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;
12 use crate::mem::{self, SizedTypeProperties};
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),
115 /// Returns the number of elements in the slice.
120 /// let a = [1, 2, 3];
121 /// assert_eq!(a.len(), 3);
123 #[lang = "slice_len_fn"]
124 #[stable(feature = "rust1", since = "1.0.0")]
125 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
126 #[rustc_allow_const_fn_unstable(ptr_metadata)]
129 pub const fn len(&self) -> usize {
133 /// Returns `true` if the slice has a length of 0.
138 /// let a = [1, 2, 3];
139 /// assert!(!a.is_empty());
141 #[stable(feature = "rust1", since = "1.0.0")]
142 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
145 pub const fn is_empty(&self) -> bool {
149 /// Returns the first element of the slice, or `None` if it is empty.
154 /// let v = [10, 40, 30];
155 /// assert_eq!(Some(&10), v.first());
157 /// let w: &[i32] = &[];
158 /// assert_eq!(None, w.first());
160 #[stable(feature = "rust1", since = "1.0.0")]
161 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
164 pub const fn first(&self) -> Option<&T> {
165 if let [first, ..] = self { Some(first) } else { None }
168 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
173 /// let x = &mut [0, 1, 2];
175 /// if let Some(first) = x.first_mut() {
178 /// assert_eq!(x, &[5, 1, 2]);
180 #[stable(feature = "rust1", since = "1.0.0")]
181 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
184 pub const fn first_mut(&mut self) -> Option<&mut T> {
185 if let [first, ..] = self { Some(first) } else { None }
188 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
193 /// let x = &[0, 1, 2];
195 /// if let Some((first, elements)) = x.split_first() {
196 /// assert_eq!(first, &0);
197 /// assert_eq!(elements, &[1, 2]);
200 #[stable(feature = "slice_splits", since = "1.5.0")]
201 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
204 pub const fn split_first(&self) -> Option<(&T, &[T])> {
205 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
208 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
213 /// let x = &mut [0, 1, 2];
215 /// if let Some((first, elements)) = x.split_first_mut() {
220 /// assert_eq!(x, &[3, 4, 5]);
222 #[stable(feature = "slice_splits", since = "1.5.0")]
223 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
226 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
227 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
230 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
235 /// let x = &[0, 1, 2];
237 /// if let Some((last, elements)) = x.split_last() {
238 /// assert_eq!(last, &2);
239 /// assert_eq!(elements, &[0, 1]);
242 #[stable(feature = "slice_splits", since = "1.5.0")]
243 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
246 pub const fn split_last(&self) -> Option<(&T, &[T])> {
247 if let [init @ .., last] = self { Some((last, init)) } else { None }
250 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
255 /// let x = &mut [0, 1, 2];
257 /// if let Some((last, elements)) = x.split_last_mut() {
262 /// assert_eq!(x, &[4, 5, 3]);
264 #[stable(feature = "slice_splits", since = "1.5.0")]
265 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
268 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
269 if let [init @ .., last] = self { Some((last, init)) } else { None }
272 /// Returns the last element of the slice, or `None` if it is empty.
277 /// let v = [10, 40, 30];
278 /// assert_eq!(Some(&30), v.last());
280 /// let w: &[i32] = &[];
281 /// assert_eq!(None, w.last());
283 #[stable(feature = "rust1", since = "1.0.0")]
284 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
287 pub const fn last(&self) -> Option<&T> {
288 if let [.., last] = self { Some(last) } else { None }
291 /// Returns a mutable pointer to the last item in the slice.
296 /// let x = &mut [0, 1, 2];
298 /// if let Some(last) = x.last_mut() {
301 /// assert_eq!(x, &[0, 1, 10]);
303 #[stable(feature = "rust1", since = "1.0.0")]
304 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
307 pub const fn last_mut(&mut self) -> Option<&mut T> {
308 if let [.., last] = self { Some(last) } else { None }
311 /// Returns a reference to an element or subslice depending on the type of
314 /// - If given a position, returns a reference to the element at that
315 /// position or `None` if out of bounds.
316 /// - If given a range, returns the subslice corresponding to that range,
317 /// or `None` if out of bounds.
322 /// let v = [10, 40, 30];
323 /// assert_eq!(Some(&40), v.get(1));
324 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
325 /// assert_eq!(None, v.get(3));
326 /// assert_eq!(None, v.get(0..4));
328 #[stable(feature = "rust1", since = "1.0.0")]
329 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
332 pub const fn get<I>(&self, index: I) -> Option<&I::Output>
334 I: ~const SliceIndex<Self>,
339 /// Returns a mutable reference to an element or subslice depending on the
340 /// type of index (see [`get`]) or `None` if the index is out of bounds.
342 /// [`get`]: slice::get
347 /// let x = &mut [0, 1, 2];
349 /// if let Some(elem) = x.get_mut(1) {
352 /// assert_eq!(x, &[0, 42, 2]);
354 #[stable(feature = "rust1", since = "1.0.0")]
355 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
358 pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
360 I: ~const SliceIndex<Self>,
365 /// Returns a reference to an element or subslice, without doing bounds
368 /// For a safe alternative see [`get`].
372 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
373 /// even if the resulting reference is not used.
375 /// [`get`]: slice::get
376 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
381 /// let x = &[1, 2, 4];
384 /// assert_eq!(x.get_unchecked(1), &2);
387 #[stable(feature = "rust1", since = "1.0.0")]
388 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
391 pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
393 I: ~const SliceIndex<Self>,
395 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
396 // the slice is dereferenceable because `self` is a safe reference.
397 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
398 unsafe { &*index.get_unchecked(self) }
401 /// Returns a mutable reference to an element or subslice, without doing
404 /// For a safe alternative see [`get_mut`].
408 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
409 /// even if the resulting reference is not used.
411 /// [`get_mut`]: slice::get_mut
412 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
417 /// let x = &mut [1, 2, 4];
420 /// let elem = x.get_unchecked_mut(1);
423 /// assert_eq!(x, &[1, 13, 4]);
425 #[stable(feature = "rust1", since = "1.0.0")]
426 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
429 pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
431 I: ~const SliceIndex<Self>,
433 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
434 // the slice is dereferenceable because `self` is a safe reference.
435 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
436 unsafe { &mut *index.get_unchecked_mut(self) }
439 /// Returns a raw pointer to the slice's buffer.
441 /// The caller must ensure that the slice outlives the pointer this
442 /// function returns, or else it will end up pointing to garbage.
444 /// The caller must also ensure that the memory the pointer (non-transitively) points to
445 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
446 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
448 /// Modifying the container referenced by this slice may cause its buffer
449 /// to be reallocated, which would also make any pointers to it invalid.
454 /// let x = &[1, 2, 4];
455 /// let x_ptr = x.as_ptr();
458 /// for i in 0..x.len() {
459 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
464 /// [`as_mut_ptr`]: slice::as_mut_ptr
465 #[stable(feature = "rust1", since = "1.0.0")]
466 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
469 pub const fn as_ptr(&self) -> *const T {
470 self as *const [T] as *const T
473 /// Returns an unsafe mutable pointer to the slice's buffer.
475 /// The caller must ensure that the slice outlives the pointer this
476 /// function returns, or else it will end up pointing to garbage.
478 /// Modifying the container referenced by this slice may cause its buffer
479 /// to be reallocated, which would also make any pointers to it invalid.
484 /// let x = &mut [1, 2, 4];
485 /// let x_ptr = x.as_mut_ptr();
488 /// for i in 0..x.len() {
489 /// *x_ptr.add(i) += 2;
492 /// assert_eq!(x, &[3, 4, 6]);
494 #[stable(feature = "rust1", since = "1.0.0")]
495 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
496 #[rustc_allow_const_fn_unstable(const_mut_refs)]
499 pub const fn as_mut_ptr(&mut self) -> *mut T {
500 self as *mut [T] as *mut T
503 /// Returns the two raw pointers spanning the slice.
505 /// The returned range is half-open, which means that the end pointer
506 /// points *one past* the last element of the slice. This way, an empty
507 /// slice is represented by two equal pointers, and the difference between
508 /// the two pointers represents the size of the slice.
510 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
511 /// requires extra caution, as it does not point to a valid element in the
514 /// This function is useful for interacting with foreign interfaces which
515 /// use two pointers to refer to a range of elements in memory, as is
518 /// It can also be useful to check if a pointer to an element refers to an
519 /// element of this slice:
522 /// let a = [1, 2, 3];
523 /// let x = &a[1] as *const _;
524 /// let y = &5 as *const _;
526 /// assert!(a.as_ptr_range().contains(&x));
527 /// assert!(!a.as_ptr_range().contains(&y));
530 /// [`as_ptr`]: slice::as_ptr
531 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
532 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
535 pub const fn as_ptr_range(&self) -> Range<*const T> {
536 let start = self.as_ptr();
537 // SAFETY: The `add` here is safe, because:
539 // - Both pointers are part of the same object, as pointing directly
540 // past the object also counts.
542 // - The size of the slice is never larger than isize::MAX bytes, as
544 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
545 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
546 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
547 // (This doesn't seem normative yet, but the very same assumption is
548 // made in many places, including the Index implementation of slices.)
550 // - There is no wrapping around involved, as slices do not wrap past
551 // the end of the address space.
553 // See the documentation of pointer::add.
554 let end = unsafe { start.add(self.len()) };
558 /// Returns the two unsafe mutable pointers spanning the slice.
560 /// The returned range is half-open, which means that the end pointer
561 /// points *one past* the last element of the slice. This way, an empty
562 /// slice is represented by two equal pointers, and the difference between
563 /// the two pointers represents the size of the slice.
565 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
566 /// pointer requires extra caution, as it does not point to a valid element
569 /// This function is useful for interacting with foreign interfaces which
570 /// use two pointers to refer to a range of elements in memory, as is
573 /// [`as_mut_ptr`]: slice::as_mut_ptr
574 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
575 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
576 #[rustc_allow_const_fn_unstable(const_mut_refs)]
579 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
580 let start = self.as_mut_ptr();
581 // SAFETY: See as_ptr_range() above for why `add` here is safe.
582 let end = unsafe { start.add(self.len()) };
586 /// Swaps two elements in the slice.
590 /// * a - The index of the first element
591 /// * b - The index of the second element
595 /// Panics if `a` or `b` are out of bounds.
600 /// let mut v = ["a", "b", "c", "d", "e"];
602 /// assert!(v == ["a", "b", "e", "d", "c"]);
604 #[stable(feature = "rust1", since = "1.0.0")]
605 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
608 pub const fn swap(&mut self, a: usize, b: usize) {
609 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
610 // Can't take two mutable loans from one vector, so instead use raw pointers.
611 let pa = ptr::addr_of_mut!(self[a]);
612 let pb = ptr::addr_of_mut!(self[b]);
613 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
614 // to elements in the slice and therefore are guaranteed to be valid and aligned.
615 // Note that accessing the elements behind `a` and `b` is checked and will
616 // panic when out of bounds.
622 /// Swaps two elements in the slice, without doing bounds checking.
624 /// For a safe alternative see [`swap`].
