1 // ignore-tidy-filelength
3 //! Slice management and manipulation.
5 //! For more details see [`std::slice`].
7 //! [`std::slice`]: ../../std/slice/index.html
9 #![stable(feature = "rust1", since = "1.0.0")]
11 use crate::cmp::Ordering::{self, Greater, Less};
12 use crate::marker::Copy;
14 use crate::num::NonZeroUsize;
15 use crate::ops::{FnMut, Range, RangeBounds};
16 use crate::option::Option;
17 use crate::option::Option::{None, Some};
19 use crate::result::Result;
20 use crate::result::Result::{Err, Ok};
24 feature = "slice_internals",
26 reason = "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Chunks, ChunksMut, Windows};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{Iter, IterMut};
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter::{RSplit, RSplitMut};
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter::{ChunksExact, ChunksExactMut};
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter::{ArrayChunks, ArrayChunksMut};
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter::ArrayWindows;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter::{GroupBy, GroupByMut};
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter::{SplitInclusive, SplitInclusiveMut};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw::{from_raw_parts, from_raw_parts_mut};
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw::{from_mut, from_ref};
74 // This function is public only because there is no other way to unit test heapsort.
75 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
76 pub use sort::heapsort;
78 #[stable(feature = "slice_get_slice", since = "1.28.0")]
79 pub use index::SliceIndex;
81 #[unstable(feature = "slice_range", issue = "76393")]
84 #[unstable(feature = "inherent_ascii_escape", issue = "77174")]
85 pub use ascii::EscapeAscii;
90 /// Returns the number of elements in the slice.
95 /// let a = [1, 2, 3];
96 /// assert_eq!(a.len(), 3);
98 #[doc(alias = "length")]
99 #[stable(feature = "rust1", since = "1.0.0")]
100 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
102 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
103 #[rustc_allow_const_fn_unstable(const_fn_union)]
104 pub const fn len(&self) -> usize {
105 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
106 // As of this writing this causes a "Const-stable functions can only call other
107 // const-stable functions" error.
109 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
110 // and PtrComponents<T> have the same memory layouts. Only std can make this
112 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
115 /// Returns `true` if the slice has a length of 0.
120 /// let a = [1, 2, 3];
121 /// assert!(!a.is_empty());
123 #[stable(feature = "rust1", since = "1.0.0")]
124 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
126 pub const fn is_empty(&self) -> bool {
130 /// Returns the first element of the slice, or `None` if it is empty.
135 /// let v = [10, 40, 30];
136 /// assert_eq!(Some(&10), v.first());
138 /// let w: &[i32] = &[];
139 /// assert_eq!(None, w.first());
141 #[stable(feature = "rust1", since = "1.0.0")]
142 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
144 pub const fn first(&self) -> Option<&T> {
145 if let [first, ..] = self { Some(first) } else { None }
148 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
153 /// let x = &mut [0, 1, 2];
155 /// if let Some(first) = x.first_mut() {
158 /// assert_eq!(x, &[5, 1, 2]);
160 #[stable(feature = "rust1", since = "1.0.0")]
161 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
163 pub const fn first_mut(&mut self) -> Option<&mut T> {
164 if let [first, ..] = self { Some(first) } else { None }
167 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
172 /// let x = &[0, 1, 2];
174 /// if let Some((first, elements)) = x.split_first() {
175 /// assert_eq!(first, &0);
176 /// assert_eq!(elements, &[1, 2]);
179 #[stable(feature = "slice_splits", since = "1.5.0")]
180 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
182 pub const fn split_first(&self) -> Option<(&T, &[T])> {
183 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
186 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
191 /// let x = &mut [0, 1, 2];
193 /// if let Some((first, elements)) = x.split_first_mut() {
198 /// assert_eq!(x, &[3, 4, 5]);
200 #[stable(feature = "slice_splits", since = "1.5.0")]
201 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
203 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
204 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
207 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
212 /// let x = &[0, 1, 2];
214 /// if let Some((last, elements)) = x.split_last() {
215 /// assert_eq!(last, &2);
216 /// assert_eq!(elements, &[0, 1]);
219 #[stable(feature = "slice_splits", since = "1.5.0")]
220 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
222 pub const fn split_last(&self) -> Option<(&T, &[T])> {
223 if let [init @ .., last] = self { Some((last, init)) } else { None }
226 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
231 /// let x = &mut [0, 1, 2];
233 /// if let Some((last, elements)) = x.split_last_mut() {
238 /// assert_eq!(x, &[4, 5, 3]);
240 #[stable(feature = "slice_splits", since = "1.5.0")]
241 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
243 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
244 if let [init @ .., last] = self { Some((last, init)) } else { None }
247 /// Returns the last element of the slice, or `None` if it is empty.
252 /// let v = [10, 40, 30];
253 /// assert_eq!(Some(&30), v.last());
255 /// let w: &[i32] = &[];
256 /// assert_eq!(None, w.last());
258 #[stable(feature = "rust1", since = "1.0.0")]
259 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
261 pub const fn last(&self) -> Option<&T> {
262 if let [.., last] = self { Some(last) } else { None }
265 /// Returns a mutable pointer to the last item in the slice.
270 /// let x = &mut [0, 1, 2];
272 /// if let Some(last) = x.last_mut() {
275 /// assert_eq!(x, &[0, 1, 10]);
277 #[stable(feature = "rust1", since = "1.0.0")]
278 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
280 pub const fn last_mut(&mut self) -> Option<&mut T> {
281 if let [.., last] = self { Some(last) } else { None }
284 /// Returns a reference to an element or subslice depending on the type of
287 /// - If given a position, returns a reference to the element at that
288 /// position or `None` if out of bounds.
289 /// - If given a range, returns the subslice corresponding to that range,
290 /// or `None` if out of bounds.
295 /// let v = [10, 40, 30];
296 /// assert_eq!(Some(&40), v.get(1));
297 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
298 /// assert_eq!(None, v.get(3));
299 /// assert_eq!(None, v.get(0..4));
301 #[stable(feature = "rust1", since = "1.0.0")]
303 pub fn get<I>(&self, index: I) -> Option<&I::Output>
310 /// Returns a mutable reference to an element or subslice depending on the
311 /// type of index (see [`get`]) or `None` if the index is out of bounds.
313 /// [`get`]: slice::get
318 /// let x = &mut [0, 1, 2];
320 /// if let Some(elem) = x.get_mut(1) {
323 /// assert_eq!(x, &[0, 42, 2]);
325 #[stable(feature = "rust1", since = "1.0.0")]
327 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
334 /// Returns a reference to an element or subslice, without doing bounds
337 /// For a safe alternative see [`get`].
341 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
342 /// even if the resulting reference is not used.
344 /// [`get`]: slice::get
345 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
350 /// let x = &[1, 2, 4];
353 /// assert_eq!(x.get_unchecked(1), &2);
356 #[stable(feature = "rust1", since = "1.0.0")]
358 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
362 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
363 // the slice is dereferencable because `self` is a safe reference.
364 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
365 unsafe { &*index.get_unchecked(self) }
368 /// Returns a mutable reference to an element or subslice, without doing
371 /// For a safe alternative see [`get_mut`].
375 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
376 /// even if the resulting reference is not used.
378 /// [`get_mut`]: slice::get_mut
379 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
384 /// let x = &mut [1, 2, 4];
387 /// let elem = x.get_unchecked_mut(1);
390 /// assert_eq!(x, &[1, 13, 4]);
392 #[stable(feature = "rust1", since = "1.0.0")]
394 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
398 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
399 // the slice is dereferencable because `self` is a safe reference.
400 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
401 unsafe { &mut *index.get_unchecked_mut(self) }
404 /// Returns a raw pointer to the slice's buffer.
406 /// The caller must ensure that the slice outlives the pointer this
407 /// function returns, or else it will end up pointing to garbage.
409 /// The caller must also ensure that the memory the pointer (non-transitively) points to
410 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
411 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
413 /// Modifying the container referenced by this slice may cause its buffer
414 /// to be reallocated, which would also make any pointers to it invalid.
419 /// let x = &[1, 2, 4];
420 /// let x_ptr = x.as_ptr();
423 /// for i in 0..x.len() {
424 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
429 /// [`as_mut_ptr`]: slice::as_mut_ptr
430 #[stable(feature = "rust1", since = "1.0.0")]
431 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
433 pub const fn as_ptr(&self) -> *const T {
434 self as *const [T] as *const T
437 /// Returns an unsafe mutable pointer to the slice's buffer.
439 /// The caller must ensure that the slice outlives the pointer this
440 /// function returns, or else it will end up pointing to garbage.
442 /// Modifying the container referenced by this slice may cause its buffer
443 /// to be reallocated, which would also make any pointers to it invalid.
448 /// let x = &mut [1, 2, 4];
449 /// let x_ptr = x.as_mut_ptr();
452 /// for i in 0..x.len() {
453 /// *x_ptr.add(i) += 2;
456 /// assert_eq!(x, &[3, 4, 6]);
458 #[stable(feature = "rust1", since = "1.0.0")]
459 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
461 pub const fn as_mut_ptr(&mut self) -> *mut T {
462 self as *mut [T] as *mut T
465 /// Returns the two raw pointers spanning the slice.
467 /// The returned range is half-open, which means that the end pointer
468 /// points *one past* the last element of the slice. This way, an empty
469 /// slice is represented by two equal pointers, and the difference between
470 /// the two pointers represents the size of the slice.
