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) {
566 // SAFETY: we just checked that both `a` and `b` are in bounds
567 unsafe { self.swap_unchecked(a, b) }
570 /// Swaps two elements in the slice, without doing bounds checking.
572 /// For a safe alternative see [`swap`].
576 /// * a - The index of the first element
577 /// * b - The index of the second element
581 /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
582 /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
587 /// #![feature(slice_swap_unchecked)]
589 /// let mut v = ["a", "b", "c", "d"];
590 /// // SAFETY: we know that 1 and 3 are both indices of the slice
591 /// unsafe { v.swap_unchecked(1, 3) };
592 /// assert!(v == ["a", "d", "c", "b"]);
595 /// [`swap`]: slice::swap
596 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
597 #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
598 pub unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
599 #[cfg(debug_assertions)]
605 let ptr = self.as_mut_ptr();
606 // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
608 ptr::swap(ptr.add(a), ptr.add(b));
612 /// Reverses the order of elements in the slice, in place.
617 /// let mut v = [1, 2, 3];
619 /// assert!(v == [3, 2, 1]);
621 #[stable(feature = "rust1", since = "1.0.0")]
623 pub fn reverse(&mut self) {
624 let mut i: usize = 0;
627 // For very small types, all the individual reads in the normal
628 // path perform poorly. We can do better, given efficient unaligned
629 // load/store, by loading a larger chunk and reversing a register.
631 // Ideally LLVM would do this for us, as it knows better than we do
632 // whether unaligned reads are efficient (since that changes between
633 // different ARM versions, for example) and what the best chunk size
634 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
635 // the loop, so we need to do this ourselves. (Hypothesis: reverse
636 // is troublesome because the sides can be aligned differently --
637 // will be, when the length is odd -- so there's no way of emitting
638 // pre- and postludes to use fully-aligned SIMD in the middle.)
640 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
642 if fast_unaligned && mem::size_of::<T>() == 1 {
643 // Use the llvm.bswap intrinsic to reverse u8s in a usize
644 let chunk = mem::size_of::<usize>();
645 while i + chunk - 1 < ln / 2 {
646 // SAFETY: There are several things to check here:
648 // - Note that `chunk` is either 4 or 8 due to the cfg check
649 // above. So `chunk - 1` is positive.
650 // - Indexing with index `i` is fine as the loop check guarantees
651 // `i + chunk - 1 < ln / 2`
652 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
653 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
654 // - `i + chunk > 0` is trivially true.
655 // - The loop check guarantees:
656 // `i + chunk - 1 < ln / 2`
657 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
658 // - The `read_unaligned` and `write_unaligned` calls are fine:
659 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
660 // (see above) and `pb` points to index `ln - i - chunk`, so
661 // both are at least `chunk`
662 // many bytes away from the end of `self`.
663 // - Any initialized memory is valid `usize`.
665 let ptr = self.as_mut_ptr();
667 let pb = ptr.add(ln - i - chunk);
668 let va = ptr::read_unaligned(pa as *mut usize);
669 let vb = ptr::read_unaligned(pb as *mut usize);
670 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
671 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
677 if fast_unaligned && mem::size_of::<T>() == 2 {
678 // Use rotate-by-16 to reverse u16s in a u32
679 let chunk = mem::size_of::<u32>() / 2;
680 while i + chunk - 1 < ln / 2 {
681 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
682 // (and obviously `i < ln`), because each element is 2 bytes and
685 // `i + chunk - 1 < ln / 2` # while condition
686 // `i + 2 - 1 < ln / 2`
689 // Since it's less than the length divided by 2, then it must be
692 // This also means that the condition `0 < i + chunk <= ln` is
693 // always respected, ensuring the `pb` pointer can be used
696 let ptr = self.as_mut_ptr();
698 let pb = ptr.add(ln - i - chunk);
699 let va = ptr::read_unaligned(pa as *mut u32);
700 let vb = ptr::read_unaligned(pb as *mut u32);
701 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
702 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
709 // SAFETY: `i` is inferior to half the length of the slice so
710 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
711 // will not go further than `ln / 2 - 1`).
712 // The resulting pointers `pa` and `pb` are therefore valid and
713 // aligned, and can be read from and written to.
715 self.swap_unchecked(i, ln - i - 1);
721 /// Returns an iterator over the slice.
726 /// let x = &[1, 2, 4];
727 /// let mut iterator = x.iter();
729 /// assert_eq!(iterator.next(), Some(&1));
730 /// assert_eq!(iterator.next(), Some(&2));
731 /// assert_eq!(iterator.next(), Some(&4));
732 /// assert_eq!(iterator.next(), None);
734 #[stable(feature = "rust1", since = "1.0.0")]
736 pub fn iter(&self) -> Iter<'_, T> {
740 /// Returns an iterator that allows modifying each value.
745 /// let x = &mut [1, 2, 4];
746 /// for elem in x.iter_mut() {
749 /// assert_eq!(x, &[3, 4, 6]);
751 #[stable(feature = "rust1", since = "1.0.0")]
753 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
757 /// Returns an iterator over all contiguous windows of length
758 /// `size`. The windows overlap. If the slice is shorter than
759 /// `size`, the iterator returns no values.
763 /// Panics if `size` is 0.
768 /// let slice = ['r', 'u', 's', 't'];
769 /// let mut iter = slice.windows(2);
770 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
771 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
772 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
773 /// assert!(iter.next().is_none());
776 /// If the slice is shorter than `size`:
779 /// let slice = ['f', 'o', 'o'];
780 /// let mut iter = slice.windows(4);
781 /// assert!(iter.next().is_none());
783 #[stable(feature = "rust1", since = "1.0.0")]
785 pub fn windows(&self, size: usize) -> Windows<'_, T> {
786 let size = NonZeroUsize::new(size).expect("size is zero");
787 Windows::new(self, size)
790 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
791 /// beginning of the slice.
793 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
794 /// slice, then the last chunk will not have length `chunk_size`.
796 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
797 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
802 /// Panics if `chunk_size` is 0.
807 /// let slice = ['l', 'o', 'r', 'e', 'm'];
808 /// let mut iter = slice.chunks(2);
809 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
810 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
811 /// assert_eq!(iter.next().unwrap(), &['m']);
812 /// assert!(iter.next().is_none());
815 /// [`chunks_exact`]: slice::chunks_exact
816 /// [`rchunks`]: slice::rchunks
817 #[stable(feature = "rust1", since = "1.0.0")]
819 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
820 assert_ne!(chunk_size, 0);
821 Chunks::new(self, chunk_size)
824 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
825 /// beginning of the slice.
827 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
828 /// length of the slice, then the last chunk will not have length `chunk_size`.
830 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
831 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
832 /// the end of the slice.
836 /// Panics if `chunk_size` is 0.