628 /// * a - The index of the first element
629 /// * b - The index of the second element
633 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
634 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
639 /// #![feature(slice_swap_unchecked)]
641 /// let mut v = ["a", "b", "c", "d"];
642 /// // SAFETY: we know that 1 and 3 are both indices of the slice
643 /// unsafe { v.swap_unchecked(1, 3) };
644 /// assert!(v == ["a", "d", "c", "b"]);
647 /// [`swap`]: slice::swap
648 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
649 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
650 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
651 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
653 let ptr = this.as_mut_ptr();
654 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
656 assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
657 ptr::swap(ptr.add(a), ptr.add(b));
661 /// Reverses the order of elements in the slice, in place.
666 /// let mut v = [1, 2, 3];
668 /// assert!(v == [3, 2, 1]);
670 #[stable(feature = "rust1", since = "1.0.0")]
671 #[rustc_const_unstable(feature = "const_reverse", issue = "100784")]
673 pub const fn reverse(&mut self) {
674 let half_len = self.len() / 2;
675 let Range { start, end } = self.as_mut_ptr_range();
677 // These slices will skip the middle item for an odd length,
678 // since that one doesn't need to move.
679 let (front_half, back_half) =
680 // SAFETY: Both are subparts of the original slice, so the memory
681 // range is valid, and they don't overlap because they're each only
682 // half (or less) of the original slice.
685 slice::from_raw_parts_mut(start, half_len),
686 slice::from_raw_parts_mut(end.sub(half_len), half_len),
690 // Introducing a function boundary here means that the two halves
691 // get `noalias` markers, allowing better optimization as LLVM
692 // knows that they're disjoint, unlike in the original slice.
693 revswap(front_half, back_half, half_len);
696 const fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
697 debug_assert!(a.len() == n);
698 debug_assert!(b.len() == n);
700 // Because this function is first compiled in isolation,
701 // this check tells LLVM that the indexing below is
702 // in-bounds. Then after inlining -- once the actual
703 // lengths of the slices are known -- it's removed.
704 let (a, b) = (&mut a[..n], &mut b[..n]);
708 mem::swap(&mut a[i], &mut b[n - 1 - i]);
714 /// Returns an iterator over the slice.
716 /// The iterator yields all items from start to end.
721 /// let x = &[1, 2, 4];
722 /// let mut iterator = x.iter();
724 /// assert_eq!(iterator.next(), Some(&1));
725 /// assert_eq!(iterator.next(), Some(&2));
726 /// assert_eq!(iterator.next(), Some(&4));
727 /// assert_eq!(iterator.next(), None);
729 #[stable(feature = "rust1", since = "1.0.0")]
731 pub fn iter(&self) -> Iter<'_, T> {
735 /// Returns an iterator that allows modifying each value.
737 /// The iterator yields all items from start to end.
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, "chunks cannot have a size of zero");
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, "chunks cannot have a size of zero");
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]] {
970 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
971 let new_len = unsafe {
972 assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
973 exact_div(self.len(), N)
975 // SAFETY: We cast a slice of `new_len * N` elements into
976 // a slice of `new_len` many `N` elements chunks.
977 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
980 /// Splits the slice into a slice of `N`-element arrays,
981 /// starting at the beginning of the slice,
982 /// and a remainder slice with length strictly less than `N`.
986 /// Panics if `N` is 0. This check will most probably get changed to a compile time
987 /// error before this method gets stabilized.
992 /// #![feature(slice_as_chunks)]
993 /// let slice = ['l', 'o', 'r', 'e', 'm'];
994 /// let (chunks, remainder) = slice.as_chunks();
995 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
996 /// assert_eq!(remainder, &['m']);
998 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1001 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1003 let len = self.len() / N;
1004 let (multiple_of_n, remainder) = self.split_at(len * N);
1005 // SAFETY: We already panicked for zero, and ensured by construction
1006 // that the length of the subslice is a multiple of N.
1007 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1008 (array_slice, remainder)
1011 /// Splits the slice into a slice of `N`-element arrays,
1012 /// starting at the end of the slice,
1013 /// and a remainder slice with length strictly less than `N`.
1017 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1018 /// error before this method gets stabilized.
1023 /// #![feature(slice_as_chunks)]
1024 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1025 /// let (remainder, chunks) = slice.as_rchunks();
1026 /// assert_eq!(remainder, &['l']);
1027 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1029 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1032 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1034 let len = self.len() / N;
1035 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1036 // SAFETY: We already panicked for zero, and ensured by construction
1037 // that the length of the subslice is a multiple of N.
1038 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1039 (remainder, array_slice)
1042 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1043 /// beginning of the slice.
1045 /// The chunks are array references and do not overlap. If `N` does not divide the
1046 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1047 /// retrieved from the `remainder` function of the iterator.
1049 /// This method is the const generic equivalent of [`chunks_exact`].
1053 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1054 /// error before this method gets stabilized.
1059 /// #![feature(array_chunks)]
1060 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1061 /// let mut iter = slice.array_chunks();
1062 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1063 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1064 /// assert!(iter.next().is_none());
1065 /// assert_eq!(iter.remainder(), &['m']);
1068 /// [`chunks_exact`]: slice::chunks_exact
1069 #[unstable(feature = "array_chunks", issue = "74985")]
1071 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1073 ArrayChunks::new(self)
1076 /// Splits the slice into a slice of `N`-element arrays,
1077 /// assuming that there's no remainder.
1081 /// This may only be called when
1082 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1088 /// #![feature(slice_as_chunks)]
1089 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1090 /// let chunks: &mut [[char; 1]] =
1091 /// // SAFETY: 1-element chunks never have remainder
1092 /// unsafe { slice.as_chunks_unchecked_mut() };
1093 /// chunks[0] = ['L'];
1094 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1095 /// let chunks: &mut [[char; 3]] =
1096 /// // SAFETY: The slice length (6) is a multiple of 3
1097 /// unsafe { slice.as_chunks_unchecked_mut() };
1098 /// chunks[1] = ['a', 'x', '?'];
1099 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1101 /// // These would be unsound:
1102 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1103 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1105 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1108 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1110 // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
1111 let new_len = unsafe {
1112 assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
1113 exact_div(this.len(), N)
1115 // SAFETY: We cast a slice of `new_len * N` elements into
1116 // a slice of `new_len` many `N` elements chunks.
1117 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1120 /// Splits the slice into a slice of `N`-element arrays,
1121 /// starting at the beginning of the slice,
1122 /// and a remainder slice with length strictly less than `N`.
1126 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1127 /// error before this method gets stabilized.
1132 /// #![feature(slice_as_chunks)]
1133 /// let v = &mut [0, 0, 0, 0, 0];
1134 /// let mut count = 1;
1136 /// let (chunks, remainder) = v.as_chunks_mut();
1137 /// remainder[0] = 9;
1138 /// for chunk in chunks {
1139 /// *chunk = [count; 2];
1142 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1144 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1147 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1149 let len = self.len() / N;
1150 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1151 // SAFETY: We already panicked for zero, and ensured by construction
1152 // that the length of the subslice is a multiple of N.
1153 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1154 (array_slice, remainder)
1157 /// Splits the slice into a slice of `N`-element arrays,
1158 /// starting at the end of the slice,
1159 /// and a remainder slice with length strictly less than `N`.
1163 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1164 /// error before this method gets stabilized.
1169 /// #![feature(slice_as_chunks)]
1170 /// let v = &mut [0, 0, 0, 0, 0];
1171 /// let mut count = 1;
1173 /// let (remainder, chunks) = v.as_rchunks_mut();
1174 /// remainder[0] = 9;
1175 /// for chunk in chunks {
1176 /// *chunk = [count; 2];
1179 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1181 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1184 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1186 let len = self.len() / N;
1187 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1188 // SAFETY: We already panicked for zero, and ensured by construction
1189 // that the length of the subslice is a multiple of N.
1190 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1191 (remainder, array_slice)
1194 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1195 /// beginning of the slice.
1197 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1198 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1199 /// can be retrieved from the `into_remainder` function of the iterator.
1201 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1205 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1206 /// error before this method gets stabilized.
1211 /// #![feature(array_chunks)]
1212 /// let v = &mut [0, 0, 0, 0, 0];
1213 /// let mut count = 1;
1215 /// for chunk in v.array_chunks_mut() {
1216 /// *chunk = [count; 2];
1219 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1222 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1223 #[unstable(feature = "array_chunks", issue = "74985")]
1225 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1227 ArrayChunksMut::new(self)
1230 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1231 /// starting at the beginning of the slice.
1233 /// This is the const generic equivalent of [`windows`].
1235 /// If `N` is greater than the size of the slice, it will return no windows.
1239 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1240 /// error before this method gets stabilized.
1245 /// #![feature(array_windows)]
1246 /// let slice = [0, 1, 2, 3];
1247 /// let mut iter = slice.array_windows();
1248 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1249 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1250 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1251 /// assert!(iter.next().is_none());
1254 /// [`windows`]: slice::windows
1255 #[unstable(feature = "array_windows", issue = "75027")]
1257 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1259 ArrayWindows::new(self)
1262 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1265 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1266 /// slice, then the last chunk will not have length `chunk_size`.
1268 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1269 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1274 /// Panics if `chunk_size` is 0.
1279 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1280 /// let mut iter = slice.rchunks(2);
1281 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1282 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1283 /// assert_eq!(iter.next().unwrap(), &['l']);
1284 /// assert!(iter.next().is_none());
1287 /// [`rchunks_exact`]: slice::rchunks_exact
1288 /// [`chunks`]: slice::chunks
1289 #[stable(feature = "rchunks", since = "1.31.0")]
1291 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1292 assert!(chunk_size != 0);
1293 RChunks::new(self, chunk_size)
1296 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1299 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1300 /// length of the slice, then the last chunk will not have length `chunk_size`.
1302 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1303 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1304 /// beginning of the slice.
1308 /// Panics if `chunk_size` is 0.
1313 /// let v = &mut [0, 0, 0, 0, 0];
1314 /// let mut count = 1;
1316 /// for chunk in v.rchunks_mut(2) {
1317 /// for elem in chunk.iter_mut() {
1322 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1325 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1326 /// [`chunks_mut`]: slice::chunks_mut
1327 #[stable(feature = "rchunks", since = "1.31.0")]
1329 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1330 assert!(chunk_size != 0);
1331 RChunksMut::new(self, chunk_size)
1334 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1335 /// end of the slice.
1337 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1338 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1339 /// from the `remainder` function of the iterator.
1341 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1342 /// resulting code better than in the case of [`rchunks`].
1344 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1345 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1350 /// Panics if `chunk_size` is 0.
1355 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1356 /// let mut iter = slice.rchunks_exact(2);
1357 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1358 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1359 /// assert!(iter.next().is_none());
1360 /// assert_eq!(iter.remainder(), &['l']);
1363 /// [`chunks`]: slice::chunks
1364 /// [`rchunks`]: slice::rchunks
1365 /// [`chunks_exact`]: slice::chunks_exact
1366 #[stable(feature = "rchunks", since = "1.31.0")]
1368 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1369 assert!(chunk_size != 0);
1370 RChunksExact::new(self, chunk_size)
1373 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1376 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1377 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1378 /// retrieved from the `into_remainder` function of the iterator.
1380 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1381 /// resulting code better than in the case of [`chunks_mut`].
1383 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1384 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1389 /// Panics if `chunk_size` is 0.
