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 {
97 // SAFETY: this is safe because `&[T]` and `FatPtr<T>` have the same layout.
98 // Only `std` can make this guarantee.
99 unsafe { crate::ptr::Repr { rust: self }.raw.len }
102 /// Returns `true` if the slice has a length of 0.
107 /// let a = [1, 2, 3];
108 /// assert!(!a.is_empty());
110 #[stable(feature = "rust1", since = "1.0.0")]
111 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.32.0")]
113 pub const fn is_empty(&self) -> bool {
117 /// Returns the first element of the slice, or `None` if it is empty.
122 /// let v = [10, 40, 30];
123 /// assert_eq!(Some(&10), v.first());
125 /// let w: &[i32] = &[];
126 /// assert_eq!(None, w.first());
128 #[stable(feature = "rust1", since = "1.0.0")]
130 pub fn first(&self) -> Option<&T> {
131 if let [first, ..] = self { Some(first) } else { None }
134 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
139 /// let x = &mut [0, 1, 2];
141 /// if let Some(first) = x.first_mut() {
144 /// assert_eq!(x, &[5, 1, 2]);
146 #[stable(feature = "rust1", since = "1.0.0")]
148 pub fn first_mut(&mut self) -> Option<&mut T> {
149 if let [first, ..] = self { Some(first) } else { None }
152 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
157 /// let x = &[0, 1, 2];
159 /// if let Some((first, elements)) = x.split_first() {
160 /// assert_eq!(first, &0);
161 /// assert_eq!(elements, &[1, 2]);
164 #[stable(feature = "slice_splits", since = "1.5.0")]
166 pub fn split_first(&self) -> Option<(&T, &[T])> {
167 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
170 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
175 /// let x = &mut [0, 1, 2];
177 /// if let Some((first, elements)) = x.split_first_mut() {
182 /// assert_eq!(x, &[3, 4, 5]);
184 #[stable(feature = "slice_splits", since = "1.5.0")]
186 pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
187 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
190 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
195 /// let x = &[0, 1, 2];
197 /// if let Some((last, elements)) = x.split_last() {
198 /// assert_eq!(last, &2);
199 /// assert_eq!(elements, &[0, 1]);
202 #[stable(feature = "slice_splits", since = "1.5.0")]
204 pub fn split_last(&self) -> Option<(&T, &[T])> {
205 if let [init @ .., last] = self { Some((last, init)) } else { None }
208 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
213 /// let x = &mut [0, 1, 2];
215 /// if let Some((last, elements)) = x.split_last_mut() {
220 /// assert_eq!(x, &[4, 5, 3]);
222 #[stable(feature = "slice_splits", since = "1.5.0")]
224 pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
225 if let [init @ .., last] = self { Some((last, init)) } else { None }
228 /// Returns the last element of the slice, or `None` if it is empty.
233 /// let v = [10, 40, 30];
234 /// assert_eq!(Some(&30), v.last());
236 /// let w: &[i32] = &[];
237 /// assert_eq!(None, w.last());
239 #[stable(feature = "rust1", since = "1.0.0")]
241 pub fn last(&self) -> Option<&T> {
242 if let [.., last] = self { Some(last) } else { None }
245 /// Returns a mutable pointer to the last item in the slice.
250 /// let x = &mut [0, 1, 2];
252 /// if let Some(last) = x.last_mut() {
255 /// assert_eq!(x, &[0, 1, 10]);
257 #[stable(feature = "rust1", since = "1.0.0")]
259 pub fn last_mut(&mut self) -> Option<&mut T> {
260 if let [.., last] = self { Some(last) } else { None }
263 /// Returns a reference to an element or subslice depending on the type of
266 /// - If given a position, returns a reference to the element at that
267 /// position or `None` if out of bounds.
268 /// - If given a range, returns the subslice corresponding to that range,
269 /// or `None` if out of bounds.
274 /// let v = [10, 40, 30];
275 /// assert_eq!(Some(&40), v.get(1));
276 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
277 /// assert_eq!(None, v.get(3));
278 /// assert_eq!(None, v.get(0..4));
280 #[stable(feature = "rust1", since = "1.0.0")]
282 pub fn get<I>(&self, index: I) -> Option<&I::Output>
289 /// Returns a mutable reference to an element or subslice depending on the
290 /// type of index (see [`get`]) or `None` if the index is out of bounds.
292 /// [`get`]: #method.get
297 /// let x = &mut [0, 1, 2];
299 /// if let Some(elem) = x.get_mut(1) {
302 /// assert_eq!(x, &[0, 42, 2]);
304 #[stable(feature = "rust1", since = "1.0.0")]
306 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
313 /// Returns a reference to an element or subslice, without doing bounds
316 /// For a safe alternative see [`get`].
320 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
321 /// even if the resulting reference is not used.
323 /// [`get`]: #method.get
324 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
329 /// let x = &[1, 2, 4];
332 /// assert_eq!(x.get_unchecked(1), &2);
335 #[stable(feature = "rust1", since = "1.0.0")]
337 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
341 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
342 // the slice is dereferencable because `self` is a safe reference.
343 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
344 unsafe { &*index.get_unchecked(self) }
347 /// Returns a mutable reference to an element or subslice, without doing
350 /// For a safe alternative see [`get_mut`].
354 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
355 /// even if the resulting reference is not used.
357 /// [`get_mut`]: #method.get_mut
358 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
363 /// let x = &mut [1, 2, 4];
366 /// let elem = x.get_unchecked_mut(1);
369 /// assert_eq!(x, &[1, 13, 4]);
371 #[stable(feature = "rust1", since = "1.0.0")]
373 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
377 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
378 // the slice is dereferencable because `self` is a safe reference.
379 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
380 unsafe { &mut *index.get_unchecked_mut(self) }
383 /// Returns a raw pointer to the slice's buffer.
385 /// The caller must ensure that the slice outlives the pointer this
386 /// function returns, or else it will end up pointing to garbage.
388 /// The caller must also ensure that the memory the pointer (non-transitively) points to
389 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
390 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
392 /// Modifying the container referenced by this slice may cause its buffer
393 /// to be reallocated, which would also make any pointers to it invalid.
398 /// let x = &[1, 2, 4];
399 /// let x_ptr = x.as_ptr();
402 /// for i in 0..x.len() {
403 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
408 /// [`as_mut_ptr`]: #method.as_mut_ptr
409 #[stable(feature = "rust1", since = "1.0.0")]
410 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
412 pub const fn as_ptr(&self) -> *const T {
413 self as *const [T] as *const T
416 /// Returns an unsafe mutable pointer to the slice's buffer.
418 /// The caller must ensure that the slice outlives the pointer this
419 /// function returns, or else it will end up pointing to garbage.
421 /// Modifying the container referenced by this slice may cause its buffer
422 /// to be reallocated, which would also make any pointers to it invalid.
427 /// let x = &mut [1, 2, 4];
428 /// let x_ptr = x.as_mut_ptr();
431 /// for i in 0..x.len() {
432 /// *x_ptr.add(i) += 2;
435 /// assert_eq!(x, &[3, 4, 6]);
437 #[stable(feature = "rust1", since = "1.0.0")]
438 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
440 pub const fn as_mut_ptr(&mut self) -> *mut T {
441 self as *mut [T] as *mut T
444 /// Returns the two raw pointers spanning the slice.
446 /// The returned range is half-open, which means that the end pointer
447 /// points *one past* the last element of the slice. This way, an empty
448 /// slice is represented by two equal pointers, and the difference between
449 /// the two pointers represents the size of the slice.
451 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
452 /// requires extra caution, as it does not point to a valid element in the
455 /// This function is useful for interacting with foreign interfaces which
456 /// use two pointers to refer to a range of elements in memory, as is
459 /// It can also be useful to check if a pointer to an element refers to an
460 /// element of this slice:
463 /// let a = [1, 2, 3];
464 /// let x = &a[1] as *const _;
465 /// let y = &5 as *const _;
467 /// assert!(a.as_ptr_range().contains(&x));
468 /// assert!(!a.as_ptr_range().contains(&y));
471 /// [`as_ptr`]: #method.as_ptr
472 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
473 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
475 pub const fn as_ptr_range(&self) -> Range<*const T> {
476 let start = self.as_ptr();
477 // SAFETY: The `add` here is safe, because:
479 // - Both pointers are part of the same object, as pointing directly
480 // past the object also counts.
482 // - The size of the slice is never larger than isize::MAX bytes, as
484 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
485 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
486 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
487 // (This doesn't seem normative yet, but the very same assumption is
488 // made in many places, including the Index implementation of slices.)
490 // - There is no wrapping around involved, as slices do not wrap past
491 // the end of the address space.
493 // See the documentation of pointer::add.
494 let end = unsafe { start.add(self.len()) };
498 /// Returns the two unsafe mutable pointers spanning the slice.
500 /// The returned range is half-open, which means that the end pointer
501 /// points *one past* the last element of the slice. This way, an empty
502 /// slice is represented by two equal pointers, and the difference between
503 /// the two pointers represents the size of the slice.
505 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
506 /// pointer requires extra caution, as it does not point to a valid element
509 /// This function is useful for interacting with foreign interfaces which
510 /// use two pointers to refer to a range of elements in memory, as is
513 /// [`as_mut_ptr`]: #method.as_mut_ptr
514 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
515 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
517 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
518 let start = self.as_mut_ptr();
519 // SAFETY: See as_ptr_range() above for why `add` here is safe.
520 let end = unsafe { start.add(self.len()) };
524 /// Swaps two elements in the slice.
528 /// * a - The index of the first element
529 /// * b - The index of the second element
533 /// Panics if `a` or `b` are out of bounds.
