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 = "1.49.0")]
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 just cast
546 // them to their raw pointers to do the swap.
547 let pa: *mut T = &mut self[a];
548 let pb: *mut T = &mut self[b];
549 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
550 // to elements in the slice and therefore are guaranteed to be valid and aligned.
551 // Note that accessing the elements behind `a` and `b` is checked and will
552 // panic when out of bounds.
558 /// Reverses the order of elements in the slice, in place.
563 /// let mut v = [1, 2, 3];
565 /// assert!(v == [3, 2, 1]);
567 #[stable(feature = "rust1", since = "1.0.0")]
569 pub fn reverse(&mut self) {
570 let mut i: usize = 0;
573 // For very small types, all the individual reads in the normal
574 // path perform poorly. We can do better, given efficient unaligned
575 // load/store, by loading a larger chunk and reversing a register.
577 // Ideally LLVM would do this for us, as it knows better than we do
578 // whether unaligned reads are efficient (since that changes between
579 // different ARM versions, for example) and what the best chunk size
580 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
581 // the loop, so we need to do this ourselves. (Hypothesis: reverse
582 // is troublesome because the sides can be aligned differently --
583 // will be, when the length is odd -- so there's no way of emitting
584 // pre- and postludes to use fully-aligned SIMD in the middle.)
586 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
588 if fast_unaligned && mem::size_of::<T>() == 1 {
589 // Use the llvm.bswap intrinsic to reverse u8s in a usize
590 let chunk = mem::size_of::<usize>();
591 while i + chunk - 1 < ln / 2 {
592 // SAFETY: There are several things to check here:
594 // - Note that `chunk` is either 4 or 8 due to the cfg check
595 // above. So `chunk - 1` is positive.
596 // - Indexing with index `i` is fine as the loop check guarantees
597 // `i + chunk - 1 < ln / 2`
598 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
599 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
600 // - `i + chunk > 0` is trivially true.
601 // - The loop check guarantees:
602 // `i + chunk - 1 < ln / 2`
603 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
604 // - The `read_unaligned` and `write_unaligned` calls are fine:
605 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
606 // (see above) and `pb` points to index `ln - i - chunk`, so
607 // both are at least `chunk`
608 // many bytes away from the end of `self`.
609 // - Any initialized memory is valid `usize`.
611 let ptr = self.as_mut_ptr();
613 let pb = ptr.add(ln - i - chunk);
614 let va = ptr::read_unaligned(pa as *mut usize);
615 let vb = ptr::read_unaligned(pb as *mut usize);
616 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
617 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
623 if fast_unaligned && mem::size_of::<T>() == 2 {
624 // Use rotate-by-16 to reverse u16s in a u32
625 let chunk = mem::size_of::<u32>() / 2;
626 while i + chunk - 1 < ln / 2 {
627 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
628 // (and obviously `i < ln`), because each element is 2 bytes and
631 // `i + chunk - 1 < ln / 2` # while condition
632 // `i + 2 - 1 < ln / 2`
635 // Since it's less than the length divided by 2, then it must be
638 // This also means that the condition `0 < i + chunk <= ln` is
639 // always respected, ensuring the `pb` pointer can be used
642 let ptr = self.as_mut_ptr();
644 let pb = ptr.add(ln - i - chunk);
645 let va = ptr::read_unaligned(pa as *mut u32);
646 let vb = ptr::read_unaligned(pb as *mut u32);
647 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
648 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
655 // SAFETY: `i` is inferior to half the length of the slice so
656 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
657 // will not go further than `ln / 2 - 1`).
658 // The resulting pointers `pa` and `pb` are therefore valid and
659 // aligned, and can be read from and written to.
661 // Unsafe swap to avoid the bounds check in safe swap.
662 let ptr = self.as_mut_ptr();
664 let pb = ptr.add(ln - i - 1);
671 /// Returns an iterator over the slice.
676 /// let x = &[1, 2, 4];
677 /// let mut iterator = x.iter();
679 /// assert_eq!(iterator.next(), Some(&1));
680 /// assert_eq!(iterator.next(), Some(&2));
681 /// assert_eq!(iterator.next(), Some(&4));
682 /// assert_eq!(iterator.next(), None);
684 #[stable(feature = "rust1", since = "1.0.0")]
686 pub fn iter(&self) -> Iter<'_, T> {
690 /// Returns an iterator that allows modifying each value.
695 /// let x = &mut [1, 2, 4];
696 /// for elem in x.iter_mut() {
699 /// assert_eq!(x, &[3, 4, 6]);
701 #[stable(feature = "rust1", since = "1.0.0")]
703 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
707 /// Returns an iterator over all contiguous windows of length
708 /// `size`. The windows overlap. If the slice is shorter than
709 /// `size`, the iterator returns no values.
713 /// Panics if `size` is 0.
718 /// let slice = ['r', 'u', 's', 't'];
719 /// let mut iter = slice.windows(2);
720 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
721 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
722 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
723 /// assert!(iter.next().is_none());
726 /// If the slice is shorter than `size`:
729 /// let slice = ['f', 'o', 'o'];
730 /// let mut iter = slice.windows(4);
731 /// assert!(iter.next().is_none());
733 #[stable(feature = "rust1", since = "1.0.0")]
735 pub fn windows(&self, size: usize) -> Windows<'_, T> {
736 let size = NonZeroUsize::new(size).expect("size is zero");
737 Windows::new(self, size)
740 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
741 /// beginning of the slice.
743 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
744 /// slice, then the last chunk will not have length `chunk_size`.
746 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
747 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
752 /// Panics if `chunk_size` is 0.
757 /// let slice = ['l', 'o', 'r', 'e', 'm'];
758 /// let mut iter = slice.chunks(2);
759 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
760 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
761 /// assert_eq!(iter.next().unwrap(), &['m']);
762 /// assert!(iter.next().is_none());
765 /// [`chunks_exact`]: #method.chunks_exact
766 /// [`rchunks`]: #method.rchunks
767 #[stable(feature = "rust1", since = "1.0.0")]
769 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
770 assert_ne!(chunk_size, 0);
771 Chunks::new(self, chunk_size)
774 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
775 /// beginning of the slice.
777 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
778 /// length of the slice, then the last chunk will not have length `chunk_size`.
780 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
781 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
782 /// the end of the slice.
786 /// Panics if `chunk_size` is 0.
791 /// let v = &mut [0, 0, 0, 0, 0];
792 /// let mut count = 1;
794 /// for chunk in v.chunks_mut(2) {
795 /// for elem in chunk.iter_mut() {
800 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
803 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
804 /// [`rchunks_mut`]: #method.rchunks_mut
805 #[stable(feature = "rust1", since = "1.0.0")]
807 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
808 assert_ne!(chunk_size, 0);
809 ChunksMut::new(self, chunk_size)
812 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
813 /// beginning of the slice.
815 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
816 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
817 /// from the `remainder` function of the iterator.
819 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
820 /// resulting code better than in the case of [`chunks`].
822 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
823 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
827 /// Panics if `chunk_size` is 0.
832 /// let slice = ['l', 'o', 'r', 'e', 'm'];
833 /// let mut iter = slice.chunks_exact(2);
834 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
835 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
836 /// assert!(iter.next().is_none());
837 /// assert_eq!(iter.remainder(), &['m']);
840 /// [`chunks`]: #method.chunks
841 /// [`rchunks_exact`]: #method.rchunks_exact
842 #[stable(feature = "chunks_exact", since = "1.31.0")]
844 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
845 assert_ne!(chunk_size, 0);
846 ChunksExact::new(self, chunk_size)
849 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
850 /// beginning of the slice.
852 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
853 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
854 /// retrieved from the `into_remainder` function of the iterator.
856 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
857 /// resulting code better than in the case of [`chunks_mut`].
859 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
860 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
865 /// Panics if `chunk_size` is 0.