1394 /// let v = &mut [0, 0, 0, 0, 0];
1395 /// let mut count = 1;
1397 /// for chunk in v.rchunks_exact_mut(2) {
1398 /// for elem in chunk.iter_mut() {
1403 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1406 /// [`chunks_mut`]: slice::chunks_mut
1407 /// [`rchunks_mut`]: slice::rchunks_mut
1408 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1409 #[stable(feature = "rchunks", since = "1.31.0")]
1411 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1412 assert!(chunk_size != 0);
1413 RChunksExactMut::new(self, chunk_size)
1416 /// Returns an iterator over the slice producing non-overlapping runs
1417 /// of elements using the predicate to separate them.
1419 /// The predicate is called on two elements following themselves,
1420 /// it means the predicate is called on `slice[0]` and `slice[1]`
1421 /// then on `slice[1]` and `slice[2]` and so on.
1426 /// #![feature(slice_group_by)]
1428 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1430 /// let mut iter = slice.group_by(|a, b| a == b);
1432 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1433 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1434 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1435 /// assert_eq!(iter.next(), None);
1438 /// This method can be used to extract the sorted subslices:
1441 /// #![feature(slice_group_by)]
1443 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1445 /// let mut iter = slice.group_by(|a, b| a <= b);
1447 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1448 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1449 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1450 /// assert_eq!(iter.next(), None);
1452 #[unstable(feature = "slice_group_by", issue = "80552")]
1454 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1456 F: FnMut(&T, &T) -> bool,
1458 GroupBy::new(self, pred)
1461 /// Returns an iterator over the slice producing non-overlapping mutable
1462 /// runs of elements using the predicate to separate them.
1464 /// The predicate is called on two elements following themselves,
1465 /// it means the predicate is called on `slice[0]` and `slice[1]`
1466 /// then on `slice[1]` and `slice[2]` and so on.
1471 /// #![feature(slice_group_by)]
1473 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1475 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1477 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1478 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1479 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1480 /// assert_eq!(iter.next(), None);
1483 /// This method can be used to extract the sorted subslices:
1486 /// #![feature(slice_group_by)]
1488 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1490 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1492 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1493 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1494 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1495 /// assert_eq!(iter.next(), None);
1497 #[unstable(feature = "slice_group_by", issue = "80552")]
1499 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1501 F: FnMut(&T, &T) -> bool,
1503 GroupByMut::new(self, pred)
1506 /// Divides one slice into two at an index.
1508 /// The first will contain all indices from `[0, mid)` (excluding
1509 /// the index `mid` itself) and the second will contain all
1510 /// indices from `[mid, len)` (excluding the index `len` itself).
1514 /// Panics if `mid > len`.
1519 /// let v = [1, 2, 3, 4, 5, 6];
1522 /// let (left, right) = v.split_at(0);
1523 /// assert_eq!(left, []);
1524 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1528 /// let (left, right) = v.split_at(2);
1529 /// assert_eq!(left, [1, 2]);
1530 /// assert_eq!(right, [3, 4, 5, 6]);
1534 /// let (left, right) = v.split_at(6);
1535 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1536 /// assert_eq!(right, []);
1539 #[stable(feature = "rust1", since = "1.0.0")]
1540 #[rustc_const_unstable(feature = "const_slice_split_at_not_mut", issue = "101158")]
1544 pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1545 assert!(mid <= self.len());
1546 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1547 // fulfills the requirements of `split_at_unchecked`.
1548 unsafe { self.split_at_unchecked(mid) }
1551 /// Divides one mutable slice into two at an index.
1553 /// The first will contain all indices from `[0, mid)` (excluding
1554 /// the index `mid` itself) and the second will contain all
1555 /// indices from `[mid, len)` (excluding the index `len` itself).
1559 /// Panics if `mid > len`.
1564 /// let mut v = [1, 0, 3, 0, 5, 6];
1565 /// let (left, right) = v.split_at_mut(2);
1566 /// assert_eq!(left, [1, 0]);
1567 /// assert_eq!(right, [3, 0, 5, 6]);
1570 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1572 #[stable(feature = "rust1", since = "1.0.0")]
1576 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
1577 pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1578 assert!(mid <= self.len());
1579 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1580 // fulfills the requirements of `from_raw_parts_mut`.
1581 unsafe { self.split_at_mut_unchecked(mid) }
1584 /// Divides one slice into two at an index, without doing bounds checking.
1586 /// The first will contain all indices from `[0, mid)` (excluding
1587 /// the index `mid` itself) and the second will contain all
1588 /// indices from `[mid, len)` (excluding the index `len` itself).
1590 /// For a safe alternative see [`split_at`].
1594 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1595 /// even if the resulting reference is not used. The caller has to ensure that
1596 /// `0 <= mid <= self.len()`.
1598 /// [`split_at`]: slice::split_at
1599 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1604 /// #![feature(slice_split_at_unchecked)]
1606 /// let v = [1, 2, 3, 4, 5, 6];
1609 /// let (left, right) = v.split_at_unchecked(0);
1610 /// assert_eq!(left, []);
1611 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1615 /// let (left, right) = v.split_at_unchecked(2);
1616 /// assert_eq!(left, [1, 2]);
1617 /// assert_eq!(right, [3, 4, 5, 6]);
1621 /// let (left, right) = v.split_at_unchecked(6);
1622 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1623 /// assert_eq!(right, []);
1626 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1627 #[rustc_const_unstable(feature = "slice_split_at_unchecked", issue = "76014")]
1630 pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1631 // HACK: the const function `from_raw_parts` is used to make this
1632 // function const; previously the implementation used
1633 // `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
1635 let len = self.len();
1636 let ptr = self.as_ptr();
1638 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1639 unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), len - mid)) }
1642 /// Divides one mutable slice into two at an index, without doing bounds checking.
1644 /// The first will contain all indices from `[0, mid)` (excluding
1645 /// the index `mid` itself) and the second will contain all
1646 /// indices from `[mid, len)` (excluding the index `len` itself).
1648 /// For a safe alternative see [`split_at_mut`].
1652 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1653 /// even if the resulting reference is not used. The caller has to ensure that
1654 /// `0 <= mid <= self.len()`.
1656 /// [`split_at_mut`]: slice::split_at_mut
1657 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1662 /// #![feature(slice_split_at_unchecked)]
1664 /// let mut v = [1, 0, 3, 0, 5, 6];
1665 /// // scoped to restrict the lifetime of the borrows
1667 /// let (left, right) = v.split_at_mut_unchecked(2);
1668 /// assert_eq!(left, [1, 0]);
1669 /// assert_eq!(right, [3, 0, 5, 6]);
1673 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1675 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1676 #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
1679 pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1680 let len = self.len();
1681 let ptr = self.as_mut_ptr();
1683 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1685 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1688 assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
1689 (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
1693 /// Divides one slice into an array and a remainder slice at an index.
1695 /// The array will contain all indices from `[0, N)` (excluding
1696 /// the index `N` itself) and the slice will contain all
1697 /// indices from `[N, len)` (excluding the index `len` itself).
1701 /// Panics if `N > len`.
1706 /// #![feature(split_array)]
1708 /// let v = &[1, 2, 3, 4, 5, 6][..];
1711 /// let (left, right) = v.split_array_ref::<0>();
1712 /// assert_eq!(left, &[]);
1713 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1717 /// let (left, right) = v.split_array_ref::<2>();
1718 /// assert_eq!(left, &[1, 2]);
1719 /// assert_eq!(right, [3, 4, 5, 6]);
1723 /// let (left, right) = v.split_array_ref::<6>();
1724 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1725 /// assert_eq!(right, []);
1728 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1732 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1733 let (a, b) = self.split_at(N);
1734 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1735 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1738 /// Divides one mutable slice into an array and a remainder slice at an index.
1740 /// The array will contain all indices from `[0, N)` (excluding
1741 /// the index `N` itself) and the slice will contain all
1742 /// indices from `[N, len)` (excluding the index `len` itself).
1746 /// Panics if `N > len`.
1751 /// #![feature(split_array)]
1753 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1754 /// let (left, right) = v.split_array_mut::<2>();
1755 /// assert_eq!(left, &mut [1, 0]);
1756 /// assert_eq!(right, [3, 0, 5, 6]);
1759 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1761 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1765 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1766 let (a, b) = self.split_at_mut(N);
1767 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1768 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1771 /// Divides one slice into an array and a remainder slice at an index from
1774 /// The slice will contain all indices from `[0, len - N)` (excluding
1775 /// the index `len - N` itself) and the array will contain all
1776 /// indices from `[len - N, len)` (excluding the index `len` itself).
1780 /// Panics if `N > len`.
1785 /// #![feature(split_array)]
1787 /// let v = &[1, 2, 3, 4, 5, 6][..];
1790 /// let (left, right) = v.rsplit_array_ref::<0>();
1791 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1792 /// assert_eq!(right, &[]);
1796 /// let (left, right) = v.rsplit_array_ref::<2>();
1797 /// assert_eq!(left, [1, 2, 3, 4]);
1798 /// assert_eq!(right, &[5, 6]);
1802 /// let (left, right) = v.rsplit_array_ref::<6>();
1803 /// assert_eq!(left, []);
1804 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1807 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1810 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1811 assert!(N <= self.len());
1812 let (a, b) = self.split_at(self.len() - N);
1813 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1814 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1817 /// Divides one mutable slice into an array and a remainder slice at an
1818 /// index from the end.
1820 /// The slice will contain all indices from `[0, len - N)` (excluding
1821 /// the index `N` itself) and the array will contain all
1822 /// indices from `[len - N, len)` (excluding the index `len` itself).
1826 /// Panics if `N > len`.
1831 /// #![feature(split_array)]
1833 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1834 /// let (left, right) = v.rsplit_array_mut::<4>();
1835 /// assert_eq!(left, [1, 0]);
1836 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1839 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1841 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1844 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1845 assert!(N <= self.len());
1846 let (a, b) = self.split_at_mut(self.len() - N);
1847 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1848 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1851 /// Returns an iterator over subslices separated by elements that match
1852 /// `pred`. The matched element is not contained in the subslices.
1857 /// let slice = [10, 40, 33, 20];
1858 /// let mut iter = slice.split(|num| num % 3 == 0);
1860 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1861 /// assert_eq!(iter.next().unwrap(), &[20]);
1862 /// assert!(iter.next().is_none());
1865 /// If the first element is matched, an empty slice will be the first item
1866 /// returned by the iterator. Similarly, if the last element in the slice
1867 /// is matched, an empty slice will be the last item returned by the
1871 /// let slice = [10, 40, 33];
1872 /// let mut iter = slice.split(|num| num % 3 == 0);
1874 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1875 /// assert_eq!(iter.next().unwrap(), &[]);
1876 /// assert!(iter.next().is_none());
1879 /// If two matched elements are directly adjacent, an empty slice will be
1880 /// present between them:
1883 /// let slice = [10, 6, 33, 20];
1884 /// let mut iter = slice.split(|num| num % 3 == 0);
1886 /// assert_eq!(iter.next().unwrap(), &[10]);
1887 /// assert_eq!(iter.next().unwrap(), &[]);
1888 /// assert_eq!(iter.next().unwrap(), &[20]);
1889 /// assert!(iter.next().is_none());
1891 #[stable(feature = "rust1", since = "1.0.0")]
1893 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1895 F: FnMut(&T) -> bool,
1897 Split::new(self, pred)
1900 /// Returns an iterator over mutable subslices separated by elements that
1901 /// match `pred`. The matched element is not contained in the subslices.
