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(miri))] // Miri does not support all SIMD intrinsics
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 // This function is public only because there is no other way to unit test heapsort.
75 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
76 pub use sort::heapsort;
78 #[stable(feature = "slice_get_slice", since = "1.28.0")]
79 pub use index::SliceIndex;
81 #[unstable(feature = "slice_range", issue = "76393")]
84 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
85 pub use ascii::EscapeAscii;
87 /// Calculates the direction and split point of a one-sided range.
89 /// This is a helper function for `take` and `take_mut` that returns
90 /// the direction of the split (front or back) as well as the index at
91 /// which to split. Returns `None` if the split index would overflow.
93 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
96 Some(match (range.start_bound(), range.end_bound()) {
97 (Unbounded, Excluded(i)) => (Direction::Front, *i),
98 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
99 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
100 (Included(i), Unbounded) => (Direction::Back, *i),
113 /// Returns the number of elements in the slice.
118 /// let a = [1, 2, 3];
119 /// assert_eq!(a.len(), 3);
121 #[lang = "slice_len_fn"]
122 #[stable(feature = "rust1", since = "1.0.0")]
123 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
125 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
126 pub const fn len(&self) -> usize {
127 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
128 // As of this writing this causes a "Const-stable functions can only call other
129 // const-stable functions" error.
131 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
132 // and PtrComponents<T> have the same memory layouts. Only std can make this
134 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
137 /// Returns `true` if the slice has a length of 0.
142 /// let a = [1, 2, 3];
143 /// assert!(!a.is_empty());
145 #[stable(feature = "rust1", since = "1.0.0")]
146 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
148 pub const fn is_empty(&self) -> bool {
152 /// Returns the first element of the slice, or `None` if it is empty.
157 /// let v = [10, 40, 30];
158 /// assert_eq!(Some(&10), v.first());
160 /// let w: &[i32] = &[];
161 /// assert_eq!(None, w.first());
163 #[stable(feature = "rust1", since = "1.0.0")]
164 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
166 pub const fn first(&self) -> Option<&T> {
167 if let [first, ..] = self { Some(first) } else { None }
170 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
175 /// let x = &mut [0, 1, 2];
177 /// if let Some(first) = x.first_mut() {
180 /// assert_eq!(x, &[5, 1, 2]);
182 #[stable(feature = "rust1", since = "1.0.0")]
183 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
185 pub const fn first_mut(&mut self) -> Option<&mut T> {
186 if let [first, ..] = self { Some(first) } else { None }
189 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
194 /// let x = &[0, 1, 2];
196 /// if let Some((first, elements)) = x.split_first() {
197 /// assert_eq!(first, &0);
198 /// assert_eq!(elements, &[1, 2]);
201 #[stable(feature = "slice_splits", since = "1.5.0")]
202 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
204 pub const fn split_first(&self) -> Option<(&T, &[T])> {
205 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
208 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
213 /// let x = &mut [0, 1, 2];
215 /// if let Some((first, elements)) = x.split_first_mut() {
220 /// assert_eq!(x, &[3, 4, 5]);
222 #[stable(feature = "slice_splits", since = "1.5.0")]
223 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
225 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
226 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
229 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
234 /// let x = &[0, 1, 2];
236 /// if let Some((last, elements)) = x.split_last() {
237 /// assert_eq!(last, &2);
238 /// assert_eq!(elements, &[0, 1]);
241 #[stable(feature = "slice_splits", since = "1.5.0")]
242 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
244 pub const fn split_last(&self) -> Option<(&T, &[T])> {
245 if let [init @ .., last] = self { Some((last, init)) } else { None }
248 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
253 /// let x = &mut [0, 1, 2];
255 /// if let Some((last, elements)) = x.split_last_mut() {
260 /// assert_eq!(x, &[4, 5, 3]);
262 #[stable(feature = "slice_splits", since = "1.5.0")]
263 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
265 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
266 if let [init @ .., last] = self { Some((last, init)) } else { None }
269 /// Returns the last element of the slice, or `None` if it is empty.
274 /// let v = [10, 40, 30];
275 /// assert_eq!(Some(&30), v.last());
277 /// let w: &[i32] = &[];
278 /// assert_eq!(None, w.last());
280 #[stable(feature = "rust1", since = "1.0.0")]
281 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
283 pub const fn last(&self) -> Option<&T> {
284 if let [.., last] = self { Some(last) } else { None }
287 /// Returns a mutable pointer to the last item in the slice.
292 /// let x = &mut [0, 1, 2];
294 /// if let Some(last) = x.last_mut() {
297 /// assert_eq!(x, &[0, 1, 10]);
299 #[stable(feature = "rust1", since = "1.0.0")]
300 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
302 pub const fn last_mut(&mut self) -> Option<&mut T> {
303 if let [.., last] = self { Some(last) } else { None }
306 /// Returns a reference to an element or subslice depending on the type of
309 /// - If given a position, returns a reference to the element at that
310 /// position or `None` if out of bounds.
311 /// - If given a range, returns the subslice corresponding to that range,
312 /// or `None` if out of bounds.
317 /// let v = [10, 40, 30];
318 /// assert_eq!(Some(&40), v.get(1));
319 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
320 /// assert_eq!(None, v.get(3));
321 /// assert_eq!(None, v.get(0..4));
323 #[stable(feature = "rust1", since = "1.0.0")]
325 pub fn get<I>(&self, index: I) -> Option<&I::Output>
332 /// Returns a mutable reference to an element or subslice depending on the
333 /// type of index (see [`get`]) or `None` if the index is out of bounds.
335 /// [`get`]: slice::get
340 /// let x = &mut [0, 1, 2];
342 /// if let Some(elem) = x.get_mut(1) {
345 /// assert_eq!(x, &[0, 42, 2]);
347 #[stable(feature = "rust1", since = "1.0.0")]
349 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
356 /// Returns a reference to an element or subslice, without doing bounds
359 /// For a safe alternative see [`get`].
363 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
364 /// even if the resulting reference is not used.
366 /// [`get`]: slice::get
367 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
372 /// let x = &[1, 2, 4];
375 /// assert_eq!(x.get_unchecked(1), &2);
378 #[stable(feature = "rust1", since = "1.0.0")]
380 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
384 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
385 // the slice is dereferenceable because `self` is a safe reference.
386 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
387 unsafe { &*index.get_unchecked(self) }
390 /// Returns a mutable reference to an element or subslice, without doing
393 /// For a safe alternative see [`get_mut`].
397 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
398 /// even if the resulting reference is not used.
400 /// [`get_mut`]: slice::get_mut
401 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
406 /// let x = &mut [1, 2, 4];
409 /// let elem = x.get_unchecked_mut(1);
412 /// assert_eq!(x, &[1, 13, 4]);
414 #[stable(feature = "rust1", since = "1.0.0")]
416 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
420 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
421 // the slice is dereferenceable because `self` is a safe reference.
422 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
423 unsafe { &mut *index.get_unchecked_mut(self) }
426 /// Returns a raw pointer to the slice's buffer.
428 /// The caller must ensure that the slice outlives the pointer this
429 /// function returns, or else it will end up pointing to garbage.
431 /// The caller must also ensure that the memory the pointer (non-transitively) points to
432 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
433 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
435 /// Modifying the container referenced by this slice may cause its buffer
436 /// to be reallocated, which would also make any pointers to it invalid.
441 /// let x = &[1, 2, 4];
442 /// let x_ptr = x.as_ptr();
445 /// for i in 0..x.len() {
446 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
451 /// [`as_mut_ptr`]: slice::as_mut_ptr
452 #[stable(feature = "rust1", since = "1.0.0")]
453 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
455 pub const fn as_ptr(&self) -> *const T {
456 self as *const [T] as *const T
459 /// Returns an unsafe mutable pointer to the slice's buffer.
461 /// The caller must ensure that the slice outlives the pointer this
462 /// function returns, or else it will end up pointing to garbage.
464 /// Modifying the container referenced by this slice may cause its buffer
465 /// to be reallocated, which would also make any pointers to it invalid.
470 /// let x = &mut [1, 2, 4];
471 /// let x_ptr = x.as_mut_ptr();
474 /// for i in 0..x.len() {
475 /// *x_ptr.add(i) += 2;
478 /// assert_eq!(x, &[3, 4, 6]);
480 #[stable(feature = "rust1", since = "1.0.0")]
481 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
483 pub const fn as_mut_ptr(&mut self) -> *mut T {
484 self as *mut [T] as *mut T
487 /// Returns the two raw pointers spanning the slice.
489 /// The returned range is half-open, which means that the end pointer
490 /// points *one past* the last element of the slice. This way, an empty
491 /// slice is represented by two equal pointers, and the difference between
492 /// the two pointers represents the size of the slice.
494 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
495 /// requires extra caution, as it does not point to a valid element in the
498 /// This function is useful for interacting with foreign interfaces which
499 /// use two pointers to refer to a range of elements in memory, as is
502 /// It can also be useful to check if a pointer to an element refers to an
503 /// element of this slice:
506 /// let a = [1, 2, 3];
507 /// let x = &a[1] as *const _;
508 /// let y = &5 as *const _;
510 /// assert!(a.as_ptr_range().contains(&x));
511 /// assert!(!a.as_ptr_range().contains(&y));
514 /// [`as_ptr`]: slice::as_ptr
515 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
516 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
518 pub const fn as_ptr_range(&self) -> Range<*const T> {
519 let start = self.as_ptr();
520 // SAFETY: The `add` here is safe, because:
522 // - Both pointers are part of the same object, as pointing directly
523 // past the object also counts.
525 // - The size of the slice is never larger than isize::MAX bytes, as
527 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
528 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
529 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
530 // (This doesn't seem normative yet, but the very same assumption is
531 // made in many places, including the Index implementation of slices.)
533 // - There is no wrapping around involved, as slices do not wrap past
534 // the end of the address space.
536 // See the documentation of pointer::add.
537 let end = unsafe { start.add(self.len()) };
541 /// Returns the two unsafe mutable pointers spanning the slice.
543 /// The returned range is half-open, which means that the end pointer
544 /// points *one past* the last element of the slice. This way, an empty
545 /// slice is represented by two equal pointers, and the difference between
546 /// the two pointers represents the size of the slice.
548 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
549 /// pointer requires extra caution, as it does not point to a valid element
552 /// This function is useful for interacting with foreign interfaces which
553 /// use two pointers to refer to a range of elements in memory, as is
556 /// [`as_mut_ptr`]: slice::as_mut_ptr
557 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
558 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
560 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
561 let start = self.as_mut_ptr();
562 // SAFETY: See as_ptr_range() above for why `add` here is safe.
563 let end = unsafe { start.add(self.len()) };
567 /// Swaps two elements in the slice.
571 /// * a - The index of the first element
572 /// * b - The index of the second element
576 /// Panics if `a` or `b` are out of bounds.
581 /// let mut v = ["a", "b", "c", "d", "e"];
583 /// assert!(v == ["a", "b", "e", "d", "c"]);
585 #[stable(feature = "rust1", since = "1.0.0")]
586 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
589 pub const fn swap(&mut self, a: usize, b: usize) {
593 // SAFETY: we just checked that both `a` and `b` are in bounds
594 unsafe { self.swap_unchecked(a, b) }
597 /// Swaps two elements in the slice, without doing bounds checking.
