1 //! Slice management and manipulation.
3 //! For more details see [`std::slice`].
5 //! [`std::slice`]: ../../std/slice/index.html
7 #![stable(feature = "rust1", since = "1.0.0")]
9 use crate::cmp::Ordering::{self, Greater, Less};
10 use crate::marker::Copy;
12 use crate::num::NonZeroUsize;
13 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
14 use crate::option::Option;
15 use crate::option::Option::{None, Some};
17 use crate::result::Result;
18 use crate::result::Result::{Err, Ok};
19 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
20 use crate::simd::{self, Simd};
24 feature = "slice_internals",
26 reason = "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Chunks, ChunksMut, Windows};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{Iter, IterMut};
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter::{RSplit, RSplitMut};
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter::{ChunksExact, ChunksExactMut};
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter::{ArrayChunks, ArrayChunksMut};
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter::ArrayWindows;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter::{GroupBy, GroupByMut};
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter::{SplitInclusive, SplitInclusiveMut};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw::{from_raw_parts, from_raw_parts_mut};
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw::{from_mut, from_ref};
74 #[unstable(feature = "slice_from_ptr_range", issue = "89792")]
75 pub use raw::{from_mut_ptr_range, from_ptr_range};
77 // This function is public only because there is no other way to unit test heapsort.
78 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
79 pub use sort::heapsort;
81 #[stable(feature = "slice_get_slice", since = "1.28.0")]
82 pub use index::SliceIndex;
84 #[unstable(feature = "slice_range", issue = "76393")]
87 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
88 pub use ascii::EscapeAscii;
90 /// Calculates the direction and split point of a one-sided range.
92 /// This is a helper function for `take` and `take_mut` that returns
93 /// the direction of the split (front or back) as well as the index at
94 /// which to split. Returns `None` if the split index would overflow.
96 fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
99 Some(match (range.start_bound(), range.end_bound()) {
100 (Unbounded, Excluded(i)) => (Direction::Front, *i),
101 (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
102 (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
103 (Included(i), Unbounded) => (Direction::Back, *i),
116 /// Returns the number of elements in the slice.
121 /// let a = [1, 2, 3];
122 /// assert_eq!(a.len(), 3);
124 #[lang = "slice_len_fn"]
125 #[stable(feature = "rust1", since = "1.0.0")]
126 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
128 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
129 pub const fn len(&self) -> usize {
130 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
131 // As of this writing this causes a "Const-stable functions can only call other
132 // const-stable functions" error.
134 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
135 // and PtrComponents<T> have the same memory layouts. Only std can make this
137 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
140 /// Returns `true` if the slice has a length of 0.
145 /// let a = [1, 2, 3];
146 /// assert!(!a.is_empty());
148 #[stable(feature = "rust1", since = "1.0.0")]
149 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
151 pub const fn is_empty(&self) -> bool {
155 /// Returns the first element of the slice, or `None` if it is empty.
160 /// let v = [10, 40, 30];
161 /// assert_eq!(Some(&10), v.first());
163 /// let w: &[i32] = &[];
164 /// assert_eq!(None, w.first());
166 #[stable(feature = "rust1", since = "1.0.0")]
167 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
169 pub const fn first(&self) -> Option<&T> {
170 if let [first, ..] = self { Some(first) } else { None }
173 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
178 /// let x = &mut [0, 1, 2];
180 /// if let Some(first) = x.first_mut() {
183 /// assert_eq!(x, &[5, 1, 2]);
185 #[stable(feature = "rust1", since = "1.0.0")]
186 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
188 pub const fn first_mut(&mut self) -> Option<&mut T> {
189 if let [first, ..] = self { Some(first) } else { None }
192 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
197 /// let x = &[0, 1, 2];
199 /// if let Some((first, elements)) = x.split_first() {
200 /// assert_eq!(first, &0);
201 /// assert_eq!(elements, &[1, 2]);
204 #[stable(feature = "slice_splits", since = "1.5.0")]
205 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
207 pub const fn split_first(&self) -> Option<(&T, &[T])> {
208 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
211 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
216 /// let x = &mut [0, 1, 2];
218 /// if let Some((first, elements)) = x.split_first_mut() {
223 /// assert_eq!(x, &[3, 4, 5]);
225 #[stable(feature = "slice_splits", since = "1.5.0")]
226 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
228 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
229 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
232 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
237 /// let x = &[0, 1, 2];
239 /// if let Some((last, elements)) = x.split_last() {
240 /// assert_eq!(last, &2);
241 /// assert_eq!(elements, &[0, 1]);
244 #[stable(feature = "slice_splits", since = "1.5.0")]
245 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
247 pub const fn split_last(&self) -> Option<(&T, &[T])> {
248 if let [init @ .., last] = self { Some((last, init)) } else { None }
251 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
256 /// let x = &mut [0, 1, 2];
258 /// if let Some((last, elements)) = x.split_last_mut() {
263 /// assert_eq!(x, &[4, 5, 3]);
265 #[stable(feature = "slice_splits", since = "1.5.0")]
266 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
268 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
269 if let [init @ .., last] = self { Some((last, init)) } else { None }
272 /// Returns the last element of the slice, or `None` if it is empty.
277 /// let v = [10, 40, 30];
278 /// assert_eq!(Some(&30), v.last());
280 /// let w: &[i32] = &[];
281 /// assert_eq!(None, w.last());
283 #[stable(feature = "rust1", since = "1.0.0")]
284 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
286 pub const fn last(&self) -> Option<&T> {
287 if let [.., last] = self { Some(last) } else { None }
290 /// Returns a mutable pointer to the last item in the slice.
295 /// let x = &mut [0, 1, 2];
297 /// if let Some(last) = x.last_mut() {
300 /// assert_eq!(x, &[0, 1, 10]);
302 #[stable(feature = "rust1", since = "1.0.0")]
303 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
305 pub const fn last_mut(&mut self) -> Option<&mut T> {
306 if let [.., last] = self { Some(last) } else { None }
309 /// Returns a reference to an element or subslice depending on the type of
312 /// - If given a position, returns a reference to the element at that
313 /// position or `None` if out of bounds.
314 /// - If given a range, returns the subslice corresponding to that range,
315 /// or `None` if out of bounds.
320 /// let v = [10, 40, 30];
321 /// assert_eq!(Some(&40), v.get(1));
322 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
323 /// assert_eq!(None, v.get(3));
324 /// assert_eq!(None, v.get(0..4));
326 #[stable(feature = "rust1", since = "1.0.0")]
328 pub fn get<I>(&self, index: I) -> Option<&I::Output>
335 /// Returns a mutable reference to an element or subslice depending on the
336 /// type of index (see [`get`]) or `None` if the index is out of bounds.
338 /// [`get`]: slice::get
343 /// let x = &mut [0, 1, 2];
345 /// if let Some(elem) = x.get_mut(1) {
348 /// assert_eq!(x, &[0, 42, 2]);
350 #[stable(feature = "rust1", since = "1.0.0")]
352 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
359 /// Returns a reference to an element or subslice, without doing bounds
362 /// For a safe alternative see [`get`].
366 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
367 /// even if the resulting reference is not used.
369 /// [`get`]: slice::get
370 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
375 /// let x = &[1, 2, 4];
378 /// assert_eq!(x.get_unchecked(1), &2);
381 #[stable(feature = "rust1", since = "1.0.0")]
383 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
387 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
388 // the slice is dereferenceable because `self` is a safe reference.
389 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
390 unsafe { &*index.get_unchecked(self) }
393 /// Returns a mutable reference to an element or subslice, without doing
396 /// For a safe alternative see [`get_mut`].
400 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
401 /// even if the resulting reference is not used.
403 /// [`get_mut`]: slice::get_mut
404 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
409 /// let x = &mut [1, 2, 4];
412 /// let elem = x.get_unchecked_mut(1);
415 /// assert_eq!(x, &[1, 13, 4]);
417 #[stable(feature = "rust1", since = "1.0.0")]
419 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
423 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
424 // the slice is dereferenceable because `self` is a safe reference.
425 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
426 unsafe { &mut *index.get_unchecked_mut(self) }
429 /// Returns a raw pointer to the slice's buffer.
431 /// The caller must ensure that the slice outlives the pointer this
432 /// function returns, or else it will end up pointing to garbage.
434 /// The caller must also ensure that the memory the pointer (non-transitively) points to
435 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
436 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
438 /// Modifying the container referenced by this slice may cause its buffer
439 /// to be reallocated, which would also make any pointers to it invalid.
444 /// let x = &[1, 2, 4];
445 /// let x_ptr = x.as_ptr();
448 /// for i in 0..x.len() {
449 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
454 /// [`as_mut_ptr`]: slice::as_mut_ptr
455 #[stable(feature = "rust1", since = "1.0.0")]
456 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
458 pub const fn as_ptr(&self) -> *const T {
459 self as *const [T] as *const T
462 /// Returns an unsafe mutable pointer to the slice's buffer.
464 /// The caller must ensure that the slice outlives the pointer this
465 /// function returns, or else it will end up pointing to garbage.
467 /// Modifying the container referenced by this slice may cause its buffer
468 /// to be reallocated, which would also make any pointers to it invalid.
473 /// let x = &mut [1, 2, 4];
474 /// let x_ptr = x.as_mut_ptr();
477 /// for i in 0..x.len() {
478 /// *x_ptr.add(i) += 2;
481 /// assert_eq!(x, &[3, 4, 6]);
483 #[stable(feature = "rust1", since = "1.0.0")]
484 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
486 pub const fn as_mut_ptr(&mut self) -> *mut T {
487 self as *mut [T] as *mut T
490 /// Returns the two raw pointers spanning the slice.
492 /// The returned range is half-open, which means that the end pointer
493 /// points *one past* the last element of the slice. This way, an empty
494 /// slice is represented by two equal pointers, and the difference between
495 /// the two pointers represents the size of the slice.
497 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
498 /// requires extra caution, as it does not point to a valid element in the
501 /// This function is useful for interacting with foreign interfaces which
502 /// use two pointers to refer to a range of elements in memory, as is
505 /// It can also be useful to check if a pointer to an element refers to an
506 /// element of this slice:
509 /// let a = [1, 2, 3];
510 /// let x = &a[1] as *const _;
511 /// let y = &5 as *const _;
513 /// assert!(a.as_ptr_range().contains(&x));
514 /// assert!(!a.as_ptr_range().contains(&y));
517 /// [`as_ptr`]: slice::as_ptr
518 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
519 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
521 pub const fn as_ptr_range(&self) -> Range<*const T> {
522 let start = self.as_ptr();
523 // SAFETY: The `add` here is safe, because:
525 // - Both pointers are part of the same object, as pointing directly
526 // past the object also counts.
528 // - The size of the slice is never larger than isize::MAX bytes, as
530 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
531 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
532 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
533 // (This doesn't seem normative yet, but the very same assumption is
534 // made in many places, including the Index implementation of slices.)
536 // - There is no wrapping around involved, as slices do not wrap past
537 // the end of the address space.
539 // See the documentation of pointer::add.
540 let end = unsafe { start.add(self.len()) };
544 /// Returns the two unsafe mutable pointers spanning the slice.
546 /// The returned range is half-open, which means that the end pointer
547 /// points *one past* the last element of the slice. This way, an empty
548 /// slice is represented by two equal pointers, and the difference between
549 /// the two pointers represents the size of the slice.
