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::intrinsics::{assert_unsafe_precondition, exact_div};
11 use crate::marker::Copy;
13 use crate::num::NonZeroUsize;
14 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
15 use crate::option::Option;
16 use crate::option::Option::{None, Some};
18 use crate::result::Result;
19 use crate::result::Result::{Err, Ok};
20 use crate::simd::{self, Simd};
24 feature = "slice_internals",
26 reason = "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Chunks, ChunksMut, Windows};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{Iter, IterMut};
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter::{RSplit, RSplitMut};
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter::{ChunksExact, ChunksExactMut};
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter::{ArrayChunks, ArrayChunksMut};
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter::ArrayWindows;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter::{GroupBy, GroupByMut};
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter::{SplitInclusive, SplitInclusiveMut};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw::{from_raw_parts, from_raw_parts_mut};
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw::{from_mut, from_ref};
74 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
75 pub use raw::{from_mut_ptr_range, from_ptr_range};
77 // This function is public only because there is no other way to unit test heapsort.
78 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
79 pub use sort::heapsort;
81 #[stable(feature = "slice_get_slice", since = "1.28.0")]
82 pub use index::SliceIndex;
84 #[unstable(feature = "slice_range", issue = "76393")]
87 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
88 pub use ascii::EscapeAscii;
90 /// Calculates the direction and split point of a one-sided range.
92 /// This is a helper function for `take` and `take_mut` that returns
93 /// the direction of the split (front or back) as well as the index at
94 /// which to split. Returns `None` if the split index would overflow.
96 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
99 Some(match (range.start_bound(), range.end_bound()) {
100 (Unbounded, Excluded(i)) => (Direction::Front, *i),
101 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
102 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
103 (Included(i), Unbounded) => (Direction::Back, *i),
113 #[cfg_attr(bootstrap, lang = "slice")]
116 /// Returns the number of elements in the slice.
121 /// let a = [1, 2, 3];
122 /// assert_eq!(a.len(), 3);
124 #[lang = "slice_len_fn"]
125 #[stable(feature = "rust1", since = "1.0.0")]
126 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
129 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
130 pub const fn len(&self) -> usize {
131 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
132 // As of this writing this causes a "Const-stable functions can only call other
133 // const-stable functions" error.
135 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
136 // and PtrComponents<T> have the same memory layouts. Only std can make this
138 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
141 /// Returns `true` if the slice has a length of 0.
146 /// let a = [1, 2, 3];
147 /// assert!(!a.is_empty());
149 #[stable(feature = "rust1", since = "1.0.0")]
150 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
153 pub const fn is_empty(&self) -> bool {
157 /// Returns the first element of the slice, or `None` if it is empty.
162 /// let v = [10, 40, 30];
163 /// assert_eq!(Some(&10), v.first());
165 /// let w: &[i32] = &[];
166 /// assert_eq!(None, w.first());
168 #[stable(feature = "rust1", since = "1.0.0")]
169 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
172 pub const fn first(&self) -> Option<&T> {
173 if let [first, ..] = self { Some(first) } else { None }
176 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
181 /// let x = &mut [0, 1, 2];
183 /// if let Some(first) = x.first_mut() {
186 /// assert_eq!(x, &[5, 1, 2]);
188 #[stable(feature = "rust1", since = "1.0.0")]
189 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
192 pub const fn first_mut(&mut self) -> Option<&mut T> {
193 if let [first, ..] = self { Some(first) } else { None }
196 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
201 /// let x = &[0, 1, 2];
203 /// if let Some((first, elements)) = x.split_first() {
204 /// assert_eq!(first, &0);
205 /// assert_eq!(elements, &[1, 2]);
208 #[stable(feature = "slice_splits", since = "1.5.0")]
209 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
212 pub const fn split_first(&self) -> Option<(&T, &[T])> {
213 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
216 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
221 /// let x = &mut [0, 1, 2];
223 /// if let Some((first, elements)) = x.split_first_mut() {
228 /// assert_eq!(x, &[3, 4, 5]);
230 #[stable(feature = "slice_splits", since = "1.5.0")]
231 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
234 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
235 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
238 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
243 /// let x = &[0, 1, 2];
245 /// if let Some((last, elements)) = x.split_last() {
246 /// assert_eq!(last, &2);
247 /// assert_eq!(elements, &[0, 1]);
250 #[stable(feature = "slice_splits", since = "1.5.0")]
251 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
254 pub const fn split_last(&self) -> Option<(&T, &[T])> {
255 if let [init @ .., last] = self { Some((last, init)) } else { None }
258 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
263 /// let x = &mut [0, 1, 2];
265 /// if let Some((last, elements)) = x.split_last_mut() {
270 /// assert_eq!(x, &[4, 5, 3]);
272 #[stable(feature = "slice_splits", since = "1.5.0")]
273 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
276 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
277 if let [init @ .., last] = self { Some((last, init)) } else { None }
280 /// Returns the last element of the slice, or `None` if it is empty.
285 /// let v = [10, 40, 30];
286 /// assert_eq!(Some(&30), v.last());
288 /// let w: &[i32] = &[];
289 /// assert_eq!(None, w.last());
291 #[stable(feature = "rust1", since = "1.0.0")]
292 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
295 pub const fn last(&self) -> Option<&T> {
296 if let [.., last] = self { Some(last) } else { None }
299 /// Returns a mutable pointer to the last item in the slice.
304 /// let x = &mut [0, 1, 2];
306 /// if let Some(last) = x.last_mut() {
309 /// assert_eq!(x, &[0, 1, 10]);
311 #[stable(feature = "rust1", since = "1.0.0")]
312 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
315 pub const fn last_mut(&mut self) -> Option<&mut T> {
316 if let [.., last] = self { Some(last) } else { None }
319 /// Returns a reference to an element or subslice depending on the type of
322 /// - If given a position, returns a reference to the element at that
323 /// position or `None` if out of bounds.
324 /// - If given a range, returns the subslice corresponding to that range,
325 /// or `None` if out of bounds.
330 /// let v = [10, 40, 30];
331 /// assert_eq!(Some(&40), v.get(1));
332 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
333 /// assert_eq!(None, v.get(3));
334 /// assert_eq!(None, v.get(0..4));
336 #[stable(feature = "rust1", since = "1.0.0")]
337 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
340 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
342 I: ~const SliceIndex<Self>,
347 /// Returns a mutable reference to an element or subslice depending on the
348 /// type of index (see [`get`]) or `None` if the index is out of bounds.
350 /// [`get`]: slice::get
355 /// let x = &mut [0, 1, 2];
357 /// if let Some(elem) = x.get_mut(1) {
360 /// assert_eq!(x, &[0, 42, 2]);
362 #[stable(feature = "rust1", since = "1.0.0")]
363 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
366 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
368 I: ~const SliceIndex<Self>,
373 /// Returns a reference to an element or subslice, without doing bounds
376 /// For a safe alternative see [`get`].
380 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
381 /// even if the resulting reference is not used.
383 /// [`get`]: slice::get
384 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
389 /// let x = &[1, 2, 4];
392 /// assert_eq!(x.get_unchecked(1), &2);
395 #[stable(feature = "rust1", since = "1.0.0")]
396 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
399 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
401 I: ~const SliceIndex<Self>,
403 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
404 // the slice is dereferenceable because `self` is a safe reference.
405 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
406 unsafe { &*index.get_unchecked(self) }
409 /// Returns a mutable reference to an element or subslice, without doing
412 /// For a safe alternative see [`get_mut`].
416 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
417 /// even if the resulting reference is not used.
419 /// [`get_mut`]: slice::get_mut
420 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
425 /// let x = &mut [1, 2, 4];
428 /// let elem = x.get_unchecked_mut(1);
431 /// assert_eq!(x, &[1, 13, 4]);
433 #[stable(feature = "rust1", since = "1.0.0")]
434 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
437 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
439 I: ~const SliceIndex<Self>,
441 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
442 // the slice is dereferenceable because `self` is a safe reference.
443 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
444 unsafe { &mut *index.get_unchecked_mut(self) }
447 /// Returns a raw pointer to the slice's buffer.
449 /// The caller must ensure that the slice outlives the pointer this
450 /// function returns, or else it will end up pointing to garbage.
452 /// The caller must also ensure that the memory the pointer (non-transitively) points to
453 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
454 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
456 /// Modifying the container referenced by this slice may cause its buffer
457 /// to be reallocated, which would also make any pointers to it invalid.
462 /// let x = &[1, 2, 4];
463 /// let x_ptr = x.as_ptr();
466 /// for i in 0..x.len() {
467 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
472 /// [`as_mut_ptr`]: slice::as_mut_ptr
473 #[stable(feature = "rust1", since = "1.0.0")]
474 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
477 pub const fn as_ptr(&self) -> *const T {
478 self as *const [T] as *const T
481 /// Returns an unsafe mutable pointer to the slice's buffer.
483 /// The caller must ensure that the slice outlives the pointer this
484 /// function returns, or else it will end up pointing to garbage.
486 /// Modifying the container referenced by this slice may cause its buffer
487 /// to be reallocated, which would also make any pointers to it invalid.
492 /// let x = &mut [1, 2, 4];
493 /// let x_ptr = x.as_mut_ptr();
496 /// for i in 0..x.len() {
497 /// *x_ptr.add(i) += 2;
500 /// assert_eq!(x, &[3, 4, 6]);
502 #[stable(feature = "rust1", since = "1.0.0")]
503 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
504 #[rustc_allow_const_fn_unstable(const_mut_refs)]
507 pub const fn as_mut_ptr(&mut self) -> *mut T {
508 self as *mut [T] as *mut T
511 /// Returns the two raw pointers spanning the slice.
513 /// The returned range is half-open, which means that the end pointer
514 /// points *one past* the last element of the slice. This way, an empty
515 /// slice is represented by two equal pointers, and the difference between
516 /// the two pointers represents the size of the slice.
518 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
519 /// requires extra caution, as it does not point to a valid element in the
522 /// This function is useful for interacting with foreign interfaces which
523 /// use two pointers to refer to a range of elements in memory, as is
526 /// It can also be useful to check if a pointer to an element refers to an
527 /// element of this slice:
530 /// let a = [1, 2, 3];
531 /// let x = &a[1] as *const _;
532 /// let y = &5 as *const _;
534 /// assert!(a.as_ptr_range().contains(&x));
535 /// assert!(!a.as_ptr_range().contains(&y));
538 /// [`as_ptr`]: slice::as_ptr
539 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
540 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
543 pub const fn as_ptr_range(&self) -> Range<*const T> {
544 let start = self.as_ptr();
545 // SAFETY: The `add` here is safe, because:
547 // - Both pointers are part of the same object, as pointing directly
548 // past the object also counts.
550 // - The size of the slice is never larger than isize::MAX bytes, as
552 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
553 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
554 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
555 // (This doesn't seem normative yet, but the very same assumption is
556 // made in many places, including the Index implementation of slices.)
558 // - There is no wrapping around involved, as slices do not wrap past
559 // the end of the address space.
561 // See the documentation of pointer::add.
562 let end = unsafe { start.add(self.len()) };
566 /// Returns the two unsafe mutable pointers spanning the slice.
