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};
10 use crate::marker::Copy;
12 use crate::num::NonZeroUsize;
13 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
14 use crate::option::Option;
15 use crate::option::Option::{None, Some};
17 use crate::result::Result;
18 use crate::result::Result::{Err, Ok};
19 use crate::simd::{self, Simd};
23 feature = "slice_internals",
25 reason = "exposed from core to be reused in std; use the memchr crate"
27 /// Pure rust memchr implementation, taken from rust-memchr
39 #[stable(feature = "rust1", since = "1.0.0")]
40 pub use iter::{Chunks, ChunksMut, Windows};
41 #[stable(feature = "rust1", since = "1.0.0")]
42 pub use iter::{Iter, IterMut};
43 #[stable(feature = "rust1", since = "1.0.0")]
44 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
46 #[stable(feature = "slice_rsplit", since = "1.27.0")]
47 pub use iter::{RSplit, RSplitMut};
49 #[stable(feature = "chunks_exact", since = "1.31.0")]
50 pub use iter::{ChunksExact, ChunksExactMut};
52 #[stable(feature = "rchunks", since = "1.31.0")]
53 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
55 #[unstable(feature = "array_chunks", issue = "74985")]
56 pub use iter::{ArrayChunks, ArrayChunksMut};
58 #[unstable(feature = "array_windows", issue = "75027")]
59 pub use iter::ArrayWindows;
61 #[unstable(feature = "slice_group_by", issue = "80552")]
62 pub use iter::{GroupBy, GroupByMut};
64 #[stable(feature = "split_inclusive", since = "1.51.0")]
65 pub use iter::{SplitInclusive, SplitInclusiveMut};
67 #[stable(feature = "rust1", since = "1.0.0")]
68 pub use raw::{from_raw_parts, from_raw_parts_mut};
70 #[stable(feature = "from_ref", since = "1.28.0")]
71 pub use raw::{from_mut, from_ref};
73 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
74 pub use raw::{from_mut_ptr_range, from_ptr_range};
76 // This function is public only because there is no other way to unit test heapsort.
77 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
78 pub use sort::heapsort;
80 #[stable(feature = "slice_get_slice", since = "1.28.0")]
81 pub use index::SliceIndex;
83 #[unstable(feature = "slice_range", issue = "76393")]
86 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
87 pub use ascii::EscapeAscii;
89 /// Calculates the direction and split point of a one-sided range.
91 /// This is a helper function for `take` and `take_mut` that returns
92 /// the direction of the split (front or back) as well as the index at
93 /// which to split. Returns `None` if the split index would overflow.
95 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
98 Some(match (range.start_bound(), range.end_bound()) {
99 (Unbounded, Excluded(i)) => (Direction::Front, *i),
100 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
101 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
102 (Included(i), Unbounded) => (Direction::Back, *i),
115 /// Returns the number of elements in the slice.
120 /// let a = [1, 2, 3];
121 /// assert_eq!(a.len(), 3);
123 #[lang = "slice_len_fn"]
124 #[stable(feature = "rust1", since = "1.0.0")]
125 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
127 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
128 pub const fn len(&self) -> usize {
129 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
130 // As of this writing this causes a "Const-stable functions can only call other
131 // const-stable functions" error.
133 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
134 // and PtrComponents<T> have the same memory layouts. Only std can make this
136 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
139 /// Returns `true` if the slice has a length of 0.
144 /// let a = [1, 2, 3];
145 /// assert!(!a.is_empty());
147 #[stable(feature = "rust1", since = "1.0.0")]
148 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
150 pub const fn is_empty(&self) -> bool {
154 /// Returns the first element of the slice, or `None` if it is empty.
159 /// let v = [10, 40, 30];
160 /// assert_eq!(Some(&10), v.first());
162 /// let w: &[i32] = &[];
163 /// assert_eq!(None, w.first());
165 #[stable(feature = "rust1", since = "1.0.0")]
166 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
168 pub const fn first(&self) -> Option<&T> {
169 if let [first, ..] = self { Some(first) } else { None }
172 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
177 /// let x = &mut [0, 1, 2];
179 /// if let Some(first) = x.first_mut() {
182 /// assert_eq!(x, &[5, 1, 2]);
184 #[stable(feature = "rust1", since = "1.0.0")]
185 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
187 pub const fn first_mut(&mut self) -> Option<&mut T> {
188 if let [first, ..] = self { Some(first) } else { None }
191 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
196 /// let x = &[0, 1, 2];
198 /// if let Some((first, elements)) = x.split_first() {
199 /// assert_eq!(first, &0);
200 /// assert_eq!(elements, &[1, 2]);
203 #[stable(feature = "slice_splits", since = "1.5.0")]
204 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
206 pub const fn split_first(&self) -> Option<(&T, &[T])> {
207 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
210 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
215 /// let x = &mut [0, 1, 2];
217 /// if let Some((first, elements)) = x.split_first_mut() {
222 /// assert_eq!(x, &[3, 4, 5]);
224 #[stable(feature = "slice_splits", since = "1.5.0")]
225 #[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")]
246 pub const fn split_last(&self) -> Option<(&T, &[T])> {
247 if let [init @ .., last] = self { Some((last, init)) } else { None }
250 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
255 /// let x = &mut [0, 1, 2];
257 /// if let Some((last, elements)) = x.split_last_mut() {
262 /// assert_eq!(x, &[4, 5, 3]);
264 #[stable(feature = "slice_splits", since = "1.5.0")]
265 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
267 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
268 if let [init @ .., last] = self { Some((last, init)) } else { None }
271 /// Returns the last element of the slice, or `None` if it is empty.
276 /// let v = [10, 40, 30];
277 /// assert_eq!(Some(&30), v.last());
279 /// let w: &[i32] = &[];
280 /// assert_eq!(None, w.last());
282 #[stable(feature = "rust1", since = "1.0.0")]
283 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
285 pub const fn last(&self) -> Option<&T> {
286 if let [.., last] = self { Some(last) } else { None }
289 /// Returns a mutable pointer to the last item in the slice.
294 /// let x = &mut [0, 1, 2];
296 /// if let Some(last) = x.last_mut() {
299 /// assert_eq!(x, &[0, 1, 10]);
301 #[stable(feature = "rust1", since = "1.0.0")]
302 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
304 pub const fn last_mut(&mut self) -> Option<&mut T> {
305 if let [.., last] = self { Some(last) } else { None }
308 /// Returns a reference to an element or subslice depending on the type of
311 /// - If given a position, returns a reference to the element at that
312 /// position or `None` if out of bounds.
313 /// - If given a range, returns the subslice corresponding to that range,
314 /// or `None` if out of bounds.
319 /// let v = [10, 40, 30];
320 /// assert_eq!(Some(&40), v.get(1));
321 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
322 /// assert_eq!(None, v.get(3));
323 /// assert_eq!(None, v.get(0..4));
325 #[stable(feature = "rust1", since = "1.0.0")]
326 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
328 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
330 I: ~const SliceIndex<Self>,
335 /// Returns a mutable reference to an element or subslice depending on the
336 /// type of index (see [`get`]) or `None` if the index is out of bounds.
338 /// [`get`]: slice::get
343 /// let x = &mut [0, 1, 2];
345 /// if let Some(elem) = x.get_mut(1) {
348 /// assert_eq!(x, &[0, 42, 2]);
350 #[stable(feature = "rust1", since = "1.0.0")]
351 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
353 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
355 I: ~const SliceIndex<Self>,
360 /// Returns a reference to an element or subslice, without doing bounds
363 /// For a safe alternative see [`get`].
367 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
368 /// even if the resulting reference is not used.
370 /// [`get`]: slice::get
371 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
376 /// let x = &[1, 2, 4];
379 /// assert_eq!(x.get_unchecked(1), &2);
382 #[stable(feature = "rust1", since = "1.0.0")]
383 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
385 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
387 I: ~const SliceIndex<Self>,
389 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
390 // the slice is dereferenceable because `self` is a safe reference.
391 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
392 unsafe { &*index.get_unchecked(self) }
395 /// Returns a mutable reference to an element or subslice, without doing
398 /// For a safe alternative see [`get_mut`].
402 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
403 /// even if the resulting reference is not used.
405 /// [`get_mut`]: slice::get_mut
406 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
411 /// let x = &mut [1, 2, 4];
414 /// let elem = x.get_unchecked_mut(1);
417 /// assert_eq!(x, &[1, 13, 4]);
419 #[stable(feature = "rust1", since = "1.0.0")]
420 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
422 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
424 I: ~const SliceIndex<Self>,
426 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
427 // the slice is dereferenceable because `self` is a safe reference.
428 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
429 unsafe { &mut *index.get_unchecked_mut(self) }
432 /// Returns a raw pointer to the slice's buffer.
434 /// The caller must ensure that the slice outlives the pointer this
435 /// function returns, or else it will end up pointing to garbage.
437 /// The caller must also ensure that the memory the pointer (non-transitively) points to
438 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
439 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
441 /// Modifying the container referenced by this slice may cause its buffer
442 /// to be reallocated, which would also make any pointers to it invalid.
447 /// let x = &[1, 2, 4];
448 /// let x_ptr = x.as_ptr();
451 /// for i in 0..x.len() {
452 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
457 /// [`as_mut_ptr`]: slice::as_mut_ptr
458 #[stable(feature = "rust1", since = "1.0.0")]
459 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
461 pub const fn as_ptr(&self) -> *const T {
462 self as *const [T] as *const T
465 /// Returns an unsafe mutable pointer to the slice's buffer.
467 /// The caller must ensure that the slice outlives the pointer this
468 /// function returns, or else it will end up pointing to garbage.
470 /// Modifying the container referenced by this slice may cause its buffer
471 /// to be reallocated, which would also make any pointers to it invalid.
476 /// let x = &mut [1, 2, 4];
477 /// let x_ptr = x.as_mut_ptr();
480 /// for i in 0..x.len() {
481 /// *x_ptr.add(i) += 2;
484 /// assert_eq!(x, &[3, 4, 6]);
486 #[stable(feature = "rust1", since = "1.0.0")]
487 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
489 pub const fn as_mut_ptr(&mut self) -> *mut T {
490 self as *mut [T] as *mut T
493 /// Returns the two raw pointers spanning the slice.
495 /// The returned range is half-open, which means that the end pointer
496 /// points *one past* the last element of the slice. This way, an empty
497 /// slice is represented by two equal pointers, and the difference between
498 /// the two pointers represents the size of the slice.
500 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
501 /// requires extra caution, as it does not point to a valid element in the
504 /// This function is useful for interacting with foreign interfaces which
505 /// use two pointers to refer to a range of elements in memory, as is
508 /// It can also be useful to check if a pointer to an element refers to an
509 /// element of this slice:
512 /// let a = [1, 2, 3];
513 /// let x = &a[1] as *const _;
514 /// let y = &5 as *const _;
516 /// assert!(a.as_ptr_range().contains(&x));
517 /// assert!(!a.as_ptr_range().contains(&y));
520 /// [`as_ptr`]: slice::as_ptr
521 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
522 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
524 pub const fn as_ptr_range(&self) -> Range<*const T> {
525 let start = self.as_ptr();
526 // SAFETY: The `add` here is safe, because:
528 // - Both pointers are part of the same object, as pointing directly
529 // past the object also counts.
