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::{FnMut, 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};
22 feature = "slice_internals",
24 reason = "exposed from core to be reused in std; use the memchr crate"
26 /// Pure rust memchr implementation, taken from rust-memchr
38 #[stable(feature = "rust1", since = "1.0.0")]
39 pub use iter::{Chunks, ChunksMut, Windows};
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Iter, IterMut};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
45 #[stable(feature = "slice_rsplit", since = "1.27.0")]
46 pub use iter::{RSplit, RSplitMut};
48 #[stable(feature = "chunks_exact", since = "1.31.0")]
49 pub use iter::{ChunksExact, ChunksExactMut};
51 #[stable(feature = "rchunks", since = "1.31.0")]
52 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
54 #[unstable(feature = "array_chunks", issue = "74985")]
55 pub use iter::{ArrayChunks, ArrayChunksMut};
57 #[unstable(feature = "array_windows", issue = "75027")]
58 pub use iter::ArrayWindows;
60 #[unstable(feature = "slice_group_by", issue = "80552")]
61 pub use iter::{GroupBy, GroupByMut};
63 #[stable(feature = "split_inclusive", since = "1.51.0")]
64 pub use iter::{SplitInclusive, SplitInclusiveMut};
66 #[stable(feature = "rust1", since = "1.0.0")]
67 pub use raw::{from_raw_parts, from_raw_parts_mut};
69 #[stable(feature = "from_ref", since = "1.28.0")]
70 pub use raw::{from_mut, from_ref};
72 // This function is public only because there is no other way to unit test heapsort.
73 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
74 pub use sort::heapsort;
76 #[stable(feature = "slice_get_slice", since = "1.28.0")]
77 pub use index::SliceIndex;
79 #[unstable(feature = "slice_range", issue = "76393")]
82 #[unstable(feature = "inherent_ascii_escape", issue = "77174")]
83 pub use ascii::EscapeAscii;
88 /// Returns the number of elements in the slice.
93 /// let a = [1, 2, 3];
94 /// assert_eq!(a.len(), 3);
96 #[lang = "slice_len_fn"]
97 #[stable(feature = "rust1", since = "1.0.0")]
98 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
100 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
101 pub const fn len(&self) -> usize {
102 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
103 // As of this writing this causes a "Const-stable functions can only call other
104 // const-stable functions" error.
106 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
107 // and PtrComponents<T> have the same memory layouts. Only std can make this
109 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
112 /// Returns `true` if the slice has a length of 0.
117 /// let a = [1, 2, 3];
118 /// assert!(!a.is_empty());
120 #[stable(feature = "rust1", since = "1.0.0")]
121 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
123 pub const fn is_empty(&self) -> bool {
127 /// Returns the first element of the slice, or `None` if it is empty.
132 /// let v = [10, 40, 30];
133 /// assert_eq!(Some(&10), v.first());
135 /// let w: &[i32] = &[];
136 /// assert_eq!(None, w.first());
138 #[stable(feature = "rust1", since = "1.0.0")]
139 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
141 pub const fn first(&self) -> Option<&T> {
142 if let [first, ..] = self { Some(first) } else { None }
145 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
150 /// let x = &mut [0, 1, 2];
152 /// if let Some(first) = x.first_mut() {
155 /// assert_eq!(x, &[5, 1, 2]);
157 #[stable(feature = "rust1", since = "1.0.0")]
158 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
160 pub const fn first_mut(&mut self) -> Option<&mut T> {
161 if let [first, ..] = self { Some(first) } else { None }
164 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
169 /// let x = &[0, 1, 2];
171 /// if let Some((first, elements)) = x.split_first() {
172 /// assert_eq!(first, &0);
173 /// assert_eq!(elements, &[1, 2]);
176 #[stable(feature = "slice_splits", since = "1.5.0")]
177 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
179 pub const fn split_first(&self) -> Option<(&T, &[T])> {
180 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
183 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
188 /// let x = &mut [0, 1, 2];
190 /// if let Some((first, elements)) = x.split_first_mut() {
195 /// assert_eq!(x, &[3, 4, 5]);
197 #[stable(feature = "slice_splits", since = "1.5.0")]
198 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
200 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
201 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
204 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
209 /// let x = &[0, 1, 2];
211 /// if let Some((last, elements)) = x.split_last() {
212 /// assert_eq!(last, &2);
213 /// assert_eq!(elements, &[0, 1]);
216 #[stable(feature = "slice_splits", since = "1.5.0")]
217 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
219 pub const fn split_last(&self) -> Option<(&T, &[T])> {
220 if let [init @ .., last] = self { Some((last, init)) } else { None }
223 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
228 /// let x = &mut [0, 1, 2];
230 /// if let Some((last, elements)) = x.split_last_mut() {
235 /// assert_eq!(x, &[4, 5, 3]);
237 #[stable(feature = "slice_splits", since = "1.5.0")]
238 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
240 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
241 if let [init @ .., last] = self { Some((last, init)) } else { None }
244 /// Returns the last element of the slice, or `None` if it is empty.
249 /// let v = [10, 40, 30];
250 /// assert_eq!(Some(&30), v.last());
252 /// let w: &[i32] = &[];
253 /// assert_eq!(None, w.last());
255 #[stable(feature = "rust1", since = "1.0.0")]
256 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
258 pub const fn last(&self) -> Option<&T> {
259 if let [.., last] = self { Some(last) } else { None }
262 /// Returns a mutable pointer to the last item in the slice.
267 /// let x = &mut [0, 1, 2];
269 /// if let Some(last) = x.last_mut() {
272 /// assert_eq!(x, &[0, 1, 10]);
274 #[stable(feature = "rust1", since = "1.0.0")]
275 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
277 pub const fn last_mut(&mut self) -> Option<&mut T> {
278 if let [.., last] = self { Some(last) } else { None }
281 /// Returns a reference to an element or subslice depending on the type of
284 /// - If given a position, returns a reference to the element at that
285 /// position or `None` if out of bounds.
286 /// - If given a range, returns the subslice corresponding to that range,
287 /// or `None` if out of bounds.
292 /// let v = [10, 40, 30];
293 /// assert_eq!(Some(&40), v.get(1));
294 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
295 /// assert_eq!(None, v.get(3));
296 /// assert_eq!(None, v.get(0..4));
298 #[stable(feature = "rust1", since = "1.0.0")]
300 pub fn get<I>(&self, index: I) -> Option<&I::Output>
307 /// Returns a mutable reference to an element or subslice depending on the
308 /// type of index (see [`get`]) or `None` if the index is out of bounds.
310 /// [`get`]: slice::get
315 /// let x = &mut [0, 1, 2];
317 /// if let Some(elem) = x.get_mut(1) {
320 /// assert_eq!(x, &[0, 42, 2]);
322 #[stable(feature = "rust1", since = "1.0.0")]
324 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
331 /// Returns a reference to an element or subslice, without doing bounds
334 /// For a safe alternative see [`get`].
338 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
339 /// even if the resulting reference is not used.
341 /// [`get`]: slice::get
342 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
347 /// let x = &[1, 2, 4];
350 /// assert_eq!(x.get_unchecked(1), &2);
353 #[stable(feature = "rust1", since = "1.0.0")]
355 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
359 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
360 // the slice is dereferencable because `self` is a safe reference.
361 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
362 unsafe { &*index.get_unchecked(self) }
365 /// Returns a mutable reference to an element or subslice, without doing
368 /// For a safe alternative see [`get_mut`].
372 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
373 /// even if the resulting reference is not used.
375 /// [`get_mut`]: slice::get_mut
376 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
381 /// let x = &mut [1, 2, 4];
384 /// let elem = x.get_unchecked_mut(1);
387 /// assert_eq!(x, &[1, 13, 4]);
389 #[stable(feature = "rust1", since = "1.0.0")]
391 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
395 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
396 // the slice is dereferencable because `self` is a safe reference.
397 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
398 unsafe { &mut *index.get_unchecked_mut(self) }
401 /// Returns a raw pointer to the slice's buffer.
403 /// The caller must ensure that the slice outlives the pointer this
404 /// function returns, or else it will end up pointing to garbage.
406 /// The caller must also ensure that the memory the pointer (non-transitively) points to
407 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
408 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
410 /// Modifying the container referenced by this slice may cause its buffer
411 /// to be reallocated, which would also make any pointers to it invalid.
416 /// let x = &[1, 2, 4];
417 /// let x_ptr = x.as_ptr();
420 /// for i in 0..x.len() {
421 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
426 /// [`as_mut_ptr`]: slice::as_mut_ptr
427 #[stable(feature = "rust1", since = "1.0.0")]
428 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
430 pub const fn as_ptr(&self) -> *const T {
431 self as *const [T] as *const T
434 /// Returns an unsafe mutable pointer to the slice's buffer.
436 /// The caller must ensure that the slice outlives the pointer this
437 /// function returns, or else it will end up pointing to garbage.
439 /// Modifying the container referenced by this slice may cause its buffer
440 /// to be reallocated, which would also make any pointers to it invalid.
445 /// let x = &mut [1, 2, 4];
446 /// let x_ptr = x.as_mut_ptr();
449 /// for i in 0..x.len() {
450 /// *x_ptr.add(i) += 2;
453 /// assert_eq!(x, &[3, 4, 6]);
455 #[stable(feature = "rust1", since = "1.0.0")]
456 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
458 pub const fn as_mut_ptr(&mut self) -> *mut T {
459 self as *mut [T] as *mut T
462 /// Returns the two raw pointers spanning the slice.
464 /// The returned range is half-open, which means that the end pointer
465 /// points *one past* the last element of the slice. This way, an empty
466 /// slice is represented by two equal pointers, and the difference between
467 /// the two pointers represents the size of the slice.
