ferrocene_certified"))]
20use crate::intrinsics::transmute_unchecked;
21#[cfg(not(feature = "ferrocene_certified"))]
22use crate::iter::{UncheckedIterator, repeat_n};
23use crate::mem::{self, MaybeUninit};
24use crate::ops::{
25 ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
26};
27#[cfg(not(feature = "ferrocene_certified"))]
28use crate::ptr::{null, null_mut};
29use crate::slice::{Iter, IterMut};
30
31// Ferrocene addition: imports for certified subset
32#[cfg(feature = "ferrocene_certified")]
33#[rustfmt::skip]
34use crate::iter::UncheckedIterator;
35
36#[cfg(not(feature = "ferrocene_certified"))]
37mod ascii;
38#[cfg(not(feature = "ferrocene_certified"))]
39mod drain;
40mod equality;
41mod iter;
42
43#[cfg(not(feature = "ferrocene_certified"))]
44pub(crate) use drain::drain_array_with;
45#[stable(feature = "array_value_iter", since = "1.51.0")]
46pub use iter::IntoIter;
47
48/// Creates an array of type `[T; N]` by repeatedly cloning a value.
49///
50/// This is the same as `[val; N]`, but it also works for types that do not
51/// implement [`Copy`].
52///
53/// The provided value will be used as an element of the resulting array and
54/// will be cloned N - 1 times to fill up the rest. If N is zero, the value
55/// will be dropped.
56///
57/// # Example
58///
59/// Creating multiple copies of a `String`:
60/// ```rust
61/// use std::array;
62///
63/// let string = "Hello there!".to_string();
64/// let strings = array::repeat(string);
65/// assert_eq!(strings, ["Hello there!", "Hello there!"]);
66/// ```
67#[inline]
68#[must_use = "cloning is often expensive and is not expected to have side effects"]
69#[stable(feature = "array_repeat", since = "1.91.0")]
70#[cfg(not(feature = "ferrocene_certified"))]
71pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {
72 from_trusted_iterator(repeat_n(val, N))
73}
74
75/// Creates an array where each element is produced by calling `f` with
76/// that element's index while walking forward through the array.
77///
78/// This is essentially the same as writing
79/// ```text
80/// [f(0), f(1), f(2), …, f(N - 2), f(N - 1)]
81/// ```
82/// and is similar to `(0..i).map(f)`, just for arrays not iterators.
83///
84/// If `N == 0`, this produces an empty array without ever calling `f`.
85///
86/// # Example
87///
88/// ```rust
89/// // type inference is helping us here, the way `from_fn` knows how many
90/// // elements to produce is the length of array down there: only arrays of
91/// // equal lengths can be compared, so the const generic parameter `N` is
92/// // inferred to be 5, thus creating array of 5 elements.
93///
94/// let array = core::array::from_fn(|i| i);
95/// // indexes are: 0 1 2 3 4
96/// assert_eq!(array, [0, 1, 2, 3, 4]);
97///
98/// let array2: [usize; 8] = core::array::from_fn(|i| i * 2);
99/// // indexes are: 0 1 2 3 4 5 6 7
100/// assert_eq!(array2, [0, 2, 4, 6, 8, 10, 12, 14]);
101///
102/// let bool_arr = core::array::from_fn::<_, 5, _>(|i| i % 2 == 0);
103/// // indexes are: 0 1 2 3 4
104/// assert_eq!(bool_arr, [true, false, true, false, true]);
105/// ```
106///
107/// You can also capture things, for example to create an array full of clones
108/// where you can't just use `[item; N]` because it's not `Copy`:
109/// ```
110/// # // TBH `array::repeat` would be better for this, but it's not stable yet.
111/// let my_string = String::from("Hello");
112/// let clones: [String; 42] = std::array::from_fn(|_| my_string.clone());
113/// assert!(clones.iter().all(|x| *x == my_string));
114/// ```
115///
116/// The array is generated in ascending index order, starting from the front
117/// and going towards the back, so you can use closures with mutable state:
118/// ```
119/// let mut state = 1;
120/// let a = std::array::from_fn(|_| { let x = state; state *= 2; x });
121/// assert_eq!(a, [1, 2, 4, 8, 16, 32]);
122/// ```
123#[inline]
124#[stable(feature = "array_from_fn", since = "1.63.0")]
125pub fn from_fn<T, const N: usize, F>(f: F) -> [T; N]
126where
127 F: FnMut(usize) -> T,
128{
129 try_from_fn(NeverShortCircuit::wrap_mut_1(f)).0
130}
131
132/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
133/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error
134/// if any element creation was unsuccessful.
