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")]
87 /// Returns the number of elements in the slice.
92 /// let a = [1, 2, 3];
93 /// assert_eq!(a.len(), 3);
95 #[doc(alias = "length")]
96 #[stable(feature = "rust1", since = "1.0.0")]
97 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
99 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
100 #[rustc_allow_const_fn_unstable(const_fn_union)]
101 pub const fn len(&self) -> usize {
104 // SAFETY: this is safe because `&[T]` and `FatPtr<T>` have the same layout.
105 // Only `std` can make this guarantee.
106 unsafe { crate::ptr::Repr { rust: self }.raw.len }
108 #[cfg(not(bootstrap))]
110 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
111 // As of this writing this causes a "Const-stable functions can only call other
112 // const-stable functions" error.
114 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
115 // and PtrComponents<T> have the same memory layouts. Only std can make this
117 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
121 /// Returns `true` if the slice has a length of 0.
126 /// let a = [1, 2, 3];
127 /// assert!(!a.is_empty());
129 #[stable(feature = "rust1", since = "1.0.0")]
130 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
132 pub const fn is_empty(&self) -> bool {
136 /// Returns the first element of the slice, or `None` if it is empty.
141 /// let v = [10, 40, 30];
142 /// assert_eq!(Some(&10), v.first());
144 /// let w: &[i32] = &[];
145 /// assert_eq!(None, w.first());
147 #[stable(feature = "rust1", since = "1.0.0")]
148 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
150 pub const fn first(&self) -> Option<&T> {
151 if let [first, ..] = self { Some(first) } else { None }
154 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
159 /// let x = &mut [0, 1, 2];
161 /// if let Some(first) = x.first_mut() {
164 /// assert_eq!(x, &[5, 1, 2]);
166 #[stable(feature = "rust1", since = "1.0.0")]
167 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
169 pub const fn first_mut(&mut self) -> Option<&mut T> {
170 if let [first, ..] = self { Some(first) } else { None }
173 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
178 /// let x = &[0, 1, 2];
180 /// if let Some((first, elements)) = x.split_first() {
181 /// assert_eq!(first, &0);
182 /// assert_eq!(elements, &[1, 2]);
185 #[stable(feature = "slice_splits", since = "1.5.0")]
186 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
188 pub const fn split_first(&self) -> Option<(&T, &[T])> {
189 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
192 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
197 /// let x = &mut [0, 1, 2];
199 /// if let Some((first, elements)) = x.split_first_mut() {
204 /// assert_eq!(x, &[3, 4, 5]);
206 #[stable(feature = "slice_splits", since = "1.5.0")]
207 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
209 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
210 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
213 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
218 /// let x = &[0, 1, 2];
220 /// if let Some((last, elements)) = x.split_last() {
221 /// assert_eq!(last, &2);
222 /// assert_eq!(elements, &[0, 1]);
225 #[stable(feature = "slice_splits", since = "1.5.0")]
226 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
228 pub const fn split_last(&self) -> Option<(&T, &[T])> {
229 if let [init @ .., last] = self { Some((last, init)) } else { None }
232 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
237 /// let x = &mut [0, 1, 2];
239 /// if let Some((last, elements)) = x.split_last_mut() {
244 /// assert_eq!(x, &[4, 5, 3]);
246 #[stable(feature = "slice_splits", since = "1.5.0")]
247 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
249 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
250 if let [init @ .., last] = self { Some((last, init)) } else { None }
253 /// Returns the last element of the slice, or `None` if it is empty.
258 /// let v = [10, 40, 30];
259 /// assert_eq!(Some(&30), v.last());
261 /// let w: &[i32] = &[];
262 /// assert_eq!(None, w.last());
264 #[stable(feature = "rust1", since = "1.0.0")]
265 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
267 pub const fn last(&self) -> Option<&T> {
268 if let [.., last] = self { Some(last) } else { None }
271 /// Returns a mutable pointer to the last item in the slice.
276 /// let x = &mut [0, 1, 2];
278 /// if let Some(last) = x.last_mut() {
281 /// assert_eq!(x, &[0, 1, 10]);
283 #[stable(feature = "rust1", since = "1.0.0")]
284 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
286 pub const fn last_mut(&mut self) -> Option<&mut T> {
287 if let [.., last] = self { Some(last) } else { None }
290 /// Returns a reference to an element or subslice depending on the type of
293 /// - If given a position, returns a reference to the element at that
294 /// position or `None` if out of bounds.