469 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
470 /// requires extra caution, as it does not point to a valid element in the
473 /// This function is useful for interacting with foreign interfaces which
474 /// use two pointers to refer to a range of elements in memory, as is
477 /// It can also be useful to check if a pointer to an element refers to an
478 /// element of this slice:
481 /// let a = [1, 2, 3];
482 /// let x = &a[1] as *const _;
483 /// let y = &5 as *const _;
485 /// assert!(a.as_ptr_range().contains(&x));
486 /// assert!(!a.as_ptr_range().contains(&y));
489 /// [`as_ptr`]: slice::as_ptr
490 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
491 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
493 pub const fn as_ptr_range(&self) -> Range<*const T> {
494 let start = self.as_ptr();
495 // SAFETY: The `add` here is safe, because:
497 // - Both pointers are part of the same object, as pointing directly
498 // past the object also counts.
500 // - The size of the slice is never larger than isize::MAX bytes, as
502 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
503 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
504 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
505 // (This doesn't seem normative yet, but the very same assumption is
506 // made in many places, including the Index implementation of slices.)
508 // - There is no wrapping around involved, as slices do not wrap past
509 // the end of the address space.
511 // See the documentation of pointer::add.
512 let end = unsafe { start.add(self.len()) };
516 /// Returns the two unsafe mutable pointers spanning the slice.
518 /// The returned range is half-open, which means that the end pointer
519 /// points *one past* the last element of the slice. This way, an empty
520 /// slice is represented by two equal pointers, and the difference between
521 /// the two pointers represents the size of the slice.
523 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
524 /// pointer requires extra caution, as it does not point to a valid element
527 /// This function is useful for interacting with foreign interfaces which
528 /// use two pointers to refer to a range of elements in memory, as is
531 /// [`as_mut_ptr`]: slice::as_mut_ptr
532 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
533 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
535 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
536 let start = self.as_mut_ptr();
537 // SAFETY: See as_ptr_range() above for why `add` here is safe.
538 let end = unsafe { start.add(self.len()) };
542 /// Swaps two elements in the slice.
546 /// * a - The index of the first element
547 /// * b - The index of the second element
551 /// Panics if `a` or `b` are out of bounds.
556 /// let mut v = ["a", "b", "c", "d"];
558 /// assert!(v == ["a", "d", "c", "b"]);
560 #[stable(feature = "rust1", since = "1.0.0")]
562 pub fn swap(&mut self, a: usize, b: usize) {
563 assert!(a < self.len());
564 assert!(b < self.len());
565 // SAFETY: we just checked that both `a` and `b` are in bounds
566 unsafe { self.swap_unchecked(a, b) }
569 /// Swaps two elements in the slice, without doing bounds checking.
571 /// For a safe alternative see [`swap`].
575 /// * a - The index of the first element
576 /// * b - The index of the second element
580 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
581 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
586 /// let mut v = ["a", "b", "c", "d"];
587 /// // SAFETY: we know that 1 and 3 are both indices of the slice
588 /// unsafe { v.swap_unchecked(1, 3) };
589 /// assert!(v == ["a", "d", "c", "b"]);
592 /// [`swap`]: slice::swap
593 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
594 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
595 pub unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
596 debug_assert!(a < self.len());
597 debug_assert!(b < self.len());
598 let ptr = self.as_mut_ptr();
599 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
601 ptr::swap(ptr.add(a), ptr.add(b));
605 /// Reverses the order of elements in the slice, in place.
610 /// let mut v = [1, 2, 3];
612 /// assert!(v == [3, 2, 1]);
614 #[stable(feature = "rust1", since = "1.0.0")]
616 pub fn reverse(&mut self) {
617 let mut i: usize = 0;
620 // For very small types, all the individual reads in the normal
621 // path perform poorly. We can do better, given efficient unaligned
622 // load/store, by loading a larger chunk and reversing a register.
624 // Ideally LLVM would do this for us, as it knows better than we do
625 // whether unaligned reads are efficient (since that changes between
626 // different ARM versions, for example) and what the best chunk size
627 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
628 // the loop, so we need to do this ourselves. (Hypothesis: reverse
629 // is troublesome because the sides can be aligned differently --
630 // will be, when the length is odd -- so there's no way of emitting
631 // pre- and postludes to use fully-aligned SIMD in the middle.)
633 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
635 if fast_unaligned && mem::size_of::<T>() == 1 {
636 // Use the llvm.bswap intrinsic to reverse u8s in a usize
637 let chunk = mem::size_of::<usize>();
638 while i + chunk - 1 < ln / 2 {
639 // SAFETY: There are several things to check here:
641 // - Note that `chunk` is either 4 or 8 due to the cfg check
642 // above. So `chunk - 1` is positive.
643 // - Indexing with index `i` is fine as the loop check guarantees
644 // `i + chunk - 1 < ln / 2`
645 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
646 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
647 // - `i + chunk > 0` is trivially true.
648 // - The loop check guarantees:
649 // `i + chunk - 1 < ln / 2`
650 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
651 // - The `read_unaligned` and `write_unaligned` calls are fine:
652 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
653 // (see above) and `pb` points to index `ln - i - chunk`, so
654 // both are at least `chunk`
655 // many bytes away from the end of `self`.
656 // - Any initialized memory is valid `usize`.
658 let ptr = self.as_mut_ptr();
660 let pb = ptr.add(ln - i - chunk);
661 let va = ptr::read_unaligned(pa as *mut usize);
662 let vb = ptr::read_unaligned(pb as *mut usize);
663 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
664 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
670 if fast_unaligned && mem::size_of::<T>() == 2 {
671 // Use rotate-by-16 to reverse u16s in a u32
672 let chunk = mem::size_of::<u32>() / 2;
673 while i + chunk - 1 < ln / 2 {
674 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
675 // (and obviously `i < ln`), because each element is 2 bytes and
678 // `i + chunk - 1 < ln / 2` # while condition
679 // `i + 2 - 1 < ln / 2`
682 // Since it's less than the length divided by 2, then it must be
685 // This also means that the condition `0 < i + chunk <= ln` is
686 // always respected, ensuring the `pb` pointer can be used
689 let ptr = self.as_mut_ptr();
691 let pb = ptr.add(ln - i - chunk);
692 let va = ptr::read_unaligned(pa as *mut u32);
693 let vb = ptr::read_unaligned(pb as *mut u32);
694 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
695 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
702 // SAFETY: `i` is inferior to half the length of the slice so
703 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
704 // will not go further than `ln / 2 - 1`).
705 // The resulting pointers `pa` and `pb` are therefore valid and
706 // aligned, and can be read from and written to.
708 // Unsafe swap to avoid the bounds check in safe swap.
709 let ptr = self.as_mut_ptr();
711 let pb = ptr.add(ln - i - 1);
718 /// Returns an iterator over the slice.
723 /// let x = &[1, 2, 4];
724 /// let mut iterator = x.iter();
726 /// assert_eq!(iterator.next(), Some(&1));
727 /// assert_eq!(iterator.next(), Some(&2));
728 /// assert_eq!(iterator.next(), Some(&4));
729 /// assert_eq!(iterator.next(), None);
731 #[stable(feature = "rust1", since = "1.0.0")]
733 pub fn iter(&self) -> Iter<'_, T> {
737 /// Returns an iterator that allows modifying each value.
742 /// let x = &mut [1, 2, 4];
743 /// for elem in x.iter_mut() {
746 /// assert_eq!(x, &[3, 4, 6]);
748 #[stable(feature = "rust1", since = "1.0.0")]
750 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
754 /// Returns an iterator over all contiguous windows of length
755 /// `size`. The windows overlap. If the slice is shorter than
756 /// `size`, the iterator returns no values.
760 /// Panics if `size` is 0.
765 /// let slice = ['r', 'u', 's', 't'];
766 /// let mut iter = slice.windows(2);
767 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
768 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
769 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
770 /// assert!(iter.next().is_none());
773 /// If the slice is shorter than `size`:
776 /// let slice = ['f', 'o', 'o'];
777 /// let mut iter = slice.windows(4);
778 /// assert!(iter.next().is_none());
780 #[stable(feature = "rust1", since = "1.0.0")]
782 pub fn windows(&self, size: usize) -> Windows<'_, T> {
783 let size = NonZeroUsize::new(size).expect("size is zero");
784 Windows::new(self, size)
787 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
788 /// beginning of the slice.
790 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
791 /// slice, then the last chunk will not have length `chunk_size`.
793 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
794 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
799 /// Panics if `chunk_size` is 0.
804 /// let slice = ['l', 'o', 'r', 'e', 'm'];
805 /// let mut iter = slice.chunks(2);
806 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
807 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
808 /// assert_eq!(iter.next().unwrap(), &['m']);
809 /// assert!(iter.next().is_none());
812 /// [`chunks_exact`]: slice::chunks_exact
813 /// [`rchunks`]: slice::rchunks
814 #[stable(feature = "rust1", since = "1.0.0")]
816 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
817 assert_ne!(chunk_size, 0);
818 Chunks::new(self, chunk_size)
821 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
822 /// beginning of the slice.
824 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
825 /// length of the slice, then the last chunk will not have length `chunk_size`.
827 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
828 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
829 /// the end of the slice.
833 /// Panics if `chunk_size` is 0.
838 /// let v = &mut [0, 0, 0, 0, 0];
839 /// let mut count = 1;
841 /// for chunk in v.chunks_mut(2) {
842 /// for elem in chunk.iter_mut() {
847 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
850 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
851 /// [`rchunks_mut`]: slice::rchunks_mut
852 #[stable(feature = "rust1", since = "1.0.0")]
854 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
855 assert_ne!(chunk_size, 0);
856 ChunksMut::new(self, chunk_size)
859 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
860 /// beginning of the slice.
862 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
863 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
864 /// from the `remainder` function of the iterator.
866 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
867 /// resulting code better than in the case of [`chunks`].
869 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
870 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
874 /// Panics if `chunk_size` is 0.
879 /// let slice = ['l', 'o', 'r', 'e', 'm'];
880 /// let mut iter = slice.chunks_exact(2);
881 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
882 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
883 /// assert!(iter.next().is_none());
884 /// assert_eq!(iter.remainder(), &['m']);
887 /// [`chunks`]: slice::chunks
888 /// [`rchunks_exact`]: slice::rchunks_exact
889 #[stable(feature = "chunks_exact", since = "1.31.0")]
891 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
892 assert_ne!(chunk_size, 0);
893 ChunksExact::new(self, chunk_size)
896 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
897 /// beginning of the slice.