472 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
473 /// requires extra caution, as it does not point to a valid element in the
476 /// This function is useful for interacting with foreign interfaces which
477 /// use two pointers to refer to a range of elements in memory, as is
480 /// It can also be useful to check if a pointer to an element refers to an
481 /// element of this slice:
484 /// let a = [1, 2, 3];
485 /// let x = &a[1] as *const _;
486 /// let y = &5 as *const _;
488 /// assert!(a.as_ptr_range().contains(&x));
489 /// assert!(!a.as_ptr_range().contains(&y));
492 /// [`as_ptr`]: slice::as_ptr
493 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
494 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
496 pub const fn as_ptr_range(&self) -> Range<*const T> {
497 let start = self.as_ptr();
498 // SAFETY: The `add` here is safe, because:
500 // - Both pointers are part of the same object, as pointing directly
501 // past the object also counts.
503 // - The size of the slice is never larger than isize::MAX bytes, as
505 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
506 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
507 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
508 // (This doesn't seem normative yet, but the very same assumption is
509 // made in many places, including the Index implementation of slices.)
511 // - There is no wrapping around involved, as slices do not wrap past
512 // the end of the address space.
514 // See the documentation of pointer::add.
515 let end = unsafe { start.add(self.len()) };
519 /// Returns the two unsafe mutable pointers spanning the slice.
521 /// The returned range is half-open, which means that the end pointer
522 /// points *one past* the last element of the slice. This way, an empty
523 /// slice is represented by two equal pointers, and the difference between
524 /// the two pointers represents the size of the slice.
526 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
527 /// pointer requires extra caution, as it does not point to a valid element
530 /// This function is useful for interacting with foreign interfaces which
531 /// use two pointers to refer to a range of elements in memory, as is
534 /// [`as_mut_ptr`]: slice::as_mut_ptr
535 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
536 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
538 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
539 let start = self.as_mut_ptr();
540 // SAFETY: See as_ptr_range() above for why `add` here is safe.
541 let end = unsafe { start.add(self.len()) };
545 /// Swaps two elements in the slice.
549 /// * a - The index of the first element
550 /// * b - The index of the second element
554 /// Panics if `a` or `b` are out of bounds.
559 /// let mut v = ["a", "b", "c", "d"];
561 /// assert!(v == ["a", "d", "c", "b"]);
563 #[stable(feature = "rust1", since = "1.0.0")]
565 pub fn swap(&mut self, a: usize, b: usize) {
566 // Can't take two mutable loans from one vector, so instead use raw pointers.
567 let pa = ptr::addr_of_mut!(self[a]);
568 let pb = ptr::addr_of_mut!(self[b]);
569 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
570 // to elements in the slice and therefore are guaranteed to be valid and aligned.
571 // Note that accessing the elements behind `a` and `b` is checked and will
572 // panic when out of bounds.
578 /// Reverses the order of elements in the slice, in place.
583 /// let mut v = [1, 2, 3];
585 /// assert!(v == [3, 2, 1]);
587 #[stable(feature = "rust1", since = "1.0.0")]
589 pub fn reverse(&mut self) {
590 let mut i: usize = 0;
593 // For very small types, all the individual reads in the normal
594 // path perform poorly. We can do better, given efficient unaligned
595 // load/store, by loading a larger chunk and reversing a register.
597 // Ideally LLVM would do this for us, as it knows better than we do
598 // whether unaligned reads are efficient (since that changes between
599 // different ARM versions, for example) and what the best chunk size
600 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
601 // the loop, so we need to do this ourselves. (Hypothesis: reverse
602 // is troublesome because the sides can be aligned differently --
603 // will be, when the length is odd -- so there's no way of emitting
604 // pre- and postludes to use fully-aligned SIMD in the middle.)
606 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
608 if fast_unaligned && mem::size_of::<T>() == 1 {
609 // Use the llvm.bswap intrinsic to reverse u8s in a usize
610 let chunk = mem::size_of::<usize>();
611 while i + chunk - 1 < ln / 2 {
612 // SAFETY: There are several things to check here:
614 // - Note that `chunk` is either 4 or 8 due to the cfg check
615 // above. So `chunk - 1` is positive.
616 // - Indexing with index `i` is fine as the loop check guarantees
617 // `i + chunk - 1 < ln / 2`
618 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
619 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
620 // - `i + chunk > 0` is trivially true.
621 // - The loop check guarantees:
622 // `i + chunk - 1 < ln / 2`
623 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
624 // - The `read_unaligned` and `write_unaligned` calls are fine:
625 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
626 // (see above) and `pb` points to index `ln - i - chunk`, so
627 // both are at least `chunk`
628 // many bytes away from the end of `self`.
629 // - Any initialized memory is valid `usize`.
631 let ptr = self.as_mut_ptr();
633 let pb = ptr.add(ln - i - chunk);
634 let va = ptr::read_unaligned(pa as *mut usize);
635 let vb = ptr::read_unaligned(pb as *mut usize);
636 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
637 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
643 if fast_unaligned && mem::size_of::<T>() == 2 {
644 // Use rotate-by-16 to reverse u16s in a u32
645 let chunk = mem::size_of::<u32>() / 2;
646 while i + chunk - 1 < ln / 2 {
647 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
648 // (and obviously `i < ln`), because each element is 2 bytes and
651 // `i + chunk - 1 < ln / 2` # while condition
652 // `i + 2 - 1 < ln / 2`
655 // Since it's less than the length divided by 2, then it must be
658 // This also means that the condition `0 < i + chunk <= ln` is
659 // always respected, ensuring the `pb` pointer can be used
662 let ptr = self.as_mut_ptr();
664 let pb = ptr.add(ln - i - chunk);
665 let va = ptr::read_unaligned(pa as *mut u32);
666 let vb = ptr::read_unaligned(pb as *mut u32);
667 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
668 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
675 // SAFETY: `i` is inferior to half the length of the slice so
676 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
677 // will not go further than `ln / 2 - 1`).
678 // The resulting pointers `pa` and `pb` are therefore valid and
679 // aligned, and can be read from and written to.
681 // Unsafe swap to avoid the bounds check in safe swap.
682 let ptr = self.as_mut_ptr();
684 let pb = ptr.add(ln - i - 1);
691 /// Returns an iterator over the slice.
696 /// let x = &[1, 2, 4];
697 /// let mut iterator = x.iter();
699 /// assert_eq!(iterator.next(), Some(&1));
700 /// assert_eq!(iterator.next(), Some(&2));
701 /// assert_eq!(iterator.next(), Some(&4));
702 /// assert_eq!(iterator.next(), None);
704 #[stable(feature = "rust1", since = "1.0.0")]
706 pub fn iter(&self) -> Iter<'_, T> {
710 /// Returns an iterator that allows modifying each value.
715 /// let x = &mut [1, 2, 4];
716 /// for elem in x.iter_mut() {
719 /// assert_eq!(x, &[3, 4, 6]);
721 #[stable(feature = "rust1", since = "1.0.0")]
723 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
727 /// Returns an iterator over all contiguous windows of length
728 /// `size`. The windows overlap. If the slice is shorter than
729 /// `size`, the iterator returns no values.
733 /// Panics if `size` is 0.
738 /// let slice = ['r', 'u', 's', 't'];
739 /// let mut iter = slice.windows(2);
740 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
741 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
742 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
743 /// assert!(iter.next().is_none());
746 /// If the slice is shorter than `size`:
749 /// let slice = ['f', 'o', 'o'];
750 /// let mut iter = slice.windows(4);
751 /// assert!(iter.next().is_none());
753 #[stable(feature = "rust1", since = "1.0.0")]
755 pub fn windows(&self, size: usize) -> Windows<'_, T> {
756 let size = NonZeroUsize::new(size).expect("size is zero");
757 Windows::new(self, size)
760 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
761 /// beginning of the slice.
763 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
764 /// slice, then the last chunk will not have length `chunk_size`.
766 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
767 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
772 /// Panics if `chunk_size` is 0.
777 /// let slice = ['l', 'o', 'r', 'e', 'm'];
778 /// let mut iter = slice.chunks(2);
779 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
780 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
781 /// assert_eq!(iter.next().unwrap(), &['m']);
782 /// assert!(iter.next().is_none());
785 /// [`chunks_exact`]: slice::chunks_exact
786 /// [`rchunks`]: slice::rchunks
787 #[stable(feature = "rust1", since = "1.0.0")]
789 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
790 assert_ne!(chunk_size, 0);
791 Chunks::new(self, chunk_size)
794 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
795 /// beginning of the slice.
797 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
798 /// length of the slice, then the last chunk will not have length `chunk_size`.
800 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
801 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
802 /// the end of the slice.
806 /// Panics if `chunk_size` is 0.
811 /// let v = &mut [0, 0, 0, 0, 0];
812 /// let mut count = 1;
814 /// for chunk in v.chunks_mut(2) {
815 /// for elem in chunk.iter_mut() {
820 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
823 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
824 /// [`rchunks_mut`]: slice::rchunks_mut
825 #[stable(feature = "rust1", since = "1.0.0")]
827 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
828 assert_ne!(chunk_size, 0);
829 ChunksMut::new(self, chunk_size)
832 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
833 /// beginning of the slice.
835 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
836 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
837 /// from the `remainder` function of the iterator.
839 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
840 /// resulting code better than in the case of [`chunks`].
842 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
843 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
847 /// Panics if `chunk_size` is 0.
852 /// let slice = ['l', 'o', 'r', 'e', 'm'];
853 /// let mut iter = slice.chunks_exact(2);
854 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
855 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
856 /// assert!(iter.next().is_none());
857 /// assert_eq!(iter.remainder(), &['m']);
860 /// [`chunks`]: slice::chunks
861 /// [`rchunks_exact`]: slice::rchunks_exact
862 #[stable(feature = "chunks_exact", since = "1.31.0")]
864 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
865 assert_ne!(chunk_size, 0);
866 ChunksExact::new(self, chunk_size)
869 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
870 /// beginning of the slice.
872 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
873 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
874 /// retrieved from the `into_remainder` function of the iterator.
876 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
877 /// resulting code better than in the case of [`chunks_mut`].
879 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
880 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
885 /// Panics if `chunk_size` is 0.