295 /// - If given a range, returns the subslice corresponding to that range,
296 /// or `None` if out of bounds.
301 /// let v = [10, 40, 30];
302 /// assert_eq!(Some(&40), v.get(1));
303 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
304 /// assert_eq!(None, v.get(3));
305 /// assert_eq!(None, v.get(0..4));
307 #[stable(feature = "rust1", since = "1.0.0")]
309 pub fn get<I>(&self, index: I) -> Option<&I::Output>
316 /// Returns a mutable reference to an element or subslice depending on the
317 /// type of index (see [`get`]) or `None` if the index is out of bounds.
319 /// [`get`]: slice::get
324 /// let x = &mut [0, 1, 2];
326 /// if let Some(elem) = x.get_mut(1) {
329 /// assert_eq!(x, &[0, 42, 2]);
331 #[stable(feature = "rust1", since = "1.0.0")]
333 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
340 /// Returns a reference to an element or subslice, without doing bounds
343 /// For a safe alternative see [`get`].
347 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
348 /// even if the resulting reference is not used.
350 /// [`get`]: slice::get
351 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
356 /// let x = &[1, 2, 4];
359 /// assert_eq!(x.get_unchecked(1), &2);
362 #[stable(feature = "rust1", since = "1.0.0")]
364 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
368 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
369 // the slice is dereferencable because `self` is a safe reference.
370 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
371 unsafe { &*index.get_unchecked(self) }
374 /// Returns a mutable reference to an element or subslice, without doing
377 /// For a safe alternative see [`get_mut`].
381 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
382 /// even if the resulting reference is not used.
384 /// [`get_mut`]: slice::get_mut
385 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
390 /// let x = &mut [1, 2, 4];
393 /// let elem = x.get_unchecked_mut(1);
396 /// assert_eq!(x, &[1, 13, 4]);
398 #[stable(feature = "rust1", since = "1.0.0")]
400 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
404 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
405 // the slice is dereferencable because `self` is a safe reference.
406 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
407 unsafe { &mut *index.get_unchecked_mut(self) }
410 /// Returns a raw pointer to the slice's buffer.
412 /// The caller must ensure that the slice outlives the pointer this
413 /// function returns, or else it will end up pointing to garbage.
415 /// The caller must also ensure that the memory the pointer (non-transitively) points to
416 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
417 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
419 /// Modifying the container referenced by this slice may cause its buffer
420 /// to be reallocated, which would also make any pointers to it invalid.
425 /// let x = &[1, 2, 4];
426 /// let x_ptr = x.as_ptr();
429 /// for i in 0..x.len() {
430 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
435 /// [`as_mut_ptr`]: slice::as_mut_ptr
436 #[stable(feature = "rust1", since = "1.0.0")]
437 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
439 pub const fn as_ptr(&self) -> *const T {
440 self as *const [T] as *const T
443 /// Returns an unsafe mutable pointer to the slice's buffer.
445 /// The caller must ensure that the slice outlives the pointer this
446 /// function returns, or else it will end up pointing to garbage.
448 /// Modifying the container referenced by this slice may cause its buffer
449 /// to be reallocated, which would also make any pointers to it invalid.
454 /// let x = &mut [1, 2, 4];
455 /// let x_ptr = x.as_mut_ptr();
458 /// for i in 0..x.len() {
459 /// *x_ptr.add(i) += 2;
462 /// assert_eq!(x, &[3, 4, 6]);
464 #[stable(feature = "rust1", since = "1.0.0")]
465 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
467 pub const fn as_mut_ptr(&mut self) -> *mut T {
468 self as *mut [T] as *mut T
471 /// Returns the two raw pointers spanning the slice.
473 /// The returned range is half-open, which means that the end pointer
474 /// points *one past* the last element of the slice. This way, an empty
475 /// slice is represented by two equal pointers, and the difference between
476 /// the two pointers represents the size of the slice.
478 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
479 /// requires extra caution, as it does not point to a valid element in the
482 /// This function is useful for interacting with foreign interfaces which
483 /// use two pointers to refer to a range of elements in memory, as is
486 /// It can also be useful to check if a pointer to an element refers to an
487 /// element of this slice:
490 /// let a = [1, 2, 3];
491 /// let x = &a[1] as *const _;
492 /// let y = &5 as *const _;
494 /// assert!(a.as_ptr_range().contains(&x));
495 /// assert!(!a.as_ptr_range().contains(&y));
498 /// [`as_ptr`]: slice::as_ptr
499 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
500 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
502 pub const fn as_ptr_range(&self) -> Range<*const T> {
503 let start = self.as_ptr();
504 // SAFETY: The `add` here is safe, because:
506 // - Both pointers are part of the same object, as pointing directly
507 // past the object also counts.