135///
136/// The return type of this function depends on the return type of the closure.
137/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
138/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
139///
140/// # Arguments
141///
142/// * `cb`: Callback where the passed argument is the current array index.
143///
144/// # Example
145///
146/// ```rust
147/// #![feature(array_try_from_fn)]
148///
149/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
150/// assert_eq!(array, Ok([0, 1, 2, 3, 4]));
151///
152/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
153/// assert!(array.is_err());
154///
155/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
156/// assert_eq!(array, Some([100, 101, 102, 103]));
157///
158/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
159/// assert_eq!(array, None);
160/// ```
161#[inline]
162#[unstable(feature = "array_try_from_fn", issue = "89379")]
163pub fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]>
164where
165 F: FnMut(usize) -> R,
166 R: Try,
167 R::Residual: Residual<[R::Output; N]>,
168{
169 let mut array = [const { MaybeUninit::uninit() }; N];
170 match try_from_fn_erased(&mut array, cb) {
171 ControlFlow::Break(r) => FromResidual::from_residual(r),
172 ControlFlow::Continue(()) => {
173 // SAFETY: All elements of the array were populated.
174 try { unsafe { MaybeUninit::array_assume_init(array) } }
175 }
176 }
177}
178
179/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
180#[stable(feature = "array_from_ref", since = "1.53.0")]
181#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
182pub const fn from_ref<T>(s: &T) -> &[T; 1] {
183 // SAFETY: Converting `&T` to `&[T; 1]` is sound.
184 unsafe { &*(s as *const T).cast::<[T; 1]>() }
185}
186
187/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
188#[stable(feature = "array_from_ref", since = "1.53.0")]
189#[rustc_const_stable(feature = "const_array_from_ref", since = "1.83.0")]
190pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
191 // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
192 unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
193}
194
195/// The error type returned when a conversion from a slice to an array fails.
196#[stable(feature = "try_from", since = "1.34.0")]
197#[cfg_attr(not(feature = "ferrocene_certified"), derive(Debug, Copy, Clone))]
198pub struct TryFromSliceError(());
199
200#[stable(feature = "core_array", since = "1.35.0")]
201#[cfg(not(feature = "ferrocene_certified"))]
202impl fmt::Display for TryFromSliceError {
203 #[inline]
204 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
205 "could not convert slice to array".fmt(f)
206 }
207}
208
209#[stable(feature = "try_from", since = "1.34.0")]
210#[cfg(not(feature = "ferrocene_certified"))]
211impl Error for TryFromSliceError {}
212
213#[stable(feature = "try_from_slice_error", since = "1.36.0")]
214#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
215#[cfg(not(feature = "ferrocene_certified"))]
216impl const From<Infallible> for TryFromSliceError {
217 fn from(x: Infallible) -> TryFromSliceError {
218 match x {}
219 }
220}
221
222#[stable(feature = "rust1", since = "1.0.0")]
223#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
224impl<T, const N: usize> const AsRef<[T]> for [T; N] {
225 #[inline]
226 fn as_ref(&self) -> &[T] {
227 &self[..]
228 }
229}
230
231#[stable(feature = "rust1", since = "1.0.0")]
232#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
233#[cfg(not(feature = "ferrocene_certified"))]
234impl<T, const N: usize> const AsMut<[T]> for [T; N] {
235 #[inline]
236 fn as_mut(&mut self) -> &mut [T] {
237 &mut self[..]
238 }
239}
240
241#[stable(feature = "array_borrow", since = "1.4.0")]
242#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
243#[cfg(not(feature = "ferrocene_certified"))]
244impl<T, const N: usize> const Borrow<[T]> for [T; N] {
245 fn borrow(&self) -> &[T] {
246 self
247 }
248}
249
250#[stable(feature = "array_borrow", since = "1.4.0")]
251#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
252#[cfg(not(feature = "ferrocene_certified"))]
253impl<T, const N: usize> const BorrowMut<[T]> for [T; N] {
254 fn borrow_mut(&mut self) -> &mut [T] {
255 self
256 }
257}
258
259/// Tries to create an array `[T; N]` by copying from a slice `&[T]`.