599 /// For a safe alternative see [`swap`].
603 /// * a - The index of the first element
604 /// * b - The index of the second element
608 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
609 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
614 /// #![feature(slice_swap_unchecked)]
616 /// let mut v = ["a", "b", "c", "d"];
617 /// // SAFETY: we know that 1 and 3 are both indices of the slice
618 /// unsafe { v.swap_unchecked(1, 3) };
619 /// assert!(v == ["a", "d", "c", "b"]);
622 /// [`swap`]: slice::swap
623 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
624 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
625 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
626 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
627 #[cfg(debug_assertions)]
633 let ptr = self.as_mut_ptr();
634 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
636 ptr::swap(ptr.add(a), ptr.add(b));
640 /// Reverses the order of elements in the slice, in place.
645 /// let mut v = [1, 2, 3];
647 /// assert!(v == [3, 2, 1]);
649 #[stable(feature = "rust1", since = "1.0.0")]
651 pub fn reverse(&mut self) {
652 let half_len = self.len() / 2;
653 let Range { start, end } = self.as_mut_ptr_range();
655 // These slices will skip the middle item for an odd length,
656 // since that one doesn't need to move.
657 let (front_half, back_half) =
658 // SAFETY: Both are subparts of the original slice, so the memory
659 // range is valid, and they don't overlap because they're each only
660 // half (or less) of the original slice.
663 slice::from_raw_parts_mut(start, half_len),
664 slice::from_raw_parts_mut(end.sub(half_len), half_len),
668 // Introducing a function boundary here means that the two halves
669 // get `noalias` markers, allowing better optimization as LLVM
670 // knows that they're disjoint, unlike in the original slice.
671 revswap(front_half, back_half, half_len);
674 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
675 debug_assert_eq!(a.len(), n);
676 debug_assert_eq!(b.len(), n);
678 // Because this function is first compiled in isolation,
679 // this check tells LLVM that the indexing below is
680 // in-bounds. Then after inlining -- once the actual
681 // lengths of the slices are known -- it's removed.
682 let (a, b) = (&mut a[..n], &mut b[..n]);
685 mem::swap(&mut a[i], &mut b[n - 1 - i]);
690 /// Returns an iterator over the slice.
695 /// let x = &[1, 2, 4];
696 /// let mut iterator = x.iter();
698 /// assert_eq!(iterator.next(), Some(&1));
699 /// assert_eq!(iterator.next(), Some(&2));
700 /// assert_eq!(iterator.next(), Some(&4));
701 /// assert_eq!(iterator.next(), None);
703 #[stable(feature = "rust1", since = "1.0.0")]
705 pub fn iter(&self) -> Iter<'_, T> {
709 /// Returns an iterator that allows modifying each value.
714 /// let x = &mut [1, 2, 4];
715 /// for elem in x.iter_mut() {
718 /// assert_eq!(x, &[3, 4, 6]);
720 #[stable(feature = "rust1", since = "1.0.0")]
722 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
726 /// Returns an iterator over all contiguous windows of length
727 /// `size`. The windows overlap. If the slice is shorter than
728 /// `size`, the iterator returns no values.
732 /// Panics if `size` is 0.
737 /// let slice = ['r', 'u', 's', 't'];
738 /// let mut iter = slice.windows(2);
739 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
740 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
741 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
742 /// assert!(iter.next().is_none());
745 /// If the slice is shorter than `size`:
748 /// let slice = ['f', 'o', 'o'];
749 /// let mut iter = slice.windows(4);
750 /// assert!(iter.next().is_none());
752 #[stable(feature = "rust1", since = "1.0.0")]
754 pub fn windows(&self, size: usize) -> Windows<'_, T> {
755 let size = NonZeroUsize::new(size).expect("size is zero");
756 Windows::new(self, size)
759 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
760 /// beginning of the slice.
762 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
763 /// slice, then the last chunk will not have length `chunk_size`.
765 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
766 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
771 /// Panics if `chunk_size` is 0.
776 /// let slice = ['l', 'o', 'r', 'e', 'm'];
777 /// let mut iter = slice.chunks(2);
778 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
779 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
780 /// assert_eq!(iter.next().unwrap(), &['m']);
781 /// assert!(iter.next().is_none());
784 /// [`chunks_exact`]: slice::chunks_exact
785 /// [`rchunks`]: slice::rchunks
786 #[stable(feature = "rust1", since = "1.0.0")]
788 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
789 assert_ne!(chunk_size, 0);
790 Chunks::new(self, chunk_size)
793 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
794 /// beginning of the slice.
796 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
797 /// length of the slice, then the last chunk will not have length `chunk_size`.
799 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
800 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
801 /// the end of the slice.
805 /// Panics if `chunk_size` is 0.
810 /// let v = &mut [0, 0, 0, 0, 0];
811 /// let mut count = 1;
813 /// for chunk in v.chunks_mut(2) {
814 /// for elem in chunk.iter_mut() {
819 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
822 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
823 /// [`rchunks_mut`]: slice::rchunks_mut
824 #[stable(feature = "rust1", since = "1.0.0")]
826 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
827 assert_ne!(chunk_size, 0);
828 ChunksMut::new(self, chunk_size)
831 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
832 /// beginning of the slice.
834 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
835 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
836 /// from the `remainder` function of the iterator.
838 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
839 /// resulting code better than in the case of [`chunks`].
841 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
842 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
846 /// Panics if `chunk_size` is 0.
851 /// let slice = ['l', 'o', 'r', 'e', 'm'];
852 /// let mut iter = slice.chunks_exact(2);
853 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
854 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
855 /// assert!(iter.next().is_none());
856 /// assert_eq!(iter.remainder(), &['m']);
859 /// [`chunks`]: slice::chunks
860 /// [`rchunks_exact`]: slice::rchunks_exact
861 #[stable(feature = "chunks_exact", since = "1.31.0")]
863 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
864 assert_ne!(chunk_size, 0);
865 ChunksExact::new(self, chunk_size)
868 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
869 /// beginning of the slice.
871 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
872 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
873 /// retrieved from the `into_remainder` function of the iterator.
875 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
876 /// resulting code better than in the case of [`chunks_mut`].
878 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
879 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
884 /// Panics if `chunk_size` is 0.
889 /// let v = &mut [0, 0, 0, 0, 0];
890 /// let mut count = 1;
892 /// for chunk in v.chunks_exact_mut(2) {
893 /// for elem in chunk.iter_mut() {
898 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
901 /// [`chunks_mut`]: slice::chunks_mut
902 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
903 #[stable(feature = "chunks_exact", since = "1.31.0")]
905 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
906 assert_ne!(chunk_size, 0);
907 ChunksExactMut::new(self, chunk_size)
910 /// Splits the slice into a slice of `N`-element arrays,
911 /// assuming that there's no remainder.
915 /// This may only be called when
916 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
922 /// #![feature(slice_as_chunks)]
923 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
924 /// let chunks: &[[char; 1]] =
925 /// // SAFETY: 1-element chunks never have remainder
926 /// unsafe { slice.as_chunks_unchecked() };
927 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
928 /// let chunks: &[[char; 3]] =
929 /// // SAFETY: The slice length (6) is a multiple of 3
930 /// unsafe { slice.as_chunks_unchecked() };
931 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
933 /// // These would be unsound:
934 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
935 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
937 #[unstable(feature = "slice_as_chunks", issue = "74985")]
939 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
940 debug_assert_ne!(N, 0);
941 debug_assert_eq!(self.len() % N, 0);
943 // SAFETY: Our precondition is exactly what's needed to call this
944 unsafe { crate::intrinsics::exact_div(self.len(), N) };
945 // SAFETY: We cast a slice of `new_len * N` elements into
946 // a slice of `new_len` many `N` elements chunks.
947 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
950 /// Splits the slice into a slice of `N`-element arrays,
951 /// starting at the beginning of the slice,
952 /// and a remainder slice with length strictly less than `N`.
956 /// Panics if `N` is 0. This check will most probably get changed to a compile time
957 /// error before this method gets stabilized.
962 /// #![feature(slice_as_chunks)]
963 /// let slice = ['l', 'o', 'r', 'e', 'm'];
964 /// let (chunks, remainder) = slice.as_chunks();
965 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
966 /// assert_eq!(remainder, &['m']);
968 #[unstable(feature = "slice_as_chunks", issue = "74985")]
970 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
972 let len = self.len() / N;
973 let (multiple_of_n, remainder) = self.split_at(len * N);
974 // SAFETY: We already panicked for zero, and ensured by construction
975 // that the length of the subslice is a multiple of N.
976 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
977 (array_slice, remainder)
980 /// Splits the slice into a slice of `N`-element arrays,
981 /// starting at the end of the slice,
982 /// and a remainder slice with length strictly less than `N`.
986 /// Panics if `N` is 0. This check will most probably get changed to a compile time
987 /// error before this method gets stabilized.
992 /// #![feature(slice_as_chunks)]
993 /// let slice = ['l', 'o', 'r', 'e', 'm'];
994 /// let (remainder, chunks) = slice.as_rchunks();
995 /// assert_eq!(remainder, &['l']);
996 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
998 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1000 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1002 let len = self.len() / N;
1003 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1004 // SAFETY: We already panicked for zero, and ensured by construction
1005 // that the length of the subslice is a multiple of N.
1006 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1007 (remainder, array_slice)
1010 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1011 /// beginning of the slice.
1013 /// The chunks are array references and do not overlap. If `N` does not divide the
1014 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1015 /// retrieved from the `remainder` function of the iterator.
1017 /// This method is the const generic equivalent of [`chunks_exact`].
1021 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1022 /// error before this method gets stabilized.
1027 /// #![feature(array_chunks)]
1028 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1029 /// let mut iter = slice.array_chunks();
1030 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1031 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1032 /// assert!(iter.next().is_none());
1033 /// assert_eq!(iter.remainder(), &['m']);
1036 /// [`chunks_exact`]: slice::chunks_exact
1037 #[unstable(feature = "array_chunks", issue = "74985")]
1039 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1041 ArrayChunks::new(self)
1044 /// Splits the slice into a slice of `N`-element arrays,
1045 /// assuming that there's no remainder.
1049 /// This may only be called when
1050 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1056 /// #![feature(slice_as_chunks)]
1057 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1058 /// let chunks: &mut [[char; 1]] =
1059 /// // SAFETY: 1-element chunks never have remainder
1060 /// unsafe { slice.as_chunks_unchecked_mut() };
1061 /// chunks[0] = ['L'];
1062 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1063 /// let chunks: &mut [[char; 3]] =
1064 /// // SAFETY: The slice length (6) is a multiple of 3
1065 /// unsafe { slice.as_chunks_unchecked_mut() };
1066 /// chunks[1] = ['a', 'x', '?'];
1067 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1069 /// // These would be unsound:
1070 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1071 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1073 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1075 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1076 debug_assert_ne!(N, 0);
1077 debug_assert_eq!(self.len() % N, 0);
1079 // SAFETY: Our precondition is exactly what's needed to call this
1080 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1081 // SAFETY: We cast a slice of `new_len * N` elements into
1082 // a slice of `new_len` many `N` elements chunks.
