1 //! Slice management and manipulation.
3 //! For more details see [`std::slice`].
5 //! [`std::slice`]: ../../std/slice/index.html
7 #![stable(feature = "rust1", since = "1.0.0")]
9 use crate::cmp::Ordering::{self, Greater, Less};
11 use crate::intrinsics::{assert_unsafe_precondition, exact_div};
12 use crate::marker::Copy;
13 use crate::mem::{self, SizedTypeProperties};
14 use crate::num::NonZeroUsize;
15 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
16 use crate::option::Option;
17 use crate::option::Option::{None, Some};
19 use crate::result::Result;
20 use crate::result::Result::{Err, Ok};
21 use crate::simd::{self, Simd};
25 feature = "slice_internals",
27 reason = "exposed from core to be reused in std; use the memchr crate"
29 /// Pure rust memchr implementation, taken from rust-memchr
41 #[stable(feature = "rust1", since = "1.0.0")]
42 pub use iter::{Chunks, ChunksMut, Windows};
43 #[stable(feature = "rust1", since = "1.0.0")]
44 pub use iter::{Iter, IterMut};
45 #[stable(feature = "rust1", since = "1.0.0")]
46 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
48 #[stable(feature = "slice_rsplit", since = "1.27.0")]
49 pub use iter::{RSplit, RSplitMut};
51 #[stable(feature = "chunks_exact", since = "1.31.0")]
52 pub use iter::{ChunksExact, ChunksExactMut};
54 #[stable(feature = "rchunks", since = "1.31.0")]
55 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
57 #[unstable(feature = "array_chunks", issue = "74985")]
58 pub use iter::{ArrayChunks, ArrayChunksMut};
60 #[unstable(feature = "array_windows", issue = "75027")]
61 pub use iter::ArrayWindows;
63 #[unstable(feature = "slice_group_by", issue = "80552")]
64 pub use iter::{GroupBy, GroupByMut};
66 #[stable(feature = "split_inclusive", since = "1.51.0")]
67 pub use iter::{SplitInclusive, SplitInclusiveMut};
69 #[stable(feature = "rust1", since = "1.0.0")]
70 pub use raw::{from_raw_parts, from_raw_parts_mut};
72 #[stable(feature = "from_ref", since = "1.28.0")]
73 pub use raw::{from_mut, from_ref};
75 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
76 pub use raw::{from_mut_ptr_range, from_ptr_range};
78 // This function is public only because there is no other way to unit test heapsort.
79 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
80 pub use sort::heapsort;
82 #[stable(feature = "slice_get_slice", since = "1.28.0")]
83 pub use index::SliceIndex;
85 #[unstable(feature = "slice_range", issue = "76393")]
88 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
89 pub use ascii::EscapeAscii;
91 /// Calculates the direction and split point of a one-sided range.
93 /// This is a helper function for `take` and `take_mut` that returns
94 /// the direction of the split (front or back) as well as the index at
95 /// which to split. Returns `None` if the split index would overflow.
97 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
100 Some(match (range.start_bound(), range.end_bound()) {
101 (Unbounded, Excluded(i)) => (Direction::Front, *i),
102 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
103 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
104 (Included(i), Unbounded) => (Direction::Back, *i),
116 /// Returns the number of elements in the slice.
121 /// let a = [1, 2, 3];
122 /// assert_eq!(a.len(), 3);
124 #[lang = "slice_len_fn"]
125 #[stable(feature = "rust1", since = "1.0.0")]
126 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
127 #[rustc_allow_const_fn_unstable(ptr_metadata)]
130 pub const fn len(&self) -> usize {
134 /// Returns `true` if the slice has a length of 0.
139 /// let a = [1, 2, 3];
140 /// assert!(!a.is_empty());
142 #[stable(feature = "rust1", since = "1.0.0")]
143 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
146 pub const fn is_empty(&self) -> bool {
150 /// Returns the first element of the slice, or `None` if it is empty.
155 /// let v = [10, 40, 30];
156 /// assert_eq!(Some(&10), v.first());
158 /// let w: &[i32] = &[];
159 /// assert_eq!(None, w.first());
161 #[stable(feature = "rust1", since = "1.0.0")]
162 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
165 pub const fn first(&self) -> Option<&T> {
166 if let [first, ..] = self { Some(first) } else { None }
169 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
174 /// let x = &mut [0, 1, 2];
176 /// if let Some(first) = x.first_mut() {
179 /// assert_eq!(x, &[5, 1, 2]);
181 #[stable(feature = "rust1", since = "1.0.0")]
182 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
185 pub const fn first_mut(&mut self) -> Option<&mut T> {
186 if let [first, ..] = self { Some(first) } else { None }
189 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
194 /// let x = &[0, 1, 2];
196 /// if let Some((first, elements)) = x.split_first() {
197 /// assert_eq!(first, &0);
198 /// assert_eq!(elements, &[1, 2]);
201 #[stable(feature = "slice_splits", since = "1.5.0")]
202 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
205 pub const fn split_first(&self) -> Option<(&T, &[T])> {
206 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
209 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
214 /// let x = &mut [0, 1, 2];
216 /// if let Some((first, elements)) = x.split_first_mut() {
221 /// assert_eq!(x, &[3, 4, 5]);
223 #[stable(feature = "slice_splits", since = "1.5.0")]
224 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
227 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
228 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
231 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
236 /// let x = &[0, 1, 2];
238 /// if let Some((last, elements)) = x.split_last() {
239 /// assert_eq!(last, &2);
240 /// assert_eq!(elements, &[0, 1]);
243 #[stable(feature = "slice_splits", since = "1.5.0")]
244 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
247 pub const fn split_last(&self) -> Option<(&T, &[T])> {
248 if let [init @ .., last] = self { Some((last, init)) } else { None }
251 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
256 /// let x = &mut [0, 1, 2];
258 /// if let Some((last, elements)) = x.split_last_mut() {
263 /// assert_eq!(x, &[4, 5, 3]);
265 #[stable(feature = "slice_splits", since = "1.5.0")]
266 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
269 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
270 if let [init @ .., last] = self { Some((last, init)) } else { None }
273 /// Returns the last element of the slice, or `None` if it is empty.
278 /// let v = [10, 40, 30];
279 /// assert_eq!(Some(&30), v.last());
281 /// let w: &[i32] = &[];
282 /// assert_eq!(None, w.last());
284 #[stable(feature = "rust1", since = "1.0.0")]
285 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
288 pub const fn last(&self) -> Option<&T> {
289 if let [.., last] = self { Some(last) } else { None }
292 /// Returns a mutable pointer to the last item in the slice.
297 /// let x = &mut [0, 1, 2];
299 /// if let Some(last) = x.last_mut() {
302 /// assert_eq!(x, &[0, 1, 10]);
304 #[stable(feature = "rust1", since = "1.0.0")]
305 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
308 pub const fn last_mut(&mut self) -> Option<&mut T> {
309 if let [.., last] = self { Some(last) } else { None }
312 /// Returns a reference to an element or subslice depending on the type of
315 /// - If given a position, returns a reference to the element at that
316 /// position or `None` if out of bounds.
317 /// - If given a range, returns the subslice corresponding to that range,
318 /// or `None` if out of bounds.
323 /// let v = [10, 40, 30];
324 /// assert_eq!(Some(&40), v.get(1));
325 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
326 /// assert_eq!(None, v.get(3));
327 /// assert_eq!(None, v.get(0..4));
329 #[stable(feature = "rust1", since = "1.0.0")]
330 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
333 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
335 I: ~const SliceIndex<Self>,
340 /// Returns a mutable reference to an element or subslice depending on the
341 /// type of index (see [`get`]) or `None` if the index is out of bounds.
343 /// [`get`]: slice::get
348 /// let x = &mut [0, 1, 2];
350 /// if let Some(elem) = x.get_mut(1) {
353 /// assert_eq!(x, &[0, 42, 2]);
355 #[stable(feature = "rust1", since = "1.0.0")]
356 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
359 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
361 I: ~const SliceIndex<Self>,
366 /// Returns a reference to an element or subslice, without doing bounds
369 /// For a safe alternative see [`get`].
373 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
374 /// even if the resulting reference is not used.
376 /// [`get`]: slice::get
377 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
382 /// let x = &[1, 2, 4];
385 /// assert_eq!(x.get_unchecked(1), &2);
388 #[stable(feature = "rust1", since = "1.0.0")]
389 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
392 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
394 I: ~const SliceIndex<Self>,
396 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
397 // the slice is dereferenceable because `self` is a safe reference.
398 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
399 unsafe { &*index.get_unchecked(self) }
402 /// Returns a mutable reference to an element or subslice, without doing
405 /// For a safe alternative see [`get_mut`].
409 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
410 /// even if the resulting reference is not used.
412 /// [`get_mut`]: slice::get_mut
413 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
418 /// let x = &mut [1, 2, 4];
421 /// let elem = x.get_unchecked_mut(1);
424 /// assert_eq!(x, &[1, 13, 4]);
426 #[stable(feature = "rust1", since = "1.0.0")]
427 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
430 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
432 I: ~const SliceIndex<Self>,
434 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
435 // the slice is dereferenceable because `self` is a safe reference.
436 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
437 unsafe { &mut *index.get_unchecked_mut(self) }
440 /// Returns a raw pointer to the slice's buffer.
442 /// The caller must ensure that the slice outlives the pointer this
443 /// function returns, or else it will end up pointing to garbage.
445 /// The caller must also ensure that the memory the pointer (non-transitively) points to
446 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
447 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
449 /// Modifying the container referenced by this slice may cause its buffer
450 /// to be reallocated, which would also make any pointers to it invalid.
455 /// let x = &[1, 2, 4];
456 /// let x_ptr = x.as_ptr();
459 /// for i in 0..x.len() {
460 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
465 /// [`as_mut_ptr`]: slice::as_mut_ptr
466 #[stable(feature = "rust1", since = "1.0.0")]
467 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
470 pub const fn as_ptr(&self) -> *const T {
471 self as *const [T] as *const T
474 /// Returns an unsafe mutable pointer to the slice's buffer.
476 /// The caller must ensure that the slice outlives the pointer this
477 /// function returns, or else it will end up pointing to garbage.
479 /// Modifying the container referenced by this slice may cause its buffer
480 /// to be reallocated, which would also make any pointers to it invalid.
485 /// let x = &mut [1, 2, 4];
486 /// let x_ptr = x.as_mut_ptr();
489 /// for i in 0..x.len() {
490 /// *x_ptr.add(i) += 2;
493 /// assert_eq!(x, &[3, 4, 6]);
495 #[stable(feature = "rust1", since = "1.0.0")]
496 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
497 #[rustc_allow_const_fn_unstable(const_mut_refs)]
500 pub const fn as_mut_ptr(&mut self) -> *mut T {
501 self as *mut [T] as *mut T
504 /// Returns the two raw pointers spanning the slice.
506 /// The returned range is half-open, which means that the end pointer
507 /// points *one past* the last element of the slice. This way, an empty
508 /// slice is represented by two equal pointers, and the difference between
509 /// the two pointers represents the size of the slice.
511 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
512 /// requires extra caution, as it does not point to a valid element in the
515 /// This function is useful for interacting with foreign interfaces which
516 /// use two pointers to refer to a range of elements in memory, as is
519 /// It can also be useful to check if a pointer to an element refers to an
520 /// element of this slice:
523 /// let a = [1, 2, 3];
524 /// let x = &a[1] as *const _;
525 /// let y = &5 as *const _;
527 /// assert!(a.as_ptr_range().contains(&x));
528 /// assert!(!a.as_ptr_range().contains(&y));
531 /// [`as_ptr`]: slice::as_ptr
532 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
533 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
536 pub const fn as_ptr_range(&self) -> Range<*const T> {
537 let start = self.as_ptr();
538 // SAFETY: The `add` here is safe, because:
540 // - Both pointers are part of the same object, as pointing directly
541 // past the object also counts.
543 // - The size of the slice is never larger than isize::MAX bytes, as
545 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
546 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
547 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
548 // (This doesn't seem normative yet, but the very same assumption is
549 // made in many places, including the Index implementation of slices.)
551 // - There is no wrapping around involved, as slices do not wrap past
552 // the end of the address space.
554 // See the documentation of pointer::add.
555 let end = unsafe { start.add(self.len()) };
559 /// Returns the two unsafe mutable pointers spanning the slice.
561 /// The returned range is half-open, which means that the end pointer
562 /// points *one past* the last element of the slice. This way, an empty
563 /// slice is represented by two equal pointers, and the difference between
564 /// the two pointers represents the size of the slice.
566 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
567 /// pointer requires extra caution, as it does not point to a valid element
570 /// This function is useful for interacting with foreign interfaces which
571 /// use two pointers to refer to a range of elements in memory, as is
574 /// [`as_mut_ptr`]: slice::as_mut_ptr
575 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
576 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
577 #[rustc_allow_const_fn_unstable(const_mut_refs)]
580 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
581 let start = self.as_mut_ptr();
582 // SAFETY: See as_ptr_range() above for why `add` here is safe.