1906 /// let mut v = [10, 40, 30, 20, 60, 50];
1908 /// for group in v.split_mut(|num| *num % 3 == 0) {
1911 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1913 #[stable(feature = "rust1", since = "1.0.0")]
1915 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1917 F: FnMut(&T) -> bool,
1919 SplitMut::new(self, pred)
1922 /// Returns an iterator over subslices separated by elements that match
1923 /// `pred`. The matched element is contained in the end of the previous
1924 /// subslice as a terminator.
1929 /// let slice = [10, 40, 33, 20];
1930 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1932 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1933 /// assert_eq!(iter.next().unwrap(), &[20]);
1934 /// assert!(iter.next().is_none());
1937 /// If the last element of the slice is matched,
1938 /// that element will be considered the terminator of the preceding slice.
1939 /// That slice will be the last item returned by the iterator.
1942 /// let slice = [3, 10, 40, 33];
1943 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1945 /// assert_eq!(iter.next().unwrap(), &[3]);
1946 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1947 /// assert!(iter.next().is_none());
1949 #[stable(feature = "split_inclusive", since = "1.51.0")]
1951 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1953 F: FnMut(&T) -> bool,
1955 SplitInclusive::new(self, pred)
1958 /// Returns an iterator over mutable subslices separated by elements that
1959 /// match `pred`. The matched element is contained in the previous
1960 /// subslice as a terminator.
1965 /// let mut v = [10, 40, 30, 20, 60, 50];
1967 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1968 /// let terminator_idx = group.len()-1;
1969 /// group[terminator_idx] = 1;
1971 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1973 #[stable(feature = "split_inclusive", since = "1.51.0")]
1975 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1977 F: FnMut(&T) -> bool,
1979 SplitInclusiveMut::new(self, pred)
1982 /// Returns an iterator over subslices separated by elements that match
1983 /// `pred`, starting at the end of the slice and working backwards.
1984 /// The matched element is not contained in the subslices.
1989 /// let slice = [11, 22, 33, 0, 44, 55];
1990 /// let mut iter = slice.rsplit(|num| *num == 0);
1992 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1993 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1994 /// assert_eq!(iter.next(), None);
1997 /// As with `split()`, if the first or last element is matched, an empty
1998 /// slice will be the first (or last) item returned by the iterator.
2001 /// let v = &[0, 1, 1, 2, 3, 5, 8];
2002 /// let mut it = v.rsplit(|n| *n % 2 == 0);
2003 /// assert_eq!(it.next().unwrap(), &[]);
2004 /// assert_eq!(it.next().unwrap(), &[3, 5]);
2005 /// assert_eq!(it.next().unwrap(), &[1, 1]);
2006 /// assert_eq!(it.next().unwrap(), &[]);
2007 /// assert_eq!(it.next(), None);
2009 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2011 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
2013 F: FnMut(&T) -> bool,
2015 RSplit::new(self, pred)
2018 /// Returns an iterator over mutable subslices separated by elements that
2019 /// match `pred`, starting at the end of the slice and working
2020 /// backwards. The matched element is not contained in the subslices.
2025 /// let mut v = [100, 400, 300, 200, 600, 500];
2027 /// let mut count = 0;
2028 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
2030 /// group[0] = count;
2032 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
2035 #[stable(feature = "slice_rsplit", since = "1.27.0")]
2037 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
2039 F: FnMut(&T) -> bool,
2041 RSplitMut::new(self, pred)
2044 /// Returns an iterator over subslices separated by elements that match
2045 /// `pred`, limited to returning at most `n` items. The matched element is
2046 /// not contained in the subslices.
2048 /// The last element returned, if any, will contain the remainder of the
2053 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2054 /// `[20, 60, 50]`):
2057 /// let v = [10, 40, 30, 20, 60, 50];
2059 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2060 /// println!("{group:?}");
2063 #[stable(feature = "rust1", since = "1.0.0")]
2065 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2067 F: FnMut(&T) -> bool,
2069 SplitN::new(self.split(pred), n)
2072 /// Returns an iterator over mutable subslices separated by elements that match
2073 /// `pred`, limited to returning at most `n` items. The matched element is
2074 /// not contained in the subslices.
2076 /// The last element returned, if any, will contain the remainder of the
2082 /// let mut v = [10, 40, 30, 20, 60, 50];
2084 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2087 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2089 #[stable(feature = "rust1", since = "1.0.0")]
2091 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2093 F: FnMut(&T) -> bool,
2095 SplitNMut::new(self.split_mut(pred), n)
2098 /// Returns an iterator over subslices separated by elements that match
2099 /// `pred` limited to returning at most `n` items. This starts at the end of
2100 /// the slice and works backwards. The matched element is not contained in
2103 /// The last element returned, if any, will contain the remainder of the
2108 /// Print the slice split once, starting from the end, by numbers divisible
2109 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2112 /// let v = [10, 40, 30, 20, 60, 50];
2114 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2115 /// println!("{group:?}");
2118 #[stable(feature = "rust1", since = "1.0.0")]
2120 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2122 F: FnMut(&T) -> bool,
2124 RSplitN::new(self.rsplit(pred), n)
2127 /// Returns an iterator over subslices separated by elements that match
2128 /// `pred` limited to returning at most `n` items. This starts at the end of
2129 /// the slice and works backwards. The matched element is not contained in
2132 /// The last element returned, if any, will contain the remainder of the
2138 /// let mut s = [10, 40, 30, 20, 60, 50];
2140 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2143 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2145 #[stable(feature = "rust1", since = "1.0.0")]
2147 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2149 F: FnMut(&T) -> bool,
2151 RSplitNMut::new(self.rsplit_mut(pred), n)
2154 /// Returns `true` if the slice contains an element with the given value.
2156 /// This operation is *O*(*n*).
2158 /// Note that if you have a sorted slice, [`binary_search`] may be faster.
2160 /// [`binary_search`]: slice::binary_search
2165 /// let v = [10, 40, 30];
2166 /// assert!(v.contains(&30));
2167 /// assert!(!v.contains(&50));
2170 /// If you do not have a `&T`, but some other value that you can compare
2171 /// with one (for example, `String` implements `PartialEq<str>`), you can
2172 /// use `iter().any`:
2175 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2176 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2177 /// assert!(!v.iter().any(|e| e == "hi"));
2179 #[stable(feature = "rust1", since = "1.0.0")]
2182 pub fn contains(&self, x: &T) -> bool
2186 cmp::SliceContains::slice_contains(x, self)
2189 /// Returns `true` if `needle` is a prefix of the slice.
2194 /// let v = [10, 40, 30];
2195 /// assert!(v.starts_with(&[10]));
2196 /// assert!(v.starts_with(&[10, 40]));
2197 /// assert!(!v.starts_with(&[50]));
2198 /// assert!(!v.starts_with(&[10, 50]));
2201 /// Always returns `true` if `needle` is an empty slice:
2204 /// let v = &[10, 40, 30];
2205 /// assert!(v.starts_with(&[]));
2206 /// let v: &[u8] = &[];
2207 /// assert!(v.starts_with(&[]));
2209 #[stable(feature = "rust1", since = "1.0.0")]
2211 pub fn starts_with(&self, needle: &[T]) -> bool
2215 let n = needle.len();
2216 self.len() >= n && needle == &self[..n]
2219 /// Returns `true` if `needle` is a suffix of the slice.
2224 /// let v = [10, 40, 30];
2225 /// assert!(v.ends_with(&[30]));
2226 /// assert!(v.ends_with(&[40, 30]));
2227 /// assert!(!v.ends_with(&[50]));
2228 /// assert!(!v.ends_with(&[50, 30]));
2231 /// Always returns `true` if `needle` is an empty slice:
2234 /// let v = &[10, 40, 30];
2235 /// assert!(v.ends_with(&[]));
2236 /// let v: &[u8] = &[];
2237 /// assert!(v.ends_with(&[]));
2239 #[stable(feature = "rust1", since = "1.0.0")]
2241 pub fn ends_with(&self, needle: &[T]) -> bool
2245 let (m, n) = (self.len(), needle.len());
2246 m >= n && needle == &self[m - n..]
2249 /// Returns a subslice with the prefix removed.
2251 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2252 /// If `prefix` is empty, simply returns the original slice.
2254 /// If the slice does not start with `prefix`, returns `None`.
2259 /// let v = &[10, 40, 30];
2260 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2261 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2262 /// assert_eq!(v.strip_prefix(&[50]), None);
2263 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2265 /// let prefix : &str = "he";
2266 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2267 /// Some(b"llo".as_ref()));
2269 #[must_use = "returns the subslice without modifying the original"]
2270 #[stable(feature = "slice_strip", since = "1.51.0")]
2271 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2275 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2276 let prefix = prefix.as_slice();
2277 let n = prefix.len();
2278 if n <= self.len() {
2279 let (head, tail) = self.split_at(n);
2287 /// Returns a subslice with the suffix removed.
2289 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2290 /// If `suffix` is empty, simply returns the original slice.
2292 /// If the slice does not end with `suffix`, returns `None`.
2297 /// let v = &[10, 40, 30];
2298 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2299 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2300 /// assert_eq!(v.strip_suffix(&[50]), None);
2301 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2303 #[must_use = "returns the subslice without modifying the original"]
2304 #[stable(feature = "slice_strip", since = "1.51.0")]
2305 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2309 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2310 let suffix = suffix.as_slice();
2311 let (len, n) = (self.len(), suffix.len());
2313 let (head, tail) = self.split_at(len - n);
2321 /// Binary searches this slice for a given element.
2322 /// This behaves similarly to [`contains`] if this slice is sorted.
2324 /// If the value is found then [`Result::Ok`] is returned, containing the
2325 /// index of the matching element. If there are multiple matches, then any
2326 /// one of the matches could be returned. The index is chosen
2327 /// deterministically, but is subject to change in future versions of Rust.
2328 /// If the value is not found then [`Result::Err`] is returned, containing
2329 /// the index where a matching element could be inserted while maintaining
2332 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2334 /// [`contains`]: slice::contains
2335 /// [`binary_search_by`]: slice::binary_search_by
2336 /// [`binary_search_by_key`]: slice::binary_search_by_key
2337 /// [`partition_point`]: slice::partition_point
2341 /// Looks up a series of four elements. The first is found, with a
2342 /// uniquely determined position; the second and third are not
2343 /// found; the fourth could match any position in `[1, 4]`.
2346 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2348 /// assert_eq!(s.binary_search(&13), Ok(9));
2349 /// assert_eq!(s.binary_search(&4), Err(7));
2350 /// assert_eq!(s.binary_search(&100), Err(13));
2351 /// let r = s.binary_search(&1);
2352 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2355 /// If you want to find that whole *range* of matching items, rather than
2356 /// an arbitrary matching one, that can be done using [`partition_point`]:
2358 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2360 /// let low = s.partition_point(|x| x < &1);
2361 /// assert_eq!(low, 1);
2362 /// let high = s.partition_point(|x| x <= &1);
2363 /// assert_eq!(high, 5);
2364 /// let r = s.binary_search(&1);
2365 /// assert!((low..high).contains(&r.unwrap()));
2367 /// assert!(s[..low].iter().all(|&x| x < 1));
2368 /// assert!(s[low..high].iter().all(|&x| x == 1));
2369 /// assert!(s[high..].iter().all(|&x| x > 1));
2371 /// // For something not found, the "range" of equal items is empty
2372 /// assert_eq!(s.partition_point(|x| x < &11), 9);
2373 /// assert_eq!(s.partition_point(|x| x <= &11), 9);
2374 /// assert_eq!(s.binary_search(&11), Err(9));
2377 /// If you want to insert an item to a sorted vector, while maintaining
2378 /// sort order, consider using [`partition_point`]:
2381 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2383 /// let idx = s.partition_point(|&x| x < num);
2384 /// // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
2385 /// s.insert(idx, num);
2386 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2388 #[stable(feature = "rust1", since = "1.0.0")]
2389 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2393 self.binary_search_by(|p| p.cmp(x))
2396 /// Binary searches this slice with a comparator function.