538 /// let mut v = ["a", "b", "c", "d"];
540 /// assert!(v == ["a", "d", "c", "b"]);
542 #[stable(feature = "rust1", since = "1.0.0")]
544 pub fn swap(&mut self, a: usize, b: usize) {
545 // Can't take two mutable loans from one vector, so instead use raw pointers.
546 let pa = ptr::addr_of_mut!(self[a]);
547 let pb = ptr::addr_of_mut!(self[b]);
548 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
549 // to elements in the slice and therefore are guaranteed to be valid and aligned.
550 // Note that accessing the elements behind `a` and `b` is checked and will
551 // panic when out of bounds.
557 /// Reverses the order of elements in the slice, in place.
562 /// let mut v = [1, 2, 3];
564 /// assert!(v == [3, 2, 1]);
566 #[stable(feature = "rust1", since = "1.0.0")]
568 pub fn reverse(&mut self) {
569 let mut i: usize = 0;
572 // For very small types, all the individual reads in the normal
573 // path perform poorly. We can do better, given efficient unaligned
574 // load/store, by loading a larger chunk and reversing a register.
576 // Ideally LLVM would do this for us, as it knows better than we do
577 // whether unaligned reads are efficient (since that changes between
578 // different ARM versions, for example) and what the best chunk size
579 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
580 // the loop, so we need to do this ourselves. (Hypothesis: reverse
581 // is troublesome because the sides can be aligned differently --
582 // will be, when the length is odd -- so there's no way of emitting
583 // pre- and postludes to use fully-aligned SIMD in the middle.)
585 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
587 if fast_unaligned && mem::size_of::<T>() == 1 {
588 // Use the llvm.bswap intrinsic to reverse u8s in a usize
589 let chunk = mem::size_of::<usize>();
590 while i + chunk - 1 < ln / 2 {
591 // SAFETY: There are several things to check here:
593 // - Note that `chunk` is either 4 or 8 due to the cfg check
594 // above. So `chunk - 1` is positive.
595 // - Indexing with index `i` is fine as the loop check guarantees
596 // `i + chunk - 1 < ln / 2`
597 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
598 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
599 // - `i + chunk > 0` is trivially true.
600 // - The loop check guarantees:
601 // `i + chunk - 1 < ln / 2`
602 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
603 // - The `read_unaligned` and `write_unaligned` calls are fine:
604 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
605 // (see above) and `pb` points to index `ln - i - chunk`, so
606 // both are at least `chunk`
607 // many bytes away from the end of `self`.
608 // - Any initialized memory is valid `usize`.
610 let ptr = self.as_mut_ptr();
612 let pb = ptr.add(ln - i - chunk);
613 let va = ptr::read_unaligned(pa as *mut usize);
614 let vb = ptr::read_unaligned(pb as *mut usize);
615 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
616 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
622 if fast_unaligned && mem::size_of::<T>() == 2 {
623 // Use rotate-by-16 to reverse u16s in a u32
624 let chunk = mem::size_of::<u32>() / 2;
625 while i + chunk - 1 < ln / 2 {
626 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
627 // (and obviously `i < ln`), because each element is 2 bytes and
630 // `i + chunk - 1 < ln / 2` # while condition
631 // `i + 2 - 1 < ln / 2`
634 // Since it's less than the length divided by 2, then it must be
637 // This also means that the condition `0 < i + chunk <= ln` is
638 // always respected, ensuring the `pb` pointer can be used
641 let ptr = self.as_mut_ptr();
643 let pb = ptr.add(ln - i - chunk);
644 let va = ptr::read_unaligned(pa as *mut u32);
645 let vb = ptr::read_unaligned(pb as *mut u32);
646 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
647 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
654 // SAFETY: `i` is inferior to half the length of the slice so
655 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
656 // will not go further than `ln / 2 - 1`).
657 // The resulting pointers `pa` and `pb` are therefore valid and
658 // aligned, and can be read from and written to.
660 // Unsafe swap to avoid the bounds check in safe swap.
661 let ptr = self.as_mut_ptr();
663 let pb = ptr.add(ln - i - 1);
670 /// Returns an iterator over the slice.
675 /// let x = &[1, 2, 4];
676 /// let mut iterator = x.iter();
678 /// assert_eq!(iterator.next(), Some(&1));
679 /// assert_eq!(iterator.next(), Some(&2));
680 /// assert_eq!(iterator.next(), Some(&4));
681 /// assert_eq!(iterator.next(), None);
683 #[stable(feature = "rust1", since = "1.0.0")]
685 pub fn iter(&self) -> Iter<'_, T> {
689 /// Returns an iterator that allows modifying each value.
694 /// let x = &mut [1, 2, 4];
695 /// for elem in x.iter_mut() {
698 /// assert_eq!(x, &[3, 4, 6]);
700 #[stable(feature = "rust1", since = "1.0.0")]
702 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
706 /// Returns an iterator over all contiguous windows of length
707 /// `size`. The windows overlap. If the slice is shorter than
708 /// `size`, the iterator returns no values.
712 /// Panics if `size` is 0.
717 /// let slice = ['r', 'u', 's', 't'];
718 /// let mut iter = slice.windows(2);
719 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
720 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
721 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
722 /// assert!(iter.next().is_none());
725 /// If the slice is shorter than `size`:
728 /// let slice = ['f', 'o', 'o'];
729 /// let mut iter = slice.windows(4);
730 /// assert!(iter.next().is_none());
732 #[stable(feature = "rust1", since = "1.0.0")]
734 pub fn windows(&self, size: usize) -> Windows<'_, T> {
735 let size = NonZeroUsize::new(size).expect("size is zero");
736 Windows::new(self, size)
739 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
740 /// beginning of the slice.
742 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
743 /// slice, then the last chunk will not have length `chunk_size`.
745 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
746 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
751 /// Panics if `chunk_size` is 0.
756 /// let slice = ['l', 'o', 'r', 'e', 'm'];
757 /// let mut iter = slice.chunks(2);
758 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
759 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
760 /// assert_eq!(iter.next().unwrap(), &['m']);
761 /// assert!(iter.next().is_none());
764 /// [`chunks_exact`]: #method.chunks_exact
765 /// [`rchunks`]: #method.rchunks
766 #[stable(feature = "rust1", since = "1.0.0")]
768 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
769 assert_ne!(chunk_size, 0);
770 Chunks::new(self, chunk_size)
773 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
774 /// beginning of the slice.
776 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
777 /// length of the slice, then the last chunk will not have length `chunk_size`.
779 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
780 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
781 /// the end of the slice.
785 /// Panics if `chunk_size` is 0.
790 /// let v = &mut [0, 0, 0, 0, 0];
791 /// let mut count = 1;
793 /// for chunk in v.chunks_mut(2) {
794 /// for elem in chunk.iter_mut() {
799 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
802 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
803 /// [`rchunks_mut`]: #method.rchunks_mut
804 #[stable(feature = "rust1", since = "1.0.0")]
806 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
807 assert_ne!(chunk_size, 0);
808 ChunksMut::new(self, chunk_size)
811 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
812 /// beginning of the slice.
814 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
815 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
816 /// from the `remainder` function of the iterator.
818 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
819 /// resulting code better than in the case of [`chunks`].
821 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
822 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
826 /// Panics if `chunk_size` is 0.
831 /// let slice = ['l', 'o', 'r', 'e', 'm'];
832 /// let mut iter = slice.chunks_exact(2);
833 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
834 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
835 /// assert!(iter.next().is_none());
836 /// assert_eq!(iter.remainder(), &['m']);
839 /// [`chunks`]: #method.chunks
840 /// [`rchunks_exact`]: #method.rchunks_exact
841 #[stable(feature = "chunks_exact", since = "1.31.0")]
843 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
844 assert_ne!(chunk_size, 0);
845 ChunksExact::new(self, chunk_size)
848 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
849 /// beginning of the slice.
851 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
852 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
853 /// retrieved from the `into_remainder` function of the iterator.
855 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
856 /// resulting code better than in the case of [`chunks_mut`].
858 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
859 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
864 /// Panics if `chunk_size` is 0.
869 /// let v = &mut [0, 0, 0, 0, 0];
870 /// let mut count = 1;
872 /// for chunk in v.chunks_exact_mut(2) {
873 /// for elem in chunk.iter_mut() {
878 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
881 /// [`chunks_mut`]: #method.chunks_mut
882 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
883 #[stable(feature = "chunks_exact", since = "1.31.0")]
885 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
886 assert_ne!(chunk_size, 0);
887 ChunksExactMut::new(self, chunk_size)
890 /// Splits the slice into a slice of `N`-element arrays,
891 /// assuming that there's no remainder.
895 /// This may only be called when
896 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
902 /// #![feature(slice_as_chunks)]
903 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
904 /// let chunks: &[[char; 1]] =
905 /// // SAFETY: 1-element chunks never have remainder
906 /// unsafe { slice.as_chunks_unchecked() };
907 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
908 /// let chunks: &[[char; 3]] =
909 /// // SAFETY: The slice length (6) is a multiple of 3
910 /// unsafe { slice.as_chunks_unchecked() };
911 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
913 /// // These would be unsound:
914 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
915 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
917 #[unstable(feature = "slice_as_chunks", issue = "74985")]
919 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
920 debug_assert_ne!(N, 0);
921 debug_assert_eq!(self.len() % N, 0);
923 // SAFETY: Our precondition is exactly what's needed to call this
924 unsafe { crate::intrinsics::exact_div(self.len(), N) };
925 // SAFETY: We cast a slice of `new_len * N` elements into
926 // a slice of `new_len` many `N` elements chunks.