890 /// let v = &mut [0, 0, 0, 0, 0];
891 /// let mut count = 1;
893 /// for chunk in v.chunks_exact_mut(2) {
894 /// for elem in chunk.iter_mut() {
899 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
902 /// [`chunks_mut`]: slice::chunks_mut
903 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
904 #[stable(feature = "chunks_exact", since = "1.31.0")]
906 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
907 assert_ne!(chunk_size, 0);
908 ChunksExactMut::new(self, chunk_size)
911 /// Splits the slice into a slice of `N`-element arrays,
912 /// assuming that there's no remainder.
916 /// This may only be called when
917 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
923 /// #![feature(slice_as_chunks)]
924 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
925 /// let chunks: &[[char; 1]] =
926 /// // SAFETY: 1-element chunks never have remainder
927 /// unsafe { slice.as_chunks_unchecked() };
928 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
929 /// let chunks: &[[char; 3]] =
930 /// // SAFETY: The slice length (6) is a multiple of 3
931 /// unsafe { slice.as_chunks_unchecked() };
932 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
934 /// // These would be unsound:
935 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
936 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
938 #[unstable(feature = "slice_as_chunks", issue = "74985")]
940 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
941 debug_assert_ne!(N, 0);
942 debug_assert_eq!(self.len() % N, 0);
944 // SAFETY: Our precondition is exactly what's needed to call this
945 unsafe { crate::intrinsics::exact_div(self.len(), N) };
946 // SAFETY: We cast a slice of `new_len * N` elements into
947 // a slice of `new_len` many `N` elements chunks.
948 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
951 /// Splits the slice into a slice of `N`-element arrays,
952 /// starting at the beginning of the slice,
953 /// and a remainder slice with length strictly less than `N`.
957 /// Panics if `N` is 0. This check will most probably get changed to a compile time
958 /// error before this method gets stabilized.
963 /// #![feature(slice_as_chunks)]
964 /// let slice = ['l', 'o', 'r', 'e', 'm'];
965 /// let (chunks, remainder) = slice.as_chunks();
966 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
967 /// assert_eq!(remainder, &['m']);
969 #[unstable(feature = "slice_as_chunks", issue = "74985")]
971 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
973 let len = self.len() / N;
974 let (multiple_of_n, remainder) = self.split_at(len * N);
975 // SAFETY: We already panicked for zero, and ensured by construction
976 // that the length of the subslice is a multiple of N.
977 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
978 (array_slice, remainder)
981 /// Splits the slice into a slice of `N`-element arrays,
982 /// starting at the end of the slice,
983 /// and a remainder slice with length strictly less than `N`.
987 /// Panics if `N` is 0. This check will most probably get changed to a compile time
988 /// error before this method gets stabilized.
993 /// #![feature(slice_as_chunks)]
994 /// let slice = ['l', 'o', 'r', 'e', 'm'];
995 /// let (remainder, chunks) = slice.as_rchunks();
996 /// assert_eq!(remainder, &['l']);
997 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
999 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1001 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1003 let len = self.len() / N;
1004 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1005 // SAFETY: We already panicked for zero, and ensured by construction
1006 // that the length of the subslice is a multiple of N.
1007 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1008 (remainder, array_slice)
1011 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1012 /// beginning of the slice.
1014 /// The chunks are array references and do not overlap. If `N` does not divide the
1015 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1016 /// retrieved from the `remainder` function of the iterator.
1018 /// This method is the const generic equivalent of [`chunks_exact`].
1022 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1023 /// error before this method gets stabilized.
1028 /// #![feature(array_chunks)]
1029 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1030 /// let mut iter = slice.array_chunks();
1031 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1032 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1033 /// assert!(iter.next().is_none());
1034 /// assert_eq!(iter.remainder(), &['m']);
1037 /// [`chunks_exact`]: slice::chunks_exact
1038 #[unstable(feature = "array_chunks", issue = "74985")]
1040 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1042 ArrayChunks::new(self)
1045 /// Splits the slice into a slice of `N`-element arrays,
1046 /// assuming that there's no remainder.
1050 /// This may only be called when
1051 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1057 /// #![feature(slice_as_chunks)]
1058 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1059 /// let chunks: &mut [[char; 1]] =
1060 /// // SAFETY: 1-element chunks never have remainder
1061 /// unsafe { slice.as_chunks_unchecked_mut() };
1062 /// chunks[0] = ['L'];
1063 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1064 /// let chunks: &mut [[char; 3]] =
1065 /// // SAFETY: The slice length (6) is a multiple of 3
1066 /// unsafe { slice.as_chunks_unchecked_mut() };
1067 /// chunks[1] = ['a', 'x', '?'];
1068 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1070 /// // These would be unsound:
1071 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1072 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1074 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1076 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1077 debug_assert_ne!(N, 0);
1078 debug_assert_eq!(self.len() % N, 0);
1080 // SAFETY: Our precondition is exactly what's needed to call this
1081 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1082 // SAFETY: We cast a slice of `new_len * N` elements into
1083 // a slice of `new_len` many `N` elements chunks.
1084 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1087 /// Splits the slice into a slice of `N`-element arrays,
1088 /// starting at the beginning of the slice,
1089 /// and a remainder slice with length strictly less than `N`.
1093 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1094 /// error before this method gets stabilized.
1099 /// #![feature(slice_as_chunks)]
1100 /// let v = &mut [0, 0, 0, 0, 0];
1101 /// let mut count = 1;
1103 /// let (chunks, remainder) = v.as_chunks_mut();
1104 /// remainder[0] = 9;
1105 /// for chunk in chunks {
1106 /// *chunk = [count; 2];
1109 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1111 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1113 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1115 let len = self.len() / N;
1116 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1117 // SAFETY: We already panicked for zero, and ensured by construction
1118 // that the length of the subslice is a multiple of N.
1119 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1120 (array_slice, remainder)
1123 /// Splits the slice into a slice of `N`-element arrays,
1124 /// starting at the end of the slice,
1125 /// and a remainder slice with length strictly less than `N`.
1129 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1130 /// error before this method gets stabilized.
1135 /// #![feature(slice_as_chunks)]
1136 /// let v = &mut [0, 0, 0, 0, 0];
1137 /// let mut count = 1;
1139 /// let (remainder, chunks) = v.as_rchunks_mut();
1140 /// remainder[0] = 9;
1141 /// for chunk in chunks {
1142 /// *chunk = [count; 2];
1145 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1147 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1149 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1151 let len = self.len() / N;
1152 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1153 // SAFETY: We already panicked for zero, and ensured by construction
1154 // that the length of the subslice is a multiple of N.
1155 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1156 (remainder, array_slice)
1159 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1160 /// beginning of the slice.
1162 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1163 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1164 /// can be retrieved from the `into_remainder` function of the iterator.
1166 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1170 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1171 /// error before this method gets stabilized.
1176 /// #![feature(array_chunks)]
1177 /// let v = &mut [0, 0, 0, 0, 0];
1178 /// let mut count = 1;
1180 /// for chunk in v.array_chunks_mut() {
1181 /// *chunk = [count; 2];
1184 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1187 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1188 #[unstable(feature = "array_chunks", issue = "74985")]
1190 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1192 ArrayChunksMut::new(self)
1195 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1196 /// starting at the beginning of the slice.
1198 /// This is the const generic equivalent of [`windows`].
1200 /// If `N` is greater than the size of the slice, it will return no windows.
1204 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1205 /// error before this method gets stabilized.
1210 /// #![feature(array_windows)]
1211 /// let slice = [0, 1, 2, 3];
1212 /// let mut iter = slice.array_windows();
1213 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1214 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1215 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1216 /// assert!(iter.next().is_none());
1219 /// [`windows`]: slice::windows
1220 #[unstable(feature = "array_windows", issue = "75027")]
1222 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1224 ArrayWindows::new(self)
1227 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1230 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1231 /// slice, then the last chunk will not have length `chunk_size`.
1233 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1234 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1239 /// Panics if `chunk_size` is 0.
1244 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1245 /// let mut iter = slice.rchunks(2);
1246 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1247 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1248 /// assert_eq!(iter.next().unwrap(), &['l']);
1249 /// assert!(iter.next().is_none());
1252 /// [`rchunks_exact`]: slice::rchunks_exact
1253 /// [`chunks`]: slice::chunks
1254 #[stable(feature = "rchunks", since = "1.31.0")]
1256 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1257 assert!(chunk_size != 0);
1258 RChunks::new(self, chunk_size)
1261 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1264 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1265 /// length of the slice, then the last chunk will not have length `chunk_size`.
1267 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1268 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1269 /// beginning of the slice.
1273 /// Panics if `chunk_size` is 0.
1278 /// let v = &mut [0, 0, 0, 0, 0];
1279 /// let mut count = 1;
1281 /// for chunk in v.rchunks_mut(2) {
1282 /// for elem in chunk.iter_mut() {
1287 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1290 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1291 /// [`chunks_mut`]: slice::chunks_mut
1292 #[stable(feature = "rchunks", since = "1.31.0")]
1294 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1295 assert!(chunk_size != 0);
1296 RChunksMut::new(self, chunk_size)
1299 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1300 /// end of the slice.
1302 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1303 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1304 /// from the `remainder` function of the iterator.
1306 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1307 /// resulting code better than in the case of [`chunks`].
1309 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1310 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1315 /// Panics if `chunk_size` is 0.
1320 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1321 /// let mut iter = slice.rchunks_exact(2);
1322 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1323 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1324 /// assert!(iter.next().is_none());
1325 /// assert_eq!(iter.remainder(), &['l']);
1328 /// [`chunks`]: slice::chunks
1329 /// [`rchunks`]: slice::rchunks
1330 /// [`chunks_exact`]: slice::chunks_exact
1331 #[stable(feature = "rchunks", since = "1.31.0")]
1333 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1334 assert!(chunk_size != 0);
1335 RChunksExact::new(self, chunk_size)
1338 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1341 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1342 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1343 /// retrieved from the `into_remainder` function of the iterator.
