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) {
590 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
591 // Can't take two mutable loans from one vector, so instead use raw pointers.
592 let pa = ptr::addr_of_mut!(self[a]);
593 let pb = ptr::addr_of_mut!(self[b]);
594 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
595 // to elements in the slice and therefore are guaranteed to be valid and aligned.
596 // Note that accessing the elements behind `a` and `b` is checked and will
597 // panic when out of bounds.
603 /// Swaps two elements in the slice, without doing bounds checking.
605 /// For a safe alternative see [`swap`].
609 /// * a - The index of the first element
610 /// * b - The index of the second element
614 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
615 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
620 /// #![feature(slice_swap_unchecked)]
622 /// let mut v = ["a", "b", "c", "d"];
623 /// // SAFETY: we know that 1 and 3 are both indices of the slice
624 /// unsafe { v.swap_unchecked(1, 3) };
625 /// assert!(v == ["a", "d", "c", "b"]);
628 /// [`swap`]: slice::swap
629 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
630 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
631 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
632 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
633 #[cfg(debug_assertions)]
639 let ptr = self.as_mut_ptr();
640 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
642 ptr::swap(ptr.add(a), ptr.add(b));
646 /// Reverses the order of elements in the slice, in place.
651 /// let mut v = [1, 2, 3];
653 /// assert!(v == [3, 2, 1]);
655 #[stable(feature = "rust1", since = "1.0.0")]
657 pub fn reverse(&mut self) {
658 let half_len = self.len() / 2;
659 let Range { start, end } = self.as_mut_ptr_range();
661 // These slices will skip the middle item for an odd length,
662 // since that one doesn't need to move.
663 let (front_half, back_half) =
664 // SAFETY: Both are subparts of the original slice, so the memory
665 // range is valid, and they don't overlap because they're each only
666 // half (or less) of the original slice.
669 slice::from_raw_parts_mut(start, half_len),
670 slice::from_raw_parts_mut(end.sub(half_len), half_len),
674 // Introducing a function boundary here means that the two halves
675 // get `noalias` markers, allowing better optimization as LLVM
676 // knows that they're disjoint, unlike in the original slice.
677 revswap(front_half, back_half, half_len);
680 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
681 debug_assert_eq!(a.len(), n);
682 debug_assert_eq!(b.len(), n);
684 // Because this function is first compiled in isolation,
685 // this check tells LLVM that the indexing below is
686 // in-bounds. Then after inlining -- once the actual
687 // lengths of the slices are known -- it's removed.
688 let (a, b) = (&mut a[..n], &mut b[..n]);
691 mem::swap(&mut a[i], &mut b[n - 1 - i]);
696 /// Returns an iterator over the slice.
701 /// let x = &[1, 2, 4];
702 /// let mut iterator = x.iter();
704 /// assert_eq!(iterator.next(), Some(&1));
705 /// assert_eq!(iterator.next(), Some(&2));
706 /// assert_eq!(iterator.next(), Some(&4));
707 /// assert_eq!(iterator.next(), None);
709 #[stable(feature = "rust1", since = "1.0.0")]
711 pub fn iter(&self) -> Iter<'_, T> {
715 /// Returns an iterator that allows modifying each value.
720 /// let x = &mut [1, 2, 4];
721 /// for elem in x.iter_mut() {
724 /// assert_eq!(x, &[3, 4, 6]);
726 #[stable(feature = "rust1", since = "1.0.0")]
728 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
732 /// Returns an iterator over all contiguous windows of length
733 /// `size`. The windows overlap. If the slice is shorter than
734 /// `size`, the iterator returns no values.
738 /// Panics if `size` is 0.
743 /// let slice = ['r', 'u', 's', 't'];
744 /// let mut iter = slice.windows(2);
745 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
746 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
747 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
748 /// assert!(iter.next().is_none());
751 /// If the slice is shorter than `size`:
754 /// let slice = ['f', 'o', 'o'];
755 /// let mut iter = slice.windows(4);
756 /// assert!(iter.next().is_none());
758 #[stable(feature = "rust1", since = "1.0.0")]
760 pub fn windows(&self, size: usize) -> Windows<'_, T> {
761 let size = NonZeroUsize::new(size).expect("size is zero");
762 Windows::new(self, size)
765 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
766 /// beginning of the slice.
768 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
769 /// slice, then the last chunk will not have length `chunk_size`.
771 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
772 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
777 /// Panics if `chunk_size` is 0.
782 /// let slice = ['l', 'o', 'r', 'e', 'm'];
783 /// let mut iter = slice.chunks(2);
784 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
785 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
786 /// assert_eq!(iter.next().unwrap(), &['m']);
787 /// assert!(iter.next().is_none());
790 /// [`chunks_exact`]: slice::chunks_exact
791 /// [`rchunks`]: slice::rchunks
792 #[stable(feature = "rust1", since = "1.0.0")]
794 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
795 assert_ne!(chunk_size, 0);
796 Chunks::new(self, chunk_size)
799 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
800 /// beginning of the slice.
802 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
803 /// length of the slice, then the last chunk will not have length `chunk_size`.
805 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
806 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
807 /// the end of the slice.
811 /// Panics if `chunk_size` is 0.
816 /// let v = &mut [0, 0, 0, 0, 0];
817 /// let mut count = 1;
819 /// for chunk in v.chunks_mut(2) {
820 /// for elem in chunk.iter_mut() {
825 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
828 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
829 /// [`rchunks_mut`]: slice::rchunks_mut
830 #[stable(feature = "rust1", since = "1.0.0")]
832 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
833 assert_ne!(chunk_size, 0);
834 ChunksMut::new(self, chunk_size)
837 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
838 /// beginning of the slice.
840 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
841 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
842 /// from the `remainder` function of the iterator.
844 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
845 /// resulting code better than in the case of [`chunks`].
847 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
848 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
852 /// Panics if `chunk_size` is 0.
857 /// let slice = ['l', 'o', 'r', 'e', 'm'];
858 /// let mut iter = slice.chunks_exact(2);
859 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
860 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
861 /// assert!(iter.next().is_none());
862 /// assert_eq!(iter.remainder(), &['m']);
865 /// [`chunks`]: slice::chunks
866 /// [`rchunks_exact`]: slice::rchunks_exact
867 #[stable(feature = "chunks_exact", since = "1.31.0")]
869 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
870 assert_ne!(chunk_size, 0);
871 ChunksExact::new(self, chunk_size)
874 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
875 /// beginning of the slice.
877 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
878 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
879 /// retrieved from the `into_remainder` function of the iterator.
881 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
882 /// resulting code better than in the case of [`chunks_mut`].
884 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
885 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
890 /// Panics if `chunk_size` is 0.
895 /// let v = &mut [0, 0, 0, 0, 0];
896 /// let mut count = 1;
898 /// for chunk in v.chunks_exact_mut(2) {
899 /// for elem in chunk.iter_mut() {
904 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
907 /// [`chunks_mut`]: slice::chunks_mut
908 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
909 #[stable(feature = "chunks_exact", since = "1.31.0")]
911 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
912 assert_ne!(chunk_size, 0);
913 ChunksExactMut::new(self, chunk_size)
916 /// Splits the slice into a slice of `N`-element arrays,
917 /// assuming that there's no remainder.
921 /// This may only be called when
922 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
928 /// #![feature(slice_as_chunks)]
929 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
930 /// let chunks: &[[char; 1]] =
931 /// // SAFETY: 1-element chunks never have remainder
932 /// unsafe { slice.as_chunks_unchecked() };
933 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
934 /// let chunks: &[[char; 3]] =
935 /// // SAFETY: The slice length (6) is a multiple of 3
936 /// unsafe { slice.as_chunks_unchecked() };
937 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
939 /// // These would be unsound:
940 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
941 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
943 #[unstable(feature = "slice_as_chunks", issue = "74985")]
945 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
946 debug_assert_ne!(N, 0);
947 debug_assert_eq!(self.len() % N, 0);
949 // SAFETY: Our precondition is exactly what's needed to call this
950 unsafe { crate::intrinsics::exact_div(self.len(), N) };
951 // SAFETY: We cast a slice of `new_len * N` elements into
952 // a slice of `new_len` many `N` elements chunks.
953 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
956 /// Splits the slice into a slice of `N`-element arrays,
957 /// starting at the beginning of the slice,
958 /// and a remainder slice with length strictly less than `N`.
962 /// Panics if `N` is 0. This check will most probably get changed to a compile time
963 /// error before this method gets stabilized.
968 /// #![feature(slice_as_chunks)]
969 /// let slice = ['l', 'o', 'r', 'e', 'm'];
970 /// let (chunks, remainder) = slice.as_chunks();
971 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
972 /// assert_eq!(remainder, &['m']);
974 #[unstable(feature = "slice_as_chunks", issue = "74985")]
976 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
978 let len = self.len() / N;
979 let (multiple_of_n, remainder) = self.split_at(len * N);
980 // SAFETY: We already panicked for zero, and ensured by construction
981 // that the length of the subslice is a multiple of N.
982 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
983 (array_slice, remainder)
986 /// Splits the slice into a slice of `N`-element arrays,
987 /// starting at the end of the slice,
988 /// and a remainder slice with length strictly less than `N`.
992 /// Panics if `N` is 0. This check will most probably get changed to a compile time
993 /// error before this method gets stabilized.
998 /// #![feature(slice_as_chunks)]
999 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1000 /// let (remainder, chunks) = slice.as_rchunks();
1001 /// assert_eq!(remainder, &['l']);
1002 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1004 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1006 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1008 let len = self.len() / N;
1009 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1010 // SAFETY: We already panicked for zero, and ensured by construction
1011 // that the length of the subslice is a multiple of N.
1012 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1013 (remainder, array_slice)
1016 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1017 /// beginning of the slice.
