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 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
20 use crate::simd::{self, Simd};
24 feature = "slice_internals",
26 reason = "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Chunks, ChunksMut, Windows};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{Iter, IterMut};
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter::{RSplit, RSplitMut};
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter::{ChunksExact, ChunksExactMut};
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter::{ArrayChunks, ArrayChunksMut};
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter::ArrayWindows;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter::{GroupBy, GroupByMut};
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter::{SplitInclusive, SplitInclusiveMut};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw::{from_raw_parts, from_raw_parts_mut};
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw::{from_mut, from_ref};
74 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
75 pub use raw::{from_mut_ptr_range, from_ptr_range};
77 // This function is public only because there is no other way to unit test heapsort.
78 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
79 pub use sort::heapsort;
81 #[stable(feature = "slice_get_slice", since = "1.28.0")]
82 pub use index::SliceIndex;
84 #[unstable(feature = "slice_range", issue = "76393")]
87 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
88 pub use ascii::EscapeAscii;
90 /// Calculates the direction and split point of a one-sided range.
92 /// This is a helper function for `take` and `take_mut` that returns
93 /// the direction of the split (front or back) as well as the index at
94 /// which to split. Returns `None` if the split index would overflow.
96 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
99 Some(match (range.start_bound(), range.end_bound()) {
100 (Unbounded, Excluded(i)) => (Direction::Front, *i),
101 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
102 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
103 (Included(i), Unbounded) => (Direction::Back, *i),
116 /// Returns the number of elements in the slice.
121 /// let a = [1, 2, 3];
122 /// assert_eq!(a.len(), 3);
124 #[lang = "slice_len_fn"]
125 #[stable(feature = "rust1", since = "1.0.0")]
126 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
128 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
129 pub const fn len(&self) -> usize {
130 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
131 // As of this writing this causes a "Const-stable functions can only call other
132 // const-stable functions" error.
134 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
135 // and PtrComponents<T> have the same memory layouts. Only std can make this
137 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
140 /// Returns `true` if the slice has a length of 0.
145 /// let a = [1, 2, 3];
146 /// assert!(!a.is_empty());
148 #[stable(feature = "rust1", since = "1.0.0")]
149 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
151 pub const fn is_empty(&self) -> bool {
155 /// Returns the first element of the slice, or `None` if it is empty.
160 /// let v = [10, 40, 30];
161 /// assert_eq!(Some(&10), v.first());
163 /// let w: &[i32] = &[];
164 /// assert_eq!(None, w.first());
166 #[stable(feature = "rust1", since = "1.0.0")]
167 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
169 pub const fn first(&self) -> Option<&T> {
170 if let [first, ..] = self { Some(first) } else { None }
173 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
178 /// let x = &mut [0, 1, 2];
180 /// if let Some(first) = x.first_mut() {
183 /// assert_eq!(x, &[5, 1, 2]);
185 #[stable(feature = "rust1", since = "1.0.0")]
186 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
188 pub const fn first_mut(&mut self) -> Option<&mut T> {
189 if let [first, ..] = self { Some(first) } else { None }
192 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
197 /// let x = &[0, 1, 2];
199 /// if let Some((first, elements)) = x.split_first() {
200 /// assert_eq!(first, &0);
201 /// assert_eq!(elements, &[1, 2]);
204 #[stable(feature = "slice_splits", since = "1.5.0")]
205 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
207 pub const fn split_first(&self) -> Option<(&T, &[T])> {
208 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
211 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
216 /// let x = &mut [0, 1, 2];
218 /// if let Some((first, elements)) = x.split_first_mut() {
223 /// assert_eq!(x, &[3, 4, 5]);
225 #[stable(feature = "slice_splits", since = "1.5.0")]
226 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
228 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
229 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
232 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
237 /// let x = &[0, 1, 2];
239 /// if let Some((last, elements)) = x.split_last() {
240 /// assert_eq!(last, &2);
241 /// assert_eq!(elements, &[0, 1]);
244 #[stable(feature = "slice_splits", since = "1.5.0")]
245 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
247 pub const fn split_last(&self) -> Option<(&T, &[T])> {
248 if let [init @ .., last] = self { Some((last, init)) } else { None }
251 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
256 /// let x = &mut [0, 1, 2];
258 /// if let Some((last, elements)) = x.split_last_mut() {
263 /// assert_eq!(x, &[4, 5, 3]);
265 #[stable(feature = "slice_splits", since = "1.5.0")]
266 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
268 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
269 if let [init @ .., last] = self { Some((last, init)) } else { None }
272 /// Returns the last element of the slice, or `None` if it is empty.
277 /// let v = [10, 40, 30];
278 /// assert_eq!(Some(&30), v.last());
280 /// let w: &[i32] = &[];
281 /// assert_eq!(None, w.last());
283 #[stable(feature = "rust1", since = "1.0.0")]
284 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
286 pub const fn last(&self) -> Option<&T> {
287 if let [.., last] = self { Some(last) } else { None }
290 /// Returns a mutable pointer to the last item in the slice.
295 /// let x = &mut [0, 1, 2];
297 /// if let Some(last) = x.last_mut() {
300 /// assert_eq!(x, &[0, 1, 10]);
302 #[stable(feature = "rust1", since = "1.0.0")]
303 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
305 pub const fn last_mut(&mut self) -> Option<&mut T> {
306 if let [.., last] = self { Some(last) } else { None }
309 /// Returns a reference to an element or subslice depending on the type of
312 /// - If given a position, returns a reference to the element at that
313 /// position or `None` if out of bounds.
314 /// - If given a range, returns the subslice corresponding to that range,
315 /// or `None` if out of bounds.
320 /// let v = [10, 40, 30];
321 /// assert_eq!(Some(&40), v.get(1));
322 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
323 /// assert_eq!(None, v.get(3));
324 /// assert_eq!(None, v.get(0..4));
326 #[stable(feature = "rust1", since = "1.0.0")]
327 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
329 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
331 I: ~const SliceIndex<Self>,
336 /// Returns a mutable reference to an element or subslice depending on the
337 /// type of index (see [`get`]) or `None` if the index is out of bounds.
339 /// [`get`]: slice::get
344 /// let x = &mut [0, 1, 2];
346 /// if let Some(elem) = x.get_mut(1) {
349 /// assert_eq!(x, &[0, 42, 2]);
351 #[stable(feature = "rust1", since = "1.0.0")]
352 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
354 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
356 I: ~const SliceIndex<Self>,
361 /// Returns a reference to an element or subslice, without doing bounds
364 /// For a safe alternative see [`get`].
368 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
369 /// even if the resulting reference is not used.
371 /// [`get`]: slice::get
372 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
377 /// let x = &[1, 2, 4];
380 /// assert_eq!(x.get_unchecked(1), &2);
383 #[stable(feature = "rust1", since = "1.0.0")]
384 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
386 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
388 I: ~const SliceIndex<Self>,
390 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
391 // the slice is dereferenceable because `self` is a safe reference.
392 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
393 unsafe { &*index.get_unchecked(self) }
396 /// Returns a mutable reference to an element or subslice, without doing
399 /// For a safe alternative see [`get_mut`].
403 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
404 /// even if the resulting reference is not used.
406 /// [`get_mut`]: slice::get_mut
407 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
412 /// let x = &mut [1, 2, 4];
415 /// let elem = x.get_unchecked_mut(1);
418 /// assert_eq!(x, &[1, 13, 4]);
420 #[stable(feature = "rust1", since = "1.0.0")]
421 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
423 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
425 I: ~const SliceIndex<Self>,
427 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
428 // the slice is dereferenceable because `self` is a safe reference.
429 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
430 unsafe { &mut *index.get_unchecked_mut(self) }
433 /// Returns a raw pointer to the slice's buffer.
435 /// The caller must ensure that the slice outlives the pointer this
436 /// function returns, or else it will end up pointing to garbage.
438 /// The caller must also ensure that the memory the pointer (non-transitively) points to
439 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
440 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
442 /// Modifying the container referenced by this slice may cause its buffer
443 /// to be reallocated, which would also make any pointers to it invalid.
448 /// let x = &[1, 2, 4];
449 /// let x_ptr = x.as_ptr();
452 /// for i in 0..x.len() {
453 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
458 /// [`as_mut_ptr`]: slice::as_mut_ptr
459 #[stable(feature = "rust1", since = "1.0.0")]
460 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
462 pub const fn as_ptr(&self) -> *const T {
463 self as *const [T] as *const T
466 /// Returns an unsafe mutable pointer to the slice's buffer.
468 /// The caller must ensure that the slice outlives the pointer this
469 /// function returns, or else it will end up pointing to garbage.
471 /// Modifying the container referenced by this slice may cause its buffer
472 /// to be reallocated, which would also make any pointers to it invalid.
477 /// let x = &mut [1, 2, 4];
478 /// let x_ptr = x.as_mut_ptr();
481 /// for i in 0..x.len() {
482 /// *x_ptr.add(i) += 2;
485 /// assert_eq!(x, &[3, 4, 6]);
487 #[stable(feature = "rust1", since = "1.0.0")]
488 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
490 pub const fn as_mut_ptr(&mut self) -> *mut T {
491 self as *mut [T] as *mut T
494 /// Returns the two raw pointers spanning the slice.
496 /// The returned range is half-open, which means that the end pointer
497 /// points *one past* the last element of the slice. This way, an empty
498 /// slice is represented by two equal pointers, and the difference between
499 /// the two pointers represents the size of the slice.
501 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
502 /// requires extra caution, as it does not point to a valid element in the
505 /// This function is useful for interacting with foreign interfaces which
506 /// use two pointers to refer to a range of elements in memory, as is
509 /// It can also be useful to check if a pointer to an element refers to an
510 /// element of this slice:
513 /// let a = [1, 2, 3];
514 /// let x = &a[1] as *const _;
515 /// let y = &5 as *const _;
517 /// assert!(a.as_ptr_range().contains(&x));
518 /// assert!(!a.as_ptr_range().contains(&y));
521 /// [`as_ptr`]: slice::as_ptr
522 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
523 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
525 pub const fn as_ptr_range(&self) -> Range<*const T> {
526 let start = self.as_ptr();
527 // SAFETY: The `add` here is safe, because:
529 // - Both pointers are part of the same object, as pointing directly
530 // past the object also counts.
532 // - The size of the slice is never larger than isize::MAX bytes, as
534 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
535 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
536 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
537 // (This doesn't seem normative yet, but the very same assumption is
538 // made in many places, including the Index implementation of slices.)
540 // - There is no wrapping around involved, as slices do not wrap past
541 // the end of the address space.
543 // See the documentation of pointer::add.
544 let end = unsafe { start.add(self.len()) };
548 /// Returns the two unsafe mutable pointers spanning the slice.
550 /// The returned range is half-open, which means that the end pointer
551 /// points *one past* the last element of the slice. This way, an empty
552 /// slice is represented by two equal pointers, and the difference between
553 /// the two pointers represents the size of the slice.
555 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
556 /// pointer requires extra caution, as it does not point to a valid element
559 /// This function is useful for interacting with foreign interfaces which
560 /// use two pointers to refer to a range of elements in memory, as is
563 /// [`as_mut_ptr`]: slice::as_mut_ptr
564 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
565 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
567 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
568 let start = self.as_mut_ptr();
569 // SAFETY: See as_ptr_range() above for why `add` here is safe.
