1 // ignore-tidy-filelength
3 //! Slice management and manipulation.
5 //! For more details see [`std::slice`].
7 //! [`std::slice`]: ../../std/slice/index.html
9 #![stable(feature = "rust1", since = "1.0.0")]
11 use crate::cmp::Ordering::{self, Equal, Greater, Less};
12 use crate::marker::Copy;
14 use crate::num::NonZeroUsize;
15 use crate::ops::{FnMut, Range, RangeBounds};
16 use crate::option::Option;
17 use crate::option::Option::{None, Some};
19 use crate::result::Result;
20 use crate::result::Result::{Err, Ok};
23 feature = "slice_internals",
25 reason = "exposed from core to be reused in std; use the memchr crate"
27 /// 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;
82 /// Returns the number of elements in the slice.
87 /// let a = [1, 2, 3];
88 /// assert_eq!(a.len(), 3);
90 #[doc(alias = "length")]
91 #[stable(feature = "rust1", since = "1.0.0")]
92 #[rustc_const_stable(feature = "const_slice_len", since = "1.32.0")]
94 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
95 #[rustc_allow_const_fn_unstable(const_fn_union)]
96 pub const fn len(&self) -> usize {
99 // SAFETY: this is safe because `&[T]` and `FatPtr<T>` have the same layout.
100 // Only `std` can make this guarantee.
101 unsafe { crate::ptr::Repr { rust: self }.raw.len }
103 #[cfg(not(bootstrap))]
105 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
106 // As of this writing this causes a "Const-stable functions can only call other
107 // const-stable functions" error.
109 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
110 // and PtrComponents<T> have the same memory layouts. Only std can make this
112 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
116 /// Returns `true` if the slice has a length of 0.
121 /// let a = [1, 2, 3];
122 /// assert!(!a.is_empty());
124 #[stable(feature = "rust1", since = "1.0.0")]
125 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.32.0")]
127 pub const fn is_empty(&self) -> bool {
131 /// Returns the first element of the slice, or `None` if it is empty.
136 /// let v = [10, 40, 30];
137 /// assert_eq!(Some(&10), v.first());
139 /// let w: &[i32] = &[];
140 /// assert_eq!(None, w.first());
142 #[stable(feature = "rust1", since = "1.0.0")]
144 pub fn first(&self) -> Option<&T> {
145 if let [first, ..] = self { Some(first) } else { None }
148 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
153 /// let x = &mut [0, 1, 2];
155 /// if let Some(first) = x.first_mut() {
158 /// assert_eq!(x, &[5, 1, 2]);
160 #[stable(feature = "rust1", since = "1.0.0")]
162 pub fn first_mut(&mut self) -> Option<&mut T> {
163 if let [first, ..] = self { Some(first) } else { None }
166 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
171 /// let x = &[0, 1, 2];
173 /// if let Some((first, elements)) = x.split_first() {
174 /// assert_eq!(first, &0);
175 /// assert_eq!(elements, &[1, 2]);
178 #[stable(feature = "slice_splits", since = "1.5.0")]
180 pub fn split_first(&self) -> Option<(&T, &[T])> {
181 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
184 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
189 /// let x = &mut [0, 1, 2];
191 /// if let Some((first, elements)) = x.split_first_mut() {
196 /// assert_eq!(x, &[3, 4, 5]);
198 #[stable(feature = "slice_splits", since = "1.5.0")]
200 pub 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")]
218 pub fn split_last(&self) -> Option<(&T, &[T])> {
219 if let [init @ .., last] = self { Some((last, init)) } else { None }
222 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
227 /// let x = &mut [0, 1, 2];
229 /// if let Some((last, elements)) = x.split_last_mut() {
234 /// assert_eq!(x, &[4, 5, 3]);
236 #[stable(feature = "slice_splits", since = "1.5.0")]
238 pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
239 if let [init @ .., last] = self { Some((last, init)) } else { None }
242 /// Returns the last element of the slice, or `None` if it is empty.
247 /// let v = [10, 40, 30];
248 /// assert_eq!(Some(&30), v.last());
250 /// let w: &[i32] = &[];
251 /// assert_eq!(None, w.last());
253 #[stable(feature = "rust1", since = "1.0.0")]
255 pub fn last(&self) -> Option<&T> {
256 if let [.., last] = self { Some(last) } else { None }
259 /// Returns a mutable pointer to the last item in the slice.
264 /// let x = &mut [0, 1, 2];
266 /// if let Some(last) = x.last_mut() {
269 /// assert_eq!(x, &[0, 1, 10]);
271 #[stable(feature = "rust1", since = "1.0.0")]
273 pub fn last_mut(&mut self) -> Option<&mut T> {
274 if let [.., last] = self { Some(last) } else { None }
277 /// Returns a reference to an element or subslice depending on the type of
280 /// - If given a position, returns a reference to the element at that
281 /// position or `None` if out of bounds.
282 /// - If given a range, returns the subslice corresponding to that range,
283 /// or `None` if out of bounds.
288 /// let v = [10, 40, 30];
289 /// assert_eq!(Some(&40), v.get(1));
290 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
291 /// assert_eq!(None, v.get(3));
292 /// assert_eq!(None, v.get(0..4));
294 #[stable(feature = "rust1", since = "1.0.0")]
296 pub fn get<I>(&self, index: I) -> Option<&I::Output>
303 /// Returns a mutable reference to an element or subslice depending on the
304 /// type of index (see [`get`]) or `None` if the index is out of bounds.
306 /// [`get`]: #method.get
311 /// let x = &mut [0, 1, 2];
313 /// if let Some(elem) = x.get_mut(1) {
316 /// assert_eq!(x, &[0, 42, 2]);
318 #[stable(feature = "rust1", since = "1.0.0")]
320 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
327 /// Returns a reference to an element or subslice, without doing bounds
330 /// For a safe alternative see [`get`].
334 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
335 /// even if the resulting reference is not used.
337 /// [`get`]: #method.get
338 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
343 /// let x = &[1, 2, 4];
346 /// assert_eq!(x.get_unchecked(1), &2);
349 #[stable(feature = "rust1", since = "1.0.0")]
351 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
355 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
356 // the slice is dereferencable because `self` is a safe reference.
357 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
358 unsafe { &*index.get_unchecked(self) }
361 /// Returns a mutable reference to an element or subslice, without doing
364 /// For a safe alternative see [`get_mut`].
368 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
369 /// even if the resulting reference is not used.
371 /// [`get_mut`]: #method.get_mut
372 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
377 /// let x = &mut [1, 2, 4];
380 /// let elem = x.get_unchecked_mut(1);
383 /// assert_eq!(x, &[1, 13, 4]);
385 #[stable(feature = "rust1", since = "1.0.0")]
387 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
391 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
392 // the slice is dereferencable because `self` is a safe reference.
393 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
394 unsafe { &mut *index.get_unchecked_mut(self) }
397 /// Returns a raw pointer to the slice's buffer.
399 /// The caller must ensure that the slice outlives the pointer this
400 /// function returns, or else it will end up pointing to garbage.
402 /// The caller must also ensure that the memory the pointer (non-transitively) points to
403 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
404 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
406 /// Modifying the container referenced by this slice may cause its buffer
407 /// to be reallocated, which would also make any pointers to it invalid.
412 /// let x = &[1, 2, 4];
413 /// let x_ptr = x.as_ptr();
416 /// for i in 0..x.len() {
417 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
422 /// [`as_mut_ptr`]: #method.as_mut_ptr
423 #[stable(feature = "rust1", since = "1.0.0")]
424 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
426 pub const fn as_ptr(&self) -> *const T {
427 self as *const [T] as *const T
430 /// Returns an unsafe mutable pointer to the slice's buffer.
432 /// The caller must ensure that the slice outlives the pointer this
433 /// function returns, or else it will end up pointing to garbage.
435 /// Modifying the container referenced by this slice may cause its buffer
436 /// to be reallocated, which would also make any pointers to it invalid.
441 /// let x = &mut [1, 2, 4];
442 /// let x_ptr = x.as_mut_ptr();
445 /// for i in 0..x.len() {
446 /// *x_ptr.add(i) += 2;
449 /// assert_eq!(x, &[3, 4, 6]);
451 #[stable(feature = "rust1", since = "1.0.0")]
452 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
454 pub const fn as_mut_ptr(&mut self) -> *mut T {
455 self as *mut [T] as *mut T
458 /// Returns the two raw pointers spanning the slice.
460 /// The returned range is half-open, which means that the end pointer
461 /// points *one past* the last element of the slice. This way, an empty
462 /// slice is represented by two equal pointers, and the difference between
463 /// the two pointers represents the size of the slice.
465 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
466 /// requires extra caution, as it does not point to a valid element in the
469 /// This function is useful for interacting with foreign interfaces which
470 /// use two pointers to refer to a range of elements in memory, as is
473 /// It can also be useful to check if a pointer to an element refers to an
474 /// element of this slice:
477 /// let a = [1, 2, 3];
478 /// let x = &a[1] as *const _;
479 /// let y = &5 as *const _;
481 /// assert!(a.as_ptr_range().contains(&x));
482 /// assert!(!a.as_ptr_range().contains(&y));
485 /// [`as_ptr`]: #method.as_ptr
486 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
487 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
489 pub const fn as_ptr_range(&self) -> Range<*const T> {
490 let start = self.as_ptr();
491 // SAFETY: The `add` here is safe, because:
493 // - Both pointers are part of the same object, as pointing directly
494 // past the object also counts.
496 // - The size of the slice is never larger than isize::MAX bytes, as
498 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
499 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
500 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
501 // (This doesn't seem normative yet, but the very same assumption is
502 // made in many places, including the Index implementation of slices.)
504 // - There is no wrapping around involved, as slices do not wrap past
505 // the end of the address space.
507 // See the documentation of pointer::add.
508 let end = unsafe { start.add(self.len()) };
512 /// Returns the two unsafe mutable pointers spanning the slice.