531 // - The size of the slice is never larger than isize::MAX bytes, as
533 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
534 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
535 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
536 // (This doesn't seem normative yet, but the very same assumption is
537 // made in many places, including the Index implementation of slices.)
539 // - There is no wrapping around involved, as slices do not wrap past
540 // the end of the address space.
542 // See the documentation of pointer::add.
543 let end = unsafe { start.add(self.len()) };
547 /// Returns the two unsafe mutable pointers spanning the slice.
549 /// The returned range is half-open, which means that the end pointer
550 /// points *one past* the last element of the slice. This way, an empty
551 /// slice is represented by two equal pointers, and the difference between
552 /// the two pointers represents the size of the slice.
554 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
555 /// pointer requires extra caution, as it does not point to a valid element
558 /// This function is useful for interacting with foreign interfaces which
559 /// use two pointers to refer to a range of elements in memory, as is
562 /// [`as_mut_ptr`]: slice::as_mut_ptr
563 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
564 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
566 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
567 let start = self.as_mut_ptr();
568 // SAFETY: See as_ptr_range() above for why `add` here is safe.
569 let end = unsafe { start.add(self.len()) };
573 /// Swaps two elements in the slice.
577 /// * a - The index of the first element
578 /// * b - The index of the second element
582 /// Panics if `a` or `b` are out of bounds.
587 /// let mut v = ["a", "b", "c", "d", "e"];
589 /// assert!(v == ["a", "b", "e", "d", "c"]);
591 #[stable(feature = "rust1", since = "1.0.0")]
592 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
595 pub const fn swap(&mut self, a: usize, b: usize) {
596 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
597 // Can't take two mutable loans from one vector, so instead use raw pointers.
598 let pa = ptr::addr_of_mut!(self[a]);
599 let pb = ptr::addr_of_mut!(self[b]);
600 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
601 // to elements in the slice and therefore are guaranteed to be valid and aligned.
602 // Note that accessing the elements behind `a` and `b` is checked and will
603 // panic when out of bounds.
609 /// Swaps two elements in the slice, without doing bounds checking.
611 /// For a safe alternative see [`swap`].
615 /// * a - The index of the first element
616 /// * b - The index of the second element
620 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
621 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
626 /// #![feature(slice_swap_unchecked)]
628 /// let mut v = ["a", "b", "c", "d"];
629 /// // SAFETY: we know that 1 and 3 are both indices of the slice
630 /// unsafe { v.swap_unchecked(1, 3) };
631 /// assert!(v == ["a", "d", "c", "b"]);
634 /// [`swap`]: slice::swap
635 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
636 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
637 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
638 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
639 #[cfg(debug_assertions)]
645 let ptr = self.as_mut_ptr();
646 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
648 ptr::swap(ptr.add(a), ptr.add(b));
652 /// Reverses the order of elements in the slice, in place.
657 /// let mut v = [1, 2, 3];
659 /// assert!(v == [3, 2, 1]);
661 #[stable(feature = "rust1", since = "1.0.0")]
663 pub fn reverse(&mut self) {
664 let half_len = self.len() / 2;
665 let Range { start, end } = self.as_mut_ptr_range();
667 // These slices will skip the middle item for an odd length,
668 // since that one doesn't need to move.
669 let (front_half, back_half) =
670 // SAFETY: Both are subparts of the original slice, so the memory
671 // range is valid, and they don't overlap because they're each only
672 // half (or less) of the original slice.
675 slice::from_raw_parts_mut(start, half_len),
676 slice::from_raw_parts_mut(end.sub(half_len), half_len),
680 // Introducing a function boundary here means that the two halves
681 // get `noalias` markers, allowing better optimization as LLVM
682 // knows that they're disjoint, unlike in the original slice.
683 revswap(front_half, back_half, half_len);
686 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
687 debug_assert_eq!(a.len(), n);
688 debug_assert_eq!(b.len(), n);
690 // Because this function is first compiled in isolation,
691 // this check tells LLVM that the indexing below is
692 // in-bounds. Then after inlining -- once the actual
693 // lengths of the slices are known -- it's removed.
694 let (a, b) = (&mut a[..n], &mut b[..n]);
697 mem::swap(&mut a[i], &mut b[n - 1 - i]);
702 /// Returns an iterator over the slice.
707 /// let x = &[1, 2, 4];
708 /// let mut iterator = x.iter();
710 /// assert_eq!(iterator.next(), Some(&1));
711 /// assert_eq!(iterator.next(), Some(&2));
712 /// assert_eq!(iterator.next(), Some(&4));
713 /// assert_eq!(iterator.next(), None);
715 #[stable(feature = "rust1", since = "1.0.0")]
717 pub fn iter(&self) -> Iter<'_, T> {
721 /// Returns an iterator that allows modifying each value.
726 /// let x = &mut [1, 2, 4];
727 /// for elem in x.iter_mut() {
730 /// assert_eq!(x, &[3, 4, 6]);
732 #[stable(feature = "rust1", since = "1.0.0")]
734 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
738 /// Returns an iterator over all contiguous windows of length
739 /// `size`. The windows overlap. If the slice is shorter than
740 /// `size`, the iterator returns no values.
744 /// Panics if `size` is 0.
749 /// let slice = ['r', 'u', 's', 't'];
750 /// let mut iter = slice.windows(2);
751 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
752 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
753 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
754 /// assert!(iter.next().is_none());
757 /// If the slice is shorter than `size`:
760 /// let slice = ['f', 'o', 'o'];
761 /// let mut iter = slice.windows(4);
762 /// assert!(iter.next().is_none());
764 #[stable(feature = "rust1", since = "1.0.0")]
766 pub fn windows(&self, size: usize) -> Windows<'_, T> {
767 let size = NonZeroUsize::new(size).expect("size is zero");
768 Windows::new(self, size)
771 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
772 /// beginning of the slice.
774 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
775 /// slice, then the last chunk will not have length `chunk_size`.
777 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
778 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
783 /// Panics if `chunk_size` is 0.
788 /// let slice = ['l', 'o', 'r', 'e', 'm'];
789 /// let mut iter = slice.chunks(2);
790 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
791 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
792 /// assert_eq!(iter.next().unwrap(), &['m']);
793 /// assert!(iter.next().is_none());
796 /// [`chunks_exact`]: slice::chunks_exact
797 /// [`rchunks`]: slice::rchunks
798 #[stable(feature = "rust1", since = "1.0.0")]
800 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
801 assert_ne!(chunk_size, 0);
802 Chunks::new(self, chunk_size)
805 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
806 /// beginning of the slice.
808 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
809 /// length of the slice, then the last chunk will not have length `chunk_size`.
811 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
812 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
813 /// the end of the slice.
817 /// Panics if `chunk_size` is 0.
822 /// let v = &mut [0, 0, 0, 0, 0];
823 /// let mut count = 1;
825 /// for chunk in v.chunks_mut(2) {
826 /// for elem in chunk.iter_mut() {
831 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
834 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
835 /// [`rchunks_mut`]: slice::rchunks_mut
836 #[stable(feature = "rust1", since = "1.0.0")]
838 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
839 assert_ne!(chunk_size, 0);
840 ChunksMut::new(self, chunk_size)
843 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
844 /// beginning of the slice.
846 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
847 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
848 /// from the `remainder` function of the iterator.
850 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
851 /// resulting code better than in the case of [`chunks`].
853 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
854 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
858 /// Panics if `chunk_size` is 0.
863 /// let slice = ['l', 'o', 'r', 'e', 'm'];
864 /// let mut iter = slice.chunks_exact(2);
865 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
866 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
867 /// assert!(iter.next().is_none());
868 /// assert_eq!(iter.remainder(), &['m']);
871 /// [`chunks`]: slice::chunks
872 /// [`rchunks_exact`]: slice::rchunks_exact
873 #[stable(feature = "chunks_exact", since = "1.31.0")]
875 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
876 assert_ne!(chunk_size, 0);
877 ChunksExact::new(self, chunk_size)
880 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
881 /// beginning of the slice.
883 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
884 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
885 /// retrieved from the `into_remainder` function of the iterator.
887 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
888 /// resulting code better than in the case of [`chunks_mut`].
890 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
891 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
896 /// Panics if `chunk_size` is 0.
901 /// let v = &mut [0, 0, 0, 0, 0];
902 /// let mut count = 1;
904 /// for chunk in v.chunks_exact_mut(2) {
905 /// for elem in chunk.iter_mut() {
910 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
913 /// [`chunks_mut`]: slice::chunks_mut
914 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
915 #[stable(feature = "chunks_exact", since = "1.31.0")]
917 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
918 assert_ne!(chunk_size, 0);
919 ChunksExactMut::new(self, chunk_size)
922 /// Splits the slice into a slice of `N`-element arrays,
923 /// assuming that there's no remainder.
927 /// This may only be called when
928 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
934 /// #![feature(slice_as_chunks)]
935 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
936 /// let chunks: &[[char; 1]] =
937 /// // SAFETY: 1-element chunks never have remainder
938 /// unsafe { slice.as_chunks_unchecked() };
939 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
940 /// let chunks: &[[char; 3]] =
941 /// // SAFETY: The slice length (6) is a multiple of 3
942 /// unsafe { slice.as_chunks_unchecked() };
943 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
945 /// // These would be unsound:
946 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
947 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
949 #[unstable(feature = "slice_as_chunks", issue = "74985")]
951 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
952 debug_assert_ne!(N, 0);
953 debug_assert_eq!(self.len() % N, 0);
955 // SAFETY: Our precondition is exactly what's needed to call this
956 unsafe { crate::intrinsics::exact_div(self.len(), N) };
957 // SAFETY: We cast a slice of `new_len * N` elements into
958 // a slice of `new_len` many `N` elements chunks.
959 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
962 /// Splits the slice into a slice of `N`-element arrays,
963 /// starting at the beginning of the slice,
964 /// and a remainder slice with length strictly less than `N`.
968 /// Panics if `N` is 0. This check will most probably get changed to a compile time
969 /// error before this method gets stabilized.
974 /// #![feature(slice_as_chunks)]
975 /// let slice = ['l', 'o', 'r', 'e', 'm'];
976 /// let (chunks, remainder) = slice.as_chunks();
977 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
978 /// assert_eq!(remainder, &['m']);
980 #[unstable(feature = "slice_as_chunks", issue = "74985")]
982 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
984 let len = self.len() / N;
985 let (multiple_of_n, remainder) = self.split_at(len * N);
986 // SAFETY: We already panicked for zero, and ensured by construction
987 // that the length of the subslice is a multiple of N.
988 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
989 (array_slice, remainder)
992 /// Splits the slice into a slice of `N`-element arrays,
993 /// starting at the end of the slice,
994 /// and a remainder slice with length strictly less than `N`.
998 /// Panics if `N` is 0. This check will most probably get changed to a compile time
999 /// error before this method gets stabilized.
1004 /// #![feature(slice_as_chunks)]
1005 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1006 /// let (remainder, chunks) = slice.as_rchunks();
1007 /// assert_eq!(remainder, &['l']);
1008 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1010 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1012 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1014 let len = self.len() / N;
1015 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1016 // SAFETY: We already panicked for zero, and ensured by construction
1017 // that the length of the subslice is a multiple of N.
1018 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1019 (remainder, array_slice)
1022 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1023 /// beginning of the slice.