260/// Succeeds if `slice.len() == N`.
261///
262/// ```
263/// let bytes: [u8; 3] = [1, 0, 2];
264///
265/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
266/// assert_eq!(1, u16::from_le_bytes(bytes_head));
267///
268/// let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
269/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
270/// ```
271#[stable(feature = "try_from", since = "1.34.0")]
272#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
273impl<T, const N: usize> const TryFrom<&[T]> for [T; N]
274where
275 T: Copy,
276{
277 type Error = TryFromSliceError;
278
279 #[inline]
280 fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
281 <&Self>::try_from(slice).copied()
282 }
283}
284
285/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
286/// Succeeds if `slice.len() == N`.
287///
288/// ```
289/// let mut bytes: [u8; 3] = [1, 0, 2];
290///
291/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
292/// assert_eq!(1, u16::from_le_bytes(bytes_head));
293///
294/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
295/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
296/// ```
297#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
298#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
299impl<T, const N: usize> const TryFrom<&mut [T]> for [T; N]
300where
301 T: Copy,
302{
303 type Error = TryFromSliceError;
304
305 #[inline]
306 fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
307 <Self>::try_from(&*slice)
308 }
309}
310
311/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
312/// `slice.len() == N`.
313///
314/// ```
315/// let bytes: [u8; 3] = [1, 0, 2];
316///
317/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
318/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
319///
320/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
321/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
322/// ```
323#[stable(feature = "try_from", since = "1.34.0")]
324#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
325impl<'a, T, const N: usize> const TryFrom<&'a [T]> for &'a [T; N] {
326 type Error = TryFromSliceError;
327
328 #[inline]
329 fn try_from(slice: &'a [T]) -> Result<&'a [T; N], TryFromSliceError> {
330 slice.as_array().ok_or(TryFromSliceError(()))
331 }
332}
333
334/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
335/// `&mut [T]`. Succeeds if `slice.len() == N`.
336///
337/// ```
338/// let mut bytes: [u8; 3] = [1, 0, 2];
339///
340/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
341/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
342///
343/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
344/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
345/// ```
346#[stable(feature = "try_from", since = "1.34.0")]
347#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
348impl<'a, T, const N: usize> const TryFrom<&'a mut [T]> for &'a mut [T; N] {
349 type Error = TryFromSliceError;
350
351 #[inline]
352 fn try_from(slice: &'a mut [T]) -> Result<&'a mut [T; N], TryFromSliceError> {
353 slice.as_mut_array().ok_or(TryFromSliceError(()))
354 }
355}
356
357/// The hash of an array is the same as that of the corresponding slice,
358/// as required by the `Borrow` implementation.
359///
360/// ```
361/// use std::hash::BuildHasher;
362///
363/// let b = std::hash::RandomState::new();
364/// let a: [u8; 3] = [0xa8, 0x3c, 0x09];
365/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
366/// assert_eq!(b.hash_one(a), b.hash_one(s));
367/// ```
368#[stable(feature = "rust1", since = "1.0.0")]
369#[cfg(not(feature = "ferrocene_certified"))]
370impl<T: Hash, const N: usize> Hash for [T; N] {
371 fn hash<H: hash::Hasher>(&self, state: &mut H) {
372 Hash::hash(&self[..], state)
373 }
374}
375
376#[stable(feature = "rust1", since = "1.0.0")]
377#[cfg(not(feature = "ferrocene_certified"))]
378impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] {
379 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
380 fmt::Debug::fmt(&&self[..], f)
381 }
382}
383
384#[stable(feature = "rust1", since = "1.0.0")]
385impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
386 type Item = &'a T;
387 type IntoIter = Iter<'a, T>;
388
389 fn into_iter(self) -> Iter<'a, T> {
390 self.iter()
391 }
392}
393
394#[stable(feature = "rust1", since = "1.0.0")]
395impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
396 type Item = &'a mut T;
397 type IntoIter = IterMut<'a, T>;
398
399 fn into_iter(self) -> IterMut<'a, T> {
400 self.iter_mut()
401 }
402}
403
404#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
405#[rustc_const_unstable(feature = "const_index", issue = "143775")]
406impl<T, I, const N: usize> const Index<I> for [T; N]
407where
408 [T]: [const] Index<I>,
409{
410 type Output = <[T] as Index<I>>::Output;
411
412 #[inline]
413 fn index(&self, index: I) -> &Self::Output {
414 Index::index(self as &[T], index)
415 }
416}
417
418#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
419#[rustc_const_unstable(feature = "const_index", issue = "143775")]
420impl<T, I, const N: usize> const IndexMut<I> for [T; N]
421where
422 [T]: [const] IndexMut<I>,
423{
424 #[inline]
425 fn index_mut(&mut self, index: I) -> &mut Self::Output {
426 IndexMut::index_mut(self as &mut [T], index)
427 }
428}
429
430/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
431#[stable(feature = "rust1", since = "1.0.0")]
432// blocked by PartialOrd
433#[cfg(not(feature = "ferrocene_certified"))]
434impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] {
435 #[inline]