514 /// The returned range is half-open, which means that the end pointer
515 /// points *one past* the last element of the slice. This way, an empty
516 /// slice is represented by two equal pointers, and the difference between
517 /// the two pointers represents the size of the slice.
519 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
520 /// pointer requires extra caution, as it does not point to a valid element
523 /// This function is useful for interacting with foreign interfaces which
524 /// use two pointers to refer to a range of elements in memory, as is
527 /// [`as_mut_ptr`]: #method.as_mut_ptr
528 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
529 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
531 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
532 let start = self.as_mut_ptr();
533 // SAFETY: See as_ptr_range() above for why `add` here is safe.
534 let end = unsafe { start.add(self.len()) };
538 /// Swaps two elements in the slice.
542 /// * a - The index of the first element
543 /// * b - The index of the second element
547 /// Panics if `a` or `b` are out of bounds.
552 /// let mut v = ["a", "b", "c", "d"];
554 /// assert!(v == ["a", "d", "c", "b"]);
556 #[stable(feature = "rust1", since = "1.0.0")]
558 pub fn swap(&mut self, a: usize, b: usize) {
559 // Can't take two mutable loans from one vector, so instead use raw pointers.
560 let pa = ptr::addr_of_mut!(self[a]);
561 let pb = ptr::addr_of_mut!(self[b]);
562 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
563 // to elements in the slice and therefore are guaranteed to be valid and aligned.
564 // Note that accessing the elements behind `a` and `b` is checked and will
565 // panic when out of bounds.
571 /// Reverses the order of elements in the slice, in place.
576 /// let mut v = [1, 2, 3];
578 /// assert!(v == [3, 2, 1]);
580 #[stable(feature = "rust1", since = "1.0.0")]
582 pub fn reverse(&mut self) {
583 let mut i: usize = 0;
586 // For very small types, all the individual reads in the normal
587 // path perform poorly. We can do better, given efficient unaligned
588 // load/store, by loading a larger chunk and reversing a register.
590 // Ideally LLVM would do this for us, as it knows better than we do
591 // whether unaligned reads are efficient (since that changes between
592 // different ARM versions, for example) and what the best chunk size
593 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
594 // the loop, so we need to do this ourselves. (Hypothesis: reverse
595 // is troublesome because the sides can be aligned differently --
596 // will be, when the length is odd -- so there's no way of emitting
597 // pre- and postludes to use fully-aligned SIMD in the middle.)
599 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
601 if fast_unaligned && mem::size_of::<T>() == 1 {
602 // Use the llvm.bswap intrinsic to reverse u8s in a usize
603 let chunk = mem::size_of::<usize>();
604 while i + chunk - 1 < ln / 2 {
605 // SAFETY: There are several things to check here:
607 // - Note that `chunk` is either 4 or 8 due to the cfg check
608 // above. So `chunk - 1` is positive.
609 // - Indexing with index `i` is fine as the loop check guarantees
610 // `i + chunk - 1 < ln / 2`
611 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
612 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
613 // - `i + chunk > 0` is trivially true.
614 // - The loop check guarantees:
615 // `i + chunk - 1 < ln / 2`
616 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
617 // - The `read_unaligned` and `write_unaligned` calls are fine:
618 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
619 // (see above) and `pb` points to index `ln - i - chunk`, so
620 // both are at least `chunk`
621 // many bytes away from the end of `self`.
622 // - Any initialized memory is valid `usize`.
624 let ptr = self.as_mut_ptr();
626 let pb = ptr.add(ln - i - chunk);
627 let va = ptr::read_unaligned(pa as *mut usize);
628 let vb = ptr::read_unaligned(pb as *mut usize);
629 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
630 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
636 if fast_unaligned && mem::size_of::<T>() == 2 {
637 // Use rotate-by-16 to reverse u16s in a u32
638 let chunk = mem::size_of::<u32>() / 2;
639 while i + chunk - 1 < ln / 2 {
640 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
641 // (and obviously `i < ln`), because each element is 2 bytes and
644 // `i + chunk - 1 < ln / 2` # while condition
645 // `i + 2 - 1 < ln / 2`
648 // Since it's less than the length divided by 2, then it must be
651 // This also means that the condition `0 < i + chunk <= ln` is
652 // always respected, ensuring the `pb` pointer can be used
655 let ptr = self.as_mut_ptr();
657 let pb = ptr.add(ln - i - chunk);
658 let va = ptr::read_unaligned(pa as *mut u32);
659 let vb = ptr::read_unaligned(pb as *mut u32);
660 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
661 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
668 // SAFETY: `i` is inferior to half the length of the slice so
669 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
670 // will not go further than `ln / 2 - 1`).
671 // The resulting pointers `pa` and `pb` are therefore valid and
672 // aligned, and can be read from and written to.
674 // Unsafe swap to avoid the bounds check in safe swap.
675 let ptr = self.as_mut_ptr();
677 let pb = ptr.add(ln - i - 1);
684 /// Returns an iterator over the slice.
689 /// let x = &[1, 2, 4];
690 /// let mut iterator = x.iter();
692 /// assert_eq!(iterator.next(), Some(&1));
693 /// assert_eq!(iterator.next(), Some(&2));
694 /// assert_eq!(iterator.next(), Some(&4));
695 /// assert_eq!(iterator.next(), None);
697 #[stable(feature = "rust1", since = "1.0.0")]
699 pub fn iter(&self) -> Iter<'_, T> {
703 /// Returns an iterator that allows modifying each value.
708 /// let x = &mut [1, 2, 4];
709 /// for elem in x.iter_mut() {
712 /// assert_eq!(x, &[3, 4, 6]);
714 #[stable(feature = "rust1", since = "1.0.0")]
716 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
720 /// Returns an iterator over all contiguous windows of length
721 /// `size`. The windows overlap. If the slice is shorter than
722 /// `size`, the iterator returns no values.
726 /// Panics if `size` is 0.
731 /// let slice = ['r', 'u', 's', 't'];
732 /// let mut iter = slice.windows(2);
733 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
734 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
735 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
736 /// assert!(iter.next().is_none());
739 /// If the slice is shorter than `size`:
742 /// let slice = ['f', 'o', 'o'];
743 /// let mut iter = slice.windows(4);
744 /// assert!(iter.next().is_none());
746 #[stable(feature = "rust1", since = "1.0.0")]
748 pub fn windows(&self, size: usize) -> Windows<'_, T> {
749 let size = NonZeroUsize::new(size).expect("size is zero");
750 Windows::new(self, size)
753 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
754 /// beginning of the slice.
756 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
757 /// slice, then the last chunk will not have length `chunk_size`.
759 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
760 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
765 /// Panics if `chunk_size` is 0.
770 /// let slice = ['l', 'o', 'r', 'e', 'm'];
771 /// let mut iter = slice.chunks(2);
772 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
773 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
774 /// assert_eq!(iter.next().unwrap(), &['m']);
775 /// assert!(iter.next().is_none());
778 /// [`chunks_exact`]: #method.chunks_exact
779 /// [`rchunks`]: #method.rchunks
780 #[stable(feature = "rust1", since = "1.0.0")]
782 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
783 assert_ne!(chunk_size, 0);
784 Chunks::new(self, chunk_size)
787 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
788 /// beginning of the slice.
790 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
791 /// length of the slice, then the last chunk will not have length `chunk_size`.
793 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
794 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
795 /// the end of the slice.
799 /// Panics if `chunk_size` is 0.
804 /// let v = &mut [0, 0, 0, 0, 0];
805 /// let mut count = 1;
807 /// for chunk in v.chunks_mut(2) {
808 /// for elem in chunk.iter_mut() {
813 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
816 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
817 /// [`rchunks_mut`]: #method.rchunks_mut
818 #[stable(feature = "rust1", since = "1.0.0")]
820 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
821 assert_ne!(chunk_size, 0);
822 ChunksMut::new(self, chunk_size)
825 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
826 /// beginning of the slice.
828 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
829 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
830 /// from the `remainder` function of the iterator.
832 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
833 /// resulting code better than in the case of [`chunks`].
835 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
836 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
840 /// Panics if `chunk_size` is 0.
845 /// let slice = ['l', 'o', 'r', 'e', 'm'];
846 /// let mut iter = slice.chunks_exact(2);
847 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
848 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
849 /// assert!(iter.next().is_none());
850 /// assert_eq!(iter.remainder(), &['m']);
853 /// [`chunks`]: #method.chunks
854 /// [`rchunks_exact`]: #method.rchunks_exact
855 #[stable(feature = "chunks_exact", since = "1.31.0")]
857 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
858 assert_ne!(chunk_size, 0);
859 ChunksExact::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 mutable slices, and do not overlap. If `chunk_size` does not divide the
866 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
867 /// retrieved from the `into_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_mut`].
872 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
873 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
878 /// Panics if `chunk_size` is 0.
883 /// let v = &mut [0, 0, 0, 0, 0];
884 /// let mut count = 1;
886 /// for chunk in v.chunks_exact_mut(2) {
887 /// for elem in chunk.iter_mut() {
892 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
895 /// [`chunks_mut`]: #method.chunks_mut
896 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
897 #[stable(feature = "chunks_exact", since = "1.31.0")]
899 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
900 assert_ne!(chunk_size, 0);
901 ChunksExactMut::new(self, chunk_size)
904 /// Splits the slice into a slice of `N`-element arrays,
905 /// assuming that there's no remainder.