1019 /// The chunks are array references and do not overlap. If `N` does not divide the
1020 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1021 /// retrieved from the `remainder` function of the iterator.
1023 /// This method is the const generic equivalent of [`chunks_exact`].
1027 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1028 /// error before this method gets stabilized.
1033 /// #![feature(array_chunks)]
1034 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1035 /// let mut iter = slice.array_chunks();
1036 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1037 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1038 /// assert!(iter.next().is_none());
1039 /// assert_eq!(iter.remainder(), &['m']);
1042 /// [`chunks_exact`]: slice::chunks_exact
1043 #[unstable(feature = "array_chunks", issue = "74985")]
1045 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1047 ArrayChunks::new(self)
1050 /// Splits the slice into a slice of `N`-element arrays,
1051 /// assuming that there's no remainder.
1055 /// This may only be called when
1056 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1062 /// #![feature(slice_as_chunks)]
1063 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1064 /// let chunks: &mut [[char; 1]] =
1065 /// // SAFETY: 1-element chunks never have remainder
1066 /// unsafe { slice.as_chunks_unchecked_mut() };
1067 /// chunks[0] = ['L'];
1068 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1069 /// let chunks: &mut [[char; 3]] =
1070 /// // SAFETY: The slice length (6) is a multiple of 3
1071 /// unsafe { slice.as_chunks_unchecked_mut() };
1072 /// chunks[1] = ['a', 'x', '?'];
1073 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1075 /// // These would be unsound:
1076 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1077 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1079 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1081 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1082 debug_assert_ne!(N, 0);
1083 debug_assert_eq!(self.len() % N, 0);
1085 // SAFETY: Our precondition is exactly what's needed to call this
1086 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1087 // SAFETY: We cast a slice of `new_len * N` elements into
1088 // a slice of `new_len` many `N` elements chunks.
1089 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1092 /// Splits the slice into a slice of `N`-element arrays,
1093 /// starting at the beginning of the slice,
1094 /// and a remainder slice with length strictly less than `N`.
1098 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1099 /// error before this method gets stabilized.
1104 /// #![feature(slice_as_chunks)]
1105 /// let v = &mut [0, 0, 0, 0, 0];
1106 /// let mut count = 1;
1108 /// let (chunks, remainder) = v.as_chunks_mut();
1109 /// remainder[0] = 9;
1110 /// for chunk in chunks {
1111 /// *chunk = [count; 2];
1114 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1116 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1118 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1120 let len = self.len() / N;
1121 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1122 // SAFETY: We already panicked for zero, and ensured by construction
1123 // that the length of the subslice is a multiple of N.
1124 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1125 (array_slice, remainder)
1128 /// Splits the slice into a slice of `N`-element arrays,
1129 /// starting at the end of the slice,
1130 /// and a remainder slice with length strictly less than `N`.
1134 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1135 /// error before this method gets stabilized.
1140 /// #![feature(slice_as_chunks)]
1141 /// let v = &mut [0, 0, 0, 0, 0];
1142 /// let mut count = 1;
1144 /// let (remainder, chunks) = v.as_rchunks_mut();
1145 /// remainder[0] = 9;
1146 /// for chunk in chunks {
1147 /// *chunk = [count; 2];
1150 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1152 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1154 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1156 let len = self.len() / N;
1157 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1158 // SAFETY: We already panicked for zero, and ensured by construction
1159 // that the length of the subslice is a multiple of N.
1160 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1161 (remainder, array_slice)
1164 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1165 /// beginning of the slice.
1167 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1168 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1169 /// can be retrieved from the `into_remainder` function of the iterator.
1171 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1175 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1176 /// error before this method gets stabilized.
1181 /// #![feature(array_chunks)]
1182 /// let v = &mut [0, 0, 0, 0, 0];
1183 /// let mut count = 1;
1185 /// for chunk in v.array_chunks_mut() {
1186 /// *chunk = [count; 2];
1189 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1192 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1193 #[unstable(feature = "array_chunks", issue = "74985")]
1195 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1197 ArrayChunksMut::new(self)
1200 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1201 /// starting at the beginning of the slice.
1203 /// This is the const generic equivalent of [`windows`].
1205 /// If `N` is greater than the size of the slice, it will return no windows.
1209 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1210 /// error before this method gets stabilized.
1215 /// #![feature(array_windows)]
1216 /// let slice = [0, 1, 2, 3];
1217 /// let mut iter = slice.array_windows();
1218 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1219 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1220 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1221 /// assert!(iter.next().is_none());
1224 /// [`windows`]: slice::windows
1225 #[unstable(feature = "array_windows", issue = "75027")]
1227 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1229 ArrayWindows::new(self)
1232 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1235 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1236 /// slice, then the last chunk will not have length `chunk_size`.
1238 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1239 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1244 /// Panics if `chunk_size` is 0.
1249 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1250 /// let mut iter = slice.rchunks(2);
1251 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1252 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1253 /// assert_eq!(iter.next().unwrap(), &['l']);
1254 /// assert!(iter.next().is_none());
1257 /// [`rchunks_exact`]: slice::rchunks_exact
1258 /// [`chunks`]: slice::chunks
1259 #[stable(feature = "rchunks", since = "1.31.0")]
1261 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1262 assert!(chunk_size != 0);
1263 RChunks::new(self, chunk_size)
1266 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1269 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1270 /// length of the slice, then the last chunk will not have length `chunk_size`.
1272 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1273 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1274 /// beginning of the slice.
1278 /// Panics if `chunk_size` is 0.
1283 /// let v = &mut [0, 0, 0, 0, 0];
1284 /// let mut count = 1;
1286 /// for chunk in v.rchunks_mut(2) {
1287 /// for elem in chunk.iter_mut() {
1292 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1295 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1296 /// [`chunks_mut`]: slice::chunks_mut
1297 #[stable(feature = "rchunks", since = "1.31.0")]
1299 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1300 assert!(chunk_size != 0);
1301 RChunksMut::new(self, chunk_size)
1304 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1305 /// end of the slice.
1307 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1308 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1309 /// from the `remainder` function of the iterator.
1311 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1312 /// resulting code better than in the case of [`chunks`].
1314 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1315 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1320 /// Panics if `chunk_size` is 0.
1325 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1326 /// let mut iter = slice.rchunks_exact(2);
1327 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1328 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1329 /// assert!(iter.next().is_none());
1330 /// assert_eq!(iter.remainder(), &['l']);
1333 /// [`chunks`]: slice::chunks
1334 /// [`rchunks`]: slice::rchunks
1335 /// [`chunks_exact`]: slice::chunks_exact
1336 #[stable(feature = "rchunks", since = "1.31.0")]
1338 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1339 assert!(chunk_size != 0);
1340 RChunksExact::new(self, chunk_size)
1343 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1346 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1347 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1348 /// retrieved from the `into_remainder` function of the iterator.
1350 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1351 /// resulting code better than in the case of [`chunks_mut`].
1353 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1354 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1359 /// Panics if `chunk_size` is 0.
1364 /// let v = &mut [0, 0, 0, 0, 0];
1365 /// let mut count = 1;
1367 /// for chunk in v.rchunks_exact_mut(2) {
1368 /// for elem in chunk.iter_mut() {
1373 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1376 /// [`chunks_mut`]: slice::chunks_mut
1377 /// [`rchunks_mut`]: slice::rchunks_mut
1378 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1379 #[stable(feature = "rchunks", since = "1.31.0")]
1381 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1382 assert!(chunk_size != 0);
1383 RChunksExactMut::new(self, chunk_size)
1386 /// Returns an iterator over the slice producing non-overlapping runs
1387 /// of elements using the predicate to separate them.
1389 /// The predicate is called on two elements following themselves,
1390 /// it means the predicate is called on `slice[0]` and `slice[1]`
1391 /// then on `slice[1]` and `slice[2]` and so on.
1396 /// #![feature(slice_group_by)]
1398 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1400 /// let mut iter = slice.group_by(|a, b| a == b);
1402 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1403 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1404 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1405 /// assert_eq!(iter.next(), None);
1408 /// This method can be used to extract the sorted subslices:
1411 /// #![feature(slice_group_by)]
1413 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1415 /// let mut iter = slice.group_by(|a, b| a <= b);
1417 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1418 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1419 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1420 /// assert_eq!(iter.next(), None);
1422 #[unstable(feature = "slice_group_by", issue = "80552")]
1424 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1426 F: FnMut(&T, &T) -> bool,
1428 GroupBy::new(self, pred)
1431 /// Returns an iterator over the slice producing non-overlapping mutable
1432 /// runs of elements using the predicate to separate them.
1434 /// The predicate is called on two elements following themselves,
1435 /// it means the predicate is called on `slice[0]` and `slice[1]`
1436 /// then on `slice[1]` and `slice[2]` and so on.
1441 /// #![feature(slice_group_by)]
1443 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1445 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1447 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1448 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1449 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1450 /// assert_eq!(iter.next(), None);
1453 /// This method can be used to extract the sorted subslices:
1456 /// #![feature(slice_group_by)]
1458 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1460 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1462 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1463 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1464 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1465 /// assert_eq!(iter.next(), None);
1467 #[unstable(feature = "slice_group_by", issue = "80552")]
1469 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1471 F: FnMut(&T, &T) -> bool,
1473 GroupByMut::new(self, pred)
1476 /// Divides one slice into two at an index.
1478 /// The first will contain all indices from `[0, mid)` (excluding
1479 /// the index `mid` itself) and the second will contain all
1480 /// indices from `[mid, len)` (excluding the index `len` itself).
1484 /// Panics if `mid > len`.