436 fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> {
437 PartialOrd::partial_cmp(&&self[..], &&other[..])
438 }
439 #[inline]
440 fn lt(&self, other: &[T; N]) -> bool {
441 PartialOrd::lt(&&self[..], &&other[..])
442 }
443 #[inline]
444 fn le(&self, other: &[T; N]) -> bool {
445 PartialOrd::le(&&self[..], &&other[..])
446 }
447 #[inline]
448 fn ge(&self, other: &[T; N]) -> bool {
449 PartialOrd::ge(&&self[..], &&other[..])
450 }
451 #[inline]
452 fn gt(&self, other: &[T; N]) -> bool {
453 PartialOrd::gt(&&self[..], &&other[..])
454 }
455}
456
457/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
458#[stable(feature = "rust1", since = "1.0.0")]
459#[cfg(not(feature = "ferrocene_certified"))]
460impl<T: Ord, const N: usize> Ord for [T; N] {
461 #[inline]
462 fn cmp(&self, other: &[T; N]) -> Ordering {
463 Ord::cmp(&&self[..], &&other[..])
464 }
465}
466
467#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
468impl<T: Copy, const N: usize> Copy for [T; N] {}
469
470#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
471impl<T: Clone, const N: usize> Clone for [T; N] {
472 #[inline]
473 fn clone(&self) -> Self {
474 SpecArrayClone::clone(self)
475 }
476
477 #[inline]
478 #[cfg(not(feature = "ferrocene_certified"))]
479 fn clone_from(&mut self, other: &Self) {
480 self.clone_from_slice(other);
481 }
482}
483
484trait SpecArrayClone: Clone {
485 fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
486}
487
488impl<T: Clone> SpecArrayClone for T {
489 #[inline]
490 default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
491 from_trusted_iterator(array.iter().cloned())
492 }
493}
494
495impl<T: Copy> SpecArrayClone for T {
496 #[inline]
497 fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
498 *array
499 }
500}
501
502// The Default impls cannot be done with const generics because `[T; 0]` doesn't
503// require Default to be implemented, and having different impl blocks for
504// different numbers isn't supported yet.
505//
506// Trying to improve the `[T; 0]` situation has proven to be difficult.
507// Please see these issues for more context on past attempts and crater runs:
508// - https://github.com/rust-lang/rust/issues/61415
509// - https://github.com/rust-lang/rust/pull/145457
510
511#[cfg(not(feature = "ferrocene_certified"))]
512macro_rules! array_impl_default {
513 {$n:expr, $t:ident $($ts:ident)*} => {
514 #[stable(since = "1.4.0", feature = "array_default")]
515 impl<T> Default for [T; $n] where T: Default {
516 fn default() -> [T; $n] {
517 [$t::default(), $($ts::default()),*]
518 }
519 }
520 array_impl_default!{($n - 1), $($ts)*}
521 };
522 {$n:expr,} => {
523 #[stable(since = "1.4.0", feature = "array_default")]
524 impl<T> Default for [T; $n] {
525 fn default() -> [T; $n] { [] }
526 }
527 };
528}
529
530#[cfg(not(feature = "ferrocene_certified"))]
531array_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}
532
533impl<T, const N: usize> [T; N] {
534 /// Returns an array of the same size as `self`, with function `f` applied to each element
535 /// in order.
536 ///
537 /// If you don't necessarily need a new fixed-size array, consider using
538 /// [`Iterator::map`] instead.