927 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
930 /// Splits the slice into a slice of `N`-element arrays,
931 /// starting at the beginning of the slice,
932 /// and a remainder slice with length strictly less than `N`.
936 /// Panics if `N` is 0. This check will most probably get changed to a compile time
937 /// error before this method gets stabilized.
942 /// #![feature(slice_as_chunks)]
943 /// let slice = ['l', 'o', 'r', 'e', 'm'];
944 /// let (chunks, remainder) = slice.as_chunks();
945 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
946 /// assert_eq!(remainder, &['m']);
948 #[unstable(feature = "slice_as_chunks", issue = "74985")]
950 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
952 let len = self.len() / N;
953 let (multiple_of_n, remainder) = self.split_at(len * N);
954 // SAFETY: We already panicked for zero, and ensured by construction
955 // that the length of the subslice is a multiple of N.
956 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
957 (array_slice, remainder)
960 /// Splits the slice into a slice of `N`-element arrays,
961 /// starting at the end of the slice,
962 /// and a remainder slice with length strictly less than `N`.
966 /// Panics if `N` is 0. This check will most probably get changed to a compile time
967 /// error before this method gets stabilized.
972 /// #![feature(slice_as_chunks)]
973 /// let slice = ['l', 'o', 'r', 'e', 'm'];
974 /// let (remainder, chunks) = slice.as_rchunks();
975 /// assert_eq!(remainder, &['l']);
976 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
978 #[unstable(feature = "slice_as_chunks", issue = "74985")]
980 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
982 let len = self.len() / N;
983 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
984 // SAFETY: We already panicked for zero, and ensured by construction
985 // that the length of the subslice is a multiple of N.
986 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
987 (remainder, array_slice)
990 /// Returns an iterator over `N` elements of the slice at a time, starting at the
991 /// beginning of the slice.
993 /// The chunks are array references and do not overlap. If `N` does not divide the
994 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
995 /// retrieved from the `remainder` function of the iterator.
997 /// This method is the const generic equivalent of [`chunks_exact`].
1001 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1002 /// error before this method gets stabilized.
1007 /// #![feature(array_chunks)]
1008 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1009 /// let mut iter = slice.array_chunks();
1010 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1011 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1012 /// assert!(iter.next().is_none());
1013 /// assert_eq!(iter.remainder(), &['m']);
1016 /// [`chunks_exact`]: #method.chunks_exact
1017 #[unstable(feature = "array_chunks", issue = "74985")]
1019 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1021 ArrayChunks::new(self)
1024 /// Splits the slice into a slice of `N`-element arrays,
1025 /// assuming that there's no remainder.
1029 /// This may only be called when
1030 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1036 /// #![feature(slice_as_chunks)]
1037 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1038 /// let chunks: &mut [[char; 1]] =
1039 /// // SAFETY: 1-element chunks never have remainder
1040 /// unsafe { slice.as_chunks_unchecked_mut() };
1041 /// chunks[0] = ['L'];
1042 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1043 /// let chunks: &mut [[char; 3]] =
1044 /// // SAFETY: The slice length (6) is a multiple of 3
1045 /// unsafe { slice.as_chunks_unchecked_mut() };
1046 /// chunks[1] = ['a', 'x', '?'];
1047 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1049 /// // These would be unsound:
1050 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1051 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1053 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1055 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1056 debug_assert_ne!(N, 0);
1057 debug_assert_eq!(self.len() % N, 0);
1059 // SAFETY: Our precondition is exactly what's needed to call this
1060 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1061 // SAFETY: We cast a slice of `new_len * N` elements into
1062 // a slice of `new_len` many `N` elements chunks.
1063 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1066 /// Splits the slice into a slice of `N`-element arrays,
1067 /// starting at the beginning of the slice,
1068 /// and a remainder slice with length strictly less than `N`.
1072 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1073 /// error before this method gets stabilized.
1078 /// #![feature(slice_as_chunks)]
1079 /// let v = &mut [0, 0, 0, 0, 0];
1080 /// let mut count = 1;
1082 /// let (chunks, remainder) = v.as_chunks_mut();
1083 /// remainder[0] = 9;
1084 /// for chunk in chunks {
1085 /// *chunk = [count; 2];
1088 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1090 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1092 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1094 let len = self.len() / N;
1095 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1096 // SAFETY: We already panicked for zero, and ensured by construction
1097 // that the length of the subslice is a multiple of N.
1098 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1099 (array_slice, remainder)
1102 /// Splits the slice into a slice of `N`-element arrays,
1103 /// starting at the end of the slice,
1104 /// and a remainder slice with length strictly less than `N`.
1108 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1109 /// error before this method gets stabilized.
1114 /// #![feature(slice_as_chunks)]
1115 /// let v = &mut [0, 0, 0, 0, 0];
1116 /// let mut count = 1;
1118 /// let (remainder, chunks) = v.as_rchunks_mut();
1119 /// remainder[0] = 9;
1120 /// for chunk in chunks {
1121 /// *chunk = [count; 2];
1124 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1126 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1128 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1130 let len = self.len() / N;
1131 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1132 // SAFETY: We already panicked for zero, and ensured by construction
1133 // that the length of the subslice is a multiple of N.
1134 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1135 (remainder, array_slice)
1138 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1139 /// beginning of the slice.
1141 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1142 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1143 /// can be retrieved from the `into_remainder` function of the iterator.
1145 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1149 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1150 /// error before this method gets stabilized.
1155 /// #![feature(array_chunks)]
1156 /// let v = &mut [0, 0, 0, 0, 0];
1157 /// let mut count = 1;
1159 /// for chunk in v.array_chunks_mut() {
1160 /// *chunk = [count; 2];
1163 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1166 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1167 #[unstable(feature = "array_chunks", issue = "74985")]
1169 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1171 ArrayChunksMut::new(self)
1174 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1175 /// starting at the beginning of the slice.
1177 /// This is the const generic equivalent of [`windows`].
1179 /// If `N` is greater than the size of the slice, it will return no windows.
1183 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1184 /// error before this method gets stabilized.
1189 /// #![feature(array_windows)]
1190 /// let slice = [0, 1, 2, 3];
1191 /// let mut iter = slice.array_windows();
1192 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1193 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1194 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1195 /// assert!(iter.next().is_none());
1198 /// [`windows`]: #method.windows
1199 #[unstable(feature = "array_windows", issue = "75027")]
1201 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1203 ArrayWindows::new(self)
1206 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1209 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1210 /// slice, then the last chunk will not have length `chunk_size`.
1212 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1213 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1218 /// Panics if `chunk_size` is 0.
1223 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1224 /// let mut iter = slice.rchunks(2);
1225 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1226 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1227 /// assert_eq!(iter.next().unwrap(), &['l']);
1228 /// assert!(iter.next().is_none());
1231 /// [`rchunks_exact`]: #method.rchunks_exact
1232 /// [`chunks`]: #method.chunks
1233 #[stable(feature = "rchunks", since = "1.31.0")]
1235 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1236 assert!(chunk_size != 0);
1237 RChunks::new(self, chunk_size)
1240 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1243 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1244 /// length of the slice, then the last chunk will not have length `chunk_size`.
1246 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1247 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1248 /// beginning of the slice.
1252 /// Panics if `chunk_size` is 0.
1257 /// let v = &mut [0, 0, 0, 0, 0];
1258 /// let mut count = 1;
1260 /// for chunk in v.rchunks_mut(2) {
1261 /// for elem in chunk.iter_mut() {
1266 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1269 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
1270 /// [`chunks_mut`]: #method.chunks_mut
1271 #[stable(feature = "rchunks", since = "1.31.0")]
1273 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1274 assert!(chunk_size != 0);
1275 RChunksMut::new(self, chunk_size)
1278 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1279 /// end of the slice.
1281 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1282 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1283 /// from the `remainder` function of the iterator.
1285 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1286 /// resulting code better than in the case of [`chunks`].
1288 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1289 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1294 /// Panics if `chunk_size` is 0.
1299 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1300 /// let mut iter = slice.rchunks_exact(2);
1301 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1302 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1303 /// assert!(iter.next().is_none());
1304 /// assert_eq!(iter.remainder(), &['l']);
1307 /// [`chunks`]: #method.chunks
1308 /// [`rchunks`]: #method.rchunks
1309 /// [`chunks_exact`]: #method.chunks_exact
1310 #[stable(feature = "rchunks", since = "1.31.0")]
1312 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1313 assert!(chunk_size != 0);
1314 RChunksExact::new(self, chunk_size)
1317 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1320 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1321 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1322 /// retrieved from the `into_remainder` function of the iterator.
1324 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1325 /// resulting code better than in the case of [`chunks_mut`].
1327 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1328 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1333 /// Panics if `chunk_size` is 0.
1338 /// let v = &mut [0, 0, 0, 0, 0];
1339 /// let mut count = 1;
1341 /// for chunk in v.rchunks_exact_mut(2) {
1342 /// for elem in chunk.iter_mut() {
1347 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1350 /// [`chunks_mut`]: #method.chunks_mut
1351 /// [`rchunks_mut`]: #method.rchunks_mut
1352 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1353 #[stable(feature = "rchunks", since = "1.31.0")]
1355 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1356 assert!(chunk_size != 0);
1357 RChunksExactMut::new(self, chunk_size)
1360 /// Returns an iterator over the slice producing non-overlapping runs
1361 /// of elements using the predicate to separate them.
1363 /// The predicate is called on two elements following themselves,
1364 /// it means the predicate is called on `slice[0]` and `slice[1]`
1365 /// then on `slice[1]` and `slice[2]` and so on.