870 /// let v = &mut [0, 0, 0, 0, 0];
871 /// let mut count = 1;
873 /// for chunk in v.chunks_exact_mut(2) {
874 /// for elem in chunk.iter_mut() {
879 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
882 /// [`chunks_mut`]: #method.chunks_mut
883 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
884 #[stable(feature = "chunks_exact", since = "1.31.0")]
886 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
887 assert_ne!(chunk_size, 0);
888 ChunksExactMut::new(self, chunk_size)
891 /// Splits the slice into a slice of `N`-element arrays,
892 /// starting at the beginning of the slice,
893 /// and a remainder slice with length strictly less than `N`.
897 /// Panics if `N` is 0. This check will most probably get changed to a compile time
898 /// error before this method gets stabilized.
903 /// #![feature(slice_as_chunks)]
904 /// let slice = ['l', 'o', 'r', 'e', 'm'];
905 /// let (chunks, remainder) = slice.as_chunks();
906 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
907 /// assert_eq!(remainder, &['m']);
909 #[unstable(feature = "slice_as_chunks", issue = "74985")]
911 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
913 let len = self.len() / N;
914 let (multiple_of_n, remainder) = self.split_at(len * N);
915 // SAFETY: We cast a slice of `len * N` elements into
916 // a slice of `len` many `N` elements chunks.
917 let array_slice: &[[T; N]] = unsafe { from_raw_parts(multiple_of_n.as_ptr().cast(), len) };
918 (array_slice, remainder)
921 /// Returns an iterator over `N` elements of the slice at a time, starting at the
922 /// beginning of the slice.
924 /// The chunks are array references and do not overlap. If `N` does not divide the
925 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
926 /// retrieved from the `remainder` function of the iterator.
928 /// This method is the const generic equivalent of [`chunks_exact`].
932 /// Panics if `N` is 0. This check will most probably get changed to a compile time
933 /// error before this method gets stabilized.
938 /// #![feature(array_chunks)]
939 /// let slice = ['l', 'o', 'r', 'e', 'm'];
940 /// let mut iter = slice.array_chunks();
941 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
942 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
943 /// assert!(iter.next().is_none());
944 /// assert_eq!(iter.remainder(), &['m']);
947 /// [`chunks_exact`]: #method.chunks_exact
948 #[unstable(feature = "array_chunks", issue = "74985")]
950 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
952 ArrayChunks::new(self)
955 /// Splits the slice into a slice of `N`-element arrays,
956 /// starting at the beginning of the slice,
957 /// and a remainder slice with length strictly less than `N`.
961 /// Panics if `N` is 0. This check will most probably get changed to a compile time
962 /// error before this method gets stabilized.
967 /// #![feature(slice_as_chunks)]
968 /// let v = &mut [0, 0, 0, 0, 0];
969 /// let mut count = 1;
971 /// let (chunks, remainder) = v.as_chunks_mut();
972 /// remainder[0] = 9;
973 /// for chunk in chunks {
974 /// *chunk = [count; 2];
977 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
979 #[unstable(feature = "slice_as_chunks", issue = "74985")]
981 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
983 let len = self.len() / N;
984 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
985 let array_slice: &mut [[T; N]] =
986 // SAFETY: We cast a slice of `len * N` elements into
987 // a slice of `len` many `N` elements chunks.
988 unsafe { from_raw_parts_mut(multiple_of_n.as_mut_ptr().cast(), len) };
989 (array_slice, remainder)
992 /// Returns an iterator over `N` elements of the slice at a time, starting at the
993 /// beginning of the slice.
995 /// The chunks are mutable array references and do not overlap. If `N` does not divide
996 /// the length of the slice, then the last up to `N-1` elements will be omitted and
997 /// can be retrieved from the `into_remainder` function of the iterator.
999 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1003 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1004 /// error before this method gets stabilized.
1009 /// #![feature(array_chunks)]
1010 /// let v = &mut [0, 0, 0, 0, 0];
1011 /// let mut count = 1;
1013 /// for chunk in v.array_chunks_mut() {
1014 /// *chunk = [count; 2];
1017 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1020 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1021 #[unstable(feature = "array_chunks", issue = "74985")]
1023 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1025 ArrayChunksMut::new(self)
1028 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1029 /// starting at the beginning of the slice.
1031 /// This is the const generic equivalent of [`windows`].
1033 /// If `N` is greater than the size of the slice, it will return no windows.
1037 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1038 /// error before this method gets stabilized.
1043 /// #![feature(array_windows)]
1044 /// let slice = [0, 1, 2, 3];
1045 /// let mut iter = slice.array_windows();
1046 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1047 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1048 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1049 /// assert!(iter.next().is_none());
1052 /// [`windows`]: #method.windows
1053 #[unstable(feature = "array_windows", issue = "75027")]
1055 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1057 ArrayWindows::new(self)
1060 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1063 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1064 /// slice, then the last chunk will not have length `chunk_size`.
1066 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1067 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1072 /// Panics if `chunk_size` is 0.
1077 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1078 /// let mut iter = slice.rchunks(2);
1079 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1080 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1081 /// assert_eq!(iter.next().unwrap(), &['l']);
1082 /// assert!(iter.next().is_none());
1085 /// [`rchunks_exact`]: #method.rchunks_exact
1086 /// [`chunks`]: #method.chunks
1087 #[stable(feature = "rchunks", since = "1.31.0")]
1089 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1090 assert!(chunk_size != 0);
1091 RChunks::new(self, chunk_size)
1094 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1097 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1098 /// length of the slice, then the last chunk will not have length `chunk_size`.
1100 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1101 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1102 /// beginning of the slice.
1106 /// Panics if `chunk_size` is 0.
1111 /// let v = &mut [0, 0, 0, 0, 0];
1112 /// let mut count = 1;
1114 /// for chunk in v.rchunks_mut(2) {
1115 /// for elem in chunk.iter_mut() {
1120 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1123 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
1124 /// [`chunks_mut`]: #method.chunks_mut
1125 #[stable(feature = "rchunks", since = "1.31.0")]
1127 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1128 assert!(chunk_size != 0);
1129 RChunksMut::new(self, chunk_size)
1132 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1133 /// end of the slice.
1135 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1136 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1137 /// from the `remainder` function of the iterator.
1139 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1140 /// resulting code better than in the case of [`chunks`].
1142 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1143 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1148 /// Panics if `chunk_size` is 0.
1153 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1154 /// let mut iter = slice.rchunks_exact(2);
1155 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1156 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1157 /// assert!(iter.next().is_none());
1158 /// assert_eq!(iter.remainder(), &['l']);
1161 /// [`chunks`]: #method.chunks
1162 /// [`rchunks`]: #method.rchunks
1163 /// [`chunks_exact`]: #method.chunks_exact
1164 #[stable(feature = "rchunks", since = "1.31.0")]
1166 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1167 assert!(chunk_size != 0);
1168 RChunksExact::new(self, chunk_size)
1171 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1174 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1175 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1176 /// retrieved from the `into_remainder` function of the iterator.
1178 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1179 /// resulting code better than in the case of [`chunks_mut`].
1181 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1182 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1187 /// Panics if `chunk_size` is 0.
1192 /// let v = &mut [0, 0, 0, 0, 0];
1193 /// let mut count = 1;
1195 /// for chunk in v.rchunks_exact_mut(2) {
1196 /// for elem in chunk.iter_mut() {
1201 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1204 /// [`chunks_mut`]: #method.chunks_mut
1205 /// [`rchunks_mut`]: #method.rchunks_mut
1206 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1207 #[stable(feature = "rchunks", since = "1.31.0")]
1209 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1210 assert!(chunk_size != 0);
1211 RChunksExactMut::new(self, chunk_size)
1214 /// Returns an iterator over the slice producing non-overlapping runs
1215 /// of elements using the predicate to separate them.
1217 /// The predicate is called on two elements following themselves,
1218 /// it means the predicate is called on `slice[0]` and `slice[1]`
1219 /// then on `slice[1]` and `slice[2]` and so on.
