1 //! Slice management and manipulation.
3 //! For more details see [`std::slice`].
5 //! [`std::slice`]: ../../std/slice/index.html
7 #![stable(feature = "rust1", since = "1.0.0")]
9 use crate::cmp::Ordering::{self, Greater, Less};
10 use crate::marker::Copy;
12 use crate::num::NonZeroUsize;
13 use crate::ops::{FnMut, Range, RangeBounds};
14 use crate::option::Option;
15 use crate::option::Option::{None, Some};
17 use crate::result::Result;
18 use crate::result::Result::{Err, Ok};
22 feature = "slice_internals",
24 reason = "exposed from core to be reused in std; use the memchr crate"
26 /// Pure rust memchr implementation, taken from rust-memchr
38 #[stable(feature = "rust1", since = "1.0.0")]
39 pub use iter::{Chunks, ChunksMut, Windows};
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Iter, IterMut};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
45 #[stable(feature = "slice_rsplit", since = "1.27.0")]
46 pub use iter::{RSplit, RSplitMut};
48 #[stable(feature = "chunks_exact", since = "1.31.0")]
49 pub use iter::{ChunksExact, ChunksExactMut};
51 #[stable(feature = "rchunks", since = "1.31.0")]
52 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
54 #[unstable(feature = "array_chunks", issue = "74985")]
55 pub use iter::{ArrayChunks, ArrayChunksMut};
57 #[unstable(feature = "array_windows", issue = "75027")]
58 pub use iter::ArrayWindows;
60 #[unstable(feature = "slice_group_by", issue = "80552")]
61 pub use iter::{GroupBy, GroupByMut};
63 #[stable(feature = "split_inclusive", since = "1.51.0")]
64 pub use iter::{SplitInclusive, SplitInclusiveMut};
66 #[stable(feature = "rust1", since = "1.0.0")]
67 pub use raw::{from_raw_parts, from_raw_parts_mut};
69 #[stable(feature = "from_ref", since = "1.28.0")]
70 pub use raw::{from_mut, from_ref};
72 // This function is public only because there is no other way to unit test heapsort.
73 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
74 pub use sort::heapsort;
76 #[stable(feature = "slice_get_slice", since = "1.28.0")]
77 pub use index::SliceIndex;
79 #[unstable(feature = "slice_range", issue = "76393")]
82 #[unstable(feature = "inherent_ascii_escape", issue = "77174")]
83 pub use ascii::EscapeAscii;
88 /// Returns the number of elements in the slice.
93 /// let a = [1, 2, 3];
94 /// assert_eq!(a.len(), 3);
96 #[lang = "slice_len_fn"]
97 #[stable(feature = "rust1", since = "1.0.0")]
98 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
100 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
101 pub const fn len(&self) -> usize {
102 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
103 // As of this writing this causes a "Const-stable functions can only call other
104 // const-stable functions" error.
106 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
107 // and PtrComponents<T> have the same memory layouts. Only std can make this
109 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
112 /// Returns `true` if the slice has a length of 0.
117 /// let a = [1, 2, 3];
118 /// assert!(!a.is_empty());
120 #[stable(feature = "rust1", since = "1.0.0")]
121 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
123 pub const fn is_empty(&self) -> bool {
127 /// Returns the first element of the slice, or `None` if it is empty.
132 /// let v = [10, 40, 30];
133 /// assert_eq!(Some(&10), v.first());
135 /// let w: &[i32] = &[];
136 /// assert_eq!(None, w.first());
138 #[stable(feature = "rust1", since = "1.0.0")]
139 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
141 pub const fn first(&self) -> Option<&T> {
142 if let [first, ..] = self { Some(first) } else { None }
145 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
150 /// let x = &mut [0, 1, 2];
152 /// if let Some(first) = x.first_mut() {
155 /// assert_eq!(x, &[5, 1, 2]);
157 #[stable(feature = "rust1", since = "1.0.0")]
158 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
160 pub const fn first_mut(&mut self) -> Option<&mut T> {
161 if let [first, ..] = self { Some(first) } else { None }
164 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
169 /// let x = &[0, 1, 2];
171 /// if let Some((first, elements)) = x.split_first() {
172 /// assert_eq!(first, &0);
173 /// assert_eq!(elements, &[1, 2]);
176 #[stable(feature = "slice_splits", since = "1.5.0")]
177 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
179 pub const fn split_first(&self) -> Option<(&T, &[T])> {
180 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
183 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
188 /// let x = &mut [0, 1, 2];
190 /// if let Some((first, elements)) = x.split_first_mut() {
195 /// assert_eq!(x, &[3, 4, 5]);
197 #[stable(feature = "slice_splits", since = "1.5.0")]
198 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
200 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
201 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
204 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
209 /// let x = &[0, 1, 2];
211 /// if let Some((last, elements)) = x.split_last() {
212 /// assert_eq!(last, &2);
213 /// assert_eq!(elements, &[0, 1]);
216 #[stable(feature = "slice_splits", since = "1.5.0")]
217 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
219 pub const fn split_last(&self) -> Option<(&T, &[T])> {
220 if let [init @ .., last] = self { Some((last, init)) } else { None }
223 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
228 /// let x = &mut [0, 1, 2];
230 /// if let Some((last, elements)) = x.split_last_mut() {
235 /// assert_eq!(x, &[4, 5, 3]);
237 #[stable(feature = "slice_splits", since = "1.5.0")]
238 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
240 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
241 if let [init @ .., last] = self { Some((last, init)) } else { None }
244 /// Returns the last element of the slice, or `None` if it is empty.
249 /// let v = [10, 40, 30];
250 /// assert_eq!(Some(&30), v.last());
252 /// let w: &[i32] = &[];
253 /// assert_eq!(None, w.last());
255 #[stable(feature = "rust1", since = "1.0.0")]
256 #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
258 pub const fn last(&self) -> Option<&T> {
259 if let [.., last] = self { Some(last) } else { None }
262 /// Returns a mutable pointer to the last item in the slice.
267 /// let x = &mut [0, 1, 2];
269 /// if let Some(last) = x.last_mut() {
272 /// assert_eq!(x, &[0, 1, 10]);
274 #[stable(feature = "rust1", since = "1.0.0")]
275 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
277 pub const fn last_mut(&mut self) -> Option<&mut T> {
278 if let [.., last] = self { Some(last) } else { None }
281 /// Returns a reference to an element or subslice depending on the type of
284 /// - If given a position, returns a reference to the element at that
285 /// position or `None` if out of bounds.
286 /// - If given a range, returns the subslice corresponding to that range,
287 /// or `None` if out of bounds.
292 /// let v = [10, 40, 30];
293 /// assert_eq!(Some(&40), v.get(1));
294 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
295 /// assert_eq!(None, v.get(3));
296 /// assert_eq!(None, v.get(0..4));
298 #[stable(feature = "rust1", since = "1.0.0")]
300 pub fn get<I>(&self, index: I) -> Option<&I::Output>
307 /// Returns a mutable reference to an element or subslice depending on the
308 /// type of index (see [`get`]) or `None` if the index is out of bounds.
310 /// [`get`]: slice::get
315 /// let x = &mut [0, 1, 2];
317 /// if let Some(elem) = x.get_mut(1) {
320 /// assert_eq!(x, &[0, 42, 2]);
322 #[stable(feature = "rust1", since = "1.0.0")]
324 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
331 /// Returns a reference to an element or subslice, without doing bounds
334 /// For a safe alternative see [`get`].
338 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
339 /// even if the resulting reference is not used.
341 /// [`get`]: slice::get
342 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
347 /// let x = &[1, 2, 4];
350 /// assert_eq!(x.get_unchecked(1), &2);
353 #[stable(feature = "rust1", since = "1.0.0")]
355 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
359 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
360 // the slice is dereferencable because `self` is a safe reference.
361 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
362 unsafe { &*index.get_unchecked(self) }
365 /// Returns a mutable reference to an element or subslice, without doing
368 /// For a safe alternative see [`get_mut`].
372 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
373 /// even if the resulting reference is not used.
375 /// [`get_mut`]: slice::get_mut
376 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
381 /// let x = &mut [1, 2, 4];
384 /// let elem = x.get_unchecked_mut(1);
387 /// assert_eq!(x, &[1, 13, 4]);
389 #[stable(feature = "rust1", since = "1.0.0")]
391 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
395 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
396 // the slice is dereferencable because `self` is a safe reference.
397 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
398 unsafe { &mut *index.get_unchecked_mut(self) }
401 /// Returns a raw pointer to the slice's buffer.
403 /// The caller must ensure that the slice outlives the pointer this
404 /// function returns, or else it will end up pointing to garbage.
406 /// The caller must also ensure that the memory the pointer (non-transitively) points to
407 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
408 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
410 /// Modifying the container referenced by this slice may cause its buffer
411 /// to be reallocated, which would also make any pointers to it invalid.
416 /// let x = &[1, 2, 4];
417 /// let x_ptr = x.as_ptr();
420 /// for i in 0..x.len() {
421 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
426 /// [`as_mut_ptr`]: slice::as_mut_ptr
427 #[stable(feature = "rust1", since = "1.0.0")]
428 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
430 pub const fn as_ptr(&self) -> *const T {
431 self as *const [T] as *const T
434 /// Returns an unsafe mutable pointer to the slice's buffer.
436 /// The caller must ensure that the slice outlives the pointer this
437 /// function returns, or else it will end up pointing to garbage.
439 /// Modifying the container referenced by this slice may cause its buffer
440 /// to be reallocated, which would also make any pointers to it invalid.
445 /// let x = &mut [1, 2, 4];
446 /// let x_ptr = x.as_mut_ptr();
449 /// for i in 0..x.len() {
450 /// *x_ptr.add(i) += 2;
453 /// assert_eq!(x, &[3, 4, 6]);
455 #[stable(feature = "rust1", since = "1.0.0")]
456 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
458 pub const fn as_mut_ptr(&mut self) -> *mut T {
459 self as *mut [T] as *mut T
462 /// Returns the two raw pointers spanning the slice.