1083 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1086 /// Splits the slice into a slice of `N`-element arrays,
1087 /// starting at the beginning of the slice,
1088 /// and a remainder slice with length strictly less than `N`.
1092 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1093 /// error before this method gets stabilized.
1098 /// #![feature(slice_as_chunks)]
1099 /// let v = &mut [0, 0, 0, 0, 0];
1100 /// let mut count = 1;
1102 /// let (chunks, remainder) = v.as_chunks_mut();
1103 /// remainder[0] = 9;
1104 /// for chunk in chunks {
1105 /// *chunk = [count; 2];
1108 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1110 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1112 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1114 let len = self.len() / N;
1115 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1116 // SAFETY: We already panicked for zero, and ensured by construction
1117 // that the length of the subslice is a multiple of N.
1118 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1119 (array_slice, remainder)
1122 /// Splits the slice into a slice of `N`-element arrays,
1123 /// starting at the end of the slice,
1124 /// and a remainder slice with length strictly less than `N`.
1128 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1129 /// error before this method gets stabilized.
1134 /// #![feature(slice_as_chunks)]
1135 /// let v = &mut [0, 0, 0, 0, 0];
1136 /// let mut count = 1;
1138 /// let (remainder, chunks) = v.as_rchunks_mut();
1139 /// remainder[0] = 9;
1140 /// for chunk in chunks {
1141 /// *chunk = [count; 2];
1144 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1146 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1148 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1150 let len = self.len() / N;
1151 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1152 // SAFETY: We already panicked for zero, and ensured by construction
1153 // that the length of the subslice is a multiple of N.
1154 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1155 (remainder, array_slice)
1158 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1159 /// beginning of the slice.
1161 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1162 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1163 /// can be retrieved from the `into_remainder` function of the iterator.
1165 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1169 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1170 /// error before this method gets stabilized.
1175 /// #![feature(array_chunks)]
1176 /// let v = &mut [0, 0, 0, 0, 0];
1177 /// let mut count = 1;
1179 /// for chunk in v.array_chunks_mut() {
1180 /// *chunk = [count; 2];
1183 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1186 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1187 #[unstable(feature = "array_chunks", issue = "74985")]
1189 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1191 ArrayChunksMut::new(self)
1194 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1195 /// starting at the beginning of the slice.
1197 /// This is the const generic equivalent of [`windows`].
1199 /// If `N` is greater than the size of the slice, it will return no windows.
1203 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1204 /// error before this method gets stabilized.
1209 /// #![feature(array_windows)]
1210 /// let slice = [0, 1, 2, 3];
1211 /// let mut iter = slice.array_windows();
1212 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1213 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1214 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1215 /// assert!(iter.next().is_none());
1218 /// [`windows`]: slice::windows
1219 #[unstable(feature = "array_windows", issue = "75027")]
1221 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1223 ArrayWindows::new(self)
1226 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1229 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1230 /// slice, then the last chunk will not have length `chunk_size`.
1232 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1233 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1238 /// Panics if `chunk_size` is 0.
1243 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1244 /// let mut iter = slice.rchunks(2);
1245 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1246 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1247 /// assert_eq!(iter.next().unwrap(), &['l']);
1248 /// assert!(iter.next().is_none());
1251 /// [`rchunks_exact`]: slice::rchunks_exact
1252 /// [`chunks`]: slice::chunks
1253 #[stable(feature = "rchunks", since = "1.31.0")]
1255 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1256 assert!(chunk_size != 0);
1257 RChunks::new(self, chunk_size)
1260 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1263 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1264 /// length of the slice, then the last chunk will not have length `chunk_size`.
1266 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1267 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1268 /// beginning of the slice.
1272 /// Panics if `chunk_size` is 0.
1277 /// let v = &mut [0, 0, 0, 0, 0];
1278 /// let mut count = 1;
1280 /// for chunk in v.rchunks_mut(2) {
1281 /// for elem in chunk.iter_mut() {
1286 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1289 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1290 /// [`chunks_mut`]: slice::chunks_mut
1291 #[stable(feature = "rchunks", since = "1.31.0")]
1293 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1294 assert!(chunk_size != 0);
1295 RChunksMut::new(self, chunk_size)
1298 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1299 /// end of the slice.
1301 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1302 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1303 /// from the `remainder` function of the iterator.
1305 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1306 /// resulting code better than in the case of [`chunks`].
1308 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1309 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1314 /// Panics if `chunk_size` is 0.
1319 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1320 /// let mut iter = slice.rchunks_exact(2);
1321 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1322 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1323 /// assert!(iter.next().is_none());
1324 /// assert_eq!(iter.remainder(), &['l']);
1327 /// [`chunks`]: slice::chunks
1328 /// [`rchunks`]: slice::rchunks
1329 /// [`chunks_exact`]: slice::chunks_exact
1330 #[stable(feature = "rchunks", since = "1.31.0")]
1332 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1333 assert!(chunk_size != 0);
1334 RChunksExact::new(self, chunk_size)
1337 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1340 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1341 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1342 /// retrieved from the `into_remainder` function of the iterator.
1344 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1345 /// resulting code better than in the case of [`chunks_mut`].
1347 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1348 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1353 /// Panics if `chunk_size` is 0.
1358 /// let v = &mut [0, 0, 0, 0, 0];
1359 /// let mut count = 1;
1361 /// for chunk in v.rchunks_exact_mut(2) {
1362 /// for elem in chunk.iter_mut() {
1367 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1370 /// [`chunks_mut`]: slice::chunks_mut
1371 /// [`rchunks_mut`]: slice::rchunks_mut
1372 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1373 #[stable(feature = "rchunks", since = "1.31.0")]
1375 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1376 assert!(chunk_size != 0);
1377 RChunksExactMut::new(self, chunk_size)
1380 /// Returns an iterator over the slice producing non-overlapping runs
1381 /// of elements using the predicate to separate them.
1383 /// The predicate is called on two elements following themselves,
1384 /// it means the predicate is called on `slice[0]` and `slice[1]`
1385 /// then on `slice[1]` and `slice[2]` and so on.
1390 /// #![feature(slice_group_by)]
1392 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1394 /// let mut iter = slice.group_by(|a, b| a == b);
1396 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1397 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1398 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1399 /// assert_eq!(iter.next(), None);
1402 /// This method can be used to extract the sorted subslices:
1405 /// #![feature(slice_group_by)]
1407 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1409 /// let mut iter = slice.group_by(|a, b| a <= b);
1411 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1412 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1413 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1414 /// assert_eq!(iter.next(), None);
1416 #[unstable(feature = "slice_group_by", issue = "80552")]
1418 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1420 F: FnMut(&T, &T) -> bool,
1422 GroupBy::new(self, pred)
1425 /// Returns an iterator over the slice producing non-overlapping mutable
1426 /// runs of elements using the predicate to separate them.
1428 /// The predicate is called on two elements following themselves,
1429 /// it means the predicate is called on `slice[0]` and `slice[1]`
1430 /// then on `slice[1]` and `slice[2]` and so on.
1435 /// #![feature(slice_group_by)]
1437 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1439 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1441 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1442 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1443 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1444 /// assert_eq!(iter.next(), None);
1447 /// This method can be used to extract the sorted subslices:
1450 /// #![feature(slice_group_by)]
1452 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1454 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1456 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1457 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1458 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1459 /// assert_eq!(iter.next(), None);
1461 #[unstable(feature = "slice_group_by", issue = "80552")]
1463 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1465 F: FnMut(&T, &T) -> bool,
1467 GroupByMut::new(self, pred)
1470 /// Divides one slice into two at an index.
1472 /// The first will contain all indices from `[0, mid)` (excluding
1473 /// the index `mid` itself) and the second will contain all
1474 /// indices from `[mid, len)` (excluding the index `len` itself).
1478 /// Panics if `mid > len`.
1483 /// let v = [1, 2, 3, 4, 5, 6];
1486 /// let (left, right) = v.split_at(0);
1487 /// assert_eq!(left, []);
1488 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1492 /// let (left, right) = v.split_at(2);
1493 /// assert_eq!(left, [1, 2]);
1494 /// assert_eq!(right, [3, 4, 5, 6]);
1498 /// let (left, right) = v.split_at(6);
1499 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1500 /// assert_eq!(right, []);
1503 #[stable(feature = "rust1", since = "1.0.0")]
1506 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1507 assert!(mid <= self.len());
1508 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1509 // fulfills the requirements of `from_raw_parts_mut`.
1510 unsafe { self.split_at_unchecked(mid) }
1513 /// Divides one mutable slice into two at an index.
1515 /// The first will contain all indices from `[0, mid)` (excluding
1516 /// the index `mid` itself) and the second will contain all
1517 /// indices from `[mid, len)` (excluding the index `len` itself).
1521 /// Panics if `mid > len`.
1526 /// let mut v = [1, 0, 3, 0, 5, 6];
1527 /// let (left, right) = v.split_at_mut(2);
1528 /// assert_eq!(left, [1, 0]);
1529 /// assert_eq!(right, [3, 0, 5, 6]);
1532 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1534 #[stable(feature = "rust1", since = "1.0.0")]
1537 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1538 assert!(mid <= self.len());
1539 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1540 // fulfills the requirements of `from_raw_parts_mut`.
1541 unsafe { self.split_at_mut_unchecked(mid) }
1544 /// Divides one slice into two at an index, without doing bounds checking.
1546 /// The first will contain all indices from `[0, mid)` (excluding
1547 /// the index `mid` itself) and the second will contain all
1548 /// indices from `[mid, len)` (excluding the index `len` itself).
1550 /// For a safe alternative see [`split_at`].
1554 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1555 /// even if the resulting reference is not used. The caller has to ensure that
1556 /// `0 <= mid <= self.len()`.
1558 /// [`split_at`]: slice::split_at
1559 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1564 /// #![feature(slice_split_at_unchecked)]
1566 /// let v = [1, 2, 3, 4, 5, 6];
1569 /// let (left, right) = v.split_at_unchecked(0);
1570 /// assert_eq!(left, []);
1571 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1575 /// let (left, right) = v.split_at_unchecked(2);
1576 /// assert_eq!(left, [1, 2]);
1577 /// assert_eq!(right, [3, 4, 5, 6]);
1581 /// let (left, right) = v.split_at_unchecked(6);
1582 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1583 /// assert_eq!(right, []);
1586 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1588 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1589 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1590 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1593 /// Divides one mutable slice into two at an index, without doing bounds checking.
1595 /// The first will contain all indices from `[0, mid)` (excluding
1596 /// the index `mid` itself) and the second will contain all
1597 /// indices from `[mid, len)` (excluding the index `len` itself).
1599 /// For a safe alternative see [`split_at_mut`].
1603 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1604 /// even if the resulting reference is not used. The caller has to ensure that
1605 /// `0 <= mid <= self.len()`.