899 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
900 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
901 /// retrieved from the `into_remainder` function of the iterator.
903 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
904 /// resulting code better than in the case of [`chunks_mut`].
906 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
907 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
912 /// Panics if `chunk_size` is 0.
917 /// let v = &mut [0, 0, 0, 0, 0];
918 /// let mut count = 1;
920 /// for chunk in v.chunks_exact_mut(2) {
921 /// for elem in chunk.iter_mut() {
926 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
929 /// [`chunks_mut`]: slice::chunks_mut
930 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
931 #[stable(feature = "chunks_exact", since = "1.31.0")]
933 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
934 assert_ne!(chunk_size, 0);
935 ChunksExactMut::new(self, chunk_size)
938 /// Splits the slice into a slice of `N`-element arrays,
939 /// assuming that there's no remainder.
943 /// This may only be called when
944 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
950 /// #![feature(slice_as_chunks)]
951 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
952 /// let chunks: &[[char; 1]] =
953 /// // SAFETY: 1-element chunks never have remainder
954 /// unsafe { slice.as_chunks_unchecked() };
955 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
956 /// let chunks: &[[char; 3]] =
957 /// // SAFETY: The slice length (6) is a multiple of 3
958 /// unsafe { slice.as_chunks_unchecked() };
959 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
961 /// // These would be unsound:
962 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
963 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
965 #[unstable(feature = "slice_as_chunks", issue = "74985")]
967 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
968 debug_assert_ne!(N, 0);
969 debug_assert_eq!(self.len() % N, 0);
971 // SAFETY: Our precondition is exactly what's needed to call this
972 unsafe { crate::intrinsics::exact_div(self.len(), N) };
973 // SAFETY: We cast a slice of `new_len * N` elements into
974 // a slice of `new_len` many `N` elements chunks.
975 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
978 /// Splits the slice into a slice of `N`-element arrays,
979 /// starting at the beginning of the slice,
980 /// and a remainder slice with length strictly less than `N`.
984 /// Panics if `N` is 0. This check will most probably get changed to a compile time
985 /// error before this method gets stabilized.
990 /// #![feature(slice_as_chunks)]
991 /// let slice = ['l', 'o', 'r', 'e', 'm'];
992 /// let (chunks, remainder) = slice.as_chunks();
993 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
994 /// assert_eq!(remainder, &['m']);
996 #[unstable(feature = "slice_as_chunks", issue = "74985")]
998 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1000 let len = self.len() / N;
1001 let (multiple_of_n, remainder) = self.split_at(len * N);
1002 // SAFETY: We already panicked for zero, and ensured by construction
1003 // that the length of the subslice is a multiple of N.
1004 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1005 (array_slice, remainder)
1008 /// Splits the slice into a slice of `N`-element arrays,
1009 /// starting at the end of the slice,
1010 /// and a remainder slice with length strictly less than `N`.
1014 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1015 /// error before this method gets stabilized.
1020 /// #![feature(slice_as_chunks)]
1021 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1022 /// let (remainder, chunks) = slice.as_rchunks();
1023 /// assert_eq!(remainder, &['l']);
1024 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1026 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1028 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1030 let len = self.len() / N;
1031 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1032 // SAFETY: We already panicked for zero, and ensured by construction
1033 // that the length of the subslice is a multiple of N.
1034 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1035 (remainder, array_slice)
1038 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1039 /// beginning of the slice.
1041 /// The chunks are array references and do not overlap. If `N` does not divide the
1042 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1043 /// retrieved from the `remainder` function of the iterator.
1045 /// This method is the const generic equivalent of [`chunks_exact`].
1049 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1050 /// error before this method gets stabilized.
1055 /// #![feature(array_chunks)]
1056 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1057 /// let mut iter = slice.array_chunks();
1058 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1059 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1060 /// assert!(iter.next().is_none());
1061 /// assert_eq!(iter.remainder(), &['m']);
1064 /// [`chunks_exact`]: slice::chunks_exact
1065 #[unstable(feature = "array_chunks", issue = "74985")]
1067 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1069 ArrayChunks::new(self)
1072 /// Splits the slice into a slice of `N`-element arrays,
1073 /// assuming that there's no remainder.
1077 /// This may only be called when
1078 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1084 /// #![feature(slice_as_chunks)]
1085 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1086 /// let chunks: &mut [[char; 1]] =
1087 /// // SAFETY: 1-element chunks never have remainder
1088 /// unsafe { slice.as_chunks_unchecked_mut() };
1089 /// chunks[0] = ['L'];
1090 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1091 /// let chunks: &mut [[char; 3]] =
1092 /// // SAFETY: The slice length (6) is a multiple of 3
1093 /// unsafe { slice.as_chunks_unchecked_mut() };
1094 /// chunks[1] = ['a', 'x', '?'];
1095 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1097 /// // These would be unsound:
1098 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1099 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1101 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1103 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1104 debug_assert_ne!(N, 0);
1105 debug_assert_eq!(self.len() % N, 0);
1107 // SAFETY: Our precondition is exactly what's needed to call this
1108 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1109 // SAFETY: We cast a slice of `new_len * N` elements into
1110 // a slice of `new_len` many `N` elements chunks.
1111 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1114 /// Splits the slice into a slice of `N`-element arrays,
1115 /// starting at the beginning of the slice,
1116 /// and a remainder slice with length strictly less than `N`.
1120 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1121 /// error before this method gets stabilized.
1126 /// #![feature(slice_as_chunks)]
1127 /// let v = &mut [0, 0, 0, 0, 0];
1128 /// let mut count = 1;
1130 /// let (chunks, remainder) = v.as_chunks_mut();
1131 /// remainder[0] = 9;
1132 /// for chunk in chunks {
1133 /// *chunk = [count; 2];
1136 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1138 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1140 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1142 let len = self.len() / N;
1143 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1144 // SAFETY: We already panicked for zero, and ensured by construction
1145 // that the length of the subslice is a multiple of N.
1146 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1147 (array_slice, remainder)
1150 /// Splits the slice into a slice of `N`-element arrays,
1151 /// starting at the end of the slice,
1152 /// and a remainder slice with length strictly less than `N`.
1156 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1157 /// error before this method gets stabilized.
1162 /// #![feature(slice_as_chunks)]
1163 /// let v = &mut [0, 0, 0, 0, 0];
1164 /// let mut count = 1;
1166 /// let (remainder, chunks) = v.as_rchunks_mut();
1167 /// remainder[0] = 9;
1168 /// for chunk in chunks {
1169 /// *chunk = [count; 2];
1172 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1174 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1176 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1178 let len = self.len() / N;
1179 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1180 // SAFETY: We already panicked for zero, and ensured by construction
1181 // that the length of the subslice is a multiple of N.
1182 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1183 (remainder, array_slice)
1186 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1187 /// beginning of the slice.
1189 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1190 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1191 /// can be retrieved from the `into_remainder` function of the iterator.
1193 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1197 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1198 /// error before this method gets stabilized.
1203 /// #![feature(array_chunks)]
1204 /// let v = &mut [0, 0, 0, 0, 0];
1205 /// let mut count = 1;
1207 /// for chunk in v.array_chunks_mut() {
1208 /// *chunk = [count; 2];
1211 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1214 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1215 #[unstable(feature = "array_chunks", issue = "74985")]
1217 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1219 ArrayChunksMut::new(self)
1222 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1223 /// starting at the beginning of the slice.
1225 /// This is the const generic equivalent of [`windows`].
1227 /// If `N` is greater than the size of the slice, it will return no windows.
1231 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1232 /// error before this method gets stabilized.
1237 /// #![feature(array_windows)]
1238 /// let slice = [0, 1, 2, 3];
1239 /// let mut iter = slice.array_windows();
1240 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1241 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1242 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1243 /// assert!(iter.next().is_none());
1246 /// [`windows`]: slice::windows
1247 #[unstable(feature = "array_windows", issue = "75027")]
1249 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1251 ArrayWindows::new(self)
1254 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1257 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1258 /// slice, then the last chunk will not have length `chunk_size`.
1260 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1261 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1266 /// Panics if `chunk_size` is 0.
1271 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1272 /// let mut iter = slice.rchunks(2);
1273 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1274 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1275 /// assert_eq!(iter.next().unwrap(), &['l']);
1276 /// assert!(iter.next().is_none());
1279 /// [`rchunks_exact`]: slice::rchunks_exact
1280 /// [`chunks`]: slice::chunks
1281 #[stable(feature = "rchunks", since = "1.31.0")]
1283 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1284 assert!(chunk_size != 0);
1285 RChunks::new(self, chunk_size)
1288 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1291 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1292 /// length of the slice, then the last chunk will not have length `chunk_size`.
1294 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1295 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1296 /// beginning of the slice.
1300 /// Panics if `chunk_size` is 0.
1305 /// let v = &mut [0, 0, 0, 0, 0];
1306 /// let mut count = 1;
1308 /// for chunk in v.rchunks_mut(2) {
1309 /// for elem in chunk.iter_mut() {
1314 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1317 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1318 /// [`chunks_mut`]: slice::chunks_mut
1319 #[stable(feature = "rchunks", since = "1.31.0")]
1321 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1322 assert!(chunk_size != 0);
1323 RChunksMut::new(self, chunk_size)
1326 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1327 /// end of the slice.
1329 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1330 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1331 /// from the `remainder` function of the iterator.
1333 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1334 /// resulting code better than in the case of [`chunks`].
1336 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1337 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1342 /// Panics if `chunk_size` is 0.
1347 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1348 /// let mut iter = slice.rchunks_exact(2);
1349 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1350 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1351 /// assert!(iter.next().is_none());
1352 /// assert_eq!(iter.remainder(), &['l']);
1355 /// [`chunks`]: slice::chunks
1356 /// [`rchunks`]: slice::rchunks
1357 /// [`chunks_exact`]: slice::chunks_exact
1358 #[stable(feature = "rchunks", since = "1.31.0")]
1360 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1361 assert!(chunk_size != 0);
1362 RChunksExact::new(self, chunk_size)
1365 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1368 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1369 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1370 /// retrieved from the `into_remainder` function of the iterator.