583 let end = unsafe { start.add(self.len()) };
587 /// Swaps two elements in the slice.
591 /// * a - The index of the first element
592 /// * b - The index of the second element
596 /// Panics if `a` or `b` are out of bounds.
601 /// let mut v = ["a", "b", "c", "d", "e"];
603 /// assert!(v == ["a", "b", "e", "d", "c"]);
605 #[stable(feature = "rust1", since = "1.0.0")]
606 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
609 pub const fn swap(&mut self, a: usize, b: usize) {
610 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
611 // Can't take two mutable loans from one vector, so instead use raw pointers.
612 let pa = ptr::addr_of_mut!(self[a]);
613 let pb = ptr::addr_of_mut!(self[b]);
614 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
615 // to elements in the slice and therefore are guaranteed to be valid and aligned.
616 // Note that accessing the elements behind `a` and `b` is checked and will
617 // panic when out of bounds.
623 /// Swaps two elements in the slice, without doing bounds checking.
625 /// For a safe alternative see [`swap`].
629 /// * a - The index of the first element
630 /// * b - The index of the second element
634 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
635 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
640 /// #![feature(slice_swap_unchecked)]
642 /// let mut v = ["a", "b", "c", "d"];
643 /// // SAFETY: we know that 1 and 3 are both indices of the slice
644 /// unsafe { v.swap_unchecked(1, 3) };
645 /// assert!(v == ["a", "d", "c", "b"]);
648 /// [`swap`]: slice::swap
649 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
650 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
651 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
652 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
654 let ptr = this.as_mut_ptr();
655 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
657 assert_unsafe_precondition!(
658 "slice::swap_unchecked requires that the indices are within the slice",
659 [T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len()
661 ptr::swap(ptr.add(a), ptr.add(b));
665 /// Reverses the order of elements in the slice, in place.
670 /// let mut v = [1, 2, 3];
672 /// assert!(v == [3, 2, 1]);
674 #[stable(feature = "rust1", since = "1.0.0")]
675 #[rustc_const_unstable(feature = "const_reverse", issue = "100784")]
677 pub const fn reverse(&mut self) {
678 let half_len = self.len() / 2;
679 let Range { start, end } = self.as_mut_ptr_range();
681 // These slices will skip the middle item for an odd length,
682 // since that one doesn't need to move.
683 let (front_half, back_half) =
684 // SAFETY: Both are subparts of the original slice, so the memory
685 // range is valid, and they don't overlap because they're each only
686 // half (or less) of the original slice.
689 slice::from_raw_parts_mut(start, half_len),
690 slice::from_raw_parts_mut(end.sub(half_len), half_len),
694 // Introducing a function boundary here means that the two halves
695 // get `noalias` markers, allowing better optimization as LLVM
696 // knows that they're disjoint, unlike in the original slice.
697 revswap(front_half, back_half, half_len);
700 const fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
701 debug_assert!(a.len() == n);
702 debug_assert!(b.len() == n);
704 // Because this function is first compiled in isolation,
705 // this check tells LLVM that the indexing below is
706 // in-bounds. Then after inlining -- once the actual
707 // lengths of the slices are known -- it's removed.
708 let (a, b) = (&mut a[..n], &mut b[..n]);
712 mem::swap(&mut a[i], &mut b[n - 1 - i]);
718 /// Returns an iterator over the slice.
720 /// The iterator yields all items from start to end.
725 /// let x = &[1, 2, 4];
726 /// let mut iterator = x.iter();
728 /// assert_eq!(iterator.next(), Some(&1));
729 /// assert_eq!(iterator.next(), Some(&2));
730 /// assert_eq!(iterator.next(), Some(&4));
731 /// assert_eq!(iterator.next(), None);
733 #[stable(feature = "rust1", since = "1.0.0")]
735 pub fn iter(&self) -> Iter<'_, T> {
739 /// Returns an iterator that allows modifying each value.
741 /// The iterator yields all items from start to end.
746 /// let x = &mut [1, 2, 4];
747 /// for elem in x.iter_mut() {
750 /// assert_eq!(x, &[3, 4, 6]);
752 #[stable(feature = "rust1", since = "1.0.0")]
754 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
758 /// Returns an iterator over all contiguous windows of length
759 /// `size`. The windows overlap. If the slice is shorter than
760 /// `size`, the iterator returns no values.
764 /// Panics if `size` is 0.
769 /// let slice = ['r', 'u', 's', 't'];
770 /// let mut iter = slice.windows(2);
771 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
772 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
773 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
774 /// assert!(iter.next().is_none());
777 /// If the slice is shorter than `size`:
780 /// let slice = ['f', 'o', 'o'];
781 /// let mut iter = slice.windows(4);
782 /// assert!(iter.next().is_none());
784 #[stable(feature = "rust1", since = "1.0.0")]
786 pub fn windows(&self, size: usize) -> Windows<'_, T> {
787 let size = NonZeroUsize::new(size).expect("size is zero");
788 Windows::new(self, size)
791 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
792 /// beginning of the slice.
794 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
795 /// slice, then the last chunk will not have length `chunk_size`.
797 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
798 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
803 /// Panics if `chunk_size` is 0.
808 /// let slice = ['l', 'o', 'r', 'e', 'm'];
809 /// let mut iter = slice.chunks(2);
810 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
811 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
812 /// assert_eq!(iter.next().unwrap(), &['m']);
813 /// assert!(iter.next().is_none());
816 /// [`chunks_exact`]: slice::chunks_exact
817 /// [`rchunks`]: slice::rchunks
818 #[stable(feature = "rust1", since = "1.0.0")]
820 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
821 assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
822 Chunks::new(self, chunk_size)
825 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
826 /// beginning of the slice.
828 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
829 /// length of the slice, then the last chunk will not have length `chunk_size`.
831 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
832 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
833 /// the end of the slice.
837 /// Panics if `chunk_size` is 0.
842 /// let v = &mut [0, 0, 0, 0, 0];
843 /// let mut count = 1;
845 /// for chunk in v.chunks_mut(2) {
846 /// for elem in chunk.iter_mut() {
851 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
854 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
855 /// [`rchunks_mut`]: slice::rchunks_mut
856 #[stable(feature = "rust1", since = "1.0.0")]
858 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
859 assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
860 ChunksMut::new(self, chunk_size)
863 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
864 /// beginning of the slice.
866 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
867 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
868 /// from the `remainder` function of the iterator.
870 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
871 /// resulting code better than in the case of [`chunks`].
873 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
874 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
878 /// Panics if `chunk_size` is 0.
883 /// let slice = ['l', 'o', 'r', 'e', 'm'];
884 /// let mut iter = slice.chunks_exact(2);
885 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
886 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
887 /// assert!(iter.next().is_none());
888 /// assert_eq!(iter.remainder(), &['m']);
891 /// [`chunks`]: slice::chunks
892 /// [`rchunks_exact`]: slice::rchunks_exact
893 #[stable(feature = "chunks_exact", since = "1.31.0")]
895 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
896 assert_ne!(chunk_size, 0);
897 ChunksExact::new(self, chunk_size)
900 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
901 /// beginning of the slice.
903 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
904 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
905 /// retrieved from the `into_remainder` function of the iterator.
907 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
908 /// resulting code better than in the case of [`chunks_mut`].
910 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
911 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
916 /// Panics if `chunk_size` is 0.
921 /// let v = &mut [0, 0, 0, 0, 0];
922 /// let mut count = 1;
924 /// for chunk in v.chunks_exact_mut(2) {
925 /// for elem in chunk.iter_mut() {
930 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
933 /// [`chunks_mut`]: slice::chunks_mut
934 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
935 #[stable(feature = "chunks_exact", since = "1.31.0")]
937 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
938 assert_ne!(chunk_size, 0);
939 ChunksExactMut::new(self, chunk_size)
942 /// Splits the slice into a slice of `N`-element arrays,
943 /// assuming that there's no remainder.
947 /// This may only be called when
948 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
954 /// #![feature(slice_as_chunks)]
955 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
956 /// let chunks: &[[char; 1]] =
957 /// // SAFETY: 1-element chunks never have remainder
958 /// unsafe { slice.as_chunks_unchecked() };
959 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
960 /// let chunks: &[[char; 3]] =
961 /// // SAFETY: The slice length (6) is a multiple of 3
962 /// unsafe { slice.as_chunks_unchecked() };
963 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
965 /// // These would be unsound:
966 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
967 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
969 #[unstable(feature = "slice_as_chunks", issue = "74985")]
972 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
974 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
975 let new_len = unsafe {
976 assert_unsafe_precondition!(
977 "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
978 [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
980 exact_div(self.len(), N)
982 // SAFETY: We cast a slice of `new_len * N` elements into
983 // a slice of `new_len` many `N` elements chunks.
984 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
987 /// Splits the slice into a slice of `N`-element arrays,
988 /// starting at the beginning of the slice,
989 /// and a remainder slice with length strictly less than `N`.
993 /// Panics if `N` is 0. This check will most probably get changed to a compile time
994 /// error before this method gets stabilized.
999 /// #![feature(slice_as_chunks)]
1000 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1001 /// let (chunks, remainder) = slice.as_chunks();
1002 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
1003 /// assert_eq!(remainder, &['m']);
1005 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1008 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1010 let len = self.len() / N;
1011 let (multiple_of_n, remainder) = self.split_at(len * N);
1012 // SAFETY: We already panicked for zero, and ensured by construction
1013 // that the length of the subslice is a multiple of N.
1014 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1015 (array_slice, remainder)
1018 /// Splits the slice into a slice of `N`-element arrays,
1019 /// starting at the end of the slice,
1020 /// and a remainder slice with length strictly less than `N`.
1024 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1025 /// error before this method gets stabilized.
1030 /// #![feature(slice_as_chunks)]
1031 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1032 /// let (remainder, chunks) = slice.as_rchunks();
1033 /// assert_eq!(remainder, &['l']);
1034 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1036 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1039 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1041 let len = self.len() / N;
1042 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1043 // SAFETY: We already panicked for zero, and ensured by construction
1044 // that the length of the subslice is a multiple of N.
1045 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1046 (remainder, array_slice)
1049 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1050 /// beginning of the slice.
1052 /// The chunks are array references and do not overlap. If `N` does not divide the
1053 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1054 /// retrieved from the `remainder` function of the iterator.
1056 /// This method is the const generic equivalent of [`chunks_exact`].
1060 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1061 /// error before this method gets stabilized.
1066 /// #![feature(array_chunks)]
1067 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1068 /// let mut iter = slice.array_chunks();
1069 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1070 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1071 /// assert!(iter.next().is_none());
1072 /// assert_eq!(iter.remainder(), &['m']);
1075 /// [`chunks_exact`]: slice::chunks_exact
1076 #[unstable(feature = "array_chunks", issue = "74985")]
1078 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1080 ArrayChunks::new(self)
1083 /// Splits the slice into a slice of `N`-element arrays,
1084 /// assuming that there's no remainder.
1088 /// This may only be called when
1089 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1095 /// #![feature(slice_as_chunks)]
1096 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1097 /// let chunks: &mut [[char; 1]] =
1098 /// // SAFETY: 1-element chunks never have remainder
1099 /// unsafe { slice.as_chunks_unchecked_mut() };
1100 /// chunks[0] = ['L'];
1101 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1102 /// let chunks: &mut [[char; 3]] =
1103 /// // SAFETY: The slice length (6) is a multiple of 3
1104 /// unsafe { slice.as_chunks_unchecked_mut() };
1105 /// chunks[1] = ['a', 'x', '?'];
1106 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1108 /// // These would be unsound:
1109 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1110 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1112 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1115 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1117 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1118 let new_len = unsafe {
1119 assert_unsafe_precondition!(
1120 "slice::as_chunks_unchecked_mut requires `N != 0` and the slice to split exactly into `N`-element chunks",
1121 [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
1123 exact_div(this.len(), N)
1125 // SAFETY: We cast a slice of `new_len * N` elements into
1126 // a slice of `new_len` many `N` elements chunks.
1127 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1130 /// Splits the slice into a slice of `N`-element arrays,
1131 /// starting at the beginning of the slice,
1132 /// and a remainder slice with length strictly less than `N`.
1136 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1137 /// error before this method gets stabilized.
1142 /// #![feature(slice_as_chunks)]
1143 /// let v = &mut [0, 0, 0, 0, 0];
1144 /// let mut count = 1;
1146 /// let (chunks, remainder) = v.as_chunks_mut();
1147 /// remainder[0] = 9;
1148 /// for chunk in chunks {
1149 /// *chunk = [count; 2];
1152 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1154 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1157 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1159 let len = self.len() / N;
1160 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1161 // SAFETY: We already panicked for zero, and ensured by construction
1162 // that the length of the subslice is a multiple of N.