1345 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1346 /// resulting code better than in the case of [`chunks_mut`].
1348 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1349 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1354 /// Panics if `chunk_size` is 0.
1359 /// let v = &mut [0, 0, 0, 0, 0];
1360 /// let mut count = 1;
1362 /// for chunk in v.rchunks_exact_mut(2) {
1363 /// for elem in chunk.iter_mut() {
1368 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1371 /// [`chunks_mut`]: slice::chunks_mut
1372 /// [`rchunks_mut`]: slice::rchunks_mut
1373 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1374 #[stable(feature = "rchunks", since = "1.31.0")]
1376 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1377 assert!(chunk_size != 0);
1378 RChunksExactMut::new(self, chunk_size)
1381 /// Returns an iterator over the slice producing non-overlapping runs
1382 /// of elements using the predicate to separate them.
1384 /// The predicate is called on two elements following themselves,
1385 /// it means the predicate is called on `slice[0]` and `slice[1]`
1386 /// then on `slice[1]` and `slice[2]` and so on.
1391 /// #![feature(slice_group_by)]
1393 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1395 /// let mut iter = slice.group_by(|a, b| a == b);
1397 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1398 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1399 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1400 /// assert_eq!(iter.next(), None);
1403 /// This method can be used to extract the sorted subslices:
1406 /// #![feature(slice_group_by)]
1408 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1410 /// let mut iter = slice.group_by(|a, b| a <= b);
1412 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1413 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1414 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1415 /// assert_eq!(iter.next(), None);
1417 #[unstable(feature = "slice_group_by", issue = "80552")]
1419 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1421 F: FnMut(&T, &T) -> bool,
1423 GroupBy::new(self, pred)
1426 /// Returns an iterator over the slice producing non-overlapping mutable
1427 /// runs of elements using the predicate to separate them.
1429 /// The predicate is called on two elements following themselves,
1430 /// it means the predicate is called on `slice[0]` and `slice[1]`
1431 /// then on `slice[1]` and `slice[2]` and so on.
1436 /// #![feature(slice_group_by)]
1438 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1440 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1442 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1443 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1444 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1445 /// assert_eq!(iter.next(), None);
1448 /// This method can be used to extract the sorted subslices:
1451 /// #![feature(slice_group_by)]
1453 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1455 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1457 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1458 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1459 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1460 /// assert_eq!(iter.next(), None);
1462 #[unstable(feature = "slice_group_by", issue = "80552")]
1464 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1466 F: FnMut(&T, &T) -> bool,
1468 GroupByMut::new(self, pred)
1471 /// Divides one slice into two at an index.
1473 /// The first will contain all indices from `[0, mid)` (excluding
1474 /// the index `mid` itself) and the second will contain all
1475 /// indices from `[mid, len)` (excluding the index `len` itself).
1479 /// Panics if `mid > len`.
1484 /// let v = [1, 2, 3, 4, 5, 6];
1487 /// let (left, right) = v.split_at(0);
1488 /// assert_eq!(left, []);
1489 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1493 /// let (left, right) = v.split_at(2);
1494 /// assert_eq!(left, [1, 2]);
1495 /// assert_eq!(right, [3, 4, 5, 6]);
1499 /// let (left, right) = v.split_at(6);
1500 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1501 /// assert_eq!(right, []);
1504 #[stable(feature = "rust1", since = "1.0.0")]
1506 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1507 assert!(mid <= self.len());
1508 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1509 // fulfills the requirements of `from_raw_parts_mut`.
1510 unsafe { self.split_at_unchecked(mid) }
1513 /// Divides one mutable slice into two at an index.
1515 /// The first will contain all indices from `[0, mid)` (excluding
1516 /// the index `mid` itself) and the second will contain all
1517 /// indices from `[mid, len)` (excluding the index `len` itself).
1521 /// Panics if `mid > len`.
1526 /// let mut v = [1, 0, 3, 0, 5, 6];
1527 /// let (left, right) = v.split_at_mut(2);
1528 /// assert_eq!(left, [1, 0]);
1529 /// assert_eq!(right, [3, 0, 5, 6]);
1532 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1534 #[stable(feature = "rust1", since = "1.0.0")]
1536 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1537 assert!(mid <= self.len());
1538 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1539 // fulfills the requirements of `from_raw_parts_mut`.
1540 unsafe { self.split_at_mut_unchecked(mid) }
1543 /// Divides one slice into two at an index, without doing bounds checking.
1545 /// The first will contain all indices from `[0, mid)` (excluding
1546 /// the index `mid` itself) and the second will contain all
1547 /// indices from `[mid, len)` (excluding the index `len` itself).
1549 /// For a safe alternative see [`split_at`].
1553 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1554 /// even if the resulting reference is not used. The caller has to ensure that
1555 /// `0 <= mid <= self.len()`.
1557 /// [`split_at`]: slice::split_at
1558 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1563 /// #![feature(slice_split_at_unchecked)]
1565 /// let v = [1, 2, 3, 4, 5, 6];
1568 /// let (left, right) = v.split_at_unchecked(0);
1569 /// assert_eq!(left, []);
1570 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1574 /// let (left, right) = v.split_at_unchecked(2);
1575 /// assert_eq!(left, [1, 2]);
1576 /// assert_eq!(right, [3, 4, 5, 6]);
1580 /// let (left, right) = v.split_at_unchecked(6);
1581 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1582 /// assert_eq!(right, []);
1585 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1587 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1588 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1589 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1592 /// Divides one mutable slice into two at an index, without doing bounds checking.
1594 /// The first will contain all indices from `[0, mid)` (excluding
1595 /// the index `mid` itself) and the second will contain all
1596 /// indices from `[mid, len)` (excluding the index `len` itself).
1598 /// For a safe alternative see [`split_at_mut`].
1602 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1603 /// even if the resulting reference is not used. The caller has to ensure that
1604 /// `0 <= mid <= self.len()`.
1606 /// [`split_at_mut`]: slice::split_at_mut
1607 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1612 /// #![feature(slice_split_at_unchecked)]
1614 /// let mut v = [1, 0, 3, 0, 5, 6];
1615 /// // scoped to restrict the lifetime of the borrows
1617 /// let (left, right) = v.split_at_mut_unchecked(2);
1618 /// assert_eq!(left, [1, 0]);
1619 /// assert_eq!(right, [3, 0, 5, 6]);
1623 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1625 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1627 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1628 let len = self.len();
1629 let ptr = self.as_mut_ptr();
1631 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1633 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1635 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1638 /// Returns an iterator over subslices separated by elements that match
1639 /// `pred`. The matched element is not contained in the subslices.
1644 /// let slice = [10, 40, 33, 20];
1645 /// let mut iter = slice.split(|num| num % 3 == 0);
1647 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1648 /// assert_eq!(iter.next().unwrap(), &[20]);
1649 /// assert!(iter.next().is_none());
1652 /// If the first element is matched, an empty slice will be the first item
1653 /// returned by the iterator. Similarly, if the last element in the slice
1654 /// is matched, an empty slice will be the last item returned by the
1658 /// let slice = [10, 40, 33];
1659 /// let mut iter = slice.split(|num| num % 3 == 0);
1661 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1662 /// assert_eq!(iter.next().unwrap(), &[]);
1663 /// assert!(iter.next().is_none());
1666 /// If two matched elements are directly adjacent, an empty slice will be
1667 /// present between them:
1670 /// let slice = [10, 6, 33, 20];
1671 /// let mut iter = slice.split(|num| num % 3 == 0);
1673 /// assert_eq!(iter.next().unwrap(), &[10]);
1674 /// assert_eq!(iter.next().unwrap(), &[]);
1675 /// assert_eq!(iter.next().unwrap(), &[20]);
1676 /// assert!(iter.next().is_none());
1678 #[stable(feature = "rust1", since = "1.0.0")]
1680 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1682 F: FnMut(&T) -> bool,
1684 Split::new(self, pred)
1687 /// Returns an iterator over mutable subslices separated by elements that
1688 /// match `pred`. The matched element is not contained in the subslices.
1693 /// let mut v = [10, 40, 30, 20, 60, 50];
1695 /// for group in v.split_mut(|num| *num % 3 == 0) {
1698 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1700 #[stable(feature = "rust1", since = "1.0.0")]
1702 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1704 F: FnMut(&T) -> bool,
1706 SplitMut::new(self, pred)
1709 /// Returns an iterator over subslices separated by elements that match
1710 /// `pred`. The matched element is contained in the end of the previous
1711 /// subslice as a terminator.
1716 /// let slice = [10, 40, 33, 20];
1717 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1719 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1720 /// assert_eq!(iter.next().unwrap(), &[20]);
1721 /// assert!(iter.next().is_none());
1724 /// If the last element of the slice is matched,
1725 /// that element will be considered the terminator of the preceding slice.
1726 /// That slice will be the last item returned by the iterator.
1729 /// let slice = [3, 10, 40, 33];
1730 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1732 /// assert_eq!(iter.next().unwrap(), &[3]);
1733 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1734 /// assert!(iter.next().is_none());
1736 #[stable(feature = "split_inclusive", since = "1.51.0")]
1738 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1740 F: FnMut(&T) -> bool,
1742 SplitInclusive::new(self, pred)
1745 /// Returns an iterator over mutable subslices separated by elements that
1746 /// match `pred`. The matched element is contained in the previous
1747 /// subslice as a terminator.
1752 /// let mut v = [10, 40, 30, 20, 60, 50];
1754 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1755 /// let terminator_idx = group.len()-1;
1756 /// group[terminator_idx] = 1;
1758 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1760 #[stable(feature = "split_inclusive", since = "1.51.0")]
1762 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1764 F: FnMut(&T) -> bool,
1766 SplitInclusiveMut::new(self, pred)
1769 /// Returns an iterator over subslices separated by elements that match
1770 /// `pred`, starting at the end of the slice and working backwards.