1607 /// [`split_at_mut`]: slice::split_at_mut
1608 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1613 /// #![feature(slice_split_at_unchecked)]
1615 /// let mut v = [1, 0, 3, 0, 5, 6];
1616 /// // scoped to restrict the lifetime of the borrows
1618 /// let (left, right) = v.split_at_mut_unchecked(2);
1619 /// assert_eq!(left, [1, 0]);
1620 /// assert_eq!(right, [3, 0, 5, 6]);
1624 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1626 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1628 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1629 let len = self.len();
1630 let ptr = self.as_mut_ptr();
1632 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1634 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1636 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1639 /// Divides one slice into an array and a remainder slice at an index.
1641 /// The array will contain all indices from `[0, N)` (excluding
1642 /// the index `N` itself) and the slice will contain all
1643 /// indices from `[N, len)` (excluding the index `len` itself).
1647 /// Panics if `N > len`.
1652 /// #![feature(split_array)]
1654 /// let v = &[1, 2, 3, 4, 5, 6][..];
1657 /// let (left, right) = v.split_array_ref::<0>();
1658 /// assert_eq!(left, &[]);
1659 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1663 /// let (left, right) = v.split_array_ref::<2>();
1664 /// assert_eq!(left, &[1, 2]);
1665 /// assert_eq!(right, [3, 4, 5, 6]);
1669 /// let (left, right) = v.split_array_ref::<6>();
1670 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1671 /// assert_eq!(right, []);
1674 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1677 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1678 let (a, b) = self.split_at(N);
1679 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1680 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1683 /// Divides one mutable slice into an array and a remainder slice at an index.
1685 /// The array will contain all indices from `[0, N)` (excluding
1686 /// the index `N` itself) and the slice will contain all
1687 /// indices from `[N, len)` (excluding the index `len` itself).
1691 /// Panics if `N > len`.
1696 /// #![feature(split_array)]
1698 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1699 /// let (left, right) = v.split_array_mut::<2>();
1700 /// assert_eq!(left, &mut [1, 0]);
1701 /// assert_eq!(right, [3, 0, 5, 6]);
1704 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1706 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1709 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1710 let (a, b) = self.split_at_mut(N);
1711 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1712 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1715 /// Divides one slice into an array and a remainder slice at an index from
1718 /// The slice will contain all indices from `[0, len - N)` (excluding
1719 /// the index `len - N` itself) and the array will contain all
1720 /// indices from `[len - N, len)` (excluding the index `len` itself).
1724 /// Panics if `N > len`.
1729 /// #![feature(split_array)]
1731 /// let v = &[1, 2, 3, 4, 5, 6][..];
1734 /// let (left, right) = v.rsplit_array_ref::<0>();
1735 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1736 /// assert_eq!(right, &[]);
1740 /// let (left, right) = v.rsplit_array_ref::<2>();
1741 /// assert_eq!(left, [1, 2, 3, 4]);
1742 /// assert_eq!(right, &[5, 6]);
1746 /// let (left, right) = v.rsplit_array_ref::<6>();
1747 /// assert_eq!(left, []);
1748 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1751 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1753 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1754 assert!(N <= self.len());
1755 let (a, b) = self.split_at(self.len() - N);
1756 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1757 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1760 /// Divides one mutable slice into an array and a remainder slice at an
1761 /// index from the end.
1763 /// The slice will contain all indices from `[0, len - N)` (excluding
1764 /// the index `N` itself) and the array will contain all
1765 /// indices from `[len - N, len)` (excluding the index `len` itself).
1769 /// Panics if `N > len`.
1774 /// #![feature(split_array)]
1776 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1777 /// let (left, right) = v.rsplit_array_mut::<4>();
1778 /// assert_eq!(left, [1, 0]);
1779 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1782 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1784 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1786 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1787 assert!(N <= self.len());
1788 let (a, b) = self.split_at_mut(self.len() - N);
1789 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1790 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1793 /// Returns an iterator over subslices separated by elements that match
1794 /// `pred`. The matched element is not contained in the subslices.
1799 /// let slice = [10, 40, 33, 20];
1800 /// let mut iter = slice.split(|num| num % 3 == 0);
1802 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1803 /// assert_eq!(iter.next().unwrap(), &[20]);
1804 /// assert!(iter.next().is_none());
1807 /// If the first element is matched, an empty slice will be the first item
1808 /// returned by the iterator. Similarly, if the last element in the slice
1809 /// is matched, an empty slice will be the last item returned by the
1813 /// let slice = [10, 40, 33];
1814 /// let mut iter = slice.split(|num| num % 3 == 0);
1816 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1817 /// assert_eq!(iter.next().unwrap(), &[]);
1818 /// assert!(iter.next().is_none());
1821 /// If two matched elements are directly adjacent, an empty slice will be
1822 /// present between them:
1825 /// let slice = [10, 6, 33, 20];
1826 /// let mut iter = slice.split(|num| num % 3 == 0);
1828 /// assert_eq!(iter.next().unwrap(), &[10]);
1829 /// assert_eq!(iter.next().unwrap(), &[]);
1830 /// assert_eq!(iter.next().unwrap(), &[20]);
1831 /// assert!(iter.next().is_none());
1833 #[stable(feature = "rust1", since = "1.0.0")]
1835 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1837 F: FnMut(&T) -> bool,
1839 Split::new(self, pred)
1842 /// Returns an iterator over mutable subslices separated by elements that
1843 /// match `pred`. The matched element is not contained in the subslices.
1848 /// let mut v = [10, 40, 30, 20, 60, 50];
1850 /// for group in v.split_mut(|num| *num % 3 == 0) {
1853 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1855 #[stable(feature = "rust1", since = "1.0.0")]
1857 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1859 F: FnMut(&T) -> bool,
1861 SplitMut::new(self, pred)
1864 /// Returns an iterator over subslices separated by elements that match
1865 /// `pred`. The matched element is contained in the end of the previous
1866 /// subslice as a terminator.
1871 /// let slice = [10, 40, 33, 20];
1872 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1874 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1875 /// assert_eq!(iter.next().unwrap(), &[20]);
1876 /// assert!(iter.next().is_none());
1879 /// If the last element of the slice is matched,
1880 /// that element will be considered the terminator of the preceding slice.
1881 /// That slice will be the last item returned by the iterator.
1884 /// let slice = [3, 10, 40, 33];
1885 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1887 /// assert_eq!(iter.next().unwrap(), &[3]);
1888 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1889 /// assert!(iter.next().is_none());
1891 #[stable(feature = "split_inclusive", since = "1.51.0")]
1893 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1895 F: FnMut(&T) -> bool,
1897 SplitInclusive::new(self, pred)
1900 /// Returns an iterator over mutable subslices separated by elements that
1901 /// match `pred`. The matched element is contained in the previous
1902 /// subslice as a terminator.
1907 /// let mut v = [10, 40, 30, 20, 60, 50];
1909 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1910 /// let terminator_idx = group.len()-1;
1911 /// group[terminator_idx] = 1;
1913 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1915 #[stable(feature = "split_inclusive", since = "1.51.0")]
1917 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1919 F: FnMut(&T) -> bool,
1921 SplitInclusiveMut::new(self, pred)
1924 /// Returns an iterator over subslices separated by elements that match
1925 /// `pred`, starting at the end of the slice and working backwards.
1926 /// The matched element is not contained in the subslices.
1931 /// let slice = [11, 22, 33, 0, 44, 55];
1932 /// let mut iter = slice.rsplit(|num| *num == 0);
1934 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1935 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1936 /// assert_eq!(iter.next(), None);
1939 /// As with `split()`, if the first or last element is matched, an empty
1940 /// slice will be the first (or last) item returned by the iterator.
1943 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1944 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1945 /// assert_eq!(it.next().unwrap(), &[]);
1946 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1947 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1948 /// assert_eq!(it.next().unwrap(), &[]);
1949 /// assert_eq!(it.next(), None);
1951 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1953 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1955 F: FnMut(&T) -> bool,
1957 RSplit::new(self, pred)
1960 /// Returns an iterator over mutable subslices separated by elements that
1961 /// match `pred`, starting at the end of the slice and working
1962 /// backwards. The matched element is not contained in the subslices.
1967 /// let mut v = [100, 400, 300, 200, 600, 500];
1969 /// let mut count = 0;
1970 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1972 /// group[0] = count;
1974 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1977 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1979 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1981 F: FnMut(&T) -> bool,
1983 RSplitMut::new(self, pred)
1986 /// Returns an iterator over subslices separated by elements that match
1987 /// `pred`, limited to returning at most `n` items. The matched element is
1988 /// not contained in the subslices.
1990 /// The last element returned, if any, will contain the remainder of the
1995 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1996 /// `[20, 60, 50]`):
1999 /// let v = [10, 40, 30, 20, 60, 50];
2001 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2002 /// println!("{:?}", group);
2005 #[stable(feature = "rust1", since = "1.0.0")]
2007 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2009 F: FnMut(&T) -> bool,
2011 SplitN::new(self.split(pred), n)
2014 /// Returns an iterator over subslices separated by elements that match
2015 /// `pred`, limited to returning at most `n` items. The matched element is
2016 /// not contained in the subslices.
2018 /// The last element returned, if any, will contain the remainder of the
2024 /// let mut v = [10, 40, 30, 20, 60, 50];
2026 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2029 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2031 #[stable(feature = "rust1", since = "1.0.0")]
2033 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2035 F: FnMut(&T) -> bool,
2037 SplitNMut::new(self.split_mut(pred), n)
2040 /// Returns an iterator over subslices separated by elements that match
2041 /// `pred` limited to returning at most `n` items. This starts at the end of
2042 /// the slice and works backwards. The matched element is not contained in
2045 /// The last element returned, if any, will contain the remainder of the
2050 /// Print the slice split once, starting from the end, by numbers divisible
2051 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2054 /// let v = [10, 40, 30, 20, 60, 50];
2056 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2057 /// println!("{:?}", group);
2060 #[stable(feature = "rust1", since = "1.0.0")]
2062 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2064 F: FnMut(&T) -> bool,
2066 RSplitN::new(self.rsplit(pred), n)
2069 /// Returns an iterator over subslices separated by elements that match
2070 /// `pred` limited to returning at most `n` items. This starts at the end of
2071 /// the slice and works backwards. The matched element is not contained in
2074 /// The last element returned, if any, will contain the remainder of the
2080 /// let mut s = [10, 40, 30, 20, 60, 50];
2082 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2085 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2087 #[stable(feature = "rust1", since = "1.0.0")]
2089 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2091 F: FnMut(&T) -> bool,
2093 RSplitNMut::new(self.rsplit_mut(pred), n)
2096 /// Returns `true` if the slice contains an element with the given value.
2101 /// let v = [10, 40, 30];
2102 /// assert!(v.contains(&30));
2103 /// assert!(!v.contains(&50));
2106 /// If you do not have a `&T`, but some other value that you can compare
2107 /// with one (for example, `String` implements `PartialEq<str>`), you can
2108 /// use `iter().any`:
2111 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2112 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2113 /// assert!(!v.iter().any(|e| e == "hi"));
2115 #[stable(feature = "rust1", since = "1.0.0")]
2117 pub fn contains(&self, x: &T) -> bool
2121 cmp::SliceContains::slice_contains(x, self)
2124 /// Returns `true` if `needle` is a prefix of the slice.