1163 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1164 (array_slice, remainder)
1167 /// Splits the slice into a slice of `N`-element arrays,
1168 /// starting at the end of the slice,
1169 /// and a remainder slice with length strictly less than `N`.
1173 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1174 /// error before this method gets stabilized.
1179 /// #![feature(slice_as_chunks)]
1180 /// let v = &mut [0, 0, 0, 0, 0];
1181 /// let mut count = 1;
1183 /// let (remainder, chunks) = v.as_rchunks_mut();
1184 /// remainder[0] = 9;
1185 /// for chunk in chunks {
1186 /// *chunk = [count; 2];
1189 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1191 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1194 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1196 let len = self.len() / N;
1197 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1198 // SAFETY: We already panicked for zero, and ensured by construction
1199 // that the length of the subslice is a multiple of N.
1200 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1201 (remainder, array_slice)
1204 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1205 /// beginning of the slice.
1207 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1208 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1209 /// can be retrieved from the `into_remainder` function of the iterator.
1211 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1215 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1216 /// error before this method gets stabilized.
1221 /// #![feature(array_chunks)]
1222 /// let v = &mut [0, 0, 0, 0, 0];
1223 /// let mut count = 1;
1225 /// for chunk in v.array_chunks_mut() {
1226 /// *chunk = [count; 2];
1229 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1232 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1233 #[unstable(feature = "array_chunks", issue = "74985")]
1235 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1237 ArrayChunksMut::new(self)
1240 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1241 /// starting at the beginning of the slice.
1243 /// This is the const generic equivalent of [`windows`].
1245 /// If `N` is greater than the size of the slice, it will return no windows.
1249 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1250 /// error before this method gets stabilized.
1255 /// #![feature(array_windows)]
1256 /// let slice = [0, 1, 2, 3];
1257 /// let mut iter = slice.array_windows();
1258 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1259 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1260 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1261 /// assert!(iter.next().is_none());
1264 /// [`windows`]: slice::windows
1265 #[unstable(feature = "array_windows", issue = "75027")]
1267 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1269 ArrayWindows::new(self)
1272 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1275 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1276 /// slice, then the last chunk will not have length `chunk_size`.
1278 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1279 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1284 /// Panics if `chunk_size` is 0.
1289 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1290 /// let mut iter = slice.rchunks(2);
1291 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1292 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1293 /// assert_eq!(iter.next().unwrap(), &['l']);
1294 /// assert!(iter.next().is_none());
1297 /// [`rchunks_exact`]: slice::rchunks_exact
1298 /// [`chunks`]: slice::chunks
1299 #[stable(feature = "rchunks", since = "1.31.0")]
1301 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1302 assert!(chunk_size != 0);
1303 RChunks::new(self, chunk_size)
1306 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1309 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1310 /// length of the slice, then the last chunk will not have length `chunk_size`.
1312 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1313 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1314 /// beginning of the slice.
1318 /// Panics if `chunk_size` is 0.
1323 /// let v = &mut [0, 0, 0, 0, 0];
1324 /// let mut count = 1;
1326 /// for chunk in v.rchunks_mut(2) {
1327 /// for elem in chunk.iter_mut() {
1332 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1335 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1336 /// [`chunks_mut`]: slice::chunks_mut
1337 #[stable(feature = "rchunks", since = "1.31.0")]
1339 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1340 assert!(chunk_size != 0);
1341 RChunksMut::new(self, chunk_size)
1344 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1345 /// end of the slice.
1347 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1348 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1349 /// from the `remainder` function of the iterator.
1351 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1352 /// resulting code better than in the case of [`rchunks`].
1354 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1355 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1360 /// Panics if `chunk_size` is 0.
1365 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1366 /// let mut iter = slice.rchunks_exact(2);
1367 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1368 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1369 /// assert!(iter.next().is_none());
1370 /// assert_eq!(iter.remainder(), &['l']);
1373 /// [`chunks`]: slice::chunks
1374 /// [`rchunks`]: slice::rchunks
1375 /// [`chunks_exact`]: slice::chunks_exact
1376 #[stable(feature = "rchunks", since = "1.31.0")]
1378 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1379 assert!(chunk_size != 0);
1380 RChunksExact::new(self, chunk_size)
1383 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1386 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1387 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1388 /// retrieved from the `into_remainder` function of the iterator.
1390 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1391 /// resulting code better than in the case of [`chunks_mut`].
1393 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1394 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1399 /// Panics if `chunk_size` is 0.
1404 /// let v = &mut [0, 0, 0, 0, 0];
1405 /// let mut count = 1;
1407 /// for chunk in v.rchunks_exact_mut(2) {
1408 /// for elem in chunk.iter_mut() {
1413 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1416 /// [`chunks_mut`]: slice::chunks_mut
1417 /// [`rchunks_mut`]: slice::rchunks_mut
1418 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1419 #[stable(feature = "rchunks", since = "1.31.0")]
1421 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1422 assert!(chunk_size != 0);
1423 RChunksExactMut::new(self, chunk_size)
1426 /// Returns an iterator over the slice producing non-overlapping runs
1427 /// of elements using the predicate to separate them.
1429 /// The predicate is called on two elements following themselves,
1430 /// it means the predicate is called on `slice[0]` and `slice[1]`
1431 /// then on `slice[1]` and `slice[2]` and so on.
1436 /// #![feature(slice_group_by)]
1438 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1440 /// let mut iter = slice.group_by(|a, b| a == b);
1442 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1443 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1444 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1445 /// assert_eq!(iter.next(), None);
1448 /// This method can be used to extract the sorted subslices:
1451 /// #![feature(slice_group_by)]
1453 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1455 /// let mut iter = slice.group_by(|a, b| a <= b);
1457 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1458 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1459 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1460 /// assert_eq!(iter.next(), None);
1462 #[unstable(feature = "slice_group_by", issue = "80552")]
1464 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1466 F: FnMut(&T, &T) -> bool,
1468 GroupBy::new(self, pred)
1471 /// Returns an iterator over the slice producing non-overlapping mutable
1472 /// runs of elements using the predicate to separate them.
1474 /// The predicate is called on two elements following themselves,
1475 /// it means the predicate is called on `slice[0]` and `slice[1]`
1476 /// then on `slice[1]` and `slice[2]` and so on.
1481 /// #![feature(slice_group_by)]
1483 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1485 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1487 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1488 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1489 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1490 /// assert_eq!(iter.next(), None);
1493 /// This method can be used to extract the sorted subslices:
1496 /// #![feature(slice_group_by)]
1498 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1500 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1502 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1503 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1504 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1505 /// assert_eq!(iter.next(), None);
1507 #[unstable(feature = "slice_group_by", issue = "80552")]
1509 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1511 F: FnMut(&T, &T) -> bool,
1513 GroupByMut::new(self, pred)
1516 /// Divides one slice into two at an index.
1518 /// The first will contain all indices from `[0, mid)` (excluding
1519 /// the index `mid` itself) and the second will contain all
1520 /// indices from `[mid, len)` (excluding the index `len` itself).
1524 /// Panics if `mid > len`.
1529 /// let v = [1, 2, 3, 4, 5, 6];
1532 /// let (left, right) = v.split_at(0);
1533 /// assert_eq!(left, []);
1534 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1538 /// let (left, right) = v.split_at(2);
1539 /// assert_eq!(left, [1, 2]);
1540 /// assert_eq!(right, [3, 4, 5, 6]);
1544 /// let (left, right) = v.split_at(6);
1545 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1546 /// assert_eq!(right, []);
1549 #[stable(feature = "rust1", since = "1.0.0")]
1550 #[rustc_const_unstable(feature = "const_slice_split_at_not_mut", issue = "101158")]
1554 pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1555 assert!(mid <= self.len());
1556 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1557 // fulfills the requirements of `split_at_unchecked`.
1558 unsafe { self.split_at_unchecked(mid) }
1561 /// Divides one mutable slice into two at an index.
1563 /// The first will contain all indices from `[0, mid)` (excluding
1564 /// the index `mid` itself) and the second will contain all
1565 /// indices from `[mid, len)` (excluding the index `len` itself).
1569 /// Panics if `mid > len`.
1574 /// let mut v = [1, 0, 3, 0, 5, 6];
1575 /// let (left, right) = v.split_at_mut(2);
1576 /// assert_eq!(left, [1, 0]);
1577 /// assert_eq!(right, [3, 0, 5, 6]);
1580 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1582 #[stable(feature = "rust1", since = "1.0.0")]
1586 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
1587 pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1588 assert!(mid <= self.len());
1589 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1590 // fulfills the requirements of `from_raw_parts_mut`.
1591 unsafe { self.split_at_mut_unchecked(mid) }
1594 /// Divides one slice into two at an index, without doing bounds checking.
1596 /// The first will contain all indices from `[0, mid)` (excluding
1597 /// the index `mid` itself) and the second will contain all
1598 /// indices from `[mid, len)` (excluding the index `len` itself).
1600 /// For a safe alternative see [`split_at`].
1604 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1605 /// even if the resulting reference is not used. The caller has to ensure that
1606 /// `0 <= mid <= self.len()`.
1608 /// [`split_at`]: slice::split_at
1609 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1614 /// #![feature(slice_split_at_unchecked)]
1616 /// let v = [1, 2, 3, 4, 5, 6];
1619 /// let (left, right) = v.split_at_unchecked(0);
1620 /// assert_eq!(left, []);
1621 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1625 /// let (left, right) = v.split_at_unchecked(2);
1626 /// assert_eq!(left, [1, 2]);
1627 /// assert_eq!(right, [3, 4, 5, 6]);
1631 /// let (left, right) = v.split_at_unchecked(6);
1632 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1633 /// assert_eq!(right, []);
1636 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1637 #[rustc_const_unstable(feature = "slice_split_at_unchecked", issue = "76014")]
1640 pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1641 // HACK: the const function `from_raw_parts` is used to make this
1642 // function const; previously the implementation used
1643 // `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
1645 let len = self.len();
1646 let ptr = self.as_ptr();
1648 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1649 unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), len - mid)) }
1652 /// Divides one mutable slice into two at an index, without doing bounds checking.
1654 /// The first will contain all indices from `[0, mid)` (excluding
1655 /// the index `mid` itself) and the second will contain all
1656 /// indices from `[mid, len)` (excluding the index `len` itself).
1658 /// For a safe alternative see [`split_at_mut`].
1662 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1663 /// even if the resulting reference is not used. The caller has to ensure that
1664 /// `0 <= mid <= self.len()`.
1666 /// [`split_at_mut`]: slice::split_at_mut
1667 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1672 /// #![feature(slice_split_at_unchecked)]
1674 /// let mut v = [1, 0, 3, 0, 5, 6];
1675 /// // scoped to restrict the lifetime of the borrows
1677 /// let (left, right) = v.split_at_mut_unchecked(2);
1678 /// assert_eq!(left, [1, 0]);
1679 /// assert_eq!(right, [3, 0, 5, 6]);
1683 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1685 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1686 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
1689 pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1690 let len = self.len();
1691 let ptr = self.as_mut_ptr();
1693 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1695 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1698 assert_unsafe_precondition!(
1699 "slice::split_at_mut_unchecked requires the index to be within the slice",
1700 (mid: usize, len: usize) => mid <= len
1702 (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
1706 /// Divides one slice into an array and a remainder slice at an index.
1708 /// The array will contain all indices from `[0, N)` (excluding
1709 /// the index `N` itself) and the slice will contain all
1710 /// indices from `[N, len)` (excluding the index `len` itself).
1714 /// Panics if `N > len`.
1719 /// #![feature(split_array)]
1721 /// let v = &[1, 2, 3, 4, 5, 6][..];
1724 /// let (left, right) = v.split_array_ref::<0>();
1725 /// assert_eq!(left, &[]);
1726 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1730 /// let (left, right) = v.split_array_ref::<2>();
1731 /// assert_eq!(left, &[1, 2]);
1732 /// assert_eq!(right, [3, 4, 5, 6]);
1736 /// let (left, right) = v.split_array_ref::<6>();
1737 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1738 /// assert_eq!(right, []);
1741 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1745 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1746 let (a, b) = self.split_at(N);
1747 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1748 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1751 /// Divides one mutable slice into an array and a remainder slice at an index.
1753 /// The array will contain all indices from `[0, N)` (excluding
1754 /// the index `N` itself) and the slice will contain all
1755 /// indices from `[N, len)` (excluding the index `len` itself).
1759 /// Panics if `N > len`.
1764 /// #![feature(split_array)]
1766 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1767 /// let (left, right) = v.split_array_mut::<2>();
1768 /// assert_eq!(left, &mut [1, 0]);
1769 /// assert_eq!(right, [3, 0, 5, 6]);
1772 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1774 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1778 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1779 let (a, b) = self.split_at_mut(N);
1780 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1781 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1784 /// Divides one slice into an array and a remainder slice at an index from
1787 /// The slice will contain all indices from `[0, len - N)` (excluding
1788 /// the index `len - N` itself) and the array will contain all
1789 /// indices from `[len - N, len)` (excluding the index `len` itself).