1370 /// #![feature(slice_group_by)]
1372 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1374 /// let mut iter = slice.group_by(|a, b| a == b);
1376 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1377 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1378 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1379 /// assert_eq!(iter.next(), None);
1382 /// This method can be used to extract the sorted subslices:
1385 /// #![feature(slice_group_by)]
1387 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1389 /// let mut iter = slice.group_by(|a, b| a <= b);
1391 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1392 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1393 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1394 /// assert_eq!(iter.next(), None);
1396 #[unstable(feature = "slice_group_by", issue = "80552")]
1398 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1400 F: FnMut(&T, &T) -> bool,
1402 GroupBy::new(self, pred)
1405 /// Returns an iterator over the slice producing non-overlapping mutable
1406 /// runs of elements using the predicate to separate them.
1408 /// The predicate is called on two elements following themselves,
1409 /// it means the predicate is called on `slice[0]` and `slice[1]`
1410 /// then on `slice[1]` and `slice[2]` and so on.
1415 /// #![feature(slice_group_by)]
1417 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1419 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1421 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1422 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1423 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1424 /// assert_eq!(iter.next(), None);
1427 /// This method can be used to extract the sorted subslices:
1430 /// #![feature(slice_group_by)]
1432 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1434 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1436 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1437 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1438 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1439 /// assert_eq!(iter.next(), None);
1441 #[unstable(feature = "slice_group_by", issue = "80552")]
1443 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1445 F: FnMut(&T, &T) -> bool,
1447 GroupByMut::new(self, pred)
1450 /// Divides one slice into two at an index.
1452 /// The first will contain all indices from `[0, mid)` (excluding
1453 /// the index `mid` itself) and the second will contain all
1454 /// indices from `[mid, len)` (excluding the index `len` itself).
1458 /// Panics if `mid > len`.
1463 /// let v = [1, 2, 3, 4, 5, 6];
1466 /// let (left, right) = v.split_at(0);
1467 /// assert_eq!(left, []);
1468 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1472 /// let (left, right) = v.split_at(2);
1473 /// assert_eq!(left, [1, 2]);
1474 /// assert_eq!(right, [3, 4, 5, 6]);
1478 /// let (left, right) = v.split_at(6);
1479 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1480 /// assert_eq!(right, []);
1483 #[stable(feature = "rust1", since = "1.0.0")]
1485 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1486 assert!(mid <= self.len());
1487 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1488 // fulfills the requirements of `from_raw_parts_mut`.
1489 unsafe { self.split_at_unchecked(mid) }
1492 /// Divides one mutable slice into two at an index.
1494 /// The first will contain all indices from `[0, mid)` (excluding
1495 /// the index `mid` itself) and the second will contain all
1496 /// indices from `[mid, len)` (excluding the index `len` itself).
1500 /// Panics if `mid > len`.
1505 /// let mut v = [1, 0, 3, 0, 5, 6];
1506 /// let (left, right) = v.split_at_mut(2);
1507 /// assert_eq!(left, [1, 0]);
1508 /// assert_eq!(right, [3, 0, 5, 6]);
1511 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1513 #[stable(feature = "rust1", since = "1.0.0")]
1515 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1516 assert!(mid <= self.len());
1517 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1518 // fulfills the requirements of `from_raw_parts_mut`.
1519 unsafe { self.split_at_mut_unchecked(mid) }
1522 /// Divides one slice into two at an index, without doing bounds checking.
1524 /// The first will contain all indices from `[0, mid)` (excluding
1525 /// the index `mid` itself) and the second will contain all
1526 /// indices from `[mid, len)` (excluding the index `len` itself).
1528 /// For a safe alternative see [`split_at`].
1532 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1533 /// even if the resulting reference is not used. The caller has to ensure that
1534 /// `0 <= mid <= self.len()`.
1536 /// [`split_at`]: #method.split_at
1537 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1542 /// #![feature(slice_split_at_unchecked)]
1544 /// let v = [1, 2, 3, 4, 5, 6];
1547 /// let (left, right) = v.split_at_unchecked(0);
1548 /// assert_eq!(left, []);
1549 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1553 /// let (left, right) = v.split_at_unchecked(2);
1554 /// assert_eq!(left, [1, 2]);
1555 /// assert_eq!(right, [3, 4, 5, 6]);
1559 /// let (left, right) = v.split_at_unchecked(6);
1560 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1561 /// assert_eq!(right, []);
1564 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1566 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1567 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1568 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1571 /// Divides one mutable slice into two at an index, without doing bounds checking.
1573 /// The first will contain all indices from `[0, mid)` (excluding
1574 /// the index `mid` itself) and the second will contain all
1575 /// indices from `[mid, len)` (excluding the index `len` itself).
1577 /// For a safe alternative see [`split_at_mut`].
1581 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1582 /// even if the resulting reference is not used. The caller has to ensure that
1583 /// `0 <= mid <= self.len()`.
1585 /// [`split_at_mut`]: #method.split_at_mut
1586 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1591 /// #![feature(slice_split_at_unchecked)]
1593 /// let mut v = [1, 0, 3, 0, 5, 6];
1594 /// // scoped to restrict the lifetime of the borrows
1596 /// let (left, right) = v.split_at_mut_unchecked(2);
1597 /// assert_eq!(left, [1, 0]);
1598 /// assert_eq!(right, [3, 0, 5, 6]);
1602 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1604 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1606 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1607 let len = self.len();
1608 let ptr = self.as_mut_ptr();
1610 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1612 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1614 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1617 /// Returns an iterator over subslices separated by elements that match
1618 /// `pred`. The matched element is not contained in the subslices.
1623 /// let slice = [10, 40, 33, 20];
1624 /// let mut iter = slice.split(|num| num % 3 == 0);
1626 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1627 /// assert_eq!(iter.next().unwrap(), &[20]);
1628 /// assert!(iter.next().is_none());
1631 /// If the first element is matched, an empty slice will be the first item
1632 /// returned by the iterator. Similarly, if the last element in the slice
1633 /// is matched, an empty slice will be the last item returned by the
1637 /// let slice = [10, 40, 33];
1638 /// let mut iter = slice.split(|num| num % 3 == 0);
1640 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1641 /// assert_eq!(iter.next().unwrap(), &[]);
1642 /// assert!(iter.next().is_none());
1645 /// If two matched elements are directly adjacent, an empty slice will be
1646 /// present between them:
1649 /// let slice = [10, 6, 33, 20];
1650 /// let mut iter = slice.split(|num| num % 3 == 0);
1652 /// assert_eq!(iter.next().unwrap(), &[10]);
1653 /// assert_eq!(iter.next().unwrap(), &[]);
1654 /// assert_eq!(iter.next().unwrap(), &[20]);
1655 /// assert!(iter.next().is_none());
1657 #[stable(feature = "rust1", since = "1.0.0")]
1659 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1661 F: FnMut(&T) -> bool,
1663 Split::new(self, pred)
1666 /// Returns an iterator over mutable subslices separated by elements that
1667 /// match `pred`. The matched element is not contained in the subslices.
1672 /// let mut v = [10, 40, 30, 20, 60, 50];
1674 /// for group in v.split_mut(|num| *num % 3 == 0) {
1677 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1679 #[stable(feature = "rust1", since = "1.0.0")]
1681 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1683 F: FnMut(&T) -> bool,
1685 SplitMut::new(self, pred)
1688 /// Returns an iterator over subslices separated by elements that match
1689 /// `pred`. The matched element is contained in the end of the previous
1690 /// subslice as a terminator.
1695 /// let slice = [10, 40, 33, 20];
1696 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1698 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1699 /// assert_eq!(iter.next().unwrap(), &[20]);
1700 /// assert!(iter.next().is_none());
1703 /// If the last element of the slice is matched,
1704 /// that element will be considered the terminator of the preceding slice.
1705 /// That slice will be the last item returned by the iterator.
1708 /// let slice = [3, 10, 40, 33];
1709 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1711 /// assert_eq!(iter.next().unwrap(), &[3]);
1712 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1713 /// assert!(iter.next().is_none());
1715 #[stable(feature = "split_inclusive", since = "1.51.0")]
1717 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1719 F: FnMut(&T) -> bool,
1721 SplitInclusive::new(self, pred)
1724 /// Returns an iterator over mutable subslices separated by elements that
1725 /// match `pred`. The matched element is contained in the previous
1726 /// subslice as a terminator.
1731 /// let mut v = [10, 40, 30, 20, 60, 50];
1733 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1734 /// let terminator_idx = group.len()-1;
1735 /// group[terminator_idx] = 1;
1737 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1739 #[stable(feature = "split_inclusive", since = "1.51.0")]
1741 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1743 F: FnMut(&T) -> bool,
1745 SplitInclusiveMut::new(self, pred)
1748 /// Returns an iterator over subslices separated by elements that match
1749 /// `pred`, starting at the end of the slice and working backwards.
1750 /// The matched element is not contained in the subslices.
1755 /// let slice = [11, 22, 33, 0, 44, 55];
1756 /// let mut iter = slice.rsplit(|num| *num == 0);
1758 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1759 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1760 /// assert_eq!(iter.next(), None);
1763 /// As with `split()`, if the first or last element is matched, an empty
1764 /// slice will be the first (or last) item returned by the iterator.
1767 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1768 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1769 /// assert_eq!(it.next().unwrap(), &[]);
1770 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1771 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1772 /// assert_eq!(it.next().unwrap(), &[]);
1773 /// assert_eq!(it.next(), None);
1775 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1777 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1779 F: FnMut(&T) -> bool,
1781 RSplit::new(self, pred)
1784 /// Returns an iterator over mutable subslices separated by elements that
1785 /// match `pred`, starting at the end of the slice and working
1786 /// backwards. The matched element is not contained in the subslices.