841 /// let v = &mut [0, 0, 0, 0, 0];
842 /// let mut count = 1;
844 /// for chunk in v.chunks_mut(2) {
845 /// for elem in chunk.iter_mut() {
850 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
853 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
854 /// [`rchunks_mut`]: slice::rchunks_mut
855 #[stable(feature = "rust1", since = "1.0.0")]
857 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
858 assert_ne!(chunk_size, 0);
859 ChunksMut::new(self, chunk_size)
862 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
863 /// beginning of the slice.
865 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
866 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
867 /// from the `remainder` function of the iterator.
869 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
870 /// resulting code better than in the case of [`chunks`].
872 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
873 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
877 /// Panics if `chunk_size` is 0.
882 /// let slice = ['l', 'o', 'r', 'e', 'm'];
883 /// let mut iter = slice.chunks_exact(2);
884 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
885 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
886 /// assert!(iter.next().is_none());
887 /// assert_eq!(iter.remainder(), &['m']);
890 /// [`chunks`]: slice::chunks
891 /// [`rchunks_exact`]: slice::rchunks_exact
892 #[stable(feature = "chunks_exact", since = "1.31.0")]
894 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
895 assert_ne!(chunk_size, 0);
896 ChunksExact::new(self, chunk_size)
899 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
900 /// beginning of the slice.
902 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
903 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
904 /// retrieved from the `into_remainder` function of the iterator.
906 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
907 /// resulting code better than in the case of [`chunks_mut`].
909 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
910 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
915 /// Panics if `chunk_size` is 0.
920 /// let v = &mut [0, 0, 0, 0, 0];
921 /// let mut count = 1;
923 /// for chunk in v.chunks_exact_mut(2) {
924 /// for elem in chunk.iter_mut() {
929 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
932 /// [`chunks_mut`]: slice::chunks_mut
933 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
934 #[stable(feature = "chunks_exact", since = "1.31.0")]
936 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
937 assert_ne!(chunk_size, 0);
938 ChunksExactMut::new(self, chunk_size)
941 /// Splits the slice into a slice of `N`-element arrays,
942 /// assuming that there's no remainder.
946 /// This may only be called when
947 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
953 /// #![feature(slice_as_chunks)]
954 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
955 /// let chunks: &[[char; 1]] =
956 /// // SAFETY: 1-element chunks never have remainder
957 /// unsafe { slice.as_chunks_unchecked() };
958 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
959 /// let chunks: &[[char; 3]] =
960 /// // SAFETY: The slice length (6) is a multiple of 3
961 /// unsafe { slice.as_chunks_unchecked() };
962 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
964 /// // These would be unsound:
965 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
966 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
968 #[unstable(feature = "slice_as_chunks", issue = "74985")]
970 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
971 debug_assert_ne!(N, 0);
972 debug_assert_eq!(self.len() % N, 0);
974 // SAFETY: Our precondition is exactly what's needed to call this
975 unsafe { crate::intrinsics::exact_div(self.len(), N) };
976 // SAFETY: We cast a slice of `new_len * N` elements into
977 // a slice of `new_len` many `N` elements chunks.
978 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
981 /// Splits the slice into a slice of `N`-element arrays,
982 /// starting at the beginning of the slice,
983 /// and a remainder slice with length strictly less than `N`.
987 /// Panics if `N` is 0. This check will most probably get changed to a compile time
988 /// error before this method gets stabilized.
993 /// #![feature(slice_as_chunks)]
994 /// let slice = ['l', 'o', 'r', 'e', 'm'];
995 /// let (chunks, remainder) = slice.as_chunks();
996 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
997 /// assert_eq!(remainder, &['m']);
999 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1001 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
1003 let len = self.len() / N;
1004 let (multiple_of_n, remainder) = self.split_at(len * N);
1005 // SAFETY: We already panicked for zero, and ensured by construction
1006 // that the length of the subslice is a multiple of N.
1007 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1008 (array_slice, remainder)
1011 /// Splits the slice into a slice of `N`-element arrays,
1012 /// starting at the end of the slice,
1013 /// and a remainder slice with length strictly less than `N`.
1017 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1018 /// error before this method gets stabilized.
1023 /// #![feature(slice_as_chunks)]
1024 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1025 /// let (remainder, chunks) = slice.as_rchunks();
1026 /// assert_eq!(remainder, &['l']);
1027 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1029 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1031 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1033 let len = self.len() / N;
1034 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1035 // SAFETY: We already panicked for zero, and ensured by construction
1036 // that the length of the subslice is a multiple of N.
1037 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1038 (remainder, array_slice)
1041 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1042 /// beginning of the slice.
1044 /// The chunks are array references and do not overlap. If `N` does not divide the
1045 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1046 /// retrieved from the `remainder` function of the iterator.
1048 /// This method is the const generic equivalent of [`chunks_exact`].
1052 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1053 /// error before this method gets stabilized.
1058 /// #![feature(array_chunks)]
1059 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1060 /// let mut iter = slice.array_chunks();
1061 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1062 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1063 /// assert!(iter.next().is_none());
1064 /// assert_eq!(iter.remainder(), &['m']);
1067 /// [`chunks_exact`]: slice::chunks_exact
1068 #[unstable(feature = "array_chunks", issue = "74985")]
1070 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1072 ArrayChunks::new(self)
1075 /// Splits the slice into a slice of `N`-element arrays,
1076 /// assuming that there's no remainder.
1080 /// This may only be called when
1081 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1087 /// #![feature(slice_as_chunks)]
1088 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1089 /// let chunks: &mut [[char; 1]] =
1090 /// // SAFETY: 1-element chunks never have remainder
1091 /// unsafe { slice.as_chunks_unchecked_mut() };
1092 /// chunks[0] = ['L'];
1093 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1094 /// let chunks: &mut [[char; 3]] =
1095 /// // SAFETY: The slice length (6) is a multiple of 3
1096 /// unsafe { slice.as_chunks_unchecked_mut() };
1097 /// chunks[1] = ['a', 'x', '?'];
1098 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1100 /// // These would be unsound:
1101 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1102 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1104 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1106 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1107 debug_assert_ne!(N, 0);
1108 debug_assert_eq!(self.len() % N, 0);
1110 // SAFETY: Our precondition is exactly what's needed to call this
1111 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1112 // SAFETY: We cast a slice of `new_len * N` elements into
1113 // a slice of `new_len` many `N` elements chunks.
1114 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1117 /// Splits the slice into a slice of `N`-element arrays,
1118 /// starting at the beginning of the slice,
1119 /// and a remainder slice with length strictly less than `N`.
1123 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1124 /// error before this method gets stabilized.
1129 /// #![feature(slice_as_chunks)]
1130 /// let v = &mut [0, 0, 0, 0, 0];
1131 /// let mut count = 1;
1133 /// let (chunks, remainder) = v.as_chunks_mut();
1134 /// remainder[0] = 9;
1135 /// for chunk in chunks {
1136 /// *chunk = [count; 2];
1139 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1141 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1143 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1145 let len = self.len() / N;
1146 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1147 // SAFETY: We already panicked for zero, and ensured by construction
1148 // that the length of the subslice is a multiple of N.