1771 /// The matched element is not contained in the subslices.
1776 /// let slice = [11, 22, 33, 0, 44, 55];
1777 /// let mut iter = slice.rsplit(|num| *num == 0);
1779 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1780 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1781 /// assert_eq!(iter.next(), None);
1784 /// As with `split()`, if the first or last element is matched, an empty
1785 /// slice will be the first (or last) item returned by the iterator.
1788 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1789 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1790 /// assert_eq!(it.next().unwrap(), &[]);
1791 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1792 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1793 /// assert_eq!(it.next().unwrap(), &[]);
1794 /// assert_eq!(it.next(), None);
1796 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1798 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1800 F: FnMut(&T) -> bool,
1802 RSplit::new(self, pred)
1805 /// Returns an iterator over mutable subslices separated by elements that
1806 /// match `pred`, starting at the end of the slice and working
1807 /// backwards. The matched element is not contained in the subslices.
1812 /// let mut v = [100, 400, 300, 200, 600, 500];
1814 /// let mut count = 0;
1815 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1817 /// group[0] = count;
1819 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1822 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1824 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1826 F: FnMut(&T) -> bool,
1828 RSplitMut::new(self, pred)
1831 /// Returns an iterator over subslices separated by elements that match
1832 /// `pred`, limited to returning at most `n` items. The matched element is
1833 /// not contained in the subslices.
1835 /// The last element returned, if any, will contain the remainder of the
1840 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1841 /// `[20, 60, 50]`):
1844 /// let v = [10, 40, 30, 20, 60, 50];
1846 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1847 /// println!("{:?}", group);
1850 #[stable(feature = "rust1", since = "1.0.0")]
1852 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1854 F: FnMut(&T) -> bool,
1856 SplitN::new(self.split(pred), n)
1859 /// Returns an iterator over subslices separated by elements that match
1860 /// `pred`, limited to returning at most `n` items. The matched element is
1861 /// not contained in the subslices.
1863 /// The last element returned, if any, will contain the remainder of the
1869 /// let mut v = [10, 40, 30, 20, 60, 50];
1871 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1874 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1876 #[stable(feature = "rust1", since = "1.0.0")]
1878 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1880 F: FnMut(&T) -> bool,
1882 SplitNMut::new(self.split_mut(pred), n)
1885 /// Returns an iterator over subslices separated by elements that match
1886 /// `pred` limited to returning at most `n` items. This starts at the end of
1887 /// the slice and works backwards. The matched element is not contained in
1890 /// The last element returned, if any, will contain the remainder of the
1895 /// Print the slice split once, starting from the end, by numbers divisible
1896 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1899 /// let v = [10, 40, 30, 20, 60, 50];
1901 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1902 /// println!("{:?}", group);
1905 #[stable(feature = "rust1", since = "1.0.0")]
1907 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1909 F: FnMut(&T) -> bool,
1911 RSplitN::new(self.rsplit(pred), n)
1914 /// Returns an iterator over subslices separated by elements that match
1915 /// `pred` limited to returning at most `n` items. This starts at the end of
1916 /// the slice and works backwards. The matched element is not contained in
1919 /// The last element returned, if any, will contain the remainder of the
1925 /// let mut s = [10, 40, 30, 20, 60, 50];
1927 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1930 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1932 #[stable(feature = "rust1", since = "1.0.0")]
1934 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1936 F: FnMut(&T) -> bool,
1938 RSplitNMut::new(self.rsplit_mut(pred), n)
1941 /// Returns `true` if the slice contains an element with the given value.
1946 /// let v = [10, 40, 30];
1947 /// assert!(v.contains(&30));
1948 /// assert!(!v.contains(&50));
1951 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1952 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1955 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1956 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1957 /// assert!(!v.iter().any(|e| e == "hi"));
1959 #[stable(feature = "rust1", since = "1.0.0")]
1961 pub fn contains(&self, x: &T) -> bool
1965 cmp::SliceContains::slice_contains(x, self)
1968 /// Returns `true` if `needle` is a prefix of the slice.
1973 /// let v = [10, 40, 30];
1974 /// assert!(v.starts_with(&[10]));
1975 /// assert!(v.starts_with(&[10, 40]));
1976 /// assert!(!v.starts_with(&[50]));
1977 /// assert!(!v.starts_with(&[10, 50]));
1980 /// Always returns `true` if `needle` is an empty slice:
1983 /// let v = &[10, 40, 30];
1984 /// assert!(v.starts_with(&[]));
1985 /// let v: &[u8] = &[];
1986 /// assert!(v.starts_with(&[]));
1988 #[stable(feature = "rust1", since = "1.0.0")]
1989 pub fn starts_with(&self, needle: &[T]) -> bool
1993 let n = needle.len();
1994 self.len() >= n && needle == &self[..n]
1997 /// Returns `true` if `needle` is a suffix of the slice.
2002 /// let v = [10, 40, 30];
2003 /// assert!(v.ends_with(&[30]));
2004 /// assert!(v.ends_with(&[40, 30]));
2005 /// assert!(!v.ends_with(&[50]));
2006 /// assert!(!v.ends_with(&[50, 30]));
2009 /// Always returns `true` if `needle` is an empty slice:
2012 /// let v = &[10, 40, 30];
2013 /// assert!(v.ends_with(&[]));
2014 /// let v: &[u8] = &[];
2015 /// assert!(v.ends_with(&[]));
2017 #[stable(feature = "rust1", since = "1.0.0")]
2018 pub fn ends_with(&self, needle: &[T]) -> bool
2022 let (m, n) = (self.len(), needle.len());
2023 m >= n && needle == &self[m - n..]
2026 /// Returns a subslice with the prefix removed.
2028 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2029 /// If `prefix` is empty, simply returns the original slice.
2031 /// If the slice does not start with `prefix`, returns `None`.
2036 /// let v = &[10, 40, 30];
2037 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2038 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2039 /// assert_eq!(v.strip_prefix(&[50]), None);
2040 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2042 /// let prefix : &str = "he";
2043 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2044 /// Some(b"llo".as_ref()));
2046 #[must_use = "returns the subslice without modifying the original"]
2047 #[stable(feature = "slice_strip", since = "1.51.0")]
2048 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2052 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2053 let prefix = prefix.as_slice();
2054 let n = prefix.len();
2055 if n <= self.len() {
2056 let (head, tail) = self.split_at(n);
2064 /// Returns a subslice with the suffix removed.
2066 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2067 /// If `suffix` is empty, simply returns the original slice.
2069 /// If the slice does not end with `suffix`, returns `None`.
2074 /// let v = &[10, 40, 30];
2075 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2076 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2077 /// assert_eq!(v.strip_suffix(&[50]), None);
2078 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2080 #[must_use = "returns the subslice without modifying the original"]
2081 #[stable(feature = "slice_strip", since = "1.51.0")]
2082 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2086 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2087 let suffix = suffix.as_slice();
2088 let (len, n) = (self.len(), suffix.len());
2090 let (head, tail) = self.split_at(len - n);
2098 /// Binary searches this sorted slice for a given element.
2100 /// If the value is found then [`Result::Ok`] is returned, containing the
2101 /// index of the matching element. If there are multiple matches, then any
2102 /// one of the matches could be returned. If the value is not found then
2103 /// [`Result::Err`] is returned, containing the index where a matching
2104 /// element could be inserted while maintaining sorted order.
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. If the value is not found then
2156 /// [`Result::Err`] is returned, containing the index where a matching
2157 /// element could be inserted while maintaining sorted order.
2159 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2161 /// [`binary_search`]: slice::binary_search
2162 /// [`binary_search_by_key`]: slice::binary_search_by_key
2163 /// [`partition_point`]: slice::partition_point
2167 /// Looks up a series of four elements. The first is found, with a
2168 /// uniquely determined position; the second and third are not
2169 /// found; the fourth could match any position in `[1, 4]`.
2172 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2175 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2177 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2179 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2181 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2182 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2184 #[stable(feature = "rust1", since = "1.0.0")]
2186 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2188 F: FnMut(&'a T) -> Ordering,
2190 let mut size = self.len();
2192 let mut right = size;
2193 while left < right {
2194 let mid = left + size / 2;
2196 // SAFETY: the call is made safe by the following invariants:
2198 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2199 let cmp = f(unsafe { self.get_unchecked(mid) });
2201 // The reason why we use if/else control flow rather than match
2202 // is because match reorders comparison operations, which is perf sensitive.
2203 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2206 } else if cmp == Greater {
2209 // SAFETY: same as the `get_unchecked` above
2210 unsafe { crate::intrinsics::assume(mid < self.len()) };
2214 size = right - left;
2219 /// Binary searches this sorted slice with a key extraction function.
2221 /// Assumes that the slice is sorted by the key, for instance with
2222 /// [`sort_by_key`] using the same key extraction function.
2224 /// If the value is found then [`Result::Ok`] is returned, containing the
2225 /// index of the matching element. If there are multiple matches, then any
2226 /// one of the matches could be returned. If the value is not found then
2227 /// [`Result::Err`] is returned, containing the index where a matching
2228 /// element could be inserted while maintaining sorted order.
2230 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2232 /// [`sort_by_key`]: slice::sort_by_key
2233 /// [`binary_search`]: slice::binary_search
2234 /// [`binary_search_by`]: slice::binary_search_by
2235 /// [`partition_point`]: slice::partition_point
2239 /// Looks up a series of four elements in a slice of pairs sorted by
2240 /// their second elements. The first is found, with a uniquely
2241 /// determined position; the second and third are not found; the
2242 /// fourth could match any position in `[1, 4]`.
2245 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2246 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2247 /// (1, 21), (2, 34), (4, 55)];
2249 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2250 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2251 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2252 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2253 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2255 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2256 // in crate `alloc`, and as such doesn't exists yet when building `core`.