1791 /// let mut v = [100, 400, 300, 200, 600, 500];
1793 /// let mut count = 0;
1794 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1796 /// group[0] = count;
1798 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1801 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1803 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1805 F: FnMut(&T) -> bool,
1807 RSplitMut::new(self, pred)
1810 /// Returns an iterator over subslices separated by elements that match
1811 /// `pred`, limited to returning at most `n` items. The matched element is
1812 /// not contained in the subslices.
1814 /// The last element returned, if any, will contain the remainder of the
1819 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1820 /// `[20, 60, 50]`):
1823 /// let v = [10, 40, 30, 20, 60, 50];
1825 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1826 /// println!("{:?}", group);
1829 #[stable(feature = "rust1", since = "1.0.0")]
1831 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1833 F: FnMut(&T) -> bool,
1835 SplitN::new(self.split(pred), n)
1838 /// Returns an iterator over subslices separated by elements that match
1839 /// `pred`, limited to returning at most `n` items. The matched element is
1840 /// not contained in the subslices.
1842 /// The last element returned, if any, will contain the remainder of the
1848 /// let mut v = [10, 40, 30, 20, 60, 50];
1850 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1853 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1855 #[stable(feature = "rust1", since = "1.0.0")]
1857 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1859 F: FnMut(&T) -> bool,
1861 SplitNMut::new(self.split_mut(pred), n)
1864 /// Returns an iterator over subslices separated by elements that match
1865 /// `pred` limited to returning at most `n` items. This starts at the end of
1866 /// the slice and works backwards. The matched element is not contained in
1869 /// The last element returned, if any, will contain the remainder of the
1874 /// Print the slice split once, starting from the end, by numbers divisible
1875 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1878 /// let v = [10, 40, 30, 20, 60, 50];
1880 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1881 /// println!("{:?}", group);
1884 #[stable(feature = "rust1", since = "1.0.0")]
1886 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1888 F: FnMut(&T) -> bool,
1890 RSplitN::new(self.rsplit(pred), n)
1893 /// Returns an iterator over subslices separated by elements that match
1894 /// `pred` limited to returning at most `n` items. This starts at the end of
1895 /// the slice and works backwards. The matched element is not contained in
1898 /// The last element returned, if any, will contain the remainder of the
1904 /// let mut s = [10, 40, 30, 20, 60, 50];
1906 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1909 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1911 #[stable(feature = "rust1", since = "1.0.0")]
1913 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1915 F: FnMut(&T) -> bool,
1917 RSplitNMut::new(self.rsplit_mut(pred), n)
1920 /// Returns `true` if the slice contains an element with the given value.
1925 /// let v = [10, 40, 30];
1926 /// assert!(v.contains(&30));
1927 /// assert!(!v.contains(&50));
1930 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1931 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1934 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1935 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1936 /// assert!(!v.iter().any(|e| e == "hi"));
1938 #[stable(feature = "rust1", since = "1.0.0")]
1940 pub fn contains(&self, x: &T) -> bool
1944 cmp::SliceContains::slice_contains(x, self)
1947 /// Returns `true` if `needle` is a prefix of the slice.
1952 /// let v = [10, 40, 30];
1953 /// assert!(v.starts_with(&[10]));
1954 /// assert!(v.starts_with(&[10, 40]));
1955 /// assert!(!v.starts_with(&[50]));
1956 /// assert!(!v.starts_with(&[10, 50]));
1959 /// Always returns `true` if `needle` is an empty slice:
1962 /// let v = &[10, 40, 30];
1963 /// assert!(v.starts_with(&[]));
1964 /// let v: &[u8] = &[];
1965 /// assert!(v.starts_with(&[]));
1967 #[stable(feature = "rust1", since = "1.0.0")]
1968 pub fn starts_with(&self, needle: &[T]) -> bool
1972 let n = needle.len();
1973 self.len() >= n && needle == &self[..n]
1976 /// Returns `true` if `needle` is a suffix of the slice.
1981 /// let v = [10, 40, 30];
1982 /// assert!(v.ends_with(&[30]));
1983 /// assert!(v.ends_with(&[40, 30]));
1984 /// assert!(!v.ends_with(&[50]));
1985 /// assert!(!v.ends_with(&[50, 30]));
1988 /// Always returns `true` if `needle` is an empty slice:
1991 /// let v = &[10, 40, 30];
1992 /// assert!(v.ends_with(&[]));
1993 /// let v: &[u8] = &[];
1994 /// assert!(v.ends_with(&[]));
1996 #[stable(feature = "rust1", since = "1.0.0")]
1997 pub fn ends_with(&self, needle: &[T]) -> bool
2001 let (m, n) = (self.len(), needle.len());
2002 m >= n && needle == &self[m - n..]
2005 /// Returns a subslice with the prefix removed.
2007 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2008 /// If `prefix` is empty, simply returns the original slice.
2010 /// If the slice does not start with `prefix`, returns `None`.
2015 /// let v = &[10, 40, 30];
2016 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2017 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2018 /// assert_eq!(v.strip_prefix(&[50]), None);
2019 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2021 /// let prefix : &str = "he";
2022 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2023 /// Some(b"llo".as_ref()));
2025 #[must_use = "returns the subslice without modifying the original"]
2026 #[stable(feature = "slice_strip", since = "1.51.0")]
2027 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2031 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2032 let prefix = prefix.as_slice();
2033 let n = prefix.len();
2034 if n <= self.len() {
2035 let (head, tail) = self.split_at(n);
2043 /// Returns a subslice with the suffix removed.
2045 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2046 /// If `suffix` is empty, simply returns the original slice.
2048 /// If the slice does not end with `suffix`, returns `None`.
2053 /// let v = &[10, 40, 30];
2054 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2055 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2056 /// assert_eq!(v.strip_suffix(&[50]), None);
2057 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2059 #[must_use = "returns the subslice without modifying the original"]
2060 #[stable(feature = "slice_strip", since = "1.51.0")]
2061 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2065 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2066 let suffix = suffix.as_slice();
2067 let (len, n) = (self.len(), suffix.len());
2069 let (head, tail) = self.split_at(len - n);
2077 /// Binary searches this sorted slice for a given element.
2079 /// If the value is found then [`Result::Ok`] is returned, containing the
2080 /// index of the matching element. If there are multiple matches, then any
2081 /// one of the matches could be returned. If the value is not found then
2082 /// [`Result::Err`] is returned, containing the index where a matching
2083 /// element could be inserted while maintaining sorted order.
2087 /// Looks up a series of four elements. The first is found, with a
2088 /// uniquely determined position; the second and third are not
2089 /// found; the fourth could match any position in `[1, 4]`.
2092 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2094 /// assert_eq!(s.binary_search(&13), Ok(9));
2095 /// assert_eq!(s.binary_search(&4), Err(7));
2096 /// assert_eq!(s.binary_search(&100), Err(13));
2097 /// let r = s.binary_search(&1);
2098 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2101 /// If you want to insert an item to a sorted vector, while maintaining
2105 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2107 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2108 /// s.insert(idx, num);
2109 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2111 #[stable(feature = "rust1", since = "1.0.0")]
2112 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2116 self.binary_search_by(|p| p.cmp(x))
2119 /// Binary searches this sorted slice with a comparator function.
2121 /// The comparator function should implement an order consistent
2122 /// with the sort order of the underlying slice, returning an
2123 /// order code that indicates whether its argument is `Less`,
2124 /// `Equal` or `Greater` the desired target.
2126 /// If the value is found then [`Result::Ok`] is returned, containing the
2127 /// index of the matching element. If there are multiple matches, then any
2128 /// one of the matches could be returned. If the value is not found then
2129 /// [`Result::Err`] is returned, containing the index where a matching
2130 /// element could be inserted while maintaining sorted order.
2134 /// Looks up a series of four elements. The first is found, with a
2135 /// uniquely determined position; the second and third are not
2136 /// found; the fourth could match any position in `[1, 4]`.
2139 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2142 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2144 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2146 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2148 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2149 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2151 #[stable(feature = "rust1", since = "1.0.0")]
2153 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2155 F: FnMut(&'a T) -> Ordering,
2158 let mut size = s.len();
2162 let mut base = 0usize;
2164 let half = size / 2;
2165 let mid = base + half;
2166 // SAFETY: the call is made safe by the following inconstants:
2167 // - `mid >= 0`: by definition
2168 // - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
2169 let cmp = f(unsafe { s.get_unchecked(mid) });
2170 base = if cmp == Greater { base } else { mid };
2173 // SAFETY: base is always in [0, size) because base <= mid.
2174 let cmp = f(unsafe { s.get_unchecked(base) });
2175 if cmp == Equal { Ok(base) } else { Err(base + (cmp == Less) as usize) }
2178 /// Binary searches this sorted slice with a key extraction function.
2180 /// Assumes that the slice is sorted by the key, for instance with
2181 /// [`sort_by_key`] using the same key extraction function.
2183 /// If the value is found then [`Result::Ok`] is returned, containing the
2184 /// index of the matching element. If there are multiple matches, then any
2185 /// one of the matches could be returned. If the value is not found then
2186 /// [`Result::Err`] is returned, containing the index where a matching
2187 /// element could be inserted while maintaining sorted order.
2189 /// [`sort_by_key`]: #method.sort_by_key
2193 /// Looks up a series of four elements in a slice of pairs sorted by
2194 /// their second elements. The first is found, with a uniquely
2195 /// determined position; the second and third are not found; the
2196 /// fourth could match any position in `[1, 4]`.