570 let end = unsafe { start.add(self.len()) };
574 /// Swaps two elements in the slice.
578 /// * a - The index of the first element
579 /// * b - The index of the second element
583 /// Panics if `a` or `b` are out of bounds.
588 /// let mut v = ["a", "b", "c", "d", "e"];
590 /// assert!(v == ["a", "b", "e", "d", "c"]);
592 #[stable(feature = "rust1", since = "1.0.0")]
593 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
596 pub const fn swap(&mut self, a: usize, b: usize) {
597 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
598 // Can't take two mutable loans from one vector, so instead use raw pointers.
599 let pa = ptr::addr_of_mut!(self[a]);
600 let pb = ptr::addr_of_mut!(self[b]);
601 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
602 // to elements in the slice and therefore are guaranteed to be valid and aligned.
603 // Note that accessing the elements behind `a` and `b` is checked and will
604 // panic when out of bounds.
610 /// Swaps two elements in the slice, without doing bounds checking.
612 /// For a safe alternative see [`swap`].
616 /// * a - The index of the first element
617 /// * b - The index of the second element
621 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
622 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
627 /// #![feature(slice_swap_unchecked)]
629 /// let mut v = ["a", "b", "c", "d"];
630 /// // SAFETY: we know that 1 and 3 are both indices of the slice
631 /// unsafe { v.swap_unchecked(1, 3) };
632 /// assert!(v == ["a", "d", "c", "b"]);
635 /// [`swap`]: slice::swap
636 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
637 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
638 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
639 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
640 #[cfg(debug_assertions)]
646 let ptr = self.as_mut_ptr();
647 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
649 ptr::swap(ptr.add(a), ptr.add(b));
653 /// Reverses the order of elements in the slice, in place.
658 /// let mut v = [1, 2, 3];
660 /// assert!(v == [3, 2, 1]);
662 #[stable(feature = "rust1", since = "1.0.0")]
664 pub fn reverse(&mut self) {
665 let half_len = self.len() / 2;
666 let Range { start, end } = self.as_mut_ptr_range();
668 // These slices will skip the middle item for an odd length,
669 // since that one doesn't need to move.
670 let (front_half, back_half) =
671 // SAFETY: Both are subparts of the original slice, so the memory
672 // range is valid, and they don't overlap because they're each only
673 // half (or less) of the original slice.
676 slice::from_raw_parts_mut(start, half_len),
677 slice::from_raw_parts_mut(end.sub(half_len), half_len),
681 // Introducing a function boundary here means that the two halves
682 // get `noalias` markers, allowing better optimization as LLVM
683 // knows that they're disjoint, unlike in the original slice.
684 revswap(front_half, back_half, half_len);
687 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
688 debug_assert_eq!(a.len(), n);
689 debug_assert_eq!(b.len(), n);
691 // Because this function is first compiled in isolation,
692 // this check tells LLVM that the indexing below is
693 // in-bounds. Then after inlining -- once the actual
694 // lengths of the slices are known -- it's removed.
695 let (a, b) = (&mut a[..n], &mut b[..n]);
698 mem::swap(&mut a[i], &mut b[n - 1 - i]);
703 /// Returns an iterator over the slice.
708 /// let x = &[1, 2, 4];
709 /// let mut iterator = x.iter();
711 /// assert_eq!(iterator.next(), Some(&1));
712 /// assert_eq!(iterator.next(), Some(&2));
713 /// assert_eq!(iterator.next(), Some(&4));
714 /// assert_eq!(iterator.next(), None);
716 #[stable(feature = "rust1", since = "1.0.0")]
718 pub fn iter(&self) -> Iter<'_, T> {
722 /// Returns an iterator that allows modifying each value.
727 /// let x = &mut [1, 2, 4];
728 /// for elem in x.iter_mut() {
731 /// assert_eq!(x, &[3, 4, 6]);
733 #[stable(feature = "rust1", since = "1.0.0")]
735 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
739 /// Returns an iterator over all contiguous windows of length
740 /// `size`. The windows overlap. If the slice is shorter than
741 /// `size`, the iterator returns no values.
745 /// Panics if `size` is 0.
750 /// let slice = ['r', 'u', 's', 't'];
751 /// let mut iter = slice.windows(2);
752 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
753 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
754 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
755 /// assert!(iter.next().is_none());
758 /// If the slice is shorter than `size`:
761 /// let slice = ['f', 'o', 'o'];
762 /// let mut iter = slice.windows(4);
763 /// assert!(iter.next().is_none());
765 #[stable(feature = "rust1", since = "1.0.0")]
767 pub fn windows(&self, size: usize) -> Windows<'_, T> {
768 let size = NonZeroUsize::new(size).expect("size is zero");
769 Windows::new(self, size)
772 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
773 /// beginning of the slice.
775 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
776 /// slice, then the last chunk will not have length `chunk_size`.
778 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
779 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
784 /// Panics if `chunk_size` is 0.
789 /// let slice = ['l', 'o', 'r', 'e', 'm'];
790 /// let mut iter = slice.chunks(2);
791 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
792 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
793 /// assert_eq!(iter.next().unwrap(), &['m']);
794 /// assert!(iter.next().is_none());
797 /// [`chunks_exact`]: slice::chunks_exact
798 /// [`rchunks`]: slice::rchunks
799 #[stable(feature = "rust1", since = "1.0.0")]
801 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
802 assert_ne!(chunk_size, 0);
803 Chunks::new(self, chunk_size)
806 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
807 /// beginning of the slice.
809 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
810 /// length of the slice, then the last chunk will not have length `chunk_size`.
812 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
813 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
814 /// the end of the slice.
818 /// Panics if `chunk_size` is 0.
823 /// let v = &mut [0, 0, 0, 0, 0];
824 /// let mut count = 1;
826 /// for chunk in v.chunks_mut(2) {
827 /// for elem in chunk.iter_mut() {
832 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
835 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
836 /// [`rchunks_mut`]: slice::rchunks_mut
837 #[stable(feature = "rust1", since = "1.0.0")]
839 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
840 assert_ne!(chunk_size, 0);
841 ChunksMut::new(self, chunk_size)
844 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
845 /// beginning of the slice.
847 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
848 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
849 /// from the `remainder` function of the iterator.
851 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
852 /// resulting code better than in the case of [`chunks`].
854 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
855 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
859 /// Panics if `chunk_size` is 0.
864 /// let slice = ['l', 'o', 'r', 'e', 'm'];
865 /// let mut iter = slice.chunks_exact(2);
866 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
867 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
868 /// assert!(iter.next().is_none());
869 /// assert_eq!(iter.remainder(), &['m']);
872 /// [`chunks`]: slice::chunks
873 /// [`rchunks_exact`]: slice::rchunks_exact
874 #[stable(feature = "chunks_exact", since = "1.31.0")]
876 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
877 assert_ne!(chunk_size, 0);
878 ChunksExact::new(self, chunk_size)
881 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
882 /// beginning of the slice.
884 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
885 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
886 /// retrieved from the `into_remainder` function of the iterator.
888 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
889 /// resulting code better than in the case of [`chunks_mut`].
891 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
892 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
897 /// Panics if `chunk_size` is 0.
902 /// let v = &mut [0, 0, 0, 0, 0];
903 /// let mut count = 1;
905 /// for chunk in v.chunks_exact_mut(2) {
906 /// for elem in chunk.iter_mut() {
911 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
914 /// [`chunks_mut`]: slice::chunks_mut
915 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
916 #[stable(feature = "chunks_exact", since = "1.31.0")]
918 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
919 assert_ne!(chunk_size, 0);
920 ChunksExactMut::new(self, chunk_size)
923 /// Splits the slice into a slice of `N`-element arrays,
924 /// assuming that there's no remainder.
928 /// This may only be called when
929 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
935 /// #![feature(slice_as_chunks)]
936 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
937 /// let chunks: &[[char; 1]] =
938 /// // SAFETY: 1-element chunks never have remainder
939 /// unsafe { slice.as_chunks_unchecked() };
940 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
941 /// let chunks: &[[char; 3]] =
942 /// // SAFETY: The slice length (6) is a multiple of 3
943 /// unsafe { slice.as_chunks_unchecked() };
944 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
946 /// // These would be unsound:
947 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
948 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
950 #[unstable(feature = "slice_as_chunks", issue = "74985")]
952 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
953 debug_assert_ne!(N, 0);
954 debug_assert_eq!(self.len() % N, 0);
956 // SAFETY: Our precondition is exactly what's needed to call this
957 unsafe { crate::intrinsics::exact_div(self.len(), N) };
958 // SAFETY: We cast a slice of `new_len * N` elements into
959 // a slice of `new_len` many `N` elements chunks.
960 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
963 /// Splits the slice into a slice of `N`-element arrays,
964 /// starting at the beginning of the slice,
965 /// and a remainder slice with length strictly less than `N`.
969 /// Panics if `N` is 0. This check will most probably get changed to a compile time
970 /// error before this method gets stabilized.
975 /// #![feature(slice_as_chunks)]
976 /// let slice = ['l', 'o', 'r', 'e', 'm'];
977 /// let (chunks, remainder) = slice.as_chunks();
978 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
979 /// assert_eq!(remainder, &['m']);
981 #[unstable(feature = "slice_as_chunks", issue = "74985")]
983 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
985 let len = self.len() / N;
986 let (multiple_of_n, remainder) = self.split_at(len * N);
987 // SAFETY: We already panicked for zero, and ensured by construction
988 // that the length of the subslice is a multiple of N.
989 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
990 (array_slice, remainder)
993 /// Splits the slice into a slice of `N`-element arrays,
994 /// starting at the end of the slice,
995 /// and a remainder slice with length strictly less than `N`.
999 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1000 /// error before this method gets stabilized.
1005 /// #![feature(slice_as_chunks)]
1006 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1007 /// let (remainder, chunks) = slice.as_rchunks();
1008 /// assert_eq!(remainder, &['l']);
1009 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1011 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1013 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1015 let len = self.len() / N;
1016 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1017 // SAFETY: We already panicked for zero, and ensured by construction
1018 // that the length of the subslice is a multiple of N.
1019 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1020 (remainder, array_slice)
1023 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1024 /// beginning of the slice.
1026 /// The chunks are array references and do not overlap. If `N` does not divide the
1027 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1028 /// retrieved from the `remainder` function of the iterator.
1030 /// This method is the const generic equivalent of [`chunks_exact`].
1034 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1035 /// error before this method gets stabilized.
1040 /// #![feature(array_chunks)]
1041 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1042 /// let mut iter = slice.array_chunks();
1043 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1044 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1045 /// assert!(iter.next().is_none());
1046 /// assert_eq!(iter.remainder(), &['m']);
1049 /// [`chunks_exact`]: slice::chunks_exact
1050 #[unstable(feature = "array_chunks", issue = "74985")]
1052 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1054 ArrayChunks::new(self)
1057 /// Splits the slice into a slice of `N`-element arrays,
1058 /// assuming that there's no remainder.