568 /// The returned range is half-open, which means that the end pointer
569 /// points *one past* the last element of the slice. This way, an empty
570 /// slice is represented by two equal pointers, and the difference between
571 /// the two pointers represents the size of the slice.
573 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
574 /// pointer requires extra caution, as it does not point to a valid element
577 /// This function is useful for interacting with foreign interfaces which
578 /// use two pointers to refer to a range of elements in memory, as is
581 /// [`as_mut_ptr`]: slice::as_mut_ptr
582 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
583 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
584 #[rustc_allow_const_fn_unstable(const_mut_refs)]
587 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
588 let start = self.as_mut_ptr();
589 // SAFETY: See as_ptr_range() above for why `add` here is safe.
590 let end = unsafe { start.add(self.len()) };
594 /// Swaps two elements in the slice.
598 /// * a - The index of the first element
599 /// * b - The index of the second element
603 /// Panics if `a` or `b` are out of bounds.
608 /// let mut v = ["a", "b", "c", "d", "e"];
610 /// assert!(v == ["a", "b", "e", "d", "c"]);
612 #[stable(feature = "rust1", since = "1.0.0")]
613 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
616 pub const fn swap(&mut self, a: usize, b: usize) {
617 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
618 // Can't take two mutable loans from one vector, so instead use raw pointers.
619 let pa = ptr::addr_of_mut!(self[a]);
620 let pb = ptr::addr_of_mut!(self[b]);
621 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
622 // to elements in the slice and therefore are guaranteed to be valid and aligned.
623 // Note that accessing the elements behind `a` and `b` is checked and will
624 // panic when out of bounds.
630 /// Swaps two elements in the slice, without doing bounds checking.
632 /// For a safe alternative see [`swap`].
636 /// * a - The index of the first element
637 /// * b - The index of the second element
641 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
642 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
647 /// #![feature(slice_swap_unchecked)]
649 /// let mut v = ["a", "b", "c", "d"];
650 /// // SAFETY: we know that 1 and 3 are both indices of the slice
651 /// unsafe { v.swap_unchecked(1, 3) };
652 /// assert!(v == ["a", "d", "c", "b"]);
655 /// [`swap`]: slice::swap
656 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
657 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
658 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
659 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
660 let ptr = self.as_mut_ptr();
661 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
663 assert_unsafe_precondition!(a < self.len() && b < self.len());
664 ptr::swap(ptr.add(a), ptr.add(b));
668 /// Reverses the order of elements in the slice, in place.
673 /// let mut v = [1, 2, 3];
675 /// assert!(v == [3, 2, 1]);
677 #[stable(feature = "rust1", since = "1.0.0")]
679 pub fn reverse(&mut self) {
680 let half_len = self.len() / 2;
681 let Range { start, end } = self.as_mut_ptr_range();
683 // These slices will skip the middle item for an odd length,
684 // since that one doesn't need to move.
685 let (front_half, back_half) =
686 // SAFETY: Both are subparts of the original slice, so the memory
687 // range is valid, and they don't overlap because they're each only
688 // half (or less) of the original slice.
691 slice::from_raw_parts_mut(start, half_len),
692 slice::from_raw_parts_mut(end.sub(half_len), half_len),
696 // Introducing a function boundary here means that the two halves
697 // get `noalias` markers, allowing better optimization as LLVM
698 // knows that they're disjoint, unlike in the original slice.
699 revswap(front_half, back_half, half_len);
702 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
703 debug_assert_eq!(a.len(), n);
704 debug_assert_eq!(b.len(), n);
706 // Because this function is first compiled in isolation,
707 // this check tells LLVM that the indexing below is
708 // in-bounds. Then after inlining -- once the actual
709 // lengths of the slices are known -- it's removed.
710 let (a, b) = (&mut a[..n], &mut b[..n]);
713 mem::swap(&mut a[i], &mut b[n - 1 - i]);
718 /// Returns an iterator over the slice.
723 /// let x = &[1, 2, 4];
724 /// let mut iterator = x.iter();
726 /// assert_eq!(iterator.next(), Some(&1));
727 /// assert_eq!(iterator.next(), Some(&2));
728 /// assert_eq!(iterator.next(), Some(&4));
729 /// assert_eq!(iterator.next(), None);
731 #[stable(feature = "rust1", since = "1.0.0")]
733 pub fn iter(&self) -> Iter<'_, T> {
737 /// Returns an iterator that allows modifying each value.
742 /// let x = &mut [1, 2, 4];
743 /// for elem in x.iter_mut() {
746 /// assert_eq!(x, &[3, 4, 6]);
748 #[stable(feature = "rust1", since = "1.0.0")]
750 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
754 /// Returns an iterator over all contiguous windows of length
755 /// `size`. The windows overlap. If the slice is shorter than
756 /// `size`, the iterator returns no values.
760 /// Panics if `size` is 0.
765 /// let slice = ['r', 'u', 's', 't'];
766 /// let mut iter = slice.windows(2);
767 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
768 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
769 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
770 /// assert!(iter.next().is_none());
773 /// If the slice is shorter than `size`:
776 /// let slice = ['f', 'o', 'o'];
777 /// let mut iter = slice.windows(4);
778 /// assert!(iter.next().is_none());
780 #[stable(feature = "rust1", since = "1.0.0")]
782 pub fn windows(&self, size: usize) -> Windows<'_, T> {
783 let size = NonZeroUsize::new(size).expect("size is zero");
784 Windows::new(self, size)
787 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
788 /// beginning of the slice.
790 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
791 /// slice, then the last chunk will not have length `chunk_size`.
793 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
794 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
799 /// Panics if `chunk_size` is 0.
804 /// let slice = ['l', 'o', 'r', 'e', 'm'];
805 /// let mut iter = slice.chunks(2);
806 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
807 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
808 /// assert_eq!(iter.next().unwrap(), &['m']);
809 /// assert!(iter.next().is_none());
812 /// [`chunks_exact`]: slice::chunks_exact
813 /// [`rchunks`]: slice::rchunks
814 #[stable(feature = "rust1", since = "1.0.0")]
816 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
817 assert_ne!(chunk_size, 0);
818 Chunks::new(self, chunk_size)
821 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
822 /// beginning of the slice.
824 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
825 /// length of the slice, then the last chunk will not have length `chunk_size`.
827 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
828 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
829 /// the end of the slice.
833 /// Panics if `chunk_size` is 0.
838 /// let v = &mut [0, 0, 0, 0, 0];
839 /// let mut count = 1;
841 /// for chunk in v.chunks_mut(2) {
842 /// for elem in chunk.iter_mut() {
847 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
850 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
851 /// [`rchunks_mut`]: slice::rchunks_mut
852 #[stable(feature = "rust1", since = "1.0.0")]
854 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
855 assert_ne!(chunk_size, 0);
856 ChunksMut::new(self, chunk_size)
859 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
860 /// beginning of the slice.
862 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
863 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
864 /// from the `remainder` function of the iterator.
866 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
867 /// resulting code better than in the case of [`chunks`].
869 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
870 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
874 /// Panics if `chunk_size` is 0.
879 /// let slice = ['l', 'o', 'r', 'e', 'm'];
880 /// let mut iter = slice.chunks_exact(2);
881 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
882 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
883 /// assert!(iter.next().is_none());
884 /// assert_eq!(iter.remainder(), &['m']);
887 /// [`chunks`]: slice::chunks
888 /// [`rchunks_exact`]: slice::rchunks_exact
889 #[stable(feature = "chunks_exact", since = "1.31.0")]
891 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
892 assert_ne!(chunk_size, 0);
893 ChunksExact::new(self, chunk_size)
896 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
897 /// beginning of the slice.
899 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
900 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
901 /// retrieved from the `into_remainder` function of the iterator.
903 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
904 /// resulting code better than in the case of [`chunks_mut`].
906 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
907 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
912 /// Panics if `chunk_size` is 0.
917 /// let v = &mut [0, 0, 0, 0, 0];
918 /// let mut count = 1;
920 /// for chunk in v.chunks_exact_mut(2) {
921 /// for elem in chunk.iter_mut() {
926 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
929 /// [`chunks_mut`]: slice::chunks_mut
930 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
931 #[stable(feature = "chunks_exact", since = "1.31.0")]
933 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
934 assert_ne!(chunk_size, 0);
935 ChunksExactMut::new(self, chunk_size)
938 /// Splits the slice into a slice of `N`-element arrays,
939 /// assuming that there's no remainder.
943 /// This may only be called when
944 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
950 /// #![feature(slice_as_chunks)]
951 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
952 /// let chunks: &[[char; 1]] =
953 /// // SAFETY: 1-element chunks never have remainder
954 /// unsafe { slice.as_chunks_unchecked() };
955 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
956 /// let chunks: &[[char; 3]] =
957 /// // SAFETY: The slice length (6) is a multiple of 3
958 /// unsafe { slice.as_chunks_unchecked() };
959 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
961 /// // These would be unsound:
962 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
963 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
965 #[unstable(feature = "slice_as_chunks", issue = "74985")]
968 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
969 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
970 let new_len = unsafe {
971 assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
972 exact_div(self.len(), N)
974 // SAFETY: We cast a slice of `new_len * N` elements into
975 // a slice of `new_len` many `N` elements chunks.
976 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
979 /// Splits the slice into a slice of `N`-element arrays,
980 /// starting at the beginning of the slice,
981 /// and a remainder slice with length strictly less than `N`.
985 /// Panics if `N` is 0. This check will most probably get changed to a compile time
986 /// error before this method gets stabilized.
991 /// #![feature(slice_as_chunks)]
992 /// let slice = ['l', 'o', 'r', 'e', 'm'];
993 /// let (chunks, remainder) = slice.as_chunks();
994 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
995 /// assert_eq!(remainder, &['m']);
997 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1000 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1002 let len = self.len() / N;
1003 let (multiple_of_n, remainder) = self.split_at(len * N);
1004 // SAFETY: We already panicked for zero, and ensured by construction
1005 // that the length of the subslice is a multiple of N.
1006 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1007 (array_slice, remainder)
1010 /// Splits the slice into a slice of `N`-element arrays,
1011 /// starting at the end of the slice,
1012 /// and a remainder slice with length strictly less than `N`.
1016 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1017 /// error before this method gets stabilized.
1022 /// #![feature(slice_as_chunks)]
1023 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1024 /// let (remainder, chunks) = slice.as_rchunks();
1025 /// assert_eq!(remainder, &['l']);
1026 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1028 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1031 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1033 let len = self.len() / N;
1034 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1035 // SAFETY: We already panicked for zero, and ensured by construction
1036 // that the length of the subslice is a multiple of N.
1037 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1038 (remainder, array_slice)
1041 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1042 /// beginning of the slice.
1044 /// The chunks are array references and do not overlap. If `N` does not divide the
1045 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1046 /// retrieved from the `remainder` function of the iterator.
1048 /// This method is the const generic equivalent of [`chunks_exact`].
1052 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1053 /// error before this method gets stabilized.