1489 /// let v = [1, 2, 3, 4, 5, 6];
1492 /// let (left, right) = v.split_at(0);
1493 /// assert_eq!(left, []);
1494 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1498 /// let (left, right) = v.split_at(2);
1499 /// assert_eq!(left, [1, 2]);
1500 /// assert_eq!(right, [3, 4, 5, 6]);
1504 /// let (left, right) = v.split_at(6);
1505 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1506 /// assert_eq!(right, []);
1509 #[stable(feature = "rust1", since = "1.0.0")]
1512 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1513 assert!(mid <= self.len());
1514 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1515 // fulfills the requirements of `from_raw_parts_mut`.
1516 unsafe { self.split_at_unchecked(mid) }
1519 /// Divides one mutable slice into two at an index.
1521 /// The first will contain all indices from `[0, mid)` (excluding
1522 /// the index `mid` itself) and the second will contain all
1523 /// indices from `[mid, len)` (excluding the index `len` itself).
1527 /// Panics if `mid > len`.
1532 /// let mut v = [1, 0, 3, 0, 5, 6];
1533 /// let (left, right) = v.split_at_mut(2);
1534 /// assert_eq!(left, [1, 0]);
1535 /// assert_eq!(right, [3, 0, 5, 6]);
1538 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1540 #[stable(feature = "rust1", since = "1.0.0")]
1543 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1544 assert!(mid <= self.len());
1545 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1546 // fulfills the requirements of `from_raw_parts_mut`.
1547 unsafe { self.split_at_mut_unchecked(mid) }
1550 /// Divides one slice into two at an index, without doing bounds checking.
1552 /// The first will contain all indices from `[0, mid)` (excluding
1553 /// the index `mid` itself) and the second will contain all
1554 /// indices from `[mid, len)` (excluding the index `len` itself).
1556 /// For a safe alternative see [`split_at`].
1560 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1561 /// even if the resulting reference is not used. The caller has to ensure that
1562 /// `0 <= mid <= self.len()`.
1564 /// [`split_at`]: slice::split_at
1565 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1570 /// #![feature(slice_split_at_unchecked)]
1572 /// let v = [1, 2, 3, 4, 5, 6];
1575 /// let (left, right) = v.split_at_unchecked(0);
1576 /// assert_eq!(left, []);
1577 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1581 /// let (left, right) = v.split_at_unchecked(2);
1582 /// assert_eq!(left, [1, 2]);
1583 /// assert_eq!(right, [3, 4, 5, 6]);
1587 /// let (left, right) = v.split_at_unchecked(6);
1588 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1589 /// assert_eq!(right, []);
1592 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1594 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1595 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1596 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1599 /// Divides one mutable slice into two at an index, without doing bounds checking.
1601 /// The first will contain all indices from `[0, mid)` (excluding
1602 /// the index `mid` itself) and the second will contain all
1603 /// indices from `[mid, len)` (excluding the index `len` itself).
1605 /// For a safe alternative see [`split_at_mut`].
1609 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1610 /// even if the resulting reference is not used. The caller has to ensure that
1611 /// `0 <= mid <= self.len()`.
1613 /// [`split_at_mut`]: slice::split_at_mut
1614 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1619 /// #![feature(slice_split_at_unchecked)]
1621 /// let mut v = [1, 0, 3, 0, 5, 6];
1622 /// // scoped to restrict the lifetime of the borrows
1624 /// let (left, right) = v.split_at_mut_unchecked(2);
1625 /// assert_eq!(left, [1, 0]);
1626 /// assert_eq!(right, [3, 0, 5, 6]);
1630 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1632 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1634 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1635 let len = self.len();
1636 let ptr = self.as_mut_ptr();
1638 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1640 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1642 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1645 /// Divides one slice into an array and a remainder slice at an index.
1647 /// The array will contain all indices from `[0, N)` (excluding
1648 /// the index `N` itself) and the slice will contain all
1649 /// indices from `[N, len)` (excluding the index `len` itself).
1653 /// Panics if `N > len`.
1658 /// #![feature(split_array)]
1660 /// let v = &[1, 2, 3, 4, 5, 6][..];
1663 /// let (left, right) = v.split_array_ref::<0>();
1664 /// assert_eq!(left, &[]);
1665 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1669 /// let (left, right) = v.split_array_ref::<2>();
1670 /// assert_eq!(left, &[1, 2]);
1671 /// assert_eq!(right, [3, 4, 5, 6]);
1675 /// let (left, right) = v.split_array_ref::<6>();
1676 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1677 /// assert_eq!(right, []);
1680 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1683 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1684 let (a, b) = self.split_at(N);
1685 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1686 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1689 /// Divides one mutable slice into an array and a remainder slice at an index.
1691 /// The array will contain all indices from `[0, N)` (excluding
1692 /// the index `N` itself) and the slice will contain all
1693 /// indices from `[N, len)` (excluding the index `len` itself).
1697 /// Panics if `N > len`.
1702 /// #![feature(split_array)]
1704 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1705 /// let (left, right) = v.split_array_mut::<2>();
1706 /// assert_eq!(left, &mut [1, 0]);
1707 /// assert_eq!(right, [3, 0, 5, 6]);
1710 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1712 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1715 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1716 let (a, b) = self.split_at_mut(N);
1717 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1718 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1721 /// Divides one slice into an array and a remainder slice at an index from
1724 /// The slice will contain all indices from `[0, len - N)` (excluding
1725 /// the index `len - N` itself) and the array will contain all
1726 /// indices from `[len - N, len)` (excluding the index `len` itself).
1730 /// Panics if `N > len`.
1735 /// #![feature(split_array)]
1737 /// let v = &[1, 2, 3, 4, 5, 6][..];
1740 /// let (left, right) = v.rsplit_array_ref::<0>();
1741 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1742 /// assert_eq!(right, &[]);
1746 /// let (left, right) = v.rsplit_array_ref::<2>();
1747 /// assert_eq!(left, [1, 2, 3, 4]);
1748 /// assert_eq!(right, &[5, 6]);
1752 /// let (left, right) = v.rsplit_array_ref::<6>();
1753 /// assert_eq!(left, []);
1754 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1757 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1759 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1760 assert!(N <= self.len());
1761 let (a, b) = self.split_at(self.len() - N);
1762 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1763 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1766 /// Divides one mutable slice into an array and a remainder slice at an
1767 /// index from the end.
1769 /// The slice will contain all indices from `[0, len - N)` (excluding
1770 /// the index `N` itself) and the array will contain all
1771 /// indices from `[len - N, len)` (excluding the index `len` itself).
1775 /// Panics if `N > len`.
1780 /// #![feature(split_array)]
1782 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1783 /// let (left, right) = v.rsplit_array_mut::<4>();
1784 /// assert_eq!(left, [1, 0]);
1785 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1788 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1790 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1792 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1793 assert!(N <= self.len());
1794 let (a, b) = self.split_at_mut(self.len() - N);
1795 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1796 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1799 /// Returns an iterator over subslices separated by elements that match
1800 /// `pred`. The matched element is not contained in the subslices.
1805 /// let slice = [10, 40, 33, 20];
1806 /// let mut iter = slice.split(|num| num % 3 == 0);
1808 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1809 /// assert_eq!(iter.next().unwrap(), &[20]);
1810 /// assert!(iter.next().is_none());
1813 /// If the first element is matched, an empty slice will be the first item
1814 /// returned by the iterator. Similarly, if the last element in the slice
1815 /// is matched, an empty slice will be the last item returned by the
1819 /// let slice = [10, 40, 33];
1820 /// let mut iter = slice.split(|num| num % 3 == 0);
1822 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1823 /// assert_eq!(iter.next().unwrap(), &[]);
1824 /// assert!(iter.next().is_none());
1827 /// If two matched elements are directly adjacent, an empty slice will be
1828 /// present between them:
1831 /// let slice = [10, 6, 33, 20];
1832 /// let mut iter = slice.split(|num| num % 3 == 0);
1834 /// assert_eq!(iter.next().unwrap(), &[10]);
1835 /// assert_eq!(iter.next().unwrap(), &[]);
1836 /// assert_eq!(iter.next().unwrap(), &[20]);
1837 /// assert!(iter.next().is_none());
1839 #[stable(feature = "rust1", since = "1.0.0")]
1841 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1843 F: FnMut(&T) -> bool,
1845 Split::new(self, pred)
1848 /// Returns an iterator over mutable subslices separated by elements that
1849 /// match `pred`. The matched element is not contained in the subslices.
1854 /// let mut v = [10, 40, 30, 20, 60, 50];
1856 /// for group in v.split_mut(|num| *num % 3 == 0) {
1859 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1861 #[stable(feature = "rust1", since = "1.0.0")]
1863 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1865 F: FnMut(&T) -> bool,
1867 SplitMut::new(self, pred)
1870 /// Returns an iterator over subslices separated by elements that match
1871 /// `pred`. The matched element is contained in the end of the previous
1872 /// subslice as a terminator.
1877 /// let slice = [10, 40, 33, 20];
1878 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1880 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1881 /// assert_eq!(iter.next().unwrap(), &[20]);
1882 /// assert!(iter.next().is_none());
1885 /// If the last element of the slice is matched,
1886 /// that element will be considered the terminator of the preceding slice.
1887 /// That slice will be the last item returned by the iterator.
1890 /// let slice = [3, 10, 40, 33];
1891 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1893 /// assert_eq!(iter.next().unwrap(), &[3]);
1894 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1895 /// assert!(iter.next().is_none());
1897 #[stable(feature = "split_inclusive", since = "1.51.0")]
1899 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1901 F: FnMut(&T) -> bool,
1903 SplitInclusive::new(self, pred)
1906 /// Returns an iterator over mutable subslices separated by elements that
1907 /// match `pred`. The matched element is contained in the previous
1908 /// subslice as a terminator.