2129 /// let v = [10, 40, 30];
2130 /// assert!(v.starts_with(&[10]));
2131 /// assert!(v.starts_with(&[10, 40]));
2132 /// assert!(!v.starts_with(&[50]));
2133 /// assert!(!v.starts_with(&[10, 50]));
2136 /// Always returns `true` if `needle` is an empty slice:
2139 /// let v = &[10, 40, 30];
2140 /// assert!(v.starts_with(&[]));
2141 /// let v: &[u8] = &[];
2142 /// assert!(v.starts_with(&[]));
2144 #[stable(feature = "rust1", since = "1.0.0")]
2145 pub fn starts_with(&self, needle: &[T]) -> bool
2149 let n = needle.len();
2150 self.len() >= n && needle == &self[..n]
2153 /// Returns `true` if `needle` is a suffix of the slice.
2158 /// let v = [10, 40, 30];
2159 /// assert!(v.ends_with(&[30]));
2160 /// assert!(v.ends_with(&[40, 30]));
2161 /// assert!(!v.ends_with(&[50]));
2162 /// assert!(!v.ends_with(&[50, 30]));
2165 /// Always returns `true` if `needle` is an empty slice:
2168 /// let v = &[10, 40, 30];
2169 /// assert!(v.ends_with(&[]));
2170 /// let v: &[u8] = &[];
2171 /// assert!(v.ends_with(&[]));
2173 #[stable(feature = "rust1", since = "1.0.0")]
2174 pub fn ends_with(&self, needle: &[T]) -> bool
2178 let (m, n) = (self.len(), needle.len());
2179 m >= n && needle == &self[m - n..]
2182 /// Returns a subslice with the prefix removed.
2184 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2185 /// If `prefix` is empty, simply returns the original slice.
2187 /// If the slice does not start with `prefix`, returns `None`.
2192 /// let v = &[10, 40, 30];
2193 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2194 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2195 /// assert_eq!(v.strip_prefix(&[50]), None);
2196 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2198 /// let prefix : &str = "he";
2199 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2200 /// Some(b"llo".as_ref()));
2202 #[must_use = "returns the subslice without modifying the original"]
2203 #[stable(feature = "slice_strip", since = "1.51.0")]
2204 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2208 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2209 let prefix = prefix.as_slice();
2210 let n = prefix.len();
2211 if n <= self.len() {
2212 let (head, tail) = self.split_at(n);
2220 /// Returns a subslice with the suffix removed.
2222 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2223 /// If `suffix` is empty, simply returns the original slice.
2225 /// If the slice does not end with `suffix`, returns `None`.
2230 /// let v = &[10, 40, 30];
2231 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2232 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2233 /// assert_eq!(v.strip_suffix(&[50]), None);
2234 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2236 #[must_use = "returns the subslice without modifying the original"]
2237 #[stable(feature = "slice_strip", since = "1.51.0")]
2238 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2242 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2243 let suffix = suffix.as_slice();
2244 let (len, n) = (self.len(), suffix.len());
2246 let (head, tail) = self.split_at(len - n);
2254 /// Binary searches this sorted slice for a given element.
2256 /// If the value is found then [`Result::Ok`] is returned, containing the
2257 /// index of the matching element. If there are multiple matches, then any
2258 /// one of the matches could be returned. The index is chosen
2259 /// deterministically, but is subject to change in future versions of Rust.
2260 /// If the value is not found then [`Result::Err`] is returned, containing
2261 /// the index where a matching element could be inserted while maintaining
2264 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2266 /// [`binary_search_by`]: slice::binary_search_by
2267 /// [`binary_search_by_key`]: slice::binary_search_by_key
2268 /// [`partition_point`]: slice::partition_point
2272 /// Looks up a series of four elements. The first is found, with a
2273 /// uniquely determined position; the second and third are not
2274 /// found; the fourth could match any position in `[1, 4]`.
2277 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2279 /// assert_eq!(s.binary_search(&13), Ok(9));
2280 /// assert_eq!(s.binary_search(&4), Err(7));
2281 /// assert_eq!(s.binary_search(&100), Err(13));
2282 /// let r = s.binary_search(&1);
2283 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2286 /// If you want to insert an item to a sorted vector, while maintaining
2290 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2292 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2293 /// s.insert(idx, num);
2294 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2296 #[stable(feature = "rust1", since = "1.0.0")]
2297 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2301 self.binary_search_by(|p| p.cmp(x))
2304 /// Binary searches this sorted slice with a comparator function.
2306 /// The comparator function should implement an order consistent
2307 /// with the sort order of the underlying slice, returning an
2308 /// order code that indicates whether its argument is `Less`,
2309 /// `Equal` or `Greater` the desired target.
2311 /// If the value is found then [`Result::Ok`] is returned, containing the
2312 /// index of the matching element. If there are multiple matches, then any
2313 /// one of the matches could be returned. The index is chosen
2314 /// deterministically, but is subject to change in future versions of Rust.
2315 /// If the value is not found then [`Result::Err`] is returned, containing
2316 /// the index where a matching element could be inserted while maintaining
2319 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2321 /// [`binary_search`]: slice::binary_search
2322 /// [`binary_search_by_key`]: slice::binary_search_by_key
2323 /// [`partition_point`]: slice::partition_point
2327 /// Looks up a series of four elements. The first is found, with a
2328 /// uniquely determined position; the second and third are not
2329 /// found; the fourth could match any position in `[1, 4]`.
2332 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2335 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2337 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2339 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2341 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2342 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2344 #[stable(feature = "rust1", since = "1.0.0")]
2346 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2348 F: FnMut(&'a T) -> Ordering,
2350 let mut size = self.len();
2352 let mut right = size;
2353 while left < right {
2354 let mid = left + size / 2;
2356 // SAFETY: the call is made safe by the following invariants:
2358 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2359 let cmp = f(unsafe { self.get_unchecked(mid) });
2361 // The reason why we use if/else control flow rather than match
2362 // is because match reorders comparison operations, which is perf sensitive.
2363 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2366 } else if cmp == Greater {
2369 // SAFETY: same as the `get_unchecked` above
2370 unsafe { crate::intrinsics::assume(mid < self.len()) };
2374 size = right - left;
2379 /// Binary searches this sorted slice with a key extraction function.
2381 /// Assumes that the slice is sorted by the key, for instance with
2382 /// [`sort_by_key`] using the same key extraction function.
2384 /// If the value is found then [`Result::Ok`] is returned, containing the
2385 /// index of the matching element. If there are multiple matches, then any
2386 /// one of the matches could be returned. The index is chosen
2387 /// deterministically, but is subject to change in future versions of Rust.
2388 /// If the value is not found then [`Result::Err`] is returned, containing
2389 /// the index where a matching element could be inserted while maintaining
2392 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2394 /// [`sort_by_key`]: slice::sort_by_key
2395 /// [`binary_search`]: slice::binary_search
2396 /// [`binary_search_by`]: slice::binary_search_by
2397 /// [`partition_point`]: slice::partition_point
2401 /// Looks up a series of four elements in a slice of pairs sorted by
2402 /// their second elements. The first is found, with a uniquely
2403 /// determined position; the second and third are not found; the
2404 /// fourth could match any position in `[1, 4]`.
2407 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2408 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2409 /// (1, 21), (2, 34), (4, 55)];
2411 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2412 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2413 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2414 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2415 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2417 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2418 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2419 // This breaks links when slice is displayed in core, but changing it to use relative links
2420 // would break when the item is re-exported. So allow the core links to be broken for now.
2421 #[allow(rustdoc::broken_intra_doc_links)]
2422 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2424 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2426 F: FnMut(&'a T) -> B,
2429 self.binary_search_by(|k| f(k).cmp(b))
2432 /// Sorts the slice, but might not preserve the order of equal elements.
2434 /// This sort is unstable (i.e., may reorder equal elements), in-place
2435 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2437 /// # Current implementation
2439 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2440 /// which combines the fast average case of randomized quicksort with the fast worst case of
2441 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2442 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2443 /// deterministic behavior.
2445 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2446 /// slice consists of several concatenated sorted sequences.
2451 /// let mut v = [-5, 4, 1, -3, 2];
2453 /// v.sort_unstable();
2454 /// assert!(v == [-5, -3, 1, 2, 4]);
2457 /// [pdqsort]: https://github.com/orlp/pdqsort
2458 #[stable(feature = "sort_unstable", since = "1.20.0")]
2460 pub fn sort_unstable(&mut self)
2464 sort::quicksort(self, |a, b| a.lt(b));
2467 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2470 /// This sort is unstable (i.e., may reorder equal elements), in-place
2471 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2473 /// The comparator function must define a total ordering for the elements in the slice. If
2474 /// the ordering is not total, the order of the elements is unspecified. An order is a
2475 /// total order if it is (for all `a`, `b` and `c`):
2477 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2478 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2480 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2481 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2484 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2485 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2486 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2489 /// # Current implementation
2491 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2492 /// which combines the fast average case of randomized quicksort with the fast worst case of
2493 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2494 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2495 /// deterministic behavior.
2497 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2498 /// slice consists of several concatenated sorted sequences.
2503 /// let mut v = [5, 4, 1, 3, 2];
2504 /// v.sort_unstable_by(|a, b| a.cmp(b));
2505 /// assert!(v == [1, 2, 3, 4, 5]);
2507 /// // reverse sorting
2508 /// v.sort_unstable_by(|a, b| b.cmp(a));
2509 /// assert!(v == [5, 4, 3, 2, 1]);
2512 /// [pdqsort]: https://github.com/orlp/pdqsort
2513 #[stable(feature = "sort_unstable", since = "1.20.0")]
2515 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2517 F: FnMut(&T, &T) -> Ordering,
2519 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2522 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2525 /// This sort is unstable (i.e., may reorder equal elements), in-place
2526 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2529 /// # Current implementation
2531 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2532 /// which combines the fast average case of randomized quicksort with the fast worst case of
2533 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2534 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2535 /// deterministic behavior.
2537 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2538 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2539 /// cases where the key function is expensive.
2544 /// let mut v = [-5i32, 4, 1, -3, 2];
2546 /// v.sort_unstable_by_key(|k| k.abs());
2547 /// assert!(v == [1, 2, -3, 4, -5]);
2550 /// [pdqsort]: https://github.com/orlp/pdqsort
2551 #[stable(feature = "sort_unstable", since = "1.20.0")]
2553 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2558 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2561 /// Reorder the slice such that the element at `index` is at its final sorted position.
2563 /// This reordering has the additional property that any value at position `i < index` will be
2564 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2565 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2566 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2567 /// element" in other libraries. It returns a triplet of the following values: all elements less
2568 /// than the one at the given index, the value at the given index, and all elements greater than
2569 /// the one at the given index.
2571 /// # Current implementation
2573 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2574 /// used for [`sort_unstable`].