551 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
552 /// pointer requires extra caution, as it does not point to a valid element
555 /// This function is useful for interacting with foreign interfaces which
556 /// use two pointers to refer to a range of elements in memory, as is
559 /// [`as_mut_ptr`]: slice::as_mut_ptr
560 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
561 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
563 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
564 let start = self.as_mut_ptr();
565 // SAFETY: See as_ptr_range() above for why `add` here is safe.
566 let end = unsafe { start.add(self.len()) };
570 /// Swaps two elements in the slice.
574 /// * a - The index of the first element
575 /// * b - The index of the second element
579 /// Panics if `a` or `b` are out of bounds.
584 /// let mut v = ["a", "b", "c", "d", "e"];
586 /// assert!(v == ["a", "b", "e", "d", "c"]);
588 #[stable(feature = "rust1", since = "1.0.0")]
589 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
592 pub const fn swap(&mut self, a: usize, b: usize) {
593 // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
594 // Can't take two mutable loans from one vector, so instead use raw pointers.
595 let pa = ptr::addr_of_mut!(self[a]);
596 let pb = ptr::addr_of_mut!(self[b]);
597 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
598 // to elements in the slice and therefore are guaranteed to be valid and aligned.
599 // Note that accessing the elements behind `a` and `b` is checked and will
600 // panic when out of bounds.
606 /// Swaps two elements in the slice, without doing bounds checking.
608 /// For a safe alternative see [`swap`].
612 /// * a - The index of the first element
613 /// * b - The index of the second element
617 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
618 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
623 /// #![feature(slice_swap_unchecked)]
625 /// let mut v = ["a", "b", "c", "d"];
626 /// // SAFETY: we know that 1 and 3 are both indices of the slice
627 /// unsafe { v.swap_unchecked(1, 3) };
628 /// assert!(v == ["a", "d", "c", "b"]);
631 /// [`swap`]: slice::swap
632 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
633 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
634 #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
635 pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
636 #[cfg(debug_assertions)]
642 let ptr = self.as_mut_ptr();
643 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
645 ptr::swap(ptr.add(a), ptr.add(b));
649 /// Reverses the order of elements in the slice, in place.
654 /// let mut v = [1, 2, 3];
656 /// assert!(v == [3, 2, 1]);
658 #[stable(feature = "rust1", since = "1.0.0")]
660 pub fn reverse(&mut self) {
661 let half_len = self.len() / 2;
662 let Range { start, end } = self.as_mut_ptr_range();
664 // These slices will skip the middle item for an odd length,
665 // since that one doesn't need to move.
666 let (front_half, back_half) =
667 // SAFETY: Both are subparts of the original slice, so the memory
668 // range is valid, and they don't overlap because they're each only
669 // half (or less) of the original slice.
672 slice::from_raw_parts_mut(start, half_len),
673 slice::from_raw_parts_mut(end.sub(half_len), half_len),
677 // Introducing a function boundary here means that the two halves
678 // get `noalias` markers, allowing better optimization as LLVM
679 // knows that they're disjoint, unlike in the original slice.
680 revswap(front_half, back_half, half_len);
683 fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
684 debug_assert_eq!(a.len(), n);
685 debug_assert_eq!(b.len(), n);
687 // Because this function is first compiled in isolation,
688 // this check tells LLVM that the indexing below is
689 // in-bounds. Then after inlining -- once the actual
690 // lengths of the slices are known -- it's removed.
691 let (a, b) = (&mut a[..n], &mut b[..n]);
694 mem::swap(&mut a[i], &mut b[n - 1 - i]);
699 /// Returns an iterator over the slice.
704 /// let x = &[1, 2, 4];
705 /// let mut iterator = x.iter();
707 /// assert_eq!(iterator.next(), Some(&1));
708 /// assert_eq!(iterator.next(), Some(&2));
709 /// assert_eq!(iterator.next(), Some(&4));
710 /// assert_eq!(iterator.next(), None);
712 #[stable(feature = "rust1", since = "1.0.0")]
714 pub fn iter(&self) -> Iter<'_, T> {
718 /// Returns an iterator that allows modifying each value.
723 /// let x = &mut [1, 2, 4];
724 /// for elem in x.iter_mut() {
727 /// assert_eq!(x, &[3, 4, 6]);
729 #[stable(feature = "rust1", since = "1.0.0")]
731 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
735 /// Returns an iterator over all contiguous windows of length
736 /// `size`. The windows overlap. If the slice is shorter than
737 /// `size`, the iterator returns no values.
741 /// Panics if `size` is 0.
746 /// let slice = ['r', 'u', 's', 't'];
747 /// let mut iter = slice.windows(2);
748 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
749 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
750 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
751 /// assert!(iter.next().is_none());
754 /// If the slice is shorter than `size`:
757 /// let slice = ['f', 'o', 'o'];
758 /// let mut iter = slice.windows(4);
759 /// assert!(iter.next().is_none());
761 #[stable(feature = "rust1", since = "1.0.0")]
763 pub fn windows(&self, size: usize) -> Windows<'_, T> {
764 let size = NonZeroUsize::new(size).expect("size is zero");
765 Windows::new(self, size)
768 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
769 /// beginning of the slice.
771 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
772 /// slice, then the last chunk will not have length `chunk_size`.
774 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
775 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
780 /// Panics if `chunk_size` is 0.
785 /// let slice = ['l', 'o', 'r', 'e', 'm'];
786 /// let mut iter = slice.chunks(2);
787 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
788 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
789 /// assert_eq!(iter.next().unwrap(), &['m']);
790 /// assert!(iter.next().is_none());
793 /// [`chunks_exact`]: slice::chunks_exact
794 /// [`rchunks`]: slice::rchunks
795 #[stable(feature = "rust1", since = "1.0.0")]
797 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
798 assert_ne!(chunk_size, 0);
799 Chunks::new(self, chunk_size)
802 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
803 /// beginning of the slice.
805 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
806 /// length of the slice, then the last chunk will not have length `chunk_size`.
808 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
809 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
810 /// the end of the slice.
814 /// Panics if `chunk_size` is 0.
819 /// let v = &mut [0, 0, 0, 0, 0];
820 /// let mut count = 1;
822 /// for chunk in v.chunks_mut(2) {
823 /// for elem in chunk.iter_mut() {
828 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
831 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
832 /// [`rchunks_mut`]: slice::rchunks_mut
833 #[stable(feature = "rust1", since = "1.0.0")]
835 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
836 assert_ne!(chunk_size, 0);
837 ChunksMut::new(self, chunk_size)
840 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
841 /// beginning of the slice.
843 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
844 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
845 /// from the `remainder` function of the iterator.
847 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
848 /// resulting code better than in the case of [`chunks`].
850 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
851 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
855 /// Panics if `chunk_size` is 0.
860 /// let slice = ['l', 'o', 'r', 'e', 'm'];
861 /// let mut iter = slice.chunks_exact(2);
862 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
863 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
864 /// assert!(iter.next().is_none());
865 /// assert_eq!(iter.remainder(), &['m']);
868 /// [`chunks`]: slice::chunks
869 /// [`rchunks_exact`]: slice::rchunks_exact
870 #[stable(feature = "chunks_exact", since = "1.31.0")]
872 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
873 assert_ne!(chunk_size, 0);
874 ChunksExact::new(self, chunk_size)
877 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
878 /// beginning of the slice.
880 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
881 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
882 /// retrieved from the `into_remainder` function of the iterator.
884 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
885 /// resulting code better than in the case of [`chunks_mut`].
887 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
888 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
893 /// Panics if `chunk_size` is 0.
898 /// let v = &mut [0, 0, 0, 0, 0];
899 /// let mut count = 1;
901 /// for chunk in v.chunks_exact_mut(2) {
902 /// for elem in chunk.iter_mut() {
907 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
910 /// [`chunks_mut`]: slice::chunks_mut
911 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
912 #[stable(feature = "chunks_exact", since = "1.31.0")]
914 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
915 assert_ne!(chunk_size, 0);
916 ChunksExactMut::new(self, chunk_size)
919 /// Splits the slice into a slice of `N`-element arrays,
920 /// assuming that there's no remainder.
924 /// This may only be called when
925 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
931 /// #![feature(slice_as_chunks)]
932 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
933 /// let chunks: &[[char; 1]] =
934 /// // SAFETY: 1-element chunks never have remainder
935 /// unsafe { slice.as_chunks_unchecked() };
936 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
937 /// let chunks: &[[char; 3]] =
938 /// // SAFETY: The slice length (6) is a multiple of 3
939 /// unsafe { slice.as_chunks_unchecked() };
940 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
942 /// // These would be unsound:
943 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
944 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
946 #[unstable(feature = "slice_as_chunks", issue = "74985")]
948 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
949 debug_assert_ne!(N, 0);
950 debug_assert_eq!(self.len() % N, 0);
952 // SAFETY: Our precondition is exactly what's needed to call this
953 unsafe { crate::intrinsics::exact_div(self.len(), N) };
954 // SAFETY: We cast a slice of `new_len * N` elements into
955 // a slice of `new_len` many `N` elements chunks.
956 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
959 /// Splits the slice into a slice of `N`-element arrays,
960 /// starting at the beginning of the slice,
961 /// and a remainder slice with length strictly less than `N`.
965 /// Panics if `N` is 0. This check will most probably get changed to a compile time
966 /// error before this method gets stabilized.
971 /// #![feature(slice_as_chunks)]
972 /// let slice = ['l', 'o', 'r', 'e', 'm'];
973 /// let (chunks, remainder) = slice.as_chunks();
974 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
975 /// assert_eq!(remainder, &['m']);
977 #[unstable(feature = "slice_as_chunks", issue = "74985")]
979 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
981 let len = self.len() / N;
982 let (multiple_of_n, remainder) = self.split_at(len * N);
983 // SAFETY: We already panicked for zero, and ensured by construction
984 // that the length of the subslice is a multiple of N.
985 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
986 (array_slice, remainder)
989 /// Splits the slice into a slice of `N`-element arrays,
990 /// starting at the end of the slice,
991 /// and a remainder slice with length strictly less than `N`.
995 /// Panics if `N` is 0. This check will most probably get changed to a compile time
996 /// error before this method gets stabilized.
1001 /// #![feature(slice_as_chunks)]
1002 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1003 /// let (remainder, chunks) = slice.as_rchunks();
1004 /// assert_eq!(remainder, &['l']);
1005 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1007 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1009 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1011 let len = self.len() / N;
1012 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1013 // SAFETY: We already panicked for zero, and ensured by construction
1014 // that the length of the subslice is a multiple of N.
1015 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1016 (remainder, array_slice)
1019 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1020 /// beginning of the slice.
1022 /// The chunks are array references and do not overlap. If `N` does not divide the
1023 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1024 /// retrieved from the `remainder` function of the iterator.
1026 /// This method is the const generic equivalent of [`chunks_exact`].
1030 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1031 /// error before this method gets stabilized.
1036 /// #![feature(array_chunks)]
1037 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1038 /// let mut iter = slice.array_chunks();
1039 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1040 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1041 /// assert!(iter.next().is_none());
1042 /// assert_eq!(iter.remainder(), &['m']);
1045 /// [`chunks_exact`]: slice::chunks_exact
1046 #[unstable(feature = "array_chunks", issue = "74985")]
1048 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1050 ArrayChunks::new(self)
1053 /// Splits the slice into a slice of `N`-element arrays,
1054 /// assuming that there's no remainder.