1058 /// #![feature(array_chunks)]
1059 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1060 /// let mut iter = slice.array_chunks();
1061 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1062 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1063 /// assert!(iter.next().is_none());
1064 /// assert_eq!(iter.remainder(), &['m']);
1067 /// [`chunks_exact`]: slice::chunks_exact
1068 #[unstable(feature = "array_chunks", issue = "74985")]
1070 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1072 ArrayChunks::new(self)
1075 /// Splits the slice into a slice of `N`-element arrays,
1076 /// assuming that there's no remainder.
1080 /// This may only be called when
1081 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1087 /// #![feature(slice_as_chunks)]
1088 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1089 /// let chunks: &mut [[char; 1]] =
1090 /// // SAFETY: 1-element chunks never have remainder
1091 /// unsafe { slice.as_chunks_unchecked_mut() };
1092 /// chunks[0] = ['L'];
1093 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1094 /// let chunks: &mut [[char; 3]] =
1095 /// // SAFETY: The slice length (6) is a multiple of 3
1096 /// unsafe { slice.as_chunks_unchecked_mut() };
1097 /// chunks[1] = ['a', 'x', '?'];
1098 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1100 /// // These would be unsound:
1101 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1102 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1104 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1107 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1108 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1109 let new_len = unsafe {
1110 assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
1111 exact_div(self.len(), N)
1113 // SAFETY: We cast a slice of `new_len * N` elements into
1114 // a slice of `new_len` many `N` elements chunks.
1115 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1118 /// Splits the slice into a slice of `N`-element arrays,
1119 /// starting at the beginning of the slice,
1120 /// and a remainder slice with length strictly less than `N`.
1124 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1125 /// error before this method gets stabilized.
1130 /// #![feature(slice_as_chunks)]
1131 /// let v = &mut [0, 0, 0, 0, 0];
1132 /// let mut count = 1;
1134 /// let (chunks, remainder) = v.as_chunks_mut();
1135 /// remainder[0] = 9;
1136 /// for chunk in chunks {
1137 /// *chunk = [count; 2];
1140 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1142 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1145 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1147 let len = self.len() / N;
1148 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1149 // SAFETY: We already panicked for zero, and ensured by construction
1150 // that the length of the subslice is a multiple of N.
1151 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1152 (array_slice, remainder)
1155 /// Splits the slice into a slice of `N`-element arrays,
1156 /// starting at the end of the slice,
1157 /// and a remainder slice with length strictly less than `N`.
1161 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1162 /// error before this method gets stabilized.
1167 /// #![feature(slice_as_chunks)]
1168 /// let v = &mut [0, 0, 0, 0, 0];
1169 /// let mut count = 1;
1171 /// let (remainder, chunks) = v.as_rchunks_mut();
1172 /// remainder[0] = 9;
1173 /// for chunk in chunks {
1174 /// *chunk = [count; 2];
1177 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1179 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1182 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1184 let len = self.len() / N;
1185 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1186 // SAFETY: We already panicked for zero, and ensured by construction
1187 // that the length of the subslice is a multiple of N.
1188 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1189 (remainder, array_slice)
1192 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1193 /// beginning of the slice.
1195 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1196 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1197 /// can be retrieved from the `into_remainder` function of the iterator.
1199 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1203 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1204 /// error before this method gets stabilized.
1209 /// #![feature(array_chunks)]
1210 /// let v = &mut [0, 0, 0, 0, 0];
1211 /// let mut count = 1;
1213 /// for chunk in v.array_chunks_mut() {
1214 /// *chunk = [count; 2];
1217 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1220 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1221 #[unstable(feature = "array_chunks", issue = "74985")]
1223 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1225 ArrayChunksMut::new(self)
1228 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1229 /// starting at the beginning of the slice.
1231 /// This is the const generic equivalent of [`windows`].
1233 /// If `N` is greater than the size of the slice, it will return no windows.
1237 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1238 /// error before this method gets stabilized.
1243 /// #![feature(array_windows)]
1244 /// let slice = [0, 1, 2, 3];
1245 /// let mut iter = slice.array_windows();
1246 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1247 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1248 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1249 /// assert!(iter.next().is_none());
1252 /// [`windows`]: slice::windows
1253 #[unstable(feature = "array_windows", issue = "75027")]
1255 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1257 ArrayWindows::new(self)
1260 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1263 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1264 /// slice, then the last chunk will not have length `chunk_size`.
1266 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1267 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1272 /// Panics if `chunk_size` is 0.
1277 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1278 /// let mut iter = slice.rchunks(2);
1279 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1280 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1281 /// assert_eq!(iter.next().unwrap(), &['l']);
1282 /// assert!(iter.next().is_none());
1285 /// [`rchunks_exact`]: slice::rchunks_exact
1286 /// [`chunks`]: slice::chunks
1287 #[stable(feature = "rchunks", since = "1.31.0")]
1289 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1290 assert!(chunk_size != 0);
1291 RChunks::new(self, chunk_size)
1294 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1297 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1298 /// length of the slice, then the last chunk will not have length `chunk_size`.
1300 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1301 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1302 /// beginning of the slice.
1306 /// Panics if `chunk_size` is 0.
1311 /// let v = &mut [0, 0, 0, 0, 0];
1312 /// let mut count = 1;
1314 /// for chunk in v.rchunks_mut(2) {
1315 /// for elem in chunk.iter_mut() {
1320 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1323 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1324 /// [`chunks_mut`]: slice::chunks_mut
1325 #[stable(feature = "rchunks", since = "1.31.0")]
1327 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1328 assert!(chunk_size != 0);
1329 RChunksMut::new(self, chunk_size)
1332 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1333 /// end of the slice.
1335 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1336 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1337 /// from the `remainder` function of the iterator.
1339 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1340 /// resulting code better than in the case of [`chunks`].
1342 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1343 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1348 /// Panics if `chunk_size` is 0.
1353 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1354 /// let mut iter = slice.rchunks_exact(2);
1355 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1356 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1357 /// assert!(iter.next().is_none());
1358 /// assert_eq!(iter.remainder(), &['l']);
1361 /// [`chunks`]: slice::chunks
1362 /// [`rchunks`]: slice::rchunks
1363 /// [`chunks_exact`]: slice::chunks_exact
1364 #[stable(feature = "rchunks", since = "1.31.0")]
1366 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1367 assert!(chunk_size != 0);
1368 RChunksExact::new(self, chunk_size)
1371 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1374 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1375 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1376 /// retrieved from the `into_remainder` function of the iterator.
1378 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1379 /// resulting code better than in the case of [`chunks_mut`].
1381 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1382 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1387 /// Panics if `chunk_size` is 0.
1392 /// let v = &mut [0, 0, 0, 0, 0];
1393 /// let mut count = 1;
1395 /// for chunk in v.rchunks_exact_mut(2) {
1396 /// for elem in chunk.iter_mut() {
1401 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1404 /// [`chunks_mut`]: slice::chunks_mut
1405 /// [`rchunks_mut`]: slice::rchunks_mut
1406 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1407 #[stable(feature = "rchunks", since = "1.31.0")]
1409 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1410 assert!(chunk_size != 0);
1411 RChunksExactMut::new(self, chunk_size)
1414 /// Returns an iterator over the slice producing non-overlapping runs
1415 /// of elements using the predicate to separate them.
1417 /// The predicate is called on two elements following themselves,
1418 /// it means the predicate is called on `slice[0]` and `slice[1]`
1419 /// then on `slice[1]` and `slice[2]` and so on.
1424 /// #![feature(slice_group_by)]
1426 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1428 /// let mut iter = slice.group_by(|a, b| a == b);
1430 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1431 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1432 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1433 /// assert_eq!(iter.next(), None);
1436 /// This method can be used to extract the sorted subslices:
1439 /// #![feature(slice_group_by)]
1441 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1443 /// let mut iter = slice.group_by(|a, b| a <= b);
1445 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1446 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1447 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1448 /// assert_eq!(iter.next(), None);
1450 #[unstable(feature = "slice_group_by", issue = "80552")]
1452 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1454 F: FnMut(&T, &T) -> bool,
1456 GroupBy::new(self, pred)
1459 /// Returns an iterator over the slice producing non-overlapping mutable
1460 /// runs of elements using the predicate to separate them.
1462 /// The predicate is called on two elements following themselves,
1463 /// it means the predicate is called on `slice[0]` and `slice[1]`
1464 /// then on `slice[1]` and `slice[2]` and so on.
1469 /// #![feature(slice_group_by)]
1471 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1473 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1475 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1476 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1477 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1478 /// assert_eq!(iter.next(), None);
1481 /// This method can be used to extract the sorted subslices:
1484 /// #![feature(slice_group_by)]
1486 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1488 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1490 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1491 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1492 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1493 /// assert_eq!(iter.next(), None);
1495 #[unstable(feature = "slice_group_by", issue = "80552")]
1497 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1499 F: FnMut(&T, &T) -> bool,
1501 GroupByMut::new(self, pred)
1504 /// Divides one slice into two at an index.
1506 /// The first will contain all indices from `[0, mid)` (excluding
1507 /// the index `mid` itself) and the second will contain all
1508 /// indices from `[mid, len)` (excluding the index `len` itself).
1512 /// Panics if `mid > len`.
1517 /// let v = [1, 2, 3, 4, 5, 6];
1520 /// let (left, right) = v.split_at(0);
1521 /// assert_eq!(left, []);
1522 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1526 /// let (left, right) = v.split_at(2);
1527 /// assert_eq!(left, [1, 2]);
1528 /// assert_eq!(right, [3, 4, 5, 6]);
1532 /// let (left, right) = v.split_at(6);
1533 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1534 /// assert_eq!(right, []);
1537 #[stable(feature = "rust1", since = "1.0.0")]
1541 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1542 assert!(mid <= self.len());
1543 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1544 // fulfills the requirements of `from_raw_parts_mut`.
1545 unsafe { self.split_at_unchecked(mid) }
1548 /// Divides one mutable slice into two at an index.
1550 /// The first will contain all indices from `[0, mid)` (excluding
1551 /// the index `mid` itself) and the second will contain all
1552 /// indices from `[mid, len)` (excluding the index `len` itself).
1556 /// Panics if `mid > len`.
1561 /// let mut v = [1, 0, 3, 0, 5, 6];
1562 /// let (left, right) = v.split_at_mut(2);
1563 /// assert_eq!(left, [1, 0]);
1564 /// assert_eq!(right, [3, 0, 5, 6]);
1567 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1569 #[stable(feature = "rust1", since = "1.0.0")]
1573 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1574 assert!(mid <= self.len());
1575 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1576 // fulfills the requirements of `from_raw_parts_mut`.
1577 unsafe { self.split_at_mut_unchecked(mid) }
1580 /// Divides one slice into two at an index, without doing bounds checking.
1582 /// The first will contain all indices from `[0, mid)` (excluding
1583 /// the index `mid` itself) and the second will contain all
1584 /// indices from `[mid, len)` (excluding the index `len` itself).
1586 /// For a safe alternative see [`split_at`].
1590 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1591 /// even if the resulting reference is not used. The caller has to ensure that
1592 /// `0 <= mid <= self.len()`.