1913 /// let mut v = [10, 40, 30, 20, 60, 50];
1915 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1916 /// let terminator_idx = group.len()-1;
1917 /// group[terminator_idx] = 1;
1919 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1921 #[stable(feature = "split_inclusive", since = "1.51.0")]
1923 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1925 F: FnMut(&T) -> bool,
1927 SplitInclusiveMut::new(self, pred)
1930 /// Returns an iterator over subslices separated by elements that match
1931 /// `pred`, starting at the end of the slice and working backwards.
1932 /// The matched element is not contained in the subslices.
1937 /// let slice = [11, 22, 33, 0, 44, 55];
1938 /// let mut iter = slice.rsplit(|num| *num == 0);
1940 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1941 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1942 /// assert_eq!(iter.next(), None);
1945 /// As with `split()`, if the first or last element is matched, an empty
1946 /// slice will be the first (or last) item returned by the iterator.
1949 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1950 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1951 /// assert_eq!(it.next().unwrap(), &[]);
1952 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1953 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1954 /// assert_eq!(it.next().unwrap(), &[]);
1955 /// assert_eq!(it.next(), None);
1957 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1959 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1961 F: FnMut(&T) -> bool,
1963 RSplit::new(self, pred)
1966 /// Returns an iterator over mutable subslices separated by elements that
1967 /// match `pred`, starting at the end of the slice and working
1968 /// backwards. The matched element is not contained in the subslices.
1973 /// let mut v = [100, 400, 300, 200, 600, 500];
1975 /// let mut count = 0;
1976 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1978 /// group[0] = count;
1980 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1983 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1985 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1987 F: FnMut(&T) -> bool,
1989 RSplitMut::new(self, pred)
1992 /// Returns an iterator over subslices separated by elements that match
1993 /// `pred`, limited to returning at most `n` items. The matched element is
1994 /// not contained in the subslices.
1996 /// The last element returned, if any, will contain the remainder of the
2001 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2002 /// `[20, 60, 50]`):
2005 /// let v = [10, 40, 30, 20, 60, 50];
2007 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2008 /// println!("{:?}", group);
2011 #[stable(feature = "rust1", since = "1.0.0")]
2013 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2015 F: FnMut(&T) -> bool,
2017 SplitN::new(self.split(pred), n)
2020 /// Returns an iterator over subslices separated by elements that match
2021 /// `pred`, limited to returning at most `n` items. The matched element is
2022 /// not contained in the subslices.
2024 /// The last element returned, if any, will contain the remainder of the
2030 /// let mut v = [10, 40, 30, 20, 60, 50];
2032 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2035 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2037 #[stable(feature = "rust1", since = "1.0.0")]
2039 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2041 F: FnMut(&T) -> bool,
2043 SplitNMut::new(self.split_mut(pred), n)
2046 /// Returns an iterator over subslices separated by elements that match
2047 /// `pred` limited to returning at most `n` items. This starts at the end of
2048 /// the slice and works backwards. The matched element is not contained in
2051 /// The last element returned, if any, will contain the remainder of the
2056 /// Print the slice split once, starting from the end, by numbers divisible
2057 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2060 /// let v = [10, 40, 30, 20, 60, 50];
2062 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2063 /// println!("{:?}", group);
2066 #[stable(feature = "rust1", since = "1.0.0")]
2068 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2070 F: FnMut(&T) -> bool,
2072 RSplitN::new(self.rsplit(pred), n)
2075 /// Returns an iterator over subslices separated by elements that match
2076 /// `pred` limited to returning at most `n` items. This starts at the end of
2077 /// the slice and works backwards. The matched element is not contained in
2080 /// The last element returned, if any, will contain the remainder of the
2086 /// let mut s = [10, 40, 30, 20, 60, 50];
2088 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2091 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2093 #[stable(feature = "rust1", since = "1.0.0")]
2095 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2097 F: FnMut(&T) -> bool,
2099 RSplitNMut::new(self.rsplit_mut(pred), n)
2102 /// Returns `true` if the slice contains an element with the given value.
2107 /// let v = [10, 40, 30];
2108 /// assert!(v.contains(&30));
2109 /// assert!(!v.contains(&50));
2112 /// If you do not have a `&T`, but some other value that you can compare
2113 /// with one (for example, `String` implements `PartialEq<str>`), you can
2114 /// use `iter().any`:
2117 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2118 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2119 /// assert!(!v.iter().any(|e| e == "hi"));
2121 #[stable(feature = "rust1", since = "1.0.0")]
2123 pub fn contains(&self, x: &T) -> bool
2127 cmp::SliceContains::slice_contains(x, self)
2130 /// Returns `true` if `needle` is a prefix of the slice.
2135 /// let v = [10, 40, 30];
2136 /// assert!(v.starts_with(&[10]));
2137 /// assert!(v.starts_with(&[10, 40]));
2138 /// assert!(!v.starts_with(&[50]));
2139 /// assert!(!v.starts_with(&[10, 50]));
2142 /// Always returns `true` if `needle` is an empty slice:
2145 /// let v = &[10, 40, 30];
2146 /// assert!(v.starts_with(&[]));
2147 /// let v: &[u8] = &[];
2148 /// assert!(v.starts_with(&[]));
2150 #[stable(feature = "rust1", since = "1.0.0")]
2151 pub fn starts_with(&self, needle: &[T]) -> bool
2155 let n = needle.len();
2156 self.len() >= n && needle == &self[..n]
2159 /// Returns `true` if `needle` is a suffix of the slice.
2164 /// let v = [10, 40, 30];
2165 /// assert!(v.ends_with(&[30]));
2166 /// assert!(v.ends_with(&[40, 30]));
2167 /// assert!(!v.ends_with(&[50]));
2168 /// assert!(!v.ends_with(&[50, 30]));
2171 /// Always returns `true` if `needle` is an empty slice:
2174 /// let v = &[10, 40, 30];
2175 /// assert!(v.ends_with(&[]));
2176 /// let v: &[u8] = &[];
2177 /// assert!(v.ends_with(&[]));
2179 #[stable(feature = "rust1", since = "1.0.0")]
2180 pub fn ends_with(&self, needle: &[T]) -> bool
2184 let (m, n) = (self.len(), needle.len());
2185 m >= n && needle == &self[m - n..]
2188 /// Returns a subslice with the prefix removed.
2190 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2191 /// If `prefix` is empty, simply returns the original slice.
2193 /// If the slice does not start with `prefix`, returns `None`.
2198 /// let v = &[10, 40, 30];
2199 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2200 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2201 /// assert_eq!(v.strip_prefix(&[50]), None);
2202 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2204 /// let prefix : &str = "he";
2205 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2206 /// Some(b"llo".as_ref()));
2208 #[must_use = "returns the subslice without modifying the original"]
2209 #[stable(feature = "slice_strip", since = "1.51.0")]
2210 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2214 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2215 let prefix = prefix.as_slice();
2216 let n = prefix.len();
2217 if n <= self.len() {
2218 let (head, tail) = self.split_at(n);
2226 /// Returns a subslice with the suffix removed.
2228 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2229 /// If `suffix` is empty, simply returns the original slice.
2231 /// If the slice does not end with `suffix`, returns `None`.
2236 /// let v = &[10, 40, 30];
2237 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2238 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2239 /// assert_eq!(v.strip_suffix(&[50]), None);
2240 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2242 #[must_use = "returns the subslice without modifying the original"]
2243 #[stable(feature = "slice_strip", since = "1.51.0")]
2244 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2248 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2249 let suffix = suffix.as_slice();
2250 let (len, n) = (self.len(), suffix.len());
2252 let (head, tail) = self.split_at(len - n);
2260 /// Binary searches this sorted slice for a given element.
2262 /// If the value is found then [`Result::Ok`] is returned, containing the
2263 /// index of the matching element. If there are multiple matches, then any
2264 /// one of the matches could be returned. The index is chosen
2265 /// deterministically, but is subject to change in future versions of Rust.
2266 /// If the value is not found then [`Result::Err`] is returned, containing
2267 /// the index where a matching element could be inserted while maintaining
2270 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2272 /// [`binary_search_by`]: slice::binary_search_by
2273 /// [`binary_search_by_key`]: slice::binary_search_by_key
2274 /// [`partition_point`]: slice::partition_point
2278 /// Looks up a series of four elements. The first is found, with a
2279 /// uniquely determined position; the second and third are not
2280 /// found; the fourth could match any position in `[1, 4]`.
2283 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2285 /// assert_eq!(s.binary_search(&13), Ok(9));
2286 /// assert_eq!(s.binary_search(&4), Err(7));
2287 /// assert_eq!(s.binary_search(&100), Err(13));
2288 /// let r = s.binary_search(&1);
2289 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2292 /// If you want to insert an item to a sorted vector, while maintaining
2296 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2298 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2299 /// s.insert(idx, num);
2300 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2302 #[stable(feature = "rust1", since = "1.0.0")]
2303 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2307 self.binary_search_by(|p| p.cmp(x))
2310 /// Binary searches this sorted slice with a comparator function.
2312 /// The comparator function should implement an order consistent
2313 /// with the sort order of the underlying slice, returning an
2314 /// order code that indicates whether its argument is `Less`,
2315 /// `Equal` or `Greater` the desired target.
2317 /// If the value is found then [`Result::Ok`] is returned, containing the
2318 /// index of the matching element. If there are multiple matches, then any
2319 /// one of the matches could be returned. The index is chosen
2320 /// deterministically, but is subject to change in future versions of Rust.
2321 /// If the value is not found then [`Result::Err`] is returned, containing
2322 /// the index where a matching element could be inserted while maintaining
2325 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2327 /// [`binary_search`]: slice::binary_search
2328 /// [`binary_search_by_key`]: slice::binary_search_by_key
2329 /// [`partition_point`]: slice::partition_point
2333 /// Looks up a series of four elements. The first is found, with a
2334 /// uniquely determined position; the second and third are not
2335 /// found; the fourth could match any position in `[1, 4]`.