1058 /// This may only be called when
1059 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1065 /// #![feature(slice_as_chunks)]
1066 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1067 /// let chunks: &mut [[char; 1]] =
1068 /// // SAFETY: 1-element chunks never have remainder
1069 /// unsafe { slice.as_chunks_unchecked_mut() };
1070 /// chunks[0] = ['L'];
1071 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1072 /// let chunks: &mut [[char; 3]] =
1073 /// // SAFETY: The slice length (6) is a multiple of 3
1074 /// unsafe { slice.as_chunks_unchecked_mut() };
1075 /// chunks[1] = ['a', 'x', '?'];
1076 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1078 /// // These would be unsound:
1079 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1080 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1082 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1084 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1085 debug_assert_ne!(N, 0);
1086 debug_assert_eq!(self.len() % N, 0);
1088 // SAFETY: Our precondition is exactly what's needed to call this
1089 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1090 // SAFETY: We cast a slice of `new_len * N` elements into
1091 // a slice of `new_len` many `N` elements chunks.
1092 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1095 /// Splits the slice into a slice of `N`-element arrays,
1096 /// starting at the beginning of the slice,
1097 /// and a remainder slice with length strictly less than `N`.
1101 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1102 /// error before this method gets stabilized.
1107 /// #![feature(slice_as_chunks)]
1108 /// let v = &mut [0, 0, 0, 0, 0];
1109 /// let mut count = 1;
1111 /// let (chunks, remainder) = v.as_chunks_mut();
1112 /// remainder[0] = 9;
1113 /// for chunk in chunks {
1114 /// *chunk = [count; 2];
1117 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1119 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1121 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1123 let len = self.len() / N;
1124 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1125 // SAFETY: We already panicked for zero, and ensured by construction
1126 // that the length of the subslice is a multiple of N.
1127 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1128 (array_slice, remainder)
1131 /// Splits the slice into a slice of `N`-element arrays,
1132 /// starting at the end of the slice,
1133 /// and a remainder slice with length strictly less than `N`.
1137 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1138 /// error before this method gets stabilized.
1143 /// #![feature(slice_as_chunks)]
1144 /// let v = &mut [0, 0, 0, 0, 0];
1145 /// let mut count = 1;
1147 /// let (remainder, chunks) = v.as_rchunks_mut();
1148 /// remainder[0] = 9;
1149 /// for chunk in chunks {
1150 /// *chunk = [count; 2];
1153 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1155 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1157 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1159 let len = self.len() / N;
1160 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1161 // SAFETY: We already panicked for zero, and ensured by construction
1162 // that the length of the subslice is a multiple of N.
1163 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1164 (remainder, array_slice)
1167 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1168 /// beginning of the slice.
1170 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1171 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1172 /// can be retrieved from the `into_remainder` function of the iterator.
1174 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1178 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1179 /// error before this method gets stabilized.
1184 /// #![feature(array_chunks)]
1185 /// let v = &mut [0, 0, 0, 0, 0];
1186 /// let mut count = 1;
1188 /// for chunk in v.array_chunks_mut() {
1189 /// *chunk = [count; 2];
1192 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1195 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1196 #[unstable(feature = "array_chunks", issue = "74985")]
1198 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1200 ArrayChunksMut::new(self)
1203 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1204 /// starting at the beginning of the slice.
1206 /// This is the const generic equivalent of [`windows`].
1208 /// If `N` is greater than the size of the slice, it will return no windows.
1212 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1213 /// error before this method gets stabilized.
1218 /// #![feature(array_windows)]
1219 /// let slice = [0, 1, 2, 3];
1220 /// let mut iter = slice.array_windows();
1221 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1222 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1223 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1224 /// assert!(iter.next().is_none());
1227 /// [`windows`]: slice::windows
1228 #[unstable(feature = "array_windows", issue = "75027")]
1230 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1232 ArrayWindows::new(self)
1235 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1238 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1239 /// slice, then the last chunk will not have length `chunk_size`.
1241 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1242 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1247 /// Panics if `chunk_size` is 0.
1252 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1253 /// let mut iter = slice.rchunks(2);
1254 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1255 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1256 /// assert_eq!(iter.next().unwrap(), &['l']);
1257 /// assert!(iter.next().is_none());
1260 /// [`rchunks_exact`]: slice::rchunks_exact
1261 /// [`chunks`]: slice::chunks
1262 #[stable(feature = "rchunks", since = "1.31.0")]
1264 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1265 assert!(chunk_size != 0);
1266 RChunks::new(self, chunk_size)
1269 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1272 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1273 /// length of the slice, then the last chunk will not have length `chunk_size`.
1275 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1276 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1277 /// beginning of the slice.
1281 /// Panics if `chunk_size` is 0.
1286 /// let v = &mut [0, 0, 0, 0, 0];
1287 /// let mut count = 1;
1289 /// for chunk in v.rchunks_mut(2) {
1290 /// for elem in chunk.iter_mut() {
1295 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1298 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1299 /// [`chunks_mut`]: slice::chunks_mut
1300 #[stable(feature = "rchunks", since = "1.31.0")]
1302 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1303 assert!(chunk_size != 0);
1304 RChunksMut::new(self, chunk_size)
1307 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1308 /// end of the slice.
1310 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1311 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1312 /// from the `remainder` function of the iterator.
1314 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1315 /// resulting code better than in the case of [`chunks`].
1317 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1318 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1323 /// Panics if `chunk_size` is 0.
1328 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1329 /// let mut iter = slice.rchunks_exact(2);
1330 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1331 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1332 /// assert!(iter.next().is_none());
1333 /// assert_eq!(iter.remainder(), &['l']);
1336 /// [`chunks`]: slice::chunks
1337 /// [`rchunks`]: slice::rchunks
1338 /// [`chunks_exact`]: slice::chunks_exact
1339 #[stable(feature = "rchunks", since = "1.31.0")]
1341 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1342 assert!(chunk_size != 0);
1343 RChunksExact::new(self, chunk_size)
1346 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1349 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1350 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1351 /// retrieved from the `into_remainder` function of the iterator.
1353 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1354 /// resulting code better than in the case of [`chunks_mut`].
1356 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1357 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1362 /// Panics if `chunk_size` is 0.
1367 /// let v = &mut [0, 0, 0, 0, 0];
1368 /// let mut count = 1;
1370 /// for chunk in v.rchunks_exact_mut(2) {
1371 /// for elem in chunk.iter_mut() {
1376 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1379 /// [`chunks_mut`]: slice::chunks_mut
1380 /// [`rchunks_mut`]: slice::rchunks_mut
1381 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1382 #[stable(feature = "rchunks", since = "1.31.0")]
1384 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1385 assert!(chunk_size != 0);
1386 RChunksExactMut::new(self, chunk_size)
1389 /// Returns an iterator over the slice producing non-overlapping runs
1390 /// of elements using the predicate to separate them.
1392 /// The predicate is called on two elements following themselves,
1393 /// it means the predicate is called on `slice[0]` and `slice[1]`
1394 /// then on `slice[1]` and `slice[2]` and so on.
1399 /// #![feature(slice_group_by)]
1401 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1403 /// let mut iter = slice.group_by(|a, b| a == b);
1405 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1406 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1407 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1408 /// assert_eq!(iter.next(), None);
1411 /// This method can be used to extract the sorted subslices:
1414 /// #![feature(slice_group_by)]
1416 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1418 /// let mut iter = slice.group_by(|a, b| a <= b);
1420 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1421 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1422 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1423 /// assert_eq!(iter.next(), None);
1425 #[unstable(feature = "slice_group_by", issue = "80552")]
1427 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1429 F: FnMut(&T, &T) -> bool,
1431 GroupBy::new(self, pred)
1434 /// Returns an iterator over the slice producing non-overlapping mutable
1435 /// runs of elements using the predicate to separate them.
1437 /// The predicate is called on two elements following themselves,
1438 /// it means the predicate is called on `slice[0]` and `slice[1]`
1439 /// then on `slice[1]` and `slice[2]` and so on.
1444 /// #![feature(slice_group_by)]
1446 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1448 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1450 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1451 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1452 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1453 /// assert_eq!(iter.next(), None);
1456 /// This method can be used to extract the sorted subslices:
1459 /// #![feature(slice_group_by)]
1461 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1463 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1465 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1466 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1467 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1468 /// assert_eq!(iter.next(), None);
1470 #[unstable(feature = "slice_group_by", issue = "80552")]
1472 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1474 F: FnMut(&T, &T) -> bool,
1476 GroupByMut::new(self, pred)
1479 /// Divides one slice into two at an index.
1481 /// The first will contain all indices from `[0, mid)` (excluding
1482 /// the index `mid` itself) and the second will contain all
1483 /// indices from `[mid, len)` (excluding the index `len` itself).
1487 /// Panics if `mid > len`.
1492 /// let v = [1, 2, 3, 4, 5, 6];
1495 /// let (left, right) = v.split_at(0);
1496 /// assert_eq!(left, []);
1497 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1501 /// let (left, right) = v.split_at(2);
1502 /// assert_eq!(left, [1, 2]);
1503 /// assert_eq!(right, [3, 4, 5, 6]);
1507 /// let (left, right) = v.split_at(6);
1508 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1509 /// assert_eq!(right, []);
1512 #[stable(feature = "rust1", since = "1.0.0")]
1515 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1516 assert!(mid <= self.len());
1517 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1518 // fulfills the requirements of `from_raw_parts_mut`.
1519 unsafe { self.split_at_unchecked(mid) }
1522 /// Divides one mutable slice into two at an index.
1524 /// The first will contain all indices from `[0, mid)` (excluding
1525 /// the index `mid` itself) and the second will contain all
1526 /// indices from `[mid, len)` (excluding the index `len` itself).
1530 /// Panics if `mid > len`.
1535 /// let mut v = [1, 0, 3, 0, 5, 6];
1536 /// let (left, right) = v.split_at_mut(2);
1537 /// assert_eq!(left, [1, 0]);
1538 /// assert_eq!(right, [3, 0, 5, 6]);
1541 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1543 #[stable(feature = "rust1", since = "1.0.0")]
1546 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1547 assert!(mid <= self.len());
1548 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1549 // fulfills the requirements of `from_raw_parts_mut`.
1550 unsafe { self.split_at_mut_unchecked(mid) }
1553 /// Divides one slice into two at an index, without doing bounds checking.
1555 /// The first will contain all indices from `[0, mid)` (excluding
1556 /// the index `mid` itself) and the second will contain all
1557 /// indices from `[mid, len)` (excluding the index `len` itself).
1559 /// For a safe alternative see [`split_at`].
1563 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1564 /// even if the resulting reference is not used. The caller has to ensure that
1565 /// `0 <= mid <= self.len()`.
1567 /// [`split_at`]: slice::split_at
1568 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1573 /// #![feature(slice_split_at_unchecked)]
1575 /// let v = [1, 2, 3, 4, 5, 6];
1578 /// let (left, right) = v.split_at_unchecked(0);
1579 /// assert_eq!(left, []);
1580 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1584 /// let (left, right) = v.split_at_unchecked(2);
1585 /// assert_eq!(left, [1, 2]);
1586 /// assert_eq!(right, [3, 4, 5, 6]);
1590 /// let (left, right) = v.split_at_unchecked(6);
1591 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1592 /// assert_eq!(right, []);
1595 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1597 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1598 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1599 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1602 /// Divides one mutable slice into two at an index, without doing bounds checking.