464 /// The returned range is half-open, which means that the end pointer
465 /// points *one past* the last element of the slice. This way, an empty
466 /// slice is represented by two equal pointers, and the difference between
467 /// the two pointers represents the size of the slice.
469 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
470 /// requires extra caution, as it does not point to a valid element in the
473 /// This function is useful for interacting with foreign interfaces which
474 /// use two pointers to refer to a range of elements in memory, as is
477 /// It can also be useful to check if a pointer to an element refers to an
478 /// element of this slice:
481 /// let a = [1, 2, 3];
482 /// let x = &a[1] as *const _;
483 /// let y = &5 as *const _;
485 /// assert!(a.as_ptr_range().contains(&x));
486 /// assert!(!a.as_ptr_range().contains(&y));
489 /// [`as_ptr`]: slice::as_ptr
490 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
491 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
493 pub const fn as_ptr_range(&self) -> Range<*const T> {
494 let start = self.as_ptr();
495 // SAFETY: The `add` here is safe, because:
497 // - Both pointers are part of the same object, as pointing directly
498 // past the object also counts.
500 // - The size of the slice is never larger than isize::MAX bytes, as
502 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
503 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
504 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
505 // (This doesn't seem normative yet, but the very same assumption is
506 // made in many places, including the Index implementation of slices.)
508 // - There is no wrapping around involved, as slices do not wrap past
509 // the end of the address space.
511 // See the documentation of pointer::add.
512 let end = unsafe { start.add(self.len()) };
516 /// Returns the two unsafe mutable pointers spanning the slice.
518 /// The returned range is half-open, which means that the end pointer
519 /// points *one past* the last element of the slice. This way, an empty
520 /// slice is represented by two equal pointers, and the difference between
521 /// the two pointers represents the size of the slice.
523 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
524 /// pointer requires extra caution, as it does not point to a valid element
527 /// This function is useful for interacting with foreign interfaces which
528 /// use two pointers to refer to a range of elements in memory, as is
531 /// [`as_mut_ptr`]: slice::as_mut_ptr
532 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
533 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
535 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
536 let start = self.as_mut_ptr();
537 // SAFETY: See as_ptr_range() above for why `add` here is safe.
538 let end = unsafe { start.add(self.len()) };
542 /// Swaps two elements in the slice.
546 /// * a - The index of the first element
547 /// * b - The index of the second element
551 /// Panics if `a` or `b` are out of bounds.
556 /// let mut v = ["a", "b", "c", "d"];
558 /// assert!(v == ["a", "d", "c", "b"]);
560 #[stable(feature = "rust1", since = "1.0.0")]
562 pub fn swap(&mut self, a: usize, b: usize) {
563 // Can't take two mutable loans from one vector, so instead use raw pointers.
564 let pa = ptr::addr_of_mut!(self[a]);
565 let pb = ptr::addr_of_mut!(self[b]);
566 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
567 // to elements in the slice and therefore are guaranteed to be valid and aligned.
568 // Note that accessing the elements behind `a` and `b` is checked and will
569 // panic when out of bounds.
575 /// Reverses the order of elements in the slice, in place.
580 /// let mut v = [1, 2, 3];
582 /// assert!(v == [3, 2, 1]);
584 #[stable(feature = "rust1", since = "1.0.0")]
586 pub fn reverse(&mut self) {
587 let mut i: usize = 0;
590 // For very small types, all the individual reads in the normal
591 // path perform poorly. We can do better, given efficient unaligned
592 // load/store, by loading a larger chunk and reversing a register.
594 // Ideally LLVM would do this for us, as it knows better than we do
595 // whether unaligned reads are efficient (since that changes between
596 // different ARM versions, for example) and what the best chunk size
597 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
598 // the loop, so we need to do this ourselves. (Hypothesis: reverse
599 // is troublesome because the sides can be aligned differently --
600 // will be, when the length is odd -- so there's no way of emitting
601 // pre- and postludes to use fully-aligned SIMD in the middle.)
603 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
605 if fast_unaligned && mem::size_of::<T>() == 1 {
606 // Use the llvm.bswap intrinsic to reverse u8s in a usize
607 let chunk = mem::size_of::<usize>();
608 while i + chunk - 1 < ln / 2 {
609 // SAFETY: There are several things to check here:
611 // - Note that `chunk` is either 4 or 8 due to the cfg check
612 // above. So `chunk - 1` is positive.
613 // - Indexing with index `i` is fine as the loop check guarantees
614 // `i + chunk - 1 < ln / 2`
615 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
616 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
617 // - `i + chunk > 0` is trivially true.
618 // - The loop check guarantees:
619 // `i + chunk - 1 < ln / 2`
620 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
621 // - The `read_unaligned` and `write_unaligned` calls are fine:
622 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
623 // (see above) and `pb` points to index `ln - i - chunk`, so
624 // both are at least `chunk`
625 // many bytes away from the end of `self`.
626 // - Any initialized memory is valid `usize`.
628 let ptr = self.as_mut_ptr();
630 let pb = ptr.add(ln - i - chunk);
631 let va = ptr::read_unaligned(pa as *mut usize);
632 let vb = ptr::read_unaligned(pb as *mut usize);
633 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
634 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
640 if fast_unaligned && mem::size_of::<T>() == 2 {
641 // Use rotate-by-16 to reverse u16s in a u32
642 let chunk = mem::size_of::<u32>() / 2;
643 while i + chunk - 1 < ln / 2 {
644 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
645 // (and obviously `i < ln`), because each element is 2 bytes and
648 // `i + chunk - 1 < ln / 2` # while condition
649 // `i + 2 - 1 < ln / 2`
652 // Since it's less than the length divided by 2, then it must be
655 // This also means that the condition `0 < i + chunk <= ln` is
656 // always respected, ensuring the `pb` pointer can be used
659 let ptr = self.as_mut_ptr();
661 let pb = ptr.add(ln - i - chunk);
662 let va = ptr::read_unaligned(pa as *mut u32);
663 let vb = ptr::read_unaligned(pb as *mut u32);
664 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
665 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
672 // SAFETY: `i` is inferior to half the length of the slice so
673 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
674 // will not go further than `ln / 2 - 1`).
675 // The resulting pointers `pa` and `pb` are therefore valid and
676 // aligned, and can be read from and written to.
678 // Unsafe swap to avoid the bounds check in safe swap.
679 let ptr = self.as_mut_ptr();
681 let pb = ptr.add(ln - i - 1);
688 /// Returns an iterator over the slice.
693 /// let x = &[1, 2, 4];
694 /// let mut iterator = x.iter();
696 /// assert_eq!(iterator.next(), Some(&1));
697 /// assert_eq!(iterator.next(), Some(&2));
698 /// assert_eq!(iterator.next(), Some(&4));
699 /// assert_eq!(iterator.next(), None);
701 #[stable(feature = "rust1", since = "1.0.0")]
703 pub fn iter(&self) -> Iter<'_, T> {
707 /// Returns an iterator that allows modifying each value.
712 /// let x = &mut [1, 2, 4];
713 /// for elem in x.iter_mut() {
716 /// assert_eq!(x, &[3, 4, 6]);
718 #[stable(feature = "rust1", since = "1.0.0")]
720 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
724 /// Returns an iterator over all contiguous windows of length
725 /// `size`. The windows overlap. If the slice is shorter than
726 /// `size`, the iterator returns no values.
730 /// Panics if `size` is 0.
735 /// let slice = ['r', 'u', 's', 't'];
736 /// let mut iter = slice.windows(2);
737 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
738 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
739 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
740 /// assert!(iter.next().is_none());
743 /// If the slice is shorter than `size`:
746 /// let slice = ['f', 'o', 'o'];
747 /// let mut iter = slice.windows(4);
748 /// assert!(iter.next().is_none());
750 #[stable(feature = "rust1", since = "1.0.0")]
752 pub fn windows(&self, size: usize) -> Windows<'_, T> {
753 let size = NonZeroUsize::new(size).expect("size is zero");
754 Windows::new(self, size)
757 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
758 /// beginning of the slice.
760 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
761 /// slice, then the last chunk will not have length `chunk_size`.
763 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
764 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
769 /// Panics if `chunk_size` is 0.
774 /// let slice = ['l', 'o', 'r', 'e', 'm'];
775 /// let mut iter = slice.chunks(2);
776 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
777 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
778 /// assert_eq!(iter.next().unwrap(), &['m']);
779 /// assert!(iter.next().is_none());
782 /// [`chunks_exact`]: slice::chunks_exact
783 /// [`rchunks`]: slice::rchunks
784 #[stable(feature = "rust1", since = "1.0.0")]
786 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
787 assert_ne!(chunk_size, 0);
788 Chunks::new(self, chunk_size)
791 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
792 /// beginning of the slice.
794 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
795 /// length of the slice, then the last chunk will not have length `chunk_size`.
797 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
798 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
799 /// the end of the slice.
803 /// Panics if `chunk_size` is 0.
808 /// let v = &mut [0, 0, 0, 0, 0];
809 /// let mut count = 1;
811 /// for chunk in v.chunks_mut(2) {
812 /// for elem in chunk.iter_mut() {
817 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
820 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
821 /// [`rchunks_mut`]: slice::rchunks_mut
822 #[stable(feature = "rust1", since = "1.0.0")]
824 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
825 assert_ne!(chunk_size, 0);
826 ChunksMut::new(self, chunk_size)
829 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
830 /// beginning of the slice.
832 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
833 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
834 /// from the `remainder` function of the iterator.
836 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
837 /// resulting code better than in the case of [`chunks`].
839 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
840 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
844 /// Panics if `chunk_size` is 0.
849 /// let slice = ['l', 'o', 'r', 'e', 'm'];
850 /// let mut iter = slice.chunks_exact(2);
851 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
852 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
853 /// assert!(iter.next().is_none());
854 /// assert_eq!(iter.remainder(), &['m']);
857 /// [`chunks`]: slice::chunks
858 /// [`rchunks_exact`]: slice::rchunks_exact
859 #[stable(feature = "chunks_exact", since = "1.31.0")]
861 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
862 assert_ne!(chunk_size, 0);
863 ChunksExact::new(self, chunk_size)
866 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
867 /// beginning of the slice.