909 /// This may only be called when
910 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
916 /// #![feature(slice_as_chunks)]
917 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
918 /// let chunks: &[[char; 1]] =
919 /// // SAFETY: 1-element chunks never have remainder
920 /// unsafe { slice.as_chunks_unchecked() };
921 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
922 /// let chunks: &[[char; 3]] =
923 /// // SAFETY: The slice length (6) is a multiple of 3
924 /// unsafe { slice.as_chunks_unchecked() };
925 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
927 /// // These would be unsound:
928 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
929 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
931 #[unstable(feature = "slice_as_chunks", issue = "74985")]
933 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
934 debug_assert_ne!(N, 0);
935 debug_assert_eq!(self.len() % N, 0);
937 // SAFETY: Our precondition is exactly what's needed to call this
938 unsafe { crate::intrinsics::exact_div(self.len(), N) };
939 // SAFETY: We cast a slice of `new_len * N` elements into
940 // a slice of `new_len` many `N` elements chunks.
941 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
944 /// Splits the slice into a slice of `N`-element arrays,
945 /// starting at the beginning of the slice,
946 /// and a remainder slice with length strictly less than `N`.
950 /// Panics if `N` is 0. This check will most probably get changed to a compile time
951 /// error before this method gets stabilized.
956 /// #![feature(slice_as_chunks)]
957 /// let slice = ['l', 'o', 'r', 'e', 'm'];
958 /// let (chunks, remainder) = slice.as_chunks();
959 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
960 /// assert_eq!(remainder, &['m']);
962 #[unstable(feature = "slice_as_chunks", issue = "74985")]
964 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
966 let len = self.len() / N;
967 let (multiple_of_n, remainder) = self.split_at(len * N);
968 // SAFETY: We already panicked for zero, and ensured by construction
969 // that the length of the subslice is a multiple of N.
970 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
971 (array_slice, remainder)
974 /// Splits the slice into a slice of `N`-element arrays,
975 /// starting at the end of the slice,
976 /// and a remainder slice with length strictly less than `N`.
980 /// Panics if `N` is 0. This check will most probably get changed to a compile time
981 /// error before this method gets stabilized.
986 /// #![feature(slice_as_chunks)]
987 /// let slice = ['l', 'o', 'r', 'e', 'm'];
988 /// let (remainder, chunks) = slice.as_rchunks();
989 /// assert_eq!(remainder, &['l']);
990 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
992 #[unstable(feature = "slice_as_chunks", issue = "74985")]
994 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
996 let len = self.len() / N;
997 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
998 // SAFETY: We already panicked for zero, and ensured by construction
999 // that the length of the subslice is a multiple of N.
1000 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1001 (remainder, array_slice)
1004 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1005 /// beginning of the slice.
1007 /// The chunks are array references and do not overlap. If `N` does not divide the
1008 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1009 /// retrieved from the `remainder` function of the iterator.
1011 /// This method is the const generic equivalent of [`chunks_exact`].
1015 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1016 /// error before this method gets stabilized.
1021 /// #![feature(array_chunks)]
1022 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1023 /// let mut iter = slice.array_chunks();
1024 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1025 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1026 /// assert!(iter.next().is_none());
1027 /// assert_eq!(iter.remainder(), &['m']);
1030 /// [`chunks_exact`]: #method.chunks_exact
1031 #[unstable(feature = "array_chunks", issue = "74985")]
1033 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1035 ArrayChunks::new(self)
1038 /// Splits the slice into a slice of `N`-element arrays,
1039 /// assuming that there's no remainder.
1043 /// This may only be called when
1044 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1050 /// #![feature(slice_as_chunks)]
1051 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1052 /// let chunks: &mut [[char; 1]] =
1053 /// // SAFETY: 1-element chunks never have remainder
1054 /// unsafe { slice.as_chunks_unchecked_mut() };
1055 /// chunks[0] = ['L'];
1056 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1057 /// let chunks: &mut [[char; 3]] =
1058 /// // SAFETY: The slice length (6) is a multiple of 3
1059 /// unsafe { slice.as_chunks_unchecked_mut() };
1060 /// chunks[1] = ['a', 'x', '?'];
1061 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1063 /// // These would be unsound:
1064 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1065 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1067 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1069 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1070 debug_assert_ne!(N, 0);
1071 debug_assert_eq!(self.len() % N, 0);
1073 // SAFETY: Our precondition is exactly what's needed to call this
1074 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1075 // SAFETY: We cast a slice of `new_len * N` elements into
1076 // a slice of `new_len` many `N` elements chunks.
1077 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1080 /// Splits the slice into a slice of `N`-element arrays,
1081 /// starting at the beginning of the slice,
1082 /// and a remainder slice with length strictly less than `N`.
1086 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1087 /// error before this method gets stabilized.
1092 /// #![feature(slice_as_chunks)]
1093 /// let v = &mut [0, 0, 0, 0, 0];
1094 /// let mut count = 1;
1096 /// let (chunks, remainder) = v.as_chunks_mut();
1097 /// remainder[0] = 9;
1098 /// for chunk in chunks {
1099 /// *chunk = [count; 2];
1102 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1104 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1106 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1108 let len = self.len() / N;
1109 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1110 // SAFETY: We already panicked for zero, and ensured by construction
1111 // that the length of the subslice is a multiple of N.
1112 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1113 (array_slice, remainder)
1116 /// Splits the slice into a slice of `N`-element arrays,
1117 /// starting at the end of the slice,
1118 /// and a remainder slice with length strictly less than `N`.
1122 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1123 /// error before this method gets stabilized.
1128 /// #![feature(slice_as_chunks)]
1129 /// let v = &mut [0, 0, 0, 0, 0];
1130 /// let mut count = 1;
1132 /// let (remainder, chunks) = v.as_rchunks_mut();
1133 /// remainder[0] = 9;
1134 /// for chunk in chunks {
1135 /// *chunk = [count; 2];
1138 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1140 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1142 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1144 let len = self.len() / N;
1145 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1146 // SAFETY: We already panicked for zero, and ensured by construction
1147 // that the length of the subslice is a multiple of N.
1148 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1149 (remainder, array_slice)
1152 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1153 /// beginning of the slice.
1155 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1156 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1157 /// can be retrieved from the `into_remainder` function of the iterator.
1159 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1163 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1164 /// error before this method gets stabilized.
1169 /// #![feature(array_chunks)]
1170 /// let v = &mut [0, 0, 0, 0, 0];
1171 /// let mut count = 1;
1173 /// for chunk in v.array_chunks_mut() {
1174 /// *chunk = [count; 2];
1177 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1180 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1181 #[unstable(feature = "array_chunks", issue = "74985")]
1183 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1185 ArrayChunksMut::new(self)
1188 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1189 /// starting at the beginning of the slice.
1191 /// This is the const generic equivalent of [`windows`].
1193 /// If `N` is greater than the size of the slice, it will return no windows.
1197 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1198 /// error before this method gets stabilized.
1203 /// #![feature(array_windows)]
1204 /// let slice = [0, 1, 2, 3];
1205 /// let mut iter = slice.array_windows();
1206 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1207 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1208 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1209 /// assert!(iter.next().is_none());
1212 /// [`windows`]: #method.windows
1213 #[unstable(feature = "array_windows", issue = "75027")]
1215 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1217 ArrayWindows::new(self)
1220 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1223 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1224 /// slice, then the last chunk will not have length `chunk_size`.
1226 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1227 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1232 /// Panics if `chunk_size` is 0.
1237 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1238 /// let mut iter = slice.rchunks(2);
1239 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1240 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1241 /// assert_eq!(iter.next().unwrap(), &['l']);
1242 /// assert!(iter.next().is_none());
1245 /// [`rchunks_exact`]: #method.rchunks_exact
1246 /// [`chunks`]: #method.chunks
1247 #[stable(feature = "rchunks", since = "1.31.0")]
1249 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1250 assert!(chunk_size != 0);
1251 RChunks::new(self, chunk_size)
1254 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1257 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1258 /// length of the slice, then the last chunk will not have length `chunk_size`.
1260 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1261 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1262 /// beginning of the slice.
1266 /// Panics if `chunk_size` is 0.
1271 /// let v = &mut [0, 0, 0, 0, 0];
1272 /// let mut count = 1;
1274 /// for chunk in v.rchunks_mut(2) {
1275 /// for elem in chunk.iter_mut() {
1280 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1283 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
1284 /// [`chunks_mut`]: #method.chunks_mut
1285 #[stable(feature = "rchunks", since = "1.31.0")]
1287 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1288 assert!(chunk_size != 0);
1289 RChunksMut::new(self, chunk_size)
1292 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1293 /// end of the slice.
1295 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1296 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1297 /// from the `remainder` function of the iterator.
1299 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1300 /// resulting code better than in the case of [`chunks`].
1302 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1303 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1308 /// Panics if `chunk_size` is 0.
1313 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1314 /// let mut iter = slice.rchunks_exact(2);
1315 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1316 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1317 /// assert!(iter.next().is_none());
1318 /// assert_eq!(iter.remainder(), &['l']);
1321 /// [`chunks`]: #method.chunks
1322 /// [`rchunks`]: #method.rchunks
1323 /// [`chunks_exact`]: #method.chunks_exact
1324 #[stable(feature = "rchunks", since = "1.31.0")]
1326 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1327 assert!(chunk_size != 0);
1328 RChunksExact::new(self, chunk_size)
1331 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1334 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1335 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1336 /// retrieved from the `into_remainder` function of the iterator.
1338 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1339 /// resulting code better than in the case of [`chunks_mut`].
1341 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1342 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1347 /// Panics if `chunk_size` is 0.
1352 /// let v = &mut [0, 0, 0, 0, 0];
1353 /// let mut count = 1;
1355 /// for chunk in v.rchunks_exact_mut(2) {
1356 /// for elem in chunk.iter_mut() {
1361 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1364 /// [`chunks_mut`]: #method.chunks_mut
1365 /// [`rchunks_mut`]: #method.rchunks_mut
1366 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1367 #[stable(feature = "rchunks", since = "1.31.0")]
1369 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1370 assert!(chunk_size != 0);
1371 RChunksExactMut::new(self, chunk_size)
1374 /// Returns an iterator over the slice producing non-overlapping runs
1375 /// of elements using the predicate to separate them.