539 ///
540 ///
541 /// # Note on performance and stack usage
542 ///
543 /// Unfortunately, usages of this method are currently not always optimized
544 /// as well as they could be. This mainly concerns large arrays, as mapping
545 /// over small arrays seem to be optimized just fine. Also note that in
546 /// debug mode (i.e. without any optimizations), this method can use a lot
547 /// of stack space (a few times the size of the array or more).
548 ///
549 /// Therefore, in performance-critical code, try to avoid using this method
550 /// on large arrays or check the emitted code. Also try to avoid chained
551 /// maps (e.g. `arr.map(...).map(...)`).
552 ///
553 /// In many cases, you can instead use [`Iterator::map`] by calling `.iter()`
554 /// or `.into_iter()` on your array. `[T; N]::map` is only necessary if you
555 /// really need a new array of the same size as the result. Rust's lazy
556 /// iterators tend to get optimized very well.
557 ///
558 ///
559 /// # Examples
560 ///
561 /// ```
562 /// let x = [1, 2, 3];
563 /// let y = x.map(|v| v + 1);
564 /// assert_eq!(y, [2, 3, 4]);
565 ///
566 /// let x = [1, 2, 3];
567 /// let mut temp = 0;
568 /// let y = x.map(|v| { temp += 1; v * temp });
569 /// assert_eq!(y, [1, 4, 9]);
570 ///
571 /// let x = ["Ferris", "Bueller's", "Day", "Off"];
572 /// let y = x.map(|v| v.len());
573 /// assert_eq!(y, [6, 9, 3, 3]);
574 /// ```
575 #[must_use]
576 #[stable(feature = "array_map", since = "1.55.0")]
577 #[cfg(not(feature = "ferrocene_certified"))]
578 pub fn map<F, U>(self, f: F) -> [U; N]
579 where
580 F: FnMut(T) -> U,
581 {
582 self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
583 }
584
585 /// A fallible function `f` applied to each element on array `self` in order to
586 /// return an array the same size as `self` or the first error encountered.
587 ///
588 /// The return type of this function depends on the return type of the closure.
589 /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
590 /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
591 ///
592 /// # Examples
593 ///
594 /// ```
595 /// #![feature(array_try_map)]
596 ///
597 /// let a = ["1", "2", "3"];
598 /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
599 /// assert_eq!(b, [2, 3, 4]);
600 ///
601 /// let a = ["1", "2a", "3"];
602 /// let b = a.try_map(|v| v.parse::<u32>());
603 /// assert!(b.is_err());
604 ///
605 /// use std::num::NonZero;
606 ///
607 /// let z = [1, 2, 0, 3, 4];
608 /// assert_eq!(z.try_map(NonZero::new), None);
609 ///
610 /// let a = [1, 2, 3];
611 /// let b = a.try_map(NonZero::new);
612 /// let c = b.map(|x| x.map(NonZero::get));
613 /// assert_eq!(c, Some(a));
614 /// ```
615 #[unstable(feature = "array_try_map", issue = "79711")]
616 #[cfg(not(feature = "ferrocene_certified"))]
617 pub fn try_map<R>(self, f: impl FnMut(T) -> R) -> ChangeOutputType<R, [R::Output; N]>
618 where
619 R: Try<Residual: Residual<[R::Output; N]>>,
620 {
621 drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f)))
622 }
623
624 /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
625 #[stable(feature = "array_as_slice", since = "1.57.0")]
626 #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
627 pub const fn as_slice(&self) -> &[T] {
628 self
629 }
630
631 /// Returns a mutable slice containing the entire array. Equivalent to
632 /// `&mut s[..]`.
633 #[stable(feature = "array_as_slice", since = "1.57.0")]
634 #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "1.89.0")]
635 pub const fn as_mut_slice(&mut self) -> &mut [T] {
636 self
637 }
638
639 /// Borrows each element and returns an array of references with the same
640 /// size as `self`.
641 ///
642 ///
643 /// # Example
644 ///
645 /// ```
646 /// let floats = [3.1, 2.7, -1.0];
647 /// let float_refs: [&f64; 3] = floats.each_ref();
648 /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
649 /// ```
650 ///
651 /// This method is particularly useful if combined with other methods, like
652 /// [`map`](#method.map). This way, you can avoid moving the original
653 /// array if its elements are not [`Copy`].