1149 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1150 (array_slice, remainder)
1153 /// Splits the slice into a slice of `N`-element arrays,
1154 /// starting at the end of the slice,
1155 /// and a remainder slice with length strictly less than `N`.
1159 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1160 /// error before this method gets stabilized.
1165 /// #![feature(slice_as_chunks)]
1166 /// let v = &mut [0, 0, 0, 0, 0];
1167 /// let mut count = 1;
1169 /// let (remainder, chunks) = v.as_rchunks_mut();
1170 /// remainder[0] = 9;
1171 /// for chunk in chunks {
1172 /// *chunk = [count; 2];
1175 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1177 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1179 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1181 let len = self.len() / N;
1182 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1183 // SAFETY: We already panicked for zero, and ensured by construction
1184 // that the length of the subslice is a multiple of N.
1185 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1186 (remainder, array_slice)
1189 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1190 /// beginning of the slice.
1192 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1193 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1194 /// can be retrieved from the `into_remainder` function of the iterator.
1196 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1200 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1201 /// error before this method gets stabilized.
1206 /// #![feature(array_chunks)]
1207 /// let v = &mut [0, 0, 0, 0, 0];
1208 /// let mut count = 1;
1210 /// for chunk in v.array_chunks_mut() {
1211 /// *chunk = [count; 2];
1214 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1217 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1218 #[unstable(feature = "array_chunks", issue = "74985")]
1220 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1222 ArrayChunksMut::new(self)
1225 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1226 /// starting at the beginning of the slice.
1228 /// This is the const generic equivalent of [`windows`].
1230 /// If `N` is greater than the size of the slice, it will return no windows.
1234 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1235 /// error before this method gets stabilized.
1240 /// #![feature(array_windows)]
1241 /// let slice = [0, 1, 2, 3];
1242 /// let mut iter = slice.array_windows();
1243 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1244 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1245 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1246 /// assert!(iter.next().is_none());
1249 /// [`windows`]: slice::windows
1250 #[unstable(feature = "array_windows", issue = "75027")]
1252 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1254 ArrayWindows::new(self)
1257 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1260 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1261 /// slice, then the last chunk will not have length `chunk_size`.
1263 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1264 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1269 /// Panics if `chunk_size` is 0.
1274 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1275 /// let mut iter = slice.rchunks(2);
1276 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1277 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1278 /// assert_eq!(iter.next().unwrap(), &['l']);
1279 /// assert!(iter.next().is_none());
1282 /// [`rchunks_exact`]: slice::rchunks_exact
1283 /// [`chunks`]: slice::chunks
1284 #[stable(feature = "rchunks", since = "1.31.0")]
1286 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1287 assert!(chunk_size != 0);
1288 RChunks::new(self, chunk_size)
1291 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1294 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1295 /// length of the slice, then the last chunk will not have length `chunk_size`.
1297 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1298 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1299 /// beginning of the slice.
1303 /// Panics if `chunk_size` is 0.
1308 /// let v = &mut [0, 0, 0, 0, 0];
1309 /// let mut count = 1;
1311 /// for chunk in v.rchunks_mut(2) {
1312 /// for elem in chunk.iter_mut() {
1317 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1320 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1321 /// [`chunks_mut`]: slice::chunks_mut
1322 #[stable(feature = "rchunks", since = "1.31.0")]
1324 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1325 assert!(chunk_size != 0);
1326 RChunksMut::new(self, chunk_size)
1329 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1330 /// end of the slice.
1332 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1333 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1334 /// from the `remainder` function of the iterator.
1336 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1337 /// resulting code better than in the case of [`chunks`].
1339 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1340 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1345 /// Panics if `chunk_size` is 0.
1350 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1351 /// let mut iter = slice.rchunks_exact(2);
1352 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1353 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1354 /// assert!(iter.next().is_none());
1355 /// assert_eq!(iter.remainder(), &['l']);
1358 /// [`chunks`]: slice::chunks
1359 /// [`rchunks`]: slice::rchunks
1360 /// [`chunks_exact`]: slice::chunks_exact
1361 #[stable(feature = "rchunks", since = "1.31.0")]
1363 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1364 assert!(chunk_size != 0);
1365 RChunksExact::new(self, chunk_size)
1368 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1371 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1372 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1373 /// retrieved from the `into_remainder` function of the iterator.
1375 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1376 /// resulting code better than in the case of [`chunks_mut`].
1378 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1379 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1384 /// Panics if `chunk_size` is 0.
1389 /// let v = &mut [0, 0, 0, 0, 0];
1390 /// let mut count = 1;
1392 /// for chunk in v.rchunks_exact_mut(2) {
1393 /// for elem in chunk.iter_mut() {
1398 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1401 /// [`chunks_mut`]: slice::chunks_mut
1402 /// [`rchunks_mut`]: slice::rchunks_mut
1403 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1404 #[stable(feature = "rchunks", since = "1.31.0")]
1406 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1407 assert!(chunk_size != 0);
1408 RChunksExactMut::new(self, chunk_size)
1411 /// Returns an iterator over the slice producing non-overlapping runs
1412 /// of elements using the predicate to separate them.
1414 /// The predicate is called on two elements following themselves,
1415 /// it means the predicate is called on `slice[0]` and `slice[1]`
1416 /// then on `slice[1]` and `slice[2]` and so on.
1421 /// #![feature(slice_group_by)]
1423 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1425 /// let mut iter = slice.group_by(|a, b| a == b);
1427 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1428 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1429 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1430 /// assert_eq!(iter.next(), None);
1433 /// This method can be used to extract the sorted subslices:
1436 /// #![feature(slice_group_by)]
1438 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1440 /// let mut iter = slice.group_by(|a, b| a <= b);
1442 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1443 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1444 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1445 /// assert_eq!(iter.next(), None);
1447 #[unstable(feature = "slice_group_by", issue = "80552")]
1449 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1451 F: FnMut(&T, &T) -> bool,
1453 GroupBy::new(self, pred)
1456 /// Returns an iterator over the slice producing non-overlapping mutable
1457 /// runs of elements using the predicate to separate them.
1459 /// The predicate is called on two elements following themselves,
1460 /// it means the predicate is called on `slice[0]` and `slice[1]`
1461 /// then on `slice[1]` and `slice[2]` and so on.
1466 /// #![feature(slice_group_by)]
1468 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1470 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1472 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1473 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1474 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1475 /// assert_eq!(iter.next(), None);
1478 /// This method can be used to extract the sorted subslices:
1481 /// #![feature(slice_group_by)]
1483 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1485 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1487 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1488 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1489 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1490 /// assert_eq!(iter.next(), None);
1492 #[unstable(feature = "slice_group_by", issue = "80552")]
1494 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1496 F: FnMut(&T, &T) -> bool,
1498 GroupByMut::new(self, pred)
1501 /// Divides one slice into two at an index.