1377 /// The predicate is called on two elements following themselves,
1378 /// it means the predicate is called on `slice[0]` and `slice[1]`
1379 /// then on `slice[1]` and `slice[2]` and so on.
1384 /// #![feature(slice_group_by)]
1386 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1388 /// let mut iter = slice.group_by(|a, b| a == b);
1390 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1391 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1392 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1393 /// assert_eq!(iter.next(), None);
1396 /// This method can be used to extract the sorted subslices:
1399 /// #![feature(slice_group_by)]
1401 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1403 /// let mut iter = slice.group_by(|a, b| a <= b);
1405 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1406 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1407 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1408 /// assert_eq!(iter.next(), None);
1410 #[unstable(feature = "slice_group_by", issue = "80552")]
1412 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1414 F: FnMut(&T, &T) -> bool,
1416 GroupBy::new(self, pred)
1419 /// Returns an iterator over the slice producing non-overlapping mutable
1420 /// runs of elements using the predicate to separate them.
1422 /// The predicate is called on two elements following themselves,
1423 /// it means the predicate is called on `slice[0]` and `slice[1]`
1424 /// then on `slice[1]` and `slice[2]` and so on.
1429 /// #![feature(slice_group_by)]
1431 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1433 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1435 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1436 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1437 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1438 /// assert_eq!(iter.next(), None);
1441 /// This method can be used to extract the sorted subslices:
1444 /// #![feature(slice_group_by)]
1446 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1448 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1450 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1451 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1452 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1453 /// assert_eq!(iter.next(), None);
1455 #[unstable(feature = "slice_group_by", issue = "80552")]
1457 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1459 F: FnMut(&T, &T) -> bool,
1461 GroupByMut::new(self, pred)
1464 /// Divides one slice into two at an index.
1466 /// The first will contain all indices from `[0, mid)` (excluding
1467 /// the index `mid` itself) and the second will contain all
1468 /// indices from `[mid, len)` (excluding the index `len` itself).
1472 /// Panics if `mid > len`.
1477 /// let v = [1, 2, 3, 4, 5, 6];
1480 /// let (left, right) = v.split_at(0);
1481 /// assert_eq!(left, []);
1482 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1486 /// let (left, right) = v.split_at(2);
1487 /// assert_eq!(left, [1, 2]);
1488 /// assert_eq!(right, [3, 4, 5, 6]);
1492 /// let (left, right) = v.split_at(6);
1493 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1494 /// assert_eq!(right, []);
1497 #[stable(feature = "rust1", since = "1.0.0")]
1499 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1500 assert!(mid <= self.len());
1501 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1502 // fulfills the requirements of `from_raw_parts_mut`.
1503 unsafe { self.split_at_unchecked(mid) }
1506 /// Divides one mutable slice into two at an index.
1508 /// The first will contain all indices from `[0, mid)` (excluding
1509 /// the index `mid` itself) and the second will contain all
1510 /// indices from `[mid, len)` (excluding the index `len` itself).
1514 /// Panics if `mid > len`.
1519 /// let mut v = [1, 0, 3, 0, 5, 6];
1520 /// let (left, right) = v.split_at_mut(2);
1521 /// assert_eq!(left, [1, 0]);
1522 /// assert_eq!(right, [3, 0, 5, 6]);
1525 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1527 #[stable(feature = "rust1", since = "1.0.0")]
1529 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1530 assert!(mid <= self.len());
1531 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1532 // fulfills the requirements of `from_raw_parts_mut`.
1533 unsafe { self.split_at_mut_unchecked(mid) }
1536 /// Divides one slice into two at an index, without doing bounds checking.
1538 /// The first will contain all indices from `[0, mid)` (excluding
1539 /// the index `mid` itself) and the second will contain all
1540 /// indices from `[mid, len)` (excluding the index `len` itself).
1542 /// For a safe alternative see [`split_at`].
1546 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1547 /// even if the resulting reference is not used. The caller has to ensure that
1548 /// `0 <= mid <= self.len()`.
1550 /// [`split_at`]: #method.split_at
1551 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1556 /// #![feature(slice_split_at_unchecked)]
1558 /// let v = [1, 2, 3, 4, 5, 6];
1561 /// let (left, right) = v.split_at_unchecked(0);
1562 /// assert_eq!(left, []);
1563 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1567 /// let (left, right) = v.split_at_unchecked(2);
1568 /// assert_eq!(left, [1, 2]);
1569 /// assert_eq!(right, [3, 4, 5, 6]);
1573 /// let (left, right) = v.split_at_unchecked(6);
1574 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1575 /// assert_eq!(right, []);
1578 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1580 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1581 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1582 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1585 /// Divides one mutable slice into two at an index, without doing bounds checking.
1587 /// The first will contain all indices from `[0, mid)` (excluding
1588 /// the index `mid` itself) and the second will contain all
1589 /// indices from `[mid, len)` (excluding the index `len` itself).
1591 /// For a safe alternative see [`split_at_mut`].
1595 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1596 /// even if the resulting reference is not used. The caller has to ensure that
1597 /// `0 <= mid <= self.len()`.
1599 /// [`split_at_mut`]: #method.split_at_mut
1600 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1605 /// #![feature(slice_split_at_unchecked)]
1607 /// let mut v = [1, 0, 3, 0, 5, 6];
1608 /// // scoped to restrict the lifetime of the borrows
1610 /// let (left, right) = v.split_at_mut_unchecked(2);
1611 /// assert_eq!(left, [1, 0]);
1612 /// assert_eq!(right, [3, 0, 5, 6]);
1616 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1618 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1620 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1621 let len = self.len();
1622 let ptr = self.as_mut_ptr();
1624 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1626 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1628 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1631 /// Returns an iterator over subslices separated by elements that match
1632 /// `pred`. The matched element is not contained in the subslices.
1637 /// let slice = [10, 40, 33, 20];
1638 /// let mut iter = slice.split(|num| num % 3 == 0);
1640 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1641 /// assert_eq!(iter.next().unwrap(), &[20]);
1642 /// assert!(iter.next().is_none());
1645 /// If the first element is matched, an empty slice will be the first item
1646 /// returned by the iterator. Similarly, if the last element in the slice
1647 /// is matched, an empty slice will be the last item returned by the
1651 /// let slice = [10, 40, 33];
1652 /// let mut iter = slice.split(|num| num % 3 == 0);
1654 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1655 /// assert_eq!(iter.next().unwrap(), &[]);
1656 /// assert!(iter.next().is_none());
1659 /// If two matched elements are directly adjacent, an empty slice will be
1660 /// present between them:
1663 /// let slice = [10, 6, 33, 20];
1664 /// let mut iter = slice.split(|num| num % 3 == 0);
1666 /// assert_eq!(iter.next().unwrap(), &[10]);
1667 /// assert_eq!(iter.next().unwrap(), &[]);
1668 /// assert_eq!(iter.next().unwrap(), &[20]);
1669 /// assert!(iter.next().is_none());
1671 #[stable(feature = "rust1", since = "1.0.0")]
1673 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1675 F: FnMut(&T) -> bool,
1677 Split::new(self, pred)
1680 /// Returns an iterator over mutable subslices separated by elements that
1681 /// match `pred`. The matched element is not contained in the subslices.
1686 /// let mut v = [10, 40, 30, 20, 60, 50];
1688 /// for group in v.split_mut(|num| *num % 3 == 0) {
1691 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1693 #[stable(feature = "rust1", since = "1.0.0")]
1695 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1697 F: FnMut(&T) -> bool,
1699 SplitMut::new(self, pred)
1702 /// Returns an iterator over subslices separated by elements that match
1703 /// `pred`. The matched element is contained in the end of the previous
1704 /// subslice as a terminator.
1709 /// let slice = [10, 40, 33, 20];
1710 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1712 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1713 /// assert_eq!(iter.next().unwrap(), &[20]);
1714 /// assert!(iter.next().is_none());
1717 /// If the last element of the slice is matched,
1718 /// that element will be considered the terminator of the preceding slice.
1719 /// That slice will be the last item returned by the iterator.
1722 /// let slice = [3, 10, 40, 33];
1723 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1725 /// assert_eq!(iter.next().unwrap(), &[3]);
1726 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1727 /// assert!(iter.next().is_none());
1729 #[stable(feature = "split_inclusive", since = "1.51.0")]
1731 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1733 F: FnMut(&T) -> bool,
1735 SplitInclusive::new(self, pred)
1738 /// Returns an iterator over mutable subslices separated by elements that
1739 /// match `pred`. The matched element is contained in the previous
1740 /// subslice as a terminator.
1745 /// let mut v = [10, 40, 30, 20, 60, 50];
1747 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1748 /// let terminator_idx = group.len()-1;
1749 /// group[terminator_idx] = 1;
1751 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1753 #[stable(feature = "split_inclusive", since = "1.51.0")]
1755 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1757 F: FnMut(&T) -> bool,
1759 SplitInclusiveMut::new(self, pred)
1762 /// Returns an iterator over subslices separated by elements that match
1763 /// `pred`, starting at the end of the slice and working backwards.
1764 /// The matched element is not contained in the subslices.
1769 /// let slice = [11, 22, 33, 0, 44, 55];
1770 /// let mut iter = slice.rsplit(|num| *num == 0);
1772 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1773 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1774 /// assert_eq!(iter.next(), None);
1777 /// As with `split()`, if the first or last element is matched, an empty
1778 /// slice will be the first (or last) item returned by the iterator.
1781 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1782 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1783 /// assert_eq!(it.next().unwrap(), &[]);
1784 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1785 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1786 /// assert_eq!(it.next().unwrap(), &[]);
1787 /// assert_eq!(it.next(), None);
1789 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1791 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1793 F: FnMut(&T) -> bool,
1795 RSplit::new(self, pred)
1798 /// Returns an iterator over mutable subslices separated by elements that
1799 /// match `pred`, starting at the end of the slice and working
1800 /// backwards. The matched element is not contained in the subslices.