1062 /// This may only be called when
1063 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1069 /// #![feature(slice_as_chunks)]
1070 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1071 /// let chunks: &mut [[char; 1]] =
1072 /// // SAFETY: 1-element chunks never have remainder
1073 /// unsafe { slice.as_chunks_unchecked_mut() };
1074 /// chunks[0] = ['L'];
1075 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1076 /// let chunks: &mut [[char; 3]] =
1077 /// // SAFETY: The slice length (6) is a multiple of 3
1078 /// unsafe { slice.as_chunks_unchecked_mut() };
1079 /// chunks[1] = ['a', 'x', '?'];
1080 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1082 /// // These would be unsound:
1083 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1084 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1086 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1088 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1089 debug_assert_ne!(N, 0);
1090 debug_assert_eq!(self.len() % N, 0);
1092 // SAFETY: Our precondition is exactly what's needed to call this
1093 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1094 // SAFETY: We cast a slice of `new_len * N` elements into
1095 // a slice of `new_len` many `N` elements chunks.
1096 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1099 /// Splits the slice into a slice of `N`-element arrays,
1100 /// starting at the beginning of the slice,
1101 /// and a remainder slice with length strictly less than `N`.
1105 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1106 /// error before this method gets stabilized.
1111 /// #![feature(slice_as_chunks)]
1112 /// let v = &mut [0, 0, 0, 0, 0];
1113 /// let mut count = 1;
1115 /// let (chunks, remainder) = v.as_chunks_mut();
1116 /// remainder[0] = 9;
1117 /// for chunk in chunks {
1118 /// *chunk = [count; 2];
1121 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1123 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1125 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1127 let len = self.len() / N;
1128 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1129 // SAFETY: We already panicked for zero, and ensured by construction
1130 // that the length of the subslice is a multiple of N.
1131 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1132 (array_slice, remainder)
1135 /// Splits the slice into a slice of `N`-element arrays,
1136 /// starting at the end of the slice,
1137 /// and a remainder slice with length strictly less than `N`.
1141 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1142 /// error before this method gets stabilized.
1147 /// #![feature(slice_as_chunks)]
1148 /// let v = &mut [0, 0, 0, 0, 0];
1149 /// let mut count = 1;
1151 /// let (remainder, chunks) = v.as_rchunks_mut();
1152 /// remainder[0] = 9;
1153 /// for chunk in chunks {
1154 /// *chunk = [count; 2];
1157 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1159 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1161 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1163 let len = self.len() / N;
1164 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1165 // SAFETY: We already panicked for zero, and ensured by construction
1166 // that the length of the subslice is a multiple of N.
1167 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1168 (remainder, array_slice)
1171 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1172 /// beginning of the slice.
1174 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1175 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1176 /// can be retrieved from the `into_remainder` function of the iterator.
1178 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1182 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1183 /// error before this method gets stabilized.
1188 /// #![feature(array_chunks)]
1189 /// let v = &mut [0, 0, 0, 0, 0];
1190 /// let mut count = 1;
1192 /// for chunk in v.array_chunks_mut() {
1193 /// *chunk = [count; 2];
1196 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1199 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1200 #[unstable(feature = "array_chunks", issue = "74985")]
1202 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1204 ArrayChunksMut::new(self)
1207 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1208 /// starting at the beginning of the slice.
1210 /// This is the const generic equivalent of [`windows`].
1212 /// If `N` is greater than the size of the slice, it will return no windows.
1216 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1217 /// error before this method gets stabilized.
1222 /// #![feature(array_windows)]
1223 /// let slice = [0, 1, 2, 3];
1224 /// let mut iter = slice.array_windows();
1225 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1226 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1227 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1228 /// assert!(iter.next().is_none());
1231 /// [`windows`]: slice::windows
1232 #[unstable(feature = "array_windows", issue = "75027")]
1234 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1236 ArrayWindows::new(self)
1239 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1242 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1243 /// slice, then the last chunk will not have length `chunk_size`.
1245 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1246 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1251 /// Panics if `chunk_size` is 0.
1256 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1257 /// let mut iter = slice.rchunks(2);
1258 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1259 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1260 /// assert_eq!(iter.next().unwrap(), &['l']);
1261 /// assert!(iter.next().is_none());
1264 /// [`rchunks_exact`]: slice::rchunks_exact
1265 /// [`chunks`]: slice::chunks
1266 #[stable(feature = "rchunks", since = "1.31.0")]
1268 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1269 assert!(chunk_size != 0);
1270 RChunks::new(self, chunk_size)
1273 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1276 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1277 /// length of the slice, then the last chunk will not have length `chunk_size`.
1279 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1280 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1281 /// beginning of the slice.
1285 /// Panics if `chunk_size` is 0.
1290 /// let v = &mut [0, 0, 0, 0, 0];
1291 /// let mut count = 1;
1293 /// for chunk in v.rchunks_mut(2) {
1294 /// for elem in chunk.iter_mut() {
1299 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1302 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1303 /// [`chunks_mut`]: slice::chunks_mut
1304 #[stable(feature = "rchunks", since = "1.31.0")]
1306 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1307 assert!(chunk_size != 0);
1308 RChunksMut::new(self, chunk_size)
1311 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1312 /// end of the slice.
1314 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1315 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1316 /// from the `remainder` function of the iterator.
1318 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1319 /// resulting code better than in the case of [`chunks`].
1321 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1322 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1327 /// Panics if `chunk_size` is 0.
1332 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1333 /// let mut iter = slice.rchunks_exact(2);
1334 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1335 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1336 /// assert!(iter.next().is_none());
1337 /// assert_eq!(iter.remainder(), &['l']);
1340 /// [`chunks`]: slice::chunks
1341 /// [`rchunks`]: slice::rchunks
1342 /// [`chunks_exact`]: slice::chunks_exact
1343 #[stable(feature = "rchunks", since = "1.31.0")]
1345 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1346 assert!(chunk_size != 0);
1347 RChunksExact::new(self, chunk_size)
1350 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1353 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1354 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1355 /// retrieved from the `into_remainder` function of the iterator.
1357 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1358 /// resulting code better than in the case of [`chunks_mut`].
1360 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1361 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1366 /// Panics if `chunk_size` is 0.
1371 /// let v = &mut [0, 0, 0, 0, 0];
1372 /// let mut count = 1;
1374 /// for chunk in v.rchunks_exact_mut(2) {
1375 /// for elem in chunk.iter_mut() {
1380 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1383 /// [`chunks_mut`]: slice::chunks_mut
1384 /// [`rchunks_mut`]: slice::rchunks_mut
1385 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1386 #[stable(feature = "rchunks", since = "1.31.0")]
1388 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1389 assert!(chunk_size != 0);
1390 RChunksExactMut::new(self, chunk_size)
1393 /// Returns an iterator over the slice producing non-overlapping runs
1394 /// of elements using the predicate to separate them.
1396 /// The predicate is called on two elements following themselves,
1397 /// it means the predicate is called on `slice[0]` and `slice[1]`
1398 /// then on `slice[1]` and `slice[2]` and so on.
1403 /// #![feature(slice_group_by)]
1405 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1407 /// let mut iter = slice.group_by(|a, b| a == b);
1409 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1410 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1411 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1412 /// assert_eq!(iter.next(), None);
1415 /// This method can be used to extract the sorted subslices:
1418 /// #![feature(slice_group_by)]
1420 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1422 /// let mut iter = slice.group_by(|a, b| a <= b);
1424 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1425 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1426 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1427 /// assert_eq!(iter.next(), None);
1429 #[unstable(feature = "slice_group_by", issue = "80552")]
1431 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1433 F: FnMut(&T, &T) -> bool,
1435 GroupBy::new(self, pred)
1438 /// Returns an iterator over the slice producing non-overlapping mutable
1439 /// runs of elements using the predicate to separate them.
1441 /// The predicate is called on two elements following themselves,
1442 /// it means the predicate is called on `slice[0]` and `slice[1]`
1443 /// then on `slice[1]` and `slice[2]` and so on.
1448 /// #![feature(slice_group_by)]
1450 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1452 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1454 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1455 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1456 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1457 /// assert_eq!(iter.next(), None);
1460 /// This method can be used to extract the sorted subslices:
1463 /// #![feature(slice_group_by)]
1465 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1467 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1469 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1470 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1471 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1472 /// assert_eq!(iter.next(), None);
1474 #[unstable(feature = "slice_group_by", issue = "80552")]
1476 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1478 F: FnMut(&T, &T) -> bool,
1480 GroupByMut::new(self, pred)
1483 /// Divides one slice into two at an index.
1485 /// The first will contain all indices from `[0, mid)` (excluding
1486 /// the index `mid` itself) and the second will contain all
1487 /// indices from `[mid, len)` (excluding the index `len` itself).
1491 /// Panics if `mid > len`.
1496 /// let v = [1, 2, 3, 4, 5, 6];
1499 /// let (left, right) = v.split_at(0);
1500 /// assert_eq!(left, []);
1501 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1505 /// let (left, right) = v.split_at(2);
1506 /// assert_eq!(left, [1, 2]);
1507 /// assert_eq!(right, [3, 4, 5, 6]);
1511 /// let (left, right) = v.split_at(6);
1512 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1513 /// assert_eq!(right, []);
1516 #[stable(feature = "rust1", since = "1.0.0")]
1519 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1520 assert!(mid <= self.len());
1521 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1522 // fulfills the requirements of `from_raw_parts_mut`.
1523 unsafe { self.split_at_unchecked(mid) }
1526 /// Divides one mutable slice into two at an index.
1528 /// The first will contain all indices from `[0, mid)` (excluding
1529 /// the index `mid` itself) and the second will contain all
1530 /// indices from `[mid, len)` (excluding the index `len` itself).
1534 /// Panics if `mid > len`.
1539 /// let mut v = [1, 0, 3, 0, 5, 6];
1540 /// let (left, right) = v.split_at_mut(2);
1541 /// assert_eq!(left, [1, 0]);
1542 /// assert_eq!(right, [3, 0, 5, 6]);
1545 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1547 #[stable(feature = "rust1", since = "1.0.0")]
1550 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1551 assert!(mid <= self.len());
1552 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1553 // fulfills the requirements of `from_raw_parts_mut`.
1554 unsafe { self.split_at_mut_unchecked(mid) }
1557 /// Divides one slice into two at an index, without doing bounds checking.
1559 /// The first will contain all indices from `[0, mid)` (excluding
1560 /// the index `mid` itself) and the second will contain all
1561 /// indices from `[mid, len)` (excluding the index `len` itself).
1563 /// For a safe alternative see [`split_at`].
1567 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1568 /// even if the resulting reference is not used. The caller has to ensure that
1569 /// `0 <= mid <= self.len()`.
1571 /// [`split_at`]: slice::split_at
1572 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1577 /// #![feature(slice_split_at_unchecked)]
1579 /// let v = [1, 2, 3, 4, 5, 6];
1582 /// let (left, right) = v.split_at_unchecked(0);
1583 /// assert_eq!(left, []);
1584 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1588 /// let (left, right) = v.split_at_unchecked(2);
1589 /// assert_eq!(left, [1, 2]);
1590 /// assert_eq!(right, [3, 4, 5, 6]);
1594 /// let (left, right) = v.split_at_unchecked(6);
1595 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1596 /// assert_eq!(right, []);
1599 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1601 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1602 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1603 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1606 /// Divides one mutable slice into two at an index, without doing bounds checking.