2397 /// This behaves similarly to [`contains`] if this slice is sorted.
2399 /// The comparator function should implement an order consistent
2400 /// with the sort order of the underlying slice, returning an
2401 /// order code that indicates whether its argument is `Less`,
2402 /// `Equal` or `Greater` the desired target.
2404 /// If the value is found then [`Result::Ok`] is returned, containing the
2405 /// index of the matching element. If there are multiple matches, then any
2406 /// one of the matches could be returned. The index is chosen
2407 /// deterministically, but is subject to change in future versions of Rust.
2408 /// If the value is not found then [`Result::Err`] is returned, containing
2409 /// the index where a matching element could be inserted while maintaining
2412 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2414 /// [`contains`]: slice::contains
2415 /// [`binary_search`]: slice::binary_search
2416 /// [`binary_search_by_key`]: slice::binary_search_by_key
2417 /// [`partition_point`]: slice::partition_point
2421 /// Looks up a series of four elements. The first is found, with a
2422 /// uniquely determined position; the second and third are not
2423 /// found; the fourth could match any position in `[1, 4]`.
2426 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2429 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2431 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2433 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2435 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2436 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2438 #[stable(feature = "rust1", since = "1.0.0")]
2440 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2442 F: FnMut(&'a T) -> Ordering,
2445 // - 0 <= left <= left + size = right <= self.len()
2446 // - f returns Less for everything in self[..left]
2447 // - f returns Greater for everything in self[right..]
2448 let mut size = self.len();
2450 let mut right = size;
2451 while left < right {
2452 let mid = left + size / 2;
2454 // SAFETY: the while condition means `size` is strictly positive, so
2455 // `size/2 < size`. Thus `left + size/2 < left + size`, which
2456 // coupled with the `left + size <= self.len()` invariant means
2457 // we have `left + size/2 < self.len()`, and this is in-bounds.
2458 let cmp = f(unsafe { self.get_unchecked(mid) });
2460 // The reason why we use if/else control flow rather than match
2461 // is because match reorders comparison operations, which is perf sensitive.
2462 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2465 } else if cmp == Greater {
2468 // SAFETY: same as the `get_unchecked` above
2469 unsafe { crate::intrinsics::assume(mid < self.len()) };
2473 size = right - left;
2476 // SAFETY: directly true from the overall invariant.
2477 // Note that this is `<=`, unlike the assume in the `Ok` path.
2478 unsafe { crate::intrinsics::assume(left <= self.len()) };
2482 /// Binary searches this slice with a key extraction function.
2483 /// This behaves similarly to [`contains`] if this slice is sorted.
2485 /// Assumes that the slice is sorted by the key, for instance with
2486 /// [`sort_by_key`] using the same key extraction function.
2488 /// If the value is found then [`Result::Ok`] is returned, containing the
2489 /// index of the matching element. If there are multiple matches, then any
2490 /// one of the matches could be returned. The index is chosen
2491 /// deterministically, but is subject to change in future versions of Rust.
2492 /// If the value is not found then [`Result::Err`] is returned, containing
2493 /// the index where a matching element could be inserted while maintaining
2496 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2498 /// [`contains`]: slice::contains
2499 /// [`sort_by_key`]: slice::sort_by_key
2500 /// [`binary_search`]: slice::binary_search
2501 /// [`binary_search_by`]: slice::binary_search_by
2502 /// [`partition_point`]: slice::partition_point
2506 /// Looks up a series of four elements in a slice of pairs sorted by
2507 /// their second elements. The first is found, with a uniquely
2508 /// determined position; the second and third are not found; the
2509 /// fourth could match any position in `[1, 4]`.
2512 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2513 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2514 /// (1, 21), (2, 34), (4, 55)];
2516 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2517 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2518 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2519 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2520 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2522 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2523 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2524 // This breaks links when slice is displayed in core, but changing it to use relative links
2525 // would break when the item is re-exported. So allow the core links to be broken for now.
2526 #[allow(rustdoc::broken_intra_doc_links)]
2527 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2529 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2531 F: FnMut(&'a T) -> B,
2534 self.binary_search_by(|k| f(k).cmp(b))
2537 /// Sorts the slice, but might not preserve the order of equal elements.
2539 /// This sort is unstable (i.e., may reorder equal elements), in-place
2540 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2542 /// # Current implementation
2544 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2545 /// which combines the fast average case of randomized quicksort with the fast worst case of
2546 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2547 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2548 /// deterministic behavior.
2550 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2551 /// slice consists of several concatenated sorted sequences.
2556 /// let mut v = [-5, 4, 1, -3, 2];
2558 /// v.sort_unstable();
2559 /// assert!(v == [-5, -3, 1, 2, 4]);
2562 /// [pdqsort]: https://github.com/orlp/pdqsort
2563 #[stable(feature = "sort_unstable", since = "1.20.0")]
2565 pub fn sort_unstable(&mut self)
2569 sort::quicksort(self, T::lt);
2572 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2575 /// This sort is unstable (i.e., may reorder equal elements), in-place
2576 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2578 /// The comparator function must define a total ordering for the elements in the slice. If
2579 /// the ordering is not total, the order of the elements is unspecified. An order is a
2580 /// total order if it is (for all `a`, `b` and `c`):
2582 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2583 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2585 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2586 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2589 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2590 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2591 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2594 /// # Current implementation
2596 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2597 /// which combines the fast average case of randomized quicksort with the fast worst case of
2598 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2599 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2600 /// deterministic behavior.
2602 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2603 /// slice consists of several concatenated sorted sequences.
2608 /// let mut v = [5, 4, 1, 3, 2];
2609 /// v.sort_unstable_by(|a, b| a.cmp(b));
2610 /// assert!(v == [1, 2, 3, 4, 5]);
2612 /// // reverse sorting
2613 /// v.sort_unstable_by(|a, b| b.cmp(a));
2614 /// assert!(v == [5, 4, 3, 2, 1]);
2617 /// [pdqsort]: https://github.com/orlp/pdqsort
2618 #[stable(feature = "sort_unstable", since = "1.20.0")]
2620 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2622 F: FnMut(&T, &T) -> Ordering,
2624 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2627 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2630 /// This sort is unstable (i.e., may reorder equal elements), in-place
2631 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2634 /// # Current implementation
2636 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2637 /// which combines the fast average case of randomized quicksort with the fast worst case of
2638 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2639 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2640 /// deterministic behavior.
2642 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2643 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2644 /// cases where the key function is expensive.
2649 /// let mut v = [-5i32, 4, 1, -3, 2];
2651 /// v.sort_unstable_by_key(|k| k.abs());
2652 /// assert!(v == [1, 2, -3, 4, -5]);
2655 /// [pdqsort]: https://github.com/orlp/pdqsort
2656 #[stable(feature = "sort_unstable", since = "1.20.0")]
2658 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2663 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2666 /// Reorder the slice such that the element at `index` is at its final sorted position.
2668 /// This reordering has the additional property that any value at position `i < index` will be
2669 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2670 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2671 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2672 /// element" in other libraries. It returns a triplet of the following from the reordered slice:
2673 /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
2674 /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
2675 /// and greater-than-or-equal-to the value of the element at `index`.
2677 /// # Current implementation
2679 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2680 /// used for [`sort_unstable`].
2682 /// [`sort_unstable`]: slice::sort_unstable
2686 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2691 /// let mut v = [-5i32, 4, 1, -3, 2];
2693 /// // Find the median
2694 /// v.select_nth_unstable(2);
2696 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2697 /// // about the specified index.
2698 /// assert!(v == [-3, -5, 1, 2, 4] ||
2699 /// v == [-5, -3, 1, 2, 4] ||
2700 /// v == [-3, -5, 1, 4, 2] ||
2701 /// v == [-5, -3, 1, 4, 2]);
2703 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2705 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2709 sort::partition_at_index(self, index, T::lt)
2712 /// Reorder the slice with a comparator function such that the element at `index` is at its
2713 /// final sorted position.
2715 /// This reordering has the additional property that any value at position `i < index` will be
2716 /// less than or equal to any value at a position `j > index` using the comparator function.
2717 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2718 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2719 /// is also known as "kth element" in other libraries. It returns a triplet of the following from
2720 /// the slice reordered according to the provided comparator function: the subslice prior to
2721 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
2722 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
2723 /// the value of the element at `index`.
2725 /// # Current implementation
2727 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2728 /// used for [`sort_unstable`].
2730 /// [`sort_unstable`]: slice::sort_unstable
2734 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2739 /// let mut v = [-5i32, 4, 1, -3, 2];
2741 /// // Find the median as if the slice were sorted in descending order.
2742 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2744 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2745 /// // about the specified index.
2746 /// assert!(v == [2, 4, 1, -5, -3] ||
2747 /// v == [2, 4, 1, -3, -5] ||
2748 /// v == [4, 2, 1, -5, -3] ||
2749 /// v == [4, 2, 1, -3, -5]);
2751 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2753 pub fn select_nth_unstable_by<F>(
2757 ) -> (&mut [T], &mut T, &mut [T])
2759 F: FnMut(&T, &T) -> Ordering,
2761 sort::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
2764 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2765 /// final sorted position.
2767 /// This reordering has the additional property that any value at position `i < index` will be
2768 /// less than or equal to any value at a position `j > index` using the key extraction function.
2769 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2770 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2771 /// is also known as "kth element" in other libraries. It returns a triplet of the following from
2772 /// the slice reordered according to the provided key extraction function: the subslice prior to
2773 /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
2774 /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
2775 /// the value of the element at `index`.
2777 /// # Current implementation
2779 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2780 /// used for [`sort_unstable`].
2782 /// [`sort_unstable`]: slice::sort_unstable
2786 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2791 /// let mut v = [-5i32, 4, 1, -3, 2];
2793 /// // Return the median as if the array were sorted according to absolute value.
2794 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2796 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2797 /// // about the specified index.
2798 /// assert!(v == [1, 2, -3, 4, -5] ||
2799 /// v == [1, 2, -3, -5, 4] ||
2800 /// v == [2, 1, -3, 4, -5] ||
2801 /// v == [2, 1, -3, -5, 4]);
2803 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2805 pub fn select_nth_unstable_by_key<K, F>(
2809 ) -> (&mut [T], &mut T, &mut [T])
2814 sort::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
2817 /// Moves all consecutive repeated elements to the end of the slice according to the
2818 /// [`PartialEq`] trait implementation.
2820 /// Returns two slices. The first contains no consecutive repeated elements.
2821 /// The second contains all the duplicates in no specified order.
2823 /// If the slice is sorted, the first returned slice contains no duplicates.