1805 /// let mut v = [100, 400, 300, 200, 600, 500];
1807 /// let mut count = 0;
1808 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1810 /// group[0] = count;
1812 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1815 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1817 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1819 F: FnMut(&T) -> bool,
1821 RSplitMut::new(self, pred)
1824 /// Returns an iterator over subslices separated by elements that match
1825 /// `pred`, limited to returning at most `n` items. The matched element is
1826 /// not contained in the subslices.
1828 /// The last element returned, if any, will contain the remainder of the
1833 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1834 /// `[20, 60, 50]`):
1837 /// let v = [10, 40, 30, 20, 60, 50];
1839 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1840 /// println!("{:?}", group);
1843 #[stable(feature = "rust1", since = "1.0.0")]
1845 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1847 F: FnMut(&T) -> bool,
1849 SplitN::new(self.split(pred), n)
1852 /// Returns an iterator over subslices separated by elements that match
1853 /// `pred`, limited to returning at most `n` items. The matched element is
1854 /// not contained in the subslices.
1856 /// The last element returned, if any, will contain the remainder of the
1862 /// let mut v = [10, 40, 30, 20, 60, 50];
1864 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1867 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1869 #[stable(feature = "rust1", since = "1.0.0")]
1871 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1873 F: FnMut(&T) -> bool,
1875 SplitNMut::new(self.split_mut(pred), n)
1878 /// Returns an iterator over subslices separated by elements that match
1879 /// `pred` limited to returning at most `n` items. This starts at the end of
1880 /// the slice and works backwards. The matched element is not contained in
1883 /// The last element returned, if any, will contain the remainder of the
1888 /// Print the slice split once, starting from the end, by numbers divisible
1889 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1892 /// let v = [10, 40, 30, 20, 60, 50];
1894 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1895 /// println!("{:?}", group);
1898 #[stable(feature = "rust1", since = "1.0.0")]
1900 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1902 F: FnMut(&T) -> bool,
1904 RSplitN::new(self.rsplit(pred), n)
1907 /// Returns an iterator over subslices separated by elements that match
1908 /// `pred` limited to returning at most `n` items. This starts at the end of
1909 /// the slice and works backwards. The matched element is not contained in
1912 /// The last element returned, if any, will contain the remainder of the
1918 /// let mut s = [10, 40, 30, 20, 60, 50];
1920 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1923 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1925 #[stable(feature = "rust1", since = "1.0.0")]
1927 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1929 F: FnMut(&T) -> bool,
1931 RSplitNMut::new(self.rsplit_mut(pred), n)
1934 /// Returns `true` if the slice contains an element with the given value.
1939 /// let v = [10, 40, 30];
1940 /// assert!(v.contains(&30));
1941 /// assert!(!v.contains(&50));
1944 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1945 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1948 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1949 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1950 /// assert!(!v.iter().any(|e| e == "hi"));
1952 #[stable(feature = "rust1", since = "1.0.0")]
1954 pub fn contains(&self, x: &T) -> bool
1958 cmp::SliceContains::slice_contains(x, self)
1961 /// Returns `true` if `needle` is a prefix of the slice.
1966 /// let v = [10, 40, 30];
1967 /// assert!(v.starts_with(&[10]));
1968 /// assert!(v.starts_with(&[10, 40]));
1969 /// assert!(!v.starts_with(&[50]));
1970 /// assert!(!v.starts_with(&[10, 50]));
1973 /// Always returns `true` if `needle` is an empty slice:
1976 /// let v = &[10, 40, 30];
1977 /// assert!(v.starts_with(&[]));
1978 /// let v: &[u8] = &[];
1979 /// assert!(v.starts_with(&[]));
1981 #[stable(feature = "rust1", since = "1.0.0")]
1982 pub fn starts_with(&self, needle: &[T]) -> bool
1986 let n = needle.len();
1987 self.len() >= n && needle == &self[..n]
1990 /// Returns `true` if `needle` is a suffix of the slice.
1995 /// let v = [10, 40, 30];
1996 /// assert!(v.ends_with(&[30]));
1997 /// assert!(v.ends_with(&[40, 30]));
1998 /// assert!(!v.ends_with(&[50]));
1999 /// assert!(!v.ends_with(&[50, 30]));
2002 /// Always returns `true` if `needle` is an empty slice:
2005 /// let v = &[10, 40, 30];
2006 /// assert!(v.ends_with(&[]));
2007 /// let v: &[u8] = &[];
2008 /// assert!(v.ends_with(&[]));
2010 #[stable(feature = "rust1", since = "1.0.0")]
2011 pub fn ends_with(&self, needle: &[T]) -> bool
2015 let (m, n) = (self.len(), needle.len());
2016 m >= n && needle == &self[m - n..]
2019 /// Returns a subslice with the prefix removed.
2021 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2022 /// If `prefix` is empty, simply returns the original slice.
2024 /// If the slice does not start with `prefix`, returns `None`.
2029 /// let v = &[10, 40, 30];
2030 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2031 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2032 /// assert_eq!(v.strip_prefix(&[50]), None);
2033 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2035 /// let prefix : &str = "he";
2036 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2037 /// Some(b"llo".as_ref()));
2039 #[must_use = "returns the subslice without modifying the original"]
2040 #[stable(feature = "slice_strip", since = "1.51.0")]
2041 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2045 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2046 let prefix = prefix.as_slice();
2047 let n = prefix.len();
2048 if n <= self.len() {
2049 let (head, tail) = self.split_at(n);
2057 /// Returns a subslice with the suffix removed.
2059 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2060 /// If `suffix` is empty, simply returns the original slice.
2062 /// If the slice does not end with `suffix`, returns `None`.
2067 /// let v = &[10, 40, 30];
2068 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2069 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2070 /// assert_eq!(v.strip_suffix(&[50]), None);
2071 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2073 #[must_use = "returns the subslice without modifying the original"]
2074 #[stable(feature = "slice_strip", since = "1.51.0")]
2075 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2079 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2080 let suffix = suffix.as_slice();
2081 let (len, n) = (self.len(), suffix.len());
2083 let (head, tail) = self.split_at(len - n);
2091 /// Binary searches this sorted slice for a given element.
2093 /// If the value is found then [`Result::Ok`] is returned, containing the
2094 /// index of the matching element. If there are multiple matches, then any
2095 /// one of the matches could be returned. If the value is not found then
2096 /// [`Result::Err`] is returned, containing the index where a matching
2097 /// element could be inserted while maintaining sorted order.
2099 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2101 /// [`binary_search_by`]: #method.binary_search_by
2102 /// [`binary_search_by_key`]: #method.binary_search_by_key
2103 /// [`partition_point`]: #method.partition_point
2107 /// Looks up a series of four elements. The first is found, with a
2108 /// uniquely determined position; the second and third are not
2109 /// found; the fourth could match any position in `[1, 4]`.
2112 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2114 /// assert_eq!(s.binary_search(&13), Ok(9));
2115 /// assert_eq!(s.binary_search(&4), Err(7));
2116 /// assert_eq!(s.binary_search(&100), Err(13));
2117 /// let r = s.binary_search(&1);
2118 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2121 /// If you want to insert an item to a sorted vector, while maintaining
2125 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2127 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2128 /// s.insert(idx, num);
2129 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2131 #[stable(feature = "rust1", since = "1.0.0")]
2132 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2136 self.binary_search_by(|p| p.cmp(x))
2139 /// Binary searches this sorted slice with a comparator function.
2141 /// The comparator function should implement an order consistent
2142 /// with the sort order of the underlying slice, returning an
2143 /// order code that indicates whether its argument is `Less`,
2144 /// `Equal` or `Greater` the desired target.
2146 /// If the value is found then [`Result::Ok`] is returned, containing the
2147 /// index of the matching element. If there are multiple matches, then any
2148 /// one of the matches could be returned. If the value is not found then
2149 /// [`Result::Err`] is returned, containing the index where a matching
2150 /// element could be inserted while maintaining sorted order.
2152 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2154 /// [`binary_search`]: #method.binary_search
2155 /// [`binary_search_by_key`]: #method.binary_search_by_key
2156 /// [`partition_point`]: #method.partition_point
2160 /// Looks up a series of four elements. The first is found, with a
2161 /// uniquely determined position; the second and third are not
2162 /// found; the fourth could match any position in `[1, 4]`.
2165 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2168 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2170 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2172 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2174 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2175 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2177 #[stable(feature = "rust1", since = "1.0.0")]
2179 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2181 F: FnMut(&'a T) -> Ordering,
2184 let mut size = s.len();
2188 let mut base = 0usize;
2190 let half = size / 2;
2191 let mid = base + half;
2192 // SAFETY: the call is made safe by the following inconstants:
2193 // - `mid >= 0`: by definition
2194 // - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
2195 let cmp = f(unsafe { s.get_unchecked(mid) });
2196 base = if cmp == Greater { base } else { mid };
2199 // SAFETY: base is always in [0, size) because base <= mid.
2200 let cmp = f(unsafe { s.get_unchecked(base) });
2201 if cmp == Equal { Ok(base) } else { Err(base + (cmp == Less) as usize) }
2204 /// Binary searches this sorted slice with a key extraction function.
2206 /// Assumes that the slice is sorted by the key, for instance with
2207 /// [`sort_by_key`] using the same key extraction function.
2209 /// If the value is found then [`Result::Ok`] is returned, containing the
2210 /// index of the matching element. If there are multiple matches, then any
2211 /// one of the matches could be returned. If the value is not found then
2212 /// [`Result::Err`] is returned, containing the index where a matching
2213 /// element could be inserted while maintaining sorted order.
2215 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2217 /// [`sort_by_key`]: #method.sort_by_key
2218 /// [`binary_search`]: #method.binary_search
2219 /// [`binary_search_by`]: #method.binary_search_by
2220 /// [`partition_point`]: #method.partition_point
2224 /// Looks up a series of four elements in a slice of pairs sorted by
2225 /// their second elements. The first is found, with a uniquely
2226 /// determined position; the second and third are not found; the
2227 /// fourth could match any position in `[1, 4]`.