1594 /// [`split_at`]: slice::split_at
1595 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1600 /// #![feature(slice_split_at_unchecked)]
1602 /// let v = [1, 2, 3, 4, 5, 6];
1605 /// let (left, right) = v.split_at_unchecked(0);
1606 /// assert_eq!(left, []);
1607 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1611 /// let (left, right) = v.split_at_unchecked(2);
1612 /// assert_eq!(left, [1, 2]);
1613 /// assert_eq!(right, [3, 4, 5, 6]);
1617 /// let (left, right) = v.split_at_unchecked(6);
1618 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1619 /// assert_eq!(right, []);
1622 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1625 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1626 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1627 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1630 /// Divides one mutable slice into two at an index, without doing bounds checking.
1632 /// The first will contain all indices from `[0, mid)` (excluding
1633 /// the index `mid` itself) and the second will contain all
1634 /// indices from `[mid, len)` (excluding the index `len` itself).
1636 /// For a safe alternative see [`split_at_mut`].
1640 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1641 /// even if the resulting reference is not used. The caller has to ensure that
1642 /// `0 <= mid <= self.len()`.
1644 /// [`split_at_mut`]: slice::split_at_mut
1645 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1650 /// #![feature(slice_split_at_unchecked)]
1652 /// let mut v = [1, 0, 3, 0, 5, 6];
1653 /// // scoped to restrict the lifetime of the borrows
1655 /// let (left, right) = v.split_at_mut_unchecked(2);
1656 /// assert_eq!(left, [1, 0]);
1657 /// assert_eq!(right, [3, 0, 5, 6]);
1661 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1663 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1666 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1667 let len = self.len();
1668 let ptr = self.as_mut_ptr();
1670 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1672 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1675 assert_unsafe_precondition!(mid <= len);
1676 (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
1680 /// Divides one slice into an array and a remainder slice at an index.
1682 /// The array will contain all indices from `[0, N)` (excluding
1683 /// the index `N` itself) and the slice will contain all
1684 /// indices from `[N, len)` (excluding the index `len` itself).
1688 /// Panics if `N > len`.
1693 /// #![feature(split_array)]
1695 /// let v = &[1, 2, 3, 4, 5, 6][..];
1698 /// let (left, right) = v.split_array_ref::<0>();
1699 /// assert_eq!(left, &[]);
1700 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1704 /// let (left, right) = v.split_array_ref::<2>();
1705 /// assert_eq!(left, &[1, 2]);
1706 /// assert_eq!(right, [3, 4, 5, 6]);
1710 /// let (left, right) = v.split_array_ref::<6>();
1711 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1712 /// assert_eq!(right, []);
1715 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1719 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1720 let (a, b) = self.split_at(N);
1721 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1722 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1725 /// Divides one mutable slice into an array and a remainder slice at an index.
1727 /// The array will contain all indices from `[0, N)` (excluding
1728 /// the index `N` itself) and the slice will contain all
1729 /// indices from `[N, len)` (excluding the index `len` itself).
1733 /// Panics if `N > len`.
1738 /// #![feature(split_array)]
1740 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1741 /// let (left, right) = v.split_array_mut::<2>();
1742 /// assert_eq!(left, &mut [1, 0]);
1743 /// assert_eq!(right, [3, 0, 5, 6]);
1746 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1748 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1752 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1753 let (a, b) = self.split_at_mut(N);
1754 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1755 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1758 /// Divides one slice into an array and a remainder slice at an index from
1761 /// The slice will contain all indices from `[0, len - N)` (excluding
1762 /// the index `len - N` itself) and the array will contain all
1763 /// indices from `[len - N, len)` (excluding the index `len` itself).
1767 /// Panics if `N > len`.
1772 /// #![feature(split_array)]
1774 /// let v = &[1, 2, 3, 4, 5, 6][..];
1777 /// let (left, right) = v.rsplit_array_ref::<0>();
1778 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1779 /// assert_eq!(right, &[]);
1783 /// let (left, right) = v.rsplit_array_ref::<2>();
1784 /// assert_eq!(left, [1, 2, 3, 4]);
1785 /// assert_eq!(right, &[5, 6]);
1789 /// let (left, right) = v.rsplit_array_ref::<6>();
1790 /// assert_eq!(left, []);
1791 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1794 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1797 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1798 assert!(N <= self.len());
1799 let (a, b) = self.split_at(self.len() - N);
1800 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1801 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1804 /// Divides one mutable slice into an array and a remainder slice at an
1805 /// index from the end.
1807 /// The slice will contain all indices from `[0, len - N)` (excluding
1808 /// the index `N` itself) and the array will contain all
1809 /// indices from `[len - N, len)` (excluding the index `len` itself).
1813 /// Panics if `N > len`.
1818 /// #![feature(split_array)]
1820 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1821 /// let (left, right) = v.rsplit_array_mut::<4>();
1822 /// assert_eq!(left, [1, 0]);
1823 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1826 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1828 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1831 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1832 assert!(N <= self.len());
1833 let (a, b) = self.split_at_mut(self.len() - N);
1834 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1835 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1838 /// Returns an iterator over subslices separated by elements that match
1839 /// `pred`. The matched element is not contained in the subslices.
1844 /// let slice = [10, 40, 33, 20];
1845 /// let mut iter = slice.split(|num| num % 3 == 0);
1847 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1848 /// assert_eq!(iter.next().unwrap(), &[20]);
1849 /// assert!(iter.next().is_none());
1852 /// If the first element is matched, an empty slice will be the first item
1853 /// returned by the iterator. Similarly, if the last element in the slice
1854 /// is matched, an empty slice will be the last item returned by the
1858 /// let slice = [10, 40, 33];
1859 /// let mut iter = slice.split(|num| num % 3 == 0);
1861 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1862 /// assert_eq!(iter.next().unwrap(), &[]);
1863 /// assert!(iter.next().is_none());
1866 /// If two matched elements are directly adjacent, an empty slice will be
1867 /// present between them:
1870 /// let slice = [10, 6, 33, 20];
1871 /// let mut iter = slice.split(|num| num % 3 == 0);
1873 /// assert_eq!(iter.next().unwrap(), &[10]);
1874 /// assert_eq!(iter.next().unwrap(), &[]);
1875 /// assert_eq!(iter.next().unwrap(), &[20]);
1876 /// assert!(iter.next().is_none());
1878 #[stable(feature = "rust1", since = "1.0.0")]
1880 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1882 F: FnMut(&T) -> bool,
1884 Split::new(self, pred)
1887 /// Returns an iterator over mutable subslices separated by elements that
1888 /// match `pred`. The matched element is not contained in the subslices.
1893 /// let mut v = [10, 40, 30, 20, 60, 50];
1895 /// for group in v.split_mut(|num| *num % 3 == 0) {
1898 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1900 #[stable(feature = "rust1", since = "1.0.0")]
1902 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1904 F: FnMut(&T) -> bool,
1906 SplitMut::new(self, pred)
1909 /// Returns an iterator over subslices separated by elements that match
1910 /// `pred`. The matched element is contained in the end of the previous
1911 /// subslice as a terminator.
1916 /// let slice = [10, 40, 33, 20];
1917 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1919 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1920 /// assert_eq!(iter.next().unwrap(), &[20]);
1921 /// assert!(iter.next().is_none());
1924 /// If the last element of the slice is matched,
1925 /// that element will be considered the terminator of the preceding slice.
1926 /// That slice will be the last item returned by the iterator.
1929 /// let slice = [3, 10, 40, 33];
1930 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1932 /// assert_eq!(iter.next().unwrap(), &[3]);
1933 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1934 /// assert!(iter.next().is_none());
1936 #[stable(feature = "split_inclusive", since = "1.51.0")]
1938 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1940 F: FnMut(&T) -> bool,
1942 SplitInclusive::new(self, pred)
1945 /// Returns an iterator over mutable subslices separated by elements that
1946 /// match `pred`. The matched element is contained in the previous
1947 /// subslice as a terminator.
1952 /// let mut v = [10, 40, 30, 20, 60, 50];
1954 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1955 /// let terminator_idx = group.len()-1;
1956 /// group[terminator_idx] = 1;
1958 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1960 #[stable(feature = "split_inclusive", since = "1.51.0")]
1962 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1964 F: FnMut(&T) -> bool,
1966 SplitInclusiveMut::new(self, pred)
1969 /// Returns an iterator over subslices separated by elements that match
1970 /// `pred`, starting at the end of the slice and working backwards.
1971 /// The matched element is not contained in the subslices.
1976 /// let slice = [11, 22, 33, 0, 44, 55];
1977 /// let mut iter = slice.rsplit(|num| *num == 0);
1979 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1980 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1981 /// assert_eq!(iter.next(), None);
1984 /// As with `split()`, if the first or last element is matched, an empty
1985 /// slice will be the first (or last) item returned by the iterator.
1988 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1989 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1990 /// assert_eq!(it.next().unwrap(), &[]);
1991 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1992 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1993 /// assert_eq!(it.next().unwrap(), &[]);
1994 /// assert_eq!(it.next(), None);
1996 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1998 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
2000 F: FnMut(&T) -> bool,
2002 RSplit::new(self, pred)
2005 /// Returns an iterator over mutable subslices separated by elements that
2006 /// match `pred`, starting at the end of the slice and working
2007 /// backwards. The matched element is not contained in the subslices.
2012 /// let mut v = [100, 400, 300, 200, 600, 500];
2014 /// let mut count = 0;
2015 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
2017 /// group[0] = count;
2019 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
2022 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2024 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
2026 F: FnMut(&T) -> bool,
2028 RSplitMut::new(self, pred)
2031 /// Returns an iterator over subslices separated by elements that match
2032 /// `pred`, limited to returning at most `n` items. The matched element is
2033 /// not contained in the subslices.
2035 /// The last element returned, if any, will contain the remainder of the
2040 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2041 /// `[20, 60, 50]`):
2044 /// let v = [10, 40, 30, 20, 60, 50];
2046 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2047 /// println!("{group:?}");
2050 #[stable(feature = "rust1", since = "1.0.0")]
2052 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2054 F: FnMut(&T) -> bool,
2056 SplitN::new(self.split(pred), n)
2059 /// Returns an iterator over subslices separated by elements that match
2060 /// `pred`, limited to returning at most `n` items. The matched element is
2061 /// not contained in the subslices.
2063 /// The last element returned, if any, will contain the remainder of the
2069 /// let mut v = [10, 40, 30, 20, 60, 50];
2071 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2074 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2076 #[stable(feature = "rust1", since = "1.0.0")]
2078 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2080 F: FnMut(&T) -> bool,
2082 SplitNMut::new(self.split_mut(pred), n)
2085 /// Returns an iterator over subslices separated by elements that match
2086 /// `pred` limited to returning at most `n` items. This starts at the end of
2087 /// the slice and works backwards. The matched element is not contained in
2090 /// The last element returned, if any, will contain the remainder of the
2095 /// Print the slice split once, starting from the end, by numbers divisible
2096 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2099 /// let v = [10, 40, 30, 20, 60, 50];
2101 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2102 /// println!("{group:?}");
2105 #[stable(feature = "rust1", since = "1.0.0")]
2107 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2109 F: FnMut(&T) -> bool,
2111 RSplitN::new(self.rsplit(pred), n)
2114 /// Returns an iterator over subslices separated by elements that match
2115 /// `pred` limited to returning at most `n` items. This starts at the end of
2116 /// the slice and works backwards. The matched element is not contained in
2119 /// The last element returned, if any, will contain the remainder of the
2125 /// let mut s = [10, 40, 30, 20, 60, 50];
2127 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2130 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2132 #[stable(feature = "rust1", since = "1.0.0")]
2134 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2136 F: FnMut(&T) -> bool,
2138 RSplitNMut::new(self.rsplit_mut(pred), n)
2141 /// Returns `true` if the slice contains an element with the given value.