869 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
870 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
871 /// retrieved from the `into_remainder` function of the iterator.
873 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
874 /// resulting code better than in the case of [`chunks_mut`].
876 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
877 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
882 /// Panics if `chunk_size` is 0.
887 /// let v = &mut [0, 0, 0, 0, 0];
888 /// let mut count = 1;
890 /// for chunk in v.chunks_exact_mut(2) {
891 /// for elem in chunk.iter_mut() {
896 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
899 /// [`chunks_mut`]: slice::chunks_mut
900 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
901 #[stable(feature = "chunks_exact", since = "1.31.0")]
903 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
904 assert_ne!(chunk_size, 0);
905 ChunksExactMut::new(self, chunk_size)
908 /// Splits the slice into a slice of `N`-element arrays,
909 /// assuming that there's no remainder.
913 /// This may only be called when
914 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
920 /// #![feature(slice_as_chunks)]
921 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
922 /// let chunks: &[[char; 1]] =
923 /// // SAFETY: 1-element chunks never have remainder
924 /// unsafe { slice.as_chunks_unchecked() };
925 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
926 /// let chunks: &[[char; 3]] =
927 /// // SAFETY: The slice length (6) is a multiple of 3
928 /// unsafe { slice.as_chunks_unchecked() };
929 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
931 /// // These would be unsound:
932 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
933 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
935 #[unstable(feature = "slice_as_chunks", issue = "74985")]
937 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
938 debug_assert_ne!(N, 0);
939 debug_assert_eq!(self.len() % N, 0);
941 // SAFETY: Our precondition is exactly what's needed to call this
942 unsafe { crate::intrinsics::exact_div(self.len(), N) };
943 // SAFETY: We cast a slice of `new_len * N` elements into
944 // a slice of `new_len` many `N` elements chunks.
945 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
948 /// Splits the slice into a slice of `N`-element arrays,
949 /// starting at the beginning of the slice,
950 /// and a remainder slice with length strictly less than `N`.
954 /// Panics if `N` is 0. This check will most probably get changed to a compile time
955 /// error before this method gets stabilized.
960 /// #![feature(slice_as_chunks)]
961 /// let slice = ['l', 'o', 'r', 'e', 'm'];
962 /// let (chunks, remainder) = slice.as_chunks();
963 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
964 /// assert_eq!(remainder, &['m']);
966 #[unstable(feature = "slice_as_chunks", issue = "74985")]
968 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
970 let len = self.len() / N;
971 let (multiple_of_n, remainder) = self.split_at(len * N);
972 // SAFETY: We already panicked for zero, and ensured by construction
973 // that the length of the subslice is a multiple of N.
974 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
975 (array_slice, remainder)
978 /// Splits the slice into a slice of `N`-element arrays,
979 /// starting at the end of the slice,
980 /// and a remainder slice with length strictly less than `N`.
984 /// Panics if `N` is 0. This check will most probably get changed to a compile time
985 /// error before this method gets stabilized.
990 /// #![feature(slice_as_chunks)]
991 /// let slice = ['l', 'o', 'r', 'e', 'm'];
992 /// let (remainder, chunks) = slice.as_rchunks();
993 /// assert_eq!(remainder, &['l']);
994 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
996 #[unstable(feature = "slice_as_chunks", issue = "74985")]
998 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1000 let len = self.len() / N;
1001 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1002 // SAFETY: We already panicked for zero, and ensured by construction
1003 // that the length of the subslice is a multiple of N.
1004 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1005 (remainder, array_slice)
1008 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1009 /// beginning of the slice.
1011 /// The chunks are array references and do not overlap. If `N` does not divide the
1012 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1013 /// retrieved from the `remainder` function of the iterator.
1015 /// This method is the const generic equivalent of [`chunks_exact`].
1019 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1020 /// error before this method gets stabilized.
1025 /// #![feature(array_chunks)]
1026 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1027 /// let mut iter = slice.array_chunks();
1028 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1029 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1030 /// assert!(iter.next().is_none());
1031 /// assert_eq!(iter.remainder(), &['m']);
1034 /// [`chunks_exact`]: slice::chunks_exact
1035 #[unstable(feature = "array_chunks", issue = "74985")]
1037 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1039 ArrayChunks::new(self)
1042 /// Splits the slice into a slice of `N`-element arrays,
1043 /// assuming that there's no remainder.
1047 /// This may only be called when
1048 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1054 /// #![feature(slice_as_chunks)]
1055 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1056 /// let chunks: &mut [[char; 1]] =
1057 /// // SAFETY: 1-element chunks never have remainder
1058 /// unsafe { slice.as_chunks_unchecked_mut() };
1059 /// chunks[0] = ['L'];
1060 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1061 /// let chunks: &mut [[char; 3]] =
1062 /// // SAFETY: The slice length (6) is a multiple of 3
1063 /// unsafe { slice.as_chunks_unchecked_mut() };
1064 /// chunks[1] = ['a', 'x', '?'];
1065 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1067 /// // These would be unsound:
1068 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1069 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1071 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1073 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1074 debug_assert_ne!(N, 0);
1075 debug_assert_eq!(self.len() % N, 0);
1077 // SAFETY: Our precondition is exactly what's needed to call this
1078 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1079 // SAFETY: We cast a slice of `new_len * N` elements into
1080 // a slice of `new_len` many `N` elements chunks.
1081 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1084 /// Splits the slice into a slice of `N`-element arrays,
1085 /// starting at the beginning of the slice,
1086 /// and a remainder slice with length strictly less than `N`.
1090 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1091 /// error before this method gets stabilized.
1096 /// #![feature(slice_as_chunks)]
1097 /// let v = &mut [0, 0, 0, 0, 0];
1098 /// let mut count = 1;
1100 /// let (chunks, remainder) = v.as_chunks_mut();
1101 /// remainder[0] = 9;
1102 /// for chunk in chunks {
1103 /// *chunk = [count; 2];
1106 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1108 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1110 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1112 let len = self.len() / N;
1113 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1114 // SAFETY: We already panicked for zero, and ensured by construction
1115 // that the length of the subslice is a multiple of N.
1116 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1117 (array_slice, remainder)
1120 /// Splits the slice into a slice of `N`-element arrays,
1121 /// starting at the end of the slice,
1122 /// and a remainder slice with length strictly less than `N`.
1126 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1127 /// error before this method gets stabilized.
1132 /// #![feature(slice_as_chunks)]
1133 /// let v = &mut [0, 0, 0, 0, 0];
1134 /// let mut count = 1;
1136 /// let (remainder, chunks) = v.as_rchunks_mut();
1137 /// remainder[0] = 9;
1138 /// for chunk in chunks {
1139 /// *chunk = [count; 2];
1142 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1144 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1146 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1148 let len = self.len() / N;
1149 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1150 // SAFETY: We already panicked for zero, and ensured by construction
1151 // that the length of the subslice is a multiple of N.
1152 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1153 (remainder, array_slice)
1156 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1157 /// beginning of the slice.
1159 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1160 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1161 /// can be retrieved from the `into_remainder` function of the iterator.
1163 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1167 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1168 /// error before this method gets stabilized.
1173 /// #![feature(array_chunks)]
1174 /// let v = &mut [0, 0, 0, 0, 0];
1175 /// let mut count = 1;
1177 /// for chunk in v.array_chunks_mut() {
1178 /// *chunk = [count; 2];
1181 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1184 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1185 #[unstable(feature = "array_chunks", issue = "74985")]
1187 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1189 ArrayChunksMut::new(self)
1192 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1193 /// starting at the beginning of the slice.
1195 /// This is the const generic equivalent of [`windows`].
1197 /// If `N` is greater than the size of the slice, it will return no windows.
1201 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1202 /// error before this method gets stabilized.
1207 /// #![feature(array_windows)]
1208 /// let slice = [0, 1, 2, 3];
1209 /// let mut iter = slice.array_windows();
1210 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1211 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1212 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1213 /// assert!(iter.next().is_none());
1216 /// [`windows`]: slice::windows
1217 #[unstable(feature = "array_windows", issue = "75027")]
1219 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1221 ArrayWindows::new(self)
1224 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1227 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1228 /// slice, then the last chunk will not have length `chunk_size`.
1230 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1231 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1236 /// Panics if `chunk_size` is 0.
1241 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1242 /// let mut iter = slice.rchunks(2);
1243 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1244 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1245 /// assert_eq!(iter.next().unwrap(), &['l']);
1246 /// assert!(iter.next().is_none());
1249 /// [`rchunks_exact`]: slice::rchunks_exact
1250 /// [`chunks`]: slice::chunks
1251 #[stable(feature = "rchunks", since = "1.31.0")]
1253 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1254 assert!(chunk_size != 0);
1255 RChunks::new(self, chunk_size)
1258 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1261 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1262 /// length of the slice, then the last chunk will not have length `chunk_size`.
1264 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1265 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1266 /// beginning of the slice.
1270 /// Panics if `chunk_size` is 0.
1275 /// let v = &mut [0, 0, 0, 0, 0];
1276 /// let mut count = 1;
1278 /// for chunk in v.rchunks_mut(2) {
1279 /// for elem in chunk.iter_mut() {
1284 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1287 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1288 /// [`chunks_mut`]: slice::chunks_mut
1289 #[stable(feature = "rchunks", since = "1.31.0")]
1291 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1292 assert!(chunk_size != 0);
1293 RChunksMut::new(self, chunk_size)
1296 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1297 /// end of the slice.
1299 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1300 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1301 /// from the `remainder` function of the iterator.
1303 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1304 /// resulting code better than in the case of [`chunks`].
1306 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1307 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1312 /// Panics if `chunk_size` is 0.
1317 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1318 /// let mut iter = slice.rchunks_exact(2);
1319 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1320 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1321 /// assert!(iter.next().is_none());
1322 /// assert_eq!(iter.remainder(), &['l']);
1325 /// [`chunks`]: slice::chunks
1326 /// [`rchunks`]: slice::rchunks
1327 /// [`chunks_exact`]: slice::chunks_exact
1328 #[stable(feature = "rchunks", since = "1.31.0")]
1330 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1331 assert!(chunk_size != 0);
1332 RChunksExact::new(self, chunk_size)
1335 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1338 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1339 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1340 /// retrieved from the `into_remainder` function of the iterator.