1503 /// The first will contain all indices from `[0, mid)` (excluding
1504 /// the index `mid` itself) and the second will contain all
1505 /// indices from `[mid, len)` (excluding the index `len` itself).
1509 /// Panics if `mid > len`.
1514 /// let v = [1, 2, 3, 4, 5, 6];
1517 /// let (left, right) = v.split_at(0);
1518 /// assert_eq!(left, []);
1519 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1523 /// let (left, right) = v.split_at(2);
1524 /// assert_eq!(left, [1, 2]);
1525 /// assert_eq!(right, [3, 4, 5, 6]);
1529 /// let (left, right) = v.split_at(6);
1530 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1531 /// assert_eq!(right, []);
1534 #[stable(feature = "rust1", since = "1.0.0")]
1536 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1537 assert!(mid <= self.len());
1538 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1539 // fulfills the requirements of `from_raw_parts_mut`.
1540 unsafe { self.split_at_unchecked(mid) }
1543 /// Divides one mutable slice into two at an index.
1545 /// The first will contain all indices from `[0, mid)` (excluding
1546 /// the index `mid` itself) and the second will contain all
1547 /// indices from `[mid, len)` (excluding the index `len` itself).
1551 /// Panics if `mid > len`.
1556 /// let mut v = [1, 0, 3, 0, 5, 6];
1557 /// let (left, right) = v.split_at_mut(2);
1558 /// assert_eq!(left, [1, 0]);
1559 /// assert_eq!(right, [3, 0, 5, 6]);
1562 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1564 #[stable(feature = "rust1", since = "1.0.0")]
1566 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1567 assert!(mid <= self.len());
1568 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1569 // fulfills the requirements of `from_raw_parts_mut`.
1570 unsafe { self.split_at_mut_unchecked(mid) }
1573 /// Divides one slice into two at an index, without doing bounds checking.
1575 /// The first will contain all indices from `[0, mid)` (excluding
1576 /// the index `mid` itself) and the second will contain all
1577 /// indices from `[mid, len)` (excluding the index `len` itself).
1579 /// For a safe alternative see [`split_at`].
1583 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1584 /// even if the resulting reference is not used. The caller has to ensure that
1585 /// `0 <= mid <= self.len()`.
1587 /// [`split_at`]: slice::split_at
1588 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1593 /// #![feature(slice_split_at_unchecked)]
1595 /// let v = [1, 2, 3, 4, 5, 6];
1598 /// let (left, right) = v.split_at_unchecked(0);
1599 /// assert_eq!(left, []);
1600 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1604 /// let (left, right) = v.split_at_unchecked(2);
1605 /// assert_eq!(left, [1, 2]);
1606 /// assert_eq!(right, [3, 4, 5, 6]);
1610 /// let (left, right) = v.split_at_unchecked(6);
1611 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1612 /// assert_eq!(right, []);
1615 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1617 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1618 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1619 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1622 /// Divides one mutable slice into two at an index, without doing bounds checking.
1624 /// The first will contain all indices from `[0, mid)` (excluding
1625 /// the index `mid` itself) and the second will contain all
1626 /// indices from `[mid, len)` (excluding the index `len` itself).
1628 /// For a safe alternative see [`split_at_mut`].
1632 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1633 /// even if the resulting reference is not used. The caller has to ensure that
1634 /// `0 <= mid <= self.len()`.
1636 /// [`split_at_mut`]: slice::split_at_mut
1637 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1642 /// #![feature(slice_split_at_unchecked)]
1644 /// let mut v = [1, 0, 3, 0, 5, 6];
1645 /// // scoped to restrict the lifetime of the borrows
1647 /// let (left, right) = v.split_at_mut_unchecked(2);
1648 /// assert_eq!(left, [1, 0]);
1649 /// assert_eq!(right, [3, 0, 5, 6]);
1653 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1655 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1657 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1658 let len = self.len();
1659 let ptr = self.as_mut_ptr();
1661 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1663 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1665 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1668 /// Returns an iterator over subslices separated by elements that match
1669 /// `pred`. The matched element is not contained in the subslices.
1674 /// let slice = [10, 40, 33, 20];
1675 /// let mut iter = slice.split(|num| num % 3 == 0);
1677 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1678 /// assert_eq!(iter.next().unwrap(), &[20]);
1679 /// assert!(iter.next().is_none());
1682 /// If the first element is matched, an empty slice will be the first item
1683 /// returned by the iterator. Similarly, if the last element in the slice
1684 /// is matched, an empty slice will be the last item returned by the
1688 /// let slice = [10, 40, 33];
1689 /// let mut iter = slice.split(|num| num % 3 == 0);
1691 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1692 /// assert_eq!(iter.next().unwrap(), &[]);
1693 /// assert!(iter.next().is_none());
1696 /// If two matched elements are directly adjacent, an empty slice will be
1697 /// present between them:
1700 /// let slice = [10, 6, 33, 20];
1701 /// let mut iter = slice.split(|num| num % 3 == 0);
1703 /// assert_eq!(iter.next().unwrap(), &[10]);
1704 /// assert_eq!(iter.next().unwrap(), &[]);
1705 /// assert_eq!(iter.next().unwrap(), &[20]);
1706 /// assert!(iter.next().is_none());
1708 #[stable(feature = "rust1", since = "1.0.0")]
1710 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1712 F: FnMut(&T) -> bool,
1714 Split::new(self, pred)
1717 /// Returns an iterator over mutable subslices separated by elements that
1718 /// match `pred`. The matched element is not contained in the subslices.
1723 /// let mut v = [10, 40, 30, 20, 60, 50];
1725 /// for group in v.split_mut(|num| *num % 3 == 0) {
1728 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1730 #[stable(feature = "rust1", since = "1.0.0")]
1732 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1734 F: FnMut(&T) -> bool,
1736 SplitMut::new(self, pred)
1739 /// Returns an iterator over subslices separated by elements that match
1740 /// `pred`. The matched element is contained in the end of the previous
1741 /// subslice as a terminator.
1746 /// let slice = [10, 40, 33, 20];
1747 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1749 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1750 /// assert_eq!(iter.next().unwrap(), &[20]);
1751 /// assert!(iter.next().is_none());
1754 /// If the last element of the slice is matched,
1755 /// that element will be considered the terminator of the preceding slice.
1756 /// That slice will be the last item returned by the iterator.