2257 // links to downstream crate: #74481. Since primitives are only documented in
2258 // libstd (#73423), this never leads to broken links in practice.
2259 #[allow(rustdoc::broken_intra_doc_links)]
2260 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2262 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2264 F: FnMut(&'a T) -> B,
2267 self.binary_search_by(|k| f(k).cmp(b))
2270 /// Sorts the slice, but may not preserve the order of equal elements.
2272 /// This sort is unstable (i.e., may reorder equal elements), in-place
2273 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2275 /// # Current implementation
2277 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2278 /// which combines the fast average case of randomized quicksort with the fast worst case of
2279 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2280 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2281 /// deterministic behavior.
2283 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2284 /// slice consists of several concatenated sorted sequences.
2289 /// let mut v = [-5, 4, 1, -3, 2];
2291 /// v.sort_unstable();
2292 /// assert!(v == [-5, -3, 1, 2, 4]);
2295 /// [pdqsort]: https://github.com/orlp/pdqsort
2296 #[stable(feature = "sort_unstable", since = "1.20.0")]
2298 pub fn sort_unstable(&mut self)
2302 sort::quicksort(self, |a, b| a.lt(b));
2305 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2308 /// This sort is unstable (i.e., may reorder equal elements), in-place
2309 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2311 /// The comparator function must define a total ordering for the elements in the slice. If
2312 /// the ordering is not total, the order of the elements is unspecified. An order is a
2313 /// total order if it is (for all `a`, `b` and `c`):
2315 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2316 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2318 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2319 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2322 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2323 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2324 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2327 /// # Current implementation
2329 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2330 /// which combines the fast average case of randomized quicksort with the fast worst case of
2331 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2332 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2333 /// deterministic behavior.
2335 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2336 /// slice consists of several concatenated sorted sequences.
2341 /// let mut v = [5, 4, 1, 3, 2];
2342 /// v.sort_unstable_by(|a, b| a.cmp(b));
2343 /// assert!(v == [1, 2, 3, 4, 5]);
2345 /// // reverse sorting
2346 /// v.sort_unstable_by(|a, b| b.cmp(a));
2347 /// assert!(v == [5, 4, 3, 2, 1]);
2350 /// [pdqsort]: https://github.com/orlp/pdqsort
2351 #[stable(feature = "sort_unstable", since = "1.20.0")]
2353 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2355 F: FnMut(&T, &T) -> Ordering,
2357 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2360 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2363 /// This sort is unstable (i.e., may reorder equal elements), in-place
2364 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2367 /// # Current implementation
2369 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2370 /// which combines the fast average case of randomized quicksort with the fast worst case of
2371 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2372 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2373 /// deterministic behavior.
2375 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2376 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2377 /// cases where the key function is expensive.
2382 /// let mut v = [-5i32, 4, 1, -3, 2];
2384 /// v.sort_unstable_by_key(|k| k.abs());
2385 /// assert!(v == [1, 2, -3, 4, -5]);
2388 /// [pdqsort]: https://github.com/orlp/pdqsort
2389 #[stable(feature = "sort_unstable", since = "1.20.0")]
2391 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2396 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2399 /// Reorder the slice such that the element at `index` is at its final sorted position.
2400 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2401 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2403 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2407 self.select_nth_unstable(index)
2410 /// Reorder the slice with a comparator function such that the element at `index` is at its
2411 /// final sorted position.
2412 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2413 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2415 pub fn partition_at_index_by<F>(
2419 ) -> (&mut [T], &mut T, &mut [T])
2421 F: FnMut(&T, &T) -> Ordering,
2423 self.select_nth_unstable_by(index, compare)
2426 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2427 /// final sorted position.
2428 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2429 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2431 pub fn partition_at_index_by_key<K, F>(
2435 ) -> (&mut [T], &mut T, &mut [T])
2440 self.select_nth_unstable_by_key(index, f)
2443 /// Reorder the slice such that the element at `index` is at its final sorted position.
2445 /// This reordering has the additional property that any value at position `i < index` will be
2446 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2447 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2448 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2449 /// element" in other libraries. It returns a triplet of the following values: all elements less
2450 /// than the one at the given index, the value at the given index, and all elements greater than
2451 /// the one at the given index.
2453 /// # Current implementation
2455 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2456 /// used for [`sort_unstable`].
2458 /// [`sort_unstable`]: slice::sort_unstable
2462 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2467 /// let mut v = [-5i32, 4, 1, -3, 2];
2469 /// // Find the median
2470 /// v.select_nth_unstable(2);
2472 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2473 /// // about the specified index.
2474 /// assert!(v == [-3, -5, 1, 2, 4] ||
2475 /// v == [-5, -3, 1, 2, 4] ||
2476 /// v == [-3, -5, 1, 4, 2] ||
2477 /// v == [-5, -3, 1, 4, 2]);
2479 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2481 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2485 let mut f = |a: &T, b: &T| a.lt(b);
2486 sort::partition_at_index(self, index, &mut f)
2489 /// Reorder the slice with a comparator function such that the element at `index` is at its
2490 /// final sorted position.
2492 /// This reordering has the additional property that any value at position `i < index` will be
2493 /// less than or equal to any value at a position `j > index` using the comparator function.
2494 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2495 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2496 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2497 /// values: all elements less than the one at the given index, the value at the given index,
2498 /// and all elements greater than the one at the given index, using the provided comparator
2501 /// # Current implementation
2503 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2504 /// used for [`sort_unstable`].
2506 /// [`sort_unstable`]: slice::sort_unstable
2510 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2515 /// let mut v = [-5i32, 4, 1, -3, 2];
2517 /// // Find the median as if the slice were sorted in descending order.
2518 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2520 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2521 /// // about the specified index.
2522 /// assert!(v == [2, 4, 1, -5, -3] ||
2523 /// v == [2, 4, 1, -3, -5] ||
2524 /// v == [4, 2, 1, -5, -3] ||
2525 /// v == [4, 2, 1, -3, -5]);
2527 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2529 pub fn select_nth_unstable_by<F>(
2533 ) -> (&mut [T], &mut T, &mut [T])
2535 F: FnMut(&T, &T) -> Ordering,
2537 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2538 sort::partition_at_index(self, index, &mut f)
2541 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2542 /// final sorted position.
2544 /// This reordering has the additional property that any value at position `i < index` will be
2545 /// less than or equal to any value at a position `j > index` using the key extraction function.
2546 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2547 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2548 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2549 /// values: all elements less than the one at the given index, the value at the given index, and
2550 /// all elements greater than the one at the given index, using the provided key extraction
2553 /// # Current implementation
2555 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2556 /// used for [`sort_unstable`].
2558 /// [`sort_unstable`]: slice::sort_unstable
2562 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2567 /// let mut v = [-5i32, 4, 1, -3, 2];
2569 /// // Return the median as if the array were sorted according to absolute value.
2570 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2572 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2573 /// // about the specified index.
2574 /// assert!(v == [1, 2, -3, 4, -5] ||
2575 /// v == [1, 2, -3, -5, 4] ||
2576 /// v == [2, 1, -3, 4, -5] ||
2577 /// v == [2, 1, -3, -5, 4]);
2579 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2581 pub fn select_nth_unstable_by_key<K, F>(
2585 ) -> (&mut [T], &mut T, &mut [T])
2590 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2591 sort::partition_at_index(self, index, &mut g)
2594 /// Moves all consecutive repeated elements to the end of the slice according to the
2595 /// [`PartialEq`] trait implementation.
2597 /// Returns two slices. The first contains no consecutive repeated elements.
2598 /// The second contains all the duplicates in no specified order.
2600 /// If the slice is sorted, the first returned slice contains no duplicates.
2605 /// #![feature(slice_partition_dedup)]
2607 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2609 /// let (dedup, duplicates) = slice.partition_dedup();
2611 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2612 /// assert_eq!(duplicates, [2, 3, 1]);
2614 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2616 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2620 self.partition_dedup_by(|a, b| a == b)
2623 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2624 /// a given equality relation.
2626 /// Returns two slices. The first contains no consecutive repeated elements.
2627 /// The second contains all the duplicates in no specified order.
2629 /// The `same_bucket` function is passed references to two elements from the slice and
2630 /// must determine if the elements compare equal. The elements are passed in opposite order
2631 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2632 /// at the end of the slice.
2634 /// If the slice is sorted, the first returned slice contains no duplicates.
2639 /// #![feature(slice_partition_dedup)]
2641 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2643 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2645 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2646 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2648 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2650 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2652 F: FnMut(&mut T, &mut T) -> bool,
2654 // Although we have a mutable reference to `self`, we cannot make
2655 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2656 // must ensure that the slice is in a valid state at all times.
2658 // The way that we handle this is by using swaps; we iterate
2659 // over all the elements, swapping as we go so that at the end
2660 // the elements we wish to keep are in the front, and those we
2661 // wish to reject are at the back. We can then split the slice.
2662 // This operation is still `O(n)`.
2664 // Example: We start in this state, where `r` represents "next
2665 // read" and `w` represents "next_write`.
2668 // +---+---+---+---+---+---+
2669 // | 0 | 1 | 1 | 2 | 3 | 3 |
2670 // +---+---+---+---+---+---+
2673 // Comparing self[r] against self[w-1], this is not a duplicate, so
2674 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2675 // r and w, leaving us with:
2678 // +---+---+---+---+---+---+
2679 // | 0 | 1 | 1 | 2 | 3 | 3 |
2680 // +---+---+---+---+---+---+
2683 // Comparing self[r] against self[w-1], this value is a duplicate,
2684 // so we increment `r` but leave everything else unchanged:
2687 // +---+---+---+---+---+---+
2688 // | 0 | 1 | 1 | 2 | 3 | 3 |
2689 // +---+---+---+---+---+---+
2692 // Comparing self[r] against self[w-1], this is not a duplicate,
2693 // so swap self[r] and self[w] and advance r and w:
2696 // +---+---+---+---+---+---+
2697 // | 0 | 1 | 2 | 1 | 3 | 3 |
2698 // +---+---+---+---+---+---+
2701 // Not a duplicate, repeat:
2704 // +---+---+---+---+---+---+
2705 // | 0 | 1 | 2 | 3 | 1 | 3 |
2706 // +---+---+---+---+---+---+
2709 // Duplicate, advance r. End of slice. Split at w.