1372 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1373 /// resulting code better than in the case of [`chunks_mut`].
1375 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1376 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1381 /// Panics if `chunk_size` is 0.
1386 /// let v = &mut [0, 0, 0, 0, 0];
1387 /// let mut count = 1;
1389 /// for chunk in v.rchunks_exact_mut(2) {
1390 /// for elem in chunk.iter_mut() {
1395 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1398 /// [`chunks_mut`]: slice::chunks_mut
1399 /// [`rchunks_mut`]: slice::rchunks_mut
1400 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1401 #[stable(feature = "rchunks", since = "1.31.0")]
1403 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1404 assert!(chunk_size != 0);
1405 RChunksExactMut::new(self, chunk_size)
1408 /// Returns an iterator over the slice producing non-overlapping runs
1409 /// of elements using the predicate to separate them.
1411 /// The predicate is called on two elements following themselves,
1412 /// it means the predicate is called on `slice[0]` and `slice[1]`
1413 /// then on `slice[1]` and `slice[2]` and so on.
1418 /// #![feature(slice_group_by)]
1420 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1422 /// let mut iter = slice.group_by(|a, b| a == b);
1424 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1425 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1426 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1427 /// assert_eq!(iter.next(), None);
1430 /// This method can be used to extract the sorted subslices:
1433 /// #![feature(slice_group_by)]
1435 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1437 /// let mut iter = slice.group_by(|a, b| a <= b);
1439 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1440 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1441 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1442 /// assert_eq!(iter.next(), None);
1444 #[unstable(feature = "slice_group_by", issue = "80552")]
1446 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1448 F: FnMut(&T, &T) -> bool,
1450 GroupBy::new(self, pred)
1453 /// Returns an iterator over the slice producing non-overlapping mutable
1454 /// runs of elements using the predicate to separate them.
1456 /// The predicate is called on two elements following themselves,
1457 /// it means the predicate is called on `slice[0]` and `slice[1]`
1458 /// then on `slice[1]` and `slice[2]` and so on.
1463 /// #![feature(slice_group_by)]
1465 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1467 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1469 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1470 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1471 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1472 /// assert_eq!(iter.next(), None);
1475 /// This method can be used to extract the sorted subslices:
1478 /// #![feature(slice_group_by)]
1480 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1482 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1484 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1485 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1486 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1487 /// assert_eq!(iter.next(), None);
1489 #[unstable(feature = "slice_group_by", issue = "80552")]
1491 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1493 F: FnMut(&T, &T) -> bool,
1495 GroupByMut::new(self, pred)
1498 /// Divides one slice into two at an index.
1500 /// The first will contain all indices from `[0, mid)` (excluding
1501 /// the index `mid` itself) and the second will contain all
1502 /// indices from `[mid, len)` (excluding the index `len` itself).
1506 /// Panics if `mid > len`.
1511 /// let v = [1, 2, 3, 4, 5, 6];
1514 /// let (left, right) = v.split_at(0);
1515 /// assert_eq!(left, []);
1516 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1520 /// let (left, right) = v.split_at(2);
1521 /// assert_eq!(left, [1, 2]);
1522 /// assert_eq!(right, [3, 4, 5, 6]);
1526 /// let (left, right) = v.split_at(6);
1527 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1528 /// assert_eq!(right, []);
1531 #[stable(feature = "rust1", since = "1.0.0")]
1533 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1534 assert!(mid <= self.len());
1535 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1536 // fulfills the requirements of `from_raw_parts_mut`.
1537 unsafe { self.split_at_unchecked(mid) }
1540 /// Divides one mutable slice into two at an index.
1542 /// The first will contain all indices from `[0, mid)` (excluding
1543 /// the index `mid` itself) and the second will contain all
1544 /// indices from `[mid, len)` (excluding the index `len` itself).
1548 /// Panics if `mid > len`.
1553 /// let mut v = [1, 0, 3, 0, 5, 6];
1554 /// let (left, right) = v.split_at_mut(2);
1555 /// assert_eq!(left, [1, 0]);
1556 /// assert_eq!(right, [3, 0, 5, 6]);
1559 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1561 #[stable(feature = "rust1", since = "1.0.0")]
1563 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1564 assert!(mid <= self.len());
1565 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1566 // fulfills the requirements of `from_raw_parts_mut`.
1567 unsafe { self.split_at_mut_unchecked(mid) }
1570 /// Divides one slice into two at an index, without doing bounds checking.
1572 /// The first will contain all indices from `[0, mid)` (excluding
1573 /// the index `mid` itself) and the second will contain all
1574 /// indices from `[mid, len)` (excluding the index `len` itself).
1576 /// For a safe alternative see [`split_at`].
1580 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1581 /// even if the resulting reference is not used. The caller has to ensure that
1582 /// `0 <= mid <= self.len()`.
1584 /// [`split_at`]: slice::split_at
1585 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1590 /// #![feature(slice_split_at_unchecked)]
1592 /// let v = [1, 2, 3, 4, 5, 6];
1595 /// let (left, right) = v.split_at_unchecked(0);
1596 /// assert_eq!(left, []);
1597 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1601 /// let (left, right) = v.split_at_unchecked(2);
1602 /// assert_eq!(left, [1, 2]);
1603 /// assert_eq!(right, [3, 4, 5, 6]);
1607 /// let (left, right) = v.split_at_unchecked(6);
1608 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1609 /// assert_eq!(right, []);
1612 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1614 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1615 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1616 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1619 /// Divides one mutable slice into two at an index, without doing bounds checking.
1621 /// The first will contain all indices from `[0, mid)` (excluding
1622 /// the index `mid` itself) and the second will contain all
1623 /// indices from `[mid, len)` (excluding the index `len` itself).
1625 /// For a safe alternative see [`split_at_mut`].
1629 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1630 /// even if the resulting reference is not used. The caller has to ensure that
1631 /// `0 <= mid <= self.len()`.
1633 /// [`split_at_mut`]: slice::split_at_mut
1634 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1639 /// #![feature(slice_split_at_unchecked)]
1641 /// let mut v = [1, 0, 3, 0, 5, 6];
1642 /// // scoped to restrict the lifetime of the borrows
1644 /// let (left, right) = v.split_at_mut_unchecked(2);
1645 /// assert_eq!(left, [1, 0]);
1646 /// assert_eq!(right, [3, 0, 5, 6]);
1650 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1652 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1654 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1655 let len = self.len();
1656 let ptr = self.as_mut_ptr();
1658 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1660 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1662 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1665 /// Returns an iterator over subslices separated by elements that match
1666 /// `pred`. The matched element is not contained in the subslices.
1671 /// let slice = [10, 40, 33, 20];
1672 /// let mut iter = slice.split(|num| num % 3 == 0);
1674 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1675 /// assert_eq!(iter.next().unwrap(), &[20]);
1676 /// assert!(iter.next().is_none());
1679 /// If the first element is matched, an empty slice will be the first item
1680 /// returned by the iterator. Similarly, if the last element in the slice
1681 /// is matched, an empty slice will be the last item returned by the
1685 /// let slice = [10, 40, 33];
1686 /// let mut iter = slice.split(|num| num % 3 == 0);
1688 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1689 /// assert_eq!(iter.next().unwrap(), &[]);
1690 /// assert!(iter.next().is_none());
1693 /// If two matched elements are directly adjacent, an empty slice will be
1694 /// present between them:
1697 /// let slice = [10, 6, 33, 20];
1698 /// let mut iter = slice.split(|num| num % 3 == 0);
1700 /// assert_eq!(iter.next().unwrap(), &[10]);
1701 /// assert_eq!(iter.next().unwrap(), &[]);
1702 /// assert_eq!(iter.next().unwrap(), &[20]);
1703 /// assert!(iter.next().is_none());
1705 #[stable(feature = "rust1", since = "1.0.0")]
1707 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1709 F: FnMut(&T) -> bool,
1711 Split::new(self, pred)
1714 /// Returns an iterator over mutable subslices separated by elements that
1715 /// match `pred`. The matched element is not contained in the subslices.
1720 /// let mut v = [10, 40, 30, 20, 60, 50];
1722 /// for group in v.split_mut(|num| *num % 3 == 0) {
1725 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1727 #[stable(feature = "rust1", since = "1.0.0")]
1729 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1731 F: FnMut(&T) -> bool,
1733 SplitMut::new(self, pred)
1736 /// Returns an iterator over subslices separated by elements that match
1737 /// `pred`. The matched element is contained in the end of the previous
1738 /// subslice as a terminator.
1743 /// let slice = [10, 40, 33, 20];
1744 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1746 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1747 /// assert_eq!(iter.next().unwrap(), &[20]);
1748 /// assert!(iter.next().is_none());
1751 /// If the last element of the slice is matched,
1752 /// that element will be considered the terminator of the preceding slice.
1753 /// That slice will be the last item returned by the iterator.
1756 /// let slice = [3, 10, 40, 33];
1757 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1759 /// assert_eq!(iter.next().unwrap(), &[3]);
1760 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1761 /// assert!(iter.next().is_none());
1763 #[stable(feature = "split_inclusive", since = "1.51.0")]
1765 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1767 F: FnMut(&T) -> bool,
1769 SplitInclusive::new(self, pred)
1772 /// Returns an iterator over mutable subslices separated by elements that
1773 /// match `pred`. The matched element is contained in the previous
1774 /// subslice as a terminator.
1779 /// let mut v = [10, 40, 30, 20, 60, 50];
1781 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1782 /// let terminator_idx = group.len()-1;
1783 /// group[terminator_idx] = 1;
1785 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1787 #[stable(feature = "split_inclusive", since = "1.51.0")]
1789 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1791 F: FnMut(&T) -> bool,
1793 SplitInclusiveMut::new(self, pred)
1796 /// Returns an iterator over subslices separated by elements that match
1797 /// `pred`, starting at the end of the slice and working backwards.
1798 /// The matched element is not contained in the subslices.