509 // - The size of the slice is never larger than isize::MAX bytes, as
511 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
512 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
513 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
514 // (This doesn't seem normative yet, but the very same assumption is
515 // made in many places, including the Index implementation of slices.)
517 // - There is no wrapping around involved, as slices do not wrap past
518 // the end of the address space.
520 // See the documentation of pointer::add.
521 let end = unsafe { start.add(self.len()) };
525 /// Returns the two unsafe mutable pointers spanning the slice.
527 /// The returned range is half-open, which means that the end pointer
528 /// points *one past* the last element of the slice. This way, an empty
529 /// slice is represented by two equal pointers, and the difference between
530 /// the two pointers represents the size of the slice.
532 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
533 /// pointer requires extra caution, as it does not point to a valid element
536 /// This function is useful for interacting with foreign interfaces which
537 /// use two pointers to refer to a range of elements in memory, as is
540 /// [`as_mut_ptr`]: slice::as_mut_ptr
541 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
542 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
544 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
545 let start = self.as_mut_ptr();
546 // SAFETY: See as_ptr_range() above for why `add` here is safe.
547 let end = unsafe { start.add(self.len()) };
551 /// Swaps two elements in the slice.
555 /// * a - The index of the first element
556 /// * b - The index of the second element
560 /// Panics if `a` or `b` are out of bounds.
565 /// let mut v = ["a", "b", "c", "d"];
567 /// assert!(v == ["a", "d", "c", "b"]);
569 #[stable(feature = "rust1", since = "1.0.0")]
571 pub fn swap(&mut self, a: usize, b: usize) {
572 // Can't take two mutable loans from one vector, so instead use raw pointers.
573 let pa = ptr::addr_of_mut!(self[a]);
574 let pb = ptr::addr_of_mut!(self[b]);
575 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
576 // to elements in the slice and therefore are guaranteed to be valid and aligned.
577 // Note that accessing the elements behind `a` and `b` is checked and will
578 // panic when out of bounds.
584 /// Reverses the order of elements in the slice, in place.
589 /// let mut v = [1, 2, 3];
591 /// assert!(v == [3, 2, 1]);
593 #[stable(feature = "rust1", since = "1.0.0")]
595 pub fn reverse(&mut self) {
596 let mut i: usize = 0;
599 // For very small types, all the individual reads in the normal
600 // path perform poorly. We can do better, given efficient unaligned
601 // load/store, by loading a larger chunk and reversing a register.
603 // Ideally LLVM would do this for us, as it knows better than we do
604 // whether unaligned reads are efficient (since that changes between
605 // different ARM versions, for example) and what the best chunk size
606 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
607 // the loop, so we need to do this ourselves. (Hypothesis: reverse
608 // is troublesome because the sides can be aligned differently --
609 // will be, when the length is odd -- so there's no way of emitting
610 // pre- and postludes to use fully-aligned SIMD in the middle.)
612 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
614 if fast_unaligned && mem::size_of::<T>() == 1 {
615 // Use the llvm.bswap intrinsic to reverse u8s in a usize
616 let chunk = mem::size_of::<usize>();
617 while i + chunk - 1 < ln / 2 {
618 // SAFETY: There are several things to check here:
620 // - Note that `chunk` is either 4 or 8 due to the cfg check
621 // above. So `chunk - 1` is positive.
622 // - Indexing with index `i` is fine as the loop check guarantees
623 // `i + chunk - 1 < ln / 2`
624 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
625 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
626 // - `i + chunk > 0` is trivially true.
627 // - The loop check guarantees:
628 // `i + chunk - 1 < ln / 2`
629 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
630 // - The `read_unaligned` and `write_unaligned` calls are fine:
631 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
632 // (see above) and `pb` points to index `ln - i - chunk`, so
633 // both are at least `chunk`
634 // many bytes away from the end of `self`.
635 // - Any initialized memory is valid `usize`.