1224 /// #![feature(slice_group_by)]
1226 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1228 /// let mut iter = slice.group_by(|a, b| a == b);
1230 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1231 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1232 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1233 /// assert_eq!(iter.next(), None);
1236 /// This method can be used to extract the sorted subslices:
1239 /// #![feature(slice_group_by)]
1241 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1243 /// let mut iter = slice.group_by(|a, b| a <= b);
1245 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1246 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1247 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1248 /// assert_eq!(iter.next(), None);
1250 #[unstable(feature = "slice_group_by", issue = "80552")]
1252 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1254 F: FnMut(&T, &T) -> bool,
1256 GroupBy::new(self, pred)
1259 /// Returns an iterator over the slice producing non-overlapping mutable
1260 /// runs of elements using the predicate to separate them.
1262 /// The predicate is called on two elements following themselves,
1263 /// it means the predicate is called on `slice[0]` and `slice[1]`
1264 /// then on `slice[1]` and `slice[2]` and so on.
1269 /// #![feature(slice_group_by)]
1271 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1273 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1275 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1276 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1277 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1278 /// assert_eq!(iter.next(), None);
1281 /// This method can be used to extract the sorted subslices:
1284 /// #![feature(slice_group_by)]
1286 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1288 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1290 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1291 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1292 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1293 /// assert_eq!(iter.next(), None);
1295 #[unstable(feature = "slice_group_by", issue = "80552")]
1297 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1299 F: FnMut(&T, &T) -> bool,
1301 GroupByMut::new(self, pred)
1304 /// Divides one slice into two at an index.
1306 /// The first will contain all indices from `[0, mid)` (excluding
1307 /// the index `mid` itself) and the second will contain all
1308 /// indices from `[mid, len)` (excluding the index `len` itself).
1312 /// Panics if `mid > len`.
1317 /// let v = [1, 2, 3, 4, 5, 6];
1320 /// let (left, right) = v.split_at(0);
1321 /// assert_eq!(left, []);
1322 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1326 /// let (left, right) = v.split_at(2);
1327 /// assert_eq!(left, [1, 2]);
1328 /// assert_eq!(right, [3, 4, 5, 6]);
1332 /// let (left, right) = v.split_at(6);
1333 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1334 /// assert_eq!(right, []);
1337 #[stable(feature = "rust1", since = "1.0.0")]
1339 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1340 assert!(mid <= self.len());
1341 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1342 // fulfills the requirements of `from_raw_parts_mut`.
1343 unsafe { self.split_at_unchecked(mid) }
1346 /// Divides one mutable slice into two at an index.
1348 /// The first will contain all indices from `[0, mid)` (excluding
1349 /// the index `mid` itself) and the second will contain all
1350 /// indices from `[mid, len)` (excluding the index `len` itself).
1354 /// Panics if `mid > len`.
1359 /// let mut v = [1, 0, 3, 0, 5, 6];
1360 /// // scoped to restrict the lifetime of the borrows
1362 /// let (left, right) = v.split_at_mut(2);
1363 /// assert_eq!(left, [1, 0]);
1364 /// assert_eq!(right, [3, 0, 5, 6]);
1368 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1370 #[stable(feature = "rust1", since = "1.0.0")]
1372 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1373 assert!(mid <= self.len());
1374 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1375 // fulfills the requirements of `from_raw_parts_mut`.
1376 unsafe { self.split_at_mut_unchecked(mid) }
1379 /// Divides one slice into two at an index, without doing bounds checking.
1381 /// The first will contain all indices from `[0, mid)` (excluding
1382 /// the index `mid` itself) and the second will contain all
1383 /// indices from `[mid, len)` (excluding the index `len` itself).
1385 /// For a safe alternative see [`split_at`].
1389 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1390 /// even if the resulting reference is not used. The caller has to ensure that
1391 /// `0 <= mid <= self.len()`.
1393 /// [`split_at`]: #method.split_at
1394 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1399 /// #![feature(slice_split_at_unchecked)]
1401 /// let v = [1, 2, 3, 4, 5, 6];
1404 /// let (left, right) = v.split_at_unchecked(0);
1405 /// assert_eq!(left, []);
1406 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1410 /// let (left, right) = v.split_at_unchecked(2);
1411 /// assert_eq!(left, [1, 2]);
1412 /// assert_eq!(right, [3, 4, 5, 6]);
1416 /// let (left, right) = v.split_at_unchecked(6);
1417 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1418 /// assert_eq!(right, []);
1421 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1423 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1424 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1425 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1428 /// Divides one mutable slice into two at an index, without doing bounds checking.
1430 /// The first will contain all indices from `[0, mid)` (excluding
1431 /// the index `mid` itself) and the second will contain all
1432 /// indices from `[mid, len)` (excluding the index `len` itself).
1434 /// For a safe alternative see [`split_at_mut`].
1438 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1439 /// even if the resulting reference is not used. The caller has to ensure that
1440 /// `0 <= mid <= self.len()`.
1442 /// [`split_at_mut`]: #method.split_at_mut
1443 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1448 /// #![feature(slice_split_at_unchecked)]
1450 /// let mut v = [1, 0, 3, 0, 5, 6];
1451 /// // scoped to restrict the lifetime of the borrows
1453 /// let (left, right) = v.split_at_mut_unchecked(2);
1454 /// assert_eq!(left, [1, 0]);
1455 /// assert_eq!(right, [3, 0, 5, 6]);
1459 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1461 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1463 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1464 let len = self.len();
1465 let ptr = self.as_mut_ptr();
1467 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1469 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1471 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1474 /// Returns an iterator over subslices separated by elements that match
1475 /// `pred`. The matched element is not contained in the subslices.
1480 /// let slice = [10, 40, 33, 20];
1481 /// let mut iter = slice.split(|num| num % 3 == 0);
1483 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1484 /// assert_eq!(iter.next().unwrap(), &[20]);
1485 /// assert!(iter.next().is_none());
1488 /// If the first element is matched, an empty slice will be the first item
1489 /// returned by the iterator. Similarly, if the last element in the slice
1490 /// is matched, an empty slice will be the last item returned by the
1494 /// let slice = [10, 40, 33];
1495 /// let mut iter = slice.split(|num| num % 3 == 0);
1497 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1498 /// assert_eq!(iter.next().unwrap(), &[]);
1499 /// assert!(iter.next().is_none());
1502 /// If two matched elements are directly adjacent, an empty slice will be
1503 /// present between them:
1506 /// let slice = [10, 6, 33, 20];
1507 /// let mut iter = slice.split(|num| num % 3 == 0);
1509 /// assert_eq!(iter.next().unwrap(), &[10]);
1510 /// assert_eq!(iter.next().unwrap(), &[]);
1511 /// assert_eq!(iter.next().unwrap(), &[20]);
1512 /// assert!(iter.next().is_none());
1514 #[stable(feature = "rust1", since = "1.0.0")]
1516 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1518 F: FnMut(&T) -> bool,
1520 Split::new(self, pred)
1523 /// Returns an iterator over mutable subslices separated by elements that
1524 /// match `pred`. The matched element is not contained in the subslices.
1529 /// let mut v = [10, 40, 30, 20, 60, 50];
1531 /// for group in v.split_mut(|num| *num % 3 == 0) {
1534 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1536 #[stable(feature = "rust1", since = "1.0.0")]
1538 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1540 F: FnMut(&T) -> bool,
1542 SplitMut::new(self, pred)
1545 /// Returns an iterator over subslices separated by elements that match
1546 /// `pred`. The matched element is contained in the end of the previous
1547 /// subslice as a terminator.
1552 /// let slice = [10, 40, 33, 20];
1553 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1555 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1556 /// assert_eq!(iter.next().unwrap(), &[20]);
1557 /// assert!(iter.next().is_none());
1560 /// If the last element of the slice is matched,
1561 /// that element will be considered the terminator of the preceding slice.
1562 /// That slice will be the last item returned by the iterator.
1565 /// let slice = [3, 10, 40, 33];
1566 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1568 /// assert_eq!(iter.next().unwrap(), &[3]);
1569 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1570 /// assert!(iter.next().is_none());
1572 #[stable(feature = "split_inclusive", since = "1.49.0")]
1574 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1576 F: FnMut(&T) -> bool,
1578 SplitInclusive::new(self, pred)
1581 /// Returns an iterator over mutable subslices separated by elements that
1582 /// match `pred`. The matched element is contained in the previous
1583 /// subslice as a terminator.