2828 /// #![feature(slice_partition_dedup)]
2830 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2832 /// let (dedup, duplicates) = slice.partition_dedup();
2834 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2835 /// assert_eq!(duplicates, [2, 3, 1]);
2837 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2839 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2843 self.partition_dedup_by(|a, b| a == b)
2846 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2847 /// a given equality relation.
2849 /// Returns two slices. The first contains no consecutive repeated elements.
2850 /// The second contains all the duplicates in no specified order.
2852 /// The `same_bucket` function is passed references to two elements from the slice and
2853 /// must determine if the elements compare equal. The elements are passed in opposite order
2854 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2855 /// at the end of the slice.
2857 /// If the slice is sorted, the first returned slice contains no duplicates.
2862 /// #![feature(slice_partition_dedup)]
2864 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2866 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2868 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2869 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2871 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2873 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2875 F: FnMut(&mut T, &mut T) -> bool,
2877 // Although we have a mutable reference to `self`, we cannot make
2878 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2879 // must ensure that the slice is in a valid state at all times.
2881 // The way that we handle this is by using swaps; we iterate
2882 // over all the elements, swapping as we go so that at the end
2883 // the elements we wish to keep are in the front, and those we
2884 // wish to reject are at the back. We can then split the slice.
2885 // This operation is still `O(n)`.
2887 // Example: We start in this state, where `r` represents "next
2888 // read" and `w` represents "next_write`.
2891 // +---+---+---+---+---+---+
2892 // | 0 | 1 | 1 | 2 | 3 | 3 |
2893 // +---+---+---+---+---+---+
2896 // Comparing self[r] against self[w-1], this is not a duplicate, so
2897 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2898 // r and w, leaving us with:
2901 // +---+---+---+---+---+---+
2902 // | 0 | 1 | 1 | 2 | 3 | 3 |
2903 // +---+---+---+---+---+---+
2906 // Comparing self[r] against self[w-1], this value is a duplicate,
2907 // so we increment `r` but leave everything else unchanged:
2910 // +---+---+---+---+---+---+
2911 // | 0 | 1 | 1 | 2 | 3 | 3 |
2912 // +---+---+---+---+---+---+
2915 // Comparing self[r] against self[w-1], this is not a duplicate,
2916 // so swap self[r] and self[w] and advance r and w:
2919 // +---+---+---+---+---+---+
2920 // | 0 | 1 | 2 | 1 | 3 | 3 |
2921 // +---+---+---+---+---+---+
2924 // Not a duplicate, repeat:
2927 // +---+---+---+---+---+---+
2928 // | 0 | 1 | 2 | 3 | 1 | 3 |
2929 // +---+---+---+---+---+---+
2932 // Duplicate, advance r. End of slice. Split at w.
2934 let len = self.len();
2936 return (self, &mut []);
2939 let ptr = self.as_mut_ptr();
2940 let mut next_read: usize = 1;
2941 let mut next_write: usize = 1;
2943 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2944 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2945 // one element before `ptr_write`, but `next_write` starts at 1, so
2946 // `prev_ptr_write` is never less than 0 and is inside the slice.
2947 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2948 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2949 // and `prev_ptr_write.offset(1)`.
2951 // `next_write` is also incremented at most once per loop at most meaning
2952 // no element is skipped when it may need to be swapped.
2954 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2955 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2956 // The explanation is simply that `next_read >= next_write` is always true,
2957 // thus `next_read > next_write - 1` is too.
2959 // Avoid bounds checks by using raw pointers.
2960 while next_read < len {
2961 let ptr_read = ptr.add(next_read);
2962 let prev_ptr_write = ptr.add(next_write - 1);
2963 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2964 if next_read != next_write {
2965 let ptr_write = prev_ptr_write.add(1);
2966 mem::swap(&mut *ptr_read, &mut *ptr_write);
2974 self.split_at_mut(next_write)
2977 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2978 /// to the same key.
2980 /// Returns two slices. The first contains no consecutive repeated elements.
2981 /// The second contains all the duplicates in no specified order.
2983 /// If the slice is sorted, the first returned slice contains no duplicates.
2988 /// #![feature(slice_partition_dedup)]
2990 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2992 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2994 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2995 /// assert_eq!(duplicates, [21, 30, 13]);
2997 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2999 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
3001 F: FnMut(&mut T) -> K,
3004 self.partition_dedup_by(|a, b| key(a) == key(b))
3007 /// Rotates the slice in-place such that the first `mid` elements of the
3008 /// slice move to the end while the last `self.len() - mid` elements move to
3009 /// the front. After calling `rotate_left`, the element previously at index
3010 /// `mid` will become the first element in the slice.
3014 /// This function will panic if `mid` is greater than the length of the
3015 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
3020 /// Takes linear (in `self.len()`) time.
3025 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3026 /// a.rotate_left(2);
3027 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
3030 /// Rotating a subslice:
3033 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3034 /// a[1..5].rotate_left(1);
3035 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
3037 #[stable(feature = "slice_rotate", since = "1.26.0")]
3038 pub fn rotate_left(&mut self, mid: usize) {
3039 assert!(mid <= self.len());
3040 let k = self.len() - mid;
3041 let p = self.as_mut_ptr();
3043 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3044 // valid for reading and writing, as required by `ptr_rotate`.
3046 rotate::ptr_rotate(mid, p.add(mid), k);
3050 /// Rotates the slice in-place such that the first `self.len() - k`
3051 /// elements of the slice move to the end while the last `k` elements move
3052 /// to the front. After calling `rotate_right`, the element previously at
3053 /// index `self.len() - k` will become the first element in the slice.
3057 /// This function will panic if `k` is greater than the length of the
3058 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
3063 /// Takes linear (in `self.len()`) time.
3068 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3069 /// a.rotate_right(2);
3070 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
3073 /// Rotate a subslice:
3076 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
3077 /// a[1..5].rotate_right(1);
3078 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
3080 #[stable(feature = "slice_rotate", since = "1.26.0")]
3081 pub fn rotate_right(&mut self, k: usize) {
3082 assert!(k <= self.len());
3083 let mid = self.len() - k;
3084 let p = self.as_mut_ptr();
3086 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
3087 // valid for reading and writing, as required by `ptr_rotate`.
3089 rotate::ptr_rotate(mid, p.add(mid), k);
3093 /// Fills `self` with elements by cloning `value`.
3098 /// let mut buf = vec![0; 10];
3100 /// assert_eq!(buf, vec![1; 10]);
3102 #[doc(alias = "memset")]
3103 #[stable(feature = "slice_fill", since = "1.50.0")]
3104 pub fn fill(&mut self, value: T)
3108 specialize::SpecFill::spec_fill(self, value);
3111 /// Fills `self` with elements returned by calling a closure repeatedly.
3113 /// This method uses a closure to create new values. If you'd rather
3114 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3115 /// trait to generate values, you can pass [`Default::default`] as the
3118 /// [`fill`]: slice::fill
3123 /// let mut buf = vec![1; 10];
3124 /// buf.fill_with(Default::default);
3125 /// assert_eq!(buf, vec![0; 10]);
3127 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3128 pub fn fill_with<F>(&mut self, mut f: F)
3137 /// Copies the elements from `src` into `self`.
3139 /// The length of `src` must be the same as `self`.
3143 /// This function will panic if the two slices have different lengths.
3147 /// Cloning two elements from a slice into another:
3150 /// let src = [1, 2, 3, 4];
3151 /// let mut dst = [0, 0];
3153 /// // Because the slices have to be the same length,
3154 /// // we slice the source slice from four elements
3155 /// // to two. It will panic if we don't do this.
3156 /// dst.clone_from_slice(&src[2..]);
3158 /// assert_eq!(src, [1, 2, 3, 4]);
3159 /// assert_eq!(dst, [3, 4]);
3162 /// Rust enforces that there can only be one mutable reference with no
3163 /// immutable references to a particular piece of data in a particular
3164 /// scope. Because of this, attempting to use `clone_from_slice` on a
3165 /// single slice will result in a compile failure:
3168 /// let mut slice = [1, 2, 3, 4, 5];
3170 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3173 /// To work around this, we can use [`split_at_mut`] to create two distinct
3174 /// sub-slices from a slice:
3177 /// let mut slice = [1, 2, 3, 4, 5];
3180 /// let (left, right) = slice.split_at_mut(2);
3181 /// left.clone_from_slice(&right[1..]);
3184 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3187 /// [`copy_from_slice`]: slice::copy_from_slice
3188 /// [`split_at_mut`]: slice::split_at_mut
3189 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3191 pub fn clone_from_slice(&mut self, src: &[T])
3195 self.spec_clone_from(src);
3198 /// Copies all elements from `src` into `self`, using a memcpy.
3200 /// The length of `src` must be the same as `self`.
3202 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3206 /// This function will panic if the two slices have different lengths.
3210 /// Copying two elements from a slice into another:
3213 /// let src = [1, 2, 3, 4];
3214 /// let mut dst = [0, 0];
3216 /// // Because the slices have to be the same length,
3217 /// // we slice the source slice from four elements
3218 /// // to two. It will panic if we don't do this.
3219 /// dst.copy_from_slice(&src[2..]);
3221 /// assert_eq!(src, [1, 2, 3, 4]);
3222 /// assert_eq!(dst, [3, 4]);
3225 /// Rust enforces that there can only be one mutable reference with no
3226 /// immutable references to a particular piece of data in a particular
3227 /// scope. Because of this, attempting to use `copy_from_slice` on a
3228 /// single slice will result in a compile failure:
3231 /// let mut slice = [1, 2, 3, 4, 5];
3233 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3236 /// To work around this, we can use [`split_at_mut`] to create two distinct
3237 /// sub-slices from a slice:
3240 /// let mut slice = [1, 2, 3, 4, 5];
3243 /// let (left, right) = slice.split_at_mut(2);
3244 /// left.copy_from_slice(&right[1..]);
3247 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3250 /// [`clone_from_slice`]: slice::clone_from_slice
3251 /// [`split_at_mut`]: slice::split_at_mut
3252 #[doc(alias = "memcpy")]
3253 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3255 pub fn copy_from_slice(&mut self, src: &[T])
3259 // The panic code path was put into a cold function to not bloat the
3264 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3266 "source slice length ({}) does not match destination slice length ({})",
3271 if self.len() != src.len() {
3272 len_mismatch_fail(self.len(), src.len());
3275 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3276 // checked to have the same length. The slices cannot overlap because
3277 // mutable references are exclusive.
3279 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3283 /// Copies elements from one part of the slice to another part of itself,
3284 /// using a memmove.
3286 /// `src` is the range within `self` to copy from. `dest` is the starting
3287 /// index of the range within `self` to copy to, which will have the same
3288 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3289 /// must be less than or equal to `self.len()`.
3293 /// This function will panic if either range exceeds the end of the slice,
3294 /// or if the end of `src` is before the start.
3298 /// Copying four bytes within a slice:
3301 /// let mut bytes = *b"Hello, World!";
3303 /// bytes.copy_within(1..5, 8);
3305 /// assert_eq!(&bytes, b"Hello, Wello!");
3307 #[stable(feature = "copy_within", since = "1.37.0")]
3309 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3313 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3314 let count = src_end - src_start;
3315 assert!(dest <= self.len() - count, "dest is out of bounds");
3316 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3317 // as have those for `ptr::add`.