1025 /// The chunks are array references and do not overlap. If `N` does not divide the
1026 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1027 /// retrieved from the `remainder` function of the iterator.
1029 /// This method is the const generic equivalent of [`chunks_exact`].
1033 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1034 /// error before this method gets stabilized.
1039 /// #![feature(array_chunks)]
1040 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1041 /// let mut iter = slice.array_chunks();
1042 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1043 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1044 /// assert!(iter.next().is_none());
1045 /// assert_eq!(iter.remainder(), &['m']);
1048 /// [`chunks_exact`]: slice::chunks_exact
1049 #[unstable(feature = "array_chunks", issue = "74985")]
1051 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1053 ArrayChunks::new(self)
1056 /// Splits the slice into a slice of `N`-element arrays,
1057 /// assuming that there's no remainder.
1061 /// This may only be called when
1062 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1068 /// #![feature(slice_as_chunks)]
1069 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1070 /// let chunks: &mut [[char; 1]] =
1071 /// // SAFETY: 1-element chunks never have remainder
1072 /// unsafe { slice.as_chunks_unchecked_mut() };
1073 /// chunks[0] = ['L'];
1074 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1075 /// let chunks: &mut [[char; 3]] =
1076 /// // SAFETY: The slice length (6) is a multiple of 3
1077 /// unsafe { slice.as_chunks_unchecked_mut() };
1078 /// chunks[1] = ['a', 'x', '?'];
1079 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1081 /// // These would be unsound:
1082 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1083 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1085 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1087 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1088 debug_assert_ne!(N, 0);
1089 debug_assert_eq!(self.len() % N, 0);
1091 // SAFETY: Our precondition is exactly what's needed to call this
1092 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1093 // SAFETY: We cast a slice of `new_len * N` elements into
1094 // a slice of `new_len` many `N` elements chunks.
1095 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1098 /// Splits the slice into a slice of `N`-element arrays,
1099 /// starting at the beginning of the slice,
1100 /// and a remainder slice with length strictly less than `N`.
1104 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1105 /// error before this method gets stabilized.
1110 /// #![feature(slice_as_chunks)]
1111 /// let v = &mut [0, 0, 0, 0, 0];
1112 /// let mut count = 1;
1114 /// let (chunks, remainder) = v.as_chunks_mut();
1115 /// remainder[0] = 9;
1116 /// for chunk in chunks {
1117 /// *chunk = [count; 2];
1120 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1122 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1124 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1126 let len = self.len() / N;
1127 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1128 // SAFETY: We already panicked for zero, and ensured by construction
1129 // that the length of the subslice is a multiple of N.
1130 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1131 (array_slice, remainder)
1134 /// Splits the slice into a slice of `N`-element arrays,
1135 /// starting at the end of the slice,
1136 /// and a remainder slice with length strictly less than `N`.
1140 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1141 /// error before this method gets stabilized.
1146 /// #![feature(slice_as_chunks)]
1147 /// let v = &mut [0, 0, 0, 0, 0];
1148 /// let mut count = 1;
1150 /// let (remainder, chunks) = v.as_rchunks_mut();
1151 /// remainder[0] = 9;
1152 /// for chunk in chunks {
1153 /// *chunk = [count; 2];
1156 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1158 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1160 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1162 let len = self.len() / N;
1163 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1164 // SAFETY: We already panicked for zero, and ensured by construction
1165 // that the length of the subslice is a multiple of N.
1166 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1167 (remainder, array_slice)
1170 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1171 /// beginning of the slice.
1173 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1174 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1175 /// can be retrieved from the `into_remainder` function of the iterator.
1177 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1181 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1182 /// error before this method gets stabilized.
1187 /// #![feature(array_chunks)]
1188 /// let v = &mut [0, 0, 0, 0, 0];
1189 /// let mut count = 1;
1191 /// for chunk in v.array_chunks_mut() {
1192 /// *chunk = [count; 2];
1195 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1198 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1199 #[unstable(feature = "array_chunks", issue = "74985")]
1201 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1203 ArrayChunksMut::new(self)
1206 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1207 /// starting at the beginning of the slice.
1209 /// This is the const generic equivalent of [`windows`].
1211 /// If `N` is greater than the size of the slice, it will return no windows.
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_windows)]
1222 /// let slice = [0, 1, 2, 3];
1223 /// let mut iter = slice.array_windows();
1224 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1225 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1226 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1227 /// assert!(iter.next().is_none());
1230 /// [`windows`]: slice::windows
1231 #[unstable(feature = "array_windows", issue = "75027")]
1233 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1235 ArrayWindows::new(self)
1238 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1241 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1242 /// slice, then the last chunk will not have length `chunk_size`.
1244 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1245 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1250 /// Panics if `chunk_size` is 0.
1255 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1256 /// let mut iter = slice.rchunks(2);
1257 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1258 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1259 /// assert_eq!(iter.next().unwrap(), &['l']);
1260 /// assert!(iter.next().is_none());
1263 /// [`rchunks_exact`]: slice::rchunks_exact
1264 /// [`chunks`]: slice::chunks
1265 #[stable(feature = "rchunks", since = "1.31.0")]
1267 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1268 assert!(chunk_size != 0);
1269 RChunks::new(self, chunk_size)
1272 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1275 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1276 /// length of the slice, then the last chunk will not have length `chunk_size`.
1278 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1279 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1280 /// beginning of the slice.
1284 /// Panics if `chunk_size` is 0.
1289 /// let v = &mut [0, 0, 0, 0, 0];
1290 /// let mut count = 1;
1292 /// for chunk in v.rchunks_mut(2) {
1293 /// for elem in chunk.iter_mut() {
1298 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1301 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1302 /// [`chunks_mut`]: slice::chunks_mut
1303 #[stable(feature = "rchunks", since = "1.31.0")]
1305 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1306 assert!(chunk_size != 0);
1307 RChunksMut::new(self, chunk_size)
1310 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1311 /// end of the slice.
1313 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1314 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1315 /// from the `remainder` function of the iterator.
1317 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1318 /// resulting code better than in the case of [`chunks`].
1320 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1321 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1326 /// Panics if `chunk_size` is 0.
1331 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1332 /// let mut iter = slice.rchunks_exact(2);
1333 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1334 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1335 /// assert!(iter.next().is_none());
1336 /// assert_eq!(iter.remainder(), &['l']);
1339 /// [`chunks`]: slice::chunks
1340 /// [`rchunks`]: slice::rchunks
1341 /// [`chunks_exact`]: slice::chunks_exact
1342 #[stable(feature = "rchunks", since = "1.31.0")]
1344 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1345 assert!(chunk_size != 0);
1346 RChunksExact::new(self, chunk_size)
1349 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1352 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1353 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1354 /// retrieved from the `into_remainder` function of the iterator.
1356 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1357 /// resulting code better than in the case of [`chunks_mut`].
1359 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1360 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1365 /// Panics if `chunk_size` is 0.
1370 /// let v = &mut [0, 0, 0, 0, 0];
1371 /// let mut count = 1;
1373 /// for chunk in v.rchunks_exact_mut(2) {
1374 /// for elem in chunk.iter_mut() {
1379 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1382 /// [`chunks_mut`]: slice::chunks_mut
1383 /// [`rchunks_mut`]: slice::rchunks_mut
1384 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1385 #[stable(feature = "rchunks", since = "1.31.0")]
1387 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1388 assert!(chunk_size != 0);
1389 RChunksExactMut::new(self, chunk_size)
1392 /// Returns an iterator over the slice producing non-overlapping runs
1393 /// of elements using the predicate to separate them.
1395 /// The predicate is called on two elements following themselves,
1396 /// it means the predicate is called on `slice[0]` and `slice[1]`
1397 /// then on `slice[1]` and `slice[2]` and so on.
1402 /// #![feature(slice_group_by)]
1404 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1406 /// let mut iter = slice.group_by(|a, b| a == b);
1408 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1409 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1410 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1411 /// assert_eq!(iter.next(), None);
1414 /// This method can be used to extract the sorted subslices:
1417 /// #![feature(slice_group_by)]
1419 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1421 /// let mut iter = slice.group_by(|a, b| a <= b);
1423 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1424 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1425 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1426 /// assert_eq!(iter.next(), None);
1428 #[unstable(feature = "slice_group_by", issue = "80552")]
1430 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1432 F: FnMut(&T, &T) -> bool,
1434 GroupBy::new(self, pred)
1437 /// Returns an iterator over the slice producing non-overlapping mutable
1438 /// runs of elements using the predicate to separate them.
1440 /// The predicate is called on two elements following themselves,
1441 /// it means the predicate is called on `slice[0]` and `slice[1]`
1442 /// then on `slice[1]` and `slice[2]` and so on.
1447 /// #![feature(slice_group_by)]
1449 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1451 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1453 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1454 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1455 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1456 /// assert_eq!(iter.next(), None);
1459 /// This method can be used to extract the sorted subslices:
1462 /// #![feature(slice_group_by)]
1464 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1466 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1468 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1469 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1470 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1471 /// assert_eq!(iter.next(), None);
1473 #[unstable(feature = "slice_group_by", issue = "80552")]
1475 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1477 F: FnMut(&T, &T) -> bool,
1479 GroupByMut::new(self, pred)
1482 /// Divides one slice into two at an index.
1484 /// The first will contain all indices from `[0, mid)` (excluding
1485 /// the index `mid` itself) and the second will contain all
1486 /// indices from `[mid, len)` (excluding the index `len` itself).
1490 /// Panics if `mid > len`.
1495 /// let v = [1, 2, 3, 4, 5, 6];
1498 /// let (left, right) = v.split_at(0);
1499 /// assert_eq!(left, []);
1500 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1504 /// let (left, right) = v.split_at(2);
1505 /// assert_eq!(left, [1, 2]);
1506 /// assert_eq!(right, [3, 4, 5, 6]);
1510 /// let (left, right) = v.split_at(6);
1511 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1512 /// assert_eq!(right, []);
1515 #[stable(feature = "rust1", since = "1.0.0")]
1518 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1519 assert!(mid <= self.len());
1520 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1521 // fulfills the requirements of `from_raw_parts_mut`.
1522 unsafe { self.split_at_unchecked(mid) }
1525 /// Divides one mutable slice into two at an index.
1527 /// The first will contain all indices from `[0, mid)` (excluding
1528 /// the index `mid` itself) and the second will contain all
1529 /// indices from `[mid, len)` (excluding the index `len` itself).
1533 /// Panics if `mid > len`.
1538 /// let mut v = [1, 0, 3, 0, 5, 6];
1539 /// let (left, right) = v.split_at_mut(2);
1540 /// assert_eq!(left, [1, 0]);
1541 /// assert_eq!(right, [3, 0, 5, 6]);
1544 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1546 #[stable(feature = "rust1", since = "1.0.0")]
1549 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1550 assert!(mid <= self.len());
1551 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1552 // fulfills the requirements of `from_raw_parts_mut`.
1553 unsafe { self.split_at_mut_unchecked(mid) }
1556 /// Divides one slice into two at an index, without doing bounds checking.
1558 /// The first will contain all indices from `[0, mid)` (excluding
1559 /// the index `mid` itself) and the second will contain all
1560 /// indices from `[mid, len)` (excluding the index `len` itself).
1562 /// For a safe alternative see [`split_at`].