1793 /// Panics if `N > len`.
1798 /// #![feature(split_array)]
1800 /// let v = &[1, 2, 3, 4, 5, 6][..];
1803 /// let (left, right) = v.rsplit_array_ref::<0>();
1804 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1805 /// assert_eq!(right, &[]);
1809 /// let (left, right) = v.rsplit_array_ref::<2>();
1810 /// assert_eq!(left, [1, 2, 3, 4]);
1811 /// assert_eq!(right, &[5, 6]);
1815 /// let (left, right) = v.rsplit_array_ref::<6>();
1816 /// assert_eq!(left, []);
1817 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1820 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1823 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1824 assert!(N <= self.len());
1825 let (a, b) = self.split_at(self.len() - N);
1826 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1827 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1830 /// Divides one mutable slice into an array and a remainder slice at an
1831 /// index from the end.
1833 /// The slice will contain all indices from `[0, len - N)` (excluding
1834 /// the index `N` itself) and the array will contain all
1835 /// indices from `[len - N, len)` (excluding the index `len` itself).
1839 /// Panics if `N > len`.
1844 /// #![feature(split_array)]
1846 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1847 /// let (left, right) = v.rsplit_array_mut::<4>();
1848 /// assert_eq!(left, [1, 0]);
1849 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1852 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1854 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1857 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1858 assert!(N <= self.len());
1859 let (a, b) = self.split_at_mut(self.len() - N);
1860 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1861 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1864 /// Returns an iterator over subslices separated by elements that match
1865 /// `pred`. The matched element is not contained in the subslices.
1870 /// let slice = [10, 40, 33, 20];
1871 /// let mut iter = slice.split(|num| num % 3 == 0);
1873 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1874 /// assert_eq!(iter.next().unwrap(), &[20]);
1875 /// assert!(iter.next().is_none());
1878 /// If the first element is matched, an empty slice will be the first item
1879 /// returned by the iterator. Similarly, if the last element in the slice
1880 /// is matched, an empty slice will be the last item returned by the
1884 /// let slice = [10, 40, 33];
1885 /// let mut iter = slice.split(|num| num % 3 == 0);
1887 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1888 /// assert_eq!(iter.next().unwrap(), &[]);
1889 /// assert!(iter.next().is_none());
1892 /// If two matched elements are directly adjacent, an empty slice will be
1893 /// present between them:
1896 /// let slice = [10, 6, 33, 20];
1897 /// let mut iter = slice.split(|num| num % 3 == 0);
1899 /// assert_eq!(iter.next().unwrap(), &[10]);
1900 /// assert_eq!(iter.next().unwrap(), &[]);
1901 /// assert_eq!(iter.next().unwrap(), &[20]);
1902 /// assert!(iter.next().is_none());
1904 #[stable(feature = "rust1", since = "1.0.0")]
1906 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1908 F: FnMut(&T) -> bool,
1910 Split::new(self, pred)
1913 /// Returns an iterator over mutable subslices separated by elements that
1914 /// match `pred`. The matched element is not contained in the subslices.
1919 /// let mut v = [10, 40, 30, 20, 60, 50];
1921 /// for group in v.split_mut(|num| *num % 3 == 0) {
1924 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1926 #[stable(feature = "rust1", since = "1.0.0")]
1928 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1930 F: FnMut(&T) -> bool,
1932 SplitMut::new(self, pred)
1935 /// Returns an iterator over subslices separated by elements that match
1936 /// `pred`. The matched element is contained in the end of the previous
1937 /// subslice as a terminator.
1942 /// let slice = [10, 40, 33, 20];
1943 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1945 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1946 /// assert_eq!(iter.next().unwrap(), &[20]);
1947 /// assert!(iter.next().is_none());
1950 /// If the last element of the slice is matched,
1951 /// that element will be considered the terminator of the preceding slice.
1952 /// That slice will be the last item returned by the iterator.
1955 /// let slice = [3, 10, 40, 33];
1956 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1958 /// assert_eq!(iter.next().unwrap(), &[3]);
1959 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1960 /// assert!(iter.next().is_none());
1962 #[stable(feature = "split_inclusive", since = "1.51.0")]
1964 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1966 F: FnMut(&T) -> bool,
1968 SplitInclusive::new(self, pred)
1971 /// Returns an iterator over mutable subslices separated by elements that
1972 /// match `pred`. The matched element is contained in the previous
1973 /// subslice as a terminator.
1978 /// let mut v = [10, 40, 30, 20, 60, 50];
1980 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1981 /// let terminator_idx = group.len()-1;
1982 /// group[terminator_idx] = 1;
1984 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1986 #[stable(feature = "split_inclusive", since = "1.51.0")]
1988 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1990 F: FnMut(&T) -> bool,
1992 SplitInclusiveMut::new(self, pred)
1995 /// Returns an iterator over subslices separated by elements that match
1996 /// `pred`, starting at the end of the slice and working backwards.
1997 /// The matched element is not contained in the subslices.
2002 /// let slice = [11, 22, 33, 0, 44, 55];
2003 /// let mut iter = slice.rsplit(|num| *num == 0);
2005 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
2006 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
2007 /// assert_eq!(iter.next(), None);
2010 /// As with `split()`, if the first or last element is matched, an empty
2011 /// slice will be the first (or last) item returned by the iterator.
2014 /// let v = &[0, 1, 1, 2, 3, 5, 8];
2015 /// let mut it = v.rsplit(|n| *n % 2 == 0);
2016 /// assert_eq!(it.next().unwrap(), &[]);
2017 /// assert_eq!(it.next().unwrap(), &[3, 5]);
2018 /// assert_eq!(it.next().unwrap(), &[1, 1]);
2019 /// assert_eq!(it.next().unwrap(), &[]);
2020 /// assert_eq!(it.next(), None);
2022 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2024 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
2026 F: FnMut(&T) -> bool,
2028 RSplit::new(self, pred)
2031 /// Returns an iterator over mutable subslices separated by elements that
2032 /// match `pred`, starting at the end of the slice and working
2033 /// backwards. The matched element is not contained in the subslices.
2038 /// let mut v = [100, 400, 300, 200, 600, 500];
2040 /// let mut count = 0;
2041 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
2043 /// group[0] = count;
2045 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
2048 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2050 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
2052 F: FnMut(&T) -> bool,
2054 RSplitMut::new(self, pred)
2057 /// Returns an iterator over subslices separated by elements that match
2058 /// `pred`, limited to returning at most `n` items. The matched element is
2059 /// not contained in the subslices.
2061 /// The last element returned, if any, will contain the remainder of the
2066 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2067 /// `[20, 60, 50]`):
2070 /// let v = [10, 40, 30, 20, 60, 50];
2072 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2073 /// println!("{group:?}");
2076 #[stable(feature = "rust1", since = "1.0.0")]
2078 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2080 F: FnMut(&T) -> bool,
2082 SplitN::new(self.split(pred), n)
2085 /// Returns an iterator over mutable subslices separated by elements that match
2086 /// `pred`, limited to returning at most `n` items. The matched element is
2087 /// not contained in the subslices.
2089 /// The last element returned, if any, will contain the remainder of the
2095 /// let mut v = [10, 40, 30, 20, 60, 50];
2097 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2100 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2102 #[stable(feature = "rust1", since = "1.0.0")]
2104 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2106 F: FnMut(&T) -> bool,
2108 SplitNMut::new(self.split_mut(pred), n)
2111 /// Returns an iterator over subslices separated by elements that match
2112 /// `pred` limited to returning at most `n` items. This starts at the end of
2113 /// the slice and works backwards. The matched element is not contained in
2116 /// The last element returned, if any, will contain the remainder of the
2121 /// Print the slice split once, starting from the end, by numbers divisible
2122 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2125 /// let v = [10, 40, 30, 20, 60, 50];
2127 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2128 /// println!("{group:?}");
2131 #[stable(feature = "rust1", since = "1.0.0")]
2133 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2135 F: FnMut(&T) -> bool,
2137 RSplitN::new(self.rsplit(pred), n)
2140 /// Returns an iterator over subslices separated by elements that match
2141 /// `pred` limited to returning at most `n` items. This starts at the end of
2142 /// the slice and works backwards. The matched element is not contained in
2145 /// The last element returned, if any, will contain the remainder of the
2151 /// let mut s = [10, 40, 30, 20, 60, 50];
2153 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2156 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2158 #[stable(feature = "rust1", since = "1.0.0")]
2160 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2162 F: FnMut(&T) -> bool,
2164 RSplitNMut::new(self.rsplit_mut(pred), n)
2167 /// Returns `true` if the slice contains an element with the given value.
2169 /// This operation is *O*(*n*).
2171 /// Note that if you have a sorted slice, [`binary_search`] may be faster.
2173 /// [`binary_search`]: slice::binary_search
2178 /// let v = [10, 40, 30];
2179 /// assert!(v.contains(&30));
2180 /// assert!(!v.contains(&50));
2183 /// If you do not have a `&T`, but some other value that you can compare
2184 /// with one (for example, `String` implements `PartialEq<str>`), you can
2185 /// use `iter().any`:
2188 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2189 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2190 /// assert!(!v.iter().any(|e| e == "hi"));
2192 #[stable(feature = "rust1", since = "1.0.0")]
2195 pub fn contains(&self, x: &T) -> bool
2199 cmp::SliceContains::slice_contains(x, self)
2202 /// Returns `true` if `needle` is a prefix of the slice.
2207 /// let v = [10, 40, 30];
2208 /// assert!(v.starts_with(&[10]));
2209 /// assert!(v.starts_with(&[10, 40]));
2210 /// assert!(!v.starts_with(&[50]));
2211 /// assert!(!v.starts_with(&[10, 50]));
2214 /// Always returns `true` if `needle` is an empty slice:
2217 /// let v = &[10, 40, 30];
2218 /// assert!(v.starts_with(&[]));
2219 /// let v: &[u8] = &[];
2220 /// assert!(v.starts_with(&[]));
2222 #[stable(feature = "rust1", since = "1.0.0")]
2224 pub fn starts_with(&self, needle: &[T]) -> bool
2228 let n = needle.len();
2229 self.len() >= n && needle == &self[..n]
2232 /// Returns `true` if `needle` is a suffix of the slice.
2237 /// let v = [10, 40, 30];
2238 /// assert!(v.ends_with(&[30]));
2239 /// assert!(v.ends_with(&[40, 30]));
2240 /// assert!(!v.ends_with(&[50]));
2241 /// assert!(!v.ends_with(&[50, 30]));
2244 /// Always returns `true` if `needle` is an empty slice:
2247 /// let v = &[10, 40, 30];
2248 /// assert!(v.ends_with(&[]));
2249 /// let v: &[u8] = &[];
2250 /// assert!(v.ends_with(&[]));
2252 #[stable(feature = "rust1", since = "1.0.0")]
2254 pub fn ends_with(&self, needle: &[T]) -> bool
2258 let (m, n) = (self.len(), needle.len());
2259 m >= n && needle == &self[m - n..]
2262 /// Returns a subslice with the prefix removed.
2264 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2265 /// If `prefix` is empty, simply returns the original slice.
2267 /// If the slice does not start with `prefix`, returns `None`.
2272 /// let v = &[10, 40, 30];
2273 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2274 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2275 /// assert_eq!(v.strip_prefix(&[50]), None);
2276 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2278 /// let prefix : &str = "he";
2279 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2280 /// Some(b"llo".as_ref()));
2282 #[must_use = "returns the subslice without modifying the original"]
2283 #[stable(feature = "slice_strip", since = "1.51.0")]
2284 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2288 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2289 let prefix = prefix.as_slice();
2290 let n = prefix.len();
2291 if n <= self.len() {
2292 let (head, tail) = self.split_at(n);
2300 /// Returns a subslice with the suffix removed.
2302 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2303 /// If `suffix` is empty, simply returns the original slice.
2305 /// If the slice does not end with `suffix`, returns `None`.
2310 /// let v = &[10, 40, 30];
2311 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2312 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2313 /// assert_eq!(v.strip_suffix(&[50]), None);
2314 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2316 #[must_use = "returns the subslice without modifying the original"]
2317 #[stable(feature = "slice_strip", since = "1.51.0")]
2318 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2322 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2323 let suffix = suffix.as_slice();
2324 let (len, n) = (self.len(), suffix.len());
2326 let (head, tail) = self.split_at(len - n);
2334 /// Binary searches this slice for a given element.
2335 /// This behaves similarly to [`contains`] if this slice is sorted.
2337 /// If the value is found then [`Result::Ok`] is returned, containing the
2338 /// index of the matching element. If there are multiple matches, then any
2339 /// one of the matches could be returned. The index is chosen
2340 /// deterministically, but is subject to change in future versions of Rust.