3319 // Derive both `src_ptr` and `dest_ptr` from the same loan
3320 let ptr = self.as_mut_ptr();
3321 let src_ptr = ptr.add(src_start);
3322 let dest_ptr = ptr.add(dest);
3323 ptr::copy(src_ptr, dest_ptr, count);
3327 /// Swaps all elements in `self` with those in `other`.
3329 /// The length of `other` must be the same as `self`.
3333 /// This function will panic if the two slices have different lengths.
3337 /// Swapping two elements across slices:
3340 /// let mut slice1 = [0, 0];
3341 /// let mut slice2 = [1, 2, 3, 4];
3343 /// slice1.swap_with_slice(&mut slice2[2..]);
3345 /// assert_eq!(slice1, [3, 4]);
3346 /// assert_eq!(slice2, [1, 2, 0, 0]);
3349 /// Rust enforces that there can only be one mutable reference to a
3350 /// particular piece of data in a particular scope. Because of this,
3351 /// attempting to use `swap_with_slice` on a single slice will result in
3352 /// a compile failure:
3355 /// let mut slice = [1, 2, 3, 4, 5];
3356 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3359 /// To work around this, we can use [`split_at_mut`] to create two distinct
3360 /// mutable sub-slices from a slice:
3363 /// let mut slice = [1, 2, 3, 4, 5];
3366 /// let (left, right) = slice.split_at_mut(2);
3367 /// left.swap_with_slice(&mut right[1..]);
3370 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3373 /// [`split_at_mut`]: slice::split_at_mut
3374 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3376 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3377 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3378 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3379 // checked to have the same length. The slices cannot overlap because
3380 // mutable references are exclusive.
3382 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3386 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3387 fn align_to_offsets<U>(&self) -> (usize, usize) {
3388 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3389 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3391 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3392 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3393 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3395 // Formula to calculate this is:
3397 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3398 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3400 // Expanded and simplified:
3402 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3403 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3405 // Luckily since all this is constant-evaluated... performance here matters not!
3407 fn gcd(a: usize, b: usize) -> usize {
3408 use crate::intrinsics;
3409 // iterative stein’s algorithm
3410 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3411 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3413 // SAFETY: `a` and `b` are checked to be non-zero values.
3414 let (ctz_a, mut ctz_b) = unsafe {
3421 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3423 let k = ctz_a.min(ctz_b);
3424 let mut a = a >> ctz_a;
3427 // remove all factors of 2 from b
3430 mem::swap(&mut a, &mut b);
3433 // SAFETY: `b` is checked to be non-zero.
3438 ctz_b = intrinsics::cttz_nonzero(b);
3443 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3444 let ts: usize = mem::size_of::<U>() / gcd;
3445 let us: usize = mem::size_of::<T>() / gcd;
3447 // Armed with this knowledge, we can find how many `U`s we can fit!
3448 let us_len = self.len() / ts * us;
3449 // And how many `T`s will be in the trailing slice!
3450 let ts_len = self.len() % ts;
3454 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3457 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3458 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3459 /// length possible for a given type and input slice, but only your algorithm's performance
3460 /// should depend on that, not its correctness. It is permissible for all of the input data to
3461 /// be returned as the prefix or suffix slice.
3463 /// This method has no purpose when either input element `T` or output element `U` are
3464 /// zero-sized and will return the original slice without splitting anything.
3468 /// This method is essentially a `transmute` with respect to the elements in the returned
3469 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3477 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3478 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3479 /// // less_efficient_algorithm_for_bytes(prefix);
3480 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3481 /// // less_efficient_algorithm_for_bytes(suffix);
3484 #[stable(feature = "slice_align_to", since = "1.30.0")]
3486 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3487 // Note that most of this function will be constant-evaluated,
3488 if U::IS_ZST || T::IS_ZST {
3489 // handle ZSTs specially, which is – don't handle them at all.
3490 return (self, &[], &[]);
3493 // First, find at what point do we split between the first and 2nd slice. Easy with
3494 // ptr.align_offset.
3495 let ptr = self.as_ptr();
3496 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3497 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3498 if offset > self.len() {
3501 let (left, rest) = self.split_at(offset);
3502 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3503 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3504 // since the caller guarantees that we can transmute `T` to `U` safely.
3508 from_raw_parts(rest.as_ptr() as *const U, us_len),
3509 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3515 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3518 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3519 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3520 /// length possible for a given type and input slice, but only your algorithm's performance
3521 /// should depend on that, not its correctness. It is permissible for all of the input data to
3522 /// be returned as the prefix or suffix slice.
3524 /// This method has no purpose when either input element `T` or output element `U` are
3525 /// zero-sized and will return the original slice without splitting anything.
3529 /// This method is essentially a `transmute` with respect to the elements in the returned
3530 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3538 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3539 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3540 /// // less_efficient_algorithm_for_bytes(prefix);
3541 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3542 /// // less_efficient_algorithm_for_bytes(suffix);
3545 #[stable(feature = "slice_align_to", since = "1.30.0")]
3547 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3548 // Note that most of this function will be constant-evaluated,
3549 if U::IS_ZST || T::IS_ZST {
3550 // handle ZSTs specially, which is – don't handle them at all.
3551 return (self, &mut [], &mut []);
3554 // First, find at what point do we split between the first and 2nd slice. Easy with
3555 // ptr.align_offset.
3556 let ptr = self.as_ptr();
3557 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3558 // rest of the method. This is done by passing a pointer to &[T] with an
3559 // alignment targeted for U.
3560 // `crate::ptr::align_offset` is called with a correctly aligned and
3561 // valid pointer `ptr` (it comes from a reference to `self`) and with
3562 // a size that is a power of two (since it comes from the alignment for U),
3563 // satisfying its safety constraints.
3564 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3565 if offset > self.len() {
3566 (self, &mut [], &mut [])
3568 let (left, rest) = self.split_at_mut(offset);
3569 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3570 let rest_len = rest.len();
3571 let mut_ptr = rest.as_mut_ptr();
3572 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3573 // SAFETY: see comments for `align_to`.
3577 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3578 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3584 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3586 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3587 /// postconditions as that method. You're only assured that
3588 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3590 /// Notably, all of the following are possible:
3591 /// - `prefix.len() >= LANES`.
3592 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3593 /// - `suffix.len() >= LANES`.
3595 /// That said, this is a safe method, so if you're only writing safe code,
3596 /// then this can at most cause incorrect logic, not unsoundness.
3600 /// This will panic if the size of the SIMD type is different from
3601 /// `LANES` times that of the scalar.
3603 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3604 /// that from ever happening, as only power-of-two numbers of lanes are
3605 /// supported. It's possible that, in the future, those restrictions might
3606 /// be lifted in a way that would make it possible to see panics from this
3607 /// method for something like `LANES == 3`.
3612 /// #![feature(portable_simd)]
3613 /// use core::simd::SimdFloat;
3615 /// let short = &[1, 2, 3];
3616 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3617 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3619 /// // They might be split in any possible way between prefix and suffix
3620 /// let it = prefix.iter().chain(suffix).copied();
3621 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3623 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3624 /// use std::ops::Add;
3625 /// use std::simd::f32x4;
3626 /// let (prefix, middle, suffix) = x.as_simd();
3627 /// let sums = f32x4::from_array([
3628 /// prefix.iter().copied().sum(),
3631 /// suffix.iter().copied().sum(),
3633 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3634 /// sums.reduce_sum()
3637 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3638 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3640 #[unstable(feature = "portable_simd", issue = "86656")]
3642 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3644 Simd<T, LANES>: AsRef<[T; LANES]>,
3645 T: simd::SimdElement,
3646 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3648 // These are expected to always match, as vector types are laid out like
3649 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3650 // might as well double-check since it'll optimize away anyhow.
3651 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3653 // SAFETY: The simd types have the same layout as arrays, just with
3654 // potentially-higher alignment, so the de-facto transmutes are sound.
3655 unsafe { self.align_to() }
3658 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3660 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3661 /// postconditions as that method. You're only assured that
3662 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3664 /// Notably, all of the following are possible:
3665 /// - `prefix.len() >= LANES`.
3666 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3667 /// - `suffix.len() >= LANES`.
3669 /// That said, this is a safe method, so if you're only writing safe code,
3670 /// then this can at most cause incorrect logic, not unsoundness.
3672 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3676 /// This will panic if the size of the SIMD type is different from
3677 /// `LANES` times that of the scalar.
3679 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3680 /// that from ever happening, as only power-of-two numbers of lanes are
3681 /// supported. It's possible that, in the future, those restrictions might
3682 /// be lifted in a way that would make it possible to see panics from this
3683 /// method for something like `LANES == 3`.
3684 #[unstable(feature = "portable_simd", issue = "86656")]
3686 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3688 Simd<T, LANES>: AsMut<[T; LANES]>,
3689 T: simd::SimdElement,
3690 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3692 // These are expected to always match, as vector types are laid out like
3693 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3694 // might as well double-check since it'll optimize away anyhow.
3695 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3697 // SAFETY: The simd types have the same layout as arrays, just with
3698 // potentially-higher alignment, so the de-facto transmutes are sound.
3699 unsafe { self.align_to_mut() }
3702 /// Checks if the elements of this slice are sorted.
3704 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3705 /// slice yields exactly zero or one element, `true` is returned.
3707 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3708 /// implies that this function returns `false` if any two consecutive items are not
3714 /// #![feature(is_sorted)]
3715 /// let empty: [i32; 0] = [];
3717 /// assert!([1, 2, 2, 9].is_sorted());
3718 /// assert!(![1, 3, 2, 4].is_sorted());
3719 /// assert!([0].is_sorted());
3720 /// assert!(empty.is_sorted());
3721 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3724 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3726 pub fn is_sorted(&self) -> bool
3730 self.is_sorted_by(|a, b| a.partial_cmp(b))
3733 /// Checks if the elements of this slice are sorted using the given comparator function.
3735 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3736 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3737 /// [`is_sorted`]; see its documentation for more information.
3739 /// [`is_sorted`]: slice::is_sorted
3740 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3742 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3744 F: FnMut(&T, &T) -> Option<Ordering>,
3746 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3749 /// Checks if the elements of this slice are sorted using the given key extraction function.
3751 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3752 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3753 /// documentation for more information.
3755 /// [`is_sorted`]: slice::is_sorted
3760 /// #![feature(is_sorted)]
3762 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3763 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3766 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3768 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3773 self.iter().is_sorted_by_key(f)
3776 /// Returns the index of the partition point according to the given predicate
3777 /// (the index of the first element of the second partition).
3779 /// The slice is assumed to be partitioned according to the given predicate.
3780 /// This means that all elements for which the predicate returns true are at the start of the slice
3781 /// and all elements for which the predicate returns false are at the end.
3782 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3783 /// (all odd numbers are at the start, all even at the end).
3785 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3786 /// as this method performs a kind of binary search.