1342 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1343 /// resulting code better than in the case of [`chunks_mut`].
1345 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1346 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1351 /// Panics if `chunk_size` is 0.
1356 /// let v = &mut [0, 0, 0, 0, 0];
1357 /// let mut count = 1;
1359 /// for chunk in v.rchunks_exact_mut(2) {
1360 /// for elem in chunk.iter_mut() {
1365 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1368 /// [`chunks_mut`]: slice::chunks_mut
1369 /// [`rchunks_mut`]: slice::rchunks_mut
1370 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1371 #[stable(feature = "rchunks", since = "1.31.0")]
1373 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1374 assert!(chunk_size != 0);
1375 RChunksExactMut::new(self, chunk_size)
1378 /// Returns an iterator over the slice producing non-overlapping runs
1379 /// of elements using the predicate to separate them.
1381 /// The predicate is called on two elements following themselves,
1382 /// it means the predicate is called on `slice[0]` and `slice[1]`
1383 /// then on `slice[1]` and `slice[2]` and so on.
1388 /// #![feature(slice_group_by)]
1390 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1392 /// let mut iter = slice.group_by(|a, b| a == b);
1394 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1395 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1396 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1397 /// assert_eq!(iter.next(), None);
1400 /// This method can be used to extract the sorted subslices:
1403 /// #![feature(slice_group_by)]
1405 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1407 /// let mut iter = slice.group_by(|a, b| a <= b);
1409 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1410 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1411 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1412 /// assert_eq!(iter.next(), None);
1414 #[unstable(feature = "slice_group_by", issue = "80552")]
1416 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1418 F: FnMut(&T, &T) -> bool,
1420 GroupBy::new(self, pred)
1423 /// Returns an iterator over the slice producing non-overlapping mutable
1424 /// runs of elements using the predicate to separate them.
1426 /// The predicate is called on two elements following themselves,
1427 /// it means the predicate is called on `slice[0]` and `slice[1]`
1428 /// then on `slice[1]` and `slice[2]` and so on.
1433 /// #![feature(slice_group_by)]
1435 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1437 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1439 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1440 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1441 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1442 /// assert_eq!(iter.next(), None);
1445 /// This method can be used to extract the sorted subslices:
1448 /// #![feature(slice_group_by)]
1450 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1452 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1454 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1455 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1456 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1457 /// assert_eq!(iter.next(), None);
1459 #[unstable(feature = "slice_group_by", issue = "80552")]
1461 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1463 F: FnMut(&T, &T) -> bool,
1465 GroupByMut::new(self, pred)
1468 /// Divides one slice into two at an index.
1470 /// The first will contain all indices from `[0, mid)` (excluding
1471 /// the index `mid` itself) and the second will contain all
1472 /// indices from `[mid, len)` (excluding the index `len` itself).
1476 /// Panics if `mid > len`.
1481 /// let v = [1, 2, 3, 4, 5, 6];
1484 /// let (left, right) = v.split_at(0);
1485 /// assert_eq!(left, []);
1486 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1490 /// let (left, right) = v.split_at(2);
1491 /// assert_eq!(left, [1, 2]);
1492 /// assert_eq!(right, [3, 4, 5, 6]);
1496 /// let (left, right) = v.split_at(6);
1497 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1498 /// assert_eq!(right, []);
1501 #[stable(feature = "rust1", since = "1.0.0")]
1503 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1504 assert!(mid <= self.len());
1505 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1506 // fulfills the requirements of `from_raw_parts_mut`.
1507 unsafe { self.split_at_unchecked(mid) }
1510 /// Divides one mutable slice into two at an index.
1512 /// The first will contain all indices from `[0, mid)` (excluding
1513 /// the index `mid` itself) and the second will contain all
1514 /// indices from `[mid, len)` (excluding the index `len` itself).
1518 /// Panics if `mid > len`.
1523 /// let mut v = [1, 0, 3, 0, 5, 6];
1524 /// let (left, right) = v.split_at_mut(2);
1525 /// assert_eq!(left, [1, 0]);
1526 /// assert_eq!(right, [3, 0, 5, 6]);
1529 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1531 #[stable(feature = "rust1", since = "1.0.0")]
1533 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1534 assert!(mid <= self.len());
1535 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1536 // fulfills the requirements of `from_raw_parts_mut`.
1537 unsafe { self.split_at_mut_unchecked(mid) }
1540 /// Divides one slice into two at an index, without doing bounds checking.
1542 /// The first will contain all indices from `[0, mid)` (excluding
1543 /// the index `mid` itself) and the second will contain all
1544 /// indices from `[mid, len)` (excluding the index `len` itself).
1546 /// For a safe alternative see [`split_at`].
1550 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1551 /// even if the resulting reference is not used. The caller has to ensure that
1552 /// `0 <= mid <= self.len()`.
1554 /// [`split_at`]: slice::split_at
1555 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1560 /// #![feature(slice_split_at_unchecked)]
1562 /// let v = [1, 2, 3, 4, 5, 6];
1565 /// let (left, right) = v.split_at_unchecked(0);
1566 /// assert_eq!(left, []);
1567 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1571 /// let (left, right) = v.split_at_unchecked(2);
1572 /// assert_eq!(left, [1, 2]);
1573 /// assert_eq!(right, [3, 4, 5, 6]);
1577 /// let (left, right) = v.split_at_unchecked(6);
1578 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1579 /// assert_eq!(right, []);
1582 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1584 pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1585 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1586 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1589 /// Divides one mutable slice into two at an index, without doing bounds checking.
1591 /// The first will contain all indices from `[0, mid)` (excluding
1592 /// the index `mid` itself) and the second will contain all
1593 /// indices from `[mid, len)` (excluding the index `len` itself).
1595 /// For a safe alternative see [`split_at_mut`].
1599 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1600 /// even if the resulting reference is not used. The caller has to ensure that
1601 /// `0 <= mid <= self.len()`.
1603 /// [`split_at_mut`]: slice::split_at_mut
1604 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1609 /// #![feature(slice_split_at_unchecked)]
1611 /// let mut v = [1, 0, 3, 0, 5, 6];
1612 /// // scoped to restrict the lifetime of the borrows
1614 /// let (left, right) = v.split_at_mut_unchecked(2);
1615 /// assert_eq!(left, [1, 0]);
1616 /// assert_eq!(right, [3, 0, 5, 6]);
1620 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1622 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1624 pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1625 let len = self.len();
1626 let ptr = self.as_mut_ptr();
1628 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1630 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1632 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1635 /// Returns an iterator over subslices separated by elements that match
1636 /// `pred`. The matched element is not contained in the subslices.
1641 /// let slice = [10, 40, 33, 20];
1642 /// let mut iter = slice.split(|num| num % 3 == 0);
1644 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1645 /// assert_eq!(iter.next().unwrap(), &[20]);
1646 /// assert!(iter.next().is_none());
1649 /// If the first element is matched, an empty slice will be the first item
1650 /// returned by the iterator. Similarly, if the last element in the slice
1651 /// is matched, an empty slice will be the last item returned by the
1655 /// let slice = [10, 40, 33];
1656 /// let mut iter = slice.split(|num| num % 3 == 0);
1658 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1659 /// assert_eq!(iter.next().unwrap(), &[]);
1660 /// assert!(iter.next().is_none());
1663 /// If two matched elements are directly adjacent, an empty slice will be
1664 /// present between them:
1667 /// let slice = [10, 6, 33, 20];
1668 /// let mut iter = slice.split(|num| num % 3 == 0);
1670 /// assert_eq!(iter.next().unwrap(), &[10]);
1671 /// assert_eq!(iter.next().unwrap(), &[]);
1672 /// assert_eq!(iter.next().unwrap(), &[20]);
1673 /// assert!(iter.next().is_none());
1675 #[stable(feature = "rust1", since = "1.0.0")]
1677 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1679 F: FnMut(&T) -> bool,
1681 Split::new(self, pred)
1684 /// Returns an iterator over mutable subslices separated by elements that
1685 /// match `pred`. The matched element is not contained in the subslices.
1690 /// let mut v = [10, 40, 30, 20, 60, 50];
1692 /// for group in v.split_mut(|num| *num % 3 == 0) {
1695 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1697 #[stable(feature = "rust1", since = "1.0.0")]
1699 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1701 F: FnMut(&T) -> bool,
1703 SplitMut::new(self, pred)
1706 /// Returns an iterator over subslices separated by elements that match
1707 /// `pred`. The matched element is contained in the end of the previous
1708 /// subslice as a terminator.
1713 /// let slice = [10, 40, 33, 20];
1714 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1716 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1717 /// assert_eq!(iter.next().unwrap(), &[20]);
1718 /// assert!(iter.next().is_none());
1721 /// If the last element of the slice is matched,
1722 /// that element will be considered the terminator of the preceding slice.
1723 /// That slice will be the last item returned by the iterator.
1726 /// let slice = [3, 10, 40, 33];
1727 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1729 /// assert_eq!(iter.next().unwrap(), &[3]);
1730 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1731 /// assert!(iter.next().is_none());
1733 #[stable(feature = "split_inclusive", since = "1.51.0")]
1735 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1737 F: FnMut(&T) -> bool,
1739 SplitInclusive::new(self, pred)
1742 /// Returns an iterator over mutable subslices separated by elements that
1743 /// match `pred`. The matched element is contained in the previous
1744 /// subslice as a terminator.
1749 /// let mut v = [10, 40, 30, 20, 60, 50];
1751 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1752 /// let terminator_idx = group.len()-1;
1753 /// group[terminator_idx] = 1;
1755 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1757 #[stable(feature = "split_inclusive", since = "1.51.0")]
1759 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1761 F: FnMut(&T) -> bool,
1763 SplitInclusiveMut::new(self, pred)
1766 /// Returns an iterator over subslices separated by elements that match
1767 /// `pred`, starting at the end of the slice and working backwards.
1768 /// The matched element is not contained in the subslices.