2341 /// If the value is not found then [`Result::Err`] is returned, containing
2342 /// the index where a matching element could be inserted while maintaining
2345 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2347 /// [`contains`]: slice::contains
2348 /// [`binary_search_by`]: slice::binary_search_by
2349 /// [`binary_search_by_key`]: slice::binary_search_by_key
2350 /// [`partition_point`]: slice::partition_point
2354 /// Looks up a series of four elements. The first is found, with a
2355 /// uniquely determined position; the second and third are not
2356 /// found; the fourth could match any position in `[1, 4]`.
2359 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2361 /// assert_eq!(s.binary_search(&13), Ok(9));
2362 /// assert_eq!(s.binary_search(&4), Err(7));
2363 /// assert_eq!(s.binary_search(&100), Err(13));
2364 /// let r = s.binary_search(&1);
2365 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2368 /// If you want to find that whole *range* of matching items, rather than
2369 /// an arbitrary matching one, that can be done using [`partition_point`]:
2371 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2373 /// let low = s.partition_point(|x| x < &1);
2374 /// assert_eq!(low, 1);
2375 /// let high = s.partition_point(|x| x <= &1);
2376 /// assert_eq!(high, 5);
2377 /// let r = s.binary_search(&1);
2378 /// assert!((low..high).contains(&r.unwrap()));
2380 /// assert!(s[..low].iter().all(|&x| x < 1));
2381 /// assert!(s[low..high].iter().all(|&x| x == 1));
2382 /// assert!(s[high..].iter().all(|&x| x > 1));
2384 /// // For something not found, the "range" of equal items is empty
2385 /// assert_eq!(s.partition_point(|x| x < &11), 9);
2386 /// assert_eq!(s.partition_point(|x| x <= &11), 9);
2387 /// assert_eq!(s.binary_search(&11), Err(9));
2390 /// If you want to insert an item to a sorted vector, while maintaining
2391 /// sort order, consider using [`partition_point`]:
2394 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2396 /// let idx = s.partition_point(|&x| x < num);
2397 /// // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
2398 /// s.insert(idx, num);
2399 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2401 #[stable(feature = "rust1", since = "1.0.0")]
2402 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2406 self.binary_search_by(|p| p.cmp(x))
2409 /// Binary searches this slice with a comparator function.
2410 /// This behaves similarly to [`contains`] if this slice is sorted.
2412 /// The comparator function should implement an order consistent
2413 /// with the sort order of the underlying slice, returning an
2414 /// order code that indicates whether its argument is `Less`,
2415 /// `Equal` or `Greater` the desired target.
2417 /// If the value is found then [`Result::Ok`] is returned, containing the
2418 /// index of the matching element. If there are multiple matches, then any
2419 /// one of the matches could be returned. The index is chosen
2420 /// deterministically, but is subject to change in future versions of Rust.
2421 /// If the value is not found then [`Result::Err`] is returned, containing
2422 /// the index where a matching element could be inserted while maintaining
2425 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2427 /// [`contains`]: slice::contains
2428 /// [`binary_search`]: slice::binary_search
2429 /// [`binary_search_by_key`]: slice::binary_search_by_key
2430 /// [`partition_point`]: slice::partition_point
2434 /// Looks up a series of four elements. The first is found, with a
2435 /// uniquely determined position; the second and third are not
2436 /// found; the fourth could match any position in `[1, 4]`.
2439 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2442 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2444 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2446 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2448 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2449 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2451 #[stable(feature = "rust1", since = "1.0.0")]
2453 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2455 F: FnMut(&'a T) -> Ordering,
2458 // - 0 <= left <= left + size = right <= self.len()
2459 // - f returns Less for everything in self[..left]
2460 // - f returns Greater for everything in self[right..]
2461 let mut size = self.len();
2463 let mut right = size;
2464 while left < right {
2465 let mid = left + size / 2;
2467 // SAFETY: the while condition means `size` is strictly positive, so
2468 // `size/2 < size`. Thus `left + size/2 < left + size`, which
2469 // coupled with the `left + size <= self.len()` invariant means
2470 // we have `left + size/2 < self.len()`, and this is in-bounds.
2471 let cmp = f(unsafe { self.get_unchecked(mid) });
2473 // The reason why we use if/else control flow rather than match
2474 // is because match reorders comparison operations, which is perf sensitive.
2475 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2478 } else if cmp == Greater {
2481 // SAFETY: same as the `get_unchecked` above
2482 unsafe { crate::intrinsics::assume(mid < self.len()) };
2486 size = right - left;
2489 // SAFETY: directly true from the overall invariant.
2490 // Note that this is `<=`, unlike the assume in the `Ok` path.
2491 unsafe { crate::intrinsics::assume(left <= self.len()) };
2495 /// Binary searches this slice with a key extraction function.
2496 /// This behaves similarly to [`contains`] if this slice is sorted.
2498 /// Assumes that the slice is sorted by the key, for instance with
2499 /// [`sort_by_key`] using the same key extraction function.
2501 /// If the value is found then [`Result::Ok`] is returned, containing the
2502 /// index of the matching element. If there are multiple matches, then any
2503 /// one of the matches could be returned. The index is chosen
2504 /// deterministically, but is subject to change in future versions of Rust.
2505 /// If the value is not found then [`Result::Err`] is returned, containing
2506 /// the index where a matching element could be inserted while maintaining
2509 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2511 /// [`contains`]: slice::contains
2512 /// [`sort_by_key`]: slice::sort_by_key
2513 /// [`binary_search`]: slice::binary_search
2514 /// [`binary_search_by`]: slice::binary_search_by
2515 /// [`partition_point`]: slice::partition_point
2519 /// Looks up a series of four elements in a slice of pairs sorted by
2520 /// their second elements. The first is found, with a uniquely
2521 /// determined position; the second and third are not found; the
2522 /// fourth could match any position in `[1, 4]`.
2525 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2526 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2527 /// (1, 21), (2, 34), (4, 55)];
2529 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2530 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2531 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2532 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2533 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2535 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2536 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2537 // This breaks links when slice is displayed in core, but changing it to use relative links
2538 // would break when the item is re-exported. So allow the core links to be broken for now.
2539 #[allow(rustdoc::broken_intra_doc_links)]
2540 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2542 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2544 F: FnMut(&'a T) -> B,
2547 self.binary_search_by(|k| f(k).cmp(b))
2550 /// Sorts the slice, but might not preserve the order of equal elements.
2552 /// This sort is unstable (i.e., may reorder equal elements), in-place
2553 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2555 /// # Current implementation
2557 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2558 /// which combines the fast average case of randomized quicksort with the fast worst case of
2559 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2560 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2561 /// deterministic behavior.
2563 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2564 /// slice consists of several concatenated sorted sequences.
2569 /// let mut v = [-5, 4, 1, -3, 2];
2571 /// v.sort_unstable();
2572 /// assert!(v == [-5, -3, 1, 2, 4]);
2575 /// [pdqsort]: https://github.com/orlp/pdqsort
2576 #[stable(feature = "sort_unstable", since = "1.20.0")]
2578 pub fn sort_unstable(&mut self)
2582 sort::quicksort(self, T::lt);
2585 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2588 /// This sort is unstable (i.e., may reorder equal elements), in-place
2589 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2591 /// The comparator function must define a total ordering for the elements in the slice. If
2592 /// the ordering is not total, the order of the elements is unspecified. An order is a
2593 /// total order if it is (for all `a`, `b` and `c`):
2595 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2596 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2598 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2599 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2602 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2603 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2604 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2607 /// # Current implementation
2609 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2610 /// which combines the fast average case of randomized quicksort with the fast worst case of
2611 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2612 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2613 /// deterministic behavior.
2615 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2616 /// slice consists of several concatenated sorted sequences.
2621 /// let mut v = [5, 4, 1, 3, 2];
2622 /// v.sort_unstable_by(|a, b| a.cmp(b));
2623 /// assert!(v == [1, 2, 3, 4, 5]);
2625 /// // reverse sorting
2626 /// v.sort_unstable_by(|a, b| b.cmp(a));
2627 /// assert!(v == [5, 4, 3, 2, 1]);
2630 /// [pdqsort]: https://github.com/orlp/pdqsort
2631 #[stable(feature = "sort_unstable", since = "1.20.0")]
2633 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2635 F: FnMut(&T, &T) -> Ordering,
2637 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2640 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2643 /// This sort is unstable (i.e., may reorder equal elements), in-place
2644 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2647 /// # Current implementation
2649 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2650 /// which combines the fast average case of randomized quicksort with the fast worst case of
2651 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2652 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2653 /// deterministic behavior.
2655 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2656 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2657 /// cases where the key function is expensive.
2662 /// let mut v = [-5i32, 4, 1, -3, 2];
2664 /// v.sort_unstable_by_key(|k| k.abs());
2665 /// assert!(v == [1, 2, -3, 4, -5]);
2668 /// [pdqsort]: https://github.com/orlp/pdqsort
2669 #[stable(feature = "sort_unstable", since = "1.20.0")]
2671 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2676 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2679 /// Reorder the slice such that the element at `index` is at its final sorted position.
2681 /// This reordering has the additional property that any value at position `i < index` will be
2682 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2683 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2684 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2685 /// element" in other libraries. It returns a triplet of the following from the reordered slice:
2686 /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
2687 /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
2688 /// and greater-than-or-equal-to the value of the element at `index`.
2690 /// # Current implementation
2692 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2693 /// used for [`sort_unstable`].
2695 /// [`sort_unstable`]: slice::sort_unstable
2699 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2704 /// let mut v = [-5i32, 4, 1, -3, 2];
2706 /// // Find the median
2707 /// v.select_nth_unstable(2);
2709 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2710 /// // about the specified index.
2711 /// assert!(v == [-3, -5, 1, 2, 4] ||
2712 /// v == [-5, -3, 1, 2, 4] ||
2713 /// v == [-3, -5, 1, 4, 2] ||
2714 /// v == [-5, -3, 1, 4, 2]);
2716 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2718 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2722 sort::partition_at_index(self, index, T::lt)
2725 /// Reorder the slice with a comparator function such that the element at `index` is at its
2726 /// final sorted position.
2728 /// This reordering has the additional property that any value at position `i < index` will be
2729 /// less than or equal to any value at a position `j > index` using the comparator function.
2730 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2731 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2732 /// is also known as "kth element" in other libraries. It returns a triplet of the following from
2733 /// the slice reordered according to the provided comparator function: the subslice prior to
2734 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
2735 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
2736 /// the value of the element at `index`.
2738 /// # Current implementation
2740 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2741 /// used for [`sort_unstable`].
2743 /// [`sort_unstable`]: slice::sort_unstable
2747 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2752 /// let mut v = [-5i32, 4, 1, -3, 2];
2754 /// // Find the median as if the slice were sorted in descending order.
2755 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2757 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2758 /// // about the specified index.
2759 /// assert!(v == [2, 4, 1, -5, -3] ||
2760 /// v == [2, 4, 1, -3, -5] ||
2761 /// v == [4, 2, 1, -5, -3] ||
2762 /// v == [4, 2, 1, -3, -5]);
2764 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2766 pub fn select_nth_unstable_by<F>(
2770 ) -> (&mut [T], &mut T, &mut [T])
2772 F: FnMut(&T, &T) -> Ordering,
2774 sort::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
2777 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2778 /// final sorted position.
2780 /// This reordering has the additional property that any value at position `i < index` will be
2781 /// less than or equal to any value at a position `j > index` using the key extraction function.
2782 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2783 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2784 /// is also known as "kth element" in other libraries. It returns a triplet of the following from
2785 /// the slice reordered according to the provided key extraction function: the subslice prior to
2786 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
2787 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
2788 /// the value of the element at `index`.
2790 /// # Current implementation
2792 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2793 /// used for [`sort_unstable`].
2795 /// [`sort_unstable`]: slice::sort_unstable
2799 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2804 /// let mut v = [-5i32, 4, 1, -3, 2];
2806 /// // Return the median as if the array were sorted according to absolute value.
2807 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2809 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2810 /// // about the specified index.
2811 /// assert!(v == [1, 2, -3, 4, -5] ||
2812 /// v == [1, 2, -3, -5, 4] ||
2813 /// v == [2, 1, -3, 4, -5] ||
2814 /// v == [2, 1, -3, -5, 4]);
2816 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2818 pub fn select_nth_unstable_by_key<K, F>(
2822 ) -> (&mut [T], &mut T, &mut [T])
2827 sort::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
2830 /// Moves all consecutive repeated elements to the end of the slice according to the
2831 /// [`PartialEq`] trait implementation.
2833 /// Returns two slices. The first contains no consecutive repeated elements.
2834 /// The second contains all the duplicates in no specified order.
2836 /// If the slice is sorted, the first returned slice contains no duplicates.