1803 /// let slice = [11, 22, 33, 0, 44, 55];
1804 /// let mut iter = slice.rsplit(|num| *num == 0);
1806 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1807 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1808 /// assert_eq!(iter.next(), None);
1811 /// As with `split()`, if the first or last element is matched, an empty
1812 /// slice will be the first (or last) item returned by the iterator.
1815 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1816 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1817 /// assert_eq!(it.next().unwrap(), &[]);
1818 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1819 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1820 /// assert_eq!(it.next().unwrap(), &[]);
1821 /// assert_eq!(it.next(), None);
1823 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1825 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1827 F: FnMut(&T) -> bool,
1829 RSplit::new(self, pred)
1832 /// Returns an iterator over mutable subslices separated by elements that
1833 /// match `pred`, starting at the end of the slice and working
1834 /// backwards. The matched element is not contained in the subslices.
1839 /// let mut v = [100, 400, 300, 200, 600, 500];
1841 /// let mut count = 0;
1842 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1844 /// group[0] = count;
1846 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1849 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1851 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1853 F: FnMut(&T) -> bool,
1855 RSplitMut::new(self, pred)
1858 /// Returns an iterator over subslices separated by elements that match
1859 /// `pred`, limited to returning at most `n` items. The matched element is
1860 /// not contained in the subslices.
1862 /// The last element returned, if any, will contain the remainder of the
1867 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1868 /// `[20, 60, 50]`):
1871 /// let v = [10, 40, 30, 20, 60, 50];
1873 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1874 /// println!("{:?}", group);
1877 #[stable(feature = "rust1", since = "1.0.0")]
1879 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1881 F: FnMut(&T) -> bool,
1883 SplitN::new(self.split(pred), n)
1886 /// Returns an iterator over subslices separated by elements that match
1887 /// `pred`, limited to returning at most `n` items. The matched element is
1888 /// not contained in the subslices.
1890 /// The last element returned, if any, will contain the remainder of the
1896 /// let mut v = [10, 40, 30, 20, 60, 50];
1898 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1901 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1903 #[stable(feature = "rust1", since = "1.0.0")]
1905 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1907 F: FnMut(&T) -> bool,
1909 SplitNMut::new(self.split_mut(pred), n)
1912 /// Returns an iterator over subslices separated by elements that match
1913 /// `pred` limited to returning at most `n` items. This starts at the end of
1914 /// the slice and works backwards. The matched element is not contained in
1917 /// The last element returned, if any, will contain the remainder of the
1922 /// Print the slice split once, starting from the end, by numbers divisible
1923 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1926 /// let v = [10, 40, 30, 20, 60, 50];
1928 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1929 /// println!("{:?}", group);
1932 #[stable(feature = "rust1", since = "1.0.0")]
1934 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1936 F: FnMut(&T) -> bool,
1938 RSplitN::new(self.rsplit(pred), n)
1941 /// Returns an iterator over subslices separated by elements that match
1942 /// `pred` limited to returning at most `n` items. This starts at the end of
1943 /// the slice and works backwards. The matched element is not contained in
1946 /// The last element returned, if any, will contain the remainder of the
1952 /// let mut s = [10, 40, 30, 20, 60, 50];
1954 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1957 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1959 #[stable(feature = "rust1", since = "1.0.0")]
1961 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1963 F: FnMut(&T) -> bool,
1965 RSplitNMut::new(self.rsplit_mut(pred), n)
1968 /// Returns `true` if the slice contains an element with the given value.
1973 /// let v = [10, 40, 30];
1974 /// assert!(v.contains(&30));
1975 /// assert!(!v.contains(&50));
1978 /// If you do not have a `&T`, but some other value that you can compare
1979 /// with one (for example, `String` implements `PartialEq<str>`), you can
1980 /// use `iter().any`:
1983 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1984 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1985 /// assert!(!v.iter().any(|e| e == "hi"));
1987 #[stable(feature = "rust1", since = "1.0.0")]
1989 pub fn contains(&self, x: &T) -> bool
1993 cmp::SliceContains::slice_contains(x, self)
1996 /// Returns `true` if `needle` is a prefix of the slice.
2001 /// let v = [10, 40, 30];
2002 /// assert!(v.starts_with(&[10]));
2003 /// assert!(v.starts_with(&[10, 40]));
2004 /// assert!(!v.starts_with(&[50]));
2005 /// assert!(!v.starts_with(&[10, 50]));
2008 /// Always returns `true` if `needle` is an empty slice:
2011 /// let v = &[10, 40, 30];
2012 /// assert!(v.starts_with(&[]));
2013 /// let v: &[u8] = &[];
2014 /// assert!(v.starts_with(&[]));
2016 #[stable(feature = "rust1", since = "1.0.0")]
2017 pub fn starts_with(&self, needle: &[T]) -> bool
2021 let n = needle.len();
2022 self.len() >= n && needle == &self[..n]
2025 /// Returns `true` if `needle` is a suffix of the slice.
2030 /// let v = [10, 40, 30];
2031 /// assert!(v.ends_with(&[30]));
2032 /// assert!(v.ends_with(&[40, 30]));
2033 /// assert!(!v.ends_with(&[50]));
2034 /// assert!(!v.ends_with(&[50, 30]));
2037 /// Always returns `true` if `needle` is an empty slice:
2040 /// let v = &[10, 40, 30];
2041 /// assert!(v.ends_with(&[]));
2042 /// let v: &[u8] = &[];
2043 /// assert!(v.ends_with(&[]));
2045 #[stable(feature = "rust1", since = "1.0.0")]
2046 pub fn ends_with(&self, needle: &[T]) -> bool
2050 let (m, n) = (self.len(), needle.len());
2051 m >= n && needle == &self[m - n..]
2054 /// Returns a subslice with the prefix removed.
2056 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2057 /// If `prefix` is empty, simply returns the original slice.
2059 /// If the slice does not start with `prefix`, returns `None`.
2064 /// let v = &[10, 40, 30];
2065 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2066 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2067 /// assert_eq!(v.strip_prefix(&[50]), None);
2068 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2070 /// let prefix : &str = "he";
2071 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2072 /// Some(b"llo".as_ref()));
2074 #[must_use = "returns the subslice without modifying the original"]
2075 #[stable(feature = "slice_strip", since = "1.51.0")]
2076 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2080 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2081 let prefix = prefix.as_slice();
2082 let n = prefix.len();
2083 if n <= self.len() {
2084 let (head, tail) = self.split_at(n);
2092 /// Returns a subslice with the suffix removed.
2094 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2095 /// If `suffix` is empty, simply returns the original slice.
2097 /// If the slice does not end with `suffix`, returns `None`.
2102 /// let v = &[10, 40, 30];
2103 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2104 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2105 /// assert_eq!(v.strip_suffix(&[50]), None);
2106 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2108 #[must_use = "returns the subslice without modifying the original"]
2109 #[stable(feature = "slice_strip", since = "1.51.0")]
2110 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2114 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2115 let suffix = suffix.as_slice();
2116 let (len, n) = (self.len(), suffix.len());
2118 let (head, tail) = self.split_at(len - n);
2126 /// Binary searches this sorted slice for a given element.
2128 /// If the value is found then [`Result::Ok`] is returned, containing the
2129 /// index of the matching element. If there are multiple matches, then any
2130 /// one of the matches could be returned. The index is chosen
2131 /// deterministically, but is subject to change in future versions of Rust.
2132 /// If the value is not found then [`Result::Err`] is returned, containing
2133 /// the index where a matching element could be inserted while maintaining
2136 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2138 /// [`binary_search_by`]: slice::binary_search_by
2139 /// [`binary_search_by_key`]: slice::binary_search_by_key
2140 /// [`partition_point`]: slice::partition_point
2144 /// Looks up a series of four elements. The first is found, with a
2145 /// uniquely determined position; the second and third are not
2146 /// found; the fourth could match any position in `[1, 4]`.
2149 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2151 /// assert_eq!(s.binary_search(&13), Ok(9));
2152 /// assert_eq!(s.binary_search(&4), Err(7));
2153 /// assert_eq!(s.binary_search(&100), Err(13));
2154 /// let r = s.binary_search(&1);
2155 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2158 /// If you want to insert an item to a sorted vector, while maintaining
2162 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2164 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2165 /// s.insert(idx, num);
2166 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2168 #[stable(feature = "rust1", since = "1.0.0")]
2169 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2173 self.binary_search_by(|p| p.cmp(x))
2176 /// Binary searches this sorted slice with a comparator function.
2178 /// The comparator function should implement an order consistent
2179 /// with the sort order of the underlying slice, returning an
2180 /// order code that indicates whether its argument is `Less`,
2181 /// `Equal` or `Greater` the desired target.
2183 /// If the value is found then [`Result::Ok`] is returned, containing the
2184 /// index of the matching element. If there are multiple matches, then any
2185 /// one of the matches could be returned. The index is chosen
2186 /// deterministically, but is subject to change in future versions of Rust.
2187 /// If the value is not found then [`Result::Err`] is returned, containing
2188 /// the index where a matching element could be inserted while maintaining
2191 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2193 /// [`binary_search`]: slice::binary_search
2194 /// [`binary_search_by_key`]: slice::binary_search_by_key
2195 /// [`partition_point`]: slice::partition_point
2199 /// Looks up a series of four elements. The first is found, with a
2200 /// uniquely determined position; the second and third are not
2201 /// found; the fourth could match any position in `[1, 4]`.
2204 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2207 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2209 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2211 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2213 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2214 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2216 #[stable(feature = "rust1", since = "1.0.0")]
2218 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2220 F: FnMut(&'a T) -> Ordering,
2222 let mut size = self.len();
2224 let mut right = size;
2225 while left < right {
2226 let mid = left + size / 2;
2228 // SAFETY: the call is made safe by the following invariants:
2230 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2231 let cmp = f(unsafe { self.get_unchecked(mid) });
2233 // The reason why we use if/else control flow rather than match
2234 // is because match reorders comparison operations, which is perf sensitive.
2235 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2238 } else if cmp == Greater {
2241 // SAFETY: same as the `get_unchecked` above
2242 unsafe { crate::intrinsics::assume(mid < self.len()) };
2246 size = right - left;
2251 /// Binary searches this sorted slice with a key extraction function.