1759 /// let slice = [3, 10, 40, 33];
1760 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1762 /// assert_eq!(iter.next().unwrap(), &[3]);
1763 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1764 /// assert!(iter.next().is_none());
1766 #[stable(feature = "split_inclusive", since = "1.51.0")]
1768 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1770 F: FnMut(&T) -> bool,
1772 SplitInclusive::new(self, pred)
1775 /// Returns an iterator over mutable subslices separated by elements that
1776 /// match `pred`. The matched element is contained in the previous
1777 /// subslice as a terminator.
1782 /// let mut v = [10, 40, 30, 20, 60, 50];
1784 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1785 /// let terminator_idx = group.len()-1;
1786 /// group[terminator_idx] = 1;
1788 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1790 #[stable(feature = "split_inclusive", since = "1.51.0")]
1792 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1794 F: FnMut(&T) -> bool,
1796 SplitInclusiveMut::new(self, pred)
1799 /// Returns an iterator over subslices separated by elements that match
1800 /// `pred`, starting at the end of the slice and working backwards.
1801 /// The matched element is not contained in the subslices.
1806 /// let slice = [11, 22, 33, 0, 44, 55];
1807 /// let mut iter = slice.rsplit(|num| *num == 0);
1809 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1810 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1811 /// assert_eq!(iter.next(), None);
1814 /// As with `split()`, if the first or last element is matched, an empty
1815 /// slice will be the first (or last) item returned by the iterator.
1818 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1819 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1820 /// assert_eq!(it.next().unwrap(), &[]);
1821 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1822 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1823 /// assert_eq!(it.next().unwrap(), &[]);
1824 /// assert_eq!(it.next(), None);
1826 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1828 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1830 F: FnMut(&T) -> bool,
1832 RSplit::new(self, pred)
1835 /// Returns an iterator over mutable subslices separated by elements that
1836 /// match `pred`, starting at the end of the slice and working
1837 /// backwards. The matched element is not contained in the subslices.
1842 /// let mut v = [100, 400, 300, 200, 600, 500];
1844 /// let mut count = 0;
1845 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1847 /// group[0] = count;
1849 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1852 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1854 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1856 F: FnMut(&T) -> bool,
1858 RSplitMut::new(self, pred)
1861 /// Returns an iterator over subslices separated by elements that match
1862 /// `pred`, limited to returning at most `n` items. The matched element is
1863 /// not contained in the subslices.
1865 /// The last element returned, if any, will contain the remainder of the
1870 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1871 /// `[20, 60, 50]`):
1874 /// let v = [10, 40, 30, 20, 60, 50];
1876 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1877 /// println!("{:?}", group);
1880 #[stable(feature = "rust1", since = "1.0.0")]
1882 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1884 F: FnMut(&T) -> bool,
1886 SplitN::new(self.split(pred), n)
1889 /// Returns an iterator over subslices separated by elements that match
1890 /// `pred`, limited to returning at most `n` items. The matched element is
1891 /// not contained in the subslices.
1893 /// The last element returned, if any, will contain the remainder of the
1899 /// let mut v = [10, 40, 30, 20, 60, 50];
1901 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1904 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1906 #[stable(feature = "rust1", since = "1.0.0")]
1908 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1910 F: FnMut(&T) -> bool,
1912 SplitNMut::new(self.split_mut(pred), n)
1915 /// Returns an iterator over subslices separated by elements that match
1916 /// `pred` limited to returning at most `n` items. This starts at the end of
1917 /// the slice and works backwards. The matched element is not contained in
1920 /// The last element returned, if any, will contain the remainder of the
1925 /// Print the slice split once, starting from the end, by numbers divisible
1926 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1929 /// let v = [10, 40, 30, 20, 60, 50];
1931 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1932 /// println!("{:?}", group);
1935 #[stable(feature = "rust1", since = "1.0.0")]
1937 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1939 F: FnMut(&T) -> bool,
1941 RSplitN::new(self.rsplit(pred), n)
1944 /// Returns an iterator over subslices separated by elements that match
1945 /// `pred` limited to returning at most `n` items. This starts at the end of
1946 /// the slice and works backwards. The matched element is not contained in
1949 /// The last element returned, if any, will contain the remainder of the
1955 /// let mut s = [10, 40, 30, 20, 60, 50];
1957 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1960 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1962 #[stable(feature = "rust1", since = "1.0.0")]
1964 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1966 F: FnMut(&T) -> bool,
1968 RSplitNMut::new(self.rsplit_mut(pred), n)
1971 /// Returns `true` if the slice contains an element with the given value.
1976 /// let v = [10, 40, 30];
1977 /// assert!(v.contains(&30));
1978 /// assert!(!v.contains(&50));
1981 /// If you do not have a `&T`, but some other value that you can compare
1982 /// with one (for example, `String` implements `PartialEq<str>`), you can
1983 /// use `iter().any`:
1986 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1987 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1988 /// assert!(!v.iter().any(|e| e == "hi"));
1990 #[stable(feature = "rust1", since = "1.0.0")]
1992 pub fn contains(&self, x: &T) -> bool
1996 cmp::SliceContains::slice_contains(x, self)
1999 /// Returns `true` if `needle` is a prefix of the slice.
2004 /// let v = [10, 40, 30];
2005 /// assert!(v.starts_with(&[10]));
2006 /// assert!(v.starts_with(&[10, 40]));
2007 /// assert!(!v.starts_with(&[50]));
2008 /// assert!(!v.starts_with(&[10, 50]));
2011 /// Always returns `true` if `needle` is an empty slice:
2014 /// let v = &[10, 40, 30];
2015 /// assert!(v.starts_with(&[]));
2016 /// let v: &[u8] = &[];
2017 /// assert!(v.starts_with(&[]));
2019 #[stable(feature = "rust1", since = "1.0.0")]
2020 pub fn starts_with(&self, needle: &[T]) -> bool
2024 let n = needle.len();
2025 self.len() >= n && needle == &self[..n]
2028 /// Returns `true` if `needle` is a suffix of the slice.
2033 /// let v = [10, 40, 30];
2034 /// assert!(v.ends_with(&[30]));
2035 /// assert!(v.ends_with(&[40, 30]));
2036 /// assert!(!v.ends_with(&[50]));
2037 /// assert!(!v.ends_with(&[50, 30]));
2040 /// Always returns `true` if `needle` is an empty slice:
2043 /// let v = &[10, 40, 30];
2044 /// assert!(v.ends_with(&[]));
2045 /// let v: &[u8] = &[];
2046 /// assert!(v.ends_with(&[]));
2048 #[stable(feature = "rust1", since = "1.0.0")]
2049 pub fn ends_with(&self, needle: &[T]) -> bool
2053 let (m, n) = (self.len(), needle.len());
2054 m >= n && needle == &self[m - n..]
2057 /// Returns a subslice with the prefix removed.
2059 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2060 /// If `prefix` is empty, simply returns the original slice.
2062 /// If the slice does not start with `prefix`, returns `None`.