2841 /// #![feature(slice_partition_dedup)]
2843 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2845 /// let (dedup, duplicates) = slice.partition_dedup();
2847 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2848 /// assert_eq!(duplicates, [2, 3, 1]);
2850 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2852 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2856 self.partition_dedup_by(|a, b| a == b)
2859 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2860 /// a given equality relation.
2862 /// Returns two slices. The first contains no consecutive repeated elements.
2863 /// The second contains all the duplicates in no specified order.
2865 /// The `same_bucket` function is passed references to two elements from the slice and
2866 /// must determine if the elements compare equal. The elements are passed in opposite order
2867 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2868 /// at the end of the slice.
2870 /// If the slice is sorted, the first returned slice contains no duplicates.
2875 /// #![feature(slice_partition_dedup)]
2877 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2879 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2881 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2882 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2884 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2886 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2888 F: FnMut(&mut T, &mut T) -> bool,
2890 // Although we have a mutable reference to `self`, we cannot make
2891 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2892 // must ensure that the slice is in a valid state at all times.
2894 // The way that we handle this is by using swaps; we iterate
2895 // over all the elements, swapping as we go so that at the end
2896 // the elements we wish to keep are in the front, and those we
2897 // wish to reject are at the back. We can then split the slice.
2898 // This operation is still `O(n)`.
2900 // Example: We start in this state, where `r` represents "next
2901 // read" and `w` represents "next_write`.
2904 // +---+---+---+---+---+---+
2905 // | 0 | 1 | 1 | 2 | 3 | 3 |
2906 // +---+---+---+---+---+---+
2909 // Comparing self[r] against self[w-1], this is not a duplicate, so
2910 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2911 // r and w, leaving us with:
2914 // +---+---+---+---+---+---+
2915 // | 0 | 1 | 1 | 2 | 3 | 3 |
2916 // +---+---+---+---+---+---+
2919 // Comparing self[r] against self[w-1], this value is a duplicate,
2920 // so we increment `r` but leave everything else unchanged:
2923 // +---+---+---+---+---+---+
2924 // | 0 | 1 | 1 | 2 | 3 | 3 |
2925 // +---+---+---+---+---+---+
2928 // Comparing self[r] against self[w-1], this is not a duplicate,
2929 // so swap self[r] and self[w] and advance r and w:
2932 // +---+---+---+---+---+---+
2933 // | 0 | 1 | 2 | 1 | 3 | 3 |
2934 // +---+---+---+---+---+---+
2937 // Not a duplicate, repeat:
2940 // +---+---+---+---+---+---+
2941 // | 0 | 1 | 2 | 3 | 1 | 3 |
2942 // +---+---+---+---+---+---+
2945 // Duplicate, advance r. End of slice. Split at w.
2947 let len = self.len();
2949 return (self, &mut []);
2952 let ptr = self.as_mut_ptr();
2953 let mut next_read: usize = 1;
2954 let mut next_write: usize = 1;
2956 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2957 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2958 // one element before `ptr_write`, but `next_write` starts at 1, so
2959 // `prev_ptr_write` is never less than 0 and is inside the slice.
2960 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2961 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2962 // and `prev_ptr_write.offset(1)`.
2964 // `next_write` is also incremented at most once per loop at most meaning
2965 // no element is skipped when it may need to be swapped.
2967 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2968 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2969 // The explanation is simply that `next_read >= next_write` is always true,
2970 // thus `next_read > next_write - 1` is too.
2972 // Avoid bounds checks by using raw pointers.
2973 while next_read < len {
2974 let ptr_read = ptr.add(next_read);
2975 let prev_ptr_write = ptr.add(next_write - 1);
2976 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2977 if next_read != next_write {
2978 let ptr_write = prev_ptr_write.add(1);
2979 mem::swap(&mut *ptr_read, &mut *ptr_write);
2987 self.split_at_mut(next_write)
2990 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2991 /// to the same key.
2993 /// Returns two slices. The first contains no consecutive repeated elements.
2994 /// The second contains all the duplicates in no specified order.
2996 /// If the slice is sorted, the first returned slice contains no duplicates.
3001 /// #![feature(slice_partition_dedup)]
3003 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
3005 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
3007 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
3008 /// assert_eq!(duplicates, [21, 30, 13]);
3010 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
3012 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
3014 F: FnMut(&mut T) -> K,
3017 self.partition_dedup_by(|a, b| key(a) == key(b))
3020 /// Rotates the slice in-place such that the first `mid` elements of the
3021 /// slice move to the end while the last `self.len() - mid` elements move to
3022 /// the front. After calling `rotate_left`, the element previously at index
3023 /// `mid` will become the first element in the slice.
3027 /// This function will panic if `mid` is greater than the length of the
3028 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
3033 /// Takes linear (in `self.len()`) time.
3038 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3039 /// a.rotate_left(2);
3040 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
3043 /// Rotating a subslice:
3046 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3047 /// a[1..5].rotate_left(1);
3048 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
3050 #[stable(feature = "slice_rotate", since = "1.26.0")]
3051 pub fn rotate_left(&mut self, mid: usize) {
3052 assert!(mid <= self.len());
3053 let k = self.len() - mid;
3054 let p = self.as_mut_ptr();
3056 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3057 // valid for reading and writing, as required by `ptr_rotate`.
3059 rotate::ptr_rotate(mid, p.add(mid), k);
3063 /// Rotates the slice in-place such that the first `self.len() - k`
3064 /// elements of the slice move to the end while the last `k` elements move
3065 /// to the front. After calling `rotate_right`, the element previously at
3066 /// index `self.len() - k` will become the first element in the slice.
3070 /// This function will panic if `k` is greater than the length of the
3071 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
3076 /// Takes linear (in `self.len()`) time.
3081 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3082 /// a.rotate_right(2);
3083 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
3086 /// Rotate a subslice:
3089 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3090 /// a[1..5].rotate_right(1);
3091 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
3093 #[stable(feature = "slice_rotate", since = "1.26.0")]
3094 pub fn rotate_right(&mut self, k: usize) {
3095 assert!(k <= self.len());
3096 let mid = self.len() - k;
3097 let p = self.as_mut_ptr();
3099 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3100 // valid for reading and writing, as required by `ptr_rotate`.
3102 rotate::ptr_rotate(mid, p.add(mid), k);
3106 /// Fills `self` with elements by cloning `value`.
3111 /// let mut buf = vec![0; 10];
3113 /// assert_eq!(buf, vec![1; 10]);
3115 #[doc(alias = "memset")]
3116 #[stable(feature = "slice_fill", since = "1.50.0")]
3117 pub fn fill(&mut self, value: T)
3121 specialize::SpecFill::spec_fill(self, value);
3124 /// Fills `self` with elements returned by calling a closure repeatedly.
3126 /// This method uses a closure to create new values. If you'd rather
3127 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3128 /// trait to generate values, you can pass [`Default::default`] as the
3131 /// [`fill`]: slice::fill
3136 /// let mut buf = vec![1; 10];
3137 /// buf.fill_with(Default::default);
3138 /// assert_eq!(buf, vec![0; 10]);
3140 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3141 pub fn fill_with<F>(&mut self, mut f: F)
3150 /// Copies the elements from `src` into `self`.
3152 /// The length of `src` must be the same as `self`.
3156 /// This function will panic if the two slices have different lengths.
3160 /// Cloning two elements from a slice into another:
3163 /// let src = [1, 2, 3, 4];
3164 /// let mut dst = [0, 0];
3166 /// // Because the slices have to be the same length,
3167 /// // we slice the source slice from four elements
3168 /// // to two. It will panic if we don't do this.
3169 /// dst.clone_from_slice(&src[2..]);
3171 /// assert_eq!(src, [1, 2, 3, 4]);
3172 /// assert_eq!(dst, [3, 4]);
3175 /// Rust enforces that there can only be one mutable reference with no
3176 /// immutable references to a particular piece of data in a particular
3177 /// scope. Because of this, attempting to use `clone_from_slice` on a
3178 /// single slice will result in a compile failure:
3181 /// let mut slice = [1, 2, 3, 4, 5];
3183 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3186 /// To work around this, we can use [`split_at_mut`] to create two distinct
3187 /// sub-slices from a slice:
3190 /// let mut slice = [1, 2, 3, 4, 5];
3193 /// let (left, right) = slice.split_at_mut(2);
3194 /// left.clone_from_slice(&right[1..]);
3197 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3200 /// [`copy_from_slice`]: slice::copy_from_slice
3201 /// [`split_at_mut`]: slice::split_at_mut
3202 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3204 pub fn clone_from_slice(&mut self, src: &[T])
3208 self.spec_clone_from(src);
3211 /// Copies all elements from `src` into `self`, using a memcpy.
3213 /// The length of `src` must be the same as `self`.
3215 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3219 /// This function will panic if the two slices have different lengths.
3223 /// Copying two elements from a slice into another:
3226 /// let src = [1, 2, 3, 4];
3227 /// let mut dst = [0, 0];
3229 /// // Because the slices have to be the same length,
3230 /// // we slice the source slice from four elements
3231 /// // to two. It will panic if we don't do this.
3232 /// dst.copy_from_slice(&src[2..]);
3234 /// assert_eq!(src, [1, 2, 3, 4]);
3235 /// assert_eq!(dst, [3, 4]);
3238 /// Rust enforces that there can only be one mutable reference with no
3239 /// immutable references to a particular piece of data in a particular
3240 /// scope. Because of this, attempting to use `copy_from_slice` on a
3241 /// single slice will result in a compile failure:
3244 /// let mut slice = [1, 2, 3, 4, 5];
3246 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3249 /// To work around this, we can use [`split_at_mut`] to create two distinct
3250 /// sub-slices from a slice:
3253 /// let mut slice = [1, 2, 3, 4, 5];
3256 /// let (left, right) = slice.split_at_mut(2);
3257 /// left.copy_from_slice(&right[1..]);
3260 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3263 /// [`clone_from_slice`]: slice::clone_from_slice
3264 /// [`split_at_mut`]: slice::split_at_mut
3265 #[doc(alias = "memcpy")]
3266 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3268 pub fn copy_from_slice(&mut self, src: &[T])
3272 // The panic code path was put into a cold function to not bloat the
3277 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3279 "source slice length ({}) does not match destination slice length ({})",
3284 if self.len() != src.len() {
3285 len_mismatch_fail(self.len(), src.len());
3288 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3289 // checked to have the same length. The slices cannot overlap because
3290 // mutable references are exclusive.
3292 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3296 /// Copies elements from one part of the slice to another part of itself,
3297 /// using a memmove.
3299 /// `src` is the range within `self` to copy from. `dest` is the starting
3300 /// index of the range within `self` to copy to, which will have the same
3301 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3302 /// must be less than or equal to `self.len()`.
3306 /// This function will panic if either range exceeds the end of the slice,
3307 /// or if the end of `src` is before the start.
3311 /// Copying four bytes within a slice:
3314 /// let mut bytes = *b"Hello, World!";
3316 /// bytes.copy_within(1..5, 8);
3318 /// assert_eq!(&bytes, b"Hello, Wello!");
3320 #[stable(feature = "copy_within", since = "1.37.0")]
3322 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3326 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3327 let count = src_end - src_start;
3328 assert!(dest <= self.len() - count, "dest is out of bounds");
3329 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3330 // as have those for `ptr::add`.
3332 // Derive both `src_ptr` and `dest_ptr` from the same loan
3333 let ptr = self.as_mut_ptr();
3334 let src_ptr = ptr.add(src_start);
3335 let dest_ptr = ptr.add(dest);
3336 ptr::copy(src_ptr, dest_ptr, count);
3340 /// Swaps all elements in `self` with those in `other`.
3342 /// The length of `other` must be the same as `self`.
3346 /// This function will panic if the two slices have different lengths.
3350 /// Swapping two elements across slices:
3353 /// let mut slice1 = [0, 0];
3354 /// let mut slice2 = [1, 2, 3, 4];
3356 /// slice1.swap_with_slice(&mut slice2[2..]);
3358 /// assert_eq!(slice1, [3, 4]);
3359 /// assert_eq!(slice2, [1, 2, 0, 0]);
3362 /// Rust enforces that there can only be one mutable reference to a
3363 /// particular piece of data in a particular scope. Because of this,
3364 /// attempting to use `swap_with_slice` on a single slice will result in
3365 /// a compile failure:
3368 /// let mut slice = [1, 2, 3, 4, 5];
3369 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3372 /// To work around this, we can use [`split_at_mut`] to create two distinct
3373 /// mutable sub-slices from a slice:
3376 /// let mut slice = [1, 2, 3, 4, 5];
3379 /// let (left, right) = slice.split_at_mut(2);
3380 /// left.swap_with_slice(&mut right[1..]);
3383 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3386 /// [`split_at_mut`]: slice::split_at_mut
3387 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3389 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3390 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3391 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3392 // checked to have the same length. The slices cannot overlap because
3393 // mutable references are exclusive.