2338 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2341 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2343 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2345 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2347 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2348 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2350 #[stable(feature = "rust1", since = "1.0.0")]
2352 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2354 F: FnMut(&'a T) -> Ordering,
2356 let mut size = self.len();
2358 let mut right = size;
2359 while left < right {
2360 let mid = left + size / 2;
2362 // SAFETY: the call is made safe by the following invariants:
2364 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2365 let cmp = f(unsafe { self.get_unchecked(mid) });
2367 // The reason why we use if/else control flow rather than match
2368 // is because match reorders comparison operations, which is perf sensitive.
2369 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2372 } else if cmp == Greater {
2375 // SAFETY: same as the `get_unchecked` above
2376 unsafe { crate::intrinsics::assume(mid < self.len()) };
2380 size = right - left;
2385 /// Binary searches this sorted slice with a key extraction function.
2387 /// Assumes that the slice is sorted by the key, for instance with
2388 /// [`sort_by_key`] using the same key extraction function.
2390 /// If the value is found then [`Result::Ok`] is returned, containing the
2391 /// index of the matching element. If there are multiple matches, then any
2392 /// one of the matches could be returned. The index is chosen
2393 /// deterministically, but is subject to change in future versions of Rust.
2394 /// If the value is not found then [`Result::Err`] is returned, containing
2395 /// the index where a matching element could be inserted while maintaining
2398 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2400 /// [`sort_by_key`]: slice::sort_by_key
2401 /// [`binary_search`]: slice::binary_search
2402 /// [`binary_search_by`]: slice::binary_search_by
2403 /// [`partition_point`]: slice::partition_point
2407 /// Looks up a series of four elements in a slice of pairs sorted by
2408 /// their second elements. The first is found, with a uniquely
2409 /// determined position; the second and third are not found; the
2410 /// fourth could match any position in `[1, 4]`.
2413 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2414 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2415 /// (1, 21), (2, 34), (4, 55)];
2417 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2418 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2419 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2420 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2421 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2423 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2424 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2425 // This breaks links when slice is displayed in core, but changing it to use relative links
2426 // would break when the item is re-exported. So allow the core links to be broken for now.
2427 #[allow(rustdoc::broken_intra_doc_links)]
2428 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2430 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2432 F: FnMut(&'a T) -> B,
2435 self.binary_search_by(|k| f(k).cmp(b))
2438 /// Sorts the slice, but might not preserve the order of equal elements.
2440 /// This sort is unstable (i.e., may reorder equal elements), in-place
2441 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2443 /// # Current implementation
2445 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2446 /// which combines the fast average case of randomized quicksort with the fast worst case of
2447 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2448 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2449 /// deterministic behavior.
2451 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2452 /// slice consists of several concatenated sorted sequences.
2457 /// let mut v = [-5, 4, 1, -3, 2];
2459 /// v.sort_unstable();
2460 /// assert!(v == [-5, -3, 1, 2, 4]);
2463 /// [pdqsort]: https://github.com/orlp/pdqsort
2464 #[stable(feature = "sort_unstable", since = "1.20.0")]
2466 pub fn sort_unstable(&mut self)
2470 sort::quicksort(self, |a, b| a.lt(b));
2473 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2476 /// This sort is unstable (i.e., may reorder equal elements), in-place
2477 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2479 /// The comparator function must define a total ordering for the elements in the slice. If
2480 /// the ordering is not total, the order of the elements is unspecified. An order is a
2481 /// total order if it is (for all `a`, `b` and `c`):
2483 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2484 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2486 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2487 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2490 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2491 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2492 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2495 /// # Current implementation
2497 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2498 /// which combines the fast average case of randomized quicksort with the fast worst case of
2499 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2500 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2501 /// deterministic behavior.
2503 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2504 /// slice consists of several concatenated sorted sequences.
2509 /// let mut v = [5, 4, 1, 3, 2];
2510 /// v.sort_unstable_by(|a, b| a.cmp(b));
2511 /// assert!(v == [1, 2, 3, 4, 5]);
2513 /// // reverse sorting
2514 /// v.sort_unstable_by(|a, b| b.cmp(a));
2515 /// assert!(v == [5, 4, 3, 2, 1]);
2518 /// [pdqsort]: https://github.com/orlp/pdqsort
2519 #[stable(feature = "sort_unstable", since = "1.20.0")]
2521 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2523 F: FnMut(&T, &T) -> Ordering,
2525 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2528 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2531 /// This sort is unstable (i.e., may reorder equal elements), in-place
2532 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2535 /// # Current implementation
2537 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2538 /// which combines the fast average case of randomized quicksort with the fast worst case of
2539 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2540 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2541 /// deterministic behavior.
2543 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2544 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2545 /// cases where the key function is expensive.
2550 /// let mut v = [-5i32, 4, 1, -3, 2];
2552 /// v.sort_unstable_by_key(|k| k.abs());
2553 /// assert!(v == [1, 2, -3, 4, -5]);
2556 /// [pdqsort]: https://github.com/orlp/pdqsort
2557 #[stable(feature = "sort_unstable", since = "1.20.0")]
2559 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2564 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2567 /// Reorder the slice such that the element at `index` is at its final sorted position.
2569 /// This reordering has the additional property that any value at position `i < index` will be
2570 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2571 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2572 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2573 /// element" in other libraries. It returns a triplet of the following values: all elements less
2574 /// than the one at the given index, the value at the given index, and all elements greater than
2575 /// the one at the given index.
2577 /// # Current implementation
2579 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2580 /// used for [`sort_unstable`].
2582 /// [`sort_unstable`]: slice::sort_unstable
2586 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2591 /// let mut v = [-5i32, 4, 1, -3, 2];
2593 /// // Find the median
2594 /// v.select_nth_unstable(2);
2596 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2597 /// // about the specified index.
2598 /// assert!(v == [-3, -5, 1, 2, 4] ||
2599 /// v == [-5, -3, 1, 2, 4] ||
2600 /// v == [-3, -5, 1, 4, 2] ||
2601 /// v == [-5, -3, 1, 4, 2]);
2603 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2605 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2609 let mut f = |a: &T, b: &T| a.lt(b);
2610 sort::partition_at_index(self, index, &mut f)
2613 /// Reorder the slice with a comparator function such that the element at `index` is at its
2614 /// final sorted position.
2616 /// This reordering has the additional property that any value at position `i < index` will be
2617 /// less than or equal to any value at a position `j > index` using the comparator function.
2618 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2619 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2620 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2621 /// values: all elements less than the one at the given index, the value at the given index,
2622 /// and all elements greater than the one at the given index, using the provided comparator
2625 /// # Current implementation
2627 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2628 /// used for [`sort_unstable`].
2630 /// [`sort_unstable`]: slice::sort_unstable
2634 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2639 /// let mut v = [-5i32, 4, 1, -3, 2];
2641 /// // Find the median as if the slice were sorted in descending order.
2642 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2644 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2645 /// // about the specified index.
2646 /// assert!(v == [2, 4, 1, -5, -3] ||
2647 /// v == [2, 4, 1, -3, -5] ||
2648 /// v == [4, 2, 1, -5, -3] ||
2649 /// v == [4, 2, 1, -3, -5]);
2651 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2653 pub fn select_nth_unstable_by<F>(
2657 ) -> (&mut [T], &mut T, &mut [T])
2659 F: FnMut(&T, &T) -> Ordering,
2661 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2662 sort::partition_at_index(self, index, &mut f)
2665 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2666 /// final sorted position.
2668 /// This reordering has the additional property that any value at position `i < index` will be
2669 /// less than or equal to any value at a position `j > index` using the key extraction function.
2670 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2671 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2672 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2673 /// values: all elements less than the one at the given index, the value at the given index, and
2674 /// all elements greater than the one at the given index, using the provided key extraction
2677 /// # Current implementation
2679 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2680 /// used for [`sort_unstable`].
2682 /// [`sort_unstable`]: slice::sort_unstable
2686 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2691 /// let mut v = [-5i32, 4, 1, -3, 2];
2693 /// // Return the median as if the array were sorted according to absolute value.
2694 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2696 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2697 /// // about the specified index.
2698 /// assert!(v == [1, 2, -3, 4, -5] ||
2699 /// v == [1, 2, -3, -5, 4] ||
2700 /// v == [2, 1, -3, 4, -5] ||
2701 /// v == [2, 1, -3, -5, 4]);
2703 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2705 pub fn select_nth_unstable_by_key<K, F>(
2709 ) -> (&mut [T], &mut T, &mut [T])
2714 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2715 sort::partition_at_index(self, index, &mut g)
2718 /// Moves all consecutive repeated elements to the end of the slice according to the
2719 /// [`PartialEq`] trait implementation.
2721 /// Returns two slices. The first contains no consecutive repeated elements.
2722 /// The second contains all the duplicates in no specified order.
2724 /// If the slice is sorted, the first returned slice contains no duplicates.
2729 /// #![feature(slice_partition_dedup)]
2731 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2733 /// let (dedup, duplicates) = slice.partition_dedup();
2735 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2736 /// assert_eq!(duplicates, [2, 3, 1]);
2738 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2740 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2744 self.partition_dedup_by(|a, b| a == b)
2747 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2748 /// a given equality relation.
2750 /// Returns two slices. The first contains no consecutive repeated elements.
2751 /// The second contains all the duplicates in no specified order.
2753 /// The `same_bucket` function is passed references to two elements from the slice and
2754 /// must determine if the elements compare equal. The elements are passed in opposite order
2755 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2756 /// at the end of the slice.
2758 /// If the slice is sorted, the first returned slice contains no duplicates.