1604 /// The first will contain all indices from `[0, mid)` (excluding
1605 /// the index `mid` itself) and the second will contain all
1606 /// indices from `[mid, len)` (excluding the index `len` itself).
1608 /// For a safe alternative see [`split_at_mut`].
1612 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1613 /// even if the resulting reference is not used. The caller has to ensure that
1614 /// `0 <= mid <= self.len()`.
1616 /// [`split_at_mut`]: slice::split_at_mut
1617 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1622 /// #![feature(slice_split_at_unchecked)]
1624 /// let mut v = [1, 0, 3, 0, 5, 6];
1625 /// // scoped to restrict the lifetime of the borrows
1627 /// let (left, right) = v.split_at_mut_unchecked(2);
1628 /// assert_eq!(left, [1, 0]);
1629 /// assert_eq!(right, [3, 0, 5, 6]);
1633 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1635 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1637 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1638 let len = self.len();
1639 let ptr = self.as_mut_ptr();
1641 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1643 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1645 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1648 /// Divides one slice into an array and a remainder slice at an index.
1650 /// The array will contain all indices from `[0, N)` (excluding
1651 /// the index `N` itself) and the slice will contain all
1652 /// indices from `[N, len)` (excluding the index `len` itself).
1656 /// Panics if `N > len`.
1661 /// #![feature(split_array)]
1663 /// let v = &[1, 2, 3, 4, 5, 6][..];
1666 /// let (left, right) = v.split_array_ref::<0>();
1667 /// assert_eq!(left, &[]);
1668 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1672 /// let (left, right) = v.split_array_ref::<2>();
1673 /// assert_eq!(left, &[1, 2]);
1674 /// assert_eq!(right, [3, 4, 5, 6]);
1678 /// let (left, right) = v.split_array_ref::<6>();
1679 /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
1680 /// assert_eq!(right, []);
1683 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1686 pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
1687 let (a, b) = self.split_at(N);
1688 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
1689 unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
1692 /// Divides one mutable slice into an array and a remainder slice at an index.
1694 /// The array will contain all indices from `[0, N)` (excluding
1695 /// the index `N` itself) and the slice will contain all
1696 /// indices from `[N, len)` (excluding the index `len` itself).
1700 /// Panics if `N > len`.
1705 /// #![feature(split_array)]
1707 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1708 /// let (left, right) = v.split_array_mut::<2>();
1709 /// assert_eq!(left, &mut [1, 0]);
1710 /// assert_eq!(right, [3, 0, 5, 6]);
1713 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1715 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1718 pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
1719 let (a, b) = self.split_at_mut(N);
1720 // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1721 unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
1724 /// Divides one slice into an array and a remainder slice at an index from
1727 /// The slice will contain all indices from `[0, len - N)` (excluding
1728 /// the index `len - N` itself) and the array will contain all
1729 /// indices from `[len - N, len)` (excluding the index `len` itself).
1733 /// Panics if `N > len`.
1738 /// #![feature(split_array)]
1740 /// let v = &[1, 2, 3, 4, 5, 6][..];
1743 /// let (left, right) = v.rsplit_array_ref::<0>();
1744 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1745 /// assert_eq!(right, &[]);
1749 /// let (left, right) = v.rsplit_array_ref::<2>();
1750 /// assert_eq!(left, [1, 2, 3, 4]);
1751 /// assert_eq!(right, &[5, 6]);
1755 /// let (left, right) = v.rsplit_array_ref::<6>();
1756 /// assert_eq!(left, []);
1757 /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
1760 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1762 pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
1763 assert!(N <= self.len());
1764 let (a, b) = self.split_at(self.len() - N);
1765 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
1766 unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
1769 /// Divides one mutable slice into an array and a remainder slice at an
1770 /// index from the end.
1772 /// The slice will contain all indices from `[0, len - N)` (excluding
1773 /// the index `N` itself) and the array will contain all
1774 /// indices from `[len - N, len)` (excluding the index `len` itself).
1778 /// Panics if `N > len`.
1783 /// #![feature(split_array)]
1785 /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
1786 /// let (left, right) = v.rsplit_array_mut::<4>();
1787 /// assert_eq!(left, [1, 0]);
1788 /// assert_eq!(right, &mut [3, 0, 5, 6]);
1791 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1793 #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
1795 pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
1796 assert!(N <= self.len());
1797 let (a, b) = self.split_at_mut(self.len() - N);
1798 // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
1799 unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
1802 /// Returns an iterator over subslices separated by elements that match
1803 /// `pred`. The matched element is not contained in the subslices.
1808 /// let slice = [10, 40, 33, 20];
1809 /// let mut iter = slice.split(|num| num % 3 == 0);
1811 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1812 /// assert_eq!(iter.next().unwrap(), &[20]);
1813 /// assert!(iter.next().is_none());
1816 /// If the first element is matched, an empty slice will be the first item
1817 /// returned by the iterator. Similarly, if the last element in the slice
1818 /// is matched, an empty slice will be the last item returned by the
1822 /// let slice = [10, 40, 33];
1823 /// let mut iter = slice.split(|num| num % 3 == 0);
1825 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1826 /// assert_eq!(iter.next().unwrap(), &[]);
1827 /// assert!(iter.next().is_none());
1830 /// If two matched elements are directly adjacent, an empty slice will be
1831 /// present between them:
1834 /// let slice = [10, 6, 33, 20];
1835 /// let mut iter = slice.split(|num| num % 3 == 0);
1837 /// assert_eq!(iter.next().unwrap(), &[10]);
1838 /// assert_eq!(iter.next().unwrap(), &[]);
1839 /// assert_eq!(iter.next().unwrap(), &[20]);
1840 /// assert!(iter.next().is_none());
1842 #[stable(feature = "rust1", since = "1.0.0")]
1844 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1846 F: FnMut(&T) -> bool,
1848 Split::new(self, pred)
1851 /// Returns an iterator over mutable subslices separated by elements that
1852 /// match `pred`. The matched element is not contained in the subslices.
1857 /// let mut v = [10, 40, 30, 20, 60, 50];
1859 /// for group in v.split_mut(|num| *num % 3 == 0) {
1862 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1864 #[stable(feature = "rust1", since = "1.0.0")]
1866 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1868 F: FnMut(&T) -> bool,
1870 SplitMut::new(self, pred)
1873 /// Returns an iterator over subslices separated by elements that match
1874 /// `pred`. The matched element is contained in the end of the previous
1875 /// subslice as a terminator.
1880 /// let slice = [10, 40, 33, 20];
1881 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1883 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1884 /// assert_eq!(iter.next().unwrap(), &[20]);
1885 /// assert!(iter.next().is_none());
1888 /// If the last element of the slice is matched,
1889 /// that element will be considered the terminator of the preceding slice.
1890 /// That slice will be the last item returned by the iterator.
1893 /// let slice = [3, 10, 40, 33];
1894 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1896 /// assert_eq!(iter.next().unwrap(), &[3]);
1897 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1898 /// assert!(iter.next().is_none());
1900 #[stable(feature = "split_inclusive", since = "1.51.0")]
1902 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1904 F: FnMut(&T) -> bool,
1906 SplitInclusive::new(self, pred)
1909 /// Returns an iterator over mutable subslices separated by elements that
1910 /// match `pred`. The matched element is contained in the previous
1911 /// subslice as a terminator.
1916 /// let mut v = [10, 40, 30, 20, 60, 50];
1918 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1919 /// let terminator_idx = group.len()-1;
1920 /// group[terminator_idx] = 1;
1922 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1924 #[stable(feature = "split_inclusive", since = "1.51.0")]
1926 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1928 F: FnMut(&T) -> bool,
1930 SplitInclusiveMut::new(self, pred)
1933 /// Returns an iterator over subslices separated by elements that match
1934 /// `pred`, starting at the end of the slice and working backwards.
1935 /// The matched element is not contained in the subslices.
1940 /// let slice = [11, 22, 33, 0, 44, 55];
1941 /// let mut iter = slice.rsplit(|num| *num == 0);
1943 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1944 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1945 /// assert_eq!(iter.next(), None);
1948 /// As with `split()`, if the first or last element is matched, an empty
1949 /// slice will be the first (or last) item returned by the iterator.
1952 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1953 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1954 /// assert_eq!(it.next().unwrap(), &[]);
1955 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1956 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1957 /// assert_eq!(it.next().unwrap(), &[]);
1958 /// assert_eq!(it.next(), None);
1960 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1962 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1964 F: FnMut(&T) -> bool,
1966 RSplit::new(self, pred)
1969 /// Returns an iterator over mutable subslices separated by elements that
1970 /// match `pred`, starting at the end of the slice and working
1971 /// backwards. The matched element is not contained in the subslices.
1976 /// let mut v = [100, 400, 300, 200, 600, 500];
1978 /// let mut count = 0;
1979 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1981 /// group[0] = count;
1983 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1986 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1988 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1990 F: FnMut(&T) -> bool,
1992 RSplitMut::new(self, pred)
1995 /// Returns an iterator over subslices separated by elements that match
1996 /// `pred`, limited to returning at most `n` items. The matched element is
1997 /// not contained in the subslices.
1999 /// The last element returned, if any, will contain the remainder of the
2004 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
2005 /// `[20, 60, 50]`):
2008 /// let v = [10, 40, 30, 20, 60, 50];
2010 /// for group in v.splitn(2, |num| *num % 3 == 0) {
2011 /// println!("{:?}", group);
2014 #[stable(feature = "rust1", since = "1.0.0")]
2016 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
2018 F: FnMut(&T) -> bool,
2020 SplitN::new(self.split(pred), n)
2023 /// Returns an iterator over subslices separated by elements that match
2024 /// `pred`, limited to returning at most `n` items. The matched element is
2025 /// not contained in the subslices.
2027 /// The last element returned, if any, will contain the remainder of the
2033 /// let mut v = [10, 40, 30, 20, 60, 50];
2035 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
2038 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
2040 #[stable(feature = "rust1", since = "1.0.0")]
2042 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
2044 F: FnMut(&T) -> bool,
2046 SplitNMut::new(self.split_mut(pred), n)
2049 /// Returns an iterator over subslices separated by elements that match
2050 /// `pred` limited to returning at most `n` items. This starts at the end of
2051 /// the slice and works backwards. The matched element is not contained in
2054 /// The last element returned, if any, will contain the remainder of the
2059 /// Print the slice split once, starting from the end, by numbers divisible
2060 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
2063 /// let v = [10, 40, 30, 20, 60, 50];
2065 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
2066 /// println!("{:?}", group);
2069 #[stable(feature = "rust1", since = "1.0.0")]
2071 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
2073 F: FnMut(&T) -> bool,
2075 RSplitN::new(self.rsplit(pred), n)
2078 /// Returns an iterator over subslices separated by elements that match
2079 /// `pred` limited to returning at most `n` items. This starts at the end of
2080 /// the slice and works backwards. The matched element is not contained in
2083 /// The last element returned, if any, will contain the remainder of the
2089 /// let mut s = [10, 40, 30, 20, 60, 50];
2091 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
2094 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
2096 #[stable(feature = "rust1", since = "1.0.0")]
2098 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
2100 F: FnMut(&T) -> bool,
2102 RSplitNMut::new(self.rsplit_mut(pred), n)
2105 /// Returns `true` if the slice contains an element with the given value.