1588 /// let mut v = [10, 40, 30, 20, 60, 50];
1590 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1591 /// let terminator_idx = group.len()-1;
1592 /// group[terminator_idx] = 1;
1594 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1596 #[stable(feature = "split_inclusive", since = "1.49.0")]
1598 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1600 F: FnMut(&T) -> bool,
1602 SplitInclusiveMut::new(self, pred)
1605 /// Returns an iterator over subslices separated by elements that match
1606 /// `pred`, starting at the end of the slice and working backwards.
1607 /// The matched element is not contained in the subslices.
1612 /// let slice = [11, 22, 33, 0, 44, 55];
1613 /// let mut iter = slice.rsplit(|num| *num == 0);
1615 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1616 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1617 /// assert_eq!(iter.next(), None);
1620 /// As with `split()`, if the first or last element is matched, an empty
1621 /// slice will be the first (or last) item returned by the iterator.
1624 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1625 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1626 /// assert_eq!(it.next().unwrap(), &[]);
1627 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1628 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1629 /// assert_eq!(it.next().unwrap(), &[]);
1630 /// assert_eq!(it.next(), None);
1632 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1634 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1636 F: FnMut(&T) -> bool,
1638 RSplit::new(self, pred)
1641 /// Returns an iterator over mutable subslices separated by elements that
1642 /// match `pred`, starting at the end of the slice and working
1643 /// backwards. The matched element is not contained in the subslices.
1648 /// let mut v = [100, 400, 300, 200, 600, 500];
1650 /// let mut count = 0;
1651 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1653 /// group[0] = count;
1655 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1658 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1660 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1662 F: FnMut(&T) -> bool,
1664 RSplitMut::new(self, pred)
1667 /// Returns an iterator over subslices separated by elements that match
1668 /// `pred`, limited to returning at most `n` items. The matched element is
1669 /// not contained in the subslices.
1671 /// The last element returned, if any, will contain the remainder of the
1676 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1677 /// `[20, 60, 50]`):
1680 /// let v = [10, 40, 30, 20, 60, 50];
1682 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1683 /// println!("{:?}", group);
1686 #[stable(feature = "rust1", since = "1.0.0")]
1688 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1690 F: FnMut(&T) -> bool,
1692 SplitN::new(self.split(pred), n)
1695 /// Returns an iterator over subslices separated by elements that match
1696 /// `pred`, limited to returning at most `n` items. The matched element is
1697 /// not contained in the subslices.
1699 /// The last element returned, if any, will contain the remainder of the
1705 /// let mut v = [10, 40, 30, 20, 60, 50];
1707 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1710 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1712 #[stable(feature = "rust1", since = "1.0.0")]
1714 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1716 F: FnMut(&T) -> bool,
1718 SplitNMut::new(self.split_mut(pred), n)
1721 /// Returns an iterator over subslices separated by elements that match
1722 /// `pred` limited to returning at most `n` items. This starts at the end of
1723 /// the slice and works backwards. The matched element is not contained in
1726 /// The last element returned, if any, will contain the remainder of the
1731 /// Print the slice split once, starting from the end, by numbers divisible
1732 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1735 /// let v = [10, 40, 30, 20, 60, 50];
1737 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1738 /// println!("{:?}", group);
1741 #[stable(feature = "rust1", since = "1.0.0")]
1743 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1745 F: FnMut(&T) -> bool,
1747 RSplitN::new(self.rsplit(pred), n)
1750 /// Returns an iterator over subslices separated by elements that match
1751 /// `pred` limited to returning at most `n` items. This starts at the end of
1752 /// the slice and works backwards. The matched element is not contained in
1755 /// The last element returned, if any, will contain the remainder of the
1761 /// let mut s = [10, 40, 30, 20, 60, 50];
1763 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1766 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1768 #[stable(feature = "rust1", since = "1.0.0")]
1770 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1772 F: FnMut(&T) -> bool,
1774 RSplitNMut::new(self.rsplit_mut(pred), n)
1777 /// Returns `true` if the slice contains an element with the given value.
1782 /// let v = [10, 40, 30];
1783 /// assert!(v.contains(&30));
1784 /// assert!(!v.contains(&50));
1787 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1788 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1791 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1792 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1793 /// assert!(!v.iter().any(|e| e == "hi"));
1795 #[stable(feature = "rust1", since = "1.0.0")]
1797 pub fn contains(&self, x: &T) -> bool
1801 cmp::SliceContains::slice_contains(x, self)
1804 /// Returns `true` if `needle` is a prefix of the slice.
1809 /// let v = [10, 40, 30];
1810 /// assert!(v.starts_with(&[10]));
1811 /// assert!(v.starts_with(&[10, 40]));
1812 /// assert!(!v.starts_with(&[50]));
1813 /// assert!(!v.starts_with(&[10, 50]));
1816 /// Always returns `true` if `needle` is an empty slice:
1819 /// let v = &[10, 40, 30];
1820 /// assert!(v.starts_with(&[]));
1821 /// let v: &[u8] = &[];
1822 /// assert!(v.starts_with(&[]));
1824 #[stable(feature = "rust1", since = "1.0.0")]
1825 pub fn starts_with(&self, needle: &[T]) -> bool
1829 let n = needle.len();
1830 self.len() >= n && needle == &self[..n]
1833 /// Returns `true` if `needle` is a suffix of the slice.
1838 /// let v = [10, 40, 30];
1839 /// assert!(v.ends_with(&[30]));
1840 /// assert!(v.ends_with(&[40, 30]));
1841 /// assert!(!v.ends_with(&[50]));
1842 /// assert!(!v.ends_with(&[50, 30]));
1845 /// Always returns `true` if `needle` is an empty slice:
1848 /// let v = &[10, 40, 30];
1849 /// assert!(v.ends_with(&[]));
1850 /// let v: &[u8] = &[];
1851 /// assert!(v.ends_with(&[]));
1853 #[stable(feature = "rust1", since = "1.0.0")]
1854 pub fn ends_with(&self, needle: &[T]) -> bool
1858 let (m, n) = (self.len(), needle.len());
1859 m >= n && needle == &self[m - n..]
1862 /// Returns a subslice with the prefix removed.
1864 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
1865 /// If `prefix` is empty, simply returns the original slice.
1867 /// If the slice does not start with `prefix`, returns `None`.
1872 /// #![feature(slice_strip)]
1873 /// let v = &[10, 40, 30];
1874 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
1875 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
1876 /// assert_eq!(v.strip_prefix(&[50]), None);
1877 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
1879 #[must_use = "returns the subslice without modifying the original"]
1880 #[unstable(feature = "slice_strip", issue = "73413")]
1881 pub fn strip_prefix(&self, prefix: &[T]) -> Option<&[T]>
1885 let n = prefix.len();
1886 if n <= self.len() {
1887 let (head, tail) = self.split_at(n);
1895 /// Returns a subslice with the suffix removed.
1897 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
1898 /// If `suffix` is empty, simply returns the original slice.
1900 /// If the slice does not end with `suffix`, returns `None`.
1905 /// #![feature(slice_strip)]
1906 /// let v = &[10, 40, 30];
1907 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
1908 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
1909 /// assert_eq!(v.strip_suffix(&[50]), None);
1910 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
1912 #[must_use = "returns the subslice without modifying the original"]
1913 #[unstable(feature = "slice_strip", issue = "73413")]
1914 pub fn strip_suffix(&self, suffix: &[T]) -> Option<&[T]>
1918 let (len, n) = (self.len(), suffix.len());
1920 let (head, tail) = self.split_at(len - n);
1928 /// Binary searches this sorted slice for a given element.
1930 /// If the value is found then [`Result::Ok`] is returned, containing the
1931 /// index of the matching element. If there are multiple matches, then any
1932 /// one of the matches could be returned. If the value is not found then
1933 /// [`Result::Err`] is returned, containing the index where a matching
1934 /// element could be inserted while maintaining sorted order.