2763 /// #![feature(slice_partition_dedup)]
2765 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2767 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2769 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2770 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2772 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2774 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2776 F: FnMut(&mut T, &mut T) -> bool,
2778 // Although we have a mutable reference to `self`, we cannot make
2779 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2780 // must ensure that the slice is in a valid state at all times.
2782 // The way that we handle this is by using swaps; we iterate
2783 // over all the elements, swapping as we go so that at the end
2784 // the elements we wish to keep are in the front, and those we
2785 // wish to reject are at the back. We can then split the slice.
2786 // This operation is still `O(n)`.
2788 // Example: We start in this state, where `r` represents "next
2789 // read" and `w` represents "next_write`.
2792 // +---+---+---+---+---+---+
2793 // | 0 | 1 | 1 | 2 | 3 | 3 |
2794 // +---+---+---+---+---+---+
2797 // Comparing self[r] against self[w-1], this is not a duplicate, so
2798 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2799 // r and w, leaving us with:
2802 // +---+---+---+---+---+---+
2803 // | 0 | 1 | 1 | 2 | 3 | 3 |
2804 // +---+---+---+---+---+---+
2807 // Comparing self[r] against self[w-1], this value is a duplicate,
2808 // so we increment `r` but leave everything else unchanged:
2811 // +---+---+---+---+---+---+
2812 // | 0 | 1 | 1 | 2 | 3 | 3 |
2813 // +---+---+---+---+---+---+
2816 // Comparing self[r] against self[w-1], this is not a duplicate,
2817 // so swap self[r] and self[w] and advance r and w:
2820 // +---+---+---+---+---+---+
2821 // | 0 | 1 | 2 | 1 | 3 | 3 |
2822 // +---+---+---+---+---+---+
2825 // Not a duplicate, repeat:
2828 // +---+---+---+---+---+---+
2829 // | 0 | 1 | 2 | 3 | 1 | 3 |
2830 // +---+---+---+---+---+---+
2833 // Duplicate, advance r. End of slice. Split at w.
2835 let len = self.len();
2837 return (self, &mut []);
2840 let ptr = self.as_mut_ptr();
2841 let mut next_read: usize = 1;
2842 let mut next_write: usize = 1;
2844 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2845 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2846 // one element before `ptr_write`, but `next_write` starts at 1, so
2847 // `prev_ptr_write` is never less than 0 and is inside the slice.
2848 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2849 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2850 // and `prev_ptr_write.offset(1)`.
2852 // `next_write` is also incremented at most once per loop at most meaning
2853 // no element is skipped when it may need to be swapped.
2855 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2856 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2857 // The explanation is simply that `next_read >= next_write` is always true,
2858 // thus `next_read > next_write - 1` is too.
2860 // Avoid bounds checks by using raw pointers.
2861 while next_read < len {
2862 let ptr_read = ptr.add(next_read);
2863 let prev_ptr_write = ptr.add(next_write - 1);
2864 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2865 if next_read != next_write {
2866 let ptr_write = prev_ptr_write.offset(1);
2867 mem::swap(&mut *ptr_read, &mut *ptr_write);
2875 self.split_at_mut(next_write)
2878 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2879 /// to the same key.
2881 /// Returns two slices. The first contains no consecutive repeated elements.
2882 /// The second contains all the duplicates in no specified order.
2884 /// If the slice is sorted, the first returned slice contains no duplicates.
2889 /// #![feature(slice_partition_dedup)]
2891 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2893 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2895 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2896 /// assert_eq!(duplicates, [21, 30, 13]);
2898 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2900 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2902 F: FnMut(&mut T) -> K,
2905 self.partition_dedup_by(|a, b| key(a) == key(b))
2908 /// Rotates the slice in-place such that the first `mid` elements of the
2909 /// slice move to the end while the last `self.len() - mid` elements move to
2910 /// the front. After calling `rotate_left`, the element previously at index
2911 /// `mid` will become the first element in the slice.
2915 /// This function will panic if `mid` is greater than the length of the
2916 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2921 /// Takes linear (in `self.len()`) time.
2926 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2927 /// a.rotate_left(2);
2928 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2931 /// Rotating a subslice:
2934 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2935 /// a[1..5].rotate_left(1);
2936 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2938 #[stable(feature = "slice_rotate", since = "1.26.0")]
2939 pub fn rotate_left(&mut self, mid: usize) {
2940 assert!(mid <= self.len());
2941 let k = self.len() - mid;
2942 let p = self.as_mut_ptr();
2944 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2945 // valid for reading and writing, as required by `ptr_rotate`.
2947 rotate::ptr_rotate(mid, p.add(mid), k);
2951 /// Rotates the slice in-place such that the first `self.len() - k`
2952 /// elements of the slice move to the end while the last `k` elements move
2953 /// to the front. After calling `rotate_right`, the element previously at
2954 /// index `self.len() - k` will become the first element in the slice.
2958 /// This function will panic if `k` is greater than the length of the
2959 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2964 /// Takes linear (in `self.len()`) time.
2969 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2970 /// a.rotate_right(2);
2971 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2974 /// Rotate a subslice:
2977 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2978 /// a[1..5].rotate_right(1);
2979 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2981 #[stable(feature = "slice_rotate", since = "1.26.0")]
2982 pub fn rotate_right(&mut self, k: usize) {
2983 assert!(k <= self.len());
2984 let mid = self.len() - k;
2985 let p = self.as_mut_ptr();
2987 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2988 // valid for reading and writing, as required by `ptr_rotate`.
2990 rotate::ptr_rotate(mid, p.add(mid), k);
2994 /// Fills `self` with elements by cloning `value`.
2999 /// let mut buf = vec![0; 10];
3001 /// assert_eq!(buf, vec![1; 10]);
3003 #[doc(alias = "memset")]
3004 #[stable(feature = "slice_fill", since = "1.50.0")]
3005 pub fn fill(&mut self, value: T)
3009 specialize::SpecFill::spec_fill(self, value);
3012 /// Fills `self` with elements returned by calling a closure repeatedly.
3014 /// This method uses a closure to create new values. If you'd rather
3015 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3016 /// trait to generate values, you can pass [`Default::default`] as the
3019 /// [`fill`]: slice::fill
3024 /// let mut buf = vec![1; 10];
3025 /// buf.fill_with(Default::default);
3026 /// assert_eq!(buf, vec![0; 10]);
3028 #[doc(alias = "memset")]
3029 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3030 pub fn fill_with<F>(&mut self, mut f: F)
3039 /// Copies the elements from `src` into `self`.
3041 /// The length of `src` must be the same as `self`.
3045 /// This function will panic if the two slices have different lengths.
3049 /// Cloning two elements from a slice into another:
3052 /// let src = [1, 2, 3, 4];
3053 /// let mut dst = [0, 0];
3055 /// // Because the slices have to be the same length,
3056 /// // we slice the source slice from four elements
3057 /// // to two. It will panic if we don't do this.
3058 /// dst.clone_from_slice(&src[2..]);
3060 /// assert_eq!(src, [1, 2, 3, 4]);
3061 /// assert_eq!(dst, [3, 4]);
3064 /// Rust enforces that there can only be one mutable reference with no
3065 /// immutable references to a particular piece of data in a particular
3066 /// scope. Because of this, attempting to use `clone_from_slice` on a
3067 /// single slice will result in a compile failure:
3070 /// let mut slice = [1, 2, 3, 4, 5];
3072 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3075 /// To work around this, we can use [`split_at_mut`] to create two distinct
3076 /// sub-slices from a slice:
3079 /// let mut slice = [1, 2, 3, 4, 5];
3082 /// let (left, right) = slice.split_at_mut(2);
3083 /// left.clone_from_slice(&right[1..]);
3086 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3089 /// [`copy_from_slice`]: slice::copy_from_slice
3090 /// [`split_at_mut`]: slice::split_at_mut
3091 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3093 pub fn clone_from_slice(&mut self, src: &[T])
3097 self.spec_clone_from(src);
3100 /// Copies all elements from `src` into `self`, using a memcpy.
3102 /// The length of `src` must be the same as `self`.
3104 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3108 /// This function will panic if the two slices have different lengths.
3112 /// Copying two elements from a slice into another:
3115 /// let src = [1, 2, 3, 4];
3116 /// let mut dst = [0, 0];
3118 /// // Because the slices have to be the same length,
3119 /// // we slice the source slice from four elements
3120 /// // to two. It will panic if we don't do this.
3121 /// dst.copy_from_slice(&src[2..]);
3123 /// assert_eq!(src, [1, 2, 3, 4]);
3124 /// assert_eq!(dst, [3, 4]);
3127 /// Rust enforces that there can only be one mutable reference with no
3128 /// immutable references to a particular piece of data in a particular
3129 /// scope. Because of this, attempting to use `copy_from_slice` on a
3130 /// single slice will result in a compile failure:
3133 /// let mut slice = [1, 2, 3, 4, 5];
3135 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3138 /// To work around this, we can use [`split_at_mut`] to create two distinct
3139 /// sub-slices from a slice:
3142 /// let mut slice = [1, 2, 3, 4, 5];
3145 /// let (left, right) = slice.split_at_mut(2);
3146 /// left.copy_from_slice(&right[1..]);
3149 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3152 /// [`clone_from_slice`]: slice::clone_from_slice
3153 /// [`split_at_mut`]: slice::split_at_mut
3154 #[doc(alias = "memcpy")]
3155 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3157 pub fn copy_from_slice(&mut self, src: &[T])
3161 // The panic code path was put into a cold function to not bloat the
3166 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3168 "source slice length ({}) does not match destination slice length ({})",
3173 if self.len() != src.len() {
3174 len_mismatch_fail(self.len(), src.len());
3177 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3178 // checked to have the same length. The slices cannot overlap because
3179 // mutable references are exclusive.