2110 /// let v = [10, 40, 30];
2111 /// assert!(v.contains(&30));
2112 /// assert!(!v.contains(&50));
2115 /// If you do not have a `&T`, but some other value that you can compare
2116 /// with one (for example, `String` implements `PartialEq<str>`), you can
2117 /// use `iter().any`:
2120 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
2121 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
2122 /// assert!(!v.iter().any(|e| e == "hi"));
2124 #[stable(feature = "rust1", since = "1.0.0")]
2126 pub fn contains(&self, x: &T) -> bool
2130 cmp::SliceContains::slice_contains(x, self)
2133 /// Returns `true` if `needle` is a prefix of the slice.
2138 /// let v = [10, 40, 30];
2139 /// assert!(v.starts_with(&[10]));
2140 /// assert!(v.starts_with(&[10, 40]));
2141 /// assert!(!v.starts_with(&[50]));
2142 /// assert!(!v.starts_with(&[10, 50]));
2145 /// Always returns `true` if `needle` is an empty slice:
2148 /// let v = &[10, 40, 30];
2149 /// assert!(v.starts_with(&[]));
2150 /// let v: &[u8] = &[];
2151 /// assert!(v.starts_with(&[]));
2153 #[stable(feature = "rust1", since = "1.0.0")]
2154 pub fn starts_with(&self, needle: &[T]) -> bool
2158 let n = needle.len();
2159 self.len() >= n && needle == &self[..n]
2162 /// Returns `true` if `needle` is a suffix of the slice.
2167 /// let v = [10, 40, 30];
2168 /// assert!(v.ends_with(&[30]));
2169 /// assert!(v.ends_with(&[40, 30]));
2170 /// assert!(!v.ends_with(&[50]));
2171 /// assert!(!v.ends_with(&[50, 30]));
2174 /// Always returns `true` if `needle` is an empty slice:
2177 /// let v = &[10, 40, 30];
2178 /// assert!(v.ends_with(&[]));
2179 /// let v: &[u8] = &[];
2180 /// assert!(v.ends_with(&[]));
2182 #[stable(feature = "rust1", since = "1.0.0")]
2183 pub fn ends_with(&self, needle: &[T]) -> bool
2187 let (m, n) = (self.len(), needle.len());
2188 m >= n && needle == &self[m - n..]
2191 /// Returns a subslice with the prefix removed.
2193 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2194 /// If `prefix` is empty, simply returns the original slice.
2196 /// If the slice does not start with `prefix`, returns `None`.
2201 /// let v = &[10, 40, 30];
2202 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2203 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2204 /// assert_eq!(v.strip_prefix(&[50]), None);
2205 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2207 /// let prefix : &str = "he";
2208 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2209 /// Some(b"llo".as_ref()));
2211 #[must_use = "returns the subslice without modifying the original"]
2212 #[stable(feature = "slice_strip", since = "1.51.0")]
2213 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2217 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2218 let prefix = prefix.as_slice();
2219 let n = prefix.len();
2220 if n <= self.len() {
2221 let (head, tail) = self.split_at(n);
2229 /// Returns a subslice with the suffix removed.
2231 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2232 /// If `suffix` is empty, simply returns the original slice.
2234 /// If the slice does not end with `suffix`, returns `None`.
2239 /// let v = &[10, 40, 30];
2240 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2241 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2242 /// assert_eq!(v.strip_suffix(&[50]), None);
2243 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2245 #[must_use = "returns the subslice without modifying the original"]
2246 #[stable(feature = "slice_strip", since = "1.51.0")]
2247 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2251 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2252 let suffix = suffix.as_slice();
2253 let (len, n) = (self.len(), suffix.len());
2255 let (head, tail) = self.split_at(len - n);
2263 /// Binary searches this sorted slice for a given element.
2265 /// If the value is found then [`Result::Ok`] is returned, containing the
2266 /// index of the matching element. If there are multiple matches, then any
2267 /// one of the matches could be returned. The index is chosen
2268 /// deterministically, but is subject to change in future versions of Rust.
2269 /// If the value is not found then [`Result::Err`] is returned, containing
2270 /// the index where a matching element could be inserted while maintaining
2273 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2275 /// [`binary_search_by`]: slice::binary_search_by
2276 /// [`binary_search_by_key`]: slice::binary_search_by_key
2277 /// [`partition_point`]: slice::partition_point
2281 /// Looks up a series of four elements. The first is found, with a
2282 /// uniquely determined position; the second and third are not
2283 /// found; the fourth could match any position in `[1, 4]`.
2286 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2288 /// assert_eq!(s.binary_search(&13), Ok(9));
2289 /// assert_eq!(s.binary_search(&4), Err(7));
2290 /// assert_eq!(s.binary_search(&100), Err(13));
2291 /// let r = s.binary_search(&1);
2292 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2295 /// If you want to insert an item to a sorted vector, while maintaining
2299 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2301 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2302 /// s.insert(idx, num);
2303 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2310 self.binary_search_by(|p| p.cmp(x))
2313 /// Binary searches this sorted slice with a comparator function.
2315 /// The comparator function should implement an order consistent
2316 /// with the sort order of the underlying slice, returning an
2317 /// order code that indicates whether its argument is `Less`,
2318 /// `Equal` or `Greater` the desired target.
2320 /// If the value is found then [`Result::Ok`] is returned, containing the
2321 /// index of the matching element. If there are multiple matches, then any
2322 /// one of the matches could be returned. The index is chosen
2323 /// deterministically, but is subject to change in future versions of Rust.
2324 /// If the value is not found then [`Result::Err`] is returned, containing
2325 /// the index where a matching element could be inserted while maintaining
2328 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2330 /// [`binary_search`]: slice::binary_search
2331 /// [`binary_search_by_key`]: slice::binary_search_by_key
2332 /// [`partition_point`]: slice::partition_point
2336 /// Looks up a series of four elements. The first is found, with a
2337 /// uniquely determined position; the second and third are not
2338 /// found; the fourth could match any position in `[1, 4]`.
2341 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2344 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2346 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2348 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2350 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2351 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2353 #[stable(feature = "rust1", since = "1.0.0")]
2355 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2357 F: FnMut(&'a T) -> Ordering,
2359 let mut size = self.len();
2361 let mut right = size;
2362 while left < right {
2363 let mid = left + size / 2;
2365 // SAFETY: the call is made safe by the following invariants:
2367 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2368 let cmp = f(unsafe { self.get_unchecked(mid) });
2370 // The reason why we use if/else control flow rather than match
2371 // is because match reorders comparison operations, which is perf sensitive.
2372 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2375 } else if cmp == Greater {
2378 // SAFETY: same as the `get_unchecked` above
2379 unsafe { crate::intrinsics::assume(mid < self.len()) };
2383 size = right - left;
2388 /// Binary searches this sorted slice with a key extraction function.
2390 /// Assumes that the slice is sorted by the key, for instance with
2391 /// [`sort_by_key`] using the same key extraction function.
2393 /// If the value is found then [`Result::Ok`] is returned, containing the
2394 /// index of the matching element. If there are multiple matches, then any
2395 /// one of the matches could be returned. The index is chosen
2396 /// deterministically, but is subject to change in future versions of Rust.
2397 /// If the value is not found then [`Result::Err`] is returned, containing
2398 /// the index where a matching element could be inserted while maintaining
2401 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2403 /// [`sort_by_key`]: slice::sort_by_key
2404 /// [`binary_search`]: slice::binary_search
2405 /// [`binary_search_by`]: slice::binary_search_by
2406 /// [`partition_point`]: slice::partition_point
2410 /// Looks up a series of four elements in a slice of pairs sorted by
2411 /// their second elements. The first is found, with a uniquely
2412 /// determined position; the second and third are not found; the
2413 /// fourth could match any position in `[1, 4]`.
2416 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2417 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2418 /// (1, 21), (2, 34), (4, 55)];
2420 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2421 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2422 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2423 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2424 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2426 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2427 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2428 // This breaks links when slice is displayed in core, but changing it to use relative links
2429 // would break when the item is re-exported. So allow the core links to be broken for now.
2430 #[allow(rustdoc::broken_intra_doc_links)]
2431 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2433 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2435 F: FnMut(&'a T) -> B,
2438 self.binary_search_by(|k| f(k).cmp(b))
2441 /// Sorts the slice, but might not preserve the order of equal elements.
2443 /// This sort is unstable (i.e., may reorder equal elements), in-place
2444 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2446 /// # Current implementation
2448 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2449 /// which combines the fast average case of randomized quicksort with the fast worst case of
2450 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2451 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2452 /// deterministic behavior.
2454 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2455 /// slice consists of several concatenated sorted sequences.
2460 /// let mut v = [-5, 4, 1, -3, 2];
2462 /// v.sort_unstable();
2463 /// assert!(v == [-5, -3, 1, 2, 4]);
2466 /// [pdqsort]: https://github.com/orlp/pdqsort
2467 #[stable(feature = "sort_unstable", since = "1.20.0")]
2469 pub fn sort_unstable(&mut self)
2473 sort::quicksort(self, |a, b| a.lt(b));
2476 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2479 /// This sort is unstable (i.e., may reorder equal elements), in-place
2480 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2482 /// The comparator function must define a total ordering for the elements in the slice. If
2483 /// the ordering is not total, the order of the elements is unspecified. An order is a
2484 /// total order if it is (for all `a`, `b` and `c`):
2486 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2487 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2489 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2490 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2493 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2494 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2495 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2498 /// # Current implementation
2500 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2501 /// which combines the fast average case of randomized quicksort with the fast worst case of
2502 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2503 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2504 /// deterministic behavior.
2506 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2507 /// slice consists of several concatenated sorted sequences.
2512 /// let mut v = [5, 4, 1, 3, 2];
2513 /// v.sort_unstable_by(|a, b| a.cmp(b));
2514 /// assert!(v == [1, 2, 3, 4, 5]);
2516 /// // reverse sorting
2517 /// v.sort_unstable_by(|a, b| b.cmp(a));
2518 /// assert!(v == [5, 4, 3, 2, 1]);
2521 /// [pdqsort]: https://github.com/orlp/pdqsort
2522 #[stable(feature = "sort_unstable", since = "1.20.0")]
2524 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2526 F: FnMut(&T, &T) -> Ordering,
2528 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2531 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2534 /// This sort is unstable (i.e., may reorder equal elements), in-place
2535 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2538 /// # Current implementation
2540 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2541 /// which combines the fast average case of randomized quicksort with the fast worst case of
2542 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2543 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2544 /// deterministic behavior.
2546 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2547 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2548 /// cases where the key function is expensive.
2553 /// let mut v = [-5i32, 4, 1, -3, 2];
2555 /// v.sort_unstable_by_key(|k| k.abs());
2556 /// assert!(v == [1, 2, -3, 4, -5]);
2559 /// [pdqsort]: https://github.com/orlp/pdqsort
2560 #[stable(feature = "sort_unstable", since = "1.20.0")]
2562 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2567 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2570 /// Reorder the slice such that the element at `index` is at its final sorted position.
2572 /// This reordering has the additional property that any value at position `i < index` will be
2573 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2574 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2575 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2576 /// element" in other libraries. It returns a triplet of the following values: all elements less
2577 /// than the one at the given index, the value at the given index, and all elements greater than
2578 /// the one at the given index.