2576 /// [`sort_unstable`]: slice::sort_unstable
2580 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2585 /// let mut v = [-5i32, 4, 1, -3, 2];
2587 /// // Find the median
2588 /// v.select_nth_unstable(2);
2590 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2591 /// // about the specified index.
2592 /// assert!(v == [-3, -5, 1, 2, 4] ||
2593 /// v == [-5, -3, 1, 2, 4] ||
2594 /// v == [-3, -5, 1, 4, 2] ||
2595 /// v == [-5, -3, 1, 4, 2]);
2597 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2599 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2603 let mut f = |a: &T, b: &T| a.lt(b);
2604 sort::partition_at_index(self, index, &mut f)
2607 /// Reorder the slice with a comparator function such that the element at `index` is at its
2608 /// final sorted position.
2610 /// This reordering has the additional property that any value at position `i < index` will be
2611 /// less than or equal to any value at a position `j > index` using the comparator function.
2612 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2613 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2614 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2615 /// values: all elements less than the one at the given index, the value at the given index,
2616 /// and all elements greater than the one at the given index, using the provided comparator
2619 /// # Current implementation
2621 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2622 /// used for [`sort_unstable`].
2624 /// [`sort_unstable`]: slice::sort_unstable
2628 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2633 /// let mut v = [-5i32, 4, 1, -3, 2];
2635 /// // Find the median as if the slice were sorted in descending order.
2636 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2638 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2639 /// // about the specified index.
2640 /// assert!(v == [2, 4, 1, -5, -3] ||
2641 /// v == [2, 4, 1, -3, -5] ||
2642 /// v == [4, 2, 1, -5, -3] ||
2643 /// v == [4, 2, 1, -3, -5]);
2645 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2647 pub fn select_nth_unstable_by<F>(
2651 ) -> (&mut [T], &mut T, &mut [T])
2653 F: FnMut(&T, &T) -> Ordering,
2655 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2656 sort::partition_at_index(self, index, &mut f)
2659 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2660 /// final sorted position.
2662 /// This reordering has the additional property that any value at position `i < index` will be
2663 /// less than or equal to any value at a position `j > index` using the key extraction function.
2664 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2665 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2666 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2667 /// values: all elements less than the one at the given index, the value at the given index, and
2668 /// all elements greater than the one at the given index, using the provided key extraction
2671 /// # Current implementation
2673 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2674 /// used for [`sort_unstable`].
2676 /// [`sort_unstable`]: slice::sort_unstable
2680 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2685 /// let mut v = [-5i32, 4, 1, -3, 2];
2687 /// // Return the median as if the array were sorted according to absolute value.
2688 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2690 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2691 /// // about the specified index.
2692 /// assert!(v == [1, 2, -3, 4, -5] ||
2693 /// v == [1, 2, -3, -5, 4] ||
2694 /// v == [2, 1, -3, 4, -5] ||
2695 /// v == [2, 1, -3, -5, 4]);
2697 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2699 pub fn select_nth_unstable_by_key<K, F>(
2703 ) -> (&mut [T], &mut T, &mut [T])
2708 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2709 sort::partition_at_index(self, index, &mut g)
2712 /// Moves all consecutive repeated elements to the end of the slice according to the
2713 /// [`PartialEq`] trait implementation.
2715 /// Returns two slices. The first contains no consecutive repeated elements.
2716 /// The second contains all the duplicates in no specified order.
2718 /// If the slice is sorted, the first returned slice contains no duplicates.
2723 /// #![feature(slice_partition_dedup)]
2725 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2727 /// let (dedup, duplicates) = slice.partition_dedup();
2729 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2730 /// assert_eq!(duplicates, [2, 3, 1]);
2732 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2734 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2738 self.partition_dedup_by(|a, b| a == b)
2741 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2742 /// a given equality relation.
2744 /// Returns two slices. The first contains no consecutive repeated elements.
2745 /// The second contains all the duplicates in no specified order.
2747 /// The `same_bucket` function is passed references to two elements from the slice and
2748 /// must determine if the elements compare equal. The elements are passed in opposite order
2749 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2750 /// at the end of the slice.
2752 /// If the slice is sorted, the first returned slice contains no duplicates.
2757 /// #![feature(slice_partition_dedup)]
2759 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2761 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2763 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2764 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2766 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2768 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2770 F: FnMut(&mut T, &mut T) -> bool,
2772 // Although we have a mutable reference to `self`, we cannot make
2773 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2774 // must ensure that the slice is in a valid state at all times.
2776 // The way that we handle this is by using swaps; we iterate
2777 // over all the elements, swapping as we go so that at the end
2778 // the elements we wish to keep are in the front, and those we
2779 // wish to reject are at the back. We can then split the slice.
2780 // This operation is still `O(n)`.
2782 // Example: We start in this state, where `r` represents "next
2783 // read" and `w` represents "next_write`.
2786 // +---+---+---+---+---+---+
2787 // | 0 | 1 | 1 | 2 | 3 | 3 |
2788 // +---+---+---+---+---+---+
2791 // Comparing self[r] against self[w-1], this is not a duplicate, so
2792 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2793 // r and w, leaving us with:
2796 // +---+---+---+---+---+---+
2797 // | 0 | 1 | 1 | 2 | 3 | 3 |
2798 // +---+---+---+---+---+---+
2801 // Comparing self[r] against self[w-1], this value is a duplicate,
2802 // so we increment `r` but leave everything else unchanged:
2805 // +---+---+---+---+---+---+
2806 // | 0 | 1 | 1 | 2 | 3 | 3 |
2807 // +---+---+---+---+---+---+
2810 // Comparing self[r] against self[w-1], this is not a duplicate,
2811 // so swap self[r] and self[w] and advance r and w:
2814 // +---+---+---+---+---+---+
2815 // | 0 | 1 | 2 | 1 | 3 | 3 |
2816 // +---+---+---+---+---+---+
2819 // Not a duplicate, repeat:
2822 // +---+---+---+---+---+---+
2823 // | 0 | 1 | 2 | 3 | 1 | 3 |
2824 // +---+---+---+---+---+---+
2827 // Duplicate, advance r. End of slice. Split at w.
2829 let len = self.len();
2831 return (self, &mut []);
2834 let ptr = self.as_mut_ptr();
2835 let mut next_read: usize = 1;
2836 let mut next_write: usize = 1;
2838 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2839 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2840 // one element before `ptr_write`, but `next_write` starts at 1, so
2841 // `prev_ptr_write` is never less than 0 and is inside the slice.
2842 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2843 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2844 // and `prev_ptr_write.offset(1)`.
2846 // `next_write` is also incremented at most once per loop at most meaning
2847 // no element is skipped when it may need to be swapped.
2849 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2850 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2851 // The explanation is simply that `next_read >= next_write` is always true,
2852 // thus `next_read > next_write - 1` is too.
2854 // Avoid bounds checks by using raw pointers.
2855 while next_read < len {
2856 let ptr_read = ptr.add(next_read);
2857 let prev_ptr_write = ptr.add(next_write - 1);
2858 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2859 if next_read != next_write {
2860 let ptr_write = prev_ptr_write.offset(1);
2861 mem::swap(&mut *ptr_read, &mut *ptr_write);
2869 self.split_at_mut(next_write)
2872 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2873 /// to the same key.
2875 /// Returns two slices. The first contains no consecutive repeated elements.
2876 /// The second contains all the duplicates in no specified order.
2878 /// If the slice is sorted, the first returned slice contains no duplicates.
2883 /// #![feature(slice_partition_dedup)]
2885 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2887 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2889 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2890 /// assert_eq!(duplicates, [21, 30, 13]);
2892 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2894 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2896 F: FnMut(&mut T) -> K,
2899 self.partition_dedup_by(|a, b| key(a) == key(b))
2902 /// Rotates the slice in-place such that the first `mid` elements of the
2903 /// slice move to the end while the last `self.len() - mid` elements move to
2904 /// the front. After calling `rotate_left`, the element previously at index
2905 /// `mid` will become the first element in the slice.
2909 /// This function will panic if `mid` is greater than the length of the
2910 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2915 /// Takes linear (in `self.len()`) time.
2920 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2921 /// a.rotate_left(2);
2922 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2925 /// Rotating a subslice:
2928 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2929 /// a[1..5].rotate_left(1);
2930 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2932 #[stable(feature = "slice_rotate", since = "1.26.0")]
2933 pub fn rotate_left(&mut self, mid: usize) {
2934 assert!(mid <= self.len());
2935 let k = self.len() - mid;
2936 let p = self.as_mut_ptr();
2938 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2939 // valid for reading and writing, as required by `ptr_rotate`.
2941 rotate::ptr_rotate(mid, p.add(mid), k);
2945 /// Rotates the slice in-place such that the first `self.len() - k`
2946 /// elements of the slice move to the end while the last `k` elements move
2947 /// to the front. After calling `rotate_right`, the element previously at
2948 /// index `self.len() - k` will become the first element in the slice.
2952 /// This function will panic if `k` is greater than the length of the
2953 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2958 /// Takes linear (in `self.len()`) time.
2963 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2964 /// a.rotate_right(2);
2965 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2968 /// Rotate a subslice:
2971 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2972 /// a[1..5].rotate_right(1);
2973 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2975 #[stable(feature = "slice_rotate", since = "1.26.0")]
2976 pub fn rotate_right(&mut self, k: usize) {
2977 assert!(k <= self.len());
2978 let mid = self.len() - k;
2979 let p = self.as_mut_ptr();
2981 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2982 // valid for reading and writing, as required by `ptr_rotate`.
2984 rotate::ptr_rotate(mid, p.add(mid), k);
2988 /// Fills `self` with elements by cloning `value`.
2993 /// let mut buf = vec![0; 10];
2995 /// assert_eq!(buf, vec![1; 10]);
2997 #[doc(alias = "memset")]
2998 #[stable(feature = "slice_fill", since = "1.50.0")]
2999 pub fn fill(&mut self, value: T)
3003 specialize::SpecFill::spec_fill(self, value);
3006 /// Fills `self` with elements returned by calling a closure repeatedly.
3008 /// This method uses a closure to create new values. If you'd rather
3009 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3010 /// trait to generate values, you can pass [`Default::default`] as the
3013 /// [`fill`]: slice::fill
3018 /// let mut buf = vec![1; 10];
3019 /// buf.fill_with(Default::default);
3020 /// assert_eq!(buf, vec![0; 10]);
3022 #[doc(alias = "memset")]
3023 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3024 pub fn fill_with<F>(&mut self, mut f: F)
3033 /// Copies the elements from `src` into `self`.
3035 /// The length of `src` must be the same as `self`.
3039 /// This function will panic if the two slices have different lengths.
3043 /// Cloning two elements from a slice into another:
3046 /// let src = [1, 2, 3, 4];
3047 /// let mut dst = [0, 0];
3049 /// // Because the slices have to be the same length,
3050 /// // we slice the source slice from four elements
3051 /// // to two. It will panic if we don't do this.