2067 /// let v = &[10, 40, 30];
2068 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2069 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2070 /// assert_eq!(v.strip_prefix(&[50]), None);
2071 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2073 /// let prefix : &str = "he";
2074 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2075 /// Some(b"llo".as_ref()));
2077 #[must_use = "returns the subslice without modifying the original"]
2078 #[stable(feature = "slice_strip", since = "1.51.0")]
2079 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2083 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2084 let prefix = prefix.as_slice();
2085 let n = prefix.len();
2086 if n <= self.len() {
2087 let (head, tail) = self.split_at(n);
2095 /// Returns a subslice with the suffix removed.
2097 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2098 /// If `suffix` is empty, simply returns the original slice.
2100 /// If the slice does not end with `suffix`, returns `None`.
2105 /// let v = &[10, 40, 30];
2106 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2107 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2108 /// assert_eq!(v.strip_suffix(&[50]), None);
2109 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2111 #[must_use = "returns the subslice without modifying the original"]
2112 #[stable(feature = "slice_strip", since = "1.51.0")]
2113 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2117 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2118 let suffix = suffix.as_slice();
2119 let (len, n) = (self.len(), suffix.len());
2121 let (head, tail) = self.split_at(len - n);
2129 /// Binary searches this sorted slice for a given element.
2131 /// If the value is found then [`Result::Ok`] is returned, containing the
2132 /// index of the matching element. If there are multiple matches, then any
2133 /// one of the matches could be returned. The index is chosen
2134 /// deterministically, but is subject to change in future versions of Rust.
2135 /// If the value is not found then [`Result::Err`] is returned, containing
2136 /// the index where a matching element could be inserted while maintaining
2139 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2141 /// [`binary_search_by`]: slice::binary_search_by
2142 /// [`binary_search_by_key`]: slice::binary_search_by_key
2143 /// [`partition_point`]: slice::partition_point
2147 /// Looks up a series of four elements. The first is found, with a
2148 /// uniquely determined position; the second and third are not
2149 /// found; the fourth could match any position in `[1, 4]`.
2152 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2154 /// assert_eq!(s.binary_search(&13), Ok(9));
2155 /// assert_eq!(s.binary_search(&4), Err(7));
2156 /// assert_eq!(s.binary_search(&100), Err(13));
2157 /// let r = s.binary_search(&1);
2158 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2161 /// If you want to insert an item to a sorted vector, while maintaining
2165 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2167 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2168 /// s.insert(idx, num);
2169 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2171 #[stable(feature = "rust1", since = "1.0.0")]
2172 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2176 self.binary_search_by(|p| p.cmp(x))
2179 /// Binary searches this sorted slice with a comparator function.
2181 /// The comparator function should implement an order consistent
2182 /// with the sort order of the underlying slice, returning an
2183 /// order code that indicates whether its argument is `Less`,
2184 /// `Equal` or `Greater` the desired target.
2186 /// If the value is found then [`Result::Ok`] is returned, containing the
2187 /// index of the matching element. If there are multiple matches, then any
2188 /// one of the matches could be returned. The index is chosen
2189 /// deterministically, but is subject to change in future versions of Rust.
2190 /// If the value is not found then [`Result::Err`] is returned, containing
2191 /// the index where a matching element could be inserted while maintaining
2194 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2196 /// [`binary_search`]: slice::binary_search
2197 /// [`binary_search_by_key`]: slice::binary_search_by_key
2198 /// [`partition_point`]: slice::partition_point
2202 /// Looks up a series of four elements. The first is found, with a
2203 /// uniquely determined position; the second and third are not
2204 /// found; the fourth could match any position in `[1, 4]`.
2207 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2210 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2212 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2214 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2216 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2217 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2219 #[stable(feature = "rust1", since = "1.0.0")]
2221 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2223 F: FnMut(&'a T) -> Ordering,
2225 let mut size = self.len();
2227 let mut right = size;
2228 while left < right {
2229 let mid = left + size / 2;
2231 // SAFETY: the call is made safe by the following invariants:
2233 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2234 let cmp = f(unsafe { self.get_unchecked(mid) });
2236 // The reason why we use if/else control flow rather than match
2237 // is because match reorders comparison operations, which is perf sensitive.
2238 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2241 } else if cmp == Greater {
2244 // SAFETY: same as the `get_unchecked` above
2245 unsafe { crate::intrinsics::assume(mid < self.len()) };
2249 size = right - left;
2254 /// Binary searches this sorted slice with a key extraction function.
2256 /// Assumes that the slice is sorted by the key, for instance with
2257 /// [`sort_by_key`] using the same key extraction function.
2259 /// If the value is found then [`Result::Ok`] is returned, containing the
2260 /// index of the matching element. If there are multiple matches, then any
2261 /// one of the matches could be returned. The index is chosen
2262 /// deterministically, but is subject to change in future versions of Rust.
2263 /// If the value is not found then [`Result::Err`] is returned, containing
2264 /// the index where a matching element could be inserted while maintaining
2267 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2269 /// [`sort_by_key`]: slice::sort_by_key
2270 /// [`binary_search`]: slice::binary_search
2271 /// [`binary_search_by`]: slice::binary_search_by
2272 /// [`partition_point`]: slice::partition_point
2276 /// Looks up a series of four elements in a slice of pairs sorted by
2277 /// their second elements. The first is found, with a uniquely
2278 /// determined position; the second and third are not found; the
2279 /// fourth could match any position in `[1, 4]`.
2282 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2283 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2284 /// (1, 21), (2, 34), (4, 55)];
2286 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2287 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2288 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2289 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2290 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2292 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2293 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2294 // This breaks links when slice is displayed in core, but changing it to use relative links
2295 // would break when the item is re-exported. So allow the core links to be broken for now.
2296 #[allow(rustdoc::broken_intra_doc_links)]
2297 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2299 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2301 F: FnMut(&'a T) -> B,
2304 self.binary_search_by(|k| f(k).cmp(b))
2307 /// Sorts the slice, but might not preserve the order of equal elements.
2309 /// This sort is unstable (i.e., may reorder equal elements), in-place
2310 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2312 /// # Current implementation
2314 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2315 /// which combines the fast average case of randomized quicksort with the fast worst case of
2316 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2317 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2318 /// deterministic behavior.
2320 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2321 /// slice consists of several concatenated sorted sequences.
2326 /// let mut v = [-5, 4, 1, -3, 2];
2328 /// v.sort_unstable();
2329 /// assert!(v == [-5, -3, 1, 2, 4]);
2332 /// [pdqsort]: https://github.com/orlp/pdqsort
2333 #[stable(feature = "sort_unstable", since = "1.20.0")]
2335 pub fn sort_unstable(&mut self)
2339 sort::quicksort(self, |a, b| a.lt(b));
2342 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2345 /// This sort is unstable (i.e., may reorder equal elements), in-place
2346 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2348 /// The comparator function must define a total ordering for the elements in the slice. If
2349 /// the ordering is not total, the order of the elements is unspecified. An order is a
2350 /// total order if it is (for all `a`, `b` and `c`):
2352 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2353 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2355 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2356 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2359 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2360 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2361 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2364 /// # Current implementation
2366 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2367 /// which combines the fast average case of randomized quicksort with the fast worst case of
2368 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2369 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2370 /// deterministic behavior.