1608 /// The first will contain all indices from `[0, mid)` (excluding
1609 /// the index `mid` itself) and the second will contain all
1610 /// indices from `[mid, len)` (excluding the index `len` itself).
1612 /// For a safe alternative see [`split_at_mut`].
1616 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1617 /// even if the resulting reference is not used. The caller has to ensure that
1618 /// `0 <= mid <= self.len()`.
1620 /// [`split_at_mut`]: slice::split_at_mut
1621 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1626 /// #![feature(slice_split_at_unchecked)]
1628 /// let mut v = [1, 0, 3, 0, 5, 6];
1629 /// // scoped to restrict the lifetime of the borrows
1631 /// let (left, right) = v.split_at_mut_unchecked(2);
1632 /// assert_eq!(left, [1, 0]);
1633 /// assert_eq!(right, [3, 0, 5, 6]);
1637 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1639 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1641 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1642 let len = self.len();
1643 let ptr = self.as_mut_ptr();
1645 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1647 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1649 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1652 /// Divides one slice into an array and a remainder slice at an index.
1654 /// The array will contain all indices from `[0, N)` (excluding
1655 /// the index `N` itself) and the slice will contain all
1656 /// indices from `[N, len)` (excluding the index `len` itself).
1660 /// Panics if `N > len`.
1665 /// #![feature(split_array)]
1667 /// let v = &[1, 2, 3, 4, 5, 6][..];
1670 /// let (left, right) = v.split_array_ref::<0>();
1671 /// assert_eq!(left, &[]);
1672 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1676 /// let (left, right) = v.split_array_ref::<2>();
1677 /// assert_eq!(left, &[1, 2]);
1678 /// assert_eq!(right, [3, 4, 5, 6]);
1682 /// let (left, right) = v.split_array_ref::<6>();
1683 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1684 /// assert_eq!(right, []);
1687 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1690 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1691 let (a, b) = self.split_at(N);
1692 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1693 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1696 /// Divides one mutable slice into an array and a remainder slice at an index.
1698 /// The array will contain all indices from `[0, N)` (excluding
1699 /// the index `N` itself) and the slice will contain all
1700 /// indices from `[N, len)` (excluding the index `len` itself).
1704 /// Panics if `N > len`.
1709 /// #![feature(split_array)]
1711 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1712 /// let (left, right) = v.split_array_mut::<2>();
1713 /// assert_eq!(left, &mut [1, 0]);
1714 /// assert_eq!(right, [3, 0, 5, 6]);
1717 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1719 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1722 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1723 let (a, b) = self.split_at_mut(N);
1724 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1725 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1728 /// Divides one slice into an array and a remainder slice at an index from
1731 /// The slice will contain all indices from `[0, len - N)` (excluding
1732 /// the index `len - N` itself) and the array will contain all
1733 /// indices from `[len - N, len)` (excluding the index `len` itself).
1737 /// Panics if `N > len`.
1742 /// #![feature(split_array)]
1744 /// let v = &[1, 2, 3, 4, 5, 6][..];
1747 /// let (left, right) = v.rsplit_array_ref::<0>();
1748 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1749 /// assert_eq!(right, &[]);
1753 /// let (left, right) = v.rsplit_array_ref::<2>();
1754 /// assert_eq!(left, [1, 2, 3, 4]);
1755 /// assert_eq!(right, &[5, 6]);
1759 /// let (left, right) = v.rsplit_array_ref::<6>();
1760 /// assert_eq!(left, []);
1761 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1764 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1766 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1767 assert!(N <= self.len());
1768 let (a, b) = self.split_at(self.len() - N);
1769 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1770 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1773 /// Divides one mutable slice into an array and a remainder slice at an
1774 /// index from the end.
1776 /// The slice will contain all indices from `[0, len - N)` (excluding
1777 /// the index `N` itself) and the array will contain all
1778 /// indices from `[len - N, len)` (excluding the index `len` itself).
1782 /// Panics if `N > len`.
1787 /// #![feature(split_array)]
1789 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1790 /// let (left, right) = v.rsplit_array_mut::<4>();
1791 /// assert_eq!(left, [1, 0]);
1792 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1795 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1797 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1799 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1800 assert!(N <= self.len());
1801 let (a, b) = self.split_at_mut(self.len() - N);
1802 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1803 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1806 /// Returns an iterator over subslices separated by elements that match
1807 /// `pred`. The matched element is not contained in the subslices.
1812 /// let slice = [10, 40, 33, 20];
1813 /// let mut iter = slice.split(|num| num % 3 == 0);
1815 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1816 /// assert_eq!(iter.next().unwrap(), &[20]);
1817 /// assert!(iter.next().is_none());
1820 /// If the first element is matched, an empty slice will be the first item
1821 /// returned by the iterator. Similarly, if the last element in the slice
1822 /// is matched, an empty slice will be the last item returned by the
1826 /// let slice = [10, 40, 33];
1827 /// let mut iter = slice.split(|num| num % 3 == 0);
1829 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1830 /// assert_eq!(iter.next().unwrap(), &[]);
1831 /// assert!(iter.next().is_none());
1834 /// If two matched elements are directly adjacent, an empty slice will be
1835 /// present between them:
1838 /// let slice = [10, 6, 33, 20];
1839 /// let mut iter = slice.split(|num| num % 3 == 0);
1841 /// assert_eq!(iter.next().unwrap(), &[10]);
1842 /// assert_eq!(iter.next().unwrap(), &[]);
1843 /// assert_eq!(iter.next().unwrap(), &[20]);
1844 /// assert!(iter.next().is_none());
1846 #[stable(feature = "rust1", since = "1.0.0")]
1848 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1850 F: FnMut(&T) -> bool,
1852 Split::new(self, pred)
1855 /// Returns an iterator over mutable subslices separated by elements that
1856 /// match `pred`. The matched element is not contained in the subslices.
1861 /// let mut v = [10, 40, 30, 20, 60, 50];
1863 /// for group in v.split_mut(|num| *num % 3 == 0) {
1866 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1868 #[stable(feature = "rust1", since = "1.0.0")]
1870 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1872 F: FnMut(&T) -> bool,
1874 SplitMut::new(self, pred)
1877 /// Returns an iterator over subslices separated by elements that match
1878 /// `pred`. The matched element is contained in the end of the previous
1879 /// subslice as a terminator.
1884 /// let slice = [10, 40, 33, 20];
1885 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1887 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1888 /// assert_eq!(iter.next().unwrap(), &[20]);
1889 /// assert!(iter.next().is_none());
1892 /// If the last element of the slice is matched,
1893 /// that element will be considered the terminator of the preceding slice.
1894 /// That slice will be the last item returned by the iterator.
1897 /// let slice = [3, 10, 40, 33];
1898 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1900 /// assert_eq!(iter.next().unwrap(), &[3]);
1901 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1902 /// assert!(iter.next().is_none());
1904 #[stable(feature = "split_inclusive", since = "1.51.0")]
1906 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1908 F: FnMut(&T) -> bool,
1910 SplitInclusive::new(self, pred)
1913 /// Returns an iterator over mutable subslices separated by elements that
1914 /// match `pred`. The matched element is contained in the previous
1915 /// subslice as a terminator.
1920 /// let mut v = [10, 40, 30, 20, 60, 50];
1922 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1923 /// let terminator_idx = group.len()-1;
1924 /// group[terminator_idx] = 1;
1926 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1928 #[stable(feature = "split_inclusive", since = "1.51.0")]
1930 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1932 F: FnMut(&T) -> bool,
1934 SplitInclusiveMut::new(self, pred)
1937 /// Returns an iterator over subslices separated by elements that match
1938 /// `pred`, starting at the end of the slice and working backwards.
1939 /// The matched element is not contained in the subslices.
1944 /// let slice = [11, 22, 33, 0, 44, 55];
1945 /// let mut iter = slice.rsplit(|num| *num == 0);
1947 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1948 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1949 /// assert_eq!(iter.next(), None);
1952 /// As with `split()`, if the first or last element is matched, an empty
1953 /// slice will be the first (or last) item returned by the iterator.
1956 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1957 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1958 /// assert_eq!(it.next().unwrap(), &[]);
1959 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1960 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1961 /// assert_eq!(it.next().unwrap(), &[]);
1962 /// assert_eq!(it.next(), None);
1964 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1966 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1968 F: FnMut(&T) -> bool,
1970 RSplit::new(self, pred)
1973 /// Returns an iterator over mutable subslices separated by elements that
1974 /// match `pred`, starting at the end of the slice and working
1975 /// backwards. The matched element is not contained in the subslices.
1980 /// let mut v = [100, 400, 300, 200, 600, 500];
1982 /// let mut count = 0;
1983 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1985 /// group[0] = count;
1987 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1990 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1992 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1994 F: FnMut(&T) -> bool,
1996 RSplitMut::new(self, pred)
1999 /// Returns an iterator over subslices separated by elements that match
2000 /// `pred`, limited to returning at most `n` items. The matched element is
2001 /// not contained in the subslices.
2003 /// The last element returned, if any, will contain the remainder of the
2008 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2009 /// `[20, 60, 50]`):
2012 /// let v = [10, 40, 30, 20, 60, 50];
2014 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2015 /// println!("{group:?}");
2018 #[stable(feature = "rust1", since = "1.0.0")]
2020 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2022 F: FnMut(&T) -> bool,
2024 SplitN::new(self.split(pred), n)
2027 /// Returns an iterator over subslices separated by elements that match
2028 /// `pred`, limited to returning at most `n` items. The matched element is
2029 /// not contained in the subslices.
2031 /// The last element returned, if any, will contain the remainder of the
2037 /// let mut v = [10, 40, 30, 20, 60, 50];
2039 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2042 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2044 #[stable(feature = "rust1", since = "1.0.0")]
2046 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2048 F: FnMut(&T) -> bool,
2050 SplitNMut::new(self.split_mut(pred), n)
2053 /// Returns an iterator over subslices separated by elements that match
2054 /// `pred` limited to returning at most `n` items. This starts at the end of
2055 /// the slice and works backwards. The matched element is not contained in
2058 /// The last element returned, if any, will contain the remainder of the
2063 /// Print the slice split once, starting from the end, by numbers divisible
2064 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2067 /// let v = [10, 40, 30, 20, 60, 50];
2069 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2070 /// println!("{group:?}");
2073 #[stable(feature = "rust1", since = "1.0.0")]
2075 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2077 F: FnMut(&T) -> bool,
2079 RSplitN::new(self.rsplit(pred), n)
2082 /// Returns an iterator over subslices separated by elements that match
2083 /// `pred` limited to returning at most `n` items. This starts at the end of
2084 /// the slice and works backwards. The matched element is not contained in
2087 /// The last element returned, if any, will contain the remainder of the
2093 /// let mut s = [10, 40, 30, 20, 60, 50];
2095 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2098 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2100 #[stable(feature = "rust1", since = "1.0.0")]
2102 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2104 F: FnMut(&T) -> bool,
2106 RSplitNMut::new(self.rsplit_mut(pred), n)
2109 /// Returns `true` if the slice contains an element with the given value.