3052 /// dst.clone_from_slice(&src[2..]);
3054 /// assert_eq!(src, [1, 2, 3, 4]);
3055 /// assert_eq!(dst, [3, 4]);
3058 /// Rust enforces that there can only be one mutable reference with no
3059 /// immutable references to a particular piece of data in a particular
3060 /// scope. Because of this, attempting to use `clone_from_slice` on a
3061 /// single slice will result in a compile failure:
3064 /// let mut slice = [1, 2, 3, 4, 5];
3066 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3069 /// To work around this, we can use [`split_at_mut`] to create two distinct
3070 /// sub-slices from a slice:
3073 /// let mut slice = [1, 2, 3, 4, 5];
3076 /// let (left, right) = slice.split_at_mut(2);
3077 /// left.clone_from_slice(&right[1..]);
3080 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3083 /// [`copy_from_slice`]: slice::copy_from_slice
3084 /// [`split_at_mut`]: slice::split_at_mut
3085 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3087 pub fn clone_from_slice(&mut self, src: &[T])
3091 self.spec_clone_from(src);
3094 /// Copies all elements from `src` into `self`, using a memcpy.
3096 /// The length of `src` must be the same as `self`.
3098 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3102 /// This function will panic if the two slices have different lengths.
3106 /// Copying two elements from a slice into another:
3109 /// let src = [1, 2, 3, 4];
3110 /// let mut dst = [0, 0];
3112 /// // Because the slices have to be the same length,
3113 /// // we slice the source slice from four elements
3114 /// // to two. It will panic if we don't do this.
3115 /// dst.copy_from_slice(&src[2..]);
3117 /// assert_eq!(src, [1, 2, 3, 4]);
3118 /// assert_eq!(dst, [3, 4]);
3121 /// Rust enforces that there can only be one mutable reference with no
3122 /// immutable references to a particular piece of data in a particular
3123 /// scope. Because of this, attempting to use `copy_from_slice` on a
3124 /// single slice will result in a compile failure:
3127 /// let mut slice = [1, 2, 3, 4, 5];
3129 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3132 /// To work around this, we can use [`split_at_mut`] to create two distinct
3133 /// sub-slices from a slice:
3136 /// let mut slice = [1, 2, 3, 4, 5];
3139 /// let (left, right) = slice.split_at_mut(2);
3140 /// left.copy_from_slice(&right[1..]);
3143 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3146 /// [`clone_from_slice`]: slice::clone_from_slice
3147 /// [`split_at_mut`]: slice::split_at_mut
3148 #[doc(alias = "memcpy")]
3149 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3151 pub fn copy_from_slice(&mut self, src: &[T])
3155 // The panic code path was put into a cold function to not bloat the
3160 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3162 "source slice length ({}) does not match destination slice length ({})",
3167 if self.len() != src.len() {
3168 len_mismatch_fail(self.len(), src.len());
3171 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3172 // checked to have the same length. The slices cannot overlap because
3173 // mutable references are exclusive.
3175 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3179 /// Copies elements from one part of the slice to another part of itself,
3180 /// using a memmove.
3182 /// `src` is the range within `self` to copy from. `dest` is the starting
3183 /// index of the range within `self` to copy to, which will have the same
3184 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3185 /// must be less than or equal to `self.len()`.
3189 /// This function will panic if either range exceeds the end of the slice,
3190 /// or if the end of `src` is before the start.
3194 /// Copying four bytes within a slice:
3197 /// let mut bytes = *b"Hello, World!";
3199 /// bytes.copy_within(1..5, 8);
3201 /// assert_eq!(&bytes, b"Hello, Wello!");
3203 #[stable(feature = "copy_within", since = "1.37.0")]
3205 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3209 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3210 let count = src_end - src_start;
3211 assert!(dest <= self.len() - count, "dest is out of bounds");
3212 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3213 // as have those for `ptr::add`.
3215 // Derive both `src_ptr` and `dest_ptr` from the same loan
3216 let ptr = self.as_mut_ptr();
3217 let src_ptr = ptr.add(src_start);
3218 let dest_ptr = ptr.add(dest);
3219 ptr::copy(src_ptr, dest_ptr, count);
3223 /// Swaps all elements in `self` with those in `other`.
3225 /// The length of `other` must be the same as `self`.
3229 /// This function will panic if the two slices have different lengths.
3233 /// Swapping two elements across slices:
3236 /// let mut slice1 = [0, 0];
3237 /// let mut slice2 = [1, 2, 3, 4];
3239 /// slice1.swap_with_slice(&mut slice2[2..]);
3241 /// assert_eq!(slice1, [3, 4]);
3242 /// assert_eq!(slice2, [1, 2, 0, 0]);
3245 /// Rust enforces that there can only be one mutable reference to a
3246 /// particular piece of data in a particular scope. Because of this,
3247 /// attempting to use `swap_with_slice` on a single slice will result in
3248 /// a compile failure:
3251 /// let mut slice = [1, 2, 3, 4, 5];
3252 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3255 /// To work around this, we can use [`split_at_mut`] to create two distinct
3256 /// mutable sub-slices from a slice:
3259 /// let mut slice = [1, 2, 3, 4, 5];
3262 /// let (left, right) = slice.split_at_mut(2);
3263 /// left.swap_with_slice(&mut right[1..]);
3266 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3269 /// [`split_at_mut`]: slice::split_at_mut
3270 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3272 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3273 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3274 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3275 // checked to have the same length. The slices cannot overlap because
3276 // mutable references are exclusive.
3278 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3282 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3283 fn align_to_offsets<U>(&self) -> (usize, usize) {
3284 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3285 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3287 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3288 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3289 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3291 // Formula to calculate this is:
3293 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3294 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3296 // Expanded and simplified:
3298 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3299 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3301 // Luckily since all this is constant-evaluated... performance here matters not!
3303 fn gcd(a: usize, b: usize) -> usize {
3304 use crate::intrinsics;
3305 // iterative stein’s algorithm
3306 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3307 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3309 // SAFETY: `a` and `b` are checked to be non-zero values.
3310 let (ctz_a, mut ctz_b) = unsafe {
3317 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3319 let k = ctz_a.min(ctz_b);
3320 let mut a = a >> ctz_a;
3323 // remove all factors of 2 from b
3326 mem::swap(&mut a, &mut b);
3329 // SAFETY: `b` is checked to be non-zero.
3334 ctz_b = intrinsics::cttz_nonzero(b);
3339 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3340 let ts: usize = mem::size_of::<U>() / gcd;
3341 let us: usize = mem::size_of::<T>() / gcd;
3343 // Armed with this knowledge, we can find how many `U`s we can fit!
3344 let us_len = self.len() / ts * us;
3345 // And how many `T`s will be in the trailing slice!
3346 let ts_len = self.len() % ts;
3350 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3353 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3354 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3355 /// length possible for a given type and input slice, but only your algorithm's performance
3356 /// should depend on that, not its correctness. It is permissible for all of the input data to
3357 /// be returned as the prefix or suffix slice.
3359 /// This method has no purpose when either input element `T` or output element `U` are
3360 /// zero-sized and will return the original slice without splitting anything.
3364 /// This method is essentially a `transmute` with respect to the elements in the returned
3365 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3373 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3374 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3375 /// // less_efficient_algorithm_for_bytes(prefix);
3376 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3377 /// // less_efficient_algorithm_for_bytes(suffix);
3380 #[stable(feature = "slice_align_to", since = "1.30.0")]
3381 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3382 // Note that most of this function will be constant-evaluated,
3383 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3384 // handle ZSTs specially, which is – don't handle them at all.
3385 return (self, &[], &[]);
3388 // First, find at what point do we split between the first and 2nd slice. Easy with
3389 // ptr.align_offset.
3390 let ptr = self.as_ptr();
3391 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3392 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3393 if offset > self.len() {
3396 let (left, rest) = self.split_at(offset);
3397 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3398 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3399 // since the caller guarantees that we can transmute `T` to `U` safely.
3403 from_raw_parts(rest.as_ptr() as *const U, us_len),
3404 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3410 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3413 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3414 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3415 /// length possible for a given type and input slice, but only your algorithm's performance
3416 /// should depend on that, not its correctness. It is permissible for all of the input data to
3417 /// be returned as the prefix or suffix slice.
3419 /// This method has no purpose when either input element `T` or output element `U` are
3420 /// zero-sized and will return the original slice without splitting anything.
3424 /// This method is essentially a `transmute` with respect to the elements in the returned
3425 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3433 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3434 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3435 /// // less_efficient_algorithm_for_bytes(prefix);
3436 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3437 /// // less_efficient_algorithm_for_bytes(suffix);
3440 #[stable(feature = "slice_align_to", since = "1.30.0")]
3441 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3442 // Note that most of this function will be constant-evaluated,
3443 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3444 // handle ZSTs specially, which is – don't handle them at all.
3445 return (self, &mut [], &mut []);
3448 // First, find at what point do we split between the first and 2nd slice. Easy with
3449 // ptr.align_offset.
3450 let ptr = self.as_ptr();
3451 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3452 // rest of the method. This is done by passing a pointer to &[T] with an
3453 // alignment targeted for U.
3454 // `crate::ptr::align_offset` is called with a correctly aligned and
3455 // valid pointer `ptr` (it comes from a reference to `self`) and with
3456 // a size that is a power of two (since it comes from the alignement for U),
3457 // satisfying its safety constraints.
3458 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3459 if offset > self.len() {
3460 (self, &mut [], &mut [])
3462 let (left, rest) = self.split_at_mut(offset);
3463 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3464 let rest_len = rest.len();
3465 let mut_ptr = rest.as_mut_ptr();
3466 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3467 // SAFETY: see comments for `align_to`.
3471 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3472 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3478 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3480 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3481 /// postconditions as that method. You're only assured that
3482 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3484 /// Notably, all of the following are possible:
3485 /// - `prefix.len() >= LANES`.
3486 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3487 /// - `suffix.len() >= LANES`.
3489 /// That said, this is a safe method, so if you're only writing safe code,
3490 /// then this can at most cause incorrect logic, not unsoundness.
3494 /// This will panic if the size of the SIMD type is different from
3495 /// `LANES` times that of the scalar.
3497 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3498 /// that from ever happening, as only power-of-two numbers of lanes are
3499 /// supported. It's possible that, in the future, those restrictions might
3500 /// be lifted in a way that would make it possible to see panics from this
3501 /// method for something like `LANES == 3`.
3506 /// #![feature(portable_simd)]
3508 /// let short = &[1, 2, 3];
3509 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3510 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3512 /// // They might be split in any possible way between prefix and suffix
3513 /// let it = prefix.iter().chain(suffix).copied();
3514 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3516 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3517 /// use std::ops::Add;
3518 /// use std::simd::f32x4;
3519 /// let (prefix, middle, suffix) = x.as_simd();
3520 /// let sums = f32x4::from_array([
3521 /// prefix.iter().copied().sum(),
3524 /// suffix.iter().copied().sum(),
3526 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3527 /// sums.horizontal_sum()
3530 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3531 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3533 #[unstable(feature = "portable_simd", issue = "86656")]
3534 #[cfg(not(miri))] // Miri does not support all SIMD intrinsics
3535 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3537 Simd<T, LANES>: AsRef<[T; LANES]>,
3538 T: simd::SimdElement,
3539 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3541 // These are expected to always match, as vector types are laid out like
3542 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3543 // might as well double-check since it'll optimize away anyhow.