1938 /// Looks up a series of four elements. The first is found, with a
1939 /// uniquely determined position; the second and third are not
1940 /// found; the fourth could match any position in `[1, 4]`.
1943 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1945 /// assert_eq!(s.binary_search(&13), Ok(9));
1946 /// assert_eq!(s.binary_search(&4), Err(7));
1947 /// assert_eq!(s.binary_search(&100), Err(13));
1948 /// let r = s.binary_search(&1);
1949 /// assert!(match r { Ok(1..=4) => true, _ => false, });
1952 /// If you want to insert an item to a sorted vector, while maintaining
1956 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1958 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
1959 /// s.insert(idx, num);
1960 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
1962 #[stable(feature = "rust1", since = "1.0.0")]
1963 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
1967 self.binary_search_by(|p| p.cmp(x))
1970 /// Binary searches this sorted slice with a comparator function.
1972 /// The comparator function should implement an order consistent
1973 /// with the sort order of the underlying slice, returning an
1974 /// order code that indicates whether its argument is `Less`,
1975 /// `Equal` or `Greater` the desired target.
1977 /// If the value is found then [`Result::Ok`] is returned, containing the
1978 /// index of the matching element. If there are multiple matches, then any
1979 /// one of the matches could be returned. If the value is not found then
1980 /// [`Result::Err`] is returned, containing the index where a matching
1981 /// element could be inserted while maintaining sorted order.
1985 /// Looks up a series of four elements. The first is found, with a
1986 /// uniquely determined position; the second and third are not
1987 /// found; the fourth could match any position in `[1, 4]`.
1990 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1993 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
1995 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
1997 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
1999 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2000 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2002 #[stable(feature = "rust1", since = "1.0.0")]
2004 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2006 F: FnMut(&'a T) -> Ordering,
2009 let mut size = s.len();
2013 let mut base = 0usize;
2015 let half = size / 2;
2016 let mid = base + half;
2017 // SAFETY: the call is made safe by the following inconstants:
2018 // - `mid >= 0`: by definition
2019 // - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
2020 let cmp = f(unsafe { s.get_unchecked(mid) });
2021 base = if cmp == Greater { base } else { mid };
2024 // SAFETY: base is always in [0, size) because base <= mid.
2025 let cmp = f(unsafe { s.get_unchecked(base) });
2026 if cmp == Equal { Ok(base) } else { Err(base + (cmp == Less) as usize) }
2029 /// Binary searches this sorted slice with a key extraction function.
2031 /// Assumes that the slice is sorted by the key, for instance with
2032 /// [`sort_by_key`] using the same key extraction function.
2034 /// If the value is found then [`Result::Ok`] is returned, containing the
2035 /// index of the matching element. If there are multiple matches, then any
2036 /// one of the matches could be returned. If the value is not found then
2037 /// [`Result::Err`] is returned, containing the index where a matching
2038 /// element could be inserted while maintaining sorted order.
2040 /// [`sort_by_key`]: #method.sort_by_key
2044 /// Looks up a series of four elements in a slice of pairs sorted by
2045 /// their second elements. The first is found, with a uniquely
2046 /// determined position; the second and third are not found; the
2047 /// fourth could match any position in `[1, 4]`.
2050 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2051 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2052 /// (1, 21), (2, 34), (4, 55)];
2054 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2055 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2056 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2057 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2058 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2060 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2062 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2064 F: FnMut(&'a T) -> B,
2067 self.binary_search_by(|k| f(k).cmp(b))
2070 /// Sorts the slice, but may not preserve the order of equal elements.
2072 /// This sort is unstable (i.e., may reorder equal elements), in-place
2073 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2075 /// # Current implementation
2077 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2078 /// which combines the fast average case of randomized quicksort with the fast worst case of
2079 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2080 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2081 /// deterministic behavior.
2083 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2084 /// slice consists of several concatenated sorted sequences.
2089 /// let mut v = [-5, 4, 1, -3, 2];
2091 /// v.sort_unstable();
2092 /// assert!(v == [-5, -3, 1, 2, 4]);
2095 /// [pdqsort]: https://github.com/orlp/pdqsort
2096 #[stable(feature = "sort_unstable", since = "1.20.0")]
2098 pub fn sort_unstable(&mut self)
2102 sort::quicksort(self, |a, b| a.lt(b));
2105 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2108 /// This sort is unstable (i.e., may reorder equal elements), in-place
2109 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2111 /// The comparator function must define a total ordering for the elements in the slice. If
2112 /// the ordering is not total, the order of the elements is unspecified. An order is a
2113 /// total order if it is (for all `a`, `b` and `c`):
2115 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2116 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2118 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2119 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2122 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2123 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2124 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2127 /// # Current implementation
2129 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2130 /// which combines the fast average case of randomized quicksort with the fast worst case of
2131 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2132 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2133 /// deterministic behavior.
2135 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2136 /// slice consists of several concatenated sorted sequences.
2141 /// let mut v = [5, 4, 1, 3, 2];
2142 /// v.sort_unstable_by(|a, b| a.cmp(b));
2143 /// assert!(v == [1, 2, 3, 4, 5]);
2145 /// // reverse sorting
2146 /// v.sort_unstable_by(|a, b| b.cmp(a));
2147 /// assert!(v == [5, 4, 3, 2, 1]);
2150 /// [pdqsort]: https://github.com/orlp/pdqsort
2151 #[stable(feature = "sort_unstable", since = "1.20.0")]
2153 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2155 F: FnMut(&T, &T) -> Ordering,
2157 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2160 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2163 /// This sort is unstable (i.e., may reorder equal elements), in-place
2164 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2167 /// # Current implementation
2169 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2170 /// which combines the fast average case of randomized quicksort with the fast worst case of
2171 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2172 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2173 /// deterministic behavior.
2175 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2176 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2177 /// cases where the key function is expensive.
2182 /// let mut v = [-5i32, 4, 1, -3, 2];
2184 /// v.sort_unstable_by_key(|k| k.abs());
2185 /// assert!(v == [1, 2, -3, 4, -5]);
2188 /// [pdqsort]: https://github.com/orlp/pdqsort
2189 #[stable(feature = "sort_unstable", since = "1.20.0")]
2191 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2196 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2199 /// Reorder the slice such that the element at `index` is at its final sorted position.
2200 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2201 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2203 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2207 self.select_nth_unstable(index)
2210 /// Reorder the slice with a comparator function such that the element at `index` is at its
2211 /// final sorted position.
2212 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2213 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2215 pub fn partition_at_index_by<F>(
2219 ) -> (&mut [T], &mut T, &mut [T])
2221 F: FnMut(&T, &T) -> Ordering,
2223 self.select_nth_unstable_by(index, compare)
2226 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2227 /// final sorted position.
2228 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2229 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2231 pub fn partition_at_index_by_key<K, F>(
2235 ) -> (&mut [T], &mut T, &mut [T])
2240 self.select_nth_unstable_by_key(index, f)
2243 /// Reorder the slice such that the element at `index` is at its final sorted position.
2245 /// This reordering has the additional property that any value at position `i < index` will be
2246 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2247 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2248 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2249 /// element" in other libraries. It returns a triplet of the following values: all elements less
2250 /// than the one at the given index, the value at the given index, and all elements greater than
2251 /// the one at the given index.
2253 /// # Current implementation
2255 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2256 /// used for [`sort_unstable`].
2258 /// [`sort_unstable`]: #method.sort_unstable
2262 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2267 /// let mut v = [-5i32, 4, 1, -3, 2];
2269 /// // Find the median
2270 /// v.select_nth_unstable(2);
2272 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2273 /// // about the specified index.
2274 /// assert!(v == [-3, -5, 1, 2, 4] ||
2275 /// v == [-5, -3, 1, 2, 4] ||
2276 /// v == [-3, -5, 1, 4, 2] ||
2277 /// v == [-5, -3, 1, 4, 2]);
2279 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2281 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2285 let mut f = |a: &T, b: &T| a.lt(b);
2286 sort::partition_at_index(self, index, &mut f)
2289 /// Reorder the slice with a comparator function such that the element at `index` is at its
2290 /// final sorted position.