2230 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2231 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2232 /// (1, 21), (2, 34), (4, 55)];
2234 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2235 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2236 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2237 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2238 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2240 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2242 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2244 F: FnMut(&'a T) -> B,
2247 self.binary_search_by(|k| f(k).cmp(b))
2250 /// Sorts the slice, but may not preserve the order of equal elements.
2252 /// This sort is unstable (i.e., may reorder equal elements), in-place
2253 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2255 /// # Current implementation
2257 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2258 /// which combines the fast average case of randomized quicksort with the fast worst case of
2259 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2260 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2261 /// deterministic behavior.
2263 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2264 /// slice consists of several concatenated sorted sequences.
2269 /// let mut v = [-5, 4, 1, -3, 2];
2271 /// v.sort_unstable();
2272 /// assert!(v == [-5, -3, 1, 2, 4]);
2275 /// [pdqsort]: https://github.com/orlp/pdqsort
2276 #[stable(feature = "sort_unstable", since = "1.20.0")]
2278 pub fn sort_unstable(&mut self)
2282 sort::quicksort(self, |a, b| a.lt(b));
2285 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2288 /// This sort is unstable (i.e., may reorder equal elements), in-place
2289 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2291 /// The comparator function must define a total ordering for the elements in the slice. If
2292 /// the ordering is not total, the order of the elements is unspecified. An order is a
2293 /// total order if it is (for all `a`, `b` and `c`):
2295 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2296 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2298 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2299 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2302 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2303 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2304 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2307 /// # Current implementation
2309 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2310 /// which combines the fast average case of randomized quicksort with the fast worst case of
2311 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2312 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2313 /// deterministic behavior.
2315 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2316 /// slice consists of several concatenated sorted sequences.
2321 /// let mut v = [5, 4, 1, 3, 2];
2322 /// v.sort_unstable_by(|a, b| a.cmp(b));
2323 /// assert!(v == [1, 2, 3, 4, 5]);
2325 /// // reverse sorting
2326 /// v.sort_unstable_by(|a, b| b.cmp(a));
2327 /// assert!(v == [5, 4, 3, 2, 1]);
2330 /// [pdqsort]: https://github.com/orlp/pdqsort
2331 #[stable(feature = "sort_unstable", since = "1.20.0")]
2333 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2335 F: FnMut(&T, &T) -> Ordering,
2337 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2340 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2343 /// This sort is unstable (i.e., may reorder equal elements), in-place
2344 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2347 /// # Current implementation
2349 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2350 /// which combines the fast average case of randomized quicksort with the fast worst case of
2351 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2352 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2353 /// deterministic behavior.
2355 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2356 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2357 /// cases where the key function is expensive.
2362 /// let mut v = [-5i32, 4, 1, -3, 2];
2364 /// v.sort_unstable_by_key(|k| k.abs());
2365 /// assert!(v == [1, 2, -3, 4, -5]);
2368 /// [pdqsort]: https://github.com/orlp/pdqsort
2369 #[stable(feature = "sort_unstable", since = "1.20.0")]
2371 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2376 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2379 /// Reorder the slice such that the element at `index` is at its final sorted position.
2380 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2381 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2383 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2387 self.select_nth_unstable(index)
2390 /// Reorder the slice with a comparator function such that the element at `index` is at its
2391 /// final sorted position.
2392 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2393 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2395 pub fn partition_at_index_by<F>(
2399 ) -> (&mut [T], &mut T, &mut [T])
2401 F: FnMut(&T, &T) -> Ordering,
2403 self.select_nth_unstable_by(index, compare)
2406 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2407 /// final sorted position.
2408 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2409 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2411 pub fn partition_at_index_by_key<K, F>(
2415 ) -> (&mut [T], &mut T, &mut [T])
2420 self.select_nth_unstable_by_key(index, f)
2423 /// Reorder the slice such that the element at `index` is at its final sorted position.
2425 /// This reordering has the additional property that any value at position `i < index` will be
2426 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2427 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2428 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2429 /// element" in other libraries. It returns a triplet of the following values: all elements less
2430 /// than the one at the given index, the value at the given index, and all elements greater than
2431 /// the one at the given index.
2433 /// # Current implementation
2435 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2436 /// used for [`sort_unstable`].
2438 /// [`sort_unstable`]: #method.sort_unstable
2442 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2447 /// let mut v = [-5i32, 4, 1, -3, 2];
2449 /// // Find the median
2450 /// v.select_nth_unstable(2);
2452 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2453 /// // about the specified index.
2454 /// assert!(v == [-3, -5, 1, 2, 4] ||
2455 /// v == [-5, -3, 1, 2, 4] ||
2456 /// v == [-3, -5, 1, 4, 2] ||
2457 /// v == [-5, -3, 1, 4, 2]);
2459 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2461 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2465 let mut f = |a: &T, b: &T| a.lt(b);
2466 sort::partition_at_index(self, index, &mut f)
2469 /// Reorder the slice with a comparator function such that the element at `index` is at its
2470 /// final sorted position.
2472 /// This reordering has the additional property that any value at position `i < index` will be
2473 /// less than or equal to any value at a position `j > index` using the comparator function.
2474 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2475 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2476 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2477 /// values: all elements less than the one at the given index, the value at the given index,
2478 /// and all elements greater than the one at the given index, using the provided comparator
2481 /// # Current implementation
2483 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2484 /// used for [`sort_unstable`].
2486 /// [`sort_unstable`]: #method.sort_unstable
2490 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2495 /// let mut v = [-5i32, 4, 1, -3, 2];
2497 /// // Find the median as if the slice were sorted in descending order.
2498 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2500 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2501 /// // about the specified index.
2502 /// assert!(v == [2, 4, 1, -5, -3] ||
2503 /// v == [2, 4, 1, -3, -5] ||
2504 /// v == [4, 2, 1, -5, -3] ||
2505 /// v == [4, 2, 1, -3, -5]);
2507 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2509 pub fn select_nth_unstable_by<F>(
2513 ) -> (&mut [T], &mut T, &mut [T])
2515 F: FnMut(&T, &T) -> Ordering,
2517 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2518 sort::partition_at_index(self, index, &mut f)
2521 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2522 /// final sorted position.
2524 /// This reordering has the additional property that any value at position `i < index` will be
2525 /// less than or equal to any value at a position `j > index` using the key extraction function.
2526 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2527 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2528 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2529 /// values: all elements less than the one at the given index, the value at the given index, and
2530 /// all elements greater than the one at the given index, using the provided key extraction
2533 /// # Current implementation
2535 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2536 /// used for [`sort_unstable`].
2538 /// [`sort_unstable`]: #method.sort_unstable
2542 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2547 /// let mut v = [-5i32, 4, 1, -3, 2];
2549 /// // Return the median as if the array were sorted according to absolute value.
2550 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2552 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2553 /// // about the specified index.
2554 /// assert!(v == [1, 2, -3, 4, -5] ||
2555 /// v == [1, 2, -3, -5, 4] ||
2556 /// v == [2, 1, -3, 4, -5] ||
2557 /// v == [2, 1, -3, -5, 4]);
2559 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2561 pub fn select_nth_unstable_by_key<K, F>(
2565 ) -> (&mut [T], &mut T, &mut [T])
2570 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2571 sort::partition_at_index(self, index, &mut g)
2574 /// Moves all consecutive repeated elements to the end of the slice according to the
2575 /// [`PartialEq`] trait implementation.
2577 /// Returns two slices. The first contains no consecutive repeated elements.
2578 /// The second contains all the duplicates in no specified order.
2580 /// If the slice is sorted, the first returned slice contains no duplicates.
2585 /// #![feature(slice_partition_dedup)]
2587 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2589 /// let (dedup, duplicates) = slice.partition_dedup();
2591 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2592 /// assert_eq!(duplicates, [2, 3, 1]);
2594 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2596 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2600 self.partition_dedup_by(|a, b| a == b)
2603 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2604 /// a given equality relation.
2606 /// Returns two slices. The first contains no consecutive repeated elements.
2607 /// The second contains all the duplicates in no specified order.
2609 /// The `same_bucket` function is passed references to two elements from the slice and
2610 /// must determine if the elements compare equal. The elements are passed in opposite order
2611 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2612 /// at the end of the slice.
2614 /// If the slice is sorted, the first returned slice contains no duplicates.
2619 /// #![feature(slice_partition_dedup)]
2621 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2623 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2625 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2626 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2628 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2630 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2632 F: FnMut(&mut T, &mut T) -> bool,
2634 // Although we have a mutable reference to `self`, we cannot make
2635 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2636 // must ensure that the slice is in a valid state at all times.
2638 // The way that we handle this is by using swaps; we iterate
2639 // over all the elements, swapping as we go so that at the end
2640 // the elements we wish to keep are in the front, and those we
2641 // wish to reject are at the back. We can then split the slice.
2642 // This operation is still `O(n)`.
2644 // Example: We start in this state, where `r` represents "next
2645 // read" and `w` represents "next_write`.
2648 // +---+---+---+---+---+---+
2649 // | 0 | 1 | 1 | 2 | 3 | 3 |
2650 // +---+---+---+---+---+---+
2653 // Comparing self[r] against self[w-1], this is not a duplicate, so
2654 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2655 // r and w, leaving us with:
2658 // +---+---+---+---+---+---+
2659 // | 0 | 1 | 1 | 2 | 3 | 3 |
2660 // +---+---+---+---+---+---+
2663 // Comparing self[r] against self[w-1], this value is a duplicate,
2664 // so we increment `r` but leave everything else unchanged:
2667 // +---+---+---+---+---+---+
2668 // | 0 | 1 | 1 | 2 | 3 | 3 |
2669 // +---+---+---+---+---+---+
2672 // Comparing self[r] against self[w-1], this is not a duplicate,
2673 // so swap self[r] and self[w] and advance r and w:
2676 // +---+---+---+---+---+---+
2677 // | 0 | 1 | 2 | 1 | 3 | 3 |
2678 // +---+---+---+---+---+---+
2681 // Not a duplicate, repeat:
2684 // +---+---+---+---+---+---+
2685 // | 0 | 1 | 2 | 3 | 1 | 3 |
2686 // +---+---+---+---+---+---+
2689 // Duplicate, advance r. End of slice. Split at w.