3395 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3399 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3400 fn align_to_offsets<U>(&self) -> (usize, usize) {
3401 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3402 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3404 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3405 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3406 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3408 // Formula to calculate this is:
3410 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3411 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3413 // Expanded and simplified:
3415 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3416 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3418 // Luckily since all this is constant-evaluated... performance here matters not!
3420 fn gcd(a: usize, b: usize) -> usize {
3421 use crate::intrinsics;
3422 // iterative stein’s algorithm
3423 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3424 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3426 // SAFETY: `a` and `b` are checked to be non-zero values.
3427 let (ctz_a, mut ctz_b) = unsafe {
3434 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3436 let k = ctz_a.min(ctz_b);
3437 let mut a = a >> ctz_a;
3440 // remove all factors of 2 from b
3443 mem::swap(&mut a, &mut b);
3446 // SAFETY: `b` is checked to be non-zero.
3451 ctz_b = intrinsics::cttz_nonzero(b);
3456 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3457 let ts: usize = mem::size_of::<U>() / gcd;
3458 let us: usize = mem::size_of::<T>() / gcd;
3460 // Armed with this knowledge, we can find how many `U`s we can fit!
3461 let us_len = self.len() / ts * us;
3462 // And how many `T`s will be in the trailing slice!
3463 let ts_len = self.len() % ts;
3467 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3470 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3471 /// slice of a new type, and the suffix slice. How exactly the slice is split up is not
3472 /// specified; the middle part may be smaller than necessary. However, if this fails to return a
3473 /// maximal middle part, that is because code is running in a context where performance does not
3474 /// matter, such as a sanitizer attempting to find alignment bugs. Regular code running
3475 /// in a default (debug or release) execution *will* return a maximal middle part.
3477 /// This method has no purpose when either input element `T` or output element `U` are
3478 /// zero-sized and will return the original slice without splitting anything.
3482 /// This method is essentially a `transmute` with respect to the elements in the returned
3483 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3491 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3492 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3493 /// // less_efficient_algorithm_for_bytes(prefix);
3494 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3495 /// // less_efficient_algorithm_for_bytes(suffix);
3498 #[stable(feature = "slice_align_to", since = "1.30.0")]
3500 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3501 // Note that most of this function will be constant-evaluated,
3502 if U::IS_ZST || T::IS_ZST {
3503 // handle ZSTs specially, which is – don't handle them at all.
3504 return (self, &[], &[]);
3507 // First, find at what point do we split between the first and 2nd slice. Easy with
3508 // ptr.align_offset.
3509 let ptr = self.as_ptr();
3510 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3511 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3512 if offset > self.len() {
3515 let (left, rest) = self.split_at(offset);
3516 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3517 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3518 // since the caller guarantees that we can transmute `T` to `U` safely.
3522 from_raw_parts(rest.as_ptr() as *const U, us_len),
3523 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3529 /// Transmute the mutable slice to a mutable slice of another type, ensuring alignment of the
3530 /// types is maintained.
3532 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3533 /// slice of a new type, and the suffix slice. How exactly the slice is split up is not
3534 /// specified; the middle part may be smaller than necessary. However, if this fails to return a
3535 /// maximal middle part, that is because code is running in a context where performance does not
3536 /// matter, such as a sanitizer attempting to find alignment bugs. Regular code running
3537 /// in a default (debug or release) execution *will* return a maximal middle part.
3539 /// This method has no purpose when either input element `T` or output element `U` are
3540 /// zero-sized and will return the original slice without splitting anything.
3544 /// This method is essentially a `transmute` with respect to the elements in the returned
3545 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3553 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3554 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3555 /// // less_efficient_algorithm_for_bytes(prefix);
3556 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3557 /// // less_efficient_algorithm_for_bytes(suffix);
3560 #[stable(feature = "slice_align_to", since = "1.30.0")]
3562 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3563 // Note that most of this function will be constant-evaluated,
3564 if U::IS_ZST || T::IS_ZST {
3565 // handle ZSTs specially, which is – don't handle them at all.
3566 return (self, &mut [], &mut []);
3569 // First, find at what point do we split between the first and 2nd slice. Easy with
3570 // ptr.align_offset.
3571 let ptr = self.as_ptr();
3572 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3573 // rest of the method. This is done by passing a pointer to &[T] with an
3574 // alignment targeted for U.
3575 // `crate::ptr::align_offset` is called with a correctly aligned and
3576 // valid pointer `ptr` (it comes from a reference to `self`) and with
3577 // a size that is a power of two (since it comes from the alignment for U),
3578 // satisfying its safety constraints.
3579 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3580 if offset > self.len() {
3581 (self, &mut [], &mut [])
3583 let (left, rest) = self.split_at_mut(offset);
3584 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3585 let rest_len = rest.len();
3586 let mut_ptr = rest.as_mut_ptr();
3587 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3588 // SAFETY: see comments for `align_to`.
3592 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3593 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3599 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3601 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3602 /// postconditions as that method. You're only assured that
3603 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3605 /// Notably, all of the following are possible:
3606 /// - `prefix.len() >= LANES`.
3607 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3608 /// - `suffix.len() >= LANES`.
3610 /// That said, this is a safe method, so if you're only writing safe code,
3611 /// then this can at most cause incorrect logic, not unsoundness.
3615 /// This will panic if the size of the SIMD type is different from
3616 /// `LANES` times that of the scalar.
3618 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3619 /// that from ever happening, as only power-of-two numbers of lanes are
3620 /// supported. It's possible that, in the future, those restrictions might
3621 /// be lifted in a way that would make it possible to see panics from this
3622 /// method for something like `LANES == 3`.
3627 /// #![feature(portable_simd)]
3628 /// use core::simd::SimdFloat;
3630 /// let short = &[1, 2, 3];
3631 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3632 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3634 /// // They might be split in any possible way between prefix and suffix
3635 /// let it = prefix.iter().chain(suffix).copied();
3636 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3638 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3639 /// use std::ops::Add;
3640 /// use std::simd::f32x4;
3641 /// let (prefix, middle, suffix) = x.as_simd();
3642 /// let sums = f32x4::from_array([
3643 /// prefix.iter().copied().sum(),
3646 /// suffix.iter().copied().sum(),
3648 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3649 /// sums.reduce_sum()
3652 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3653 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3655 #[unstable(feature = "portable_simd", issue = "86656")]
3657 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3659 Simd<T, LANES>: AsRef<[T; LANES]>,
3660 T: simd::SimdElement,
3661 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3663 // These are expected to always match, as vector types are laid out like
3664 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3665 // might as well double-check since it'll optimize away anyhow.
3666 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3668 // SAFETY: The simd types have the same layout as arrays, just with
3669 // potentially-higher alignment, so the de-facto transmutes are sound.
3670 unsafe { self.align_to() }
3673 /// Split a mutable slice into a mutable prefix, a middle of aligned SIMD types,
3674 /// and a mutable suffix.
3676 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3677 /// postconditions as that method. You're only assured that
3678 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3680 /// Notably, all of the following are possible:
3681 /// - `prefix.len() >= LANES`.
3682 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3683 /// - `suffix.len() >= LANES`.
3685 /// That said, this is a safe method, so if you're only writing safe code,
3686 /// then this can at most cause incorrect logic, not unsoundness.
3688 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3692 /// This will panic if the size of the SIMD type is different from
3693 /// `LANES` times that of the scalar.
3695 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3696 /// that from ever happening, as only power-of-two numbers of lanes are
3697 /// supported. It's possible that, in the future, those restrictions might
3698 /// be lifted in a way that would make it possible to see panics from this
3699 /// method for something like `LANES == 3`.
3700 #[unstable(feature = "portable_simd", issue = "86656")]
3702 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3704 Simd<T, LANES>: AsMut<[T; LANES]>,
3705 T: simd::SimdElement,
3706 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3708 // These are expected to always match, as vector types are laid out like
3709 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3710 // might as well double-check since it'll optimize away anyhow.
3711 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3713 // SAFETY: The simd types have the same layout as arrays, just with
3714 // potentially-higher alignment, so the de-facto transmutes are sound.
3715 unsafe { self.align_to_mut() }
3718 /// Checks if the elements of this slice are sorted.
3720 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3721 /// slice yields exactly zero or one element, `true` is returned.
3723 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3724 /// implies that this function returns `false` if any two consecutive items are not
3730 /// #![feature(is_sorted)]
3731 /// let empty: [i32; 0] = [];
3733 /// assert!([1, 2, 2, 9].is_sorted());
3734 /// assert!(![1, 3, 2, 4].is_sorted());
3735 /// assert!([0].is_sorted());
3736 /// assert!(empty.is_sorted());
3737 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3740 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3742 pub fn is_sorted(&self) -> bool
3746 self.is_sorted_by(|a, b| a.partial_cmp(b))
3749 /// Checks if the elements of this slice are sorted using the given comparator function.
3751 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3752 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3753 /// [`is_sorted`]; see its documentation for more information.
3755 /// [`is_sorted`]: slice::is_sorted
3756 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3758 pub fn is_sorted_by<'a, F>(&'a self, mut compare: F) -> bool
3760 F: FnMut(&'a T, &'a T) -> Option<Ordering>,
3762 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3765 /// Checks if the elements of this slice are sorted using the given key extraction function.
3767 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3768 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3769 /// documentation for more information.
3771 /// [`is_sorted`]: slice::is_sorted
3776 /// #![feature(is_sorted)]
3778 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3779 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3782 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3784 pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool
3786 F: FnMut(&'a T) -> K,
3789 self.iter().is_sorted_by_key(f)
3792 /// Returns the index of the partition point according to the given predicate
3793 /// (the index of the first element of the second partition).
3795 /// The slice is assumed to be partitioned according to the given predicate.
3796 /// This means that all elements for which the predicate returns true are at the start of the slice
3797 /// and all elements for which the predicate returns false are at the end.
3798 /// For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0`
3799 /// (all odd numbers are at the start, all even at the end).
3801 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3802 /// as this method performs a kind of binary search.
3804 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3806 /// [`binary_search`]: slice::binary_search
3807 /// [`binary_search_by`]: slice::binary_search_by
3808 /// [`binary_search_by_key`]: slice::binary_search_by_key
3813 /// let v = [1, 2, 3, 3, 5, 6, 7];
3814 /// let i = v.partition_point(|&x| x < 5);
3816 /// assert_eq!(i, 4);
3817 /// assert!(v[..i].iter().all(|&x| x < 5));
3818 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3821 /// If all elements of the slice match the predicate, including if the slice
3822 /// is empty, then the length of the slice will be returned:
3825 /// let a = [2, 4, 8];
3826 /// assert_eq!(a.partition_point(|x| x < &100), a.len());
3827 /// let a: [i32; 0] = [];
3828 /// assert_eq!(a.partition_point(|x| x < &100), 0);
3831 /// If you want to insert an item to a sorted vector, while maintaining
3835 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
3837 /// let idx = s.partition_point(|&x| x < num);
3838 /// s.insert(idx, num);
3839 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
3841 #[stable(feature = "partition_point", since = "1.52.0")]
3843 pub fn partition_point<P>(&self, mut pred: P) -> usize
3845 P: FnMut(&T) -> bool,
3847 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3850 /// Removes the subslice corresponding to the given range
3851 /// and returns a reference to it.
3853 /// Returns `None` and does not modify the slice if the given
3854 /// range is out of bounds.
3856 /// Note that this method only accepts one-sided ranges such as
3857 /// `2..` or `..6`, but not `2..6`.
3861 /// Taking the first three elements of a slice:
3864 /// #![feature(slice_take)]
3866 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3867 /// let mut first_three = slice.take(..3).unwrap();
3869 /// assert_eq!(slice, &['d']);
3870 /// assert_eq!(first_three, &['a', 'b', 'c']);
3873 /// Taking the last two elements of a slice:
3876 /// #![feature(slice_take)]
3878 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3879 /// let mut tail = slice.take(2..).unwrap();
3881 /// assert_eq!(slice, &['a', 'b']);
3882 /// assert_eq!(tail, &['c', 'd']);
3885 /// Getting `None` when `range` is out of bounds:
3888 /// #![feature(slice_take)]
3890 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3892 /// assert_eq!(None, slice.take(5..));
3893 /// assert_eq!(None, slice.take(..5));
3894 /// assert_eq!(None, slice.take(..=4));
3895 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3896 /// assert_eq!(Some(expected), slice.take(..4));
3899 #[must_use = "method does not modify the slice if the range is out of bounds"]
3900 #[unstable(feature = "slice_take", issue = "62280")]
3901 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3902 let (direction, split_index) = split_point_of(range)?;
3903 if split_index > self.len() {
3906 let (front, back) = self.split_at(split_index);
3908 Direction::Front => {
3912 Direction::Back => {
3919 /// Removes the subslice corresponding to the given range
3920 /// and returns a mutable reference to it.
3922 /// Returns `None` and does not modify the slice if the given
3923 /// range is out of bounds.