2292 /// This reordering has the additional property that any value at position `i < index` will be
2293 /// less than or equal to any value at a position `j > index` using the comparator function.
2294 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2295 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2296 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2297 /// values: all elements less than the one at the given index, the value at the given index,
2298 /// and all elements greater than the one at the given index, using the provided comparator
2301 /// # Current implementation
2303 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2304 /// used for [`sort_unstable`].
2306 /// [`sort_unstable`]: #method.sort_unstable
2310 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2315 /// let mut v = [-5i32, 4, 1, -3, 2];
2317 /// // Find the median as if the slice were sorted in descending order.
2318 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2320 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2321 /// // about the specified index.
2322 /// assert!(v == [2, 4, 1, -5, -3] ||
2323 /// v == [2, 4, 1, -3, -5] ||
2324 /// v == [4, 2, 1, -5, -3] ||
2325 /// v == [4, 2, 1, -3, -5]);
2327 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2329 pub fn select_nth_unstable_by<F>(
2333 ) -> (&mut [T], &mut T, &mut [T])
2335 F: FnMut(&T, &T) -> Ordering,
2337 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2338 sort::partition_at_index(self, index, &mut f)
2341 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2342 /// final sorted position.
2344 /// This reordering has the additional property that any value at position `i < index` will be
2345 /// less than or equal to any value at a position `j > index` using the key extraction function.
2346 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2347 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2348 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2349 /// values: all elements less than the one at the given index, the value at the given index, and
2350 /// all elements greater than the one at the given index, using the provided key extraction
2353 /// # Current implementation
2355 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2356 /// used for [`sort_unstable`].
2358 /// [`sort_unstable`]: #method.sort_unstable
2362 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2367 /// let mut v = [-5i32, 4, 1, -3, 2];
2369 /// // Return the median as if the array were sorted according to absolute value.
2370 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2372 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2373 /// // about the specified index.
2374 /// assert!(v == [1, 2, -3, 4, -5] ||
2375 /// v == [1, 2, -3, -5, 4] ||
2376 /// v == [2, 1, -3, 4, -5] ||
2377 /// v == [2, 1, -3, -5, 4]);
2379 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2381 pub fn select_nth_unstable_by_key<K, F>(
2385 ) -> (&mut [T], &mut T, &mut [T])
2390 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2391 sort::partition_at_index(self, index, &mut g)
2394 /// Moves all consecutive repeated elements to the end of the slice according to the
2395 /// [`PartialEq`] trait implementation.
2397 /// Returns two slices. The first contains no consecutive repeated elements.
2398 /// The second contains all the duplicates in no specified order.
2400 /// If the slice is sorted, the first returned slice contains no duplicates.
2405 /// #![feature(slice_partition_dedup)]
2407 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2409 /// let (dedup, duplicates) = slice.partition_dedup();
2411 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2412 /// assert_eq!(duplicates, [2, 3, 1]);
2414 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2416 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2420 self.partition_dedup_by(|a, b| a == b)
2423 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2424 /// a given equality relation.
2426 /// Returns two slices. The first contains no consecutive repeated elements.
2427 /// The second contains all the duplicates in no specified order.
2429 /// The `same_bucket` function is passed references to two elements from the slice and
2430 /// must determine if the elements compare equal. The elements are passed in opposite order
2431 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2432 /// at the end of the slice.
2434 /// If the slice is sorted, the first returned slice contains no duplicates.
2439 /// #![feature(slice_partition_dedup)]
2441 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2443 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2445 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2446 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2448 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2450 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2452 F: FnMut(&mut T, &mut T) -> bool,
2454 // Although we have a mutable reference to `self`, we cannot make
2455 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2456 // must ensure that the slice is in a valid state at all times.
2458 // The way that we handle this is by using swaps; we iterate
2459 // over all the elements, swapping as we go so that at the end
2460 // the elements we wish to keep are in the front, and those we
2461 // wish to reject are at the back. We can then split the slice.
2462 // This operation is still `O(n)`.
2464 // Example: We start in this state, where `r` represents "next
2465 // read" and `w` represents "next_write`.
2468 // +---+---+---+---+---+---+
2469 // | 0 | 1 | 1 | 2 | 3 | 3 |
2470 // +---+---+---+---+---+---+
2473 // Comparing self[r] against self[w-1], this is not a duplicate, so
2474 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2475 // r and w, leaving us with:
2478 // +---+---+---+---+---+---+
2479 // | 0 | 1 | 1 | 2 | 3 | 3 |
2480 // +---+---+---+---+---+---+
2483 // Comparing self[r] against self[w-1], this value is a duplicate,
2484 // so we increment `r` but leave everything else unchanged:
2487 // +---+---+---+---+---+---+
2488 // | 0 | 1 | 1 | 2 | 3 | 3 |
2489 // +---+---+---+---+---+---+
2492 // Comparing self[r] against self[w-1], this is not a duplicate,
2493 // so swap self[r] and self[w] and advance r and w:
2496 // +---+---+---+---+---+---+
2497 // | 0 | 1 | 2 | 1 | 3 | 3 |
2498 // +---+---+---+---+---+---+
2501 // Not a duplicate, repeat:
2504 // +---+---+---+---+---+---+
2505 // | 0 | 1 | 2 | 3 | 1 | 3 |
2506 // +---+---+---+---+---+---+
2509 // Duplicate, advance r. End of slice. Split at w.
2511 let len = self.len();
2513 return (self, &mut []);
2516 let ptr = self.as_mut_ptr();
2517 let mut next_read: usize = 1;
2518 let mut next_write: usize = 1;
2520 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2521 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2522 // one element before `ptr_write`, but `next_write` starts at 1, so
2523 // `prev_ptr_write` is never less than 0 and is inside the slice.
2524 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2525 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2526 // and `prev_ptr_write.offset(1)`.
2528 // `next_write` is also incremented at most once per loop at most meaning
2529 // no element is skipped when it may need to be swapped.
2531 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2532 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2533 // The explanation is simply that `next_read >= next_write` is always true,
2534 // thus `next_read > next_write - 1` is too.
2536 // Avoid bounds checks by using raw pointers.
2537 while next_read < len {
2538 let ptr_read = ptr.add(next_read);
2539 let prev_ptr_write = ptr.add(next_write - 1);
2540 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2541 if next_read != next_write {
2542 let ptr_write = prev_ptr_write.offset(1);
2543 mem::swap(&mut *ptr_read, &mut *ptr_write);
2551 self.split_at_mut(next_write)
2554 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2555 /// to the same key.
2557 /// Returns two slices. The first contains no consecutive repeated elements.
2558 /// The second contains all the duplicates in no specified order.
2560 /// If the slice is sorted, the first returned slice contains no duplicates.
2565 /// #![feature(slice_partition_dedup)]
2567 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2569 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2571 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2572 /// assert_eq!(duplicates, [21, 30, 13]);
2574 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2576 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2578 F: FnMut(&mut T) -> K,
2581 self.partition_dedup_by(|a, b| key(a) == key(b))
2584 /// Rotates the slice in-place such that the first `mid` elements of the
2585 /// slice move to the end while the last `self.len() - mid` elements move to
2586 /// the front. After calling `rotate_left`, the element previously at index
2587 /// `mid` will become the first element in the slice.
2591 /// This function will panic if `mid` is greater than the length of the
2592 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2597 /// Takes linear (in `self.len()`) time.
2602 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2603 /// a.rotate_left(2);
2604 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2607 /// Rotating a subslice:
2610 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2611 /// a[1..5].rotate_left(1);
2612 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2614 #[stable(feature = "slice_rotate", since = "1.26.0")]
2615 pub fn rotate_left(&mut self, mid: usize) {
2616 assert!(mid <= self.len());
2617 let k = self.len() - mid;
2618 let p = self.as_mut_ptr();
2620 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2621 // valid for reading and writing, as required by `ptr_rotate`.