1773 /// let slice = [11, 22, 33, 0, 44, 55];
1774 /// let mut iter = slice.rsplit(|num| *num == 0);
1776 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1777 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1778 /// assert_eq!(iter.next(), None);
1781 /// As with `split()`, if the first or last element is matched, an empty
1782 /// slice will be the first (or last) item returned by the iterator.
1785 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1786 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1787 /// assert_eq!(it.next().unwrap(), &[]);
1788 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1789 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1790 /// assert_eq!(it.next().unwrap(), &[]);
1791 /// assert_eq!(it.next(), None);
1793 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1795 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1797 F: FnMut(&T) -> bool,
1799 RSplit::new(self, pred)
1802 /// Returns an iterator over mutable subslices separated by elements that
1803 /// match `pred`, starting at the end of the slice and working
1804 /// backwards. The matched element is not contained in the subslices.
1809 /// let mut v = [100, 400, 300, 200, 600, 500];
1811 /// let mut count = 0;
1812 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1814 /// group[0] = count;
1816 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1819 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1821 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1823 F: FnMut(&T) -> bool,
1825 RSplitMut::new(self, pred)
1828 /// Returns an iterator over subslices separated by elements that match
1829 /// `pred`, limited to returning at most `n` items. The matched element is
1830 /// not contained in the subslices.
1832 /// The last element returned, if any, will contain the remainder of the
1837 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1838 /// `[20, 60, 50]`):
1841 /// let v = [10, 40, 30, 20, 60, 50];
1843 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1844 /// println!("{:?}", group);
1847 #[stable(feature = "rust1", since = "1.0.0")]
1849 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1851 F: FnMut(&T) -> bool,
1853 SplitN::new(self.split(pred), n)
1856 /// Returns an iterator over subslices separated by elements that match
1857 /// `pred`, limited to returning at most `n` items. The matched element is
1858 /// not contained in the subslices.
1860 /// The last element returned, if any, will contain the remainder of the
1866 /// let mut v = [10, 40, 30, 20, 60, 50];
1868 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1871 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1873 #[stable(feature = "rust1", since = "1.0.0")]
1875 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1877 F: FnMut(&T) -> bool,
1879 SplitNMut::new(self.split_mut(pred), n)
1882 /// Returns an iterator over subslices separated by elements that match
1883 /// `pred` limited to returning at most `n` items. This starts at the end of
1884 /// the slice and works backwards. The matched element is not contained in
1887 /// The last element returned, if any, will contain the remainder of the
1892 /// Print the slice split once, starting from the end, by numbers divisible
1893 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1896 /// let v = [10, 40, 30, 20, 60, 50];
1898 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1899 /// println!("{:?}", group);
1902 #[stable(feature = "rust1", since = "1.0.0")]
1904 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1906 F: FnMut(&T) -> bool,
1908 RSplitN::new(self.rsplit(pred), n)
1911 /// Returns an iterator over subslices separated by elements that match
1912 /// `pred` limited to returning at most `n` items. This starts at the end of
1913 /// the slice and works backwards. The matched element is not contained in
1916 /// The last element returned, if any, will contain the remainder of the
1922 /// let mut s = [10, 40, 30, 20, 60, 50];
1924 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1927 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1929 #[stable(feature = "rust1", since = "1.0.0")]
1931 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1933 F: FnMut(&T) -> bool,
1935 RSplitNMut::new(self.rsplit_mut(pred), n)
1938 /// Returns `true` if the slice contains an element with the given value.
1943 /// let v = [10, 40, 30];
1944 /// assert!(v.contains(&30));
1945 /// assert!(!v.contains(&50));
1948 /// If you do not have a `&T`, but some other value that you can compare
1949 /// with one (for example, `String` implements `PartialEq<str>`), you can
1950 /// use `iter().any`:
1953 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1954 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1955 /// assert!(!v.iter().any(|e| e == "hi"));
1957 #[stable(feature = "rust1", since = "1.0.0")]
1959 pub fn contains(&self, x: &T) -> bool
1963 cmp::SliceContains::slice_contains(x, self)
1966 /// Returns `true` if `needle` is a prefix of the slice.
1971 /// let v = [10, 40, 30];
1972 /// assert!(v.starts_with(&[10]));
1973 /// assert!(v.starts_with(&[10, 40]));
1974 /// assert!(!v.starts_with(&[50]));
1975 /// assert!(!v.starts_with(&[10, 50]));
1978 /// Always returns `true` if `needle` is an empty slice:
1981 /// let v = &[10, 40, 30];
1982 /// assert!(v.starts_with(&[]));
1983 /// let v: &[u8] = &[];
1984 /// assert!(v.starts_with(&[]));
1986 #[stable(feature = "rust1", since = "1.0.0")]
1987 pub fn starts_with(&self, needle: &[T]) -> bool
1991 let n = needle.len();
1992 self.len() >= n && needle == &self[..n]
1995 /// Returns `true` if `needle` is a suffix of the slice.
2000 /// let v = [10, 40, 30];
2001 /// assert!(v.ends_with(&[30]));
2002 /// assert!(v.ends_with(&[40, 30]));
2003 /// assert!(!v.ends_with(&[50]));
2004 /// assert!(!v.ends_with(&[50, 30]));
2007 /// Always returns `true` if `needle` is an empty slice:
2010 /// let v = &[10, 40, 30];
2011 /// assert!(v.ends_with(&[]));
2012 /// let v: &[u8] = &[];
2013 /// assert!(v.ends_with(&[]));
2015 #[stable(feature = "rust1", since = "1.0.0")]
2016 pub fn ends_with(&self, needle: &[T]) -> bool
2020 let (m, n) = (self.len(), needle.len());
2021 m >= n && needle == &self[m - n..]
2024 /// Returns a subslice with the prefix removed.
2026 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2027 /// If `prefix` is empty, simply returns the original slice.
2029 /// If the slice does not start with `prefix`, returns `None`.
2034 /// let v = &[10, 40, 30];
2035 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2036 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2037 /// assert_eq!(v.strip_prefix(&[50]), None);
2038 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2040 /// let prefix : &str = "he";
2041 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2042 /// Some(b"llo".as_ref()));
2044 #[must_use = "returns the subslice without modifying the original"]
2045 #[stable(feature = "slice_strip", since = "1.51.0")]
2046 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2050 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2051 let prefix = prefix.as_slice();
2052 let n = prefix.len();
2053 if n <= self.len() {
2054 let (head, tail) = self.split_at(n);
2062 /// Returns a subslice with the suffix removed.
2064 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2065 /// If `suffix` is empty, simply returns the original slice.
2067 /// If the slice does not end with `suffix`, returns `None`.
2072 /// let v = &[10, 40, 30];
2073 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2074 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2075 /// assert_eq!(v.strip_suffix(&[50]), None);
2076 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2078 #[must_use = "returns the subslice without modifying the original"]
2079 #[stable(feature = "slice_strip", since = "1.51.0")]
2080 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2084 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2085 let suffix = suffix.as_slice();
2086 let (len, n) = (self.len(), suffix.len());
2088 let (head, tail) = self.split_at(len - n);
2096 /// Binary searches this sorted slice for a given element.
2098 /// If the value is found then [`Result::Ok`] is returned, containing the
2099 /// index of the matching element. If there are multiple matches, then any
2100 /// one of the matches could be returned. The index is chosen
2101 /// deterministically, but is subject to change in future versions of Rust.
2102 /// If the value is not found then [`Result::Err`] is returned, containing
2103 /// the index where a matching element could be inserted while maintaining
2106 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2108 /// [`binary_search_by`]: slice::binary_search_by
2109 /// [`binary_search_by_key`]: slice::binary_search_by_key
2110 /// [`partition_point`]: slice::partition_point
2114 /// Looks up a series of four elements. The first is found, with a
2115 /// uniquely determined position; the second and third are not
2116 /// found; the fourth could match any position in `[1, 4]`.
2119 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2121 /// assert_eq!(s.binary_search(&13), Ok(9));
2122 /// assert_eq!(s.binary_search(&4), Err(7));
2123 /// assert_eq!(s.binary_search(&100), Err(13));
2124 /// let r = s.binary_search(&1);
2125 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2128 /// If you want to insert an item to a sorted vector, while maintaining
2132 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2134 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2135 /// s.insert(idx, num);
2136 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2138 #[stable(feature = "rust1", since = "1.0.0")]
2139 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2143 self.binary_search_by(|p| p.cmp(x))
2146 /// Binary searches this sorted slice with a comparator function.
2148 /// The comparator function should implement an order consistent
2149 /// with the sort order of the underlying slice, returning an
2150 /// order code that indicates whether its argument is `Less`,
2151 /// `Equal` or `Greater` the desired target.
2153 /// If the value is found then [`Result::Ok`] is returned, containing the
2154 /// index of the matching element. If there are multiple matches, then any
2155 /// one of the matches could be returned. The index is chosen
2156 /// deterministically, but is subject to change in future versions of Rust.
2157 /// If the value is not found then [`Result::Err`] is returned, containing
2158 /// the index where a matching element could be inserted while maintaining
2161 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2163 /// [`binary_search`]: slice::binary_search
2164 /// [`binary_search_by_key`]: slice::binary_search_by_key
2165 /// [`partition_point`]: slice::partition_point
2169 /// Looks up a series of four elements. The first is found, with a
2170 /// uniquely determined position; the second and third are not
2171 /// found; the fourth could match any position in `[1, 4]`.
2174 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2177 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2179 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2181 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2183 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2184 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2186 #[stable(feature = "rust1", since = "1.0.0")]
2188 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2190 F: FnMut(&'a T) -> Ordering,
2192 let mut size = self.len();
2194 let mut right = size;
2195 while left < right {
2196 let mid = left + size / 2;
2198 // SAFETY: the call is made safe by the following invariants:
2200 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2201 let cmp = f(unsafe { self.get_unchecked(mid) });
2203 // The reason why we use if/else control flow rather than match
2204 // is because match reorders comparison operations, which is perf sensitive.
2205 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2208 } else if cmp == Greater {
2211 // SAFETY: same as the `get_unchecked` above
2212 unsafe { crate::intrinsics::assume(mid < self.len()) };
2216 size = right - left;
2221 /// Binary searches this sorted slice with a key extraction function.