2691 let len = self.len();
2693 return (self, &mut []);
2696 let ptr = self.as_mut_ptr();
2697 let mut next_read: usize = 1;
2698 let mut next_write: usize = 1;
2700 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2701 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2702 // one element before `ptr_write`, but `next_write` starts at 1, so
2703 // `prev_ptr_write` is never less than 0 and is inside the slice.
2704 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2705 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2706 // and `prev_ptr_write.offset(1)`.
2708 // `next_write` is also incremented at most once per loop at most meaning
2709 // no element is skipped when it may need to be swapped.
2711 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2712 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2713 // The explanation is simply that `next_read >= next_write` is always true,
2714 // thus `next_read > next_write - 1` is too.
2716 // Avoid bounds checks by using raw pointers.
2717 while next_read < len {
2718 let ptr_read = ptr.add(next_read);
2719 let prev_ptr_write = ptr.add(next_write - 1);
2720 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2721 if next_read != next_write {
2722 let ptr_write = prev_ptr_write.offset(1);
2723 mem::swap(&mut *ptr_read, &mut *ptr_write);
2731 self.split_at_mut(next_write)
2734 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2735 /// to the same key.
2737 /// Returns two slices. The first contains no consecutive repeated elements.
2738 /// The second contains all the duplicates in no specified order.
2740 /// If the slice is sorted, the first returned slice contains no duplicates.
2745 /// #![feature(slice_partition_dedup)]
2747 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2749 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2751 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2752 /// assert_eq!(duplicates, [21, 30, 13]);
2754 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2756 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2758 F: FnMut(&mut T) -> K,
2761 self.partition_dedup_by(|a, b| key(a) == key(b))
2764 /// Rotates the slice in-place such that the first `mid` elements of the
2765 /// slice move to the end while the last `self.len() - mid` elements move to
2766 /// the front. After calling `rotate_left`, the element previously at index
2767 /// `mid` will become the first element in the slice.
2771 /// This function will panic if `mid` is greater than the length of the
2772 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2777 /// Takes linear (in `self.len()`) time.
2782 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2783 /// a.rotate_left(2);
2784 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2787 /// Rotating a subslice:
2790 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2791 /// a[1..5].rotate_left(1);
2792 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2794 #[stable(feature = "slice_rotate", since = "1.26.0")]
2795 pub fn rotate_left(&mut self, mid: usize) {
2796 assert!(mid <= self.len());
2797 let k = self.len() - mid;
2798 let p = self.as_mut_ptr();
2800 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2801 // valid for reading and writing, as required by `ptr_rotate`.
2803 rotate::ptr_rotate(mid, p.add(mid), k);
2807 /// Rotates the slice in-place such that the first `self.len() - k`
2808 /// elements of the slice move to the end while the last `k` elements move
2809 /// to the front. After calling `rotate_right`, the element previously at
2810 /// index `self.len() - k` will become the first element in the slice.
2814 /// This function will panic if `k` is greater than the length of the
2815 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2820 /// Takes linear (in `self.len()`) time.
2825 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2826 /// a.rotate_right(2);
2827 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2830 /// Rotate a subslice:
2833 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2834 /// a[1..5].rotate_right(1);
2835 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2837 #[stable(feature = "slice_rotate", since = "1.26.0")]
2838 pub fn rotate_right(&mut self, k: usize) {
2839 assert!(k <= self.len());
2840 let mid = self.len() - k;
2841 let p = self.as_mut_ptr();
2843 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2844 // valid for reading and writing, as required by `ptr_rotate`.
2846 rotate::ptr_rotate(mid, p.add(mid), k);
2850 /// Fills `self` with elements by cloning `value`.
2855 /// let mut buf = vec![0; 10];
2857 /// assert_eq!(buf, vec![1; 10]);
2859 #[doc(alias = "memset")]
2860 #[stable(feature = "slice_fill", since = "1.50.0")]
2861 pub fn fill(&mut self, value: T)
2865 if let Some((last, elems)) = self.split_last_mut() {
2867 el.clone_from(&value);
2874 /// Fills `self` with elements returned by calling a closure repeatedly.
2876 /// This method uses a closure to create new values. If you'd rather
2877 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2878 /// trait to generate values, you can pass [`Default::default`] as the
2881 /// [`fill`]: #method.fill
2886 /// let mut buf = vec![1; 10];
2887 /// buf.fill_with(Default::default);
2888 /// assert_eq!(buf, vec![0; 10]);
2890 #[doc(alias = "memset")]
2891 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2892 pub fn fill_with<F>(&mut self, mut f: F)
2901 /// Copies the elements from `src` into `self`.
2903 /// The length of `src` must be the same as `self`.
2905 /// If `T` implements `Copy`, it can be more performant to use
2906 /// [`copy_from_slice`].
2910 /// This function will panic if the two slices have different lengths.
2914 /// Cloning two elements from a slice into another:
2917 /// let src = [1, 2, 3, 4];
2918 /// let mut dst = [0, 0];
2920 /// // Because the slices have to be the same length,
2921 /// // we slice the source slice from four elements
2922 /// // to two. It will panic if we don't do this.
2923 /// dst.clone_from_slice(&src[2..]);
2925 /// assert_eq!(src, [1, 2, 3, 4]);
2926 /// assert_eq!(dst, [3, 4]);
2929 /// Rust enforces that there can only be one mutable reference with no
2930 /// immutable references to a particular piece of data in a particular
2931 /// scope. Because of this, attempting to use `clone_from_slice` on a
2932 /// single slice will result in a compile failure:
2935 /// let mut slice = [1, 2, 3, 4, 5];
2937 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2940 /// To work around this, we can use [`split_at_mut`] to create two distinct
2941 /// sub-slices from a slice:
2944 /// let mut slice = [1, 2, 3, 4, 5];
2947 /// let (left, right) = slice.split_at_mut(2);
2948 /// left.clone_from_slice(&right[1..]);
2951 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2954 /// [`copy_from_slice`]: #method.copy_from_slice
2955 /// [`split_at_mut`]: #method.split_at_mut
2956 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2957 pub fn clone_from_slice(&mut self, src: &[T])
2961 self.spec_clone_from(src);
2964 /// Copies all elements from `src` into `self`, using a memcpy.
2966 /// The length of `src` must be the same as `self`.
2968 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2972 /// This function will panic if the two slices have different lengths.
2976 /// Copying two elements from a slice into another:
2979 /// let src = [1, 2, 3, 4];
2980 /// let mut dst = [0, 0];
2982 /// // Because the slices have to be the same length,
2983 /// // we slice the source slice from four elements
2984 /// // to two. It will panic if we don't do this.
2985 /// dst.copy_from_slice(&src[2..]);
2987 /// assert_eq!(src, [1, 2, 3, 4]);
2988 /// assert_eq!(dst, [3, 4]);
2991 /// Rust enforces that there can only be one mutable reference with no
2992 /// immutable references to a particular piece of data in a particular
2993 /// scope. Because of this, attempting to use `copy_from_slice` on a
2994 /// single slice will result in a compile failure:
2997 /// let mut slice = [1, 2, 3, 4, 5];
2999 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3002 /// To work around this, we can use [`split_at_mut`] to create two distinct
3003 /// sub-slices from a slice:
3006 /// let mut slice = [1, 2, 3, 4, 5];
3009 /// let (left, right) = slice.split_at_mut(2);
3010 /// left.copy_from_slice(&right[1..]);
3013 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3016 /// [`clone_from_slice`]: #method.clone_from_slice
3017 /// [`split_at_mut`]: #method.split_at_mut
3018 #[doc(alias = "memcpy")]
3019 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3020 pub fn copy_from_slice(&mut self, src: &[T])
3024 // The panic code path was put into a cold function to not bloat the
3029 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3031 "source slice length ({}) does not match destination slice length ({})",
3036 if self.len() != src.len() {
3037 len_mismatch_fail(self.len(), src.len());
3040 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3041 // checked to have the same length. The slices cannot overlap because
3042 // mutable references are exclusive.
3044 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3048 /// Copies elements from one part of the slice to another part of itself,
3049 /// using a memmove.
3051 /// `src` is the range within `self` to copy from. `dest` is the starting
3052 /// index of the range within `self` to copy to, which will have the same
3053 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3054 /// must be less than or equal to `self.len()`.
3058 /// This function will panic if either range exceeds the end of the slice,
3059 /// or if the end of `src` is before the start.
3063 /// Copying four bytes within a slice:
3066 /// let mut bytes = *b"Hello, World!";
3068 /// bytes.copy_within(1..5, 8);
3070 /// assert_eq!(&bytes, b"Hello, Wello!");
3072 #[stable(feature = "copy_within", since = "1.37.0")]
3074 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3078 let Range { start: src_start, end: src_end } = src.assert_len(self.len());
3079 let count = src_end - src_start;
3080 assert!(dest <= self.len() - count, "dest is out of bounds");
3081 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3082 // as have those for `ptr::add`.
3084 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3088 /// Swaps all elements in `self` with those in `other`.
3090 /// The length of `other` must be the same as `self`.
3094 /// This function will panic if the two slices have different lengths.