2623 rotate::ptr_rotate(mid, p.add(mid), k);
2627 /// Rotates the slice in-place such that the first `self.len() - k`
2628 /// elements of the slice move to the end while the last `k` elements move
2629 /// to the front. After calling `rotate_right`, the element previously at
2630 /// index `self.len() - k` will become the first element in the slice.
2634 /// This function will panic if `k` is greater than the length of the
2635 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2640 /// Takes linear (in `self.len()`) time.
2645 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2646 /// a.rotate_right(2);
2647 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2650 /// Rotate a subslice:
2653 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2654 /// a[1..5].rotate_right(1);
2655 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2657 #[stable(feature = "slice_rotate", since = "1.26.0")]
2658 pub fn rotate_right(&mut self, k: usize) {
2659 assert!(k <= self.len());
2660 let mid = self.len() - k;
2661 let p = self.as_mut_ptr();
2663 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2664 // valid for reading and writing, as required by `ptr_rotate`.
2666 rotate::ptr_rotate(mid, p.add(mid), k);
2670 /// Fills `self` with elements by cloning `value`.
2675 /// let mut buf = vec![0; 10];
2677 /// assert_eq!(buf, vec![1; 10]);
2679 #[doc(alias = "memset")]
2680 #[stable(feature = "slice_fill", since = "1.50.0")]
2681 pub fn fill(&mut self, value: T)
2685 if let Some((last, elems)) = self.split_last_mut() {
2687 el.clone_from(&value);
2694 /// Fills `self` with elements returned by calling a closure repeatedly.
2696 /// This method uses a closure to create new values. If you'd rather
2697 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2698 /// trait to generate values, you can pass [`Default::default`] as the
2701 /// [`fill`]: #method.fill
2706 /// #![feature(slice_fill_with)]
2708 /// let mut buf = vec![1; 10];
2709 /// buf.fill_with(Default::default);
2710 /// assert_eq!(buf, vec![0; 10]);
2712 #[unstable(feature = "slice_fill_with", issue = "79221")]
2713 pub fn fill_with<F>(&mut self, mut f: F)
2722 /// Copies the elements from `src` into `self`.
2724 /// The length of `src` must be the same as `self`.
2726 /// If `T` implements `Copy`, it can be more performant to use
2727 /// [`copy_from_slice`].
2731 /// This function will panic if the two slices have different lengths.
2735 /// Cloning two elements from a slice into another:
2738 /// let src = [1, 2, 3, 4];
2739 /// let mut dst = [0, 0];
2741 /// // Because the slices have to be the same length,
2742 /// // we slice the source slice from four elements
2743 /// // to two. It will panic if we don't do this.
2744 /// dst.clone_from_slice(&src[2..]);
2746 /// assert_eq!(src, [1, 2, 3, 4]);
2747 /// assert_eq!(dst, [3, 4]);
2750 /// Rust enforces that there can only be one mutable reference with no
2751 /// immutable references to a particular piece of data in a particular
2752 /// scope. Because of this, attempting to use `clone_from_slice` on a
2753 /// single slice will result in a compile failure:
2756 /// let mut slice = [1, 2, 3, 4, 5];
2758 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2761 /// To work around this, we can use [`split_at_mut`] to create two distinct
2762 /// sub-slices from a slice:
2765 /// let mut slice = [1, 2, 3, 4, 5];
2768 /// let (left, right) = slice.split_at_mut(2);
2769 /// left.clone_from_slice(&right[1..]);
2772 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2775 /// [`copy_from_slice`]: #method.copy_from_slice
2776 /// [`split_at_mut`]: #method.split_at_mut
2777 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2778 pub fn clone_from_slice(&mut self, src: &[T])
2782 assert!(self.len() == src.len(), "destination and source slices have different lengths");
2783 // NOTE: We need to explicitly slice them to the same length
2784 // for bounds checking to be elided, and the optimizer will
2785 // generate memcpy for simple cases (for example T = u8).
2786 let len = self.len();
2787 let src = &src[..len];
2789 self[i].clone_from(&src[i]);
2793 /// Copies all elements from `src` into `self`, using a memcpy.
2795 /// The length of `src` must be the same as `self`.
2797 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2801 /// This function will panic if the two slices have different lengths.
2805 /// Copying two elements from a slice into another:
2808 /// let src = [1, 2, 3, 4];
2809 /// let mut dst = [0, 0];
2811 /// // Because the slices have to be the same length,
2812 /// // we slice the source slice from four elements
2813 /// // to two. It will panic if we don't do this.
2814 /// dst.copy_from_slice(&src[2..]);
2816 /// assert_eq!(src, [1, 2, 3, 4]);
2817 /// assert_eq!(dst, [3, 4]);
2820 /// Rust enforces that there can only be one mutable reference with no
2821 /// immutable references to a particular piece of data in a particular
2822 /// scope. Because of this, attempting to use `copy_from_slice` on a
2823 /// single slice will result in a compile failure:
2826 /// let mut slice = [1, 2, 3, 4, 5];
2828 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
2831 /// To work around this, we can use [`split_at_mut`] to create two distinct
2832 /// sub-slices from a slice:
2835 /// let mut slice = [1, 2, 3, 4, 5];
2838 /// let (left, right) = slice.split_at_mut(2);
2839 /// left.copy_from_slice(&right[1..]);
2842 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2845 /// [`clone_from_slice`]: #method.clone_from_slice
2846 /// [`split_at_mut`]: #method.split_at_mut
2847 #[doc(alias = "memcpy")]
2848 #[stable(feature = "copy_from_slice", since = "1.9.0")]
2849 pub fn copy_from_slice(&mut self, src: &[T])
2853 // The panic code path was put into a cold function to not bloat the
2858 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
2860 "source slice length ({}) does not match destination slice length ({})",
2865 if self.len() != src.len() {
2866 len_mismatch_fail(self.len(), src.len());
2869 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
2870 // checked to have the same length. The slices cannot overlap because
2871 // mutable references are exclusive.
2873 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
2877 /// Copies elements from one part of the slice to another part of itself,
2878 /// using a memmove.
2880 /// `src` is the range within `self` to copy from. `dest` is the starting
2881 /// index of the range within `self` to copy to, which will have the same
2882 /// length as `src`. The two ranges may overlap. The ends of the two ranges
2883 /// must be less than or equal to `self.len()`.
2887 /// This function will panic if either range exceeds the end of the slice,
2888 /// or if the end of `src` is before the start.
2892 /// Copying four bytes within a slice:
2895 /// let mut bytes = *b"Hello, World!";
2897 /// bytes.copy_within(1..5, 8);
2899 /// assert_eq!(&bytes, b"Hello, Wello!");
2901 #[stable(feature = "copy_within", since = "1.37.0")]
2903 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
2907 let Range { start: src_start, end: src_end } = src.assert_len(self.len());
2908 let count = src_end - src_start;
2909 assert!(dest <= self.len() - count, "dest is out of bounds");
2910 // SAFETY: the conditions for `ptr::copy` have all been checked above,
2911 // as have those for `ptr::add`.
2913 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
2917 /// Swaps all elements in `self` with those in `other`.
2919 /// The length of `other` must be the same as `self`.
2923 /// This function will panic if the two slices have different lengths.
2927 /// Swapping two elements across slices:
2930 /// let mut slice1 = [0, 0];
2931 /// let mut slice2 = [1, 2, 3, 4];
2933 /// slice1.swap_with_slice(&mut slice2[2..]);
2935 /// assert_eq!(slice1, [3, 4]);
2936 /// assert_eq!(slice2, [1, 2, 0, 0]);
2939 /// Rust enforces that there can only be one mutable reference to a
2940 /// particular piece of data in a particular scope. Because of this,
2941 /// attempting to use `swap_with_slice` on a single slice will result in
2942 /// a compile failure:
2945 /// let mut slice = [1, 2, 3, 4, 5];
2946 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
2949 /// To work around this, we can use [`split_at_mut`] to create two distinct
2950 /// mutable sub-slices from a slice:
2953 /// let mut slice = [1, 2, 3, 4, 5];
2956 /// let (left, right) = slice.split_at_mut(2);
2957 /// left.swap_with_slice(&mut right[1..]);
2960 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
2963 /// [`split_at_mut`]: #method.split_at_mut
2964 #[stable(feature = "swap_with_slice", since = "1.27.0")]
2965 pub fn swap_with_slice(&mut self, other: &mut [T]) {
2966 assert!(self.len() == other.len(), "destination and source slices have different lengths");
2967 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
2968 // checked to have the same length. The slices cannot overlap because
2969 // mutable references are exclusive.