2253 /// Assumes that the slice is sorted by the key, for instance with
2254 /// [`sort_by_key`] using the same key extraction function.
2256 /// If the value is found then [`Result::Ok`] is returned, containing the
2257 /// index of the matching element. If there are multiple matches, then any
2258 /// one of the matches could be returned. The index is chosen
2259 /// deterministically, but is subject to change in future versions of Rust.
2260 /// If the value is not found then [`Result::Err`] is returned, containing
2261 /// the index where a matching element could be inserted while maintaining
2264 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2266 /// [`sort_by_key`]: slice::sort_by_key
2267 /// [`binary_search`]: slice::binary_search
2268 /// [`binary_search_by`]: slice::binary_search_by
2269 /// [`partition_point`]: slice::partition_point
2273 /// Looks up a series of four elements in a slice of pairs sorted by
2274 /// their second elements. The first is found, with a uniquely
2275 /// determined position; the second and third are not found; the
2276 /// fourth could match any position in `[1, 4]`.
2279 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2280 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2281 /// (1, 21), (2, 34), (4, 55)];
2283 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2284 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2285 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2286 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2287 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2289 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2290 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2291 // This breaks links when slice is displayed in core, but changing it to use relative links
2292 // would break when the item is re-exported. So allow the core links to be broken for now.
2293 #[allow(rustdoc::broken_intra_doc_links)]
2294 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2296 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2298 F: FnMut(&'a T) -> B,
2301 self.binary_search_by(|k| f(k).cmp(b))
2304 /// Sorts the slice, but might not preserve the order of equal elements.
2306 /// This sort is unstable (i.e., may reorder equal elements), in-place
2307 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2309 /// # Current implementation
2311 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2312 /// which combines the fast average case of randomized quicksort with the fast worst case of
2313 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2314 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2315 /// deterministic behavior.
2317 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2318 /// slice consists of several concatenated sorted sequences.
2323 /// let mut v = [-5, 4, 1, -3, 2];
2325 /// v.sort_unstable();
2326 /// assert!(v == [-5, -3, 1, 2, 4]);
2329 /// [pdqsort]: https://github.com/orlp/pdqsort
2330 #[stable(feature = "sort_unstable", since = "1.20.0")]
2332 pub fn sort_unstable(&mut self)
2336 sort::quicksort(self, |a, b| a.lt(b));
2339 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2342 /// This sort is unstable (i.e., may reorder equal elements), in-place
2343 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2345 /// The comparator function must define a total ordering for the elements in the slice. If
2346 /// the ordering is not total, the order of the elements is unspecified. An order is a
2347 /// total order if it is (for all `a`, `b` and `c`):
2349 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2350 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2352 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2353 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2356 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2357 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2358 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2361 /// # Current implementation
2363 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2364 /// which combines the fast average case of randomized quicksort with the fast worst case of
2365 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2366 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2367 /// deterministic behavior.
2369 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2370 /// slice consists of several concatenated sorted sequences.
2375 /// let mut v = [5, 4, 1, 3, 2];
2376 /// v.sort_unstable_by(|a, b| a.cmp(b));
2377 /// assert!(v == [1, 2, 3, 4, 5]);
2379 /// // reverse sorting
2380 /// v.sort_unstable_by(|a, b| b.cmp(a));
2381 /// assert!(v == [5, 4, 3, 2, 1]);
2384 /// [pdqsort]: https://github.com/orlp/pdqsort
2385 #[stable(feature = "sort_unstable", since = "1.20.0")]
2387 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2389 F: FnMut(&T, &T) -> Ordering,
2391 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2394 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2397 /// This sort is unstable (i.e., may reorder equal elements), in-place
2398 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2401 /// # Current implementation
2403 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2404 /// which combines the fast average case of randomized quicksort with the fast worst case of
2405 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2406 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2407 /// deterministic behavior.
2409 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2410 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2411 /// cases where the key function is expensive.
2416 /// let mut v = [-5i32, 4, 1, -3, 2];
2418 /// v.sort_unstable_by_key(|k| k.abs());
2419 /// assert!(v == [1, 2, -3, 4, -5]);
2422 /// [pdqsort]: https://github.com/orlp/pdqsort
2423 #[stable(feature = "sort_unstable", since = "1.20.0")]
2425 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2430 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2433 /// Reorder the slice such that the element at `index` is at its final sorted position.
2434 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2435 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2437 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2441 self.select_nth_unstable(index)
2444 /// Reorder the slice with a comparator function such that the element at `index` is at its
2445 /// final sorted position.
2446 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2447 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2449 pub fn partition_at_index_by<F>(
2453 ) -> (&mut [T], &mut T, &mut [T])
2455 F: FnMut(&T, &T) -> Ordering,
2457 self.select_nth_unstable_by(index, compare)
2460 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2461 /// final sorted position.
2462 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2463 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2465 pub fn partition_at_index_by_key<K, F>(
2469 ) -> (&mut [T], &mut T, &mut [T])
2474 self.select_nth_unstable_by_key(index, f)
2477 /// Reorder the slice such that the element at `index` is at its final sorted position.
2479 /// This reordering has the additional property that any value at position `i < index` will be
2480 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2481 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2482 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2483 /// element" in other libraries. It returns a triplet of the following values: all elements less
2484 /// than the one at the given index, the value at the given index, and all elements greater than
2485 /// the one at the given index.
2487 /// # Current implementation
2489 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2490 /// used for [`sort_unstable`].
2492 /// [`sort_unstable`]: slice::sort_unstable
2496 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2501 /// let mut v = [-5i32, 4, 1, -3, 2];
2503 /// // Find the median
2504 /// v.select_nth_unstable(2);
2506 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2507 /// // about the specified index.
2508 /// assert!(v == [-3, -5, 1, 2, 4] ||
2509 /// v == [-5, -3, 1, 2, 4] ||
2510 /// v == [-3, -5, 1, 4, 2] ||
2511 /// v == [-5, -3, 1, 4, 2]);
2513 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2515 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2519 let mut f = |a: &T, b: &T| a.lt(b);
2520 sort::partition_at_index(self, index, &mut f)
2523 /// Reorder the slice with a comparator function such that the element at `index` is at its
2524 /// final sorted position.
2526 /// This reordering has the additional property that any value at position `i < index` will be
2527 /// less than or equal to any value at a position `j > index` using the comparator function.
2528 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2529 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2530 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2531 /// values: all elements less than the one at the given index, the value at the given index,
2532 /// and all elements greater than the one at the given index, using the provided comparator
2535 /// # Current implementation
2537 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2538 /// used for [`sort_unstable`].
2540 /// [`sort_unstable`]: slice::sort_unstable
2544 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2549 /// let mut v = [-5i32, 4, 1, -3, 2];
2551 /// // Find the median as if the slice were sorted in descending order.
2552 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2554 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2555 /// // about the specified index.
2556 /// assert!(v == [2, 4, 1, -5, -3] ||
2557 /// v == [2, 4, 1, -3, -5] ||
2558 /// v == [4, 2, 1, -5, -3] ||
2559 /// v == [4, 2, 1, -3, -5]);
2561 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2563 pub fn select_nth_unstable_by<F>(
2567 ) -> (&mut [T], &mut T, &mut [T])
2569 F: FnMut(&T, &T) -> Ordering,
2571 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2572 sort::partition_at_index(self, index, &mut f)
2575 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2576 /// final sorted position.
2578 /// This reordering has the additional property that any value at position `i < index` will be
2579 /// less than or equal to any value at a position `j > index` using the key extraction function.
2580 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2581 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2582 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2583 /// values: all elements less than the one at the given index, the value at the given index, and
2584 /// all elements greater than the one at the given index, using the provided key extraction
2587 /// # Current implementation
2589 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2590 /// used for [`sort_unstable`].
2592 /// [`sort_unstable`]: slice::sort_unstable
2596 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2601 /// let mut v = [-5i32, 4, 1, -3, 2];
2603 /// // Return the median as if the array were sorted according to absolute value.
2604 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2606 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2607 /// // about the specified index.
2608 /// assert!(v == [1, 2, -3, 4, -5] ||
2609 /// v == [1, 2, -3, -5, 4] ||
2610 /// v == [2, 1, -3, 4, -5] ||
2611 /// v == [2, 1, -3, -5, 4]);
2613 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2615 pub fn select_nth_unstable_by_key<K, F>(
2619 ) -> (&mut [T], &mut T, &mut [T])
2624 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2625 sort::partition_at_index(self, index, &mut g)
2628 /// Moves all consecutive repeated elements to the end of the slice according to the
2629 /// [`PartialEq`] trait implementation.
2631 /// Returns two slices. The first contains no consecutive repeated elements.
2632 /// The second contains all the duplicates in no specified order.
2634 /// If the slice is sorted, the first returned slice contains no duplicates.
2639 /// #![feature(slice_partition_dedup)]
2641 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2643 /// let (dedup, duplicates) = slice.partition_dedup();
2645 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2646 /// assert_eq!(duplicates, [2, 3, 1]);
2648 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2650 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2654 self.partition_dedup_by(|a, b| a == b)
2657 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2658 /// a given equality relation.
2660 /// Returns two slices. The first contains no consecutive repeated elements.
2661 /// The second contains all the duplicates in no specified order.
2663 /// The `same_bucket` function is passed references to two elements from the slice and
2664 /// must determine if the elements compare equal. The elements are passed in opposite order
2665 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2666 /// at the end of the slice.
2668 /// If the slice is sorted, the first returned slice contains no duplicates.
2673 /// #![feature(slice_partition_dedup)]
2675 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2677 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2679 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2680 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2682 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2684 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2686 F: FnMut(&mut T, &mut T) -> bool,
2688 // Although we have a mutable reference to `self`, we cannot make
2689 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2690 // must ensure that the slice is in a valid state at all times.
2692 // The way that we handle this is by using swaps; we iterate
2693 // over all the elements, swapping as we go so that at the end
2694 // the elements we wish to keep are in the front, and those we
2695 // wish to reject are at the back. We can then split the slice.
2696 // This operation is still `O(n)`.