2114 /// let v = [10, 40, 30];
2115 /// assert!(v.contains(&30));
2116 /// assert!(!v.contains(&50));
2119 /// If you do not have a `&T`, but some other value that you can compare
2120 /// with one (for example, `String` implements `PartialEq<str>`), you can
2121 /// use `iter().any`:
2124 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2125 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2126 /// assert!(!v.iter().any(|e| e == "hi"));
2128 #[stable(feature = "rust1", since = "1.0.0")]
2130 pub fn contains(&self, x: &T) -> bool
2134 cmp::SliceContains::slice_contains(x, self)
2137 /// Returns `true` if `needle` is a prefix of the slice.
2142 /// let v = [10, 40, 30];
2143 /// assert!(v.starts_with(&[10]));
2144 /// assert!(v.starts_with(&[10, 40]));
2145 /// assert!(!v.starts_with(&[50]));
2146 /// assert!(!v.starts_with(&[10, 50]));
2149 /// Always returns `true` if `needle` is an empty slice:
2152 /// let v = &[10, 40, 30];
2153 /// assert!(v.starts_with(&[]));
2154 /// let v: &[u8] = &[];
2155 /// assert!(v.starts_with(&[]));
2157 #[stable(feature = "rust1", since = "1.0.0")]
2158 pub fn starts_with(&self, needle: &[T]) -> bool
2162 let n = needle.len();
2163 self.len() >= n && needle == &self[..n]
2166 /// Returns `true` if `needle` is a suffix of the slice.
2171 /// let v = [10, 40, 30];
2172 /// assert!(v.ends_with(&[30]));
2173 /// assert!(v.ends_with(&[40, 30]));
2174 /// assert!(!v.ends_with(&[50]));
2175 /// assert!(!v.ends_with(&[50, 30]));
2178 /// Always returns `true` if `needle` is an empty slice:
2181 /// let v = &[10, 40, 30];
2182 /// assert!(v.ends_with(&[]));
2183 /// let v: &[u8] = &[];
2184 /// assert!(v.ends_with(&[]));
2186 #[stable(feature = "rust1", since = "1.0.0")]
2187 pub fn ends_with(&self, needle: &[T]) -> bool
2191 let (m, n) = (self.len(), needle.len());
2192 m >= n && needle == &self[m - n..]
2195 /// Returns a subslice with the prefix removed.
2197 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2198 /// If `prefix` is empty, simply returns the original slice.
2200 /// If the slice does not start with `prefix`, returns `None`.
2205 /// let v = &[10, 40, 30];
2206 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2207 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2208 /// assert_eq!(v.strip_prefix(&[50]), None);
2209 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2211 /// let prefix : &str = "he";
2212 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2213 /// Some(b"llo".as_ref()));
2215 #[must_use = "returns the subslice without modifying the original"]
2216 #[stable(feature = "slice_strip", since = "1.51.0")]
2217 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2221 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2222 let prefix = prefix.as_slice();
2223 let n = prefix.len();
2224 if n <= self.len() {
2225 let (head, tail) = self.split_at(n);
2233 /// Returns a subslice with the suffix removed.
2235 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2236 /// If `suffix` is empty, simply returns the original slice.
2238 /// If the slice does not end with `suffix`, returns `None`.
2243 /// let v = &[10, 40, 30];
2244 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2245 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2246 /// assert_eq!(v.strip_suffix(&[50]), None);
2247 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2249 #[must_use = "returns the subslice without modifying the original"]
2250 #[stable(feature = "slice_strip", since = "1.51.0")]
2251 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2255 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2256 let suffix = suffix.as_slice();
2257 let (len, n) = (self.len(), suffix.len());
2259 let (head, tail) = self.split_at(len - n);
2267 /// Binary searches this sorted slice for a given element.
2269 /// If the value is found then [`Result::Ok`] is returned, containing the
2270 /// index of the matching element. If there are multiple matches, then any
2271 /// one of the matches could be returned. The index is chosen
2272 /// deterministically, but is subject to change in future versions of Rust.
2273 /// If the value is not found then [`Result::Err`] is returned, containing
2274 /// the index where a matching element could be inserted while maintaining
2277 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2279 /// [`binary_search_by`]: slice::binary_search_by
2280 /// [`binary_search_by_key`]: slice::binary_search_by_key
2281 /// [`partition_point`]: slice::partition_point
2285 /// Looks up a series of four elements. The first is found, with a
2286 /// uniquely determined position; the second and third are not
2287 /// found; the fourth could match any position in `[1, 4]`.
2290 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2292 /// assert_eq!(s.binary_search(&13), Ok(9));
2293 /// assert_eq!(s.binary_search(&4), Err(7));
2294 /// assert_eq!(s.binary_search(&100), Err(13));
2295 /// let r = s.binary_search(&1);
2296 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2299 /// If you want to insert an item to a sorted vector, while maintaining
2303 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2305 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2306 /// s.insert(idx, num);
2307 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2309 #[stable(feature = "rust1", since = "1.0.0")]
2310 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2314 self.binary_search_by(|p| p.cmp(x))
2317 /// Binary searches this sorted slice with a comparator function.
2319 /// The comparator function should implement an order consistent
2320 /// with the sort order of the underlying slice, returning an
2321 /// order code that indicates whether its argument is `Less`,
2322 /// `Equal` or `Greater` the desired target.
2324 /// If the value is found then [`Result::Ok`] is returned, containing the
2325 /// index of the matching element. If there are multiple matches, then any
2326 /// one of the matches could be returned. The index is chosen
2327 /// deterministically, but is subject to change in future versions of Rust.
2328 /// If the value is not found then [`Result::Err`] is returned, containing
2329 /// the index where a matching element could be inserted while maintaining
2332 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2334 /// [`binary_search`]: slice::binary_search
2335 /// [`binary_search_by_key`]: slice::binary_search_by_key
2336 /// [`partition_point`]: slice::partition_point
2340 /// Looks up a series of four elements. The first is found, with a
2341 /// uniquely determined position; the second and third are not
2342 /// found; the fourth could match any position in `[1, 4]`.
2345 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2348 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2350 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2352 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2354 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2355 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2357 #[stable(feature = "rust1", since = "1.0.0")]
2359 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2361 F: FnMut(&'a T) -> Ordering,
2363 let mut size = self.len();
2365 let mut right = size;
2366 while left < right {
2367 let mid = left + size / 2;
2369 // SAFETY: the call is made safe by the following invariants:
2371 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2372 let cmp = f(unsafe { self.get_unchecked(mid) });
2374 // The reason why we use if/else control flow rather than match
2375 // is because match reorders comparison operations, which is perf sensitive.
2376 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2379 } else if cmp == Greater {
2382 // SAFETY: same as the `get_unchecked` above
2383 unsafe { crate::intrinsics::assume(mid < self.len()) };
2387 size = right - left;
2392 /// Binary searches this sorted slice with a key extraction function.
2394 /// Assumes that the slice is sorted by the key, for instance with
2395 /// [`sort_by_key`] using the same key extraction function.
2397 /// If the value is found then [`Result::Ok`] is returned, containing the
2398 /// index of the matching element. If there are multiple matches, then any
2399 /// one of the matches could be returned. The index is chosen
2400 /// deterministically, but is subject to change in future versions of Rust.
2401 /// If the value is not found then [`Result::Err`] is returned, containing
2402 /// the index where a matching element could be inserted while maintaining
2405 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2407 /// [`sort_by_key`]: slice::sort_by_key
2408 /// [`binary_search`]: slice::binary_search
2409 /// [`binary_search_by`]: slice::binary_search_by
2410 /// [`partition_point`]: slice::partition_point
2414 /// Looks up a series of four elements in a slice of pairs sorted by
2415 /// their second elements. The first is found, with a uniquely
2416 /// determined position; the second and third are not found; the
2417 /// fourth could match any position in `[1, 4]`.
2420 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2421 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2422 /// (1, 21), (2, 34), (4, 55)];
2424 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2425 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2426 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2427 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2428 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2430 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2431 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2432 // This breaks links when slice is displayed in core, but changing it to use relative links
2433 // would break when the item is re-exported. So allow the core links to be broken for now.
2434 #[allow(rustdoc::broken_intra_doc_links)]
2435 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2437 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2439 F: FnMut(&'a T) -> B,
2442 self.binary_search_by(|k| f(k).cmp(b))
2445 /// Sorts the slice, but might not preserve the order of equal elements.
2447 /// This sort is unstable (i.e., may reorder equal elements), in-place
2448 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2450 /// # Current implementation
2452 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2453 /// which combines the fast average case of randomized quicksort with the fast worst case of
2454 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2455 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2456 /// deterministic behavior.
2458 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2459 /// slice consists of several concatenated sorted sequences.
2464 /// let mut v = [-5, 4, 1, -3, 2];
2466 /// v.sort_unstable();
2467 /// assert!(v == [-5, -3, 1, 2, 4]);
2470 /// [pdqsort]: https://github.com/orlp/pdqsort
2471 #[stable(feature = "sort_unstable", since = "1.20.0")]
2473 pub fn sort_unstable(&mut self)
2477 sort::quicksort(self, |a, b| a.lt(b));
2480 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2483 /// This sort is unstable (i.e., may reorder equal elements), in-place
2484 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2486 /// The comparator function must define a total ordering for the elements in the slice. If
2487 /// the ordering is not total, the order of the elements is unspecified. An order is a
2488 /// total order if it is (for all `a`, `b` and `c`):
2490 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2491 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2493 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2494 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2497 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2498 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2499 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2502 /// # Current implementation
2504 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2505 /// which combines the fast average case of randomized quicksort with the fast worst case of
2506 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2507 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2508 /// deterministic behavior.
2510 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2511 /// slice consists of several concatenated sorted sequences.
2516 /// let mut v = [5, 4, 1, 3, 2];
2517 /// v.sort_unstable_by(|a, b| a.cmp(b));
2518 /// assert!(v == [1, 2, 3, 4, 5]);
2520 /// // reverse sorting
2521 /// v.sort_unstable_by(|a, b| b.cmp(a));
2522 /// assert!(v == [5, 4, 3, 2, 1]);
2525 /// [pdqsort]: https://github.com/orlp/pdqsort
2526 #[stable(feature = "sort_unstable", since = "1.20.0")]
2528 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2530 F: FnMut(&T, &T) -> Ordering,
2532 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2535 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2538 /// This sort is unstable (i.e., may reorder equal elements), in-place
2539 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2542 /// # Current implementation
2544 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2545 /// which combines the fast average case of randomized quicksort with the fast worst case of
2546 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2547 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2548 /// deterministic behavior.
2550 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2551 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2552 /// cases where the key function is expensive.
2557 /// let mut v = [-5i32, 4, 1, -3, 2];
2559 /// v.sort_unstable_by_key(|k| k.abs());
2560 /// assert!(v == [1, 2, -3, 4, -5]);
2563 /// [pdqsort]: https://github.com/orlp/pdqsort
2564 #[stable(feature = "sort_unstable", since = "1.20.0")]
2566 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2571 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2574 /// Reorder the slice such that the element at `index` is at its final sorted position.