654 ///
655 /// ```
656 /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
657 /// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
658 /// assert_eq!(is_ascii, [true, false, true]);
659 ///
660 /// // We can still access the original array: it has not been moved.
661 /// assert_eq!(strings.len(), 3);
662 /// ```
663 #[stable(feature = "array_methods", since = "1.77.0")]
664 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
665 #[cfg(not(feature = "ferrocene_certified"))]
666 pub const fn each_ref(&self) -> [&T; N] {
667 let mut buf = [null::<T>(); N];
668
669 // 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.
670 let mut i = 0;
671 while i < N {
672 buf[i] = &raw const self[i];
673
674 i += 1;
675 }
676
677 // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.
678 unsafe { transmute_unchecked(buf) }
679 }
680
681 /// Borrows each element mutably and returns an array of mutable references
682 /// with the same size as `self`.
683 ///
684 ///
685 /// # Example
686 ///
687 /// ```
688 ///
689 /// let mut floats = [3.1, 2.7, -1.0];
690 /// let float_refs: [&mut f64; 3] = floats.each_mut();
691 /// *float_refs[0] = 0.0;
692 /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
693 /// assert_eq!(floats, [0.0, 2.7, -1.0]);
694 /// ```
695 #[stable(feature = "array_methods", since = "1.77.0")]
696 #[rustc_const_stable(feature = "const_array_each_ref", since = "1.91.0")]
697 #[cfg(not(feature = "ferrocene_certified"))]
698 pub const fn each_mut(&mut self) -> [&mut T; N] {
699 let mut buf = [null_mut::<T>(); N];
700
701 // 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.
702 let mut i = 0;
703 while i < N {
704 buf[i] = &raw mut self[i];
705
706 i += 1;
707 }
708
709 // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.
710 unsafe { transmute_unchecked(buf) }
711 }
712
713 /// Divides one array reference into two at an index.
714 ///
715 /// The first will contain all indices from `[0, M)` (excluding
716 /// the index `M` itself) and the second will contain all
717 /// indices from `[M, N)` (excluding the index `N` itself).
718 ///
719 /// # Panics
720 ///
721 /// Panics if `M > N`.
722 ///
723 /// # Examples
724 ///
725 /// ```
726 /// #![feature(split_array)]
727 ///
728 /// let v = [1, 2, 3, 4, 5, 6];
729 ///
730 /// {
731 /// let (left, right) = v.split_array_ref::<0>();
732 /// assert_eq!(left, &[]);
733 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
734 /// }
735 ///
736 /// {
737 /// let (left, right) = v.split_array_ref::<2>();
738 /// assert_eq!(left, &[1, 2]);
739 /// assert_eq!(right, &[3, 4, 5, 6]);
740 /// }
741 ///
742 /// {
743 /// let (left, right) = v.split_array_ref::<6>();
744 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
745 /// assert_eq!(right, &[]);
746 /// }
747 /// ```
748 #[unstable(
749 feature = "split_array",
750 reason = "return type should have array as 2nd element",
751 issue = "90091"
752 )]
753 #[inline]
754 #[cfg(not(feature = "ferrocene_certified"))]
755 pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
756 self.split_first_chunk::<M>().unwrap()
757 }
758
759 /// Divides one mutable array reference into two at an index.
760 ///
761 /// The first will contain all indices from `[0, M)` (excluding
762 /// the index `M` itself) and the second will contain all
763 /// indices from `[M, N)` (excluding the index `N` itself).
764 ///
765 /// # Panics
766 ///
767 /// Panics if `M > N`.
768 ///
769 /// # Examples
770 ///
771 /// ```
772 /// #![feature(split_array)]
773 ///
774 /// let mut v = [1, 0, 3, 0, 5, 6];
775 /// let (left, right) = v.split_array_mut::<2>();
776 /// assert_eq!(left, &mut [1, 0][..]);
777 /// assert_eq!(right, &mut [3, 0, 5, 6]);
778 /// left[1] = 2;
779 /// right[1] = 4;
780 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
781 /// ```
782 #[unstable(
783 feature = "split_array",
784 reason = "return type should have array as 2nd element",
785 issue = "90091"
786 )]
787 #[inline]
788 #[cfg(not(feature = "ferrocene_certified"))]
789 pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
790 self.split_first_chunk_mut::<M>().unwrap()
791 }
792
793 /// Divides one array reference into two at an index from the end.