2199 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2200 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2201 /// (1, 21), (2, 34), (4, 55)];
2203 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2204 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2205 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2206 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2207 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2209 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2211 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2213 F: FnMut(&'a T) -> B,
2216 self.binary_search_by(|k| f(k).cmp(b))
2219 /// Sorts the slice, but may not preserve the order of equal elements.
2221 /// This sort is unstable (i.e., may reorder equal elements), in-place
2222 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2224 /// # Current implementation
2226 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2227 /// which combines the fast average case of randomized quicksort with the fast worst case of
2228 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2229 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2230 /// deterministic behavior.
2232 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2233 /// slice consists of several concatenated sorted sequences.
2238 /// let mut v = [-5, 4, 1, -3, 2];
2240 /// v.sort_unstable();
2241 /// assert!(v == [-5, -3, 1, 2, 4]);
2244 /// [pdqsort]: https://github.com/orlp/pdqsort
2245 #[stable(feature = "sort_unstable", since = "1.20.0")]
2247 pub fn sort_unstable(&mut self)
2251 sort::quicksort(self, |a, b| a.lt(b));
2254 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2257 /// This sort is unstable (i.e., may reorder equal elements), in-place
2258 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2260 /// The comparator function must define a total ordering for the elements in the slice. If
2261 /// the ordering is not total, the order of the elements is unspecified. An order is a
2262 /// total order if it is (for all `a`, `b` and `c`):
2264 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2265 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2267 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2268 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2271 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2272 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2273 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2276 /// # Current implementation
2278 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2279 /// which combines the fast average case of randomized quicksort with the fast worst case of
2280 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2281 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2282 /// deterministic behavior.
2284 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2285 /// slice consists of several concatenated sorted sequences.
2290 /// let mut v = [5, 4, 1, 3, 2];
2291 /// v.sort_unstable_by(|a, b| a.cmp(b));
2292 /// assert!(v == [1, 2, 3, 4, 5]);
2294 /// // reverse sorting
2295 /// v.sort_unstable_by(|a, b| b.cmp(a));
2296 /// assert!(v == [5, 4, 3, 2, 1]);
2299 /// [pdqsort]: https://github.com/orlp/pdqsort
2300 #[stable(feature = "sort_unstable", since = "1.20.0")]
2302 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2304 F: FnMut(&T, &T) -> Ordering,
2306 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2309 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2312 /// This sort is unstable (i.e., may reorder equal elements), in-place
2313 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2316 /// # Current implementation
2318 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2319 /// which combines the fast average case of randomized quicksort with the fast worst case of
2320 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2321 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2322 /// deterministic behavior.
2324 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2325 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2326 /// cases where the key function is expensive.
2331 /// let mut v = [-5i32, 4, 1, -3, 2];
2333 /// v.sort_unstable_by_key(|k| k.abs());
2334 /// assert!(v == [1, 2, -3, 4, -5]);
2337 /// [pdqsort]: https://github.com/orlp/pdqsort
2338 #[stable(feature = "sort_unstable", since = "1.20.0")]
2340 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2345 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2348 /// Reorder the slice such that the element at `index` is at its final sorted position.
2349 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2350 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2352 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2356 self.select_nth_unstable(index)
2359 /// Reorder the slice with a comparator function such that the element at `index` is at its
2360 /// final sorted position.
2361 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2362 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2364 pub fn partition_at_index_by<F>(
2368 ) -> (&mut [T], &mut T, &mut [T])
2370 F: FnMut(&T, &T) -> Ordering,
2372 self.select_nth_unstable_by(index, compare)
2375 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2376 /// final sorted position.
2377 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2378 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2380 pub fn partition_at_index_by_key<K, F>(
2384 ) -> (&mut [T], &mut T, &mut [T])
2389 self.select_nth_unstable_by_key(index, f)
2392 /// Reorder the slice such that the element at `index` is at its final sorted position.
2394 /// This reordering has the additional property that any value at position `i < index` will be
2395 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2396 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2397 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2398 /// element" in other libraries. It returns a triplet of the following values: all elements less
2399 /// than the one at the given index, the value at the given index, and all elements greater than
2400 /// the one at the given index.
2402 /// # Current implementation
2404 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2405 /// used for [`sort_unstable`].
2407 /// [`sort_unstable`]: #method.sort_unstable
2411 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2416 /// let mut v = [-5i32, 4, 1, -3, 2];
2418 /// // Find the median
2419 /// v.select_nth_unstable(2);
2421 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2422 /// // about the specified index.
2423 /// assert!(v == [-3, -5, 1, 2, 4] ||
2424 /// v == [-5, -3, 1, 2, 4] ||
2425 /// v == [-3, -5, 1, 4, 2] ||
2426 /// v == [-5, -3, 1, 4, 2]);
2428 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2430 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2434 let mut f = |a: &T, b: &T| a.lt(b);
2435 sort::partition_at_index(self, index, &mut f)
2438 /// Reorder the slice with a comparator function such that the element at `index` is at its
2439 /// final sorted position.
2441 /// This reordering has the additional property that any value at position `i < index` will be
2442 /// less than or equal to any value at a position `j > index` using the comparator function.
2443 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2444 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2445 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2446 /// values: all elements less than the one at the given index, the value at the given index,
2447 /// and all elements greater than the one at the given index, using the provided comparator
2450 /// # Current implementation
2452 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2453 /// used for [`sort_unstable`].
2455 /// [`sort_unstable`]: #method.sort_unstable
2459 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2464 /// let mut v = [-5i32, 4, 1, -3, 2];
2466 /// // Find the median as if the slice were sorted in descending order.
2467 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2469 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2470 /// // about the specified index.
2471 /// assert!(v == [2, 4, 1, -5, -3] ||
2472 /// v == [2, 4, 1, -3, -5] ||
2473 /// v == [4, 2, 1, -5, -3] ||
2474 /// v == [4, 2, 1, -3, -5]);
2476 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2478 pub fn select_nth_unstable_by<F>(
2482 ) -> (&mut [T], &mut T, &mut [T])
2484 F: FnMut(&T, &T) -> Ordering,
2486 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2487 sort::partition_at_index(self, index, &mut f)
2490 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2491 /// final sorted position.
2493 /// This reordering has the additional property that any value at position `i < index` will be
2494 /// less than or equal to any value at a position `j > index` using the key extraction function.
2495 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2496 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2497 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2498 /// values: all elements less than the one at the given index, the value at the given index, and
2499 /// all elements greater than the one at the given index, using the provided key extraction
2502 /// # Current implementation
2504 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2505 /// used for [`sort_unstable`].
2507 /// [`sort_unstable`]: #method.sort_unstable
2511 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2516 /// let mut v = [-5i32, 4, 1, -3, 2];
2518 /// // Return the median as if the array were sorted according to absolute value.
2519 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2521 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2522 /// // about the specified index.
2523 /// assert!(v == [1, 2, -3, 4, -5] ||
2524 /// v == [1, 2, -3, -5, 4] ||
2525 /// v == [2, 1, -3, 4, -5] ||
2526 /// v == [2, 1, -3, -5, 4]);
2528 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2530 pub fn select_nth_unstable_by_key<K, F>(
2534 ) -> (&mut [T], &mut T, &mut [T])
2539 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2540 sort::partition_at_index(self, index, &mut g)
2543 /// Moves all consecutive repeated elements to the end of the slice according to the
2544 /// [`PartialEq`] trait implementation.
2546 /// Returns two slices. The first contains no consecutive repeated elements.
2547 /// The second contains all the duplicates in no specified order.
2549 /// If the slice is sorted, the first returned slice contains no duplicates.
2554 /// #![feature(slice_partition_dedup)]
2556 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2558 /// let (dedup, duplicates) = slice.partition_dedup();
2560 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2561 /// assert_eq!(duplicates, [2, 3, 1]);
2563 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2565 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2569 self.partition_dedup_by(|a, b| a == b)
2572 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2573 /// a given equality relation.
2575 /// Returns two slices. The first contains no consecutive repeated elements.
2576 /// The second contains all the duplicates in no specified order.
2578 /// The `same_bucket` function is passed references to two elements from the slice and
2579 /// must determine if the elements compare equal. The elements are passed in opposite order
2580 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2581 /// at the end of the slice.
2583 /// If the slice is sorted, the first returned slice contains no duplicates.
2588 /// #![feature(slice_partition_dedup)]
2590 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2592 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2594 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2595 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2597 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2599 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2601 F: FnMut(&mut T, &mut T) -> bool,
2603 // Although we have a mutable reference to `self`, we cannot make
2604 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2605 // must ensure that the slice is in a valid state at all times.
2607 // The way that we handle this is by using swaps; we iterate
2608 // over all the elements, swapping as we go so that at the end
2609 // the elements we wish to keep are in the front, and those we
2610 // wish to reject are at the back. We can then split the slice.
2611 // This operation is still `O(n)`.
2613 // Example: We start in this state, where `r` represents "next
2614 // read" and `w` represents "next_write`.
2617 // +---+---+---+---+---+---+
2618 // | 0 | 1 | 1 | 2 | 3 | 3 |
2619 // +---+---+---+---+---+---+
2622 // Comparing self[r] against self[w-1], this is not a duplicate, so
2623 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2624 // r and w, leaving us with:
2627 // +---+---+---+---+---+---+
2628 // | 0 | 1 | 1 | 2 | 3 | 3 |
2629 // +---+---+---+---+---+---+
2632 // Comparing self[r] against self[w-1], this value is a duplicate,
2633 // so we increment `r` but leave everything else unchanged:
2636 // +---+---+---+---+---+---+
2637 // | 0 | 1 | 1 | 2 | 3 | 3 |
2638 // +---+---+---+---+---+---+
2641 // Comparing self[r] against self[w-1], this is not a duplicate,
2642 // so swap self[r] and self[w] and advance r and w:
2645 // +---+---+---+---+---+---+
2646 // | 0 | 1 | 2 | 1 | 3 | 3 |
2647 // +---+---+---+---+---+---+
2650 // Not a duplicate, repeat:
2653 // +---+---+---+---+---+---+
2654 // | 0 | 1 | 2 | 3 | 1 | 3 |
2655 // +---+---+---+---+---+---+
2658 // Duplicate, advance r. End of slice. Split at w.