3544 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3546 // SAFETY: The simd types have the same layout as arrays, just with
3547 // potentially-higher alignment, so the de-facto transmutes are sound.
3548 unsafe { self.align_to() }
3551 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3553 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3554 /// postconditions as that method. You're only assured that
3555 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3557 /// Notably, all of the following are possible:
3558 /// - `prefix.len() >= LANES`.
3559 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3560 /// - `suffix.len() >= LANES`.
3562 /// That said, this is a safe method, so if you're only writing safe code,
3563 /// then this can at most cause incorrect logic, not unsoundness.
3565 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3569 /// This will panic if the size of the SIMD type is different from
3570 /// `LANES` times that of the scalar.
3572 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3573 /// that from ever happening, as only power-of-two numbers of lanes are
3574 /// supported. It's possible that, in the future, those restrictions might
3575 /// be lifted in a way that would make it possible to see panics from this
3576 /// method for something like `LANES == 3`.
3577 #[unstable(feature = "portable_simd", issue = "86656")]
3578 #[cfg(not(miri))] // Miri does not support all SIMD intrinsics
3579 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3581 Simd<T, LANES>: AsMut<[T; LANES]>,
3582 T: simd::SimdElement,
3583 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3585 // These are expected to always match, as vector types are laid out like
3586 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3587 // might as well double-check since it'll optimize away anyhow.
3588 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3590 // SAFETY: The simd types have the same layout as arrays, just with
3591 // potentially-higher alignment, so the de-facto transmutes are sound.
3592 unsafe { self.align_to_mut() }
3595 /// Checks if the elements of this slice are sorted.
3597 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3598 /// slice yields exactly zero or one element, `true` is returned.
3600 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3601 /// implies that this function returns `false` if any two consecutive items are not
3607 /// #![feature(is_sorted)]
3608 /// let empty: [i32; 0] = [];
3610 /// assert!([1, 2, 2, 9].is_sorted());
3611 /// assert!(![1, 3, 2, 4].is_sorted());
3612 /// assert!([0].is_sorted());
3613 /// assert!(empty.is_sorted());
3614 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3617 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3618 pub fn is_sorted(&self) -> bool
3622 self.is_sorted_by(|a, b| a.partial_cmp(b))
3625 /// Checks if the elements of this slice are sorted using the given comparator function.
3627 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3628 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3629 /// [`is_sorted`]; see its documentation for more information.
3631 /// [`is_sorted`]: slice::is_sorted
3632 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3633 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3635 F: FnMut(&T, &T) -> Option<Ordering>,
3637 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3640 /// Checks if the elements of this slice are sorted using the given key extraction function.
3642 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3643 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3644 /// documentation for more information.
3646 /// [`is_sorted`]: slice::is_sorted
3651 /// #![feature(is_sorted)]
3653 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3654 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3657 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3658 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3663 self.iter().is_sorted_by_key(f)
3666 /// Returns the index of the partition point according to the given predicate
3667 /// (the index of the first element of the second partition).
3669 /// The slice is assumed to be partitioned according to the given predicate.
3670 /// This means that all elements for which the predicate returns true are at the start of the slice
3671 /// and all elements for which the predicate returns false are at the end.
3672 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3673 /// (all odd numbers are at the start, all even at the end).
3675 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3676 /// as this method performs a kind of binary search.
3678 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3680 /// [`binary_search`]: slice::binary_search
3681 /// [`binary_search_by`]: slice::binary_search_by
3682 /// [`binary_search_by_key`]: slice::binary_search_by_key
3687 /// let v = [1, 2, 3, 3, 5, 6, 7];
3688 /// let i = v.partition_point(|&x| x < 5);
3690 /// assert_eq!(i, 4);
3691 /// assert!(v[..i].iter().all(|&x| x < 5));
3692 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3694 #[stable(feature = "partition_point", since = "1.52.0")]
3695 pub fn partition_point<P>(&self, mut pred: P) -> usize
3697 P: FnMut(&T) -> bool,
3699 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3702 /// Removes the subslice corresponding to the given range
3703 /// and returns a reference to it.
3705 /// Returns `None` and does not modify the slice if the given
3706 /// range is out of bounds.
3708 /// Note that this method only accepts one-sided ranges such as
3709 /// `2..` or `..6`, but not `2..6`.
3713 /// Taking the first three elements of a slice:
3716 /// #![feature(slice_take)]
3718 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3719 /// let mut first_three = slice.take(..3).unwrap();
3721 /// assert_eq!(slice, &['d']);
3722 /// assert_eq!(first_three, &['a', 'b', 'c']);
3725 /// Taking the last two elements of a slice:
3728 /// #![feature(slice_take)]
3730 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3731 /// let mut tail = slice.take(2..).unwrap();
3733 /// assert_eq!(slice, &['a', 'b']);
3734 /// assert_eq!(tail, &['c', 'd']);
3737 /// Getting `None` when `range` is out of bounds:
3740 /// #![feature(slice_take)]
3742 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3744 /// assert_eq!(None, slice.take(5..));
3745 /// assert_eq!(None, slice.take(..5));
3746 /// assert_eq!(None, slice.take(..=4));
3747 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3748 /// assert_eq!(Some(expected), slice.take(..4));
3751 #[must_use = "method does not modify the slice if the range is out of bounds"]
3752 #[unstable(feature = "slice_take", issue = "62280")]
3753 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3754 let (direction, split_index) = split_point_of(range)?;
3755 if split_index > self.len() {
3758 let (front, back) = self.split_at(split_index);
3760 Direction::Front => {
3764 Direction::Back => {
3771 /// Removes the subslice corresponding to the given range
3772 /// and returns a mutable reference to it.
3774 /// Returns `None` and does not modify the slice if the given
3775 /// range is out of bounds.
3777 /// Note that this method only accepts one-sided ranges such as
3778 /// `2..` or `..6`, but not `2..6`.
3782 /// Taking the first three elements of a slice:
3785 /// #![feature(slice_take)]
3787 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3788 /// let mut first_three = slice.take_mut(..3).unwrap();
3790 /// assert_eq!(slice, &mut ['d']);
3791 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3794 /// Taking the last two elements of a slice:
3797 /// #![feature(slice_take)]
3799 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3800 /// let mut tail = slice.take_mut(2..).unwrap();
3802 /// assert_eq!(slice, &mut ['a', 'b']);
3803 /// assert_eq!(tail, &mut ['c', 'd']);
3806 /// Getting `None` when `range` is out of bounds:
3809 /// #![feature(slice_take)]
3811 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3813 /// assert_eq!(None, slice.take_mut(5..));
3814 /// assert_eq!(None, slice.take_mut(..5));
3815 /// assert_eq!(None, slice.take_mut(..=4));
3816 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3817 /// assert_eq!(Some(expected), slice.take_mut(..4));
3820 #[must_use = "method does not modify the slice if the range is out of bounds"]
3821 #[unstable(feature = "slice_take", issue = "62280")]
3822 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3823 self: &mut &'a mut Self,
3825 ) -> Option<&'a mut Self> {
3826 let (direction, split_index) = split_point_of(range)?;
3827 if split_index > self.len() {
3830 let (front, back) = mem::take(self).split_at_mut(split_index);
3832 Direction::Front => {
3836 Direction::Back => {
3843 /// Removes the first element of the slice and returns a reference
3846 /// Returns `None` if the slice is empty.
3851 /// #![feature(slice_take)]
3853 /// let mut slice: &[_] = &['a', 'b', 'c'];
3854 /// let first = slice.take_first().unwrap();
3856 /// assert_eq!(slice, &['b', 'c']);
3857 /// assert_eq!(first, &'a');
3860 #[unstable(feature = "slice_take", issue = "62280")]
3861 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3862 let (first, rem) = self.split_first()?;
3867 /// Removes the first element of the slice and returns a mutable
3868 /// reference to it.
3870 /// Returns `None` if the slice is empty.
3875 /// #![feature(slice_take)]
3877 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3878 /// let first = slice.take_first_mut().unwrap();
3881 /// assert_eq!(slice, &['b', 'c']);
3882 /// assert_eq!(first, &'d');
3885 #[unstable(feature = "slice_take", issue = "62280")]
3886 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3887 let (first, rem) = mem::take(self).split_first_mut()?;
3892 /// Removes the last element of the slice and returns a reference
3895 /// Returns `None` if the slice is empty.
3900 /// #![feature(slice_take)]
3902 /// let mut slice: &[_] = &['a', 'b', 'c'];
3903 /// let last = slice.take_last().unwrap();
3905 /// assert_eq!(slice, &['a', 'b']);
3906 /// assert_eq!(last, &'c');
3909 #[unstable(feature = "slice_take", issue = "62280")]
3910 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3911 let (last, rem) = self.split_last()?;
3916 /// Removes the last element of the slice and returns a mutable
3917 /// reference to it.
3919 /// Returns `None` if the slice is empty.
3924 /// #![feature(slice_take)]
3926 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3927 /// let last = slice.take_last_mut().unwrap();
3930 /// assert_eq!(slice, &['a', 'b']);
3931 /// assert_eq!(last, &'d');
3934 #[unstable(feature = "slice_take", issue = "62280")]
3935 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3936 let (last, rem) = mem::take(self).split_last_mut()?;
3942 trait CloneFromSpec<T> {
3943 fn spec_clone_from(&mut self, src: &[T]);
3946 impl<T> CloneFromSpec<T> for [T]
3951 default fn spec_clone_from(&mut self, src: &[T]) {
3952 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3953 // NOTE: We need to explicitly slice them to the same length
3954 // to make it easier for the optimizer to elide bounds checking.
3955 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3956 let len = self.len();
3957 let src = &src[..len];
3959 self[i].clone_from(&src[i]);
3964 impl<T> CloneFromSpec<T> for [T]
3969 fn spec_clone_from(&mut self, src: &[T]) {
3970 self.copy_from_slice(src);
3974 #[stable(feature = "rust1", since = "1.0.0")]
3975 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3976 impl<T> const Default for &[T] {
3977 /// Creates an empty slice.
3978 fn default() -> Self {
3983 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3984 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3985 impl<T> const Default for &mut [T] {
3986 /// Creates a mutable empty slice.
3987 fn default() -> Self {
3992 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3993 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3994 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3995 /// `str`) to slices, and then this trait will be replaced or abolished.
3996 pub trait SlicePattern {
3997 /// The element type of the slice being matched on.
4000 /// Currently, the consumers of `SlicePattern` need a slice.
4001 fn as_slice(&self) -> &[Self::Item];
4004 #[stable(feature = "slice_strip", since = "1.51.0")]
4005 impl<T> SlicePattern for [T] {
4009 fn as_slice(&self) -> &[Self::Item] {
4014 #[stable(feature = "slice_strip", since = "1.51.0")]
4015 impl<T, const N: usize> SlicePattern for [T; N] {
4019 fn as_slice(&self) -> &[Self::Item] {