2223 /// Assumes that the slice is sorted by the key, for instance with
2224 /// [`sort_by_key`] using the same key extraction function.
2226 /// If the value is found then [`Result::Ok`] is returned, containing the
2227 /// index of the matching element. If there are multiple matches, then any
2228 /// one of the matches could be returned. The index is chosen
2229 /// deterministically, but is subject to change in future versions of Rust.
2230 /// If the value is not found then [`Result::Err`] is returned, containing
2231 /// the index where a matching element could be inserted while maintaining
2234 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2236 /// [`sort_by_key`]: slice::sort_by_key
2237 /// [`binary_search`]: slice::binary_search
2238 /// [`binary_search_by`]: slice::binary_search_by
2239 /// [`partition_point`]: slice::partition_point
2243 /// Looks up a series of four elements in a slice of pairs sorted by
2244 /// their second elements. The first is found, with a uniquely
2245 /// determined position; the second and third are not found; the
2246 /// fourth could match any position in `[1, 4]`.
2249 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2250 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2251 /// (1, 21), (2, 34), (4, 55)];
2253 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2254 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2255 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2256 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2257 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2259 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2260 // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
2261 // This breaks links when slice is displayed in core, but changing it to use relative links
2262 // would break when the item is re-exported. So allow the core links to be broken for now.
2263 #[allow(rustdoc::broken_intra_doc_links)]
2264 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2266 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2268 F: FnMut(&'a T) -> B,
2271 self.binary_search_by(|k| f(k).cmp(b))
2274 /// Sorts the slice, but might not preserve the order of equal elements.
2276 /// This sort is unstable (i.e., may reorder equal elements), in-place
2277 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2279 /// # Current implementation
2281 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2282 /// which combines the fast average case of randomized quicksort with the fast worst case of
2283 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2284 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2285 /// deterministic behavior.
2287 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2288 /// slice consists of several concatenated sorted sequences.
2293 /// let mut v = [-5, 4, 1, -3, 2];
2295 /// v.sort_unstable();
2296 /// assert!(v == [-5, -3, 1, 2, 4]);
2299 /// [pdqsort]: https://github.com/orlp/pdqsort
2300 #[stable(feature = "sort_unstable", since = "1.20.0")]
2302 pub fn sort_unstable(&mut self)
2306 sort::quicksort(self, |a, b| a.lt(b));
2309 /// Sorts the slice with a comparator function, but might not preserve the order of equal
2312 /// This sort is unstable (i.e., may reorder equal elements), in-place
2313 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2315 /// The comparator function must define a total ordering for the elements in the slice. If
2316 /// the ordering is not total, the order of the elements is unspecified. An order is a
2317 /// total order if it is (for all `a`, `b` and `c`):
2319 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2320 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2322 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2323 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2326 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2327 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2328 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2331 /// # Current implementation
2333 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2334 /// which combines the fast average case of randomized quicksort with the fast worst case of
2335 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2336 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2337 /// deterministic behavior.
2339 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2340 /// slice consists of several concatenated sorted sequences.
2345 /// let mut v = [5, 4, 1, 3, 2];
2346 /// v.sort_unstable_by(|a, b| a.cmp(b));
2347 /// assert!(v == [1, 2, 3, 4, 5]);
2349 /// // reverse sorting
2350 /// v.sort_unstable_by(|a, b| b.cmp(a));
2351 /// assert!(v == [5, 4, 3, 2, 1]);
2354 /// [pdqsort]: https://github.com/orlp/pdqsort
2355 #[stable(feature = "sort_unstable", since = "1.20.0")]
2357 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2359 F: FnMut(&T, &T) -> Ordering,
2361 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2364 /// Sorts the slice with a key extraction function, but might not preserve the order of equal
2367 /// This sort is unstable (i.e., may reorder equal elements), in-place
2368 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2371 /// # Current implementation
2373 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2374 /// which combines the fast average case of randomized quicksort with the fast worst case of
2375 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2376 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2377 /// deterministic behavior.
2379 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2380 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2381 /// cases where the key function is expensive.
2386 /// let mut v = [-5i32, 4, 1, -3, 2];
2388 /// v.sort_unstable_by_key(|k| k.abs());
2389 /// assert!(v == [1, 2, -3, 4, -5]);
2392 /// [pdqsort]: https://github.com/orlp/pdqsort
2393 #[stable(feature = "sort_unstable", since = "1.20.0")]
2395 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2400 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2403 /// Reorder the slice such that the element at `index` is at its final sorted position.
2404 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2405 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2407 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2411 self.select_nth_unstable(index)
2414 /// Reorder the slice with a comparator function such that the element at `index` is at its
2415 /// final sorted position.
2416 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2417 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2419 pub fn partition_at_index_by<F>(
2423 ) -> (&mut [T], &mut T, &mut [T])
2425 F: FnMut(&T, &T) -> Ordering,
2427 self.select_nth_unstable_by(index, compare)
2430 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2431 /// final sorted position.
2432 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2433 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2435 pub fn partition_at_index_by_key<K, F>(
2439 ) -> (&mut [T], &mut T, &mut [T])
2444 self.select_nth_unstable_by_key(index, f)
2447 /// Reorder the slice such that the element at `index` is at its final sorted position.
2449 /// This reordering has the additional property that any value at position `i < index` will be
2450 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2451 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2452 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2453 /// element" in other libraries. It returns a triplet of the following values: all elements less
2454 /// than the one at the given index, the value at the given index, and all elements greater than
2455 /// the one at the given index.
2457 /// # Current implementation
2459 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2460 /// used for [`sort_unstable`].
2462 /// [`sort_unstable`]: slice::sort_unstable
2466 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2471 /// let mut v = [-5i32, 4, 1, -3, 2];
2473 /// // Find the median
2474 /// v.select_nth_unstable(2);
2476 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2477 /// // about the specified index.
2478 /// assert!(v == [-3, -5, 1, 2, 4] ||
2479 /// v == [-5, -3, 1, 2, 4] ||
2480 /// v == [-3, -5, 1, 4, 2] ||
2481 /// v == [-5, -3, 1, 4, 2]);
2483 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2485 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2489 let mut f = |a: &T, b: &T| a.lt(b);
2490 sort::partition_at_index(self, index, &mut f)
2493 /// Reorder the slice with a comparator function such that the element at `index` is at its
2494 /// final sorted position.
2496 /// This reordering has the additional property that any value at position `i < index` will be
2497 /// less than or equal to any value at a position `j > index` using the comparator function.
2498 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2499 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2500 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2501 /// values: all elements less than the one at the given index, the value at the given index,
2502 /// and all elements greater than the one at the given index, using the provided comparator
2505 /// # Current implementation
2507 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2508 /// used for [`sort_unstable`].
2510 /// [`sort_unstable`]: slice::sort_unstable
2514 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2519 /// let mut v = [-5i32, 4, 1, -3, 2];
2521 /// // Find the median as if the slice were sorted in descending order.
2522 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2524 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2525 /// // about the specified index.
2526 /// assert!(v == [2, 4, 1, -5, -3] ||
2527 /// v == [2, 4, 1, -3, -5] ||
2528 /// v == [4, 2, 1, -5, -3] ||
2529 /// v == [4, 2, 1, -3, -5]);
2531 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2533 pub fn select_nth_unstable_by<F>(
2537 ) -> (&mut [T], &mut T, &mut [T])
2539 F: FnMut(&T, &T) -> Ordering,
2541 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2542 sort::partition_at_index(self, index, &mut f)
2545 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2546 /// final sorted position.
2548 /// This reordering has the additional property that any value at position `i < index` will be
2549 /// less than or equal to any value at a position `j > index` using the key extraction function.
2550 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2551 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2552 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2553 /// values: all elements less than the one at the given index, the value at the given index, and
2554 /// all elements greater than the one at the given index, using the provided key extraction
2557 /// # Current implementation
2559 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2560 /// used for [`sort_unstable`].
2562 /// [`sort_unstable`]: slice::sort_unstable
2566 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2571 /// let mut v = [-5i32, 4, 1, -3, 2];
2573 /// // Return the median as if the array were sorted according to absolute value.
2574 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2576 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2577 /// // about the specified index.
2578 /// assert!(v == [1, 2, -3, 4, -5] ||
2579 /// v == [1, 2, -3, -5, 4] ||
2580 /// v == [2, 1, -3, 4, -5] ||
2581 /// v == [2, 1, -3, -5, 4]);
2583 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2585 pub fn select_nth_unstable_by_key<K, F>(
2589 ) -> (&mut [T], &mut T, &mut [T])
2594 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2595 sort::partition_at_index(self, index, &mut g)
2598 /// Moves all consecutive repeated elements to the end of the slice according to the
2599 /// [`PartialEq`] trait implementation.
2601 /// Returns two slices. The first contains no consecutive repeated elements.
2602 /// The second contains all the duplicates in no specified order.
2604 /// If the slice is sorted, the first returned slice contains no duplicates.
2609 /// #![feature(slice_partition_dedup)]
2611 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2613 /// let (dedup, duplicates) = slice.partition_dedup();
2615 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2616 /// assert_eq!(duplicates, [2, 3, 1]);
2618 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2620 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2624 self.partition_dedup_by(|a, b| a == b)
2627 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2628 /// a given equality relation.
2630 /// Returns two slices. The first contains no consecutive repeated elements.
2631 /// The second contains all the duplicates in no specified order.
2633 /// The `same_bucket` function is passed references to two elements from the slice and
2634 /// must determine if the elements compare equal. The elements are passed in opposite order
2635 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2636 /// at the end of the slice.
2638 /// If the slice is sorted, the first returned slice contains no duplicates.
2643 /// #![feature(slice_partition_dedup)]
2645 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2647 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2649 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2650 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2652 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2654 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2656 F: FnMut(&mut T, &mut T) -> bool,
2658 // Although we have a mutable reference to `self`, we cannot make
2659 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2660 // must ensure that the slice is in a valid state at all times.
2662 // The way that we handle this is by using swaps; we iterate
2663 // over all the elements, swapping as we go so that at the end
2664 // the elements we wish to keep are in the front, and those we
2665 // wish to reject are at the back. We can then split the slice.