2660 let len = self.len();
2662 return (self, &mut []);
2665 let ptr = self.as_mut_ptr();
2666 let mut next_read: usize = 1;
2667 let mut next_write: usize = 1;
2669 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2670 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2671 // one element before `ptr_write`, but `next_write` starts at 1, so
2672 // `prev_ptr_write` is never less than 0 and is inside the slice.
2673 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2674 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2675 // and `prev_ptr_write.offset(1)`.
2677 // `next_write` is also incremented at most once per loop at most meaning
2678 // no element is skipped when it may need to be swapped.
2680 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2681 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2682 // The explanation is simply that `next_read >= next_write` is always true,
2683 // thus `next_read > next_write - 1` is too.
2685 // Avoid bounds checks by using raw pointers.
2686 while next_read < len {
2687 let ptr_read = ptr.add(next_read);
2688 let prev_ptr_write = ptr.add(next_write - 1);
2689 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2690 if next_read != next_write {
2691 let ptr_write = prev_ptr_write.offset(1);
2692 mem::swap(&mut *ptr_read, &mut *ptr_write);
2700 self.split_at_mut(next_write)
2703 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2704 /// to the same key.
2706 /// Returns two slices. The first contains no consecutive repeated elements.
2707 /// The second contains all the duplicates in no specified order.
2709 /// If the slice is sorted, the first returned slice contains no duplicates.
2714 /// #![feature(slice_partition_dedup)]
2716 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2718 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2720 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2721 /// assert_eq!(duplicates, [21, 30, 13]);
2723 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2725 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2727 F: FnMut(&mut T) -> K,
2730 self.partition_dedup_by(|a, b| key(a) == key(b))
2733 /// Rotates the slice in-place such that the first `mid` elements of the
2734 /// slice move to the end while the last `self.len() - mid` elements move to
2735 /// the front. After calling `rotate_left`, the element previously at index
2736 /// `mid` will become the first element in the slice.
2740 /// This function will panic if `mid` is greater than the length of the
2741 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2746 /// Takes linear (in `self.len()`) time.
2751 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2752 /// a.rotate_left(2);
2753 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2756 /// Rotating a subslice:
2759 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2760 /// a[1..5].rotate_left(1);
2761 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2763 #[stable(feature = "slice_rotate", since = "1.26.0")]
2764 pub fn rotate_left(&mut self, mid: usize) {
2765 assert!(mid <= self.len());
2766 let k = self.len() - mid;
2767 let p = self.as_mut_ptr();
2769 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2770 // valid for reading and writing, as required by `ptr_rotate`.
2772 rotate::ptr_rotate(mid, p.add(mid), k);
2776 /// Rotates the slice in-place such that the first `self.len() - k`
2777 /// elements of the slice move to the end while the last `k` elements move
2778 /// to the front. After calling `rotate_right`, the element previously at
2779 /// index `self.len() - k` will become the first element in the slice.
2783 /// This function will panic if `k` is greater than the length of the
2784 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2789 /// Takes linear (in `self.len()`) time.
2794 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2795 /// a.rotate_right(2);
2796 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2799 /// Rotate a subslice:
2802 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2803 /// a[1..5].rotate_right(1);
2804 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2806 #[stable(feature = "slice_rotate", since = "1.26.0")]
2807 pub fn rotate_right(&mut self, k: usize) {
2808 assert!(k <= self.len());
2809 let mid = self.len() - k;
2810 let p = self.as_mut_ptr();
2812 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2813 // valid for reading and writing, as required by `ptr_rotate`.
2815 rotate::ptr_rotate(mid, p.add(mid), k);
2819 /// Fills `self` with elements by cloning `value`.
2824 /// let mut buf = vec![0; 10];
2826 /// assert_eq!(buf, vec![1; 10]);
2828 #[doc(alias = "memset")]
2829 #[stable(feature = "slice_fill", since = "1.50.0")]
2830 pub fn fill(&mut self, value: T)
2834 if let Some((last, elems)) = self.split_last_mut() {
2836 el.clone_from(&value);
2843 /// Fills `self` with elements returned by calling a closure repeatedly.
2845 /// This method uses a closure to create new values. If you'd rather
2846 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2847 /// trait to generate values, you can pass [`Default::default`] as the
2850 /// [`fill`]: #method.fill
2855 /// let mut buf = vec![1; 10];
2856 /// buf.fill_with(Default::default);
2857 /// assert_eq!(buf, vec![0; 10]);
2859 #[doc(alias = "memset")]
2860 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2861 pub fn fill_with<F>(&mut self, mut f: F)
2870 /// Copies the elements from `src` into `self`.
2872 /// The length of `src` must be the same as `self`.
2874 /// If `T` implements `Copy`, it can be more performant to use
2875 /// [`copy_from_slice`].
2879 /// This function will panic if the two slices have different lengths.
2883 /// Cloning two elements from a slice into another:
2886 /// let src = [1, 2, 3, 4];
2887 /// let mut dst = [0, 0];
2889 /// // Because the slices have to be the same length,
2890 /// // we slice the source slice from four elements
2891 /// // to two. It will panic if we don't do this.
2892 /// dst.clone_from_slice(&src[2..]);
2894 /// assert_eq!(src, [1, 2, 3, 4]);
2895 /// assert_eq!(dst, [3, 4]);
2898 /// Rust enforces that there can only be one mutable reference with no
2899 /// immutable references to a particular piece of data in a particular
2900 /// scope. Because of this, attempting to use `clone_from_slice` on a
2901 /// single slice will result in a compile failure:
2904 /// let mut slice = [1, 2, 3, 4, 5];
2906 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2909 /// To work around this, we can use [`split_at_mut`] to create two distinct
2910 /// sub-slices from a slice:
2913 /// let mut slice = [1, 2, 3, 4, 5];
2916 /// let (left, right) = slice.split_at_mut(2);
2917 /// left.clone_from_slice(&right[1..]);
2920 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2923 /// [`copy_from_slice`]: #method.copy_from_slice
2924 /// [`split_at_mut`]: #method.split_at_mut
2925 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2926 pub fn clone_from_slice(&mut self, src: &[T])
2930 assert!(self.len() == src.len(), "destination and source slices have different lengths");
2931 // NOTE: We need to explicitly slice them to the same length
2932 // for bounds checking to be elided, and the optimizer will
2933 // generate memcpy for simple cases (for example T = u8).
2934 let len = self.len();
2935 let src = &src[..len];
2937 self[i].clone_from(&src[i]);
2941 /// Copies all elements from `src` into `self`, using a memcpy.
2943 /// The length of `src` must be the same as `self`.
2945 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2949 /// This function will panic if the two slices have different lengths.
2953 /// Copying two elements from a slice into another:
2956 /// let src = [1, 2, 3, 4];
2957 /// let mut dst = [0, 0];
2959 /// // Because the slices have to be the same length,
2960 /// // we slice the source slice from four elements
2961 /// // to two. It will panic if we don't do this.
2962 /// dst.copy_from_slice(&src[2..]);
2964 /// assert_eq!(src, [1, 2, 3, 4]);
2965 /// assert_eq!(dst, [3, 4]);
2968 /// Rust enforces that there can only be one mutable reference with no
2969 /// immutable references to a particular piece of data in a particular
2970 /// scope. Because of this, attempting to use `copy_from_slice` on a
2971 /// single slice will result in a compile failure:
2974 /// let mut slice = [1, 2, 3, 4, 5];
2976 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
2979 /// To work around this, we can use [`split_at_mut`] to create two distinct
2980 /// sub-slices from a slice:
2983 /// let mut slice = [1, 2, 3, 4, 5];
2986 /// let (left, right) = slice.split_at_mut(2);
2987 /// left.copy_from_slice(&right[1..]);
2990 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2993 /// [`clone_from_slice`]: #method.clone_from_slice
2994 /// [`split_at_mut`]: #method.split_at_mut
2995 #[doc(alias = "memcpy")]
2996 #[stable(feature = "copy_from_slice", since = "1.9.0")]
2997 pub fn copy_from_slice(&mut self, src: &[T])
3001 // The panic code path was put into a cold function to not bloat the
3006 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3008 "source slice length ({}) does not match destination slice length ({})",
3013 if self.len() != src.len() {
3014 len_mismatch_fail(self.len(), src.len());
3017 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3018 // checked to have the same length. The slices cannot overlap because
3019 // mutable references are exclusive.
3021 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3025 /// Copies elements from one part of the slice to another part of itself,
3026 /// using a memmove.
3028 /// `src` is the range within `self` to copy from. `dest` is the starting
3029 /// index of the range within `self` to copy to, which will have the same
3030 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3031 /// must be less than or equal to `self.len()`.
3035 /// This function will panic if either range exceeds the end of the slice,
3036 /// or if the end of `src` is before the start.
3040 /// Copying four bytes within a slice:
3043 /// let mut bytes = *b"Hello, World!";
3045 /// bytes.copy_within(1..5, 8);
3047 /// assert_eq!(&bytes, b"Hello, Wello!");
3049 #[stable(feature = "copy_within", since = "1.37.0")]
3051 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3055 let Range { start: src_start, end: src_end } = src.assert_len(self.len());
3056 let count = src_end - src_start;
3057 assert!(dest <= self.len() - count, "dest is out of bounds");
3058 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3059 // as have those for `ptr::add`.