1566 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1567 /// even if the resulting reference is not used. The caller has to ensure that
1568 /// `0 <= mid <= self.len()`.
1570 /// [`split_at`]: slice::split_at
1571 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1576 /// #![feature(slice_split_at_unchecked)]
1578 /// let v = [1, 2, 3, 4, 5, 6];
1581 /// let (left, right) = v.split_at_unchecked(0);
1582 /// assert_eq!(left, []);
1583 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1587 /// let (left, right) = v.split_at_unchecked(2);
1588 /// assert_eq!(left, [1, 2]);
1589 /// assert_eq!(right, [3, 4, 5, 6]);
1593 /// let (left, right) = v.split_at_unchecked(6);
1594 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1595 /// assert_eq!(right, []);
1598 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1600 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1601 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1602 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1605 /// Divides one mutable slice into two at an index, without doing bounds checking.
1607 /// The first will contain all indices from `[0, mid)` (excluding
1608 /// the index `mid` itself) and the second will contain all
1609 /// indices from `[mid, len)` (excluding the index `len` itself).
1611 /// For a safe alternative see [`split_at_mut`].
1615 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1616 /// even if the resulting reference is not used. The caller has to ensure that
1617 /// `0 <= mid <= self.len()`.
1619 /// [`split_at_mut`]: slice::split_at_mut
1620 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1625 /// #![feature(slice_split_at_unchecked)]
1627 /// let mut v = [1, 0, 3, 0, 5, 6];
1628 /// // scoped to restrict the lifetime of the borrows
1630 /// let (left, right) = v.split_at_mut_unchecked(2);
1631 /// assert_eq!(left, [1, 0]);
1632 /// assert_eq!(right, [3, 0, 5, 6]);
1636 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1638 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1640 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1641 let len = self.len();
1642 let ptr = self.as_mut_ptr();
1644 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1646 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1648 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1651 /// Divides one slice into an array and a remainder slice at an index.
1653 /// The array will contain all indices from `[0, N)` (excluding
1654 /// the index `N` itself) and the slice will contain all
1655 /// indices from `[N, len)` (excluding the index `len` itself).
1659 /// Panics if `N > len`.
1664 /// #![feature(split_array)]
1666 /// let v = &[1, 2, 3, 4, 5, 6][..];
1669 /// let (left, right) = v.split_array_ref::<0>();
1670 /// assert_eq!(left, &[]);
1671 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1675 /// let (left, right) = v.split_array_ref::<2>();
1676 /// assert_eq!(left, &[1, 2]);
1677 /// assert_eq!(right, [3, 4, 5, 6]);
1681 /// let (left, right) = v.split_array_ref::<6>();
1682 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1683 /// assert_eq!(right, []);
1686 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1689 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1690 let (a, b) = self.split_at(N);
1691 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1692 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1695 /// Divides one mutable slice into an array and a remainder slice at an index.
1697 /// The array will contain all indices from `[0, N)` (excluding
1698 /// the index `N` itself) and the slice will contain all
1699 /// indices from `[N, len)` (excluding the index `len` itself).
1703 /// Panics if `N > len`.
1708 /// #![feature(split_array)]
1710 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1711 /// let (left, right) = v.split_array_mut::<2>();
1712 /// assert_eq!(left, &mut [1, 0]);
1713 /// assert_eq!(right, [3, 0, 5, 6]);
1716 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1718 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1721 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1722 let (a, b) = self.split_at_mut(N);
1723 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1724 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1727 /// Divides one slice into an array and a remainder slice at an index from
1730 /// The slice will contain all indices from `[0, len - N)` (excluding
1731 /// the index `len - N` itself) and the array will contain all
1732 /// indices from `[len - N, len)` (excluding the index `len` itself).
1736 /// Panics if `N > len`.
1741 /// #![feature(split_array)]
1743 /// let v = &[1, 2, 3, 4, 5, 6][..];
1746 /// let (left, right) = v.rsplit_array_ref::<0>();
1747 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1748 /// assert_eq!(right, &[]);
1752 /// let (left, right) = v.rsplit_array_ref::<2>();
1753 /// assert_eq!(left, [1, 2, 3, 4]);
1754 /// assert_eq!(right, &[5, 6]);
1758 /// let (left, right) = v.rsplit_array_ref::<6>();
1759 /// assert_eq!(left, []);
1760 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1763 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1765 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1766 assert!(N <= self.len());
1767 let (a, b) = self.split_at(self.len() - N);
1768 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1769 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1772 /// Divides one mutable slice into an array and a remainder slice at an
1773 /// index from the end.
1775 /// The slice will contain all indices from `[0, len - N)` (excluding
1776 /// the index `N` itself) and the array will contain all
1777 /// indices from `[len - N, len)` (excluding the index `len` itself).
1781 /// Panics if `N > len`.
1786 /// #![feature(split_array)]
1788 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1789 /// let (left, right) = v.rsplit_array_mut::<4>();
1790 /// assert_eq!(left, [1, 0]);
1791 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1794 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1796 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1798 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1799 assert!(N <= self.len());
1800 let (a, b) = self.split_at_mut(self.len() - N);
1801 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1802 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1805 /// Returns an iterator over subslices separated by elements that match
1806 /// `pred`. The matched element is not contained in the subslices.
1811 /// let slice = [10, 40, 33, 20];
1812 /// let mut iter = slice.split(|num| num % 3 == 0);
1814 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1815 /// assert_eq!(iter.next().unwrap(), &[20]);
1816 /// assert!(iter.next().is_none());
1819 /// If the first element is matched, an empty slice will be the first item
1820 /// returned by the iterator. Similarly, if the last element in the slice
1821 /// is matched, an empty slice will be the last item returned by the
1825 /// let slice = [10, 40, 33];
1826 /// let mut iter = slice.split(|num| num % 3 == 0);
1828 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1829 /// assert_eq!(iter.next().unwrap(), &[]);
1830 /// assert!(iter.next().is_none());
1833 /// If two matched elements are directly adjacent, an empty slice will be
1834 /// present between them:
1837 /// let slice = [10, 6, 33, 20];
1838 /// let mut iter = slice.split(|num| num % 3 == 0);
1840 /// assert_eq!(iter.next().unwrap(), &[10]);
1841 /// assert_eq!(iter.next().unwrap(), &[]);
1842 /// assert_eq!(iter.next().unwrap(), &[20]);
1843 /// assert!(iter.next().is_none());
1845 #[stable(feature = "rust1", since = "1.0.0")]
1847 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1849 F: FnMut(&T) -> bool,
1851 Split::new(self, pred)
1854 /// Returns an iterator over mutable subslices separated by elements that
1855 /// match `pred`. The matched element is not contained in the subslices.
1860 /// let mut v = [10, 40, 30, 20, 60, 50];
1862 /// for group in v.split_mut(|num| *num % 3 == 0) {
1865 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1867 #[stable(feature = "rust1", since = "1.0.0")]
1869 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1871 F: FnMut(&T) -> bool,
1873 SplitMut::new(self, pred)
1876 /// Returns an iterator over subslices separated by elements that match
1877 /// `pred`. The matched element is contained in the end of the previous
1878 /// subslice as a terminator.
1883 /// let slice = [10, 40, 33, 20];
1884 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1886 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1887 /// assert_eq!(iter.next().unwrap(), &[20]);
1888 /// assert!(iter.next().is_none());
1891 /// If the last element of the slice is matched,
1892 /// that element will be considered the terminator of the preceding slice.
1893 /// That slice will be the last item returned by the iterator.
1896 /// let slice = [3, 10, 40, 33];
1897 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1899 /// assert_eq!(iter.next().unwrap(), &[3]);
1900 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1901 /// assert!(iter.next().is_none());
1903 #[stable(feature = "split_inclusive", since = "1.51.0")]
1905 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1907 F: FnMut(&T) -> bool,
1909 SplitInclusive::new(self, pred)
1912 /// Returns an iterator over mutable subslices separated by elements that
1913 /// match `pred`. The matched element is contained in the previous
1914 /// subslice as a terminator.
1919 /// let mut v = [10, 40, 30, 20, 60, 50];
1921 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1922 /// let terminator_idx = group.len()-1;
1923 /// group[terminator_idx] = 1;
1925 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1927 #[stable(feature = "split_inclusive", since = "1.51.0")]
1929 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1931 F: FnMut(&T) -> bool,
1933 SplitInclusiveMut::new(self, pred)
1936 /// Returns an iterator over subslices separated by elements that match
1937 /// `pred`, starting at the end of the slice and working backwards.
1938 /// The matched element is not contained in the subslices.
1943 /// let slice = [11, 22, 33, 0, 44, 55];
1944 /// let mut iter = slice.rsplit(|num| *num == 0);
1946 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1947 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1948 /// assert_eq!(iter.next(), None);
1951 /// As with `split()`, if the first or last element is matched, an empty
1952 /// slice will be the first (or last) item returned by the iterator.
1955 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1956 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1957 /// assert_eq!(it.next().unwrap(), &[]);
1958 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1959 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1960 /// assert_eq!(it.next().unwrap(), &[]);
1961 /// assert_eq!(it.next(), None);
1963 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1965 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1967 F: FnMut(&T) -> bool,
1969 RSplit::new(self, pred)
1972 /// Returns an iterator over mutable subslices separated by elements that
1973 /// match `pred`, starting at the end of the slice and working
1974 /// backwards. The matched element is not contained in the subslices.
1979 /// let mut v = [100, 400, 300, 200, 600, 500];
1981 /// let mut count = 0;
1982 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1984 /// group[0] = count;
1986 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1989 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1991 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1993 F: FnMut(&T) -> bool,
1995 RSplitMut::new(self, pred)
1998 /// Returns an iterator over subslices separated by elements that match
1999 /// `pred`, limited to returning at most `n` items. The matched element is
2000 /// not contained in the subslices.
2002 /// The last element returned, if any, will contain the remainder of the
2007 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2008 /// `[20, 60, 50]`):
2011 /// let v = [10, 40, 30, 20, 60, 50];
2013 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2014 /// println!("{group:?}");
2017 #[stable(feature = "rust1", since = "1.0.0")]
2019 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2021 F: FnMut(&T) -> bool,
2023 SplitN::new(self.split(pred), n)
2026 /// Returns an iterator over subslices separated by elements that match
2027 /// `pred`, limited to returning at most `n` items. The matched element is
2028 /// not contained in the subslices.
2030 /// The last element returned, if any, will contain the remainder of the
2036 /// let mut v = [10, 40, 30, 20, 60, 50];
2038 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2041 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2043 #[stable(feature = "rust1", since = "1.0.0")]
2045 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2047 F: FnMut(&T) -> bool,
2049 SplitNMut::new(self.split_mut(pred), n)
2052 /// Returns an iterator over subslices separated by elements that match
2053 /// `pred` limited to returning at most `n` items. This starts at the end of
2054 /// the slice and works backwards. The matched element is not contained in
2057 /// The last element returned, if any, will contain the remainder of the
2062 /// Print the slice split once, starting from the end, by numbers divisible
2063 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2066 /// let v = [10, 40, 30, 20, 60, 50];
2068 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2069 /// println!("{group:?}");
2072 #[stable(feature = "rust1", since = "1.0.0")]
2074 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2076 F: FnMut(&T) -> bool,
2078 RSplitN::new(self.rsplit(pred), n)
2081 /// Returns an iterator over subslices separated by elements that match
2082 /// `pred` limited to returning at most `n` items. This starts at the end of
2083 /// the slice and works backwards. The matched element is not contained in
2086 /// The last element returned, if any, will contain the remainder of the
2092 /// let mut s = [10, 40, 30, 20, 60, 50];
2094 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2097 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2099 #[stable(feature = "rust1", since = "1.0.0")]
2101 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2103 F: FnMut(&T) -> bool,
2105 RSplitNMut::new(self.rsplit_mut(pred), n)
2108 /// Returns `true` if the slice contains an element with the given value.