2576 /// This reordering has the additional property that any value at position `i < index` will be
2577 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2578 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2579 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2580 /// element" in other libraries. It returns a triplet of the following values: all elements less
2581 /// than the one at the given index, the value at the given index, and all elements greater than
2582 /// the one at the given index.
2584 /// # Current implementation
2586 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2587 /// used for [`sort_unstable`].
2589 /// [`sort_unstable`]: slice::sort_unstable
2593 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2598 /// let mut v = [-5i32, 4, 1, -3, 2];
2600 /// // Find the median
2601 /// v.select_nth_unstable(2);
2603 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2604 /// // about the specified index.
2605 /// assert!(v == [-3, -5, 1, 2, 4] ||
2606 /// v == [-5, -3, 1, 2, 4] ||
2607 /// v == [-3, -5, 1, 4, 2] ||
2608 /// v == [-5, -3, 1, 4, 2]);
2610 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2612 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2616 let mut f = |a: &T, b: &T| a.lt(b);
2617 sort::partition_at_index(self, index, &mut f)
2620 /// Reorder the slice with a comparator function such that the element at `index` is at its
2621 /// final sorted position.
2623 /// This reordering has the additional property that any value at position `i < index` will be
2624 /// less than or equal to any value at a position `j > index` using the comparator function.
2625 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2626 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2627 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2628 /// values: all elements less than the one at the given index, the value at the given index,
2629 /// and all elements greater than the one at the given index, using the provided comparator
2632 /// # Current implementation
2634 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2635 /// used for [`sort_unstable`].
2637 /// [`sort_unstable`]: slice::sort_unstable
2641 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2646 /// let mut v = [-5i32, 4, 1, -3, 2];
2648 /// // Find the median as if the slice were sorted in descending order.
2649 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2651 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2652 /// // about the specified index.
2653 /// assert!(v == [2, 4, 1, -5, -3] ||
2654 /// v == [2, 4, 1, -3, -5] ||
2655 /// v == [4, 2, 1, -5, -3] ||
2656 /// v == [4, 2, 1, -3, -5]);
2658 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2660 pub fn select_nth_unstable_by<F>(
2664 ) -> (&mut [T], &mut T, &mut [T])
2666 F: FnMut(&T, &T) -> Ordering,
2668 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2669 sort::partition_at_index(self, index, &mut f)
2672 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2673 /// final sorted position.
2675 /// This reordering has the additional property that any value at position `i < index` will be
2676 /// less than or equal to any value at a position `j > index` using the key extraction function.
2677 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2678 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2679 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2680 /// values: all elements less than the one at the given index, the value at the given index, and
2681 /// all elements greater than the one at the given index, using the provided key extraction
2684 /// # Current implementation
2686 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2687 /// used for [`sort_unstable`].
2689 /// [`sort_unstable`]: slice::sort_unstable
2693 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2698 /// let mut v = [-5i32, 4, 1, -3, 2];
2700 /// // Return the median as if the array were sorted according to absolute value.
2701 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2703 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2704 /// // about the specified index.
2705 /// assert!(v == [1, 2, -3, 4, -5] ||
2706 /// v == [1, 2, -3, -5, 4] ||
2707 /// v == [2, 1, -3, 4, -5] ||
2708 /// v == [2, 1, -3, -5, 4]);
2710 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2712 pub fn select_nth_unstable_by_key<K, F>(
2716 ) -> (&mut [T], &mut T, &mut [T])
2721 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2722 sort::partition_at_index(self, index, &mut g)
2725 /// Moves all consecutive repeated elements to the end of the slice according to the
2726 /// [`PartialEq`] trait implementation.
2728 /// Returns two slices. The first contains no consecutive repeated elements.
2729 /// The second contains all the duplicates in no specified order.
2731 /// If the slice is sorted, the first returned slice contains no duplicates.
2736 /// #![feature(slice_partition_dedup)]
2738 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2740 /// let (dedup, duplicates) = slice.partition_dedup();
2742 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2743 /// assert_eq!(duplicates, [2, 3, 1]);
2745 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2747 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2751 self.partition_dedup_by(|a, b| a == b)
2754 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2755 /// a given equality relation.
2757 /// Returns two slices. The first contains no consecutive repeated elements.
2758 /// The second contains all the duplicates in no specified order.
2760 /// The `same_bucket` function is passed references to two elements from the slice and
2761 /// must determine if the elements compare equal. The elements are passed in opposite order
2762 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2763 /// at the end of the slice.
2765 /// If the slice is sorted, the first returned slice contains no duplicates.
2770 /// #![feature(slice_partition_dedup)]
2772 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2774 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2776 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2777 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2779 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2781 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2783 F: FnMut(&mut T, &mut T) -> bool,
2785 // Although we have a mutable reference to `self`, we cannot make
2786 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2787 // must ensure that the slice is in a valid state at all times.
2789 // The way that we handle this is by using swaps; we iterate
2790 // over all the elements, swapping as we go so that at the end
2791 // the elements we wish to keep are in the front, and those we
2792 // wish to reject are at the back. We can then split the slice.
2793 // This operation is still `O(n)`.
2795 // Example: We start in this state, where `r` represents "next
2796 // read" and `w` represents "next_write`.
2799 // +---+---+---+---+---+---+
2800 // | 0 | 1 | 1 | 2 | 3 | 3 |
2801 // +---+---+---+---+---+---+
2804 // Comparing self[r] against self[w-1], this is not a duplicate, so
2805 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2806 // r and w, leaving us with:
2809 // +---+---+---+---+---+---+
2810 // | 0 | 1 | 1 | 2 | 3 | 3 |
2811 // +---+---+---+---+---+---+
2814 // Comparing self[r] against self[w-1], this value is a duplicate,
2815 // so we increment `r` but leave everything else unchanged:
2818 // +---+---+---+---+---+---+
2819 // | 0 | 1 | 1 | 2 | 3 | 3 |
2820 // +---+---+---+---+---+---+
2823 // Comparing self[r] against self[w-1], this is not a duplicate,
2824 // so swap self[r] and self[w] and advance r and w:
2827 // +---+---+---+---+---+---+
2828 // | 0 | 1 | 2 | 1 | 3 | 3 |
2829 // +---+---+---+---+---+---+
2832 // Not a duplicate, repeat:
2835 // +---+---+---+---+---+---+
2836 // | 0 | 1 | 2 | 3 | 1 | 3 |
2837 // +---+---+---+---+---+---+
2840 // Duplicate, advance r. End of slice. Split at w.
2842 let len = self.len();
2844 return (self, &mut []);
2847 let ptr = self.as_mut_ptr();
2848 let mut next_read: usize = 1;
2849 let mut next_write: usize = 1;
2851 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2852 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2853 // one element before `ptr_write`, but `next_write` starts at 1, so
2854 // `prev_ptr_write` is never less than 0 and is inside the slice.
2855 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2856 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2857 // and `prev_ptr_write.offset(1)`.
2859 // `next_write` is also incremented at most once per loop at most meaning
2860 // no element is skipped when it may need to be swapped.
2862 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2863 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2864 // The explanation is simply that `next_read >= next_write` is always true,
2865 // thus `next_read > next_write - 1` is too.
2867 // Avoid bounds checks by using raw pointers.
2868 while next_read < len {
2869 let ptr_read = ptr.add(next_read);
2870 let prev_ptr_write = ptr.add(next_write - 1);
2871 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2872 if next_read != next_write {
2873 let ptr_write = prev_ptr_write.offset(1);
2874 mem::swap(&mut *ptr_read, &mut *ptr_write);
2882 self.split_at_mut(next_write)
2885 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2886 /// to the same key.
2888 /// Returns two slices. The first contains no consecutive repeated elements.
2889 /// The second contains all the duplicates in no specified order.
2891 /// If the slice is sorted, the first returned slice contains no duplicates.
2896 /// #![feature(slice_partition_dedup)]
2898 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2900 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2902 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2903 /// assert_eq!(duplicates, [21, 30, 13]);
2905 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2907 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2909 F: FnMut(&mut T) -> K,
2912 self.partition_dedup_by(|a, b| key(a) == key(b))
2915 /// Rotates the slice in-place such that the first `mid` elements of the
2916 /// slice move to the end while the last `self.len() - mid` elements move to
2917 /// the front. After calling `rotate_left`, the element previously at index
2918 /// `mid` will become the first element in the slice.
2922 /// This function will panic if `mid` is greater than the length of the
2923 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2928 /// Takes linear (in `self.len()`) time.
2933 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2934 /// a.rotate_left(2);
2935 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2938 /// Rotating a subslice:
2941 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2942 /// a[1..5].rotate_left(1);
2943 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2945 #[stable(feature = "slice_rotate", since = "1.26.0")]
2946 pub fn rotate_left(&mut self, mid: usize) {
2947 assert!(mid <= self.len());
2948 let k = self.len() - mid;
2949 let p = self.as_mut_ptr();
2951 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2952 // valid for reading and writing, as required by `ptr_rotate`.
2954 rotate::ptr_rotate(mid, p.add(mid), k);
2958 /// Rotates the slice in-place such that the first `self.len() - k`
2959 /// elements of the slice move to the end while the last `k` elements move
2960 /// to the front. After calling `rotate_right`, the element previously at
2961 /// index `self.len() - k` will become the first element in the slice.
2965 /// This function will panic if `k` is greater than the length of the
2966 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2971 /// Takes linear (in `self.len()`) time.
2976 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2977 /// a.rotate_right(2);
2978 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2981 /// Rotate a subslice:
2984 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2985 /// a[1..5].rotate_right(1);
2986 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2988 #[stable(feature = "slice_rotate", since = "1.26.0")]
2989 pub fn rotate_right(&mut self, k: usize) {
2990 assert!(k <= self.len());
2991 let mid = self.len() - k;
2992 let p = self.as_mut_ptr();
2994 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2995 // valid for reading and writing, as required by `ptr_rotate`.
2997 rotate::ptr_rotate(mid, p.add(mid), k);
3001 /// Fills `self` with elements by cloning `value`.
3006 /// let mut buf = vec![0; 10];
3008 /// assert_eq!(buf, vec![1; 10]);
3010 #[doc(alias = "memset")]
3011 #[stable(feature = "slice_fill", since = "1.50.0")]
3012 pub fn fill(&mut self, value: T)
3016 specialize::SpecFill::spec_fill(self, value);
3019 /// Fills `self` with elements returned by calling a closure repeatedly.
3021 /// This method uses a closure to create new values. If you'd rather
3022 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3023 /// trait to generate values, you can pass [`Default::default`] as the
3026 /// [`fill`]: slice::fill
3031 /// let mut buf = vec![1; 10];
3032 /// buf.fill_with(Default::default);
3033 /// assert_eq!(buf, vec![0; 10]);
3035 #[doc(alias = "memset")]
3036 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3037 pub fn fill_with<F>(&mut self, mut f: F)
3046 /// Copies the elements from `src` into `self`.
3048 /// The length of `src` must be the same as `self`.
3052 /// This function will panic if the two slices have different lengths.