2711 let len = self.len();
2713 return (self, &mut []);
2716 let ptr = self.as_mut_ptr();
2717 let mut next_read: usize = 1;
2718 let mut next_write: usize = 1;
2720 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2721 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2722 // one element before `ptr_write`, but `next_write` starts at 1, so
2723 // `prev_ptr_write` is never less than 0 and is inside the slice.
2724 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2725 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2726 // and `prev_ptr_write.offset(1)`.
2728 // `next_write` is also incremented at most once per loop at most meaning
2729 // no element is skipped when it may need to be swapped.
2731 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2732 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2733 // The explanation is simply that `next_read >= next_write` is always true,
2734 // thus `next_read > next_write - 1` is too.
2736 // Avoid bounds checks by using raw pointers.
2737 while next_read < len {
2738 let ptr_read = ptr.add(next_read);
2739 let prev_ptr_write = ptr.add(next_write - 1);
2740 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2741 if next_read != next_write {
2742 let ptr_write = prev_ptr_write.offset(1);
2743 mem::swap(&mut *ptr_read, &mut *ptr_write);
2751 self.split_at_mut(next_write)
2754 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2755 /// to the same key.
2757 /// Returns two slices. The first contains no consecutive repeated elements.
2758 /// The second contains all the duplicates in no specified order.
2760 /// If the slice is sorted, the first returned slice contains no duplicates.
2765 /// #![feature(slice_partition_dedup)]
2767 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2769 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2771 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2772 /// assert_eq!(duplicates, [21, 30, 13]);
2774 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2776 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2778 F: FnMut(&mut T) -> K,
2781 self.partition_dedup_by(|a, b| key(a) == key(b))
2784 /// Rotates the slice in-place such that the first `mid` elements of the
2785 /// slice move to the end while the last `self.len() - mid` elements move to
2786 /// the front. After calling `rotate_left`, the element previously at index
2787 /// `mid` will become the first element in the slice.
2791 /// This function will panic if `mid` is greater than the length of the
2792 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2797 /// Takes linear (in `self.len()`) time.
2802 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2803 /// a.rotate_left(2);
2804 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2807 /// Rotating a subslice:
2810 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2811 /// a[1..5].rotate_left(1);
2812 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2814 #[stable(feature = "slice_rotate", since = "1.26.0")]
2815 pub fn rotate_left(&mut self, mid: usize) {
2816 assert!(mid <= self.len());
2817 let k = self.len() - mid;
2818 let p = self.as_mut_ptr();
2820 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2821 // valid for reading and writing, as required by `ptr_rotate`.
2823 rotate::ptr_rotate(mid, p.add(mid), k);
2827 /// Rotates the slice in-place such that the first `self.len() - k`
2828 /// elements of the slice move to the end while the last `k` elements move
2829 /// to the front. After calling `rotate_right`, the element previously at
2830 /// index `self.len() - k` will become the first element in the slice.
2834 /// This function will panic if `k` is greater than the length of the
2835 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2840 /// Takes linear (in `self.len()`) time.
2845 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2846 /// a.rotate_right(2);
2847 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2850 /// Rotate a subslice:
2853 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2854 /// a[1..5].rotate_right(1);
2855 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2857 #[stable(feature = "slice_rotate", since = "1.26.0")]
2858 pub fn rotate_right(&mut self, k: usize) {
2859 assert!(k <= self.len());
2860 let mid = self.len() - k;
2861 let p = self.as_mut_ptr();
2863 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2864 // valid for reading and writing, as required by `ptr_rotate`.
2866 rotate::ptr_rotate(mid, p.add(mid), k);
2870 /// Fills `self` with elements by cloning `value`.
2875 /// let mut buf = vec![0; 10];
2877 /// assert_eq!(buf, vec![1; 10]);
2879 #[doc(alias = "memset")]
2880 #[stable(feature = "slice_fill", since = "1.50.0")]
2881 pub fn fill(&mut self, value: T)
2885 specialize::SpecFill::spec_fill(self, value);
2888 /// Fills `self` with elements returned by calling a closure repeatedly.
2890 /// This method uses a closure to create new values. If you'd rather
2891 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2892 /// trait to generate values, you can pass [`Default::default`] as the
2895 /// [`fill`]: slice::fill
2900 /// let mut buf = vec![1; 10];
2901 /// buf.fill_with(Default::default);
2902 /// assert_eq!(buf, vec![0; 10]);
2904 #[doc(alias = "memset")]
2905 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2906 pub fn fill_with<F>(&mut self, mut f: F)
2915 /// Copies the elements from `src` into `self`.
2917 /// The length of `src` must be the same as `self`.
2919 /// If `T` implements `Copy`, it can be more performant to use
2920 /// [`copy_from_slice`].
2924 /// This function will panic if the two slices have different lengths.
2928 /// Cloning two elements from a slice into another:
2931 /// let src = [1, 2, 3, 4];
2932 /// let mut dst = [0, 0];
2934 /// // Because the slices have to be the same length,
2935 /// // we slice the source slice from four elements
2936 /// // to two. It will panic if we don't do this.
2937 /// dst.clone_from_slice(&src[2..]);
2939 /// assert_eq!(src, [1, 2, 3, 4]);
2940 /// assert_eq!(dst, [3, 4]);
2943 /// Rust enforces that there can only be one mutable reference with no
2944 /// immutable references to a particular piece of data in a particular
2945 /// scope. Because of this, attempting to use `clone_from_slice` on a
2946 /// single slice will result in a compile failure:
2949 /// let mut slice = [1, 2, 3, 4, 5];
2951 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2954 /// To work around this, we can use [`split_at_mut`] to create two distinct
2955 /// sub-slices from a slice:
2958 /// let mut slice = [1, 2, 3, 4, 5];
2961 /// let (left, right) = slice.split_at_mut(2);
2962 /// left.clone_from_slice(&right[1..]);
2965 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2968 /// [`copy_from_slice`]: slice::copy_from_slice
2969 /// [`split_at_mut`]: slice::split_at_mut
2970 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2971 pub fn clone_from_slice(&mut self, src: &[T])
2975 self.spec_clone_from(src);
2978 /// Copies all elements from `src` into `self`, using a memcpy.
2980 /// The length of `src` must be the same as `self`.
2982 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2986 /// This function will panic if the two slices have different lengths.
2990 /// Copying two elements from a slice into another:
2993 /// let src = [1, 2, 3, 4];
2994 /// let mut dst = [0, 0];
2996 /// // Because the slices have to be the same length,
2997 /// // we slice the source slice from four elements
2998 /// // to two. It will panic if we don't do this.
2999 /// dst.copy_from_slice(&src[2..]);
3001 /// assert_eq!(src, [1, 2, 3, 4]);
3002 /// assert_eq!(dst, [3, 4]);
3005 /// Rust enforces that there can only be one mutable reference with no
3006 /// immutable references to a particular piece of data in a particular
3007 /// scope. Because of this, attempting to use `copy_from_slice` on a
3008 /// single slice will result in a compile failure:
3011 /// let mut slice = [1, 2, 3, 4, 5];
3013 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3016 /// To work around this, we can use [`split_at_mut`] to create two distinct
3017 /// sub-slices from a slice:
3020 /// let mut slice = [1, 2, 3, 4, 5];
3023 /// let (left, right) = slice.split_at_mut(2);
3024 /// left.copy_from_slice(&right[1..]);
3027 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3030 /// [`clone_from_slice`]: slice::clone_from_slice
3031 /// [`split_at_mut`]: slice::split_at_mut
3032 #[doc(alias = "memcpy")]
3033 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3034 pub fn copy_from_slice(&mut self, src: &[T])
3038 // The panic code path was put into a cold function to not bloat the
3043 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3045 "source slice length ({}) does not match destination slice length ({})",
3050 if self.len() != src.len() {
3051 len_mismatch_fail(self.len(), src.len());
3054 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3055 // checked to have the same length. The slices cannot overlap because
3056 // mutable references are exclusive.
3058 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3062 /// Copies elements from one part of the slice to another part of itself,
3063 /// using a memmove.
3065 /// `src` is the range within `self` to copy from. `dest` is the starting
3066 /// index of the range within `self` to copy to, which will have the same
3067 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3068 /// must be less than or equal to `self.len()`.
3072 /// This function will panic if either range exceeds the end of the slice,
3073 /// or if the end of `src` is before the start.
3077 /// Copying four bytes within a slice:
3080 /// let mut bytes = *b"Hello, World!";
3082 /// bytes.copy_within(1..5, 8);
3084 /// assert_eq!(&bytes, b"Hello, Wello!");
3086 #[stable(feature = "copy_within", since = "1.37.0")]
3088 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3092 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3093 let count = src_end - src_start;
3094 assert!(dest <= self.len() - count, "dest is out of bounds");
3095 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3096 // as have those for `ptr::add`.
3098 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3102 /// Swaps all elements in `self` with those in `other`.
3104 /// The length of `other` must be the same as `self`.
3108 /// This function will panic if the two slices have different lengths.