3181 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3185 /// Copies elements from one part of the slice to another part of itself,
3186 /// using a memmove.
3188 /// `src` is the range within `self` to copy from. `dest` is the starting
3189 /// index of the range within `self` to copy to, which will have the same
3190 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3191 /// must be less than or equal to `self.len()`.
3195 /// This function will panic if either range exceeds the end of the slice,
3196 /// or if the end of `src` is before the start.
3200 /// Copying four bytes within a slice:
3203 /// let mut bytes = *b"Hello, World!";
3205 /// bytes.copy_within(1..5, 8);
3207 /// assert_eq!(&bytes, b"Hello, Wello!");
3209 #[stable(feature = "copy_within", since = "1.37.0")]
3211 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3215 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3216 let count = src_end - src_start;
3217 assert!(dest <= self.len() - count, "dest is out of bounds");
3218 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3219 // as have those for `ptr::add`.
3221 // Derive both `src_ptr` and `dest_ptr` from the same loan
3222 let ptr = self.as_mut_ptr();
3223 let src_ptr = ptr.add(src_start);
3224 let dest_ptr = ptr.add(dest);
3225 ptr::copy(src_ptr, dest_ptr, count);
3229 /// Swaps all elements in `self` with those in `other`.
3231 /// The length of `other` must be the same as `self`.
3235 /// This function will panic if the two slices have different lengths.
3239 /// Swapping two elements across slices:
3242 /// let mut slice1 = [0, 0];
3243 /// let mut slice2 = [1, 2, 3, 4];
3245 /// slice1.swap_with_slice(&mut slice2[2..]);
3247 /// assert_eq!(slice1, [3, 4]);
3248 /// assert_eq!(slice2, [1, 2, 0, 0]);
3251 /// Rust enforces that there can only be one mutable reference to a
3252 /// particular piece of data in a particular scope. Because of this,
3253 /// attempting to use `swap_with_slice` on a single slice will result in
3254 /// a compile failure:
3257 /// let mut slice = [1, 2, 3, 4, 5];
3258 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3261 /// To work around this, we can use [`split_at_mut`] to create two distinct
3262 /// mutable sub-slices from a slice:
3265 /// let mut slice = [1, 2, 3, 4, 5];
3268 /// let (left, right) = slice.split_at_mut(2);
3269 /// left.swap_with_slice(&mut right[1..]);
3272 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3275 /// [`split_at_mut`]: slice::split_at_mut
3276 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3278 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3279 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3280 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3281 // checked to have the same length. The slices cannot overlap because
3282 // mutable references are exclusive.
3284 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3288 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3289 fn align_to_offsets<U>(&self) -> (usize, usize) {
3290 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3291 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3293 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3294 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3295 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3297 // Formula to calculate this is:
3299 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3300 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3302 // Expanded and simplified:
3304 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3305 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3307 // Luckily since all this is constant-evaluated... performance here matters not!
3309 fn gcd(a: usize, b: usize) -> usize {
3310 use crate::intrinsics;
3311 // iterative stein’s algorithm
3312 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3313 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3315 // SAFETY: `a` and `b` are checked to be non-zero values.
3316 let (ctz_a, mut ctz_b) = unsafe {
3323 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3325 let k = ctz_a.min(ctz_b);
3326 let mut a = a >> ctz_a;
3329 // remove all factors of 2 from b
3332 mem::swap(&mut a, &mut b);
3335 // SAFETY: `b` is checked to be non-zero.
3340 ctz_b = intrinsics::cttz_nonzero(b);
3345 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3346 let ts: usize = mem::size_of::<U>() / gcd;
3347 let us: usize = mem::size_of::<T>() / gcd;
3349 // Armed with this knowledge, we can find how many `U`s we can fit!
3350 let us_len = self.len() / ts * us;
3351 // And how many `T`s will be in the trailing slice!
3352 let ts_len = self.len() % ts;
3356 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3359 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3360 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3361 /// length possible for a given type and input slice, but only your algorithm's performance
3362 /// should depend on that, not its correctness. It is permissible for all of the input data to
3363 /// be returned as the prefix or suffix slice.
3365 /// This method has no purpose when either input element `T` or output element `U` are
3366 /// zero-sized and will return the original slice without splitting anything.
3370 /// This method is essentially a `transmute` with respect to the elements in the returned
3371 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3379 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3380 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3381 /// // less_efficient_algorithm_for_bytes(prefix);
3382 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3383 /// // less_efficient_algorithm_for_bytes(suffix);
3386 #[stable(feature = "slice_align_to", since = "1.30.0")]
3387 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3388 // Note that most of this function will be constant-evaluated,
3389 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3390 // handle ZSTs specially, which is – don't handle them at all.
3391 return (self, &[], &[]);
3394 // First, find at what point do we split between the first and 2nd slice. Easy with
3395 // ptr.align_offset.
3396 let ptr = self.as_ptr();
3397 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3398 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3399 if offset > self.len() {
3402 let (left, rest) = self.split_at(offset);
3403 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3404 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3405 // since the caller guarantees that we can transmute `T` to `U` safely.
3409 from_raw_parts(rest.as_ptr() as *const U, us_len),
3410 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3416 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3419 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3420 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3421 /// length possible for a given type and input slice, but only your algorithm's performance
3422 /// should depend on that, not its correctness. It is permissible for all of the input data to
3423 /// be returned as the prefix or suffix slice.
3425 /// This method has no purpose when either input element `T` or output element `U` are
3426 /// zero-sized and will return the original slice without splitting anything.
3430 /// This method is essentially a `transmute` with respect to the elements in the returned
3431 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3439 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3440 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3441 /// // less_efficient_algorithm_for_bytes(prefix);
3442 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3443 /// // less_efficient_algorithm_for_bytes(suffix);
3446 #[stable(feature = "slice_align_to", since = "1.30.0")]
3447 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3448 // Note that most of this function will be constant-evaluated,
3449 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3450 // handle ZSTs specially, which is – don't handle them at all.
3451 return (self, &mut [], &mut []);
3454 // First, find at what point do we split between the first and 2nd slice. Easy with
3455 // ptr.align_offset.
3456 let ptr = self.as_ptr();
3457 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3458 // rest of the method. This is done by passing a pointer to &[T] with an
3459 // alignment targeted for U.
3460 // `crate::ptr::align_offset` is called with a correctly aligned and
3461 // valid pointer `ptr` (it comes from a reference to `self`) and with
3462 // a size that is a power of two (since it comes from the alignement for U),
3463 // satisfying its safety constraints.
3464 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3465 if offset > self.len() {
3466 (self, &mut [], &mut [])
3468 let (left, rest) = self.split_at_mut(offset);
3469 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3470 let rest_len = rest.len();
3471 let mut_ptr = rest.as_mut_ptr();
3472 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3473 // SAFETY: see comments for `align_to`.
3477 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3478 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3484 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3486 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3487 /// postconditions as that method. You're only assured that
3488 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3490 /// Notably, all of the following are possible:
3491 /// - `prefix.len() >= LANES`.
3492 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3493 /// - `suffix.len() >= LANES`.
3495 /// That said, this is a safe method, so if you're only writing safe code,
3496 /// then this can at most cause incorrect logic, not unsoundness.
3500 /// This will panic if the size of the SIMD type is different from
3501 /// `LANES` times that of the scalar.
3503 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3504 /// that from ever happening, as only power-of-two numbers of lanes are
3505 /// supported. It's possible that, in the future, those restrictions might
3506 /// be lifted in a way that would make it possible to see panics from this
3507 /// method for something like `LANES == 3`.
3512 /// #![feature(portable_simd)]
3514 /// let short = &[1, 2, 3];
3515 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3516 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3518 /// // They might be split in any possible way between prefix and suffix
3519 /// let it = prefix.iter().chain(suffix).copied();
3520 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3522 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3523 /// use std::ops::Add;
3524 /// use std::simd::f32x4;
3525 /// let (prefix, middle, suffix) = x.as_simd();
3526 /// let sums = f32x4::from_array([
3527 /// prefix.iter().copied().sum(),
3530 /// suffix.iter().copied().sum(),
3532 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3533 /// sums.horizontal_sum()
3536 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3537 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3539 #[unstable(feature = "portable_simd", issue = "86656")]
3540 #[cfg(not(miri))] // Miri does not support all SIMD intrinsics
3541 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3543 Simd<T, LANES>: AsRef<[T; LANES]>,
3544 T: simd::SimdElement,
3545 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3547 // These are expected to always match, as vector types are laid out like
3548 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3549 // might as well double-check since it'll optimize away anyhow.
3550 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3552 // SAFETY: The simd types have the same layout as arrays, just with
3553 // potentially-higher alignment, so the de-facto transmutes are sound.
3554 unsafe { self.align_to() }
3557 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3559 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3560 /// postconditions as that method. You're only assured that
3561 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3563 /// Notably, all of the following are possible:
3564 /// - `prefix.len() >= LANES`.
3565 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3566 /// - `suffix.len() >= LANES`.
3568 /// That said, this is a safe method, so if you're only writing safe code,
3569 /// then this can at most cause incorrect logic, not unsoundness.
3571 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3575 /// This will panic if the size of the SIMD type is different from
3576 /// `LANES` times that of the scalar.
3578 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3579 /// that from ever happening, as only power-of-two numbers of lanes are
3580 /// supported. It's possible that, in the future, those restrictions might
3581 /// be lifted in a way that would make it possible to see panics from this
3582 /// method for something like `LANES == 3`.
3583 #[unstable(feature = "portable_simd", issue = "86656")]
3584 #[cfg(not(miri))] // Miri does not support all SIMD intrinsics
3585 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3587 Simd<T, LANES>: AsMut<[T; LANES]>,
3588 T: simd::SimdElement,
3589 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3591 // These are expected to always match, as vector types are laid out like
3592 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3593 // might as well double-check since it'll optimize away anyhow.