3056 /// Cloning two elements from a slice into another:
3059 /// let src = [1, 2, 3, 4];
3060 /// let mut dst = [0, 0];
3062 /// // Because the slices have to be the same length,
3063 /// // we slice the source slice from four elements
3064 /// // to two. It will panic if we don't do this.
3065 /// dst.clone_from_slice(&src[2..]);
3067 /// assert_eq!(src, [1, 2, 3, 4]);
3068 /// assert_eq!(dst, [3, 4]);
3071 /// Rust enforces that there can only be one mutable reference with no
3072 /// immutable references to a particular piece of data in a particular
3073 /// scope. Because of this, attempting to use `clone_from_slice` on a
3074 /// single slice will result in a compile failure:
3077 /// let mut slice = [1, 2, 3, 4, 5];
3079 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3082 /// To work around this, we can use [`split_at_mut`] to create two distinct
3083 /// sub-slices from a slice:
3086 /// let mut slice = [1, 2, 3, 4, 5];
3089 /// let (left, right) = slice.split_at_mut(2);
3090 /// left.clone_from_slice(&right[1..]);
3093 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3096 /// [`copy_from_slice`]: slice::copy_from_slice
3097 /// [`split_at_mut`]: slice::split_at_mut
3098 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3100 pub fn clone_from_slice(&mut self, src: &[T])
3104 self.spec_clone_from(src);
3107 /// Copies all elements from `src` into `self`, using a memcpy.
3109 /// The length of `src` must be the same as `self`.
3111 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3115 /// This function will panic if the two slices have different lengths.
3119 /// Copying two elements from a slice into another:
3122 /// let src = [1, 2, 3, 4];
3123 /// let mut dst = [0, 0];
3125 /// // Because the slices have to be the same length,
3126 /// // we slice the source slice from four elements
3127 /// // to two. It will panic if we don't do this.
3128 /// dst.copy_from_slice(&src[2..]);
3130 /// assert_eq!(src, [1, 2, 3, 4]);
3131 /// assert_eq!(dst, [3, 4]);
3134 /// Rust enforces that there can only be one mutable reference with no
3135 /// immutable references to a particular piece of data in a particular
3136 /// scope. Because of this, attempting to use `copy_from_slice` on a
3137 /// single slice will result in a compile failure:
3140 /// let mut slice = [1, 2, 3, 4, 5];
3142 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3145 /// To work around this, we can use [`split_at_mut`] to create two distinct
3146 /// sub-slices from a slice:
3149 /// let mut slice = [1, 2, 3, 4, 5];
3152 /// let (left, right) = slice.split_at_mut(2);
3153 /// left.copy_from_slice(&right[1..]);
3156 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3159 /// [`clone_from_slice`]: slice::clone_from_slice
3160 /// [`split_at_mut`]: slice::split_at_mut
3161 #[doc(alias = "memcpy")]
3162 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3164 pub fn copy_from_slice(&mut self, src: &[T])
3168 // The panic code path was put into a cold function to not bloat the
3173 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3175 "source slice length ({}) does not match destination slice length ({})",
3180 if self.len() != src.len() {
3181 len_mismatch_fail(self.len(), src.len());
3184 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3185 // checked to have the same length. The slices cannot overlap because
3186 // mutable references are exclusive.
3188 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3192 /// Copies elements from one part of the slice to another part of itself,
3193 /// using a memmove.
3195 /// `src` is the range within `self` to copy from. `dest` is the starting
3196 /// index of the range within `self` to copy to, which will have the same
3197 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3198 /// must be less than or equal to `self.len()`.
3202 /// This function will panic if either range exceeds the end of the slice,
3203 /// or if the end of `src` is before the start.
3207 /// Copying four bytes within a slice:
3210 /// let mut bytes = *b"Hello, World!";
3212 /// bytes.copy_within(1..5, 8);
3214 /// assert_eq!(&bytes, b"Hello, Wello!");
3216 #[stable(feature = "copy_within", since = "1.37.0")]
3218 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3222 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3223 let count = src_end - src_start;
3224 assert!(dest <= self.len() - count, "dest is out of bounds");
3225 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3226 // as have those for `ptr::add`.
3228 // Derive both `src_ptr` and `dest_ptr` from the same loan
3229 let ptr = self.as_mut_ptr();
3230 let src_ptr = ptr.add(src_start);
3231 let dest_ptr = ptr.add(dest);
3232 ptr::copy(src_ptr, dest_ptr, count);
3236 /// Swaps all elements in `self` with those in `other`.
3238 /// The length of `other` must be the same as `self`.
3242 /// This function will panic if the two slices have different lengths.
3246 /// Swapping two elements across slices:
3249 /// let mut slice1 = [0, 0];
3250 /// let mut slice2 = [1, 2, 3, 4];
3252 /// slice1.swap_with_slice(&mut slice2[2..]);
3254 /// assert_eq!(slice1, [3, 4]);
3255 /// assert_eq!(slice2, [1, 2, 0, 0]);
3258 /// Rust enforces that there can only be one mutable reference to a
3259 /// particular piece of data in a particular scope. Because of this,
3260 /// attempting to use `swap_with_slice` on a single slice will result in
3261 /// a compile failure:
3264 /// let mut slice = [1, 2, 3, 4, 5];
3265 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3268 /// To work around this, we can use [`split_at_mut`] to create two distinct
3269 /// mutable sub-slices from a slice:
3272 /// let mut slice = [1, 2, 3, 4, 5];
3275 /// let (left, right) = slice.split_at_mut(2);
3276 /// left.swap_with_slice(&mut right[1..]);
3279 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3282 /// [`split_at_mut`]: slice::split_at_mut
3283 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3285 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3286 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3287 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3288 // checked to have the same length. The slices cannot overlap because
3289 // mutable references are exclusive.
3291 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3295 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3296 fn align_to_offsets<U>(&self) -> (usize, usize) {
3297 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3298 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3300 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3301 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3302 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3304 // Formula to calculate this is:
3306 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3307 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3309 // Expanded and simplified:
3311 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3312 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3314 // Luckily since all this is constant-evaluated... performance here matters not!
3316 fn gcd(a: usize, b: usize) -> usize {
3317 use crate::intrinsics;
3318 // iterative stein’s algorithm
3319 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3320 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3322 // SAFETY: `a` and `b` are checked to be non-zero values.
3323 let (ctz_a, mut ctz_b) = unsafe {
3330 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3332 let k = ctz_a.min(ctz_b);
3333 let mut a = a >> ctz_a;
3336 // remove all factors of 2 from b
3339 mem::swap(&mut a, &mut b);
3342 // SAFETY: `b` is checked to be non-zero.
3347 ctz_b = intrinsics::cttz_nonzero(b);
3352 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3353 let ts: usize = mem::size_of::<U>() / gcd;
3354 let us: usize = mem::size_of::<T>() / gcd;
3356 // Armed with this knowledge, we can find how many `U`s we can fit!
3357 let us_len = self.len() / ts * us;
3358 // And how many `T`s will be in the trailing slice!
3359 let ts_len = self.len() % ts;
3363 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3366 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3367 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3368 /// length possible for a given type and input slice, but only your algorithm's performance
3369 /// should depend on that, not its correctness. It is permissible for all of the input data to
3370 /// be returned as the prefix or suffix slice.
3372 /// This method has no purpose when either input element `T` or output element `U` are
3373 /// zero-sized and will return the original slice without splitting anything.
3377 /// This method is essentially a `transmute` with respect to the elements in the returned
3378 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3386 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3387 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3388 /// // less_efficient_algorithm_for_bytes(prefix);
3389 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3390 /// // less_efficient_algorithm_for_bytes(suffix);
3393 #[stable(feature = "slice_align_to", since = "1.30.0")]
3394 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3395 // Note that most of this function will be constant-evaluated,
3396 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3397 // handle ZSTs specially, which is – don't handle them at all.
3398 return (self, &[], &[]);
3401 // First, find at what point do we split between the first and 2nd slice. Easy with
3402 // ptr.align_offset.
3403 let ptr = self.as_ptr();
3404 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3405 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3406 if offset > self.len() {
3409 let (left, rest) = self.split_at(offset);
3410 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3411 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3412 // since the caller guarantees that we can transmute `T` to `U` safely.
3416 from_raw_parts(rest.as_ptr() as *const U, us_len),
3417 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3423 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3426 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3427 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3428 /// length possible for a given type and input slice, but only your algorithm's performance
3429 /// should depend on that, not its correctness. It is permissible for all of the input data to
3430 /// be returned as the prefix or suffix slice.
3432 /// This method has no purpose when either input element `T` or output element `U` are
3433 /// zero-sized and will return the original slice without splitting anything.
3437 /// This method is essentially a `transmute` with respect to the elements in the returned
3438 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3446 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3447 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3448 /// // less_efficient_algorithm_for_bytes(prefix);
3449 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3450 /// // less_efficient_algorithm_for_bytes(suffix);
3453 #[stable(feature = "slice_align_to", since = "1.30.0")]
3454 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3455 // Note that most of this function will be constant-evaluated,
3456 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3457 // handle ZSTs specially, which is – don't handle them at all.
3458 return (self, &mut [], &mut []);
3461 // First, find at what point do we split between the first and 2nd slice. Easy with
3462 // ptr.align_offset.
3463 let ptr = self.as_ptr();
3464 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3465 // rest of the method. This is done by passing a pointer to &[T] with an
3466 // alignment targeted for U.
3467 // `crate::ptr::align_offset` is called with a correctly aligned and
3468 // valid pointer `ptr` (it comes from a reference to `self`) and with
3469 // a size that is a power of two (since it comes from the alignement for U),
3470 // satisfying its safety constraints.
3471 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3472 if offset > self.len() {
3473 (self, &mut [], &mut [])
3475 let (left, rest) = self.split_at_mut(offset);
3476 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3477 let rest_len = rest.len();
3478 let mut_ptr = rest.as_mut_ptr();
3479 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3480 // SAFETY: see comments for `align_to`.
3484 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3485 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3491 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3493 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3494 /// postconditions as that method. You're only assured that
3495 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3497 /// Notably, all of the following are possible:
3498 /// - `prefix.len() >= LANES`.
3499 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3500 /// - `suffix.len() >= LANES`.
3502 /// That said, this is a safe method, so if you're only writing safe code,
3503 /// then this can at most cause incorrect logic, not unsoundness.
3507 /// This will panic if the size of the SIMD type is different from
3508 /// `LANES` times that of the scalar.
3510 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3511 /// that from ever happening, as only power-of-two numbers of lanes are
3512 /// supported. It's possible that, in the future, those restrictions might
3513 /// be lifted in a way that would make it possible to see panics from this
3514 /// method for something like `LANES == 3`.
3519 /// #![feature(portable_simd)]
3521 /// let short = &[1, 2, 3];
3522 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3523 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3525 /// // They might be split in any possible way between prefix and suffix
3526 /// let it = prefix.iter().chain(suffix).copied();
3527 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3529 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3530 /// use std::ops::Add;
3531 /// use std::simd::f32x4;
3532 /// let (prefix, middle, suffix) = x.as_simd();
3533 /// let sums = f32x4::from_array([
3534 /// prefix.iter().copied().sum(),
3537 /// suffix.iter().copied().sum(),
3539 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3540 /// sums.horizontal_sum()
3543 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3544 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3546 #[unstable(feature = "portable_simd", issue = "86656")]
3547 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
3548 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3550 Simd<T, LANES>: AsRef<[T; LANES]>,
3551 T: simd::SimdElement,
3552 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3554 // These are expected to always match, as vector types are laid out like
3555 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3556 // might as well double-check since it'll optimize away anyhow.