3788 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3790 /// [`binary_search`]: slice::binary_search
3791 /// [`binary_search_by`]: slice::binary_search_by
3792 /// [`binary_search_by_key`]: slice::binary_search_by_key
3797 /// let v = [1, 2, 3, 3, 5, 6, 7];
3798 /// let i = v.partition_point(|&x| x < 5);
3800 /// assert_eq!(i, 4);
3801 /// assert!(v[..i].iter().all(|&x| x < 5));
3802 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3805 /// If all elements of the slice match the predicate, including if the slice
3806 /// is empty, then the length of the slice will be returned:
3809 /// let a = [2, 4, 8];
3810 /// assert_eq!(a.partition_point(|x| x < &100), a.len());
3811 /// let a: [i32; 0] = [];
3812 /// assert_eq!(a.partition_point(|x| x < &100), 0);
3815 /// If you want to insert an item to a sorted vector, while maintaining
3819 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
3821 /// let idx = s.partition_point(|&x| x < num);
3822 /// s.insert(idx, num);
3823 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
3825 #[stable(feature = "partition_point", since = "1.52.0")]
3827 pub fn partition_point<P>(&self, mut pred: P) -> usize
3829 P: FnMut(&T) -> bool,
3831 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3834 /// Removes the subslice corresponding to the given range
3835 /// and returns a reference to it.
3837 /// Returns `None` and does not modify the slice if the given
3838 /// range is out of bounds.
3840 /// Note that this method only accepts one-sided ranges such as
3841 /// `2..` or `..6`, but not `2..6`.
3845 /// Taking the first three elements of a slice:
3848 /// #![feature(slice_take)]
3850 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3851 /// let mut first_three = slice.take(..3).unwrap();
3853 /// assert_eq!(slice, &['d']);
3854 /// assert_eq!(first_three, &['a', 'b', 'c']);
3857 /// Taking the last two elements of a slice:
3860 /// #![feature(slice_take)]
3862 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3863 /// let mut tail = slice.take(2..).unwrap();
3865 /// assert_eq!(slice, &['a', 'b']);
3866 /// assert_eq!(tail, &['c', 'd']);
3869 /// Getting `None` when `range` is out of bounds:
3872 /// #![feature(slice_take)]
3874 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3876 /// assert_eq!(None, slice.take(5..));
3877 /// assert_eq!(None, slice.take(..5));
3878 /// assert_eq!(None, slice.take(..=4));
3879 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3880 /// assert_eq!(Some(expected), slice.take(..4));
3883 #[must_use = "method does not modify the slice if the range is out of bounds"]
3884 #[unstable(feature = "slice_take", issue = "62280")]
3885 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3886 let (direction, split_index) = split_point_of(range)?;
3887 if split_index > self.len() {
3890 let (front, back) = self.split_at(split_index);
3892 Direction::Front => {
3896 Direction::Back => {
3903 /// Removes the subslice corresponding to the given range
3904 /// and returns a mutable reference to it.
3906 /// Returns `None` and does not modify the slice if the given
3907 /// range is out of bounds.
3909 /// Note that this method only accepts one-sided ranges such as
3910 /// `2..` or `..6`, but not `2..6`.
3914 /// Taking the first three elements of a slice:
3917 /// #![feature(slice_take)]
3919 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3920 /// let mut first_three = slice.take_mut(..3).unwrap();
3922 /// assert_eq!(slice, &mut ['d']);
3923 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3926 /// Taking the last two elements of a slice:
3929 /// #![feature(slice_take)]
3931 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3932 /// let mut tail = slice.take_mut(2..).unwrap();
3934 /// assert_eq!(slice, &mut ['a', 'b']);
3935 /// assert_eq!(tail, &mut ['c', 'd']);
3938 /// Getting `None` when `range` is out of bounds:
3941 /// #![feature(slice_take)]
3943 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3945 /// assert_eq!(None, slice.take_mut(5..));
3946 /// assert_eq!(None, slice.take_mut(..5));
3947 /// assert_eq!(None, slice.take_mut(..=4));
3948 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3949 /// assert_eq!(Some(expected), slice.take_mut(..4));
3952 #[must_use = "method does not modify the slice if the range is out of bounds"]
3953 #[unstable(feature = "slice_take", issue = "62280")]
3954 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3955 self: &mut &'a mut Self,
3957 ) -> Option<&'a mut Self> {
3958 let (direction, split_index) = split_point_of(range)?;
3959 if split_index > self.len() {
3962 let (front, back) = mem::take(self).split_at_mut(split_index);
3964 Direction::Front => {
3968 Direction::Back => {
3975 /// Removes the first element of the slice and returns a reference
3978 /// Returns `None` if the slice is empty.
3983 /// #![feature(slice_take)]
3985 /// let mut slice: &[_] = &['a', 'b', 'c'];
3986 /// let first = slice.take_first().unwrap();
3988 /// assert_eq!(slice, &['b', 'c']);
3989 /// assert_eq!(first, &'a');
3992 #[unstable(feature = "slice_take", issue = "62280")]
3993 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3994 let (first, rem) = self.split_first()?;
3999 /// Removes the first element of the slice and returns a mutable
4000 /// reference to it.
4002 /// Returns `None` if the slice is empty.
4007 /// #![feature(slice_take)]
4009 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4010 /// let first = slice.take_first_mut().unwrap();
4013 /// assert_eq!(slice, &['b', 'c']);
4014 /// assert_eq!(first, &'d');
4017 #[unstable(feature = "slice_take", issue = "62280")]
4018 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4019 let (first, rem) = mem::take(self).split_first_mut()?;
4024 /// Removes the last element of the slice and returns a reference
4027 /// Returns `None` if the slice is empty.
4032 /// #![feature(slice_take)]
4034 /// let mut slice: &[_] = &['a', 'b', 'c'];
4035 /// let last = slice.take_last().unwrap();
4037 /// assert_eq!(slice, &['a', 'b']);
4038 /// assert_eq!(last, &'c');
4041 #[unstable(feature = "slice_take", issue = "62280")]
4042 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
4043 let (last, rem) = self.split_last()?;
4048 /// Removes the last element of the slice and returns a mutable
4049 /// reference to it.
4051 /// Returns `None` if the slice is empty.
4056 /// #![feature(slice_take)]
4058 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
4059 /// let last = slice.take_last_mut().unwrap();
4062 /// assert_eq!(slice, &['a', 'b']);
4063 /// assert_eq!(last, &'d');
4066 #[unstable(feature = "slice_take", issue = "62280")]
4067 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
4068 let (last, rem) = mem::take(self).split_last_mut()?;
4074 impl<T, const N: usize> [[T; N]] {
4075 /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
4079 /// This panics if the length of the resulting slice would overflow a `usize`.
4081 /// This is only possible when flattening a slice of arrays of zero-sized
4082 /// types, and thus tends to be irrelevant in practice. If
4083 /// `size_of::<T>() > 0`, this will never panic.
4088 /// #![feature(slice_flatten)]
4090 /// assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);
4093 /// [[1, 2, 3], [4, 5, 6]].flatten(),
4094 /// [[1, 2], [3, 4], [5, 6]].flatten(),
4097 /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
4098 /// assert!(slice_of_empty_arrays.flatten().is_empty());
4100 /// let empty_slice_of_arrays: &[[u32; 10]] = &[];
4101 /// assert!(empty_slice_of_arrays.flatten().is_empty());
4103 #[unstable(feature = "slice_flatten", issue = "95629")]
4104 pub fn flatten(&self) -> &[T] {
4105 let len = if T::IS_ZST {
4106 self.len().checked_mul(N).expect("slice len overflow")
4108 // SAFETY: `self.len() * N` cannot overflow because `self` is
4109 // already in the address space.
4110 unsafe { self.len().unchecked_mul(N) }
4112 // SAFETY: `[T]` is layout-identical to `[T; N]`
4113 unsafe { from_raw_parts(self.as_ptr().cast(), len) }
4116 /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
4120 /// This panics if the length of the resulting slice would overflow a `usize`.
4122 /// This is only possible when flattening a slice of arrays of zero-sized
4123 /// types, and thus tends to be irrelevant in practice. If
4124 /// `size_of::<T>() > 0`, this will never panic.
4129 /// #![feature(slice_flatten)]
4131 /// fn add_5_to_all(slice: &mut [i32]) {
4132 /// for i in slice {
4137 /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
4138 /// add_5_to_all(array.flatten_mut());
4139 /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
4141 #[unstable(feature = "slice_flatten", issue = "95629")]
4142 pub fn flatten_mut(&mut self) -> &mut [T] {
4143 let len = if T::IS_ZST {
4144 self.len().checked_mul(N).expect("slice len overflow")
4146 // SAFETY: `self.len() * N` cannot overflow because `self` is
4147 // already in the address space.
4148 unsafe { self.len().unchecked_mul(N) }
4150 // SAFETY: `[T]` is layout-identical to `[T; N]`
4151 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
4157 /// Sorts the slice of floats.
4159 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4160 /// the ordering defined by [`f32::total_cmp`].
4162 /// # Current implementation
4164 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4169 /// #![feature(sort_floats)]
4170 /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
4172 /// v.sort_floats();
4173 /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
4174 /// assert_eq!(&v[..8], &sorted[..8]);
4175 /// assert!(v[8].is_nan());
4177 #[unstable(feature = "sort_floats", issue = "93396")]
4179 pub fn sort_floats(&mut self) {
4180 self.sort_unstable_by(f32::total_cmp);
4186 /// Sorts the slice of floats.
4188 /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
4189 /// the ordering defined by [`f64::total_cmp`].
4191 /// # Current implementation
4193 /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
4198 /// #![feature(sort_floats)]
4199 /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
4201 /// v.sort_floats();
4202 /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
4203 /// assert_eq!(&v[..8], &sorted[..8]);
4204 /// assert!(v[8].is_nan());
4206 #[unstable(feature = "sort_floats", issue = "93396")]
4208 pub fn sort_floats(&mut self) {
4209 self.sort_unstable_by(f64::total_cmp);
4213 trait CloneFromSpec<T> {
4214 fn spec_clone_from(&mut self, src: &[T]);
4217 impl<T> CloneFromSpec<T> for [T]
4222 default fn spec_clone_from(&mut self, src: &[T]) {
4223 assert!(self.len() == src.len(), "destination and source slices have different lengths");
4224 // NOTE: We need to explicitly slice them to the same length
4225 // to make it easier for the optimizer to elide bounds checking.
4226 // But since it can't be relied on we also have an explicit specialization for T: Copy.
4227 let len = self.len();
4228 let src = &src[..len];
4230 self[i].clone_from(&src[i]);
4235 impl<T> CloneFromSpec<T> for [T]
4240 fn spec_clone_from(&mut self, src: &[T]) {
4241 self.copy_from_slice(src);
4245 #[stable(feature = "rust1", since = "1.0.0")]
4246 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4247 impl<T> const Default for &[T] {
4248 /// Creates an empty slice.
4249 fn default() -> Self {
4254 #[stable(feature = "mut_slice_default", since = "1.5.0")]
4255 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
4256 impl<T> const Default for &mut [T] {
4257 /// Creates a mutable empty slice.
4258 fn default() -> Self {
4263 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4264 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4265 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4266 /// `str`) to slices, and then this trait will be replaced or abolished.
4267 pub trait SlicePattern {
4268 /// The element type of the slice being matched on.
4271 /// Currently, the consumers of `SlicePattern` need a slice.
4272 fn as_slice(&self) -> &[Self::Item];
4275 #[stable(feature = "slice_strip", since = "1.51.0")]
4276 impl<T> SlicePattern for [T] {
4280 fn as_slice(&self) -> &[Self::Item] {
4285 #[stable(feature = "slice_strip", since = "1.51.0")]
4286 impl<T, const N: usize> SlicePattern for [T; N] {
4290 fn as_slice(&self) -> &[Self::Item] {