2372 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2373 /// slice consists of several concatenated sorted sequences.
2378 /// let mut v = [5, 4, 1, 3, 2];
2379 /// v.sort_unstable_by(|a, b| a.cmp(b));
2380 /// assert!(v == [1, 2, 3, 4, 5]);
2382 /// // reverse sorting
2383 /// v.sort_unstable_by(|a, b| b.cmp(a));
2384 /// assert!(v == [5, 4, 3, 2, 1]);
2387 /// [pdqsort]: https://github.com/orlp/pdqsort
2388 #[stable(feature = "sort_unstable", since = "1.20.0")]
2390 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2392 F: FnMut(&T, &T) -> Ordering,
2394 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2397 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2400 /// This sort is unstable (i.e., may reorder equal elements), in-place
2401 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2404 /// # Current implementation
2406 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2407 /// which combines the fast average case of randomized quicksort with the fast worst case of
2408 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2409 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2410 /// deterministic behavior.
2412 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2413 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2414 /// cases where the key function is expensive.
2419 /// let mut v = [-5i32, 4, 1, -3, 2];
2421 /// v.sort_unstable_by_key(|k| k.abs());
2422 /// assert!(v == [1, 2, -3, 4, -5]);
2425 /// [pdqsort]: https://github.com/orlp/pdqsort
2426 #[stable(feature = "sort_unstable", since = "1.20.0")]
2428 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2433 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2436 /// Reorder the slice such that the element at `index` is at its final sorted position.
2437 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2438 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2440 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2444 self.select_nth_unstable(index)
2447 /// Reorder the slice with a comparator function such that the element at `index` is at its
2448 /// final sorted position.
2449 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2450 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2452 pub fn partition_at_index_by<F>(
2456 ) -> (&mut [T], &mut T, &mut [T])
2458 F: FnMut(&T, &T) -> Ordering,
2460 self.select_nth_unstable_by(index, compare)
2463 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2464 /// final sorted position.
2465 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2466 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2468 pub fn partition_at_index_by_key<K, F>(
2472 ) -> (&mut [T], &mut T, &mut [T])
2477 self.select_nth_unstable_by_key(index, f)
2480 /// Reorder the slice such that the element at `index` is at its final sorted position.
2482 /// This reordering has the additional property that any value at position `i < index` will be
2483 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2484 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2485 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2486 /// element" in other libraries. It returns a triplet of the following values: all elements less
2487 /// than the one at the given index, the value at the given index, and all elements greater than
2488 /// the one at the given index.
2490 /// # Current implementation
2492 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2493 /// used for [`sort_unstable`].
2495 /// [`sort_unstable`]: slice::sort_unstable
2499 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2504 /// let mut v = [-5i32, 4, 1, -3, 2];
2506 /// // Find the median
2507 /// v.select_nth_unstable(2);
2509 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2510 /// // about the specified index.
2511 /// assert!(v == [-3, -5, 1, 2, 4] ||
2512 /// v == [-5, -3, 1, 2, 4] ||
2513 /// v == [-3, -5, 1, 4, 2] ||
2514 /// v == [-5, -3, 1, 4, 2]);
2516 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2518 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2522 let mut f = |a: &T, b: &T| a.lt(b);
2523 sort::partition_at_index(self, index, &mut f)
2526 /// Reorder the slice with a comparator function such that the element at `index` is at its
2527 /// final sorted position.
2529 /// This reordering has the additional property that any value at position `i < index` will be
2530 /// less than or equal to any value at a position `j > index` using the comparator function.
2531 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2532 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2533 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2534 /// values: all elements less than the one at the given index, the value at the given index,
2535 /// and all elements greater than the one at the given index, using the provided comparator
2538 /// # Current implementation
2540 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2541 /// used for [`sort_unstable`].
2543 /// [`sort_unstable`]: slice::sort_unstable
2547 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2552 /// let mut v = [-5i32, 4, 1, -3, 2];
2554 /// // Find the median as if the slice were sorted in descending order.
2555 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2557 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2558 /// // about the specified index.
2559 /// assert!(v == [2, 4, 1, -5, -3] ||
2560 /// v == [2, 4, 1, -3, -5] ||
2561 /// v == [4, 2, 1, -5, -3] ||
2562 /// v == [4, 2, 1, -3, -5]);
2564 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2566 pub fn select_nth_unstable_by<F>(
2570 ) -> (&mut [T], &mut T, &mut [T])
2572 F: FnMut(&T, &T) -> Ordering,
2574 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2575 sort::partition_at_index(self, index, &mut f)
2578 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2579 /// final sorted position.
2581 /// This reordering has the additional property that any value at position `i < index` will be
2582 /// less than or equal to any value at a position `j > index` using the key extraction function.
2583 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2584 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2585 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2586 /// values: all elements less than the one at the given index, the value at the given index, and
2587 /// all elements greater than the one at the given index, using the provided key extraction
2590 /// # Current implementation
2592 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2593 /// used for [`sort_unstable`].
2595 /// [`sort_unstable`]: slice::sort_unstable
2599 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2604 /// let mut v = [-5i32, 4, 1, -3, 2];
2606 /// // Return the median as if the array were sorted according to absolute value.
2607 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2609 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2610 /// // about the specified index.
2611 /// assert!(v == [1, 2, -3, 4, -5] ||
2612 /// v == [1, 2, -3, -5, 4] ||
2613 /// v == [2, 1, -3, 4, -5] ||
2614 /// v == [2, 1, -3, -5, 4]);
2616 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2618 pub fn select_nth_unstable_by_key<K, F>(
2622 ) -> (&mut [T], &mut T, &mut [T])
2627 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2628 sort::partition_at_index(self, index, &mut g)
2631 /// Moves all consecutive repeated elements to the end of the slice according to the
2632 /// [`PartialEq`] trait implementation.
2634 /// Returns two slices. The first contains no consecutive repeated elements.
2635 /// The second contains all the duplicates in no specified order.
2637 /// If the slice is sorted, the first returned slice contains no duplicates.
2642 /// #![feature(slice_partition_dedup)]
2644 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2646 /// let (dedup, duplicates) = slice.partition_dedup();
2648 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2649 /// assert_eq!(duplicates, [2, 3, 1]);
2651 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2653 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2657 self.partition_dedup_by(|a, b| a == b)
2660 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2661 /// a given equality relation.
2663 /// Returns two slices. The first contains no consecutive repeated elements.
2664 /// The second contains all the duplicates in no specified order.