2146 /// let v = [10, 40, 30];
2147 /// assert!(v.contains(&30));
2148 /// assert!(!v.contains(&50));
2151 /// If you do not have a `&T`, but some other value that you can compare
2152 /// with one (for example, `String` implements `PartialEq<str>`), you can
2153 /// use `iter().any`:
2156 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2157 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2158 /// assert!(!v.iter().any(|e| e == "hi"));
2160 #[stable(feature = "rust1", since = "1.0.0")]
2163 pub fn contains(&self, x: &T) -> bool
2167 cmp::SliceContains::slice_contains(x, self)
2170 /// Returns `true` if `needle` is a prefix of the slice.
2175 /// let v = [10, 40, 30];
2176 /// assert!(v.starts_with(&[10]));
2177 /// assert!(v.starts_with(&[10, 40]));
2178 /// assert!(!v.starts_with(&[50]));
2179 /// assert!(!v.starts_with(&[10, 50]));
2182 /// Always returns `true` if `needle` is an empty slice:
2185 /// let v = &[10, 40, 30];
2186 /// assert!(v.starts_with(&[]));
2187 /// let v: &[u8] = &[];
2188 /// assert!(v.starts_with(&[]));
2190 #[stable(feature = "rust1", since = "1.0.0")]
2192 pub fn starts_with(&self, needle: &[T]) -> bool
2196 let n = needle.len();
2197 self.len() >= n && needle == &self[..n]
2200 /// Returns `true` if `needle` is a suffix of the slice.
2205 /// let v = [10, 40, 30];
2206 /// assert!(v.ends_with(&[30]));
2207 /// assert!(v.ends_with(&[40, 30]));
2208 /// assert!(!v.ends_with(&[50]));
2209 /// assert!(!v.ends_with(&[50, 30]));
2212 /// Always returns `true` if `needle` is an empty slice:
2215 /// let v = &[10, 40, 30];
2216 /// assert!(v.ends_with(&[]));
2217 /// let v: &[u8] = &[];
2218 /// assert!(v.ends_with(&[]));
2220 #[stable(feature = "rust1", since = "1.0.0")]
2222 pub fn ends_with(&self, needle: &[T]) -> bool
2226 let (m, n) = (self.len(), needle.len());
2227 m >= n && needle == &self[m - n..]
2230 /// Returns a subslice with the prefix removed.
2232 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2233 /// If `prefix` is empty, simply returns the original slice.
2235 /// If the slice does not start with `prefix`, returns `None`.
2240 /// let v = &[10, 40, 30];
2241 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2242 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2243 /// assert_eq!(v.strip_prefix(&[50]), None);
2244 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2246 /// let prefix : &str = "he";
2247 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2248 /// Some(b"llo".as_ref()));
2250 #[must_use = "returns the subslice without modifying the original"]
2251 #[stable(feature = "slice_strip", since = "1.51.0")]
2252 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2256 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2257 let prefix = prefix.as_slice();
2258 let n = prefix.len();
2259 if n <= self.len() {
2260 let (head, tail) = self.split_at(n);
2268 /// Returns a subslice with the suffix removed.
2270 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2271 /// If `suffix` is empty, simply returns the original slice.
2273 /// If the slice does not end with `suffix`, returns `None`.
2278 /// let v = &[10, 40, 30];
2279 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2280 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2281 /// assert_eq!(v.strip_suffix(&[50]), None);
2282 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2284 #[must_use = "returns the subslice without modifying the original"]
2285 #[stable(feature = "slice_strip", since = "1.51.0")]
2286 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2290 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2291 let suffix = suffix.as_slice();
2292 let (len, n) = (self.len(), suffix.len());
2294 let (head, tail) = self.split_at(len - n);
2302 /// Binary searches this sorted slice for a given element.
2304 /// If the value is found then [`Result::Ok`] is returned, containing the
2305 /// index of the matching element. If there are multiple matches, then any
2306 /// one of the matches could be returned. The index is chosen
2307 /// deterministically, but is subject to change in future versions of Rust.
2308 /// If the value is not found then [`Result::Err`] is returned, containing
2309 /// the index where a matching element could be inserted while maintaining
2312 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2314 /// [`binary_search_by`]: slice::binary_search_by
2315 /// [`binary_search_by_key`]: slice::binary_search_by_key
2316 /// [`partition_point`]: slice::partition_point
2320 /// Looks up a series of four elements. The first is found, with a
2321 /// uniquely determined position; the second and third are not
2322 /// found; the fourth could match any position in `[1, 4]`.
2325 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2327 /// assert_eq!(s.binary_search(&13), Ok(9));
2328 /// assert_eq!(s.binary_search(&4), Err(7));
2329 /// assert_eq!(s.binary_search(&100), Err(13));
2330 /// let r = s.binary_search(&1);
2331 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2334 /// If you want to insert an item to a sorted vector, while maintaining
2338 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2340 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2341 /// s.insert(idx, num);
2342 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2344 #[stable(feature = "rust1", since = "1.0.0")]
2345 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2349 self.binary_search_by(|p| p.cmp(x))
2352 /// Binary searches this sorted slice with a comparator function.
2354 /// The comparator function should implement an order consistent
2355 /// with the sort order of the underlying slice, returning an
2356 /// order code that indicates whether its argument is `Less`,
2357 /// `Equal` or `Greater` the desired target.
2359 /// If the value is found then [`Result::Ok`] is returned, containing the
2360 /// index of the matching element. If there are multiple matches, then any
2361 /// one of the matches could be returned. The index is chosen
2362 /// deterministically, but is subject to change in future versions of Rust.
2363 /// If the value is not found then [`Result::Err`] is returned, containing
2364 /// the index where a matching element could be inserted while maintaining
2367 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2369 /// [`binary_search`]: slice::binary_search
2370 /// [`binary_search_by_key`]: slice::binary_search_by_key
2371 /// [`partition_point`]: slice::partition_point
2375 /// Looks up a series of four elements. The first is found, with a
2376 /// uniquely determined position; the second and third are not
2377 /// found; the fourth could match any position in `[1, 4]`.
2380 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2383 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2385 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2387 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2389 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2390 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2392 #[stable(feature = "rust1", since = "1.0.0")]
2394 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2396 F: FnMut(&'a T) -> Ordering,
2398 let mut size = self.len();
2400 let mut right = size;
2401 while left < right {
2402 let mid = left + size / 2;
2404 // SAFETY: the call is made safe by the following invariants:
2406 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2407 let cmp = f(unsafe { self.get_unchecked(mid) });
2409 // The reason why we use if/else control flow rather than match
2410 // is because match reorders comparison operations, which is perf sensitive.
2411 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2414 } else if cmp == Greater {
2417 // SAFETY: same as the `get_unchecked` above
2418 unsafe { crate::intrinsics::assume(mid < self.len()) };
2422 size = right - left;
2427 /// Binary searches this sorted slice with a key extraction function.
2429 /// Assumes that the slice is sorted by the key, for instance with
2430 /// [`sort_by_key`] using the same key extraction function.
2432 /// If the value is found then [`Result::Ok`] is returned, containing the
2433 /// index of the matching element. If there are multiple matches, then any
2434 /// one of the matches could be returned. The index is chosen
2435 /// deterministically, but is subject to change in future versions of Rust.
2436 /// If the value is not found then [`Result::Err`] is returned, containing
2437 /// the index where a matching element could be inserted while maintaining
2440 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2442 /// [`sort_by_key`]: slice::sort_by_key
2443 /// [`binary_search`]: slice::binary_search
2444 /// [`binary_search_by`]: slice::binary_search_by
2445 /// [`partition_point`]: slice::partition_point
2449 /// Looks up a series of four elements in a slice of pairs sorted by
2450 /// their second elements. The first is found, with a uniquely
2451 /// determined position; the second and third are not found; the
2452 /// fourth could match any position in `[1, 4]`.
2455 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2456 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2457 /// (1, 21), (2, 34), (4, 55)];
2459 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2460 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2461 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2462 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2463 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2465 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2466 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2467 // This breaks links when slice is displayed in core, but changing it to use relative links
2468 // would break when the item is re-exported. So allow the core links to be broken for now.
2469 #[allow(rustdoc::broken_intra_doc_links)]
2470 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2472 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2474 F: FnMut(&'a T) -> B,
2477 self.binary_search_by(|k| f(k).cmp(b))
2480 /// Sorts the slice, but might not preserve the order of equal elements.
2482 /// This sort is unstable (i.e., may reorder equal elements), in-place
2483 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2485 /// # Current implementation
2487 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2488 /// which combines the fast average case of randomized quicksort with the fast worst case of
2489 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2490 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2491 /// deterministic behavior.
2493 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2494 /// slice consists of several concatenated sorted sequences.
2499 /// let mut v = [-5, 4, 1, -3, 2];
2501 /// v.sort_unstable();
2502 /// assert!(v == [-5, -3, 1, 2, 4]);
2505 /// [pdqsort]: https://github.com/orlp/pdqsort
2506 #[stable(feature = "sort_unstable", since = "1.20.0")]
2508 pub fn sort_unstable(&mut self)
2512 sort::quicksort(self, |a, b| a.lt(b));
2515 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2518 /// This sort is unstable (i.e., may reorder equal elements), in-place
2519 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2521 /// The comparator function must define a total ordering for the elements in the slice. If
2522 /// the ordering is not total, the order of the elements is unspecified. An order is a
2523 /// total order if it is (for all `a`, `b` and `c`):
2525 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2526 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2528 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2529 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2532 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2533 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2534 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2537 /// # Current implementation
2539 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2540 /// which combines the fast average case of randomized quicksort with the fast worst case of
2541 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2542 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2543 /// deterministic behavior.
2545 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2546 /// slice consists of several concatenated sorted sequences.
2551 /// let mut v = [5, 4, 1, 3, 2];
2552 /// v.sort_unstable_by(|a, b| a.cmp(b));
2553 /// assert!(v == [1, 2, 3, 4, 5]);
2555 /// // reverse sorting
2556 /// v.sort_unstable_by(|a, b| b.cmp(a));
2557 /// assert!(v == [5, 4, 3, 2, 1]);
2560 /// [pdqsort]: https://github.com/orlp/pdqsort
2561 #[stable(feature = "sort_unstable", since = "1.20.0")]
2563 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2565 F: FnMut(&T, &T) -> Ordering,
2567 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2570 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2573 /// This sort is unstable (i.e., may reorder equal elements), in-place
2574 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2577 /// # Current implementation
2579 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2580 /// which combines the fast average case of randomized quicksort with the fast worst case of
2581 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2582 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2583 /// deterministic behavior.
2585 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2586 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2587 /// cases where the key function is expensive.