794 ///
795 /// The first will contain all indices from `[0, N - M)` (excluding
796 /// the index `N - M` itself) and the second will contain all
797 /// indices from `[N - 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 v = [1, 2, 3, 4, 5, 6];
809 ///
810 /// {
811 /// let (left, right) = v.rsplit_array_ref::<0>();
812 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
813 /// assert_eq!(right, &[]);
814 /// }
815 ///
816 /// {
817 /// let (left, right) = v.rsplit_array_ref::<2>();
818 /// assert_eq!(left, &[1, 2, 3, 4]);
819 /// assert_eq!(right, &[5, 6]);
820 /// }
821 ///
822 /// {
823 /// let (left, right) = v.rsplit_array_ref::<6>();
824 /// assert_eq!(left, &[]);
825 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
826 /// }
827 /// ```
828 #[unstable(
829 feature = "split_array",
830 reason = "return type should have array as 2nd element",
831 issue = "90091"
832 )]
833 #[inline]
834 #[cfg(not(feature = "ferrocene_certified"))]
835 pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
836 self.split_last_chunk::<M>().unwrap()
837 }
838
839 /// Divides one mutable array reference into two at an index from the end.
840 ///
841 /// The first will contain all indices from `[0, N - M)` (excluding
842 /// the index `N - M` itself) and the second will contain all
843 /// indices from `[N - M, N)` (excluding the index `N` itself).
844 ///
845 /// # Panics
846 ///
847 /// Panics if `M > N`.
848 ///
849 /// # Examples
850 ///
851 /// ```
852 /// #![feature(split_array)]
853 ///
854 /// let mut v = [1, 0, 3, 0, 5, 6];
855 /// let (left, right) = v.rsplit_array_mut::<4>();
856 /// assert_eq!(left, &mut [1, 0]);
857 /// assert_eq!(right, &mut [3, 0, 5, 6][..]);
858 /// left[1] = 2;
859 /// right[1] = 4;
860 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
861 /// ```
862 #[unstable(
863 feature = "split_array",
864 reason = "return type should have array as 2nd element",
865 issue = "90091"
866 )]
867 #[inline]
868 #[cfg(not(feature = "ferrocene_certified"))]
869 pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
870 self.split_last_chunk_mut::<M>().unwrap()
871 }
872}
873
874/// Populate an array from the first `N` elements of `iter`
875///
876/// # Panics
877///
878/// If the iterator doesn't actually have enough items.
879///
880/// By depending on `TrustedLen`, however, we can do that check up-front (where
881/// it easily optimizes away) so it doesn't impact the loop that fills the array.
882#[inline]
883fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
884 try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
885}
886
887#[inline]
888fn try_from_trusted_iterator<T, R, const N: usize>(
889 iter: impl UncheckedIterator<Item = R>,
890) -> ChangeOutputType<R, [T; N]>
891where
892 R: Try<Output = T>,
893 R::Residual: Residual<[T; N]>,
894{
895 assert!(iter.size_hint().0 >= N);
896 fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
897 move |_| {
898 // SAFETY: We know that `from_fn` will call this at most N times,
899 // and we checked to ensure that we have at least that many items.
900 unsafe { iter.next_unchecked() }
901 }
902 }
903
904 try_from_fn(next(iter))
905}
906
907/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
908/// needing to monomorphize for every array length.
909///
910/// This takes a generator rather than an iterator so that *at the type level*
911/// it never needs to worry about running out of items. When combined with
912/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
913/// it to optimize well.
914///
915/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
916/// function that does the union of both things, but last time it was that way
917/// it resulted in poor codegen from the "are there enough source items?" checks
918/// not optimizing away. So if you give it a shot, make sure to watch what
919/// happens in the codegen tests.
920#[inline]
921fn try_from_fn_erased<T, R>(
922 buffer: &mut [MaybeUninit<T>],
923 mut generator: impl FnMut(usize) -> R,
924) -> ControlFlow<R::Residual>
925where
926 R: Try<Output = T>,
927{
928 let mut guard = Guard { array_mut: buffer, initialized: 0 };
929
930 while guard.initialized < guard.array_mut.len() {
931 let item = generator(guard.initialized).branch()?;
932
933 // SAFETY: The loop condition ensures we have space to push the item
934 unsafe { guard.push_unchecked(item) };
935 }
936
937 mem::forget(guard);
938 ControlFlow::Continue(())
939}
940
941/// Panic guard for incremental initialization of arrays.