2971 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
2975 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
2976 fn align_to_offsets<U>(&self) -> (usize, usize) {
2977 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
2978 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
2980 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
2981 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
2982 // place of every 3 Ts in the `rest` slice. A bit more complicated.
2984 // Formula to calculate this is:
2986 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
2987 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
2989 // Expanded and simplified:
2991 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
2992 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
2994 // Luckily since all this is constant-evaluated... performance here matters not!
2996 fn gcd(a: usize, b: usize) -> usize {
2997 use crate::intrinsics;
2998 // iterative stein’s algorithm
2999 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3000 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3002 // SAFETY: `a` and `b` are checked to be non-zero values.
3003 let (ctz_a, mut ctz_b) = unsafe {
3010 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3012 let k = ctz_a.min(ctz_b);
3013 let mut a = a >> ctz_a;
3016 // remove all factors of 2 from b
3019 mem::swap(&mut a, &mut b);
3022 // SAFETY: `b` is checked to be non-zero.
3027 ctz_b = intrinsics::cttz_nonzero(b);
3032 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3033 let ts: usize = mem::size_of::<U>() / gcd;
3034 let us: usize = mem::size_of::<T>() / gcd;
3036 // Armed with this knowledge, we can find how many `U`s we can fit!
3037 let us_len = self.len() / ts * us;
3038 // And how many `T`s will be in the trailing slice!
3039 let ts_len = self.len() % ts;
3043 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3046 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3047 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3048 /// length possible for a given type and input slice, but only your algorithm's performance
3049 /// should depend on that, not its correctness. It is permissible for all of the input data to
3050 /// be returned as the prefix or suffix slice.
3052 /// This method has no purpose when either input element `T` or output element `U` are
3053 /// zero-sized and will return the original slice without splitting anything.
3057 /// This method is essentially a `transmute` with respect to the elements in the returned
3058 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3066 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3067 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3068 /// // less_efficient_algorithm_for_bytes(prefix);
3069 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3070 /// // less_efficient_algorithm_for_bytes(suffix);
3073 #[stable(feature = "slice_align_to", since = "1.30.0")]
3074 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3075 // Note that most of this function will be constant-evaluated,
3076 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3077 // handle ZSTs specially, which is – don't handle them at all.
3078 return (self, &[], &[]);
3081 // First, find at what point do we split between the first and 2nd slice. Easy with
3082 // ptr.align_offset.
3083 let ptr = self.as_ptr();
3084 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3085 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3086 if offset > self.len() {
3089 let (left, rest) = self.split_at(offset);
3090 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3091 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3092 // since the caller guarantees that we can transmute `T` to `U` safely.
3096 from_raw_parts(rest.as_ptr() as *const U, us_len),
3097 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3103 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3106 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3107 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3108 /// length possible for a given type and input slice, but only your algorithm's performance
3109 /// should depend on that, not its correctness. It is permissible for all of the input data to
3110 /// be returned as the prefix or suffix slice.
3112 /// This method has no purpose when either input element `T` or output element `U` are
3113 /// zero-sized and will return the original slice without splitting anything.
3117 /// This method is essentially a `transmute` with respect to the elements in the returned
3118 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3126 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3127 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3128 /// // less_efficient_algorithm_for_bytes(prefix);
3129 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3130 /// // less_efficient_algorithm_for_bytes(suffix);
3133 #[stable(feature = "slice_align_to", since = "1.30.0")]
3134 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3135 // Note that most of this function will be constant-evaluated,
3136 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3137 // handle ZSTs specially, which is – don't handle them at all.
3138 return (self, &mut [], &mut []);
3141 // First, find at what point do we split between the first and 2nd slice. Easy with
3142 // ptr.align_offset.
3143 let ptr = self.as_ptr();
3144 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3145 // rest of the method. This is done by passing a pointer to &[T] with an
3146 // alignment targeted for U.
3147 // `crate::ptr::align_offset` is called with a correctly aligned and
3148 // valid pointer `ptr` (it comes from a reference to `self`) and with
3149 // a size that is a power of two (since it comes from the alignement for U),
3150 // satisfying its safety constraints.
3151 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3152 if offset > self.len() {
3153 (self, &mut [], &mut [])
3155 let (left, rest) = self.split_at_mut(offset);
3156 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3157 let rest_len = rest.len();
3158 let mut_ptr = rest.as_mut_ptr();
3159 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3160 // SAFETY: see comments for `align_to`.
3164 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3165 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3171 /// Checks if the elements of this slice are sorted.
3173 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3174 /// slice yields exactly zero or one element, `true` is returned.
3176 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3177 /// implies that this function returns `false` if any two consecutive items are not
3183 /// #![feature(is_sorted)]
3184 /// let empty: [i32; 0] = [];
3186 /// assert!([1, 2, 2, 9].is_sorted());
3187 /// assert!(![1, 3, 2, 4].is_sorted());
3188 /// assert!([0].is_sorted());
3189 /// assert!(empty.is_sorted());
3190 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3193 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3194 pub fn is_sorted(&self) -> bool
3198 self.is_sorted_by(|a, b| a.partial_cmp(b))
3201 /// Checks if the elements of this slice are sorted using the given comparator function.
3203 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3204 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3205 /// [`is_sorted`]; see its documentation for more information.
3207 /// [`is_sorted`]: #method.is_sorted
3208 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3209 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3211 F: FnMut(&T, &T) -> Option<Ordering>,
3213 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3216 /// Checks if the elements of this slice are sorted using the given key extraction function.
3218 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3219 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3220 /// documentation for more information.
3222 /// [`is_sorted`]: #method.is_sorted
3227 /// #![feature(is_sorted)]
3229 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3230 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3233 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3234 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3239 self.iter().is_sorted_by_key(f)
3242 /// Returns the index of the partition point according to the given predicate
3243 /// (the index of the first element of the second partition).
3245 /// The slice is assumed to be partitioned according to the given predicate.
3246 /// This means that all elements for which the predicate returns true are at the start of the slice
3247 /// and all elements for which the predicate returns false are at the end.
3248 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3249 /// (all odd numbers are at the start, all even at the end).
3251 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3252 /// as this method performs a kind of binary search.
3257 /// #![feature(partition_point)]
3259 /// let v = [1, 2, 3, 3, 5, 6, 7];
3260 /// let i = v.partition_point(|&x| x < 5);
3262 /// assert_eq!(i, 4);
3263 /// assert!(v[..i].iter().all(|&x| x < 5));
3264 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3266 #[unstable(feature = "partition_point", reason = "new API", issue = "73831")]
3267 pub fn partition_point<P>(&self, mut pred: P) -> usize
3269 P: FnMut(&T) -> bool,
3272 let mut right = self.len();
3274 while left != right {
3275 let mid = left + (right - left) / 2;
3276 // SAFETY: When `left < right`, `left <= mid < right`.
3277 // Therefore `left` always increases and `right` always decreases,
3278 // and either of them is selected. In both cases `left <= right` is
3279 // satisfied. Therefore if `left < right` in a step, `left <= right`
3280 // is satisfied in the next step. Therefore as long as `left != right`,
3281 // `0 <= left < right <= len` is satisfied and if this case
3282 // `0 <= mid < len` is satisfied too.
3283 let value = unsafe { self.get_unchecked(mid) };
3295 #[stable(feature = "rust1", since = "1.0.0")]
3296 impl<T> Default for &[T] {
3297 /// Creates an empty slice.
3298 fn default() -> Self {
3303 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3304 impl<T> Default for &mut [T] {
3305 /// Creates a mutable empty slice.
3306 fn default() -> Self {