2592 /// let mut v = [-5i32, 4, 1, -3, 2];
2594 /// v.sort_unstable_by_key(|k| k.abs());
2595 /// assert!(v == [1, 2, -3, 4, -5]);
2598 /// [pdqsort]: https://github.com/orlp/pdqsort
2599 #[stable(feature = "sort_unstable", since = "1.20.0")]
2601 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2606 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2609 /// Reorder the slice such that the element at `index` is at its final sorted position.
2611 /// This reordering has the additional property that any value at position `i < index` will be
2612 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2613 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2614 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2615 /// element" in other libraries. It returns a triplet of the following values: all elements less
2616 /// than the one at the given index, the value at the given index, and all elements greater than
2617 /// the one at the given index.
2619 /// # Current implementation
2621 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2622 /// used for [`sort_unstable`].
2624 /// [`sort_unstable`]: slice::sort_unstable
2628 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2633 /// let mut v = [-5i32, 4, 1, -3, 2];
2635 /// // Find the median
2636 /// v.select_nth_unstable(2);
2638 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2639 /// // about the specified index.
2640 /// assert!(v == [-3, -5, 1, 2, 4] ||
2641 /// v == [-5, -3, 1, 2, 4] ||
2642 /// v == [-3, -5, 1, 4, 2] ||
2643 /// v == [-5, -3, 1, 4, 2]);
2645 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2647 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2651 let mut f = |a: &T, b: &T| a.lt(b);
2652 sort::partition_at_index(self, index, &mut f)
2655 /// Reorder the slice with a comparator function such that the element at `index` is at its
2656 /// final sorted position.
2658 /// This reordering has the additional property that any value at position `i < index` will be
2659 /// less than or equal to any value at a position `j > index` using the comparator function.
2660 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2661 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2662 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2663 /// values: all elements less than the one at the given index, the value at the given index,
2664 /// and all elements greater than the one at the given index, using the provided comparator
2667 /// # Current implementation
2669 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2670 /// used for [`sort_unstable`].
2672 /// [`sort_unstable`]: slice::sort_unstable
2676 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2681 /// let mut v = [-5i32, 4, 1, -3, 2];
2683 /// // Find the median as if the slice were sorted in descending order.
2684 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2686 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2687 /// // about the specified index.
2688 /// assert!(v == [2, 4, 1, -5, -3] ||
2689 /// v == [2, 4, 1, -3, -5] ||
2690 /// v == [4, 2, 1, -5, -3] ||
2691 /// v == [4, 2, 1, -3, -5]);
2693 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2695 pub fn select_nth_unstable_by<F>(
2699 ) -> (&mut [T], &mut T, &mut [T])
2701 F: FnMut(&T, &T) -> Ordering,
2703 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2704 sort::partition_at_index(self, index, &mut f)
2707 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2708 /// final sorted position.
2710 /// This reordering has the additional property that any value at position `i < index` will be
2711 /// less than or equal to any value at a position `j > index` using the key extraction function.
2712 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2713 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2714 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2715 /// values: all elements less than the one at the given index, the value at the given index, and
2716 /// all elements greater than the one at the given index, using the provided key extraction
2719 /// # Current implementation
2721 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2722 /// used for [`sort_unstable`].
2724 /// [`sort_unstable`]: slice::sort_unstable
2728 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2733 /// let mut v = [-5i32, 4, 1, -3, 2];
2735 /// // Return the median as if the array were sorted according to absolute value.
2736 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2738 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2739 /// // about the specified index.
2740 /// assert!(v == [1, 2, -3, 4, -5] ||
2741 /// v == [1, 2, -3, -5, 4] ||
2742 /// v == [2, 1, -3, 4, -5] ||
2743 /// v == [2, 1, -3, -5, 4]);
2745 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2747 pub fn select_nth_unstable_by_key<K, F>(
2751 ) -> (&mut [T], &mut T, &mut [T])
2756 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2757 sort::partition_at_index(self, index, &mut g)
2760 /// Moves all consecutive repeated elements to the end of the slice according to the
2761 /// [`PartialEq`] trait implementation.
2763 /// Returns two slices. The first contains no consecutive repeated elements.
2764 /// The second contains all the duplicates in no specified order.
2766 /// If the slice is sorted, the first returned slice contains no duplicates.
2771 /// #![feature(slice_partition_dedup)]
2773 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2775 /// let (dedup, duplicates) = slice.partition_dedup();
2777 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2778 /// assert_eq!(duplicates, [2, 3, 1]);
2780 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2782 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2786 self.partition_dedup_by(|a, b| a == b)
2789 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2790 /// a given equality relation.
2792 /// Returns two slices. The first contains no consecutive repeated elements.
2793 /// The second contains all the duplicates in no specified order.
2795 /// The `same_bucket` function is passed references to two elements from the slice and
2796 /// must determine if the elements compare equal. The elements are passed in opposite order
2797 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2798 /// at the end of the slice.
2800 /// If the slice is sorted, the first returned slice contains no duplicates.
2805 /// #![feature(slice_partition_dedup)]
2807 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2809 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2811 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2812 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2814 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2816 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2818 F: FnMut(&mut T, &mut T) -> bool,
2820 // Although we have a mutable reference to `self`, we cannot make
2821 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2822 // must ensure that the slice is in a valid state at all times.
2824 // The way that we handle this is by using swaps; we iterate
2825 // over all the elements, swapping as we go so that at the end
2826 // the elements we wish to keep are in the front, and those we
2827 // wish to reject are at the back. We can then split the slice.
2828 // This operation is still `O(n)`.
2830 // Example: We start in this state, where `r` represents "next
2831 // read" and `w` represents "next_write`.
2834 // +---+---+---+---+---+---+
2835 // | 0 | 1 | 1 | 2 | 3 | 3 |
2836 // +---+---+---+---+---+---+
2839 // Comparing self[r] against self[w-1], this is not a duplicate, so
2840 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2841 // r and w, leaving us with:
2844 // +---+---+---+---+---+---+
2845 // | 0 | 1 | 1 | 2 | 3 | 3 |
2846 // +---+---+---+---+---+---+
2849 // Comparing self[r] against self[w-1], this value is a duplicate,
2850 // so we increment `r` but leave everything else unchanged:
2853 // +---+---+---+---+---+---+
2854 // | 0 | 1 | 1 | 2 | 3 | 3 |
2855 // +---+---+---+---+---+---+
2858 // Comparing self[r] against self[w-1], this is not a duplicate,
2859 // so swap self[r] and self[w] and advance r and w:
2862 // +---+---+---+---+---+---+
2863 // | 0 | 1 | 2 | 1 | 3 | 3 |
2864 // +---+---+---+---+---+---+
2867 // Not a duplicate, repeat:
2870 // +---+---+---+---+---+---+
2871 // | 0 | 1 | 2 | 3 | 1 | 3 |
2872 // +---+---+---+---+---+---+
2875 // Duplicate, advance r. End of slice. Split at w.
2877 let len = self.len();
2879 return (self, &mut []);
2882 let ptr = self.as_mut_ptr();
2883 let mut next_read: usize = 1;
2884 let mut next_write: usize = 1;
2886 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2887 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2888 // one element before `ptr_write`, but `next_write` starts at 1, so
2889 // `prev_ptr_write` is never less than 0 and is inside the slice.
2890 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2891 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2892 // and `prev_ptr_write.offset(1)`.
2894 // `next_write` is also incremented at most once per loop at most meaning
2895 // no element is skipped when it may need to be swapped.
2897 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2898 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2899 // The explanation is simply that `next_read >= next_write` is always true,
2900 // thus `next_read > next_write - 1` is too.
2902 // Avoid bounds checks by using raw pointers.
2903 while next_read < len {
2904 let ptr_read = ptr.add(next_read);
2905 let prev_ptr_write = ptr.add(next_write - 1);
2906 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2907 if next_read != next_write {
2908 let ptr_write = prev_ptr_write.offset(1);
2909 mem::swap(&mut *ptr_read, &mut *ptr_write);
2917 self.split_at_mut(next_write)
2920 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2921 /// to the same key.
2923 /// Returns two slices. The first contains no consecutive repeated elements.
2924 /// The second contains all the duplicates in no specified order.
2926 /// If the slice is sorted, the first returned slice contains no duplicates.
2931 /// #![feature(slice_partition_dedup)]
2933 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2935 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2937 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2938 /// assert_eq!(duplicates, [21, 30, 13]);
2940 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2942 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2944 F: FnMut(&mut T) -> K,
2947 self.partition_dedup_by(|a, b| key(a) == key(b))
2950 /// Rotates the slice in-place such that the first `mid` elements of the
2951 /// slice move to the end while the last `self.len() - mid` elements move to
2952 /// the front. After calling `rotate_left`, the element previously at index
2953 /// `mid` will become the first element in the slice.
2957 /// This function will panic if `mid` is greater than the length of the
2958 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2963 /// Takes linear (in `self.len()`) time.
2968 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2969 /// a.rotate_left(2);
2970 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2973 /// Rotating a subslice:
2976 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2977 /// a[1..5].rotate_left(1);
2978 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2980 #[stable(feature = "slice_rotate", since = "1.26.0")]
2981 pub fn rotate_left(&mut self, mid: usize) {
2982 assert!(mid <= self.len());
2983 let k = self.len() - mid;
2984 let p = self.as_mut_ptr();
2986 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2987 // valid for reading and writing, as required by `ptr_rotate`.
2989 rotate::ptr_rotate(mid, p.add(mid), k);
2993 /// Rotates the slice in-place such that the first `self.len() - k`
2994 /// elements of the slice move to the end while the last `k` elements move
2995 /// to the front. After calling `rotate_right`, the element previously at
2996 /// index `self.len() - k` will become the first element in the slice.
3000 /// This function will panic if `k` is greater than the length of the
3001 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
3006 /// Takes linear (in `self.len()`) time.
3011 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3012 /// a.rotate_right(2);
3013 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
3016 /// Rotate a subslice:
3019 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3020 /// a[1..5].rotate_right(1);
3021 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
3023 #[stable(feature = "slice_rotate", since = "1.26.0")]
3024 pub fn rotate_right(&mut self, k: usize) {
3025 assert!(k <= self.len());
3026 let mid = self.len() - k;
3027 let p = self.as_mut_ptr();
3029 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3030 // valid for reading and writing, as required by `ptr_rotate`.
3032 rotate::ptr_rotate(mid, p.add(mid), k);
3036 /// Fills `self` with elements by cloning `value`.
3041 /// let mut buf = vec![0; 10];
3043 /// assert_eq!(buf, vec![1; 10]);
3045 #[doc(alias = "memset")]
3046 #[stable(feature = "slice_fill", since = "1.50.0")]
3047 pub fn fill(&mut self, value: T)
3051 specialize::SpecFill::spec_fill(self, value);
3054 /// Fills `self` with elements returned by calling a closure repeatedly.
3056 /// This method uses a closure to create new values. If you'd rather
3057 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3058 /// trait to generate values, you can pass [`Default::default`] as the
3061 /// [`fill`]: slice::fill
3066 /// let mut buf = vec![1; 10];
3067 /// buf.fill_with(Default::default);
3068 /// assert_eq!(buf, vec![0; 10]);
3070 #[doc(alias = "memset")]
3071 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3072 pub fn fill_with<F>(&mut self, mut f: F)
3081 /// Copies the elements from `src` into `self`.