2666 /// The `same_bucket` function is passed references to two elements from the slice and
2667 /// must determine if the elements compare equal. The elements are passed in opposite order
2668 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2669 /// at the end of the slice.
2671 /// If the slice is sorted, the first returned slice contains no duplicates.
2676 /// #![feature(slice_partition_dedup)]
2678 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2680 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2682 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2683 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2685 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2687 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2689 F: FnMut(&mut T, &mut T) -> bool,
2691 // Although we have a mutable reference to `self`, we cannot make
2692 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2693 // must ensure that the slice is in a valid state at all times.
2695 // The way that we handle this is by using swaps; we iterate
2696 // over all the elements, swapping as we go so that at the end
2697 // the elements we wish to keep are in the front, and those we
2698 // wish to reject are at the back. We can then split the slice.
2699 // This operation is still `O(n)`.
2701 // Example: We start in this state, where `r` represents "next
2702 // read" and `w` represents "next_write`.
2705 // +---+---+---+---+---+---+
2706 // | 0 | 1 | 1 | 2 | 3 | 3 |
2707 // +---+---+---+---+---+---+
2710 // Comparing self[r] against self[w-1], this is not a duplicate, so
2711 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2712 // r and w, leaving us with:
2715 // +---+---+---+---+---+---+
2716 // | 0 | 1 | 1 | 2 | 3 | 3 |
2717 // +---+---+---+---+---+---+
2720 // Comparing self[r] against self[w-1], this value is a duplicate,
2721 // so we increment `r` but leave everything else unchanged:
2724 // +---+---+---+---+---+---+
2725 // | 0 | 1 | 1 | 2 | 3 | 3 |
2726 // +---+---+---+---+---+---+
2729 // Comparing self[r] against self[w-1], this is not a duplicate,
2730 // so swap self[r] and self[w] and advance r and w:
2733 // +---+---+---+---+---+---+
2734 // | 0 | 1 | 2 | 1 | 3 | 3 |
2735 // +---+---+---+---+---+---+
2738 // Not a duplicate, repeat:
2741 // +---+---+---+---+---+---+
2742 // | 0 | 1 | 2 | 3 | 1 | 3 |
2743 // +---+---+---+---+---+---+
2746 // Duplicate, advance r. End of slice. Split at w.
2748 let len = self.len();
2750 return (self, &mut []);
2753 let ptr = self.as_mut_ptr();
2754 let mut next_read: usize = 1;
2755 let mut next_write: usize = 1;
2757 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2758 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2759 // one element before `ptr_write`, but `next_write` starts at 1, so
2760 // `prev_ptr_write` is never less than 0 and is inside the slice.
2761 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2762 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2763 // and `prev_ptr_write.offset(1)`.
2765 // `next_write` is also incremented at most once per loop at most meaning
2766 // no element is skipped when it may need to be swapped.
2768 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2769 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2770 // The explanation is simply that `next_read >= next_write` is always true,
2771 // thus `next_read > next_write - 1` is too.
2773 // Avoid bounds checks by using raw pointers.
2774 while next_read < len {
2775 let ptr_read = ptr.add(next_read);
2776 let prev_ptr_write = ptr.add(next_write - 1);
2777 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2778 if next_read != next_write {
2779 let ptr_write = prev_ptr_write.offset(1);
2780 mem::swap(&mut *ptr_read, &mut *ptr_write);
2788 self.split_at_mut(next_write)
2791 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2792 /// to the same key.
2794 /// Returns two slices. The first contains no consecutive repeated elements.
2795 /// The second contains all the duplicates in no specified order.
2797 /// If the slice is sorted, the first returned slice contains no duplicates.
2802 /// #![feature(slice_partition_dedup)]
2804 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2806 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2808 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2809 /// assert_eq!(duplicates, [21, 30, 13]);
2811 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2813 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2815 F: FnMut(&mut T) -> K,
2818 self.partition_dedup_by(|a, b| key(a) == key(b))
2821 /// Rotates the slice in-place such that the first `mid` elements of the
2822 /// slice move to the end while the last `self.len() - mid` elements move to
2823 /// the front. After calling `rotate_left`, the element previously at index
2824 /// `mid` will become the first element in the slice.
2828 /// This function will panic if `mid` is greater than the length of the
2829 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2834 /// Takes linear (in `self.len()`) time.
2839 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2840 /// a.rotate_left(2);
2841 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2844 /// Rotating a subslice:
2847 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2848 /// a[1..5].rotate_left(1);
2849 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2851 #[stable(feature = "slice_rotate", since = "1.26.0")]
2852 pub fn rotate_left(&mut self, mid: usize) {
2853 assert!(mid <= self.len());
2854 let k = self.len() - mid;
2855 let p = self.as_mut_ptr();
2857 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2858 // valid for reading and writing, as required by `ptr_rotate`.
2860 rotate::ptr_rotate(mid, p.add(mid), k);
2864 /// Rotates the slice in-place such that the first `self.len() - k`
2865 /// elements of the slice move to the end while the last `k` elements move
2866 /// to the front. After calling `rotate_right`, the element previously at
2867 /// index `self.len() - k` will become the first element in the slice.
2871 /// This function will panic if `k` is greater than the length of the
2872 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2877 /// Takes linear (in `self.len()`) time.
2882 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2883 /// a.rotate_right(2);
2884 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2887 /// Rotate a subslice:
2890 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2891 /// a[1..5].rotate_right(1);
2892 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2894 #[stable(feature = "slice_rotate", since = "1.26.0")]
2895 pub fn rotate_right(&mut self, k: usize) {
2896 assert!(k <= self.len());
2897 let mid = self.len() - k;
2898 let p = self.as_mut_ptr();
2900 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2901 // valid for reading and writing, as required by `ptr_rotate`.
2903 rotate::ptr_rotate(mid, p.add(mid), k);
2907 /// Fills `self` with elements by cloning `value`.
2912 /// let mut buf = vec![0; 10];
2914 /// assert_eq!(buf, vec![1; 10]);
2916 #[doc(alias = "memset")]
2917 #[stable(feature = "slice_fill", since = "1.50.0")]
2918 pub fn fill(&mut self, value: T)
2922 specialize::SpecFill::spec_fill(self, value);
2925 /// Fills `self` with elements returned by calling a closure repeatedly.
2927 /// This method uses a closure to create new values. If you'd rather
2928 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2929 /// trait to generate values, you can pass [`Default::default`] as the
2932 /// [`fill`]: slice::fill
2937 /// let mut buf = vec![1; 10];
2938 /// buf.fill_with(Default::default);
2939 /// assert_eq!(buf, vec![0; 10]);
2941 #[doc(alias = "memset")]
2942 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2943 pub fn fill_with<F>(&mut self, mut f: F)
2952 /// Copies the elements from `src` into `self`.
2954 /// The length of `src` must be the same as `self`.
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] {