2580 /// # Current implementation
2582 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2583 /// used for [`sort_unstable`].
2585 /// [`sort_unstable`]: slice::sort_unstable
2589 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2594 /// let mut v = [-5i32, 4, 1, -3, 2];
2596 /// // Find the median
2597 /// v.select_nth_unstable(2);
2599 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2600 /// // about the specified index.
2601 /// assert!(v == [-3, -5, 1, 2, 4] ||
2602 /// v == [-5, -3, 1, 2, 4] ||
2603 /// v == [-3, -5, 1, 4, 2] ||
2604 /// v == [-5, -3, 1, 4, 2]);
2606 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2608 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2612 let mut f = |a: &T, b: &T| a.lt(b);
2613 sort::partition_at_index(self, index, &mut f)
2616 /// Reorder the slice with a comparator function such that the element at `index` is at its
2617 /// final sorted position.
2619 /// This reordering has the additional property that any value at position `i < index` will be
2620 /// less than or equal to any value at a position `j > index` using the comparator function.
2621 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2622 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2623 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2624 /// values: all elements less than the one at the given index, the value at the given index,
2625 /// and all elements greater than the one at the given index, using the provided comparator
2628 /// # Current implementation
2630 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2631 /// used for [`sort_unstable`].
2633 /// [`sort_unstable`]: slice::sort_unstable
2637 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2642 /// let mut v = [-5i32, 4, 1, -3, 2];
2644 /// // Find the median as if the slice were sorted in descending order.
2645 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2647 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2648 /// // about the specified index.
2649 /// assert!(v == [2, 4, 1, -5, -3] ||
2650 /// v == [2, 4, 1, -3, -5] ||
2651 /// v == [4, 2, 1, -5, -3] ||
2652 /// v == [4, 2, 1, -3, -5]);
2654 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2656 pub fn select_nth_unstable_by<F>(
2660 ) -> (&mut [T], &mut T, &mut [T])
2662 F: FnMut(&T, &T) -> Ordering,
2664 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2665 sort::partition_at_index(self, index, &mut f)
2668 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2669 /// final sorted position.
2671 /// This reordering has the additional property that any value at position `i < index` will be
2672 /// less than or equal to any value at a position `j > index` using the key extraction function.
2673 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2674 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2675 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2676 /// values: all elements less than the one at the given index, the value at the given index, and
2677 /// all elements greater than the one at the given index, using the provided key extraction
2680 /// # Current implementation
2682 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2683 /// used for [`sort_unstable`].
2685 /// [`sort_unstable`]: slice::sort_unstable
2689 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2694 /// let mut v = [-5i32, 4, 1, -3, 2];
2696 /// // Return the median as if the array were sorted according to absolute value.
2697 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2699 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2700 /// // about the specified index.
2701 /// assert!(v == [1, 2, -3, 4, -5] ||
2702 /// v == [1, 2, -3, -5, 4] ||
2703 /// v == [2, 1, -3, 4, -5] ||
2704 /// v == [2, 1, -3, -5, 4]);
2706 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2708 pub fn select_nth_unstable_by_key<K, F>(
2712 ) -> (&mut [T], &mut T, &mut [T])
2717 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2718 sort::partition_at_index(self, index, &mut g)
2721 /// Moves all consecutive repeated elements to the end of the slice according to the
2722 /// [`PartialEq`] trait implementation.
2724 /// Returns two slices. The first contains no consecutive repeated elements.
2725 /// The second contains all the duplicates in no specified order.
2727 /// If the slice is sorted, the first returned slice contains no duplicates.
2732 /// #![feature(slice_partition_dedup)]
2734 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2736 /// let (dedup, duplicates) = slice.partition_dedup();
2738 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2739 /// assert_eq!(duplicates, [2, 3, 1]);
2741 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2743 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2747 self.partition_dedup_by(|a, b| a == b)
2750 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2751 /// a given equality relation.
2753 /// Returns two slices. The first contains no consecutive repeated elements.
2754 /// The second contains all the duplicates in no specified order.
2756 /// The `same_bucket` function is passed references to two elements from the slice and
2757 /// must determine if the elements compare equal. The elements are passed in opposite order
2758 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2759 /// at the end of the slice.
2761 /// If the slice is sorted, the first returned slice contains no duplicates.
2766 /// #![feature(slice_partition_dedup)]
2768 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2770 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2772 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2773 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2775 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2777 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2779 F: FnMut(&mut T, &mut T) -> bool,
2781 // Although we have a mutable reference to `self`, we cannot make
2782 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2783 // must ensure that the slice is in a valid state at all times.
2785 // The way that we handle this is by using swaps; we iterate
2786 // over all the elements, swapping as we go so that at the end
2787 // the elements we wish to keep are in the front, and those we
2788 // wish to reject are at the back. We can then split the slice.
2789 // This operation is still `O(n)`.
2791 // Example: We start in this state, where `r` represents "next
2792 // read" and `w` represents "next_write`.
2795 // +---+---+---+---+---+---+
2796 // | 0 | 1 | 1 | 2 | 3 | 3 |
2797 // +---+---+---+---+---+---+
2800 // Comparing self[r] against self[w-1], this is not a duplicate, so
2801 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2802 // r and w, leaving us with:
2805 // +---+---+---+---+---+---+
2806 // | 0 | 1 | 1 | 2 | 3 | 3 |
2807 // +---+---+---+---+---+---+
2810 // Comparing self[r] against self[w-1], this value is a duplicate,
2811 // so we increment `r` but leave everything else unchanged:
2814 // +---+---+---+---+---+---+
2815 // | 0 | 1 | 1 | 2 | 3 | 3 |
2816 // +---+---+---+---+---+---+
2819 // Comparing self[r] against self[w-1], this is not a duplicate,
2820 // so swap self[r] and self[w] and advance r and w:
2823 // +---+---+---+---+---+---+
2824 // | 0 | 1 | 2 | 1 | 3 | 3 |
2825 // +---+---+---+---+---+---+
2828 // Not a duplicate, repeat:
2831 // +---+---+---+---+---+---+
2832 // | 0 | 1 | 2 | 3 | 1 | 3 |
2833 // +---+---+---+---+---+---+
2836 // Duplicate, advance r. End of slice. Split at w.
2838 let len = self.len();
2840 return (self, &mut []);
2843 let ptr = self.as_mut_ptr();
2844 let mut next_read: usize = 1;
2845 let mut next_write: usize = 1;
2847 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2848 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2849 // one element before `ptr_write`, but `next_write` starts at 1, so
2850 // `prev_ptr_write` is never less than 0 and is inside the slice.
2851 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2852 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2853 // and `prev_ptr_write.offset(1)`.
2855 // `next_write` is also incremented at most once per loop at most meaning
2856 // no element is skipped when it may need to be swapped.
2858 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2859 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2860 // The explanation is simply that `next_read >= next_write` is always true,
2861 // thus `next_read > next_write - 1` is too.
2863 // Avoid bounds checks by using raw pointers.
2864 while next_read < len {
2865 let ptr_read = ptr.add(next_read);
2866 let prev_ptr_write = ptr.add(next_write - 1);
2867 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2868 if next_read != next_write {
2869 let ptr_write = prev_ptr_write.offset(1);
2870 mem::swap(&mut *ptr_read, &mut *ptr_write);
2878 self.split_at_mut(next_write)
2881 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2882 /// to the same key.
2884 /// Returns two slices. The first contains no consecutive repeated elements.
2885 /// The second contains all the duplicates in no specified order.
2887 /// If the slice is sorted, the first returned slice contains no duplicates.
2892 /// #![feature(slice_partition_dedup)]
2894 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2896 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2898 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2899 /// assert_eq!(duplicates, [21, 30, 13]);
2901 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2903 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2905 F: FnMut(&mut T) -> K,
2908 self.partition_dedup_by(|a, b| key(a) == key(b))
2911 /// Rotates the slice in-place such that the first `mid` elements of the
2912 /// slice move to the end while the last `self.len() - mid` elements move to
2913 /// the front. After calling `rotate_left`, the element previously at index
2914 /// `mid` will become the first element in the slice.
2918 /// This function will panic if `mid` is greater than the length of the
2919 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2924 /// Takes linear (in `self.len()`) time.
2929 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2930 /// a.rotate_left(2);
2931 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2934 /// Rotating a subslice:
2937 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2938 /// a[1..5].rotate_left(1);
2939 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2941 #[stable(feature = "slice_rotate", since = "1.26.0")]
2942 pub fn rotate_left(&mut self, mid: usize) {
2943 assert!(mid <= self.len());
2944 let k = self.len() - mid;
2945 let p = self.as_mut_ptr();
2947 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2948 // valid for reading and writing, as required by `ptr_rotate`.
2950 rotate::ptr_rotate(mid, p.add(mid), k);
2954 /// Rotates the slice in-place such that the first `self.len() - k`
2955 /// elements of the slice move to the end while the last `k` elements move
2956 /// to the front. After calling `rotate_right`, the element previously at
2957 /// index `self.len() - k` will become the first element in the slice.
2961 /// This function will panic if `k` is greater than the length of the
2962 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2967 /// Takes linear (in `self.len()`) time.
2972 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2973 /// a.rotate_right(2);
2974 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2977 /// Rotate a subslice:
2980 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2981 /// a[1..5].rotate_right(1);
2982 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2984 #[stable(feature = "slice_rotate", since = "1.26.0")]
2985 pub fn rotate_right(&mut self, k: usize) {
2986 assert!(k <= self.len());
2987 let mid = self.len() - k;
2988 let p = self.as_mut_ptr();
2990 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2991 // valid for reading and writing, as required by `ptr_rotate`.
2993 rotate::ptr_rotate(mid, p.add(mid), k);
2997 /// Fills `self` with elements by cloning `value`.
3002 /// let mut buf = vec![0; 10];
3004 /// assert_eq!(buf, vec![1; 10]);
3006 #[doc(alias = "memset")]
3007 #[stable(feature = "slice_fill", since = "1.50.0")]
3008 pub fn fill(&mut self, value: T)
3012 specialize::SpecFill::spec_fill(self, value);
3015 /// Fills `self` with elements returned by calling a closure repeatedly.
3017 /// This method uses a closure to create new values. If you'd rather
3018 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
3019 /// trait to generate values, you can pass [`Default::default`] as the
3022 /// [`fill`]: slice::fill
3027 /// let mut buf = vec![1; 10];
3028 /// buf.fill_with(Default::default);
3029 /// assert_eq!(buf, vec![0; 10]);
3031 #[doc(alias = "memset")]
3032 #[stable(feature = "slice_fill_with", since = "1.51.0")]
3033 pub fn fill_with<F>(&mut self, mut f: F)
3042 /// Copies the elements from `src` into `self`.
3044 /// The length of `src` must be the same as `self`.
3048 /// This function will panic if the two slices have different lengths.
3052 /// Cloning two elements from a slice into another:
3055 /// let src = [1, 2, 3, 4];
3056 /// let mut dst = [0, 0];
3058 /// // Because the slices have to be the same length,
3059 /// // we slice the source slice from four elements
3060 /// // to two. It will panic if we don't do this.