3083 /// The length of `src` must be the same as `self`.
3087 /// This function will panic if the two slices have different lengths.
3091 /// Cloning two elements from a slice into another:
3094 /// let src = [1, 2, 3, 4];
3095 /// let mut dst = [0, 0];
3097 /// // Because the slices have to be the same length,
3098 /// // we slice the source slice from four elements
3099 /// // to two. It will panic if we don't do this.
3100 /// dst.clone_from_slice(&src[2..]);
3102 /// assert_eq!(src, [1, 2, 3, 4]);
3103 /// assert_eq!(dst, [3, 4]);
3106 /// Rust enforces that there can only be one mutable reference with no
3107 /// immutable references to a particular piece of data in a particular
3108 /// scope. Because of this, attempting to use `clone_from_slice` on a
3109 /// single slice will result in a compile failure:
3112 /// let mut slice = [1, 2, 3, 4, 5];
3114 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3117 /// To work around this, we can use [`split_at_mut`] to create two distinct
3118 /// sub-slices from a slice:
3121 /// let mut slice = [1, 2, 3, 4, 5];
3124 /// let (left, right) = slice.split_at_mut(2);
3125 /// left.clone_from_slice(&right[1..]);
3128 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3131 /// [`copy_from_slice`]: slice::copy_from_slice
3132 /// [`split_at_mut`]: slice::split_at_mut
3133 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3135 pub fn clone_from_slice(&mut self, src: &[T])
3139 self.spec_clone_from(src);
3142 /// Copies all elements from `src` into `self`, using a memcpy.
3144 /// The length of `src` must be the same as `self`.
3146 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3150 /// This function will panic if the two slices have different lengths.
3154 /// Copying two elements from a slice into another:
3157 /// let src = [1, 2, 3, 4];
3158 /// let mut dst = [0, 0];
3160 /// // Because the slices have to be the same length,
3161 /// // we slice the source slice from four elements
3162 /// // to two. It will panic if we don't do this.
3163 /// dst.copy_from_slice(&src[2..]);
3165 /// assert_eq!(src, [1, 2, 3, 4]);
3166 /// assert_eq!(dst, [3, 4]);
3169 /// Rust enforces that there can only be one mutable reference with no
3170 /// immutable references to a particular piece of data in a particular
3171 /// scope. Because of this, attempting to use `copy_from_slice` on a
3172 /// single slice will result in a compile failure:
3175 /// let mut slice = [1, 2, 3, 4, 5];
3177 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3180 /// To work around this, we can use [`split_at_mut`] to create two distinct
3181 /// sub-slices from a slice:
3184 /// let mut slice = [1, 2, 3, 4, 5];
3187 /// let (left, right) = slice.split_at_mut(2);
3188 /// left.copy_from_slice(&right[1..]);
3191 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3194 /// [`clone_from_slice`]: slice::clone_from_slice
3195 /// [`split_at_mut`]: slice::split_at_mut
3196 #[doc(alias = "memcpy")]
3197 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3199 pub fn copy_from_slice(&mut self, src: &[T])
3203 // The panic code path was put into a cold function to not bloat the
3208 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3210 "source slice length ({}) does not match destination slice length ({})",
3215 if self.len() != src.len() {
3216 len_mismatch_fail(self.len(), src.len());
3219 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3220 // checked to have the same length. The slices cannot overlap because
3221 // mutable references are exclusive.
3223 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3227 /// Copies elements from one part of the slice to another part of itself,
3228 /// using a memmove.
3230 /// `src` is the range within `self` to copy from. `dest` is the starting
3231 /// index of the range within `self` to copy to, which will have the same
3232 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3233 /// must be less than or equal to `self.len()`.
3237 /// This function will panic if either range exceeds the end of the slice,
3238 /// or if the end of `src` is before the start.
3242 /// Copying four bytes within a slice:
3245 /// let mut bytes = *b"Hello, World!";
3247 /// bytes.copy_within(1..5, 8);
3249 /// assert_eq!(&bytes, b"Hello, Wello!");
3251 #[stable(feature = "copy_within", since = "1.37.0")]
3253 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3257 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3258 let count = src_end - src_start;
3259 assert!(dest <= self.len() - count, "dest is out of bounds");
3260 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3261 // as have those for `ptr::add`.
3263 // Derive both `src_ptr` and `dest_ptr` from the same loan
3264 let ptr = self.as_mut_ptr();
3265 let src_ptr = ptr.add(src_start);
3266 let dest_ptr = ptr.add(dest);
3267 ptr::copy(src_ptr, dest_ptr, count);
3271 /// Swaps all elements in `self` with those in `other`.
3273 /// The length of `other` must be the same as `self`.
3277 /// This function will panic if the two slices have different lengths.
3281 /// Swapping two elements across slices:
3284 /// let mut slice1 = [0, 0];
3285 /// let mut slice2 = [1, 2, 3, 4];
3287 /// slice1.swap_with_slice(&mut slice2[2..]);
3289 /// assert_eq!(slice1, [3, 4]);
3290 /// assert_eq!(slice2, [1, 2, 0, 0]);
3293 /// Rust enforces that there can only be one mutable reference to a
3294 /// particular piece of data in a particular scope. Because of this,
3295 /// attempting to use `swap_with_slice` on a single slice will result in
3296 /// a compile failure:
3299 /// let mut slice = [1, 2, 3, 4, 5];
3300 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3303 /// To work around this, we can use [`split_at_mut`] to create two distinct
3304 /// mutable sub-slices from a slice:
3307 /// let mut slice = [1, 2, 3, 4, 5];
3310 /// let (left, right) = slice.split_at_mut(2);
3311 /// left.swap_with_slice(&mut right[1..]);
3314 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3317 /// [`split_at_mut`]: slice::split_at_mut
3318 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3320 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3321 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3322 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3323 // checked to have the same length. The slices cannot overlap because
3324 // mutable references are exclusive.
3326 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3330 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3331 fn align_to_offsets<U>(&self) -> (usize, usize) {
3332 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3333 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3335 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3336 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3337 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3339 // Formula to calculate this is:
3341 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3342 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3344 // Expanded and simplified:
3346 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3347 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3349 // Luckily since all this is constant-evaluated... performance here matters not!
3351 fn gcd(a: usize, b: usize) -> usize {
3352 use crate::intrinsics;
3353 // iterative stein’s algorithm
3354 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3355 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3357 // SAFETY: `a` and `b` are checked to be non-zero values.
3358 let (ctz_a, mut ctz_b) = unsafe {
3365 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3367 let k = ctz_a.min(ctz_b);
3368 let mut a = a >> ctz_a;
3371 // remove all factors of 2 from b
3374 mem::swap(&mut a, &mut b);
3377 // SAFETY: `b` is checked to be non-zero.
3382 ctz_b = intrinsics::cttz_nonzero(b);
3387 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3388 let ts: usize = mem::size_of::<U>() / gcd;
3389 let us: usize = mem::size_of::<T>() / gcd;
3391 // Armed with this knowledge, we can find how many `U`s we can fit!
3392 let us_len = self.len() / ts * us;
3393 // And how many `T`s will be in the trailing slice!
3394 let ts_len = self.len() % ts;
3398 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3401 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3402 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3403 /// length possible for a given type and input slice, but only your algorithm's performance
3404 /// should depend on that, not its correctness. It is permissible for all of the input data to
3405 /// be returned as the prefix or suffix slice.
3407 /// This method has no purpose when either input element `T` or output element `U` are
3408 /// zero-sized and will return the original slice without splitting anything.
3412 /// This method is essentially a `transmute` with respect to the elements in the returned
3413 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3421 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3422 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3423 /// // less_efficient_algorithm_for_bytes(prefix);
3424 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3425 /// // less_efficient_algorithm_for_bytes(suffix);
3428 #[stable(feature = "slice_align_to", since = "1.30.0")]
3430 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3431 // Note that most of this function will be constant-evaluated,
3432 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3433 // handle ZSTs specially, which is – don't handle them at all.
3434 return (self, &[], &[]);
3437 // First, find at what point do we split between the first and 2nd slice. Easy with
3438 // ptr.align_offset.
3439 let ptr = self.as_ptr();
3440 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3441 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3442 if offset > self.len() {
3445 let (left, rest) = self.split_at(offset);
3446 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3447 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3448 // since the caller guarantees that we can transmute `T` to `U` safely.
3452 from_raw_parts(rest.as_ptr() as *const U, us_len),
3453 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3459 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3462 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3463 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3464 /// length possible for a given type and input slice, but only your algorithm's performance
3465 /// should depend on that, not its correctness. It is permissible for all of the input data to
3466 /// be returned as the prefix or suffix slice.
3468 /// This method has no purpose when either input element `T` or output element `U` are
3469 /// zero-sized and will return the original slice without splitting anything.
3473 /// This method is essentially a `transmute` with respect to the elements in the returned
3474 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3482 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3483 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3484 /// // less_efficient_algorithm_for_bytes(prefix);
3485 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3486 /// // less_efficient_algorithm_for_bytes(suffix);
3489 #[stable(feature = "slice_align_to", since = "1.30.0")]
3491 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3492 // Note that most of this function will be constant-evaluated,
3493 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3494 // handle ZSTs specially, which is – don't handle them at all.
3495 return (self, &mut [], &mut []);
3498 // First, find at what point do we split between the first and 2nd slice. Easy with
3499 // ptr.align_offset.
3500 let ptr = self.as_ptr();
3501 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3502 // rest of the method. This is done by passing a pointer to &[T] with an
3503 // alignment targeted for U.
3504 // `crate::ptr::align_offset` is called with a correctly aligned and
3505 // valid pointer `ptr` (it comes from a reference to `self`) and with
3506 // a size that is a power of two (since it comes from the alignement for U),
3507 // satisfying its safety constraints.
3508 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3509 if offset > self.len() {
3510 (self, &mut [], &mut [])
3512 let (left, rest) = self.split_at_mut(offset);
3513 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3514 let rest_len = rest.len();
3515 let mut_ptr = rest.as_mut_ptr();
3516 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3517 // SAFETY: see comments for `align_to`.
3521 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3522 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3528 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3530 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3531 /// postconditions as that method. You're only assured that
3532 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3534 /// Notably, all of the following are possible:
3535 /// - `prefix.len() >= LANES`.
3536 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3537 /// - `suffix.len() >= LANES`.
3539 /// That said, this is a safe method, so if you're only writing safe code,
3540 /// then this can at most cause incorrect logic, not unsoundness.
3544 /// This will panic if the size of the SIMD type is different from
3545 /// `LANES` times that of the scalar.
3547 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3548 /// that from ever happening, as only power-of-two numbers of lanes are
3549 /// supported. It's possible that, in the future, those restrictions might
3550 /// be lifted in a way that would make it possible to see panics from this
3551 /// method for something like `LANES == 3`.