2666 // This operation is still `O(n)`.
2668 // Example: We start in this state, where `r` represents "next
2669 // read" and `w` represents "next_write`.
2672 // +---+---+---+---+---+---+
2673 // | 0 | 1 | 1 | 2 | 3 | 3 |
2674 // +---+---+---+---+---+---+
2677 // Comparing self[r] against self[w-1], this is not a duplicate, so
2678 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2679 // r and w, leaving us with:
2682 // +---+---+---+---+---+---+
2683 // | 0 | 1 | 1 | 2 | 3 | 3 |
2684 // +---+---+---+---+---+---+
2687 // Comparing self[r] against self[w-1], this value is a duplicate,
2688 // so we increment `r` but leave everything else unchanged:
2691 // +---+---+---+---+---+---+
2692 // | 0 | 1 | 1 | 2 | 3 | 3 |
2693 // +---+---+---+---+---+---+
2696 // Comparing self[r] against self[w-1], this is not a duplicate,
2697 // so swap self[r] and self[w] and advance r and w:
2700 // +---+---+---+---+---+---+
2701 // | 0 | 1 | 2 | 1 | 3 | 3 |
2702 // +---+---+---+---+---+---+
2705 // Not a duplicate, repeat:
2708 // +---+---+---+---+---+---+
2709 // | 0 | 1 | 2 | 3 | 1 | 3 |
2710 // +---+---+---+---+---+---+
2713 // Duplicate, advance r. End of slice. Split at w.
2715 let len = self.len();
2717 return (self, &mut []);
2720 let ptr = self.as_mut_ptr();
2721 let mut next_read: usize = 1;
2722 let mut next_write: usize = 1;
2724 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2725 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2726 // one element before `ptr_write`, but `next_write` starts at 1, so
2727 // `prev_ptr_write` is never less than 0 and is inside the slice.
2728 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2729 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2730 // and `prev_ptr_write.offset(1)`.
2732 // `next_write` is also incremented at most once per loop at most meaning
2733 // no element is skipped when it may need to be swapped.
2735 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2736 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2737 // The explanation is simply that `next_read >= next_write` is always true,
2738 // thus `next_read > next_write - 1` is too.
2740 // Avoid bounds checks by using raw pointers.
2741 while next_read < len {
2742 let ptr_read = ptr.add(next_read);
2743 let prev_ptr_write = ptr.add(next_write - 1);
2744 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2745 if next_read != next_write {
2746 let ptr_write = prev_ptr_write.offset(1);
2747 mem::swap(&mut *ptr_read, &mut *ptr_write);
2755 self.split_at_mut(next_write)
2758 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2759 /// to the same key.
2761 /// Returns two slices. The first contains no consecutive repeated elements.
2762 /// The second contains all the duplicates in no specified order.
2764 /// If the slice is sorted, the first returned slice contains no duplicates.
2769 /// #![feature(slice_partition_dedup)]
2771 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2773 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2775 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2776 /// assert_eq!(duplicates, [21, 30, 13]);
2778 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2780 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2782 F: FnMut(&mut T) -> K,
2785 self.partition_dedup_by(|a, b| key(a) == key(b))
2788 /// Rotates the slice in-place such that the first `mid` elements of the
2789 /// slice move to the end while the last `self.len() - mid` elements move to
2790 /// the front. After calling `rotate_left`, the element previously at index
2791 /// `mid` will become the first element in the slice.
2795 /// This function will panic if `mid` is greater than the length of the
2796 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2801 /// Takes linear (in `self.len()`) time.
2806 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2807 /// a.rotate_left(2);
2808 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2811 /// Rotating a subslice:
2814 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2815 /// a[1..5].rotate_left(1);
2816 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2818 #[stable(feature = "slice_rotate", since = "1.26.0")]
2819 pub fn rotate_left(&mut self, mid: usize) {
2820 assert!(mid <= self.len());
2821 let k = self.len() - mid;
2822 let p = self.as_mut_ptr();
2824 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2825 // valid for reading and writing, as required by `ptr_rotate`.
2827 rotate::ptr_rotate(mid, p.add(mid), k);
2831 /// Rotates the slice in-place such that the first `self.len() - k`
2832 /// elements of the slice move to the end while the last `k` elements move
2833 /// to the front. After calling `rotate_right`, the element previously at
2834 /// index `self.len() - k` will become the first element in the slice.
2838 /// This function will panic if `k` is greater than the length of the
2839 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2844 /// Takes linear (in `self.len()`) time.
2849 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2850 /// a.rotate_right(2);
2851 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2854 /// Rotate a subslice:
2857 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2858 /// a[1..5].rotate_right(1);
2859 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2861 #[stable(feature = "slice_rotate", since = "1.26.0")]
2862 pub fn rotate_right(&mut self, k: usize) {
2863 assert!(k <= self.len());
2864 let mid = self.len() - k;
2865 let p = self.as_mut_ptr();
2867 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2868 // valid for reading and writing, as required by `ptr_rotate`.
2870 rotate::ptr_rotate(mid, p.add(mid), k);
2874 /// Fills `self` with elements by cloning `value`.
2879 /// let mut buf = vec![0; 10];
2881 /// assert_eq!(buf, vec![1; 10]);
2883 #[doc(alias = "memset")]
2884 #[stable(feature = "slice_fill", since = "1.50.0")]
2885 pub fn fill(&mut self, value: T)
2889 specialize::SpecFill::spec_fill(self, value);
2892 /// Fills `self` with elements returned by calling a closure repeatedly.
2894 /// This method uses a closure to create new values. If you'd rather
2895 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2896 /// trait to generate values, you can pass [`Default::default`] as the
2899 /// [`fill`]: slice::fill
2904 /// let mut buf = vec![1; 10];
2905 /// buf.fill_with(Default::default);
2906 /// assert_eq!(buf, vec![0; 10]);
2908 #[doc(alias = "memset")]
2909 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2910 pub fn fill_with<F>(&mut self, mut f: F)
2919 /// Copies the elements from `src` into `self`.
2921 /// The length of `src` must be the same as `self`.
2923 /// If `T` implements `Copy`, it can be more performant to use
2924 /// [`copy_from_slice`].
2928 /// This function will panic if the two slices have different lengths.
2932 /// Cloning two elements from a slice into another:
2935 /// let src = [1, 2, 3, 4];
2936 /// let mut dst = [0, 0];
2938 /// // Because the slices have to be the same length,
2939 /// // we slice the source slice from four elements
2940 /// // to two. It will panic if we don't do this.
2941 /// dst.clone_from_slice(&src[2..]);
2943 /// assert_eq!(src, [1, 2, 3, 4]);
2944 /// assert_eq!(dst, [3, 4]);
2947 /// Rust enforces that there can only be one mutable reference with no
2948 /// immutable references to a particular piece of data in a particular
2949 /// scope. Because of this, attempting to use `clone_from_slice` on a
2950 /// single slice will result in a compile failure:
2953 /// let mut slice = [1, 2, 3, 4, 5];
2955 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2958 /// To work around this, we can use [`split_at_mut`] to create two distinct
2959 /// sub-slices from a slice:
2962 /// let mut slice = [1, 2, 3, 4, 5];
2965 /// let (left, right) = slice.split_at_mut(2);
2966 /// left.clone_from_slice(&right[1..]);
2969 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2972 /// [`copy_from_slice`]: slice::copy_from_slice
2973 /// [`split_at_mut`]: slice::split_at_mut
2974 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2975 pub fn clone_from_slice(&mut self, src: &[T])
2979 self.spec_clone_from(src);
2982 /// Copies all elements from `src` into `self`, using a memcpy.
2984 /// The length of `src` must be the same as `self`.
2986 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2990 /// This function will panic if the two slices have different lengths.
2994 /// Copying two elements from a slice into another:
2997 /// let src = [1, 2, 3, 4];
2998 /// let mut dst = [0, 0];
3000 /// // Because the slices have to be the same length,
3001 /// // we slice the source slice from four elements
3002 /// // to two. It will panic if we don't do this.
3003 /// dst.copy_from_slice(&src[2..]);
3005 /// assert_eq!(src, [1, 2, 3, 4]);
3006 /// assert_eq!(dst, [3, 4]);
3009 /// Rust enforces that there can only be one mutable reference with no
3010 /// immutable references to a particular piece of data in a particular
3011 /// scope. Because of this, attempting to use `copy_from_slice` on a
3012 /// single slice will result in a compile failure:
3015 /// let mut slice = [1, 2, 3, 4, 5];
3017 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3020 /// To work around this, we can use [`split_at_mut`] to create two distinct
3021 /// sub-slices from a slice:
3024 /// let mut slice = [1, 2, 3, 4, 5];
3027 /// let (left, right) = slice.split_at_mut(2);
3028 /// left.copy_from_slice(&right[1..]);
3031 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3034 /// [`clone_from_slice`]: slice::clone_from_slice
3035 /// [`split_at_mut`]: slice::split_at_mut
3036 #[doc(alias = "memcpy")]
3037 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3038 pub fn copy_from_slice(&mut self, src: &[T])
3042 // The panic code path was put into a cold function to not bloat the
3047 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3049 "source slice length ({}) does not match destination slice length ({})",
3054 if self.len() != src.len() {
3055 len_mismatch_fail(self.len(), src.len());
3058 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3059 // checked to have the same length. The slices cannot overlap because
3060 // mutable references are exclusive.
3062 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3066 /// Copies elements from one part of the slice to another part of itself,
3067 /// using a memmove.
3069 /// `src` is the range within `self` to copy from. `dest` is the starting
3070 /// index of the range within `self` to copy to, which will have the same
3071 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3072 /// must be less than or equal to `self.len()`.
3076 /// This function will panic if either range exceeds the end of the slice,
3077 /// or if the end of `src` is before the start.
3081 /// Copying four bytes within a slice:
3084 /// let mut bytes = *b"Hello, World!";
3086 /// bytes.copy_within(1..5, 8);
3088 /// assert_eq!(&bytes, b"Hello, Wello!");
3090 #[stable(feature = "copy_within", since = "1.37.0")]
3092 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3096 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3097 let count = src_end - src_start;
3098 assert!(dest <= self.len() - count, "dest is out of bounds");
3099 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3100 // as have those for `ptr::add`.