2698 // Example: We start in this state, where `r` represents "next
2699 // read" and `w` represents "next_write`.
2702 // +---+---+---+---+---+---+
2703 // | 0 | 1 | 1 | 2 | 3 | 3 |
2704 // +---+---+---+---+---+---+
2707 // Comparing self[r] against self[w-1], this is not a duplicate, so
2708 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2709 // r and w, leaving us with:
2712 // +---+---+---+---+---+---+
2713 // | 0 | 1 | 1 | 2 | 3 | 3 |
2714 // +---+---+---+---+---+---+
2717 // Comparing self[r] against self[w-1], this value is a duplicate,
2718 // so we increment `r` but leave everything else unchanged:
2721 // +---+---+---+---+---+---+
2722 // | 0 | 1 | 1 | 2 | 3 | 3 |
2723 // +---+---+---+---+---+---+
2726 // Comparing self[r] against self[w-1], this is not a duplicate,
2727 // so swap self[r] and self[w] and advance r and w:
2730 // +---+---+---+---+---+---+
2731 // | 0 | 1 | 2 | 1 | 3 | 3 |
2732 // +---+---+---+---+---+---+
2735 // Not a duplicate, repeat:
2738 // +---+---+---+---+---+---+
2739 // | 0 | 1 | 2 | 3 | 1 | 3 |
2740 // +---+---+---+---+---+---+
2743 // Duplicate, advance r. End of slice. Split at w.
2745 let len = self.len();
2747 return (self, &mut []);
2750 let ptr = self.as_mut_ptr();
2751 let mut next_read: usize = 1;
2752 let mut next_write: usize = 1;
2754 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2755 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2756 // one element before `ptr_write`, but `next_write` starts at 1, so
2757 // `prev_ptr_write` is never less than 0 and is inside the slice.
2758 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2759 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2760 // and `prev_ptr_write.offset(1)`.
2762 // `next_write` is also incremented at most once per loop at most meaning
2763 // no element is skipped when it may need to be swapped.
2765 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2766 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2767 // The explanation is simply that `next_read >= next_write` is always true,
2768 // thus `next_read > next_write - 1` is too.
2770 // Avoid bounds checks by using raw pointers.
2771 while next_read < len {
2772 let ptr_read = ptr.add(next_read);
2773 let prev_ptr_write = ptr.add(next_write - 1);
2774 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2775 if next_read != next_write {
2776 let ptr_write = prev_ptr_write.offset(1);
2777 mem::swap(&mut *ptr_read, &mut *ptr_write);
2785 self.split_at_mut(next_write)
2788 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2789 /// to the same key.
2791 /// Returns two slices. The first contains no consecutive repeated elements.
2792 /// The second contains all the duplicates in no specified order.
2794 /// If the slice is sorted, the first returned slice contains no duplicates.
2799 /// #![feature(slice_partition_dedup)]
2801 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2803 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2805 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2806 /// assert_eq!(duplicates, [21, 30, 13]);
2808 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2810 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2812 F: FnMut(&mut T) -> K,
2815 self.partition_dedup_by(|a, b| key(a) == key(b))
2818 /// Rotates the slice in-place such that the first `mid` elements of the
2819 /// slice move to the end while the last `self.len() - mid` elements move to
2820 /// the front. After calling `rotate_left`, the element previously at index
2821 /// `mid` will become the first element in the slice.
2825 /// This function will panic if `mid` is greater than the length of the
2826 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2831 /// Takes linear (in `self.len()`) time.
2836 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2837 /// a.rotate_left(2);
2838 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2841 /// Rotating a subslice:
2844 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2845 /// a[1..5].rotate_left(1);
2846 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2848 #[stable(feature = "slice_rotate", since = "1.26.0")]
2849 pub fn rotate_left(&mut self, mid: usize) {
2850 assert!(mid <= self.len());
2851 let k = self.len() - mid;
2852 let p = self.as_mut_ptr();
2854 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2855 // valid for reading and writing, as required by `ptr_rotate`.
2857 rotate::ptr_rotate(mid, p.add(mid), k);
2861 /// Rotates the slice in-place such that the first `self.len() - k`
2862 /// elements of the slice move to the end while the last `k` elements move
2863 /// to the front. After calling `rotate_right`, the element previously at
2864 /// index `self.len() - k` will become the first element in the slice.
2868 /// This function will panic if `k` is greater than the length of the
2869 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2874 /// Takes linear (in `self.len()`) time.
2879 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2880 /// a.rotate_right(2);
2881 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2884 /// Rotate a subslice:
2887 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2888 /// a[1..5].rotate_right(1);
2889 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2891 #[stable(feature = "slice_rotate", since = "1.26.0")]
2892 pub fn rotate_right(&mut self, k: usize) {
2893 assert!(k <= self.len());
2894 let mid = self.len() - k;
2895 let p = self.as_mut_ptr();
2897 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2898 // valid for reading and writing, as required by `ptr_rotate`.
2900 rotate::ptr_rotate(mid, p.add(mid), k);
2904 /// Fills `self` with elements by cloning `value`.
2909 /// let mut buf = vec![0; 10];
2911 /// assert_eq!(buf, vec![1; 10]);
2913 #[doc(alias = "memset")]
2914 #[stable(feature = "slice_fill", since = "1.50.0")]
2915 pub fn fill(&mut self, value: T)
2919 specialize::SpecFill::spec_fill(self, value);
2922 /// Fills `self` with elements returned by calling a closure repeatedly.
2924 /// This method uses a closure to create new values. If you'd rather
2925 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2926 /// trait to generate values, you can pass [`Default::default`] as the
2929 /// [`fill`]: slice::fill
2934 /// let mut buf = vec![1; 10];
2935 /// buf.fill_with(Default::default);
2936 /// assert_eq!(buf, vec![0; 10]);
2938 #[doc(alias = "memset")]
2939 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2940 pub fn fill_with<F>(&mut self, mut f: F)
2949 /// Copies the elements from `src` into `self`.
2951 /// The length of `src` must be the same as `self`.
2953 /// If `T` implements `Copy`, it can be more performant to use
2954 /// [`copy_from_slice`].
2958 /// This function will panic if the two slices have different lengths.
2962 /// Cloning two elements from a slice into another:
2965 /// let src = [1, 2, 3, 4];
2966 /// let mut dst = [0, 0];
2968 /// // Because the slices have to be the same length,
2969 /// // we slice the source slice from four elements
2970 /// // to two. It will panic if we don't do this.
2971 /// dst.clone_from_slice(&src[2..]);
2973 /// assert_eq!(src, [1, 2, 3, 4]);
2974 /// assert_eq!(dst, [3, 4]);
2977 /// Rust enforces that there can only be one mutable reference with no
2978 /// immutable references to a particular piece of data in a particular
2979 /// scope. Because of this, attempting to use `clone_from_slice` on a
2980 /// single slice will result in a compile failure:
2983 /// let mut slice = [1, 2, 3, 4, 5];
2985 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2988 /// To work around this, we can use [`split_at_mut`] to create two distinct
2989 /// sub-slices from a slice:
2992 /// let mut slice = [1, 2, 3, 4, 5];
2995 /// let (left, right) = slice.split_at_mut(2);
2996 /// left.clone_from_slice(&right[1..]);
2999 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3002 /// [`copy_from_slice`]: slice::copy_from_slice
3003 /// [`split_at_mut`]: slice::split_at_mut
3004 #[stable(feature = "clone_from_slice", since = "1.7.0")]
3005 pub fn clone_from_slice(&mut self, src: &[T])
3009 self.spec_clone_from(src);
3012 /// Copies all elements from `src` into `self`, using a memcpy.
3014 /// The length of `src` must be the same as `self`.
3016 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
3020 /// This function will panic if the two slices have different lengths.
3024 /// Copying two elements from a slice into another:
3027 /// let src = [1, 2, 3, 4];
3028 /// let mut dst = [0, 0];
3030 /// // Because the slices have to be the same length,
3031 /// // we slice the source slice from four elements
3032 /// // to two. It will panic if we don't do this.
3033 /// dst.copy_from_slice(&src[2..]);
3035 /// assert_eq!(src, [1, 2, 3, 4]);
3036 /// assert_eq!(dst, [3, 4]);
3039 /// Rust enforces that there can only be one mutable reference with no
3040 /// immutable references to a particular piece of data in a particular
3041 /// scope. Because of this, attempting to use `copy_from_slice` on a
3042 /// single slice will result in a compile failure:
3045 /// let mut slice = [1, 2, 3, 4, 5];
3047 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3050 /// To work around this, we can use [`split_at_mut`] to create two distinct
3051 /// sub-slices from a slice:
3054 /// let mut slice = [1, 2, 3, 4, 5];
3057 /// let (left, right) = slice.split_at_mut(2);
3058 /// left.copy_from_slice(&right[1..]);
3061 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3064 /// [`clone_from_slice`]: slice::clone_from_slice
3065 /// [`split_at_mut`]: slice::split_at_mut
3066 #[doc(alias = "memcpy")]
3067 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3068 pub fn copy_from_slice(&mut self, src: &[T])
3072 // The panic code path was put into a cold function to not bloat the
3077 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3079 "source slice length ({}) does not match destination slice length ({})",
3084 if self.len() != src.len() {
3085 len_mismatch_fail(self.len(), src.len());
3088 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3089 // checked to have the same length. The slices cannot overlap because
3090 // mutable references are exclusive.
3092 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3096 /// Copies elements from one part of the slice to another part of itself,
3097 /// using a memmove.
3099 /// `src` is the range within `self` to copy from. `dest` is the starting
3100 /// index of the range within `self` to copy to, which will have the same
3101 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3102 /// must be less than or equal to `self.len()`.
3106 /// This function will panic if either range exceeds the end of the slice,
3107 /// or if the end of `src` is before the start.
3111 /// Copying four bytes within a slice:
3114 /// let mut bytes = *b"Hello, World!";
3116 /// bytes.copy_within(1..5, 8);
3118 /// assert_eq!(&bytes, b"Hello, Wello!");
3120 #[stable(feature = "copy_within", since = "1.37.0")]
3122 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3126 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3127 let count = src_end - src_start;
3128 assert!(dest <= self.len() - count, "dest is out of bounds");
3129 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3130 // as have those for `ptr::add`.