942///
943/// Disarm the guard with `mem::forget` once the array has been initialized.
944///
945/// # Safety
946///
947/// All write accesses to this structure are unsafe and must maintain a correct
948/// count of `initialized` elements.
949///
950/// To minimize indirection fields are still pub but callers should at least use
951/// `push_unchecked` to signal that something unsafe is going on.
952struct Guard<'a, T> {
953 /// The array to be initialized.
954 pub array_mut: &'a mut [MaybeUninit<T>],
955 /// The number of items that have been initialized so far.
956 pub initialized: usize,
957}
958
959impl<T> Guard<'_, T> {
960 /// Adds an item to the array and updates the initialized item counter.
961 ///
962 /// # Safety
963 ///
964 /// No more than N elements must be initialized.
965 #[inline]
966 pub(crate) unsafe fn push_unchecked(&mut self, item: T) {
967 // SAFETY: If `initialized` was correct before and the caller does not
968 // invoke this method more than N times then writes will be in-bounds
969 // and slots will not be initialized more than once.
970 unsafe {
971 self.array_mut.get_unchecked_mut(self.initialized).write(item);
972 self.initialized = self.initialized.unchecked_add(1);
973 }
974 }
975}
976
977impl<T> Drop for Guard<'_, T> {
978 #[inline]
979 fn drop(&mut self) {
980 debug_assert!(self.initialized <= self.array_mut.len());
981
982 // SAFETY: this slice will contain only initialized objects.
983 unsafe {
984 self.array_mut.get_unchecked_mut(..self.initialized).assume_init_drop();
985 }
986 }
987}
988
989/// Pulls `N` items from `iter` and returns them as an array. If the iterator
990/// yields fewer than `N` items, `Err` is returned containing an iterator over
991/// the already yielded items.
992///
993/// Since the iterator is passed as a mutable reference and this function calls
994/// `next` at most `N` times, the iterator can still be used afterwards to
995/// retrieve the remaining items.
996///
997/// If `iter.next()` panicks, all items already yielded by the iterator are
998/// dropped.
999///
1000/// Used for [`Iterator::next_chunk`].
1001#[inline]
1002#[cfg(not(feature = "ferrocene_certified"))]
1003pub(crate) fn iter_next_chunk<T, const N: usize>(
1004 iter: &mut impl Iterator<Item = T>,
1005) -> Result<[T; N], IntoIter<T, N>> {
1006 let mut array = [const { MaybeUninit::uninit() }; N];
1007 let r = iter_next_chunk_erased(&mut array, iter);
1008 match r {
1009 Ok(()) => {
1010 // SAFETY: All elements of `array` were populated.
1011 Ok(unsafe { MaybeUninit::array_assume_init(array) })
1012 }
1013 Err(initialized) => {
1014 // SAFETY: Only the first `initialized` elements were populated
1015 Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
1016 }
1017 }
1018}
1019
1020/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
1021/// needing to monomorphize for every array length.
1022///
1023/// Unfortunately this loop has two exit conditions, the buffer filling up
1024/// or the iterator running out of items, making it tend to optimize poorly.
1025#[inline]
1026#[cfg(not(feature = "ferrocene_certified"))]
1027fn iter_next_chunk_erased<T>(
1028 buffer: &mut [MaybeUninit<T>],
1029 iter: &mut impl Iterator<Item = T>,
1030) -> Result<(), usize> {
1031 let mut guard = Guard { array_mut: buffer, initialized: 0 };
1032 while guard.initialized < guard.array_mut.len() {
1033 let Some(item) = iter.next() else {
1034 // Unlike `try_from_fn_erased`, we want to keep the partial results,
1035 // so we need to defuse the guard instead of using `?`.
1036 let initialized = guard.initialized;
1037 mem::forget(guard);
1038 return Err(initialized);
1039 };
1040
1041 // SAFETY: The loop condition ensures we have space to push the item
1042 unsafe { guard.push_unchecked(item) };
1043 }
1044
1045 mem::forget(guard);
1046 Ok(())
1047}