3556 /// #![feature(portable_simd)]
3558 /// let short = &[1, 2, 3];
3559 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3560 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3562 /// // They might be split in any possible way between prefix and suffix
3563 /// let it = prefix.iter().chain(suffix).copied();
3564 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3566 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3567 /// use std::ops::Add;
3568 /// use std::simd::f32x4;
3569 /// let (prefix, middle, suffix) = x.as_simd();
3570 /// let sums = f32x4::from_array([
3571 /// prefix.iter().copied().sum(),
3574 /// suffix.iter().copied().sum(),
3576 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3577 /// sums.reduce_sum()
3580 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3581 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3583 #[unstable(feature = "portable_simd", issue = "86656")]
3585 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3587 Simd<T, LANES>: AsRef<[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() }
3601 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3603 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3604 /// postconditions as that method. You're only assured that
3605 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3607 /// Notably, all of the following are possible:
3608 /// - `prefix.len() >= LANES`.
3609 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3610 /// - `suffix.len() >= LANES`.
3612 /// That said, this is a safe method, so if you're only writing safe code,
3613 /// then this can at most cause incorrect logic, not unsoundness.
3615 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3619 /// This will panic if the size of the SIMD type is different from
3620 /// `LANES` times that of the scalar.
3622 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3623 /// that from ever happening, as only power-of-two numbers of lanes are
3624 /// supported. It's possible that, in the future, those restrictions might
3625 /// be lifted in a way that would make it possible to see panics from this
3626 /// method for something like `LANES == 3`.
3627 #[unstable(feature = "portable_simd", issue = "86656")]
3629 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3631 Simd<T, LANES>: AsMut<[T; LANES]>,
3632 T: simd::SimdElement,
3633 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3635 // These are expected to always match, as vector types are laid out like
3636 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3637 // might as well double-check since it'll optimize away anyhow.
3638 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3640 // SAFETY: The simd types have the same layout as arrays, just with
3641 // potentially-higher alignment, so the de-facto transmutes are sound.
3642 unsafe { self.align_to_mut() }
3645 /// Checks if the elements of this slice are sorted.
3647 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3648 /// slice yields exactly zero or one element, `true` is returned.
3650 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3651 /// implies that this function returns `false` if any two consecutive items are not
3657 /// #![feature(is_sorted)]
3658 /// let empty: [i32; 0] = [];
3660 /// assert!([1, 2, 2, 9].is_sorted());
3661 /// assert!(![1, 3, 2, 4].is_sorted());
3662 /// assert!([0].is_sorted());
3663 /// assert!(empty.is_sorted());
3664 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3667 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3669 pub fn is_sorted(&self) -> bool
3673 self.is_sorted_by(|a, b| a.partial_cmp(b))
3676 /// Checks if the elements of this slice are sorted using the given comparator function.
3678 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3679 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3680 /// [`is_sorted`]; see its documentation for more information.
3682 /// [`is_sorted`]: slice::is_sorted
3683 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3685 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3687 F: FnMut(&T, &T) -> Option<Ordering>,
3689 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3692 /// Checks if the elements of this slice are sorted using the given key extraction function.
3694 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3695 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3696 /// documentation for more information.
3698 /// [`is_sorted`]: slice::is_sorted
3703 /// #![feature(is_sorted)]
3705 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3706 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3709 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3711 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3716 self.iter().is_sorted_by_key(f)
3719 /// Returns the index of the partition point according to the given predicate
3720 /// (the index of the first element of the second partition).
3722 /// The slice is assumed to be partitioned according to the given predicate.
3723 /// This means that all elements for which the predicate returns true are at the start of the slice
3724 /// and all elements for which the predicate returns false are at the end.
3725 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3726 /// (all odd numbers are at the start, all even at the end).
3728 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3729 /// as this method performs a kind of binary search.
3731 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3733 /// [`binary_search`]: slice::binary_search
3734 /// [`binary_search_by`]: slice::binary_search_by
3735 /// [`binary_search_by_key`]: slice::binary_search_by_key
3740 /// let v = [1, 2, 3, 3, 5, 6, 7];
3741 /// let i = v.partition_point(|&x| x < 5);
3743 /// assert_eq!(i, 4);
3744 /// assert!(v[..i].iter().all(|&x| x < 5));
3745 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3747 #[stable(feature = "partition_point", since = "1.52.0")]
3749 pub fn partition_point<P>(&self, mut pred: P) -> usize
3751 P: FnMut(&T) -> bool,
3753 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3756 /// Removes the subslice corresponding to the given range
3757 /// and returns a reference to it.
3759 /// Returns `None` and does not modify the slice if the given
3760 /// range is out of bounds.
3762 /// Note that this method only accepts one-sided ranges such as
3763 /// `2..` or `..6`, but not `2..6`.
3767 /// Taking the first three elements of a slice:
3770 /// #![feature(slice_take)]
3772 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3773 /// let mut first_three = slice.take(..3).unwrap();
3775 /// assert_eq!(slice, &['d']);
3776 /// assert_eq!(first_three, &['a', 'b', 'c']);
3779 /// Taking the last two elements of a slice:
3782 /// #![feature(slice_take)]
3784 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3785 /// let mut tail = slice.take(2..).unwrap();
3787 /// assert_eq!(slice, &['a', 'b']);
3788 /// assert_eq!(tail, &['c', 'd']);
3791 /// Getting `None` when `range` is out of bounds:
3794 /// #![feature(slice_take)]
3796 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3798 /// assert_eq!(None, slice.take(5..));
3799 /// assert_eq!(None, slice.take(..5));
3800 /// assert_eq!(None, slice.take(..=4));
3801 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3802 /// assert_eq!(Some(expected), slice.take(..4));
3805 #[must_use = "method does not modify the slice if the range is out of bounds"]
3806 #[unstable(feature = "slice_take", issue = "62280")]
3807 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3808 let (direction, split_index) = split_point_of(range)?;
3809 if split_index > self.len() {
3812 let (front, back) = self.split_at(split_index);
3814 Direction::Front => {
3818 Direction::Back => {
3825 /// Removes the subslice corresponding to the given range
3826 /// and returns a mutable reference to it.
3828 /// Returns `None` and does not modify the slice if the given
3829 /// range is out of bounds.
3831 /// Note that this method only accepts one-sided ranges such as
3832 /// `2..` or `..6`, but not `2..6`.
3836 /// Taking the first three elements of a slice:
3839 /// #![feature(slice_take)]
3841 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3842 /// let mut first_three = slice.take_mut(..3).unwrap();
3844 /// assert_eq!(slice, &mut ['d']);
3845 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3848 /// Taking the last two elements of a slice:
3851 /// #![feature(slice_take)]
3853 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3854 /// let mut tail = slice.take_mut(2..).unwrap();
3856 /// assert_eq!(slice, &mut ['a', 'b']);
3857 /// assert_eq!(tail, &mut ['c', 'd']);
3860 /// Getting `None` when `range` is out of bounds:
3863 /// #![feature(slice_take)]
3865 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3867 /// assert_eq!(None, slice.take_mut(5..));
3868 /// assert_eq!(None, slice.take_mut(..5));
3869 /// assert_eq!(None, slice.take_mut(..=4));
3870 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3871 /// assert_eq!(Some(expected), slice.take_mut(..4));
3874 #[must_use = "method does not modify the slice if the range is out of bounds"]
3875 #[unstable(feature = "slice_take", issue = "62280")]
3876 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3877 self: &mut &'a mut Self,
3879 ) -> Option<&'a mut Self> {
3880 let (direction, split_index) = split_point_of(range)?;
3881 if split_index > self.len() {
3884 let (front, back) = mem::take(self).split_at_mut(split_index);
3886 Direction::Front => {
3890 Direction::Back => {
3897 /// Removes the first element of the slice and returns a reference
3900 /// Returns `None` if the slice is empty.
3905 /// #![feature(slice_take)]
3907 /// let mut slice: &[_] = &['a', 'b', 'c'];
3908 /// let first = slice.take_first().unwrap();
3910 /// assert_eq!(slice, &['b', 'c']);
3911 /// assert_eq!(first, &'a');
3914 #[unstable(feature = "slice_take", issue = "62280")]
3915 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3916 let (first, rem) = self.split_first()?;
3921 /// Removes the first element of the slice and returns a mutable
3922 /// reference to it.
3924 /// Returns `None` if the slice is empty.
3929 /// #![feature(slice_take)]
3931 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3932 /// let first = slice.take_first_mut().unwrap();
3935 /// assert_eq!(slice, &['b', 'c']);
3936 /// assert_eq!(first, &'d');
3939 #[unstable(feature = "slice_take", issue = "62280")]
3940 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3941 let (first, rem) = mem::take(self).split_first_mut()?;
3946 /// Removes the last element of the slice and returns a reference
3949 /// Returns `None` if the slice is empty.
3954 /// #![feature(slice_take)]
3956 /// let mut slice: &[_] = &['a', 'b', 'c'];
3957 /// let last = slice.take_last().unwrap();
3959 /// assert_eq!(slice, &['a', 'b']);
3960 /// assert_eq!(last, &'c');
3963 #[unstable(feature = "slice_take", issue = "62280")]
3964 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3965 let (last, rem) = self.split_last()?;
3970 /// Removes the last element of the slice and returns a mutable
3971 /// reference to it.
3973 /// Returns `None` if the slice is empty.
3978 /// #![feature(slice_take)]
3980 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3981 /// let last = slice.take_last_mut().unwrap();
3984 /// assert_eq!(slice, &['a', 'b']);
3985 /// assert_eq!(last, &'d');
3988 #[unstable(feature = "slice_take", issue = "62280")]
3989 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3990 let (last, rem) = mem::take(self).split_last_mut()?;
3996 trait CloneFromSpec<T> {
3997 fn spec_clone_from(&mut self, src: &[T]);
4000 impl<T> CloneFromSpec<T> for [T]
4005 default fn spec_clone_from(&mut self, src: &[T]) {
4006 assert!(self.len() == src.len(), "destination and source slices have different lengths");
4007 // NOTE: We need to explicitly slice them to the same length
4008 // to make it easier for the optimizer to elide bounds checking.
4009 // But since it can't be relied on we also have an explicit specialization for T: Copy.
4010 let len = self.len();
4011 let src = &src[..len];
4013 self[i].clone_from(&src[i]);
4018 impl<T> CloneFromSpec<T> for [T]
4023 fn spec_clone_from(&mut self, src: &[T]) {
4024 self.copy_from_slice(src);
4028 #[stable(feature = "rust1", since = "1.0.0")]
4029 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4030 impl<T> const Default for &[T] {
4031 /// Creates an empty slice.
4032 fn default() -> Self {
4037 #[stable(feature = "mut_slice_default", since = "1.5.0")]
4038 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4039 impl<T> const Default for &mut [T] {
4040 /// Creates a mutable empty slice.
4041 fn default() -> Self {
4046 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4047 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4048 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4049 /// `str`) to slices, and then this trait will be replaced or abolished.
4050 pub trait SlicePattern {
4051 /// The element type of the slice being matched on.
4054 /// Currently, the consumers of `SlicePattern` need a slice.
4055 fn as_slice(&self) -> &[Self::Item];
4058 #[stable(feature = "slice_strip", since = "1.51.0")]
4059 impl<T> SlicePattern for [T] {
4063 fn as_slice(&self) -> &[Self::Item] {
4068 #[stable(feature = "slice_strip", since = "1.51.0")]
4069 impl<T, const N: usize> SlicePattern for [T; N] {
4073 fn as_slice(&self) -> &[Self::Item] {