3594 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3596 // SAFETY: The simd types have the same layout as arrays, just with
3597 // potentially-higher alignment, so the de-facto transmutes are sound.
3598 unsafe { self.align_to_mut() }
3601 /// Checks if the elements of this slice are sorted.
3603 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3604 /// slice yields exactly zero or one element, `true` is returned.
3606 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3607 /// implies that this function returns `false` if any two consecutive items are not
3613 /// #![feature(is_sorted)]
3614 /// let empty: [i32; 0] = [];
3616 /// assert!([1, 2, 2, 9].is_sorted());
3617 /// assert!(![1, 3, 2, 4].is_sorted());
3618 /// assert!([0].is_sorted());
3619 /// assert!(empty.is_sorted());
3620 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3623 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3624 pub fn is_sorted(&self) -> bool
3628 self.is_sorted_by(|a, b| a.partial_cmp(b))
3631 /// Checks if the elements of this slice are sorted using the given comparator function.
3633 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3634 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3635 /// [`is_sorted`]; see its documentation for more information.
3637 /// [`is_sorted`]: slice::is_sorted
3638 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3639 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3641 F: FnMut(&T, &T) -> Option<Ordering>,
3643 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3646 /// Checks if the elements of this slice are sorted using the given key extraction function.
3648 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3649 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3650 /// documentation for more information.
3652 /// [`is_sorted`]: slice::is_sorted
3657 /// #![feature(is_sorted)]
3659 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3660 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3663 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3664 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3669 self.iter().is_sorted_by_key(f)
3672 /// Returns the index of the partition point according to the given predicate
3673 /// (the index of the first element of the second partition).
3675 /// The slice is assumed to be partitioned according to the given predicate.
3676 /// This means that all elements for which the predicate returns true are at the start of the slice
3677 /// and all elements for which the predicate returns false are at the end.
3678 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3679 /// (all odd numbers are at the start, all even at the end).
3681 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3682 /// as this method performs a kind of binary search.
3684 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3686 /// [`binary_search`]: slice::binary_search
3687 /// [`binary_search_by`]: slice::binary_search_by
3688 /// [`binary_search_by_key`]: slice::binary_search_by_key
3693 /// let v = [1, 2, 3, 3, 5, 6, 7];
3694 /// let i = v.partition_point(|&x| x < 5);
3696 /// assert_eq!(i, 4);
3697 /// assert!(v[..i].iter().all(|&x| x < 5));
3698 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3700 #[stable(feature = "partition_point", since = "1.52.0")]
3701 pub fn partition_point<P>(&self, mut pred: P) -> usize
3703 P: FnMut(&T) -> bool,
3705 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3708 /// Removes the subslice corresponding to the given range
3709 /// and returns a reference to it.
3711 /// Returns `None` and does not modify the slice if the given
3712 /// range is out of bounds.
3714 /// Note that this method only accepts one-sided ranges such as
3715 /// `2..` or `..6`, but not `2..6`.
3719 /// Taking the first three elements of a slice:
3722 /// #![feature(slice_take)]
3724 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3725 /// let mut first_three = slice.take(..3).unwrap();
3727 /// assert_eq!(slice, &['d']);
3728 /// assert_eq!(first_three, &['a', 'b', 'c']);
3731 /// Taking the last two elements of a slice:
3734 /// #![feature(slice_take)]
3736 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3737 /// let mut tail = slice.take(2..).unwrap();
3739 /// assert_eq!(slice, &['a', 'b']);
3740 /// assert_eq!(tail, &['c', 'd']);
3743 /// Getting `None` when `range` is out of bounds:
3746 /// #![feature(slice_take)]
3748 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3750 /// assert_eq!(None, slice.take(5..));
3751 /// assert_eq!(None, slice.take(..5));
3752 /// assert_eq!(None, slice.take(..=4));
3753 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3754 /// assert_eq!(Some(expected), slice.take(..4));
3757 #[must_use = "method does not modify the slice if the range is out of bounds"]
3758 #[unstable(feature = "slice_take", issue = "62280")]
3759 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3760 let (direction, split_index) = split_point_of(range)?;
3761 if split_index > self.len() {
3764 let (front, back) = self.split_at(split_index);
3766 Direction::Front => {
3770 Direction::Back => {
3777 /// Removes the subslice corresponding to the given range
3778 /// and returns a mutable reference to it.
3780 /// Returns `None` and does not modify the slice if the given
3781 /// range is out of bounds.
3783 /// Note that this method only accepts one-sided ranges such as
3784 /// `2..` or `..6`, but not `2..6`.
3788 /// Taking the first three elements of a slice:
3791 /// #![feature(slice_take)]
3793 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3794 /// let mut first_three = slice.take_mut(..3).unwrap();
3796 /// assert_eq!(slice, &mut ['d']);
3797 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3800 /// Taking the last two elements of a slice:
3803 /// #![feature(slice_take)]
3805 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3806 /// let mut tail = slice.take_mut(2..).unwrap();
3808 /// assert_eq!(slice, &mut ['a', 'b']);
3809 /// assert_eq!(tail, &mut ['c', 'd']);
3812 /// Getting `None` when `range` is out of bounds:
3815 /// #![feature(slice_take)]
3817 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3819 /// assert_eq!(None, slice.take_mut(5..));
3820 /// assert_eq!(None, slice.take_mut(..5));
3821 /// assert_eq!(None, slice.take_mut(..=4));
3822 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3823 /// assert_eq!(Some(expected), slice.take_mut(..4));
3826 #[must_use = "method does not modify the slice if the range is out of bounds"]
3827 #[unstable(feature = "slice_take", issue = "62280")]
3828 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3829 self: &mut &'a mut Self,
3831 ) -> Option<&'a mut Self> {
3832 let (direction, split_index) = split_point_of(range)?;
3833 if split_index > self.len() {
3836 let (front, back) = mem::take(self).split_at_mut(split_index);
3838 Direction::Front => {
3842 Direction::Back => {
3849 /// Removes the first element of the slice and returns a reference
3852 /// Returns `None` if the slice is empty.
3857 /// #![feature(slice_take)]
3859 /// let mut slice: &[_] = &['a', 'b', 'c'];
3860 /// let first = slice.take_first().unwrap();
3862 /// assert_eq!(slice, &['b', 'c']);
3863 /// assert_eq!(first, &'a');
3866 #[unstable(feature = "slice_take", issue = "62280")]
3867 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3868 let (first, rem) = self.split_first()?;
3873 /// Removes the first element of the slice and returns a mutable
3874 /// reference to it.
3876 /// Returns `None` if the slice is empty.
3881 /// #![feature(slice_take)]
3883 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3884 /// let first = slice.take_first_mut().unwrap();
3887 /// assert_eq!(slice, &['b', 'c']);
3888 /// assert_eq!(first, &'d');
3891 #[unstable(feature = "slice_take", issue = "62280")]
3892 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3893 let (first, rem) = mem::take(self).split_first_mut()?;
3898 /// Removes the last element of the slice and returns a reference
3901 /// Returns `None` if the slice is empty.
3906 /// #![feature(slice_take)]
3908 /// let mut slice: &[_] = &['a', 'b', 'c'];
3909 /// let last = slice.take_last().unwrap();
3911 /// assert_eq!(slice, &['a', 'b']);
3912 /// assert_eq!(last, &'c');
3915 #[unstable(feature = "slice_take", issue = "62280")]
3916 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3917 let (last, rem) = self.split_last()?;
3922 /// Removes the last element of the slice and returns a mutable
3923 /// reference to it.
3925 /// Returns `None` if the slice is empty.
3930 /// #![feature(slice_take)]
3932 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3933 /// let last = slice.take_last_mut().unwrap();
3936 /// assert_eq!(slice, &['a', 'b']);
3937 /// assert_eq!(last, &'d');
3940 #[unstable(feature = "slice_take", issue = "62280")]
3941 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3942 let (last, rem) = mem::take(self).split_last_mut()?;
3948 trait CloneFromSpec<T> {
3949 fn spec_clone_from(&mut self, src: &[T]);
3952 impl<T> CloneFromSpec<T> for [T]
3957 default fn spec_clone_from(&mut self, src: &[T]) {
3958 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3959 // NOTE: We need to explicitly slice them to the same length
3960 // to make it easier for the optimizer to elide bounds checking.
3961 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3962 let len = self.len();
3963 let src = &src[..len];
3965 self[i].clone_from(&src[i]);
3970 impl<T> CloneFromSpec<T> for [T]
3975 fn spec_clone_from(&mut self, src: &[T]) {
3976 self.copy_from_slice(src);
3980 #[stable(feature = "rust1", since = "1.0.0")]
3981 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3982 impl<T> const Default for &[T] {
3983 /// Creates an empty slice.
3984 fn default() -> Self {
3989 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3990 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3991 impl<T> const Default for &mut [T] {
3992 /// Creates a mutable empty slice.
3993 fn default() -> Self {
3998 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3999 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4000 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4001 /// `str`) to slices, and then this trait will be replaced or abolished.
4002 pub trait SlicePattern {
4003 /// The element type of the slice being matched on.
4006 /// Currently, the consumers of `SlicePattern` need a slice.
4007 fn as_slice(&self) -> &[Self::Item];
4010 #[stable(feature = "slice_strip", since = "1.51.0")]
4011 impl<T> SlicePattern for [T] {
4015 fn as_slice(&self) -> &[Self::Item] {
4020 #[stable(feature = "slice_strip", since = "1.51.0")]
4021 impl<T, const N: usize> SlicePattern for [T; N] {
4025 fn as_slice(&self) -> &[Self::Item] {