3557 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3559 // SAFETY: The simd types have the same layout as arrays, just with
3560 // potentially-higher alignment, so the de-facto transmutes are sound.
3561 unsafe { self.align_to() }
3564 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3566 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3567 /// postconditions as that method. You're only assured that
3568 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3570 /// Notably, all of the following are possible:
3571 /// - `prefix.len() >= LANES`.
3572 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3573 /// - `suffix.len() >= LANES`.
3575 /// That said, this is a safe method, so if you're only writing safe code,
3576 /// then this can at most cause incorrect logic, not unsoundness.
3578 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3582 /// This will panic if the size of the SIMD type is different from
3583 /// `LANES` times that of the scalar.
3585 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3586 /// that from ever happening, as only power-of-two numbers of lanes are
3587 /// supported. It's possible that, in the future, those restrictions might
3588 /// be lifted in a way that would make it possible to see panics from this
3589 /// method for something like `LANES == 3`.
3590 #[unstable(feature = "portable_simd", issue = "86656")]
3591 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
3592 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3594 Simd<T, LANES>: AsMut<[T; LANES]>,
3595 T: simd::SimdElement,
3596 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3598 // These are expected to always match, as vector types are laid out like
3599 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3600 // might as well double-check since it'll optimize away anyhow.
3601 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3603 // SAFETY: The simd types have the same layout as arrays, just with
3604 // potentially-higher alignment, so the de-facto transmutes are sound.
3605 unsafe { self.align_to_mut() }
3608 /// Checks if the elements of this slice are sorted.
3610 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3611 /// slice yields exactly zero or one element, `true` is returned.
3613 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3614 /// implies that this function returns `false` if any two consecutive items are not
3620 /// #![feature(is_sorted)]
3621 /// let empty: [i32; 0] = [];
3623 /// assert!([1, 2, 2, 9].is_sorted());
3624 /// assert!(![1, 3, 2, 4].is_sorted());
3625 /// assert!([0].is_sorted());
3626 /// assert!(empty.is_sorted());
3627 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3630 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3631 pub fn is_sorted(&self) -> bool
3635 self.is_sorted_by(|a, b| a.partial_cmp(b))
3638 /// Checks if the elements of this slice are sorted using the given comparator function.
3640 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3641 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3642 /// [`is_sorted`]; see its documentation for more information.
3644 /// [`is_sorted`]: slice::is_sorted
3645 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3646 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3648 F: FnMut(&T, &T) -> Option<Ordering>,
3650 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3653 /// Checks if the elements of this slice are sorted using the given key extraction function.
3655 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3656 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3657 /// documentation for more information.
3659 /// [`is_sorted`]: slice::is_sorted
3664 /// #![feature(is_sorted)]
3666 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3667 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3670 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3671 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3676 self.iter().is_sorted_by_key(f)
3679 /// Returns the index of the partition point according to the given predicate
3680 /// (the index of the first element of the second partition).
3682 /// The slice is assumed to be partitioned according to the given predicate.
3683 /// This means that all elements for which the predicate returns true are at the start of the slice
3684 /// and all elements for which the predicate returns false are at the end.
3685 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3686 /// (all odd numbers are at the start, all even at the end).
3688 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3689 /// as this method performs a kind of binary search.
3691 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3693 /// [`binary_search`]: slice::binary_search
3694 /// [`binary_search_by`]: slice::binary_search_by
3695 /// [`binary_search_by_key`]: slice::binary_search_by_key
3700 /// let v = [1, 2, 3, 3, 5, 6, 7];
3701 /// let i = v.partition_point(|&x| x < 5);
3703 /// assert_eq!(i, 4);
3704 /// assert!(v[..i].iter().all(|&x| x < 5));
3705 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3707 #[stable(feature = "partition_point", since = "1.52.0")]
3708 pub fn partition_point<P>(&self, mut pred: P) -> usize
3710 P: FnMut(&T) -> bool,
3712 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3715 /// Removes the subslice corresponding to the given range
3716 /// and returns a reference to it.
3718 /// Returns `None` and does not modify the slice if the given
3719 /// range is out of bounds.
3721 /// Note that this method only accepts one-sided ranges such as
3722 /// `2..` or `..6`, but not `2..6`.
3726 /// Taking the first three elements of a slice:
3729 /// #![feature(slice_take)]
3731 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3732 /// let mut first_three = slice.take(..3).unwrap();
3734 /// assert_eq!(slice, &['d']);
3735 /// assert_eq!(first_three, &['a', 'b', 'c']);
3738 /// Taking the last two elements of a slice:
3741 /// #![feature(slice_take)]
3743 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3744 /// let mut tail = slice.take(2..).unwrap();
3746 /// assert_eq!(slice, &['a', 'b']);
3747 /// assert_eq!(tail, &['c', 'd']);
3750 /// Getting `None` when `range` is out of bounds:
3753 /// #![feature(slice_take)]
3755 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3757 /// assert_eq!(None, slice.take(5..));
3758 /// assert_eq!(None, slice.take(..5));
3759 /// assert_eq!(None, slice.take(..=4));
3760 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3761 /// assert_eq!(Some(expected), slice.take(..4));
3764 #[must_use = "method does not modify the slice if the range is out of bounds"]
3765 #[unstable(feature = "slice_take", issue = "62280")]
3766 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3767 let (direction, split_index) = split_point_of(range)?;
3768 if split_index > self.len() {
3771 let (front, back) = self.split_at(split_index);
3773 Direction::Front => {
3777 Direction::Back => {
3784 /// Removes the subslice corresponding to the given range
3785 /// and returns a mutable reference to it.
3787 /// Returns `None` and does not modify the slice if the given
3788 /// range is out of bounds.
3790 /// Note that this method only accepts one-sided ranges such as
3791 /// `2..` or `..6`, but not `2..6`.
3795 /// Taking the first three elements of a slice:
3798 /// #![feature(slice_take)]
3800 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3801 /// let mut first_three = slice.take_mut(..3).unwrap();
3803 /// assert_eq!(slice, &mut ['d']);
3804 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3807 /// Taking the last two elements of a slice:
3810 /// #![feature(slice_take)]
3812 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3813 /// let mut tail = slice.take_mut(2..).unwrap();
3815 /// assert_eq!(slice, &mut ['a', 'b']);
3816 /// assert_eq!(tail, &mut ['c', 'd']);
3819 /// Getting `None` when `range` is out of bounds:
3822 /// #![feature(slice_take)]
3824 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3826 /// assert_eq!(None, slice.take_mut(5..));
3827 /// assert_eq!(None, slice.take_mut(..5));
3828 /// assert_eq!(None, slice.take_mut(..=4));
3829 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3830 /// assert_eq!(Some(expected), slice.take_mut(..4));
3833 #[must_use = "method does not modify the slice if the range is out of bounds"]
3834 #[unstable(feature = "slice_take", issue = "62280")]
3835 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3836 self: &mut &'a mut Self,
3838 ) -> Option<&'a mut Self> {
3839 let (direction, split_index) = split_point_of(range)?;
3840 if split_index > self.len() {
3843 let (front, back) = mem::take(self).split_at_mut(split_index);
3845 Direction::Front => {
3849 Direction::Back => {
3856 /// Removes the first element of the slice and returns a reference
3859 /// Returns `None` if the slice is empty.
3864 /// #![feature(slice_take)]
3866 /// let mut slice: &[_] = &['a', 'b', 'c'];
3867 /// let first = slice.take_first().unwrap();
3869 /// assert_eq!(slice, &['b', 'c']);
3870 /// assert_eq!(first, &'a');
3873 #[unstable(feature = "slice_take", issue = "62280")]
3874 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3875 let (first, rem) = self.split_first()?;
3880 /// Removes the first element of the slice and returns a mutable
3881 /// reference to it.
3883 /// Returns `None` if the slice is empty.
3888 /// #![feature(slice_take)]
3890 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3891 /// let first = slice.take_first_mut().unwrap();
3894 /// assert_eq!(slice, &['b', 'c']);
3895 /// assert_eq!(first, &'d');
3898 #[unstable(feature = "slice_take", issue = "62280")]
3899 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3900 let (first, rem) = mem::take(self).split_first_mut()?;
3905 /// Removes the last element of the slice and returns a reference
3908 /// Returns `None` if the slice is empty.
3913 /// #![feature(slice_take)]
3915 /// let mut slice: &[_] = &['a', 'b', 'c'];
3916 /// let last = slice.take_last().unwrap();
3918 /// assert_eq!(slice, &['a', 'b']);
3919 /// assert_eq!(last, &'c');
3922 #[unstable(feature = "slice_take", issue = "62280")]
3923 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3924 let (last, rem) = self.split_last()?;
3929 /// Removes the last element of the slice and returns a mutable
3930 /// reference to it.
3932 /// Returns `None` if the slice is empty.
3937 /// #![feature(slice_take)]
3939 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3940 /// let last = slice.take_last_mut().unwrap();
3943 /// assert_eq!(slice, &['a', 'b']);
3944 /// assert_eq!(last, &'d');
3947 #[unstable(feature = "slice_take", issue = "62280")]
3948 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3949 let (last, rem) = mem::take(self).split_last_mut()?;
3955 trait CloneFromSpec<T> {
3956 fn spec_clone_from(&mut self, src: &[T]);
3959 impl<T> CloneFromSpec<T> for [T]
3964 default fn spec_clone_from(&mut self, src: &[T]) {
3965 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3966 // NOTE: We need to explicitly slice them to the same length
3967 // to make it easier for the optimizer to elide bounds checking.
3968 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3969 let len = self.len();
3970 let src = &src[..len];
3972 self[i].clone_from(&src[i]);
3977 impl<T> CloneFromSpec<T> for [T]
3982 fn spec_clone_from(&mut self, src: &[T]) {
3983 self.copy_from_slice(src);
3987 #[stable(feature = "rust1", since = "1.0.0")]
3988 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3989 impl<T> const Default for &[T] {
3990 /// Creates an empty slice.
3991 fn default() -> Self {
3996 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3997 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3998 impl<T> const Default for &mut [T] {
3999 /// Creates a mutable empty slice.
4000 fn default() -> Self {
4005 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4006 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4007 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4008 /// `str`) to slices, and then this trait will be replaced or abolished.
4009 pub trait SlicePattern {
4010 /// The element type of the slice being matched on.
4013 /// Currently, the consumers of `SlicePattern` need a slice.
4014 fn as_slice(&self) -> &[Self::Item];
4017 #[stable(feature = "slice_strip", since = "1.51.0")]
4018 impl<T> SlicePattern for [T] {
4022 fn as_slice(&self) -> &[Self::Item] {
4027 #[stable(feature = "slice_strip", since = "1.51.0")]
4028 impl<T, const N: usize> SlicePattern for [T; N] {
4032 fn as_slice(&self) -> &[Self::Item] {