2113 /// let v = [10, 40, 30];
2114 /// assert!(v.contains(&30));
2115 /// assert!(!v.contains(&50));
2118 /// If you do not have a `&T`, but some other value that you can compare
2119 /// with one (for example, `String` implements `PartialEq<str>`), you can
2120 /// use `iter().any`:
2123 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2124 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2125 /// assert!(!v.iter().any(|e| e == "hi"));
2127 #[stable(feature = "rust1", since = "1.0.0")]
2129 pub fn contains(&self, x: &T) -> bool
2133 cmp::SliceContains::slice_contains(x, self)
2136 /// Returns `true` if `needle` is a prefix of the slice.
2141 /// let v = [10, 40, 30];
2142 /// assert!(v.starts_with(&[10]));
2143 /// assert!(v.starts_with(&[10, 40]));
2144 /// assert!(!v.starts_with(&[50]));
2145 /// assert!(!v.starts_with(&[10, 50]));
2148 /// Always returns `true` if `needle` is an empty slice:
2151 /// let v = &[10, 40, 30];
2152 /// assert!(v.starts_with(&[]));
2153 /// let v: &[u8] = &[];
2154 /// assert!(v.starts_with(&[]));
2156 #[stable(feature = "rust1", since = "1.0.0")]
2157 pub fn starts_with(&self, needle: &[T]) -> bool
2161 let n = needle.len();
2162 self.len() >= n && needle == &self[..n]
2165 /// Returns `true` if `needle` is a suffix of the slice.
2170 /// let v = [10, 40, 30];
2171 /// assert!(v.ends_with(&[30]));
2172 /// assert!(v.ends_with(&[40, 30]));
2173 /// assert!(!v.ends_with(&[50]));
2174 /// assert!(!v.ends_with(&[50, 30]));
2177 /// Always returns `true` if `needle` is an empty slice:
2180 /// let v = &[10, 40, 30];
2181 /// assert!(v.ends_with(&[]));
2182 /// let v: &[u8] = &[];
2183 /// assert!(v.ends_with(&[]));
2185 #[stable(feature = "rust1", since = "1.0.0")]
2186 pub fn ends_with(&self, needle: &[T]) -> bool
2190 let (m, n) = (self.len(), needle.len());
2191 m >= n && needle == &self[m - n..]
2194 /// Returns a subslice with the prefix removed.
2196 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2197 /// If `prefix` is empty, simply returns the original slice.
2199 /// If the slice does not start with `prefix`, returns `None`.
2204 /// let v = &[10, 40, 30];
2205 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2206 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2207 /// assert_eq!(v.strip_prefix(&[50]), None);
2208 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2210 /// let prefix : &str = "he";
2211 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2212 /// Some(b"llo".as_ref()));
2214 #[must_use = "returns the subslice without modifying the original"]
2215 #[stable(feature = "slice_strip", since = "1.51.0")]
2216 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2220 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2221 let prefix = prefix.as_slice();
2222 let n = prefix.len();
2223 if n <= self.len() {
2224 let (head, tail) = self.split_at(n);
2232 /// Returns a subslice with the suffix removed.
2234 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2235 /// If `suffix` is empty, simply returns the original slice.
2237 /// If the slice does not end with `suffix`, returns `None`.
2242 /// let v = &[10, 40, 30];
2243 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2244 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2245 /// assert_eq!(v.strip_suffix(&[50]), None);
2246 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2248 #[must_use = "returns the subslice without modifying the original"]
2249 #[stable(feature = "slice_strip", since = "1.51.0")]
2250 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2254 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2255 let suffix = suffix.as_slice();
2256 let (len, n) = (self.len(), suffix.len());
2258 let (head, tail) = self.split_at(len - n);
2266 /// Binary searches this sorted slice for a given element.
2268 /// If the value is found then [`Result::Ok`] is returned, containing the
2269 /// index of the matching element. If there are multiple matches, then any
2270 /// one of the matches could be returned. The index is chosen
2271 /// deterministically, but is subject to change in future versions of Rust.
2272 /// If the value is not found then [`Result::Err`] is returned, containing
2273 /// the index where a matching element could be inserted while maintaining
2276 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2278 /// [`binary_search_by`]: slice::binary_search_by
2279 /// [`binary_search_by_key`]: slice::binary_search_by_key
2280 /// [`partition_point`]: slice::partition_point
2284 /// Looks up a series of four elements. The first is found, with a
2285 /// uniquely determined position; the second and third are not
2286 /// found; the fourth could match any position in `[1, 4]`.
2289 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2291 /// assert_eq!(s.binary_search(&13), Ok(9));
2292 /// assert_eq!(s.binary_search(&4), Err(7));
2293 /// assert_eq!(s.binary_search(&100), Err(13));
2294 /// let r = s.binary_search(&1);
2295 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2298 /// If you want to insert an item to a sorted vector, while maintaining
2302 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2304 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2305 /// s.insert(idx, num);
2306 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2308 #[stable(feature = "rust1", since = "1.0.0")]
2309 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2313 self.binary_search_by(|p| p.cmp(x))
2316 /// Binary searches this sorted slice with a comparator function.
2318 /// The comparator function should implement an order consistent
2319 /// with the sort order of the underlying slice, returning an
2320 /// order code that indicates whether its argument is `Less`,
2321 /// `Equal` or `Greater` the desired target.
2323 /// If the value is found then [`Result::Ok`] is returned, containing the
2324 /// index of the matching element. If there are multiple matches, then any
2325 /// one of the matches could be returned. The index is chosen
2326 /// deterministically, but is subject to change in future versions of Rust.
2327 /// If the value is not found then [`Result::Err`] is returned, containing
2328 /// the index where a matching element could be inserted while maintaining
2331 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2333 /// [`binary_search`]: slice::binary_search
2334 /// [`binary_search_by_key`]: slice::binary_search_by_key
2335 /// [`partition_point`]: slice::partition_point
2339 /// Looks up a series of four elements. The first is found, with a
2340 /// uniquely determined position; the second and third are not
2341 /// found; the fourth could match any position in `[1, 4]`.
2344 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2347 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2349 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2351 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2353 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2354 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2356 #[stable(feature = "rust1", since = "1.0.0")]
2358 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2360 F: FnMut(&'a T) -> Ordering,
2362 let mut size = self.len();
2364 let mut right = size;
2365 while left < right {
2366 let mid = left + size / 2;
2368 // SAFETY: the call is made safe by the following invariants:
2370 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2371 let cmp = f(unsafe { self.get_unchecked(mid) });
2373 // The reason why we use if/else control flow rather than match
2374 // is because match reorders comparison operations, which is perf sensitive.
2375 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2378 } else if cmp == Greater {
2381 // SAFETY: same as the `get_unchecked` above
2382 unsafe { crate::intrinsics::assume(mid < self.len()) };
2386 size = right - left;
2391 /// Binary searches this sorted slice with a key extraction function.
2393 /// Assumes that the slice is sorted by the key, for instance with
2394 /// [`sort_by_key`] using the same key extraction function.
2396 /// If the value is found then [`Result::Ok`] is returned, containing the
2397 /// index of the matching element. If there are multiple matches, then any
2398 /// one of the matches could be returned. The index is chosen
2399 /// deterministically, but is subject to change in future versions of Rust.
2400 /// If the value is not found then [`Result::Err`] is returned, containing
2401 /// the index where a matching element could be inserted while maintaining
2404 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2406 /// [`sort_by_key`]: slice::sort_by_key
2407 /// [`binary_search`]: slice::binary_search
2408 /// [`binary_search_by`]: slice::binary_search_by
2409 /// [`partition_point`]: slice::partition_point
2413 /// Looks up a series of four elements in a slice of pairs sorted by
2414 /// their second elements. The first is found, with a uniquely
2415 /// determined position; the second and third are not found; the
2416 /// fourth could match any position in `[1, 4]`.
2419 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2420 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2421 /// (1, 21), (2, 34), (4, 55)];
2423 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2424 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2425 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2426 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2427 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2429 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2430 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2431 // This breaks links when slice is displayed in core, but changing it to use relative links
2432 // would break when the item is re-exported. So allow the core links to be broken for now.
2433 #[allow(rustdoc::broken_intra_doc_links)]
2434 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2436 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2438 F: FnMut(&'a T) -> B,
2441 self.binary_search_by(|k| f(k).cmp(b))
2444 /// Sorts the slice, but might not preserve the order of equal elements.
2446 /// This sort is unstable (i.e., may reorder equal elements), in-place
2447 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2449 /// # Current implementation
2451 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2452 /// which combines the fast average case of randomized quicksort with the fast worst case of
2453 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2454 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2455 /// deterministic behavior.
2457 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2458 /// slice consists of several concatenated sorted sequences.
2463 /// let mut v = [-5, 4, 1, -3, 2];
2465 /// v.sort_unstable();
2466 /// assert!(v == [-5, -3, 1, 2, 4]);
2469 /// [pdqsort]: https://github.com/orlp/pdqsort
2470 #[stable(feature = "sort_unstable", since = "1.20.0")]
2472 pub fn sort_unstable(&mut self)
2476 sort::quicksort(self, |a, b| a.lt(b));
2479 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2482 /// This sort is unstable (i.e., may reorder equal elements), in-place
2483 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2485 /// The comparator function must define a total ordering for the elements in the slice. If
2486 /// the ordering is not total, the order of the elements is unspecified. An order is a
2487 /// total order if it is (for all `a`, `b` and `c`):
2489 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2490 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2492 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2493 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2496 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2497 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2498 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2501 /// # Current implementation
2503 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2504 /// which combines the fast average case of randomized quicksort with the fast worst case of
2505 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2506 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2507 /// deterministic behavior.
2509 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2510 /// slice consists of several concatenated sorted sequences.
2515 /// let mut v = [5, 4, 1, 3, 2];
2516 /// v.sort_unstable_by(|a, b| a.cmp(b));
2517 /// assert!(v == [1, 2, 3, 4, 5]);
2519 /// // reverse sorting
2520 /// v.sort_unstable_by(|a, b| b.cmp(a));
2521 /// assert!(v == [5, 4, 3, 2, 1]);
2524 /// [pdqsort]: https://github.com/orlp/pdqsort
2525 #[stable(feature = "sort_unstable", since = "1.20.0")]
2527 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2529 F: FnMut(&T, &T) -> Ordering,
2531 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2534 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2537 /// This sort is unstable (i.e., may reorder equal elements), in-place
2538 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2541 /// # Current implementation
2543 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2544 /// which combines the fast average case of randomized quicksort with the fast worst case of
2545 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2546 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2547 /// deterministic behavior.
2549 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2550 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2551 /// cases where the key function is expensive.