3132 // Derive both `src_ptr` and `dest_ptr` from the same loan
3133 let ptr = self.as_mut_ptr();
3134 let src_ptr = ptr.add(src_start);
3135 let dest_ptr = ptr.add(dest);
3136 ptr::copy(src_ptr, dest_ptr, count);
3140 /// Swaps all elements in `self` with those in `other`.
3142 /// The length of `other` must be the same as `self`.
3146 /// This function will panic if the two slices have different lengths.
3150 /// Swapping two elements across slices:
3153 /// let mut slice1 = [0, 0];
3154 /// let mut slice2 = [1, 2, 3, 4];
3156 /// slice1.swap_with_slice(&mut slice2[2..]);
3158 /// assert_eq!(slice1, [3, 4]);
3159 /// assert_eq!(slice2, [1, 2, 0, 0]);
3162 /// Rust enforces that there can only be one mutable reference to a
3163 /// particular piece of data in a particular scope. Because of this,
3164 /// attempting to use `swap_with_slice` on a single slice will result in
3165 /// a compile failure:
3168 /// let mut slice = [1, 2, 3, 4, 5];
3169 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3172 /// To work around this, we can use [`split_at_mut`] to create two distinct
3173 /// mutable sub-slices from a slice:
3176 /// let mut slice = [1, 2, 3, 4, 5];
3179 /// let (left, right) = slice.split_at_mut(2);
3180 /// left.swap_with_slice(&mut right[1..]);
3183 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3186 /// [`split_at_mut`]: slice::split_at_mut
3187 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3188 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3189 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3190 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3191 // checked to have the same length. The slices cannot overlap because
3192 // mutable references are exclusive.
3194 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3198 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3199 fn align_to_offsets<U>(&self) -> (usize, usize) {
3200 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3201 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3203 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3204 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3205 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3207 // Formula to calculate this is:
3209 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3210 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3212 // Expanded and simplified:
3214 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3215 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3217 // Luckily since all this is constant-evaluated... performance here matters not!
3219 fn gcd(a: usize, b: usize) -> usize {
3220 use crate::intrinsics;
3221 // iterative stein’s algorithm
3222 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3223 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3225 // SAFETY: `a` and `b` are checked to be non-zero values.
3226 let (ctz_a, mut ctz_b) = unsafe {
3233 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3235 let k = ctz_a.min(ctz_b);
3236 let mut a = a >> ctz_a;
3239 // remove all factors of 2 from b
3242 mem::swap(&mut a, &mut b);
3245 // SAFETY: `b` is checked to be non-zero.
3250 ctz_b = intrinsics::cttz_nonzero(b);
3255 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3256 let ts: usize = mem::size_of::<U>() / gcd;
3257 let us: usize = mem::size_of::<T>() / gcd;
3259 // Armed with this knowledge, we can find how many `U`s we can fit!
3260 let us_len = self.len() / ts * us;
3261 // And how many `T`s will be in the trailing slice!
3262 let ts_len = self.len() % ts;
3266 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3269 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3270 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3271 /// length possible for a given type and input slice, but only your algorithm's performance
3272 /// should depend on that, not its correctness. It is permissible for all of the input data to
3273 /// be returned as the prefix or suffix slice.
3275 /// This method has no purpose when either input element `T` or output element `U` are
3276 /// zero-sized and will return the original slice without splitting anything.
3280 /// This method is essentially a `transmute` with respect to the elements in the returned
3281 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3289 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3290 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3291 /// // less_efficient_algorithm_for_bytes(prefix);
3292 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3293 /// // less_efficient_algorithm_for_bytes(suffix);
3296 #[stable(feature = "slice_align_to", since = "1.30.0")]
3297 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3298 // Note that most of this function will be constant-evaluated,
3299 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3300 // handle ZSTs specially, which is – don't handle them at all.
3301 return (self, &[], &[]);
3304 // First, find at what point do we split between the first and 2nd slice. Easy with
3305 // ptr.align_offset.
3306 let ptr = self.as_ptr();
3307 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3308 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3309 if offset > self.len() {
3312 let (left, rest) = self.split_at(offset);
3313 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3314 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3315 // since the caller guarantees that we can transmute `T` to `U` safely.
3319 from_raw_parts(rest.as_ptr() as *const U, us_len),
3320 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3326 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3329 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3330 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3331 /// length possible for a given type and input slice, but only your algorithm's performance
3332 /// should depend on that, not its correctness. It is permissible for all of the input data to
3333 /// be returned as the prefix or suffix slice.
3335 /// This method has no purpose when either input element `T` or output element `U` are
3336 /// zero-sized and will return the original slice without splitting anything.
3340 /// This method is essentially a `transmute` with respect to the elements in the returned
3341 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3349 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3350 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3351 /// // less_efficient_algorithm_for_bytes(prefix);
3352 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3353 /// // less_efficient_algorithm_for_bytes(suffix);
3356 #[stable(feature = "slice_align_to", since = "1.30.0")]
3357 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3358 // Note that most of this function will be constant-evaluated,
3359 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3360 // handle ZSTs specially, which is – don't handle them at all.
3361 return (self, &mut [], &mut []);
3364 // First, find at what point do we split between the first and 2nd slice. Easy with
3365 // ptr.align_offset.
3366 let ptr = self.as_ptr();
3367 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3368 // rest of the method. This is done by passing a pointer to &[T] with an
3369 // alignment targeted for U.
3370 // `crate::ptr::align_offset` is called with a correctly aligned and
3371 // valid pointer `ptr` (it comes from a reference to `self`) and with
3372 // a size that is a power of two (since it comes from the alignement for U),
3373 // satisfying its safety constraints.
3374 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3375 if offset > self.len() {
3376 (self, &mut [], &mut [])
3378 let (left, rest) = self.split_at_mut(offset);
3379 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3380 let rest_len = rest.len();
3381 let mut_ptr = rest.as_mut_ptr();
3382 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3383 // SAFETY: see comments for `align_to`.
3387 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3388 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3394 /// Checks if the elements of this slice are sorted.
3396 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3397 /// slice yields exactly zero or one element, `true` is returned.
3399 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3400 /// implies that this function returns `false` if any two consecutive items are not
3406 /// #![feature(is_sorted)]
3407 /// let empty: [i32; 0] = [];
3409 /// assert!([1, 2, 2, 9].is_sorted());
3410 /// assert!(![1, 3, 2, 4].is_sorted());
3411 /// assert!([0].is_sorted());
3412 /// assert!(empty.is_sorted());
3413 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3416 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3417 pub fn is_sorted(&self) -> bool
3421 self.is_sorted_by(|a, b| a.partial_cmp(b))
3424 /// Checks if the elements of this slice are sorted using the given comparator function.
3426 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3427 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3428 /// [`is_sorted`]; see its documentation for more information.
3430 /// [`is_sorted`]: slice::is_sorted
3431 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3432 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3434 F: FnMut(&T, &T) -> Option<Ordering>,
3436 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3439 /// Checks if the elements of this slice are sorted using the given key extraction function.
3441 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3442 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3443 /// documentation for more information.
3445 /// [`is_sorted`]: slice::is_sorted
3450 /// #![feature(is_sorted)]
3452 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3453 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3456 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3457 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3462 self.iter().is_sorted_by_key(f)
3465 /// Returns the index of the partition point according to the given predicate
3466 /// (the index of the first element of the second partition).
3468 /// The slice is assumed to be partitioned according to the given predicate.
3469 /// This means that all elements for which the predicate returns true are at the start of the slice
3470 /// and all elements for which the predicate returns false are at the end.
3471 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3472 /// (all odd numbers are at the start, all even at the end).
3474 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3475 /// as this method performs a kind of binary search.
3477 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3479 /// [`binary_search`]: slice::binary_search
3480 /// [`binary_search_by`]: slice::binary_search_by
3481 /// [`binary_search_by_key`]: slice::binary_search_by_key
3486 /// let v = [1, 2, 3, 3, 5, 6, 7];
3487 /// let i = v.partition_point(|&x| x < 5);
3489 /// assert_eq!(i, 4);
3490 /// assert!(v[..i].iter().all(|&x| x < 5));
3491 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3493 #[stable(feature = "partition_point", since = "1.52.0")]
3494 pub fn partition_point<P>(&self, mut pred: P) -> usize
3496 P: FnMut(&T) -> bool,
3498 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3502 trait CloneFromSpec<T> {
3503 fn spec_clone_from(&mut self, src: &[T]);
3506 impl<T> CloneFromSpec<T> for [T]
3510 default fn spec_clone_from(&mut self, src: &[T]) {
3511 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3512 // NOTE: We need to explicitly slice them to the same length
3513 // to make it easier for the optimizer to elide bounds checking.
3514 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3515 let len = self.len();
3516 let src = &src[..len];
3518 self[i].clone_from(&src[i]);
3523 impl<T> CloneFromSpec<T> for [T]
3527 fn spec_clone_from(&mut self, src: &[T]) {
3528 self.copy_from_slice(src);
3532 #[stable(feature = "rust1", since = "1.0.0")]
3533 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3534 impl<T> const Default for &[T] {
3535 /// Creates an empty slice.
3536 fn default() -> Self {
3541 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3542 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3543 impl<T> const Default for &mut [T] {
3544 /// Creates a mutable empty slice.
3545 fn default() -> Self {
3550 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3551 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3552 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3553 /// `str`) to slices, and then this trait will be replaced or abolished.
3554 pub trait SlicePattern {
3555 /// The element type of the slice being matched on.
3558 /// Currently, the consumers of `SlicePattern` need a slice.
3559 fn as_slice(&self) -> &[Self::Item];
3562 #[stable(feature = "slice_strip", since = "1.51.0")]
3563 impl<T> SlicePattern for [T] {
3567 fn as_slice(&self) -> &[Self::Item] {
3572 #[stable(feature = "slice_strip", since = "1.51.0")]
3573 impl<T, const N: usize> SlicePattern for [T; N] {
3577 fn as_slice(&self) -> &[Self::Item] {