3112 /// Swapping two elements across slices:
3115 /// let mut slice1 = [0, 0];
3116 /// let mut slice2 = [1, 2, 3, 4];
3118 /// slice1.swap_with_slice(&mut slice2[2..]);
3120 /// assert_eq!(slice1, [3, 4]);
3121 /// assert_eq!(slice2, [1, 2, 0, 0]);
3124 /// Rust enforces that there can only be one mutable reference to a
3125 /// particular piece of data in a particular scope. Because of this,
3126 /// attempting to use `swap_with_slice` on a single slice will result in
3127 /// a compile failure:
3130 /// let mut slice = [1, 2, 3, 4, 5];
3131 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3134 /// To work around this, we can use [`split_at_mut`] to create two distinct
3135 /// mutable sub-slices from a slice:
3138 /// let mut slice = [1, 2, 3, 4, 5];
3141 /// let (left, right) = slice.split_at_mut(2);
3142 /// left.swap_with_slice(&mut right[1..]);
3145 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3148 /// [`split_at_mut`]: slice::split_at_mut
3149 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3150 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3151 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3152 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3153 // checked to have the same length. The slices cannot overlap because
3154 // mutable references are exclusive.
3156 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3160 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3161 fn align_to_offsets<U>(&self) -> (usize, usize) {
3162 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3163 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3165 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3166 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3167 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3169 // Formula to calculate this is:
3171 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3172 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3174 // Expanded and simplified:
3176 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3177 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3179 // Luckily since all this is constant-evaluated... performance here matters not!
3181 fn gcd(a: usize, b: usize) -> usize {
3182 use crate::intrinsics;
3183 // iterative stein’s algorithm
3184 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3185 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3187 // SAFETY: `a` and `b` are checked to be non-zero values.
3188 let (ctz_a, mut ctz_b) = unsafe {
3195 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3197 let k = ctz_a.min(ctz_b);
3198 let mut a = a >> ctz_a;
3201 // remove all factors of 2 from b
3204 mem::swap(&mut a, &mut b);
3207 // SAFETY: `b` is checked to be non-zero.
3212 ctz_b = intrinsics::cttz_nonzero(b);
3217 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3218 let ts: usize = mem::size_of::<U>() / gcd;
3219 let us: usize = mem::size_of::<T>() / gcd;
3221 // Armed with this knowledge, we can find how many `U`s we can fit!
3222 let us_len = self.len() / ts * us;
3223 // And how many `T`s will be in the trailing slice!
3224 let ts_len = self.len() % ts;
3228 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3231 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3232 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3233 /// length possible for a given type and input slice, but only your algorithm's performance
3234 /// should depend on that, not its correctness. It is permissible for all of the input data to
3235 /// be returned as the prefix or suffix slice.
3237 /// This method has no purpose when either input element `T` or output element `U` are
3238 /// zero-sized and will return the original slice without splitting anything.
3242 /// This method is essentially a `transmute` with respect to the elements in the returned
3243 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3251 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3252 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3253 /// // less_efficient_algorithm_for_bytes(prefix);
3254 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3255 /// // less_efficient_algorithm_for_bytes(suffix);
3258 #[stable(feature = "slice_align_to", since = "1.30.0")]
3259 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3260 // Note that most of this function will be constant-evaluated,
3261 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3262 // handle ZSTs specially, which is – don't handle them at all.
3263 return (self, &[], &[]);
3266 // First, find at what point do we split between the first and 2nd slice. Easy with
3267 // ptr.align_offset.
3268 let ptr = self.as_ptr();
3269 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3270 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3271 if offset > self.len() {
3274 let (left, rest) = self.split_at(offset);
3275 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3276 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3277 // since the caller guarantees that we can transmute `T` to `U` safely.
3281 from_raw_parts(rest.as_ptr() as *const U, us_len),
3282 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3288 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3291 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3292 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3293 /// length possible for a given type and input slice, but only your algorithm's performance
3294 /// should depend on that, not its correctness. It is permissible for all of the input data to
3295 /// be returned as the prefix or suffix slice.
3297 /// This method has no purpose when either input element `T` or output element `U` are
3298 /// zero-sized and will return the original slice without splitting anything.
3302 /// This method is essentially a `transmute` with respect to the elements in the returned
3303 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3311 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3312 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3313 /// // less_efficient_algorithm_for_bytes(prefix);
3314 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3315 /// // less_efficient_algorithm_for_bytes(suffix);
3318 #[stable(feature = "slice_align_to", since = "1.30.0")]
3319 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3320 // Note that most of this function will be constant-evaluated,
3321 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3322 // handle ZSTs specially, which is – don't handle them at all.
3323 return (self, &mut [], &mut []);
3326 // First, find at what point do we split between the first and 2nd slice. Easy with
3327 // ptr.align_offset.
3328 let ptr = self.as_ptr();
3329 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3330 // rest of the method. This is done by passing a pointer to &[T] with an
3331 // alignment targeted for U.
3332 // `crate::ptr::align_offset` is called with a correctly aligned and
3333 // valid pointer `ptr` (it comes from a reference to `self`) and with
3334 // a size that is a power of two (since it comes from the alignement for U),
3335 // satisfying its safety constraints.
3336 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3337 if offset > self.len() {
3338 (self, &mut [], &mut [])
3340 let (left, rest) = self.split_at_mut(offset);
3341 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3342 let rest_len = rest.len();
3343 let mut_ptr = rest.as_mut_ptr();
3344 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3345 // SAFETY: see comments for `align_to`.
3349 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3350 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3356 /// Checks if the elements of this slice are sorted.
3358 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3359 /// slice yields exactly zero or one element, `true` is returned.
3361 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3362 /// implies that this function returns `false` if any two consecutive items are not
3368 /// #![feature(is_sorted)]
3369 /// let empty: [i32; 0] = [];
3371 /// assert!([1, 2, 2, 9].is_sorted());
3372 /// assert!(![1, 3, 2, 4].is_sorted());
3373 /// assert!([0].is_sorted());
3374 /// assert!(empty.is_sorted());
3375 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3378 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3379 pub fn is_sorted(&self) -> bool
3383 self.is_sorted_by(|a, b| a.partial_cmp(b))
3386 /// Checks if the elements of this slice are sorted using the given comparator function.
3388 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3389 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3390 /// [`is_sorted`]; see its documentation for more information.
3392 /// [`is_sorted`]: slice::is_sorted
3393 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3394 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3396 F: FnMut(&T, &T) -> Option<Ordering>,
3398 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3401 /// Checks if the elements of this slice are sorted using the given key extraction function.
3403 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3404 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3405 /// documentation for more information.
3407 /// [`is_sorted`]: slice::is_sorted
3412 /// #![feature(is_sorted)]
3414 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3415 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3418 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3419 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3424 self.iter().is_sorted_by_key(f)
3427 /// Returns the index of the partition point according to the given predicate
3428 /// (the index of the first element of the second partition).
3430 /// The slice is assumed to be partitioned according to the given predicate.
3431 /// This means that all elements for which the predicate returns true are at the start of the slice
3432 /// and all elements for which the predicate returns false are at the end.
3433 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3434 /// (all odd numbers are at the start, all even at the end).
3436 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3437 /// as this method performs a kind of binary search.
3439 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3441 /// [`binary_search`]: slice::binary_search
3442 /// [`binary_search_by`]: slice::binary_search_by
3443 /// [`binary_search_by_key`]: slice::binary_search_by_key
3448 /// let v = [1, 2, 3, 3, 5, 6, 7];
3449 /// let i = v.partition_point(|&x| x < 5);
3451 /// assert_eq!(i, 4);
3452 /// assert!(v[..i].iter().all(|&x| x < 5));
3453 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3455 #[stable(feature = "partition_point", since = "1.52.0")]
3456 pub fn partition_point<P>(&self, mut pred: P) -> usize
3458 P: FnMut(&T) -> bool,
3461 let mut right = self.len();
3463 while left != right {
3464 let mid = left + (right - left) / 2;
3465 // SAFETY: When `left < right`, `left <= mid < right`.
3466 // Therefore `left` always increases and `right` always decreases,
3467 // and either of them is selected. In both cases `left <= right` is
3468 // satisfied. Therefore if `left < right` in a step, `left <= right`
3469 // is satisfied in the next step. Therefore as long as `left != right`,
3470 // `0 <= left < right <= len` is satisfied and if this case
3471 // `0 <= mid < len` is satisfied too.
3472 let value = unsafe { self.get_unchecked(mid) };
3484 trait CloneFromSpec<T> {
3485 fn spec_clone_from(&mut self, src: &[T]);
3488 impl<T> CloneFromSpec<T> for [T]
3492 default fn spec_clone_from(&mut self, src: &[T]) {
3493 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3494 // NOTE: We need to explicitly slice them to the same length
3495 // to make it easier for the optimizer to elide bounds checking.
3496 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3497 let len = self.len();
3498 let src = &src[..len];
3500 self[i].clone_from(&src[i]);
3505 impl<T> CloneFromSpec<T> for [T]
3509 fn spec_clone_from(&mut self, src: &[T]) {
3510 self.copy_from_slice(src);
3514 #[stable(feature = "rust1", since = "1.0.0")]
3515 impl<T> Default for &[T] {
3516 /// Creates an empty slice.
3517 fn default() -> Self {
3522 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3523 impl<T> Default for &mut [T] {
3524 /// Creates a mutable empty slice.
3525 fn default() -> Self {
3530 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3531 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3532 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3533 /// `str`) to slices, and then this trait will be replaced or abolished.
3534 pub trait SlicePattern {
3535 /// The element type of the slice being matched on.
3538 /// Currently, the consumers of `SlicePattern` need a slice.
3539 fn as_slice(&self) -> &[Self::Item];
3542 #[stable(feature = "slice_strip", since = "1.51.0")]
3543 impl<T> SlicePattern for [T] {
3547 fn as_slice(&self) -> &[Self::Item] {
3552 #[stable(feature = "slice_strip", since = "1.51.0")]
3553 impl<T, const N: usize> SlicePattern for [T; N] {
3557 fn as_slice(&self) -> &[Self::Item] {