2556 /// let mut v = [-5i32, 4, 1, -3, 2];
2558 /// v.sort_unstable_by_key(|k| k.abs());
2559 /// assert!(v == [1, 2, -3, 4, -5]);
2562 /// [pdqsort]: https://github.com/orlp/pdqsort
2563 #[stable(feature = "sort_unstable", since = "1.20.0")]
2565 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2570 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2573 /// Reorder the slice such that the element at `index` is at its final sorted position.
2575 /// This reordering has the additional property that any value at position `i < index` will be
2576 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2577 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2578 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2579 /// element" in other libraries. It returns a triplet of the following values: all elements less
2580 /// than the one at the given index, the value at the given index, and all elements greater than
2581 /// the one at the given index.
2583 /// # Current implementation
2585 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2586 /// used for [`sort_unstable`].
2588 /// [`sort_unstable`]: slice::sort_unstable
2592 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2597 /// let mut v = [-5i32, 4, 1, -3, 2];
2599 /// // Find the median
2600 /// v.select_nth_unstable(2);
2602 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2603 /// // about the specified index.
2604 /// assert!(v == [-3, -5, 1, 2, 4] ||
2605 /// v == [-5, -3, 1, 2, 4] ||
2606 /// v == [-3, -5, 1, 4, 2] ||
2607 /// v == [-5, -3, 1, 4, 2]);
2609 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2611 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2615 let mut f = |a: &T, b: &T| a.lt(b);
2616 sort::partition_at_index(self, index, &mut f)
2619 /// Reorder the slice with a comparator function such that the element at `index` is at its
2620 /// final sorted position.
2622 /// This reordering has the additional property that any value at position `i < index` will be
2623 /// less than or equal to any value at a position `j > index` using the comparator function.
2624 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2625 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2626 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2627 /// values: all elements less than the one at the given index, the value at the given index,
2628 /// and all elements greater than the one at the given index, using the provided comparator
2631 /// # Current implementation
2633 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2634 /// used for [`sort_unstable`].
2636 /// [`sort_unstable`]: slice::sort_unstable
2640 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2645 /// let mut v = [-5i32, 4, 1, -3, 2];
2647 /// // Find the median as if the slice were sorted in descending order.
2648 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2650 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2651 /// // about the specified index.
2652 /// assert!(v == [2, 4, 1, -5, -3] ||
2653 /// v == [2, 4, 1, -3, -5] ||
2654 /// v == [4, 2, 1, -5, -3] ||
2655 /// v == [4, 2, 1, -3, -5]);
2657 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2659 pub fn select_nth_unstable_by<F>(
2663 ) -> (&mut [T], &mut T, &mut [T])
2665 F: FnMut(&T, &T) -> Ordering,
2667 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2668 sort::partition_at_index(self, index, &mut f)
2671 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2672 /// final sorted position.
2674 /// This reordering has the additional property that any value at position `i < index` will be
2675 /// less than or equal to any value at a position `j > index` using the key extraction function.
2676 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2677 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2678 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2679 /// values: all elements less than the one at the given index, the value at the given index, and
2680 /// all elements greater than the one at the given index, using the provided key extraction
2683 /// # Current implementation
2685 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2686 /// used for [`sort_unstable`].
2688 /// [`sort_unstable`]: slice::sort_unstable
2692 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2697 /// let mut v = [-5i32, 4, 1, -3, 2];
2699 /// // Return the median as if the array were sorted according to absolute value.
2700 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2702 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2703 /// // about the specified index.
2704 /// assert!(v == [1, 2, -3, 4, -5] ||
2705 /// v == [1, 2, -3, -5, 4] ||
2706 /// v == [2, 1, -3, 4, -5] ||
2707 /// v == [2, 1, -3, -5, 4]);
2709 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2711 pub fn select_nth_unstable_by_key<K, F>(
2715 ) -> (&mut [T], &mut T, &mut [T])
2720 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2721 sort::partition_at_index(self, index, &mut g)
2724 /// Moves all consecutive repeated elements to the end of the slice according to the
2725 /// [`PartialEq`] trait implementation.
2727 /// Returns two slices. The first contains no consecutive repeated elements.
2728 /// The second contains all the duplicates in no specified order.
2730 /// If the slice is sorted, the first returned slice contains no duplicates.
2735 /// #![feature(slice_partition_dedup)]
2737 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2739 /// let (dedup, duplicates) = slice.partition_dedup();
2741 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2742 /// assert_eq!(duplicates, [2, 3, 1]);
2744 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2746 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2750 self.partition_dedup_by(|a, b| a == b)
2753 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2754 /// a given equality relation.
2756 /// Returns two slices. The first contains no consecutive repeated elements.
2757 /// The second contains all the duplicates in no specified order.
2759 /// The `same_bucket` function is passed references to two elements from the slice and
2760 /// must determine if the elements compare equal. The elements are passed in opposite order
2761 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2762 /// at the end of the slice.
2764 /// If the slice is sorted, the first returned slice contains no duplicates.
2769 /// #![feature(slice_partition_dedup)]
2771 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2773 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2775 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2776 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2778 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2780 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2782 F: FnMut(&mut T, &mut T) -> bool,
2784 // Although we have a mutable reference to `self`, we cannot make
2785 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2786 // must ensure that the slice is in a valid state at all times.
2788 // The way that we handle this is by using swaps; we iterate
2789 // over all the elements, swapping as we go so that at the end
2790 // the elements we wish to keep are in the front, and those we
2791 // wish to reject are at the back. We can then split the slice.
2792 // This operation is still `O(n)`.
2794 // Example: We start in this state, where `r` represents "next
2795 // read" and `w` represents "next_write`.
2798 // +---+---+---+---+---+---+
2799 // | 0 | 1 | 1 | 2 | 3 | 3 |
2800 // +---+---+---+---+---+---+
2803 // Comparing self[r] against self[w-1], this is not a duplicate, so
2804 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2805 // r and w, leaving us with:
2808 // +---+---+---+---+---+---+
2809 // | 0 | 1 | 1 | 2 | 3 | 3 |
2810 // +---+---+---+---+---+---+
2813 // Comparing self[r] against self[w-1], this value is a duplicate,
2814 // so we increment `r` but leave everything else unchanged:
2817 // +---+---+---+---+---+---+
2818 // | 0 | 1 | 1 | 2 | 3 | 3 |
2819 // +---+---+---+---+---+---+
2822 // Comparing self[r] against self[w-1], this is not a duplicate,
2823 // so swap self[r] and self[w] and advance r and w:
2826 // +---+---+---+---+---+---+
2827 // | 0 | 1 | 2 | 1 | 3 | 3 |
2828 // +---+---+---+---+---+---+
2831 // Not a duplicate, repeat:
2834 // +---+---+---+---+---+---+
2835 // | 0 | 1 | 2 | 3 | 1 | 3 |
2836 // +---+---+---+---+---+---+
2839 // Duplicate, advance r. End of slice. Split at w.
2841 let len = self.len();
2843 return (self, &mut []);
2846 let ptr = self.as_mut_ptr();
2847 let mut next_read: usize = 1;
2848 let mut next_write: usize = 1;
2850 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2851 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2852 // one element before `ptr_write`, but `next_write` starts at 1, so
2853 // `prev_ptr_write` is never less than 0 and is inside the slice.
2854 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2855 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2856 // and `prev_ptr_write.offset(1)`.
2858 // `next_write` is also incremented at most once per loop at most meaning
2859 // no element is skipped when it may need to be swapped.
2861 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2862 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2863 // The explanation is simply that `next_read >= next_write` is always true,
2864 // thus `next_read > next_write - 1` is too.
2866 // Avoid bounds checks by using raw pointers.
2867 while next_read < len {
2868 let ptr_read = ptr.add(next_read);
2869 let prev_ptr_write = ptr.add(next_write - 1);
2870 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2871 if next_read != next_write {
2872 let ptr_write = prev_ptr_write.offset(1);
2873 mem::swap(&mut *ptr_read, &mut *ptr_write);
2881 self.split_at_mut(next_write)
2884 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2885 /// to the same key.
2887 /// Returns two slices. The first contains no consecutive repeated elements.
2888 /// The second contains all the duplicates in no specified order.
2890 /// If the slice is sorted, the first returned slice contains no duplicates.
2895 /// #![feature(slice_partition_dedup)]
2897 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2899 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2901 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2902 /// assert_eq!(duplicates, [21, 30, 13]);
2904 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2906 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2908 F: FnMut(&mut T) -> K,
2911 self.partition_dedup_by(|a, b| key(a) == key(b))
2914 /// Rotates the slice in-place such that the first `mid` elements of the
2915 /// slice move to the end while the last `self.len() - mid` elements move to
2916 /// the front. After calling `rotate_left`, the element previously at index
2917 /// `mid` will become the first element in the slice.
2921 /// This function will panic if `mid` is greater than the length of the
2922 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2927 /// Takes linear (in `self.len()`) time.
2932 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2933 /// a.rotate_left(2);
2934 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2937 /// Rotating a subslice:
2940 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2941 /// a[1..5].rotate_left(1);
2942 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2944 #[stable(feature = "slice_rotate", since = "1.26.0")]
2945 pub fn rotate_left(&mut self, mid: usize) {
2946 assert!(mid <= self.len());
2947 let k = self.len() - mid;
2948 let p = self.as_mut_ptr();
2950 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2951 // valid for reading and writing, as required by `ptr_rotate`.
2953 rotate::ptr_rotate(mid, p.add(mid), k);
2957 /// Rotates the slice in-place such that the first `self.len() - k`
2958 /// elements of the slice move to the end while the last `k` elements move
2959 /// to the front. After calling `rotate_right`, the element previously at
2960 /// index `self.len() - k` will become the first element in the slice.
2964 /// This function will panic if `k` is greater than the length of the
2965 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2970 /// Takes linear (in `self.len()`) time.
2975 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2976 /// a.rotate_right(2);
2977 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2980 /// Rotate a subslice:
2983 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2984 /// a[1..5].rotate_right(1);
2985 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2987 #[stable(feature = "slice_rotate", since = "1.26.0")]
2988 pub fn rotate_right(&mut self, k: usize) {
2989 assert!(k <= self.len());
2990 let mid = self.len() - k;
2991 let p = self.as_mut_ptr();
2993 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2994 // valid for reading and writing, as required by `ptr_rotate`.
2996 rotate::ptr_rotate(mid, p.add(mid), k);
3000 /// Fills `self` with elements by cloning `value`.
3005 /// let mut buf = vec![0; 10];
3007 /// assert_eq!(buf, vec![1; 10]);
3009 #[doc(alias = "memset")]
3010 #[stable(feature = "slice_fill", since = "1.50.0")]
3011 pub fn fill(&mut self, value: T)
3015 specialize::SpecFill::spec_fill(self, value);
3018 /// Fills `self` with elements returned by calling a closure repeatedly.
3020 /// This method uses a closure to create new values. If you'd rather
3021 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3022 /// trait to generate values, you can pass [`Default::default`] as the
3025 /// [`fill`]: slice::fill
3030 /// let mut buf = vec![1; 10];
3031 /// buf.fill_with(Default::default);
3032 /// assert_eq!(buf, vec![0; 10]);
3034 #[doc(alias = "memset")]
3035 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3036 pub fn fill_with<F>(&mut self, mut f: F)
3045 /// Copies the elements from `src` into `self`.