3925 /// Note that this method only accepts one-sided ranges such as
3926 /// `2..` or `..6`, but not `2..6`.
3930 /// Taking the first three elements of a slice:
3933 /// #![feature(slice_take)]
3935 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3936 /// let mut first_three = slice.take_mut(..3).unwrap();
3938 /// assert_eq!(slice, &mut ['d']);
3939 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3942 /// Taking the last two elements of a slice:
3945 /// #![feature(slice_take)]
3947 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3948 /// let mut tail = slice.take_mut(2..).unwrap();
3950 /// assert_eq!(slice, &mut ['a', 'b']);
3951 /// assert_eq!(tail, &mut ['c', 'd']);
3954 /// Getting `None` when `range` is out of bounds:
3957 /// #![feature(slice_take)]
3959 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3961 /// assert_eq!(None, slice.take_mut(5..));
3962 /// assert_eq!(None, slice.take_mut(..5));
3963 /// assert_eq!(None, slice.take_mut(..=4));
3964 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3965 /// assert_eq!(Some(expected), slice.take_mut(..4));
3968 #[must_use = "method does not modify the slice if the range is out of bounds"]
3969 #[unstable(feature = "slice_take", issue = "62280")]
3970 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3971 self: &mut &'a mut Self,
3973 ) -> Option<&'a mut Self> {
3974 let (direction, split_index) = split_point_of(range)?;
3975 if split_index > self.len() {
3978 let (front, back) = mem::take(self).split_at_mut(split_index);
3980 Direction::Front => {
3984 Direction::Back => {
3991 /// Removes the first element of the slice and returns a reference
3994 /// Returns `None` if the slice is empty.
3999 /// #![feature(slice_take)]
4001 /// let mut slice: &[_] = &['a', 'b', 'c'];
4002 /// let first = slice.take_first().unwrap();
4004 /// assert_eq!(slice, &['b', 'c']);
4005 /// assert_eq!(first, &'a');
4008 #[unstable(feature = "slice_take", issue = "62280")]
4009 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
4010 let (first, rem) = self.split_first()?;
4015 /// Removes the first element of the slice and returns a mutable
4016 /// reference to it.
4018 /// Returns `None` if the slice is empty.
4023 /// #![feature(slice_take)]
4025 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4026 /// let first = slice.take_first_mut().unwrap();
4029 /// assert_eq!(slice, &['b', 'c']);
4030 /// assert_eq!(first, &'d');
4033 #[unstable(feature = "slice_take", issue = "62280")]
4034 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4035 let (first, rem) = mem::take(self).split_first_mut()?;
4040 /// Removes the last element of the slice and returns a reference
4043 /// Returns `None` if the slice is empty.
4048 /// #![feature(slice_take)]
4050 /// let mut slice: &[_] = &['a', 'b', 'c'];
4051 /// let last = slice.take_last().unwrap();
4053 /// assert_eq!(slice, &['a', 'b']);
4054 /// assert_eq!(last, &'c');
4057 #[unstable(feature = "slice_take", issue = "62280")]
4058 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
4059 let (last, rem) = self.split_last()?;
4064 /// Removes the last element of the slice and returns a mutable
4065 /// reference to it.
4067 /// Returns `None` if the slice is empty.
4072 /// #![feature(slice_take)]
4074 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4075 /// let last = slice.take_last_mut().unwrap();
4078 /// assert_eq!(slice, &['a', 'b']);
4079 /// assert_eq!(last, &'d');
4082 #[unstable(feature = "slice_take", issue = "62280")]
4083 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4084 let (last, rem) = mem::take(self).split_last_mut()?;
4089 /// Returns mutable references to many indices at once, without doing any checks.
4091 /// For a safe alternative see [`get_many_mut`].
4095 /// Calling this method with overlapping or out-of-bounds indices is *[undefined behavior]*
4096 /// even if the resulting references are not used.
4101 /// #![feature(get_many_mut)]
4103 /// let x = &mut [1, 2, 4];
4106 /// let [a, b] = x.get_many_unchecked_mut([0, 2]);
4110 /// assert_eq!(x, &[10, 2, 400]);
4113 /// [`get_many_mut`]: slice::get_many_mut
4114 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
4115 #[unstable(feature = "get_many_mut", issue = "104642")]
4117 pub unsafe fn get_many_unchecked_mut<const N: usize>(
4119 indices: [usize; N],
4121 // NB: This implementation is written as it is because any variation of
4122 // `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
4123 // or generate worse code otherwise. This is also why we need to go
4124 // through a raw pointer here.
4125 let slice: *mut [T] = self;
4126 let mut arr: mem::MaybeUninit<[&mut T; N]> = mem::MaybeUninit::uninit();
4127 let arr_ptr = arr.as_mut_ptr();
4129 // SAFETY: We expect `indices` to contain disjunct values that are
4130 // in bounds of `self`.
4133 let idx = *indices.get_unchecked(i);
4134 *(*arr_ptr).get_unchecked_mut(i) = &mut *slice.get_unchecked_mut(idx);
4140 /// Returns mutable references to many indices at once.
4142 /// Returns an error if any index is out-of-bounds, or if the same index was
4143 /// passed more than once.
4148 /// #![feature(get_many_mut)]
4150 /// let v = &mut [1, 2, 3];
4151 /// if let Ok([a, b]) = v.get_many_mut([0, 2]) {
4155 /// assert_eq!(v, &[413, 2, 612]);
4157 #[unstable(feature = "get_many_mut", issue = "104642")]
4159 pub fn get_many_mut<const N: usize>(
4161 indices: [usize; N],
4162 ) -> Result<[&mut T; N], GetManyMutError<N>> {
4163 if !get_many_check_valid(&indices, self.len()) {
4164 return Err(GetManyMutError { _private: () });
4166 // SAFETY: The `get_many_check_valid()` call checked that all indices
4167 // are disjunct and in bounds.
4168 unsafe { Ok(self.get_many_unchecked_mut(indices)) }
4172 impl<T, const N: usize> [[T; N]] {
4173 /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
4177 /// This panics if the length of the resulting slice would overflow a `usize`.
4179 /// This is only possible when flattening a slice of arrays of zero-sized
4180 /// types, and thus tends to be irrelevant in practice. If
4181 /// `size_of::<T>() > 0`, this will never panic.
4186 /// #![feature(slice_flatten)]
4188 /// assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);
4191 /// [[1, 2, 3], [4, 5, 6]].flatten(),
4192 /// [[1, 2], [3, 4], [5, 6]].flatten(),
4195 /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
4196 /// assert!(slice_of_empty_arrays.flatten().is_empty());
4198 /// let empty_slice_of_arrays: &[[u32; 10]] = &[];
4199 /// assert!(empty_slice_of_arrays.flatten().is_empty());
4201 #[unstable(feature = "slice_flatten", issue = "95629")]
4202 pub fn flatten(&self) -> &[T] {
4203 let len = if T::IS_ZST {
4204 self.len().checked_mul(N).expect("slice len overflow")
4206 // SAFETY: `self.len() * N` cannot overflow because `self` is
4207 // already in the address space.
4208 unsafe { self.len().unchecked_mul(N) }
4210 // SAFETY: `[T]` is layout-identical to `[T; N]`
4211 unsafe { from_raw_parts(self.as_ptr().cast(), len) }
4214 /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
4218 /// This panics if the length of the resulting slice would overflow a `usize`.
4220 /// This is only possible when flattening a slice of arrays of zero-sized
4221 /// types, and thus tends to be irrelevant in practice. If
4222 /// `size_of::<T>() > 0`, this will never panic.
4227 /// #![feature(slice_flatten)]
4229 /// fn add_5_to_all(slice: &mut [i32]) {
4230 /// for i in slice {
4235 /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
4236 /// add_5_to_all(array.flatten_mut());
4237 /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
4239 #[unstable(feature = "slice_flatten", issue = "95629")]
4240 pub fn flatten_mut(&mut self) -> &mut [T] {
4241 let len = if T::IS_ZST {
4242 self.len().checked_mul(N).expect("slice len overflow")
4244 // SAFETY: `self.len() * N` cannot overflow because `self` is
4245 // already in the address space.
4246 unsafe { self.len().unchecked_mul(N) }
4248 // SAFETY: `[T]` is layout-identical to `[T; N]`
4249 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
4255 /// Sorts the slice of floats.
4257 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4258 /// the ordering defined by [`f32::total_cmp`].
4260 /// # Current implementation
4262 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4267 /// #![feature(sort_floats)]
4268 /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
4270 /// v.sort_floats();
4271 /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
4272 /// assert_eq!(&v[..8], &sorted[..8]);
4273 /// assert!(v[8].is_nan());
4275 #[unstable(feature = "sort_floats", issue = "93396")]
4277 pub fn sort_floats(&mut self) {
4278 self.sort_unstable_by(f32::total_cmp);
4284 /// Sorts the slice of floats.
4286 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4287 /// the ordering defined by [`f64::total_cmp`].
4289 /// # Current implementation
4291 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4296 /// #![feature(sort_floats)]
4297 /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
4299 /// v.sort_floats();
4300 /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
4301 /// assert_eq!(&v[..8], &sorted[..8]);
4302 /// assert!(v[8].is_nan());
4304 #[unstable(feature = "sort_floats", issue = "93396")]
4306 pub fn sort_floats(&mut self) {
4307 self.sort_unstable_by(f64::total_cmp);
4311 trait CloneFromSpec<T> {
4312 fn spec_clone_from(&mut self, src: &[T]);
4315 impl<T> CloneFromSpec<T> for [T]
4320 default fn spec_clone_from(&mut self, src: &[T]) {
4321 assert!(self.len() == src.len(), "destination and source slices have different lengths");
4322 // NOTE: We need to explicitly slice them to the same length
4323 // to make it easier for the optimizer to elide bounds checking.
4324 // But since it can't be relied on we also have an explicit specialization for T: Copy.
4325 let len = self.len();
4326 let src = &src[..len];
4328 self[i].clone_from(&src[i]);
4333 impl<T> CloneFromSpec<T> for [T]
4338 fn spec_clone_from(&mut self, src: &[T]) {
4339 self.copy_from_slice(src);
4343 #[stable(feature = "rust1", since = "1.0.0")]
4344 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4345 impl<T> const Default for &[T] {
4346 /// Creates an empty slice.
4347 fn default() -> Self {
4352 #[stable(feature = "mut_slice_default", since = "1.5.0")]
4353 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4354 impl<T> const Default for &mut [T] {
4355 /// Creates a mutable empty slice.
4356 fn default() -> Self {
4361 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4362 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4363 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4364 /// `str`) to slices, and then this trait will be replaced or abolished.
4365 pub trait SlicePattern {
4366 /// The element type of the slice being matched on.
4369 /// Currently, the consumers of `SlicePattern` need a slice.
4370 fn as_slice(&self) -> &[Self::Item];
4373 #[stable(feature = "slice_strip", since = "1.51.0")]
4374 impl<T> SlicePattern for [T] {
4378 fn as_slice(&self) -> &[Self::Item] {
4383 #[stable(feature = "slice_strip", since = "1.51.0")]
4384 impl<T, const N: usize> SlicePattern for [T; N] {
4388 fn as_slice(&self) -> &[Self::Item] {
4393 /// This checks every index against each other, and against `len`.
4395 /// This will do `binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, ..`
4396 /// comparison operations.
4397 fn get_many_check_valid<const N: usize>(indices: &[usize; N], len: usize) -> bool {
4398 // NB: The optimzer should inline the loops into a sequence
4399 // of instructions without additional branching.
4400 let mut valid = true;
4401 for (i, &idx) in indices.iter().enumerate() {
4403 for &idx2 in &indices[..i] {
4404 valid &= idx != idx2;
4410 /// The error type returned by [`get_many_mut<N>`][`slice::get_many_mut`].
4412 /// It indicates one of two possible errors:
4413 /// - An index is out-of-bounds.
4414 /// - The same index appeared multiple times in the array.
4419 /// #![feature(get_many_mut)]
4421 /// let v = &mut [1, 2, 3];
4422 /// assert!(v.get_many_mut([0, 999]).is_err());
4423 /// assert!(v.get_many_mut([1, 1]).is_err());
4425 #[unstable(feature = "get_many_mut", issue = "104642")]
4426 // NB: The N here is there to be forward-compatible with adding more details
4427 // to the error type at a later point
4428 pub struct GetManyMutError<const N: usize> {
4432 #[unstable(feature = "get_many_mut", issue = "104642")]
4433 impl<const N: usize> fmt::Debug for GetManyMutError<N> {
4434 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
4435 f.debug_struct("GetManyMutError").finish_non_exhaustive()
4439 #[unstable(feature = "get_many_mut", issue = "104642")]
4440 impl<const N: usize> fmt::Display for GetManyMutError<N> {
4441 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
4442 fmt::Display::fmt("an index is out of bounds or appeared multiple times in the array", f)