3061 /// dst.clone_from_slice(&src[2..]);
3063 /// assert_eq!(src, [1, 2, 3, 4]);
3064 /// assert_eq!(dst, [3, 4]);
3067 /// Rust enforces that there can only be one mutable reference with no
3068 /// immutable references to a particular piece of data in a particular
3069 /// scope. Because of this, attempting to use `clone_from_slice` on a
3070 /// single slice will result in a compile failure:
3073 /// let mut slice = [1, 2, 3, 4, 5];
3075 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
3078 /// To work around this, we can use [`split_at_mut`] to create two distinct
3079 /// sub-slices from a slice:
3082 /// let mut slice = [1, 2, 3, 4, 5];
3085 /// let (left, right) = slice.split_at_mut(2);
3086 /// left.clone_from_slice(&right[1..]);
3089 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3092 /// [`copy_from_slice`]: slice::copy_from_slice
3093 /// [`split_at_mut`]: slice::split_at_mut
3094 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3096 pub fn clone_from_slice(&mut self, src: &[T])
3100 self.spec_clone_from(src);
3103 /// Copies all elements from `src` into `self`, using a memcpy.
3105 /// The length of `src` must be the same as `self`.
3107 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3111 /// This function will panic if the two slices have different lengths.
3115 /// Copying two elements from a slice into another:
3118 /// let src = [1, 2, 3, 4];
3119 /// let mut dst = [0, 0];
3121 /// // Because the slices have to be the same length,
3122 /// // we slice the source slice from four elements
3123 /// // to two. It will panic if we don't do this.
3124 /// dst.copy_from_slice(&src[2..]);
3126 /// assert_eq!(src, [1, 2, 3, 4]);
3127 /// assert_eq!(dst, [3, 4]);
3130 /// Rust enforces that there can only be one mutable reference with no
3131 /// immutable references to a particular piece of data in a particular
3132 /// scope. Because of this, attempting to use `copy_from_slice` on a
3133 /// single slice will result in a compile failure:
3136 /// let mut slice = [1, 2, 3, 4, 5];
3138 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3141 /// To work around this, we can use [`split_at_mut`] to create two distinct
3142 /// sub-slices from a slice:
3145 /// let mut slice = [1, 2, 3, 4, 5];
3148 /// let (left, right) = slice.split_at_mut(2);
3149 /// left.copy_from_slice(&right[1..]);
3152 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3155 /// [`clone_from_slice`]: slice::clone_from_slice
3156 /// [`split_at_mut`]: slice::split_at_mut
3157 #[doc(alias = "memcpy")]
3158 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3160 pub fn copy_from_slice(&mut self, src: &[T])
3164 // The panic code path was put into a cold function to not bloat the
3169 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3171 "source slice length ({}) does not match destination slice length ({})",
3176 if self.len() != src.len() {
3177 len_mismatch_fail(self.len(), src.len());
3180 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3181 // checked to have the same length. The slices cannot overlap because
3182 // mutable references are exclusive.
3184 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3188 /// Copies elements from one part of the slice to another part of itself,
3189 /// using a memmove.
3191 /// `src` is the range within `self` to copy from. `dest` is the starting
3192 /// index of the range within `self` to copy to, which will have the same
3193 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3194 /// must be less than or equal to `self.len()`.
3198 /// This function will panic if either range exceeds the end of the slice,
3199 /// or if the end of `src` is before the start.
3203 /// Copying four bytes within a slice:
3206 /// let mut bytes = *b"Hello, World!";
3208 /// bytes.copy_within(1..5, 8);
3210 /// assert_eq!(&bytes, b"Hello, Wello!");
3212 #[stable(feature = "copy_within", since = "1.37.0")]
3214 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3218 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3219 let count = src_end - src_start;
3220 assert!(dest <= self.len() - count, "dest is out of bounds");
3221 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3222 // as have those for `ptr::add`.
3224 // Derive both `src_ptr` and `dest_ptr` from the same loan
3225 let ptr = self.as_mut_ptr();
3226 let src_ptr = ptr.add(src_start);
3227 let dest_ptr = ptr.add(dest);
3228 ptr::copy(src_ptr, dest_ptr, count);
3232 /// Swaps all elements in `self` with those in `other`.
3234 /// The length of `other` must be the same as `self`.
3238 /// This function will panic if the two slices have different lengths.
3242 /// Swapping two elements across slices:
3245 /// let mut slice1 = [0, 0];
3246 /// let mut slice2 = [1, 2, 3, 4];
3248 /// slice1.swap_with_slice(&mut slice2[2..]);
3250 /// assert_eq!(slice1, [3, 4]);
3251 /// assert_eq!(slice2, [1, 2, 0, 0]);
3254 /// Rust enforces that there can only be one mutable reference to a
3255 /// particular piece of data in a particular scope. Because of this,
3256 /// attempting to use `swap_with_slice` on a single slice will result in
3257 /// a compile failure:
3260 /// let mut slice = [1, 2, 3, 4, 5];
3261 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3264 /// To work around this, we can use [`split_at_mut`] to create two distinct
3265 /// mutable sub-slices from a slice:
3268 /// let mut slice = [1, 2, 3, 4, 5];
3271 /// let (left, right) = slice.split_at_mut(2);
3272 /// left.swap_with_slice(&mut right[1..]);
3275 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3278 /// [`split_at_mut`]: slice::split_at_mut
3279 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3281 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3282 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3283 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3284 // checked to have the same length. The slices cannot overlap because
3285 // mutable references are exclusive.
3287 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3291 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3292 fn align_to_offsets<U>(&self) -> (usize, usize) {
3293 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3294 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3296 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3297 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3298 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3300 // Formula to calculate this is:
3302 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3303 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3305 // Expanded and simplified:
3307 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3308 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3310 // Luckily since all this is constant-evaluated... performance here matters not!
3312 fn gcd(a: usize, b: usize) -> usize {
3313 use crate::intrinsics;
3314 // iterative stein’s algorithm
3315 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3316 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3318 // SAFETY: `a` and `b` are checked to be non-zero values.
3319 let (ctz_a, mut ctz_b) = unsafe {
3326 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3328 let k = ctz_a.min(ctz_b);
3329 let mut a = a >> ctz_a;
3332 // remove all factors of 2 from b
3335 mem::swap(&mut a, &mut b);
3338 // SAFETY: `b` is checked to be non-zero.
3343 ctz_b = intrinsics::cttz_nonzero(b);
3348 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3349 let ts: usize = mem::size_of::<U>() / gcd;
3350 let us: usize = mem::size_of::<T>() / gcd;
3352 // Armed with this knowledge, we can find how many `U`s we can fit!
3353 let us_len = self.len() / ts * us;
3354 // And how many `T`s will be in the trailing slice!
3355 let ts_len = self.len() % ts;
3359 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3362 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3363 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3364 /// length possible for a given type and input slice, but only your algorithm's performance
3365 /// should depend on that, not its correctness. It is permissible for all of the input data to
3366 /// be returned as the prefix or suffix slice.
3368 /// This method has no purpose when either input element `T` or output element `U` are
3369 /// zero-sized and will return the original slice without splitting anything.
3373 /// This method is essentially a `transmute` with respect to the elements in the returned
3374 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3382 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3383 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3384 /// // less_efficient_algorithm_for_bytes(prefix);
3385 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3386 /// // less_efficient_algorithm_for_bytes(suffix);
3389 #[stable(feature = "slice_align_to", since = "1.30.0")]
3390 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3391 // Note that most of this function will be constant-evaluated,
3392 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3393 // handle ZSTs specially, which is – don't handle them at all.
3394 return (self, &[], &[]);
3397 // First, find at what point do we split between the first and 2nd slice. Easy with
3398 // ptr.align_offset.
3399 let ptr = self.as_ptr();
3400 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3401 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3402 if offset > self.len() {
3405 let (left, rest) = self.split_at(offset);
3406 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3407 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3408 // since the caller guarantees that we can transmute `T` to `U` safely.
3412 from_raw_parts(rest.as_ptr() as *const U, us_len),
3413 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3419 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3422 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3423 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3424 /// length possible for a given type and input slice, but only your algorithm's performance
3425 /// should depend on that, not its correctness. It is permissible for all of the input data to
3426 /// be returned as the prefix or suffix slice.
3428 /// This method has no purpose when either input element `T` or output element `U` are
3429 /// zero-sized and will return the original slice without splitting anything.
3433 /// This method is essentially a `transmute` with respect to the elements in the returned
3434 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3442 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3443 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3444 /// // less_efficient_algorithm_for_bytes(prefix);
3445 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3446 /// // less_efficient_algorithm_for_bytes(suffix);
3449 #[stable(feature = "slice_align_to", since = "1.30.0")]
3450 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3451 // Note that most of this function will be constant-evaluated,
3452 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3453 // handle ZSTs specially, which is – don't handle them at all.
3454 return (self, &mut [], &mut []);
3457 // First, find at what point do we split between the first and 2nd slice. Easy with
3458 // ptr.align_offset.
3459 let ptr = self.as_ptr();
3460 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3461 // rest of the method. This is done by passing a pointer to &[T] with an
3462 // alignment targeted for U.
3463 // `crate::ptr::align_offset` is called with a correctly aligned and
3464 // valid pointer `ptr` (it comes from a reference to `self`) and with
3465 // a size that is a power of two (since it comes from the alignement for U),
3466 // satisfying its safety constraints.
3467 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3468 if offset > self.len() {
3469 (self, &mut [], &mut [])
3471 let (left, rest) = self.split_at_mut(offset);
3472 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3473 let rest_len = rest.len();
3474 let mut_ptr = rest.as_mut_ptr();
3475 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3476 // SAFETY: see comments for `align_to`.
3480 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3481 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3487 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3489 /// This is a safe wrapper around [`slice::align_to`], so has the same weak
3490 /// postconditions as that method. You're only assured that
3491 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3493 /// Notably, all of the following are possible:
3494 /// - `prefix.len() >= LANES`.
3495 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3496 /// - `suffix.len() >= LANES`.
3498 /// That said, this is a safe method, so if you're only writing safe code,
3499 /// then this can at most cause incorrect logic, not unsoundness.
3503 /// This will panic if the size of the SIMD type is different from
3504 /// `LANES` times that of the scalar.
3506 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3507 /// that from ever happening, as only power-of-two numbers of lanes are
3508 /// supported. It's possible that, in the future, those restrictions might
3509 /// be lifted in a way that would make it possible to see panics from this
3510 /// method for something like `LANES == 3`.
3515 /// #![feature(portable_simd)]
3517 /// let short = &[1, 2, 3];
3518 /// let (prefix, middle, suffix) = short.as_simd::<4>();
3519 /// assert_eq!(middle, []); // Not enough elements for anything in the middle
3521 /// // They might be split in any possible way between prefix and suffix
3522 /// let it = prefix.iter().chain(suffix).copied();
3523 /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
3525 /// fn basic_simd_sum(x: &[f32]) -> f32 {
3526 /// use std::ops::Add;
3527 /// use std::simd::f32x4;
3528 /// let (prefix, middle, suffix) = x.as_simd();
3529 /// let sums = f32x4::from_array([
3530 /// prefix.iter().copied().sum(),
3533 /// suffix.iter().copied().sum(),
3535 /// let sums = middle.iter().copied().fold(sums, f32x4::add);
3536 /// sums.horizontal_sum()
3539 /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
3540 /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
3542 #[unstable(feature = "portable_simd", issue = "86656")]
3543 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
3544 pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
3546 Simd<T, LANES>: AsRef<[T; LANES]>,
3547 T: simd::SimdElement,
3548 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3550 // These are expected to always match, as vector types are laid out like
3551 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3552 // might as well double-check since it'll optimize away anyhow.