3047 /// The length of `src` must be the same as `self`.
3051 /// This function will panic if the two slices have different lengths.
3055 /// Cloning two elements from a slice into another:
3058 /// let src = [1, 2, 3, 4];
3059 /// let mut dst = [0, 0];
3061 /// // Because the slices have to be the same length,
3062 /// // we slice the source slice from four elements
3063 /// // to two. It will panic if we don't do this.
3064 /// dst.clone_from_slice(&src[2..]);
3066 /// assert_eq!(src, [1, 2, 3, 4]);
3067 /// assert_eq!(dst, [3, 4]);
3070 /// Rust enforces that there can only be one mutable reference with no
3071 /// immutable references to a particular piece of data in a particular
3072 /// scope. Because of this, attempting to use `clone_from_slice` on a
3073 /// single slice will result in a compile failure:
3076 /// let mut slice = [1, 2, 3, 4, 5];
3078 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3081 /// To work around this, we can use [`split_at_mut`] to create two distinct
3082 /// sub-slices from a slice:
3085 /// let mut slice = [1, 2, 3, 4, 5];
3088 /// let (left, right) = slice.split_at_mut(2);
3089 /// left.clone_from_slice(&right[1..]);
3092 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3095 /// [`copy_from_slice`]: slice::copy_from_slice
3096 /// [`split_at_mut`]: slice::split_at_mut
3097 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3099 pub fn clone_from_slice(&mut self, src: &[T])
3103 self.spec_clone_from(src);
3106 /// Copies all elements from `src` into `self`, using a memcpy.
3108 /// The length of `src` must be the same as `self`.
3110 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3114 /// This function will panic if the two slices have different lengths.
3118 /// Copying two elements from a slice into another:
3121 /// let src = [1, 2, 3, 4];
3122 /// let mut dst = [0, 0];
3124 /// // Because the slices have to be the same length,
3125 /// // we slice the source slice from four elements
3126 /// // to two. It will panic if we don't do this.
3127 /// dst.copy_from_slice(&src[2..]);
3129 /// assert_eq!(src, [1, 2, 3, 4]);
3130 /// assert_eq!(dst, [3, 4]);
3133 /// Rust enforces that there can only be one mutable reference with no
3134 /// immutable references to a particular piece of data in a particular
3135 /// scope. Because of this, attempting to use `copy_from_slice` on a
3136 /// single slice will result in a compile failure:
3139 /// let mut slice = [1, 2, 3, 4, 5];
3141 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3144 /// To work around this, we can use [`split_at_mut`] to create two distinct
3145 /// sub-slices from a slice:
3148 /// let mut slice = [1, 2, 3, 4, 5];
3151 /// let (left, right) = slice.split_at_mut(2);
3152 /// left.copy_from_slice(&right[1..]);
3155 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3158 /// [`clone_from_slice`]: slice::clone_from_slice
3159 /// [`split_at_mut`]: slice::split_at_mut
3160 #[doc(alias = "memcpy")]
3161 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3163 pub fn copy_from_slice(&mut self, src: &[T])
3167 // The panic code path was put into a cold function to not bloat the
3172 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3174 "source slice length ({}) does not match destination slice length ({})",
3179 if self.len() != src.len() {
3180 len_mismatch_fail(self.len(), src.len());
3183 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3184 // checked to have the same length. The slices cannot overlap because
3185 // mutable references are exclusive.
3187 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3191 /// Copies elements from one part of the slice to another part of itself,
3192 /// using a memmove.
3194 /// `src` is the range within `self` to copy from. `dest` is the starting
3195 /// index of the range within `self` to copy to, which will have the same
3196 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3197 /// must be less than or equal to `self.len()`.
3201 /// This function will panic if either range exceeds the end of the slice,
3202 /// or if the end of `src` is before the start.
3206 /// Copying four bytes within a slice:
3209 /// let mut bytes = *b"Hello, World!";
3211 /// bytes.copy_within(1..5, 8);
3213 /// assert_eq!(&bytes, b"Hello, Wello!");
3215 #[stable(feature = "copy_within", since = "1.37.0")]
3217 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3221 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3222 let count = src_end - src_start;
3223 assert!(dest <= self.len() - count, "dest is out of bounds");
3224 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3225 // as have those for `ptr::add`.
3227 // Derive both `src_ptr` and `dest_ptr` from the same loan
3228 let ptr = self.as_mut_ptr();
3229 let src_ptr = ptr.add(src_start);
3230 let dest_ptr = ptr.add(dest);
3231 ptr::copy(src_ptr, dest_ptr, count);
3235 /// Swaps all elements in `self` with those in `other`.
3237 /// The length of `other` must be the same as `self`.
3241 /// This function will panic if the two slices have different lengths.
3245 /// Swapping two elements across slices:
3248 /// let mut slice1 = [0, 0];
3249 /// let mut slice2 = [1, 2, 3, 4];
3251 /// slice1.swap_with_slice(&mut slice2[2..]);
3253 /// assert_eq!(slice1, [3, 4]);
3254 /// assert_eq!(slice2, [1, 2, 0, 0]);
3257 /// Rust enforces that there can only be one mutable reference to a
3258 /// particular piece of data in a particular scope. Because of this,
3259 /// attempting to use `swap_with_slice` on a single slice will result in
3260 /// a compile failure:
3263 /// let mut slice = [1, 2, 3, 4, 5];
3264 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3267 /// To work around this, we can use [`split_at_mut`] to create two distinct
3268 /// mutable sub-slices from a slice:
3271 /// let mut slice = [1, 2, 3, 4, 5];
3274 /// let (left, right) = slice.split_at_mut(2);
3275 /// left.swap_with_slice(&mut right[1..]);
3278 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3281 /// [`split_at_mut`]: slice::split_at_mut
3282 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3284 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3285 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3286 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3287 // checked to have the same length. The slices cannot overlap because
3288 // mutable references are exclusive.
3290 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3294 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3295 fn align_to_offsets<U>(&self) -> (usize, usize) {
3296 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3297 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3299 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3300 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3301 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3303 // Formula to calculate this is:
3305 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3306 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3308 // Expanded and simplified:
3310 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3311 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3313 // Luckily since all this is constant-evaluated... performance here matters not!
3315 fn gcd(a: usize, b: usize) -> usize {
3316 use crate::intrinsics;
3317 // iterative stein’s algorithm
3318 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3319 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3321 // SAFETY: `a` and `b` are checked to be non-zero values.
3322 let (ctz_a, mut ctz_b) = unsafe {
3329 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3331 let k = ctz_a.min(ctz_b);
3332 let mut a = a >> ctz_a;
3335 // remove all factors of 2 from b
3338 mem::swap(&mut a, &mut b);
3341 // SAFETY: `b` is checked to be non-zero.
3346 ctz_b = intrinsics::cttz_nonzero(b);
3351 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3352 let ts: usize = mem::size_of::<U>() / gcd;
3353 let us: usize = mem::size_of::<T>() / gcd;
3355 // Armed with this knowledge, we can find how many `U`s we can fit!
3356 let us_len = self.len() / ts * us;
3357 // And how many `T`s will be in the trailing slice!
3358 let ts_len = self.len() % ts;
3362 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3365 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3366 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3367 /// length possible for a given type and input slice, but only your algorithm's performance
3368 /// should depend on that, not its correctness. It is permissible for all of the input data to
3369 /// be returned as the prefix or suffix slice.
3371 /// This method has no purpose when either input element `T` or output element `U` are
3372 /// zero-sized and will return the original slice without splitting anything.
3376 /// This method is essentially a `transmute` with respect to the elements in the returned
3377 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3385 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3386 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3387 /// // less_efficient_algorithm_for_bytes(prefix);
3388 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3389 /// // less_efficient_algorithm_for_bytes(suffix);
3392 #[stable(feature = "slice_align_to", since = "1.30.0")]
3393 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3394 // Note that most of this function will be constant-evaluated,
3395 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3396 // handle ZSTs specially, which is – don't handle them at all.
3397 return (self, &[], &[]);
3400 // First, find at what point do we split between the first and 2nd slice. Easy with
3401 // ptr.align_offset.
3402 let ptr = self.as_ptr();
3403 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3404 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3405 if offset > self.len() {
3408 let (left, rest) = self.split_at(offset);
3409 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3410 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3411 // since the caller guarantees that we can transmute `T` to `U` safely.
3415 from_raw_parts(rest.as_ptr() as *const U, us_len),
3416 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3422 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3425 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3426 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3427 /// length possible for a given type and input slice, but only your algorithm's performance
3428 /// should depend on that, not its correctness. It is permissible for all of the input data to
3429 /// be returned as the prefix or suffix slice.
3431 /// This method has no purpose when either input element `T` or output element `U` are
3432 /// zero-sized and will return the original slice without splitting anything.
3436 /// This method is essentially a `transmute` with respect to the elements in the returned
3437 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3445 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3446 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3447 /// // less_efficient_algorithm_for_bytes(prefix);
3448 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3449 /// // less_efficient_algorithm_for_bytes(suffix);
3452 #[stable(feature = "slice_align_to", since = "1.30.0")]
3453 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3454 // Note that most of this function will be constant-evaluated,
3455 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3456 // handle ZSTs specially, which is – don't handle them at all.
3457 return (self, &mut [], &mut []);
3460 // First, find at what point do we split between the first and 2nd slice. Easy with
3461 // ptr.align_offset.
3462 let ptr = self.as_ptr();
3463 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3464 // rest of the method. This is done by passing a pointer to &[T] with an
3465 // alignment targeted for U.
3466 // `crate::ptr::align_offset` is called with a correctly aligned and
3467 // valid pointer `ptr` (it comes from a reference to `self`) and with
3468 // a size that is a power of two (since it comes from the alignement for U),
3469 // satisfying its safety constraints.
3470 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3471 if offset > self.len() {
3472 (self, &mut [], &mut [])
3474 let (left, rest) = self.split_at_mut(offset);
3475 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3476 let rest_len = rest.len();
3477 let mut_ptr = rest.as_mut_ptr();
3478 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3479 // SAFETY: see comments for `align_to`.
3483 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3484 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3490 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3492 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3493 /// postconditions as that method. You're only assured that
3494 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3496 /// Notably, all of the following are possible:
3497 /// - `prefix.len() >= LANES`.
3498 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3499 /// - `suffix.len() >= LANES`.
3501 /// That said, this is a safe method, so if you're only writing safe code,
3502 /// then this can at most cause incorrect logic, not unsoundness.
3506 /// This will panic if the size of the SIMD type is different from
3507 /// `LANES` times that of the scalar.
3509 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3510 /// that from ever happening, as only power-of-two numbers of lanes are
3511 /// supported. It's possible that, in the future, those restrictions might
3512 /// be lifted in a way that would make it possible to see panics from this
3513 /// method for something like `LANES == 3`.