3102 // Derive both `src_ptr` and `dest_ptr` from the same loan
3103 let ptr = self.as_mut_ptr();
3104 let src_ptr = ptr.add(src_start);
3105 let dest_ptr = ptr.add(dest);
3106 ptr::copy(src_ptr, dest_ptr, count);
3110 /// Swaps all elements in `self` with those in `other`.
3112 /// The length of `other` must be the same as `self`.
3116 /// This function will panic if the two slices have different lengths.
3120 /// Swapping two elements across slices:
3123 /// let mut slice1 = [0, 0];
3124 /// let mut slice2 = [1, 2, 3, 4];
3126 /// slice1.swap_with_slice(&mut slice2[2..]);
3128 /// assert_eq!(slice1, [3, 4]);
3129 /// assert_eq!(slice2, [1, 2, 0, 0]);
3132 /// Rust enforces that there can only be one mutable reference to a
3133 /// particular piece of data in a particular scope. Because of this,
3134 /// attempting to use `swap_with_slice` on a single slice will result in
3135 /// a compile failure:
3138 /// let mut slice = [1, 2, 3, 4, 5];
3139 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3142 /// To work around this, we can use [`split_at_mut`] to create two distinct
3143 /// mutable sub-slices from a slice:
3146 /// let mut slice = [1, 2, 3, 4, 5];
3149 /// let (left, right) = slice.split_at_mut(2);
3150 /// left.swap_with_slice(&mut right[1..]);
3153 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3156 /// [`split_at_mut`]: slice::split_at_mut
3157 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3158 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3159 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3160 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3161 // checked to have the same length. The slices cannot overlap because
3162 // mutable references are exclusive.
3164 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3168 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3169 fn align_to_offsets<U>(&self) -> (usize, usize) {
3170 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3171 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3173 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3174 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3175 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3177 // Formula to calculate this is:
3179 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3180 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3182 // Expanded and simplified:
3184 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3185 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3187 // Luckily since all this is constant-evaluated... performance here matters not!
3189 fn gcd(a: usize, b: usize) -> usize {
3190 use crate::intrinsics;
3191 // iterative stein’s algorithm
3192 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3193 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3195 // SAFETY: `a` and `b` are checked to be non-zero values.
3196 let (ctz_a, mut ctz_b) = unsafe {
3203 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3205 let k = ctz_a.min(ctz_b);
3206 let mut a = a >> ctz_a;
3209 // remove all factors of 2 from b
3212 mem::swap(&mut a, &mut b);
3215 // SAFETY: `b` is checked to be non-zero.
3220 ctz_b = intrinsics::cttz_nonzero(b);
3225 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3226 let ts: usize = mem::size_of::<U>() / gcd;
3227 let us: usize = mem::size_of::<T>() / gcd;
3229 // Armed with this knowledge, we can find how many `U`s we can fit!
3230 let us_len = self.len() / ts * us;
3231 // And how many `T`s will be in the trailing slice!
3232 let ts_len = self.len() % ts;
3236 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3239 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3240 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3241 /// length possible for a given type and input slice, but only your algorithm's performance
3242 /// should depend on that, not its correctness. It is permissible for all of the input data to
3243 /// be returned as the prefix or suffix slice.
3245 /// This method has no purpose when either input element `T` or output element `U` are
3246 /// zero-sized and will return the original slice without splitting anything.
3250 /// This method is essentially a `transmute` with respect to the elements in the returned
3251 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3259 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3260 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3261 /// // less_efficient_algorithm_for_bytes(prefix);
3262 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3263 /// // less_efficient_algorithm_for_bytes(suffix);
3266 #[stable(feature = "slice_align_to", since = "1.30.0")]
3267 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3268 // Note that most of this function will be constant-evaluated,
3269 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3270 // handle ZSTs specially, which is – don't handle them at all.
3271 return (self, &[], &[]);
3274 // First, find at what point do we split between the first and 2nd slice. Easy with
3275 // ptr.align_offset.
3276 let ptr = self.as_ptr();
3277 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3278 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3279 if offset > self.len() {
3282 let (left, rest) = self.split_at(offset);
3283 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3284 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3285 // since the caller guarantees that we can transmute `T` to `U` safely.
3289 from_raw_parts(rest.as_ptr() as *const U, us_len),
3290 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3296 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3299 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3300 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3301 /// length possible for a given type and input slice, but only your algorithm's performance
3302 /// should depend on that, not its correctness. It is permissible for all of the input data to
3303 /// be returned as the prefix or suffix slice.
3305 /// This method has no purpose when either input element `T` or output element `U` are
3306 /// zero-sized and will return the original slice without splitting anything.
3310 /// This method is essentially a `transmute` with respect to the elements in the returned
3311 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3319 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3320 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3321 /// // less_efficient_algorithm_for_bytes(prefix);
3322 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3323 /// // less_efficient_algorithm_for_bytes(suffix);
3326 #[stable(feature = "slice_align_to", since = "1.30.0")]
3327 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3328 // Note that most of this function will be constant-evaluated,
3329 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3330 // handle ZSTs specially, which is – don't handle them at all.
3331 return (self, &mut [], &mut []);
3334 // First, find at what point do we split between the first and 2nd slice. Easy with
3335 // ptr.align_offset.
3336 let ptr = self.as_ptr();
3337 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3338 // rest of the method. This is done by passing a pointer to &[T] with an
3339 // alignment targeted for U.
3340 // `crate::ptr::align_offset` is called with a correctly aligned and
3341 // valid pointer `ptr` (it comes from a reference to `self`) and with
3342 // a size that is a power of two (since it comes from the alignement for U),
3343 // satisfying its safety constraints.
3344 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3345 if offset > self.len() {
3346 (self, &mut [], &mut [])
3348 let (left, rest) = self.split_at_mut(offset);
3349 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3350 let rest_len = rest.len();
3351 let mut_ptr = rest.as_mut_ptr();
3352 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3353 // SAFETY: see comments for `align_to`.
3357 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3358 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3364 /// Checks if the elements of this slice are sorted.
3366 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3367 /// slice yields exactly zero or one element, `true` is returned.
3369 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3370 /// implies that this function returns `false` if any two consecutive items are not
3376 /// #![feature(is_sorted)]
3377 /// let empty: [i32; 0] = [];
3379 /// assert!([1, 2, 2, 9].is_sorted());
3380 /// assert!(![1, 3, 2, 4].is_sorted());
3381 /// assert!([0].is_sorted());
3382 /// assert!(empty.is_sorted());
3383 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3386 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3387 pub fn is_sorted(&self) -> bool
3391 self.is_sorted_by(|a, b| a.partial_cmp(b))
3394 /// Checks if the elements of this slice are sorted using the given comparator function.
3396 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3397 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3398 /// [`is_sorted`]; see its documentation for more information.
3400 /// [`is_sorted`]: slice::is_sorted
3401 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3402 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3404 F: FnMut(&T, &T) -> Option<Ordering>,
3406 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3409 /// Checks if the elements of this slice are sorted using the given key extraction function.
3411 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3412 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3413 /// documentation for more information.
3415 /// [`is_sorted`]: slice::is_sorted
3420 /// #![feature(is_sorted)]
3422 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3423 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3426 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3427 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3432 self.iter().is_sorted_by_key(f)
3435 /// Returns the index of the partition point according to the given predicate
3436 /// (the index of the first element of the second partition).
3438 /// The slice is assumed to be partitioned according to the given predicate.
3439 /// This means that all elements for which the predicate returns true are at the start of the slice
3440 /// and all elements for which the predicate returns false are at the end.
3441 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3442 /// (all odd numbers are at the start, all even at the end).
3444 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3445 /// as this method performs a kind of binary search.
3447 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3449 /// [`binary_search`]: slice::binary_search
3450 /// [`binary_search_by`]: slice::binary_search_by
3451 /// [`binary_search_by_key`]: slice::binary_search_by_key
3456 /// let v = [1, 2, 3, 3, 5, 6, 7];
3457 /// let i = v.partition_point(|&x| x < 5);
3459 /// assert_eq!(i, 4);
3460 /// assert!(v[..i].iter().all(|&x| x < 5));
3461 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3463 #[stable(feature = "partition_point", since = "1.52.0")]
3464 pub fn partition_point<P>(&self, mut pred: P) -> usize
3466 P: FnMut(&T) -> bool,
3468 self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
3472 trait CloneFromSpec<T> {
3473 fn spec_clone_from(&mut self, src: &[T]);
3476 impl<T> CloneFromSpec<T> for [T]
3480 default fn spec_clone_from(&mut self, src: &[T]) {
3481 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3482 // NOTE: We need to explicitly slice them to the same length
3483 // to make it easier for the optimizer to elide bounds checking.
3484 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3485 let len = self.len();
3486 let src = &src[..len];
3488 self[i].clone_from(&src[i]);
3493 impl<T> CloneFromSpec<T> for [T]
3497 fn spec_clone_from(&mut self, src: &[T]) {
3498 self.copy_from_slice(src);
3502 #[stable(feature = "rust1", since = "1.0.0")]
3503 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3504 impl<T> const Default for &[T] {
3505 /// Creates an empty slice.
3506 fn default() -> Self {
3511 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3512 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
3513 impl<T> const Default for &mut [T] {
3514 /// Creates a mutable empty slice.
3515 fn default() -> Self {
3520 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3521 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3522 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3523 /// `str`) to slices, and then this trait will be replaced or abolished.
3524 pub trait SlicePattern {
3525 /// The element type of the slice being matched on.
3528 /// Currently, the consumers of `SlicePattern` need a slice.
3529 fn as_slice(&self) -> &[Self::Item];
3532 #[stable(feature = "slice_strip", since = "1.51.0")]
3533 impl<T> SlicePattern for [T] {
3537 fn as_slice(&self) -> &[Self::Item] {
3542 #[stable(feature = "slice_strip", since = "1.51.0")]
3543 impl<T, const N: usize> SlicePattern for [T; N] {
3547 fn as_slice(&self) -> &[Self::Item] {