3098 /// Swapping two elements across slices:
3101 /// let mut slice1 = [0, 0];
3102 /// let mut slice2 = [1, 2, 3, 4];
3104 /// slice1.swap_with_slice(&mut slice2[2..]);
3106 /// assert_eq!(slice1, [3, 4]);
3107 /// assert_eq!(slice2, [1, 2, 0, 0]);
3110 /// Rust enforces that there can only be one mutable reference to a
3111 /// particular piece of data in a particular scope. Because of this,
3112 /// attempting to use `swap_with_slice` on a single slice will result in
3113 /// a compile failure:
3116 /// let mut slice = [1, 2, 3, 4, 5];
3117 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3120 /// To work around this, we can use [`split_at_mut`] to create two distinct
3121 /// mutable sub-slices from a slice:
3124 /// let mut slice = [1, 2, 3, 4, 5];
3127 /// let (left, right) = slice.split_at_mut(2);
3128 /// left.swap_with_slice(&mut right[1..]);
3131 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3134 /// [`split_at_mut`]: #method.split_at_mut
3135 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3136 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3137 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3138 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3139 // checked to have the same length. The slices cannot overlap because
3140 // mutable references are exclusive.
3142 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3146 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3147 fn align_to_offsets<U>(&self) -> (usize, usize) {
3148 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3149 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3151 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3152 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3153 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3155 // Formula to calculate this is:
3157 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3158 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3160 // Expanded and simplified:
3162 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3163 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3165 // Luckily since all this is constant-evaluated... performance here matters not!
3167 fn gcd(a: usize, b: usize) -> usize {
3168 use crate::intrinsics;
3169 // iterative stein’s algorithm
3170 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3171 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3173 // SAFETY: `a` and `b` are checked to be non-zero values.
3174 let (ctz_a, mut ctz_b) = unsafe {
3181 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3183 let k = ctz_a.min(ctz_b);
3184 let mut a = a >> ctz_a;
3187 // remove all factors of 2 from b
3190 mem::swap(&mut a, &mut b);
3193 // SAFETY: `b` is checked to be non-zero.
3198 ctz_b = intrinsics::cttz_nonzero(b);
3203 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3204 let ts: usize = mem::size_of::<U>() / gcd;
3205 let us: usize = mem::size_of::<T>() / gcd;
3207 // Armed with this knowledge, we can find how many `U`s we can fit!
3208 let us_len = self.len() / ts * us;
3209 // And how many `T`s will be in the trailing slice!
3210 let ts_len = self.len() % ts;
3214 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3217 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3218 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3219 /// length possible for a given type and input slice, but only your algorithm's performance
3220 /// should depend on that, not its correctness. It is permissible for all of the input data to
3221 /// be returned as the prefix or suffix slice.
3223 /// This method has no purpose when either input element `T` or output element `U` are
3224 /// zero-sized and will return the original slice without splitting anything.
3228 /// This method is essentially a `transmute` with respect to the elements in the returned
3229 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3237 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3238 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3239 /// // less_efficient_algorithm_for_bytes(prefix);
3240 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3241 /// // less_efficient_algorithm_for_bytes(suffix);
3244 #[stable(feature = "slice_align_to", since = "1.30.0")]
3245 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3246 // Note that most of this function will be constant-evaluated,
3247 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3248 // handle ZSTs specially, which is – don't handle them at all.
3249 return (self, &[], &[]);
3252 // First, find at what point do we split between the first and 2nd slice. Easy with
3253 // ptr.align_offset.
3254 let ptr = self.as_ptr();
3255 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3256 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3257 if offset > self.len() {
3260 let (left, rest) = self.split_at(offset);
3261 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3262 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3263 // since the caller guarantees that we can transmute `T` to `U` safely.
3267 from_raw_parts(rest.as_ptr() as *const U, us_len),
3268 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3274 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3277 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3278 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3279 /// length possible for a given type and input slice, but only your algorithm's performance
3280 /// should depend on that, not its correctness. It is permissible for all of the input data to
3281 /// be returned as the prefix or suffix slice.
3283 /// This method has no purpose when either input element `T` or output element `U` are
3284 /// zero-sized and will return the original slice without splitting anything.
3288 /// This method is essentially a `transmute` with respect to the elements in the returned
3289 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3297 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3298 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3299 /// // less_efficient_algorithm_for_bytes(prefix);
3300 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3301 /// // less_efficient_algorithm_for_bytes(suffix);
3304 #[stable(feature = "slice_align_to", since = "1.30.0")]
3305 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3306 // Note that most of this function will be constant-evaluated,
3307 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3308 // handle ZSTs specially, which is – don't handle them at all.
3309 return (self, &mut [], &mut []);
3312 // First, find at what point do we split between the first and 2nd slice. Easy with
3313 // ptr.align_offset.
3314 let ptr = self.as_ptr();
3315 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3316 // rest of the method. This is done by passing a pointer to &[T] with an
3317 // alignment targeted for U.
3318 // `crate::ptr::align_offset` is called with a correctly aligned and
3319 // valid pointer `ptr` (it comes from a reference to `self`) and with
3320 // a size that is a power of two (since it comes from the alignement for U),
3321 // satisfying its safety constraints.
3322 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3323 if offset > self.len() {
3324 (self, &mut [], &mut [])
3326 let (left, rest) = self.split_at_mut(offset);
3327 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3328 let rest_len = rest.len();
3329 let mut_ptr = rest.as_mut_ptr();
3330 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3331 // SAFETY: see comments for `align_to`.
3335 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3336 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3342 /// Checks if the elements of this slice are sorted.
3344 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3345 /// slice yields exactly zero or one element, `true` is returned.
3347 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3348 /// implies that this function returns `false` if any two consecutive items are not
3354 /// #![feature(is_sorted)]
3355 /// let empty: [i32; 0] = [];
3357 /// assert!([1, 2, 2, 9].is_sorted());
3358 /// assert!(![1, 3, 2, 4].is_sorted());
3359 /// assert!([0].is_sorted());
3360 /// assert!(empty.is_sorted());
3361 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3364 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3365 pub fn is_sorted(&self) -> bool
3369 self.is_sorted_by(|a, b| a.partial_cmp(b))
3372 /// Checks if the elements of this slice are sorted using the given comparator function.
3374 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3375 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3376 /// [`is_sorted`]; see its documentation for more information.
3378 /// [`is_sorted`]: #method.is_sorted
3379 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3380 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3382 F: FnMut(&T, &T) -> Option<Ordering>,
3384 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3387 /// Checks if the elements of this slice are sorted using the given key extraction function.
3389 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3390 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3391 /// documentation for more information.
3393 /// [`is_sorted`]: #method.is_sorted
3398 /// #![feature(is_sorted)]
3400 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3401 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3404 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3405 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3410 self.iter().is_sorted_by_key(f)
3413 /// Returns the index of the partition point according to the given predicate
3414 /// (the index of the first element of the second partition).
3416 /// The slice is assumed to be partitioned according to the given predicate.
3417 /// This means that all elements for which the predicate returns true are at the start of the slice
3418 /// and all elements for which the predicate returns false are at the end.
3419 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3420 /// (all odd numbers are at the start, all even at the end).
3422 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3423 /// as this method performs a kind of binary search.
3425 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3427 /// [`binary_search`]: #method.binary_search
3428 /// [`binary_search_by`]: #method.binary_search_by
3429 /// [`binary_search_by_key`]: #method.binary_search_by_key
3434 /// let v = [1, 2, 3, 3, 5, 6, 7];
3435 /// let i = v.partition_point(|&x| x < 5);
3437 /// assert_eq!(i, 4);
3438 /// assert!(v[..i].iter().all(|&x| x < 5));
3439 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3441 #[stable(feature = "partition_point", since = "1.52.0")]
3442 pub fn partition_point<P>(&self, mut pred: P) -> usize
3444 P: FnMut(&T) -> bool,
3447 let mut right = self.len();
3449 while left != right {
3450 let mid = left + (right - left) / 2;
3451 // SAFETY: When `left < right`, `left <= mid < right`.
3452 // Therefore `left` always increases and `right` always decreases,
3453 // and either of them is selected. In both cases `left <= right` is
3454 // satisfied. Therefore if `left < right` in a step, `left <= right`
3455 // is satisfied in the next step. Therefore as long as `left != right`,
3456 // `0 <= left < right <= len` is satisfied and if this case
3457 // `0 <= mid < len` is satisfied too.
3458 let value = unsafe { self.get_unchecked(mid) };
3470 trait CloneFromSpec<T> {
3471 fn spec_clone_from(&mut self, src: &[T]);
3474 impl<T> CloneFromSpec<T> for [T]
3478 default fn spec_clone_from(&mut self, src: &[T]) {
3479 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3480 // NOTE: We need to explicitly slice them to the same length
3481 // to make it easier for the optimizer to elide bounds checking.
3482 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3483 let len = self.len();
3484 let src = &src[..len];
3486 self[i].clone_from(&src[i]);
3491 impl<T> CloneFromSpec<T> for [T]
3495 fn spec_clone_from(&mut self, src: &[T]) {
3496 self.copy_from_slice(src);
3500 #[stable(feature = "rust1", since = "1.0.0")]
3501 impl<T> Default for &[T] {
3502 /// Creates an empty slice.
3503 fn default() -> Self {
3508 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3509 impl<T> Default for &mut [T] {
3510 /// Creates a mutable empty slice.
3511 fn default() -> Self {
3516 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3517 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3518 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3519 /// `str`) to slices, and then this trait will be replaced or abolished.
3520 pub trait SlicePattern {
3521 /// The element type of the slice being matched on.
3524 /// Currently, the consumers of `SlicePattern` need a slice.
3525 fn as_slice(&self) -> &[Self::Item];
3528 #[stable(feature = "slice_strip", since = "1.51.0")]
3529 impl<T> SlicePattern for [T] {
3533 fn as_slice(&self) -> &[Self::Item] {
3538 #[stable(feature = "slice_strip", since = "1.51.0")]
3539 impl<T, const N: usize> SlicePattern for [T; N] {
3543 fn as_slice(&self) -> &[Self::Item] {