3518 /// #![feature(portable_simd)]
3520 /// let short = &[1, 2, 3];
3521 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3522 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3524 /// // They might be split in any possible way between prefix and suffix
3525 /// let it = prefix.iter().chain(suffix).copied();
3526 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3528 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3529 /// use std::ops::Add;
3530 /// use std::simd::f32x4;
3531 /// let (prefix, middle, suffix) = x.as_simd();
3532 /// let sums = f32x4::from_array([
3533 /// prefix.iter().copied().sum(),
3536 /// suffix.iter().copied().sum(),
3538 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3539 /// sums.reduce_sum()
3542 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3543 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3545 #[unstable(feature = "portable_simd", issue = "86656")]
3546 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3548 Simd<T, LANES>: AsRef<[T; LANES]>,
3549 T: simd::SimdElement,
3550 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3552 // These are expected to always match, as vector types are laid out like
3553 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3554 // might as well double-check since it'll optimize away anyhow.
3555 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3557 // SAFETY: The simd types have the same layout as arrays, just with
3558 // potentially-higher alignment, so the de-facto transmutes are sound.
3559 unsafe { self.align_to() }
3562 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3564 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3565 /// postconditions as that method. You're only assured that
3566 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3568 /// Notably, all of the following are possible:
3569 /// - `prefix.len() >= LANES`.
3570 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3571 /// - `suffix.len() >= LANES`.
3573 /// That said, this is a safe method, so if you're only writing safe code,
3574 /// then this can at most cause incorrect logic, not unsoundness.
3576 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3580 /// This will panic if the size of the SIMD type is different from
3581 /// `LANES` times that of the scalar.
3583 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3584 /// that from ever happening, as only power-of-two numbers of lanes are
3585 /// supported. It's possible that, in the future, those restrictions might
3586 /// be lifted in a way that would make it possible to see panics from this
3587 /// method for something like `LANES == 3`.
3588 #[unstable(feature = "portable_simd", issue = "86656")]
3589 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3591 Simd<T, LANES>: AsMut<[T; LANES]>,
3592 T: simd::SimdElement,
3593 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3595 // These are expected to always match, as vector types are laid out like
3596 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3597 // might as well double-check since it'll optimize away anyhow.
3598 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3600 // SAFETY: The simd types have the same layout as arrays, just with
3601 // potentially-higher alignment, so the de-facto transmutes are sound.
3602 unsafe { self.align_to_mut() }
3605 /// Checks if the elements of this slice are sorted.
3607 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3608 /// slice yields exactly zero or one element, `true` is returned.
3610 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3611 /// implies that this function returns `false` if any two consecutive items are not
3617 /// #![feature(is_sorted)]
3618 /// let empty: [i32; 0] = [];
3620 /// assert!([1, 2, 2, 9].is_sorted());
3621 /// assert!(![1, 3, 2, 4].is_sorted());
3622 /// assert!([0].is_sorted());
3623 /// assert!(empty.is_sorted());
3624 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3627 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3628 pub fn is_sorted(&self) -> bool
3632 self.is_sorted_by(|a, b| a.partial_cmp(b))
3635 /// Checks if the elements of this slice are sorted using the given comparator function.
3637 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3638 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3639 /// [`is_sorted`]; see its documentation for more information.
3641 /// [`is_sorted`]: slice::is_sorted
3642 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3643 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3645 F: FnMut(&T, &T) -> Option<Ordering>,
3647 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3650 /// Checks if the elements of this slice are sorted using the given key extraction function.
3652 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3653 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3654 /// documentation for more information.
3656 /// [`is_sorted`]: slice::is_sorted
3661 /// #![feature(is_sorted)]
3663 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3664 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3667 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3668 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3673 self.iter().is_sorted_by_key(f)
3676 /// Returns the index of the partition point according to the given predicate
3677 /// (the index of the first element of the second partition).
3679 /// The slice is assumed to be partitioned according to the given predicate.
3680 /// This means that all elements for which the predicate returns true are at the start of the slice
3681 /// and all elements for which the predicate returns false are at the end.
3682 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3683 /// (all odd numbers are at the start, all even at the end).
3685 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3686 /// as this method performs a kind of binary search.
3688 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3690 /// [`binary_search`]: slice::binary_search
3691 /// [`binary_search_by`]: slice::binary_search_by
3692 /// [`binary_search_by_key`]: slice::binary_search_by_key
3697 /// let v = [1, 2, 3, 3, 5, 6, 7];
3698 /// let i = v.partition_point(|&x| x < 5);
3700 /// assert_eq!(i, 4);
3701 /// assert!(v[..i].iter().all(|&x| x < 5));
3702 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3704 #[stable(feature = "partition_point", since = "1.52.0")]
3705 pub fn partition_point<P>(&self, mut pred: P) -> usize
3707 P: FnMut(&T) -> bool,
3709 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3712 /// Removes the subslice corresponding to the given range
3713 /// and returns a reference to it.
3715 /// Returns `None` and does not modify the slice if the given
3716 /// range is out of bounds.
3718 /// Note that this method only accepts one-sided ranges such as
3719 /// `2..` or `..6`, but not `2..6`.
3723 /// Taking the first three elements of a slice:
3726 /// #![feature(slice_take)]
3728 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3729 /// let mut first_three = slice.take(..3).unwrap();
3731 /// assert_eq!(slice, &['d']);
3732 /// assert_eq!(first_three, &['a', 'b', 'c']);
3735 /// Taking the last two elements of a slice:
3738 /// #![feature(slice_take)]
3740 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3741 /// let mut tail = slice.take(2..).unwrap();
3743 /// assert_eq!(slice, &['a', 'b']);
3744 /// assert_eq!(tail, &['c', 'd']);
3747 /// Getting `None` when `range` is out of bounds:
3750 /// #![feature(slice_take)]
3752 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3754 /// assert_eq!(None, slice.take(5..));
3755 /// assert_eq!(None, slice.take(..5));
3756 /// assert_eq!(None, slice.take(..=4));
3757 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3758 /// assert_eq!(Some(expected), slice.take(..4));
3761 #[must_use = "method does not modify the slice if the range is out of bounds"]
3762 #[unstable(feature = "slice_take", issue = "62280")]
3763 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3764 let (direction, split_index) = split_point_of(range)?;
3765 if split_index > self.len() {
3768 let (front, back) = self.split_at(split_index);
3770 Direction::Front => {
3774 Direction::Back => {
3781 /// Removes the subslice corresponding to the given range
3782 /// and returns a mutable reference to it.
3784 /// Returns `None` and does not modify the slice if the given
3785 /// range is out of bounds.
3787 /// Note that this method only accepts one-sided ranges such as
3788 /// `2..` or `..6`, but not `2..6`.
3792 /// Taking the first three elements of a slice:
3795 /// #![feature(slice_take)]
3797 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3798 /// let mut first_three = slice.take_mut(..3).unwrap();
3800 /// assert_eq!(slice, &mut ['d']);
3801 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3804 /// Taking the last two elements of a slice:
3807 /// #![feature(slice_take)]
3809 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3810 /// let mut tail = slice.take_mut(2..).unwrap();
3812 /// assert_eq!(slice, &mut ['a', 'b']);
3813 /// assert_eq!(tail, &mut ['c', 'd']);
3816 /// Getting `None` when `range` is out of bounds:
3819 /// #![feature(slice_take)]
3821 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3823 /// assert_eq!(None, slice.take_mut(5..));
3824 /// assert_eq!(None, slice.take_mut(..5));
3825 /// assert_eq!(None, slice.take_mut(..=4));
3826 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3827 /// assert_eq!(Some(expected), slice.take_mut(..4));
3830 #[must_use = "method does not modify the slice if the range is out of bounds"]
3831 #[unstable(feature = "slice_take", issue = "62280")]
3832 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3833 self: &mut &'a mut Self,
3835 ) -> Option<&'a mut Self> {
3836 let (direction, split_index) = split_point_of(range)?;
3837 if split_index > self.len() {
3840 let (front, back) = mem::take(self).split_at_mut(split_index);
3842 Direction::Front => {
3846 Direction::Back => {
3853 /// Removes the first element of the slice and returns a reference
3856 /// Returns `None` if the slice is empty.
3861 /// #![feature(slice_take)]
3863 /// let mut slice: &[_] = &['a', 'b', 'c'];
3864 /// let first = slice.take_first().unwrap();
3866 /// assert_eq!(slice, &['b', 'c']);
3867 /// assert_eq!(first, &'a');
3870 #[unstable(feature = "slice_take", issue = "62280")]
3871 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3872 let (first, rem) = self.split_first()?;
3877 /// Removes the first element of the slice and returns a mutable
3878 /// reference to it.
3880 /// Returns `None` if the slice is empty.
3885 /// #![feature(slice_take)]
3887 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3888 /// let first = slice.take_first_mut().unwrap();
3891 /// assert_eq!(slice, &['b', 'c']);
3892 /// assert_eq!(first, &'d');
3895 #[unstable(feature = "slice_take", issue = "62280")]
3896 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3897 let (first, rem) = mem::take(self).split_first_mut()?;
3902 /// Removes the last element of the slice and returns a reference
3905 /// Returns `None` if the slice is empty.
3910 /// #![feature(slice_take)]
3912 /// let mut slice: &[_] = &['a', 'b', 'c'];
3913 /// let last = slice.take_last().unwrap();
3915 /// assert_eq!(slice, &['a', 'b']);
3916 /// assert_eq!(last, &'c');
3919 #[unstable(feature = "slice_take", issue = "62280")]
3920 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3921 let (last, rem) = self.split_last()?;
3926 /// Removes the last element of the slice and returns a mutable
3927 /// reference to it.
3929 /// Returns `None` if the slice is empty.
3934 /// #![feature(slice_take)]
3936 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3937 /// let last = slice.take_last_mut().unwrap();
3940 /// assert_eq!(slice, &['a', 'b']);
3941 /// assert_eq!(last, &'d');
3944 #[unstable(feature = "slice_take", issue = "62280")]
3945 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3946 let (last, rem) = mem::take(self).split_last_mut()?;
3952 trait CloneFromSpec<T> {
3953 fn spec_clone_from(&mut self, src: &[T]);
3956 impl<T> CloneFromSpec<T> for [T]
3961 default fn spec_clone_from(&mut self, src: &[T]) {
3962 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3963 // NOTE: We need to explicitly slice them to the same length
3964 // to make it easier for the optimizer to elide bounds checking.
3965 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3966 let len = self.len();
3967 let src = &src[..len];
3969 self[i].clone_from(&src[i]);
3974 impl<T> CloneFromSpec<T> for [T]
3979 fn spec_clone_from(&mut self, src: &[T]) {
3980 self.copy_from_slice(src);
3984 #[stable(feature = "rust1", since = "1.0.0")]
3985 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3986 impl<T> const Default for &[T] {
3987 /// Creates an empty slice.
3988 fn default() -> Self {
3993 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3994 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3995 impl<T> const Default for &mut [T] {
3996 /// Creates a mutable empty slice.
3997 fn default() -> Self {
4002 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4003 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4004 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4005 /// `str`) to slices, and then this trait will be replaced or abolished.
4006 pub trait SlicePattern {
4007 /// The element type of the slice being matched on.
4010 /// Currently, the consumers of `SlicePattern` need a slice.
4011 fn as_slice(&self) -> &[Self::Item];
4014 #[stable(feature = "slice_strip", since = "1.51.0")]
4015 impl<T> SlicePattern for [T] {
4019 fn as_slice(&self) -> &[Self::Item] {
4024 #[stable(feature = "slice_strip", since = "1.51.0")]
4025 impl<T, const N: usize> SlicePattern for [T; N] {
4029 fn as_slice(&self) -> &[Self::Item] {