3061 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3065 /// Swaps all elements in `self` with those in `other`.
3067 /// The length of `other` must be the same as `self`.
3071 /// This function will panic if the two slices have different lengths.
3075 /// Swapping two elements across slices:
3078 /// let mut slice1 = [0, 0];
3079 /// let mut slice2 = [1, 2, 3, 4];
3081 /// slice1.swap_with_slice(&mut slice2[2..]);
3083 /// assert_eq!(slice1, [3, 4]);
3084 /// assert_eq!(slice2, [1, 2, 0, 0]);
3087 /// Rust enforces that there can only be one mutable reference to a
3088 /// particular piece of data in a particular scope. Because of this,
3089 /// attempting to use `swap_with_slice` on a single slice will result in
3090 /// a compile failure:
3093 /// let mut slice = [1, 2, 3, 4, 5];
3094 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3097 /// To work around this, we can use [`split_at_mut`] to create two distinct
3098 /// mutable sub-slices from a slice:
3101 /// let mut slice = [1, 2, 3, 4, 5];
3104 /// let (left, right) = slice.split_at_mut(2);
3105 /// left.swap_with_slice(&mut right[1..]);
3108 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3111 /// [`split_at_mut`]: #method.split_at_mut
3112 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3113 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3114 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3115 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3116 // checked to have the same length. The slices cannot overlap because
3117 // mutable references are exclusive.
3119 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3123 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3124 fn align_to_offsets<U>(&self) -> (usize, usize) {
3125 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3126 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3128 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3129 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3130 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3132 // Formula to calculate this is:
3134 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3135 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3137 // Expanded and simplified:
3139 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3140 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3142 // Luckily since all this is constant-evaluated... performance here matters not!
3144 fn gcd(a: usize, b: usize) -> usize {
3145 use crate::intrinsics;
3146 // iterative stein’s algorithm
3147 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3148 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3150 // SAFETY: `a` and `b` are checked to be non-zero values.
3151 let (ctz_a, mut ctz_b) = unsafe {
3158 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3160 let k = ctz_a.min(ctz_b);
3161 let mut a = a >> ctz_a;
3164 // remove all factors of 2 from b
3167 mem::swap(&mut a, &mut b);
3170 // SAFETY: `b` is checked to be non-zero.
3175 ctz_b = intrinsics::cttz_nonzero(b);
3180 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3181 let ts: usize = mem::size_of::<U>() / gcd;
3182 let us: usize = mem::size_of::<T>() / gcd;
3184 // Armed with this knowledge, we can find how many `U`s we can fit!
3185 let us_len = self.len() / ts * us;
3186 // And how many `T`s will be in the trailing slice!
3187 let ts_len = self.len() % ts;
3191 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3194 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3195 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3196 /// length possible for a given type and input slice, but only your algorithm's performance
3197 /// should depend on that, not its correctness. It is permissible for all of the input data to
3198 /// be returned as the prefix or suffix slice.
3200 /// This method has no purpose when either input element `T` or output element `U` are
3201 /// zero-sized and will return the original slice without splitting anything.
3205 /// This method is essentially a `transmute` with respect to the elements in the returned
3206 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3214 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3215 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3216 /// // less_efficient_algorithm_for_bytes(prefix);
3217 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3218 /// // less_efficient_algorithm_for_bytes(suffix);
3221 #[stable(feature = "slice_align_to", since = "1.30.0")]
3222 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3223 // Note that most of this function will be constant-evaluated,
3224 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3225 // handle ZSTs specially, which is – don't handle them at all.
3226 return (self, &[], &[]);
3229 // First, find at what point do we split between the first and 2nd slice. Easy with
3230 // ptr.align_offset.
3231 let ptr = self.as_ptr();
3232 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3233 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3234 if offset > self.len() {
3237 let (left, rest) = self.split_at(offset);
3238 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3239 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3240 // since the caller guarantees that we can transmute `T` to `U` safely.
3244 from_raw_parts(rest.as_ptr() as *const U, us_len),
3245 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3251 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3254 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3255 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3256 /// length possible for a given type and input slice, but only your algorithm's performance
3257 /// should depend on that, not its correctness. It is permissible for all of the input data to
3258 /// be returned as the prefix or suffix slice.
3260 /// This method has no purpose when either input element `T` or output element `U` are
3261 /// zero-sized and will return the original slice without splitting anything.
3265 /// This method is essentially a `transmute` with respect to the elements in the returned
3266 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3274 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3275 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3276 /// // less_efficient_algorithm_for_bytes(prefix);
3277 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3278 /// // less_efficient_algorithm_for_bytes(suffix);
3281 #[stable(feature = "slice_align_to", since = "1.30.0")]
3282 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3283 // Note that most of this function will be constant-evaluated,
3284 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3285 // handle ZSTs specially, which is – don't handle them at all.
3286 return (self, &mut [], &mut []);
3289 // First, find at what point do we split between the first and 2nd slice. Easy with
3290 // ptr.align_offset.
3291 let ptr = self.as_ptr();
3292 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3293 // rest of the method. This is done by passing a pointer to &[T] with an
3294 // alignment targeted for U.
3295 // `crate::ptr::align_offset` is called with a correctly aligned and
3296 // valid pointer `ptr` (it comes from a reference to `self`) and with
3297 // a size that is a power of two (since it comes from the alignement for U),
3298 // satisfying its safety constraints.
3299 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3300 if offset > self.len() {
3301 (self, &mut [], &mut [])
3303 let (left, rest) = self.split_at_mut(offset);
3304 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3305 let rest_len = rest.len();
3306 let mut_ptr = rest.as_mut_ptr();
3307 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3308 // SAFETY: see comments for `align_to`.
3312 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3313 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3319 /// Checks if the elements of this slice are sorted.
3321 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3322 /// slice yields exactly zero or one element, `true` is returned.
3324 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3325 /// implies that this function returns `false` if any two consecutive items are not
3331 /// #![feature(is_sorted)]
3332 /// let empty: [i32; 0] = [];
3334 /// assert!([1, 2, 2, 9].is_sorted());
3335 /// assert!(![1, 3, 2, 4].is_sorted());
3336 /// assert!([0].is_sorted());
3337 /// assert!(empty.is_sorted());
3338 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3341 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3342 pub fn is_sorted(&self) -> bool
3346 self.is_sorted_by(|a, b| a.partial_cmp(b))
3349 /// Checks if the elements of this slice are sorted using the given comparator function.
3351 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3352 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3353 /// [`is_sorted`]; see its documentation for more information.
3355 /// [`is_sorted`]: #method.is_sorted
3356 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3357 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3359 F: FnMut(&T, &T) -> Option<Ordering>,
3361 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3364 /// Checks if the elements of this slice are sorted using the given key extraction function.
3366 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3367 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3368 /// documentation for more information.
3370 /// [`is_sorted`]: #method.is_sorted
3375 /// #![feature(is_sorted)]
3377 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3378 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3381 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3382 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3387 self.iter().is_sorted_by_key(f)
3390 /// Returns the index of the partition point according to the given predicate
3391 /// (the index of the first element of the second partition).
3393 /// The slice is assumed to be partitioned according to the given predicate.
3394 /// This means that all elements for which the predicate returns true are at the start of the slice
3395 /// and all elements for which the predicate returns false are at the end.
3396 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3397 /// (all odd numbers are at the start, all even at the end).
3399 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3400 /// as this method performs a kind of binary search.
3405 /// #![feature(partition_point)]
3407 /// let v = [1, 2, 3, 3, 5, 6, 7];
3408 /// let i = v.partition_point(|&x| x < 5);
3410 /// assert_eq!(i, 4);
3411 /// assert!(v[..i].iter().all(|&x| x < 5));
3412 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3414 #[unstable(feature = "partition_point", reason = "new API", issue = "73831")]
3415 pub fn partition_point<P>(&self, mut pred: P) -> usize
3417 P: FnMut(&T) -> bool,
3420 let mut right = self.len();
3422 while left != right {
3423 let mid = left + (right - left) / 2;
3424 // SAFETY: When `left < right`, `left <= mid < right`.
3425 // Therefore `left` always increases and `right` always decreases,
3426 // and either of them is selected. In both cases `left <= right` is
3427 // satisfied. Therefore if `left < right` in a step, `left <= right`
3428 // is satisfied in the next step. Therefore as long as `left != right`,
3429 // `0 <= left < right <= len` is satisfied and if this case
3430 // `0 <= mid < len` is satisfied too.
3431 let value = unsafe { self.get_unchecked(mid) };
3443 #[stable(feature = "rust1", since = "1.0.0")]
3444 impl<T> Default for &[T] {
3445 /// Creates an empty slice.
3446 fn default() -> Self {
3451 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3452 impl<T> Default for &mut [T] {
3453 /// Creates a mutable empty slice.
3454 fn default() -> Self {
3459 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3460 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3461 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3462 /// `str`) to slices, and then this trait will be replaced or abolished.
3463 pub trait SlicePattern {
3464 /// The element type of the slice being matched on.
3467 /// Currently, the consumers of `SlicePattern` need a slice.
3468 fn as_slice(&self) -> &[Self::Item];
3471 #[stable(feature = "slice_strip", since = "1.51.0")]
3472 impl<T> SlicePattern for [T] {
3476 fn as_slice(&self) -> &[Self::Item] {
3481 #[stable(feature = "slice_strip", since = "1.51.0")]
3482 impl<T, const N: usize> SlicePattern for [T; N] {
3486 fn as_slice(&self) -> &[Self::Item] {