3553 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3555 // SAFETY: The simd types have the same layout as arrays, just with
3556 // potentially-higher alignment, so the de-facto transmutes are sound.
3557 unsafe { self.align_to() }
3560 /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
3562 /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
3563 /// postconditions as that method. You're only assured that
3564 /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
3566 /// Notably, all of the following are possible:
3567 /// - `prefix.len() >= LANES`.
3568 /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
3569 /// - `suffix.len() >= LANES`.
3571 /// That said, this is a safe method, so if you're only writing safe code,
3572 /// then this can at most cause incorrect logic, not unsoundness.
3574 /// This is the mutable version of [`slice::as_simd`]; see that for examples.
3578 /// This will panic if the size of the SIMD type is different from
3579 /// `LANES` times that of the scalar.
3581 /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
3582 /// that from ever happening, as only power-of-two numbers of lanes are
3583 /// supported. It's possible that, in the future, those restrictions might
3584 /// be lifted in a way that would make it possible to see panics from this
3585 /// method for something like `LANES == 3`.
3586 #[unstable(feature = "portable_simd", issue = "86656")]
3587 #[cfg(not(all(miri, doctest)))] // Miri skips SIMD doctests
3588 pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
3590 Simd<T, LANES>: AsMut<[T; LANES]>,
3591 T: simd::SimdElement,
3592 simd::LaneCount<LANES>: simd::SupportedLaneCount,
3594 // These are expected to always match, as vector types are laid out like
3595 // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
3596 // might as well double-check since it'll optimize away anyhow.
3597 assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
3599 // SAFETY: The simd types have the same layout as arrays, just with
3600 // potentially-higher alignment, so the de-facto transmutes are sound.
3601 unsafe { self.align_to_mut() }
3604 /// Checks if the elements of this slice are sorted.
3606 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3607 /// slice yields exactly zero or one element, `true` is returned.
3609 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3610 /// implies that this function returns `false` if any two consecutive items are not
3616 /// #![feature(is_sorted)]
3617 /// let empty: [i32; 0] = [];
3619 /// assert!([1, 2, 2, 9].is_sorted());
3620 /// assert!(![1, 3, 2, 4].is_sorted());
3621 /// assert!([0].is_sorted());
3622 /// assert!(empty.is_sorted());
3623 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3626 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3627 pub fn is_sorted(&self) -> bool
3631 self.is_sorted_by(|a, b| a.partial_cmp(b))
3634 /// Checks if the elements of this slice are sorted using the given comparator function.
3636 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3637 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3638 /// [`is_sorted`]; see its documentation for more information.
3640 /// [`is_sorted`]: slice::is_sorted
3641 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3642 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3644 F: FnMut(&T, &T) -> Option<Ordering>,
3646 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3649 /// Checks if the elements of this slice are sorted using the given key extraction function.
3651 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3652 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3653 /// documentation for more information.
3655 /// [`is_sorted`]: slice::is_sorted
3660 /// #![feature(is_sorted)]
3662 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3663 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3666 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3667 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3672 self.iter().is_sorted_by_key(f)
3675 /// Returns the index of the partition point according to the given predicate
3676 /// (the index of the first element of the second partition).
3678 /// The slice is assumed to be partitioned according to the given predicate.
3679 /// This means that all elements for which the predicate returns true are at the start of the slice
3680 /// and all elements for which the predicate returns false are at the end.
3681 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3682 /// (all odd numbers are at the start, all even at the end).
3684 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3685 /// as this method performs a kind of binary search.
3687 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3689 /// [`binary_search`]: slice::binary_search
3690 /// [`binary_search_by`]: slice::binary_search_by
3691 /// [`binary_search_by_key`]: slice::binary_search_by_key
3696 /// let v = [1, 2, 3, 3, 5, 6, 7];
3697 /// let i = v.partition_point(|&x| x < 5);
3699 /// assert_eq!(i, 4);
3700 /// assert!(v[..i].iter().all(|&x| x < 5));
3701 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3703 #[stable(feature = "partition_point", since = "1.52.0")]
3704 pub fn partition_point<P>(&self, mut pred: P) -> usize
3706 P: FnMut(&T) -> bool,
3708 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3711 /// Removes the subslice corresponding to the given range
3712 /// and returns a reference to it.
3714 /// Returns `None` and does not modify the slice if the given
3715 /// range is out of bounds.
3717 /// Note that this method only accepts one-sided ranges such as
3718 /// `2..` or `..6`, but not `2..6`.
3722 /// Taking the first three elements of a slice:
3725 /// #![feature(slice_take)]
3727 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3728 /// let mut first_three = slice.take(..3).unwrap();
3730 /// assert_eq!(slice, &['d']);
3731 /// assert_eq!(first_three, &['a', 'b', 'c']);
3734 /// Taking the last two elements of a slice:
3737 /// #![feature(slice_take)]
3739 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3740 /// let mut tail = slice.take(2..).unwrap();
3742 /// assert_eq!(slice, &['a', 'b']);
3743 /// assert_eq!(tail, &['c', 'd']);
3746 /// Getting `None` when `range` is out of bounds:
3749 /// #![feature(slice_take)]
3751 /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
3753 /// assert_eq!(None, slice.take(5..));
3754 /// assert_eq!(None, slice.take(..5));
3755 /// assert_eq!(None, slice.take(..=4));
3756 /// let expected: &[char] = &['a', 'b', 'c', 'd'];
3757 /// assert_eq!(Some(expected), slice.take(..4));
3760 #[must_use = "method does not modify the slice if the range is out of bounds"]
3761 #[unstable(feature = "slice_take", issue = "62280")]
3762 pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
3763 let (direction, split_index) = split_point_of(range)?;
3764 if split_index > self.len() {
3767 let (front, back) = self.split_at(split_index);
3769 Direction::Front => {
3773 Direction::Back => {
3780 /// Removes the subslice corresponding to the given range
3781 /// and returns a mutable reference to it.
3783 /// Returns `None` and does not modify the slice if the given
3784 /// range is out of bounds.
3786 /// Note that this method only accepts one-sided ranges such as
3787 /// `2..` or `..6`, but not `2..6`.
3791 /// Taking the first three elements of a slice:
3794 /// #![feature(slice_take)]
3796 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3797 /// let mut first_three = slice.take_mut(..3).unwrap();
3799 /// assert_eq!(slice, &mut ['d']);
3800 /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
3803 /// Taking the last two elements of a slice:
3806 /// #![feature(slice_take)]
3808 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3809 /// let mut tail = slice.take_mut(2..).unwrap();
3811 /// assert_eq!(slice, &mut ['a', 'b']);
3812 /// assert_eq!(tail, &mut ['c', 'd']);
3815 /// Getting `None` when `range` is out of bounds:
3818 /// #![feature(slice_take)]
3820 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3822 /// assert_eq!(None, slice.take_mut(5..));
3823 /// assert_eq!(None, slice.take_mut(..5));
3824 /// assert_eq!(None, slice.take_mut(..=4));
3825 /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
3826 /// assert_eq!(Some(expected), slice.take_mut(..4));
3829 #[must_use = "method does not modify the slice if the range is out of bounds"]
3830 #[unstable(feature = "slice_take", issue = "62280")]
3831 pub fn take_mut<'a, R: OneSidedRange<usize>>(
3832 self: &mut &'a mut Self,
3834 ) -> Option<&'a mut Self> {
3835 let (direction, split_index) = split_point_of(range)?;
3836 if split_index > self.len() {
3839 let (front, back) = mem::take(self).split_at_mut(split_index);
3841 Direction::Front => {
3845 Direction::Back => {
3852 /// Removes the first element of the slice and returns a reference
3855 /// Returns `None` if the slice is empty.
3860 /// #![feature(slice_take)]
3862 /// let mut slice: &[_] = &['a', 'b', 'c'];
3863 /// let first = slice.take_first().unwrap();
3865 /// assert_eq!(slice, &['b', 'c']);
3866 /// assert_eq!(first, &'a');
3869 #[unstable(feature = "slice_take", issue = "62280")]
3870 pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
3871 let (first, rem) = self.split_first()?;
3876 /// Removes the first element of the slice and returns a mutable
3877 /// reference to it.
3879 /// Returns `None` if the slice is empty.
3884 /// #![feature(slice_take)]
3886 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3887 /// let first = slice.take_first_mut().unwrap();
3890 /// assert_eq!(slice, &['b', 'c']);
3891 /// assert_eq!(first, &'d');
3894 #[unstable(feature = "slice_take", issue = "62280")]
3895 pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3896 let (first, rem) = mem::take(self).split_first_mut()?;
3901 /// Removes the last element of the slice and returns a reference
3904 /// Returns `None` if the slice is empty.
3909 /// #![feature(slice_take)]
3911 /// let mut slice: &[_] = &['a', 'b', 'c'];
3912 /// let last = slice.take_last().unwrap();
3914 /// assert_eq!(slice, &['a', 'b']);
3915 /// assert_eq!(last, &'c');
3918 #[unstable(feature = "slice_take", issue = "62280")]
3919 pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
3920 let (last, rem) = self.split_last()?;
3925 /// Removes the last element of the slice and returns a mutable
3926 /// reference to it.
3928 /// Returns `None` if the slice is empty.
3933 /// #![feature(slice_take)]
3935 /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
3936 /// let last = slice.take_last_mut().unwrap();
3939 /// assert_eq!(slice, &['a', 'b']);
3940 /// assert_eq!(last, &'d');
3943 #[unstable(feature = "slice_take", issue = "62280")]
3944 pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
3945 let (last, rem) = mem::take(self).split_last_mut()?;
3951 trait CloneFromSpec<T> {
3952 fn spec_clone_from(&mut self, src: &[T]);
3955 impl<T> CloneFromSpec<T> for [T]
3960 default fn spec_clone_from(&mut self, src: &[T]) {
3961 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3962 // NOTE: We need to explicitly slice them to the same length
3963 // to make it easier for the optimizer to elide bounds checking.
3964 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3965 let len = self.len();
3966 let src = &src[..len];
3968 self[i].clone_from(&src[i]);
3973 impl<T> CloneFromSpec<T> for [T]
3978 fn spec_clone_from(&mut self, src: &[T]) {
3979 self.copy_from_slice(src);
3983 #[stable(feature = "rust1", since = "1.0.0")]
3984 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3985 impl<T> const Default for &[T] {
3986 /// Creates an empty slice.
3987 fn default() -> Self {
3992 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3993 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3994 impl<T> const Default for &mut [T] {
3995 /// Creates a mutable empty slice.
3996 fn default() -> Self {
4001 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
4002 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
4003 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
4004 /// `str`) to slices, and then this trait will be replaced or abolished.
4005 pub trait SlicePattern {
4006 /// The element type of the slice being matched on.
4009 /// Currently, the consumers of `SlicePattern` need a slice.
4010 fn as_slice(&self) -> &[Self::Item];
4013 #[stable(feature = "slice_strip", since = "1.51.0")]
4014 impl<T> SlicePattern for [T] {
4018 fn as_slice(&self) -> &[Self::Item] {
4023 #[stable(feature = "slice_strip", since = "1.51.0")]
4024 impl<T, const N: usize> SlicePattern for [T; N] {
4028 fn as_slice(&self) -> &[Self::Item] {