637 let ptr = self.as_mut_ptr();
639 let pb = ptr.add(ln - i - chunk);
640 let va = ptr::read_unaligned(pa as *mut usize);
641 let vb = ptr::read_unaligned(pb as *mut usize);
642 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
643 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
649 if fast_unaligned && mem::size_of::<T>() == 2 {
650 // Use rotate-by-16 to reverse u16s in a u32
651 let chunk = mem::size_of::<u32>() / 2;
652 while i + chunk - 1 < ln / 2 {
653 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
654 // (and obviously `i < ln`), because each element is 2 bytes and
657 // `i + chunk - 1 < ln / 2` # while condition
658 // `i + 2 - 1 < ln / 2`
661 // Since it's less than the length divided by 2, then it must be
664 // This also means that the condition `0 < i + chunk <= ln` is
665 // always respected, ensuring the `pb` pointer can be used
668 let ptr = self.as_mut_ptr();
670 let pb = ptr.add(ln - i - chunk);
671 let va = ptr::read_unaligned(pa as *mut u32);
672 let vb = ptr::read_unaligned(pb as *mut u32);
673 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
674 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
681 // SAFETY: `i` is inferior to half the length of the slice so
682 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
683 // will not go further than `ln / 2 - 1`).
684 // The resulting pointers `pa` and `pb` are therefore valid and
685 // aligned, and can be read from and written to.
687 // Unsafe swap to avoid the bounds check in safe swap.
688 let ptr = self.as_mut_ptr();
690 let pb = ptr.add(ln - i - 1);
697 /// Returns an iterator over the slice.
702 /// let x = &[1, 2, 4];
703 /// let mut iterator = x.iter();
705 /// assert_eq!(iterator.next(), Some(&1));
706 /// assert_eq!(iterator.next(), Some(&2));
707 /// assert_eq!(iterator.next(), Some(&4));
708 /// assert_eq!(iterator.next(), None);
710 #[stable(feature = "rust1", since = "1.0.0")]
712 pub fn iter(&self) -> Iter<'_, T> {
716 /// Returns an iterator that allows modifying each value.
721 /// let x = &mut [1, 2, 4];
722 /// for elem in x.iter_mut() {
725 /// assert_eq!(x, &[3, 4, 6]);
727 #[stable(feature = "rust1", since = "1.0.0")]
729 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
733 /// Returns an iterator over all contiguous windows of length
734 /// `size`. The windows overlap. If the slice is shorter than
735 /// `size`, the iterator returns no values.
739 /// Panics if `size` is 0.
744 /// let slice = ['r', 'u', 's', 't'];
745 /// let mut iter = slice.windows(2);
746 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
747 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
748 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
749 /// assert!(iter.next().is_none());
752 /// If the slice is shorter than `size`:
755 /// let slice = ['f', 'o', 'o'];
756 /// let mut iter = slice.windows(4);
757 /// assert!(iter.next().is_none());
759 #[stable(feature = "rust1", since = "1.0.0")]
761 pub fn windows(&self, size: usize) -> Windows<'_, T> {
762 let size = NonZeroUsize::new(size).expect("size is zero");
763 Windows::new(self, size)
766 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
767 /// beginning of the slice.
769 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
770 /// slice, then the last chunk will not have length `chunk_size`.
772 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
773 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
778 /// Panics if `chunk_size` is 0.
783 /// let slice = ['l', 'o', 'r', 'e', 'm'];
784 /// let mut iter = slice.chunks(2);
785 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
786 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
787 /// assert_eq!(iter.next().unwrap(), &['m']);
788 /// assert!(iter.next().is_none());
791 /// [`chunks_exact`]: slice::chunks_exact
792 /// [`rchunks`]: slice::rchunks
793 #[stable(feature = "rust1", since = "1.0.0")]
795 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
796 assert_ne!(chunk_size, 0);
797 Chunks::new(self, chunk_size)
800 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
801 /// beginning of the slice.
803 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
804 /// length of the slice, then the last chunk will not have length `chunk_size`.
806 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
807 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
808 /// the end of the slice.
812 /// Panics if `chunk_size` is 0.
817 /// let v = &mut [0, 0, 0, 0, 0];
818 /// let mut count = 1;
820 /// for chunk in v.chunks_mut(2) {
821 /// for elem in chunk.iter_mut() {
826 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
829 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
830 /// [`rchunks_mut`]: slice::rchunks_mut
831 #[stable(feature = "rust1", since = "1.0.0")]
833 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
834 assert_ne!(chunk_size, 0);
835 ChunksMut::new(self, chunk_size)
838 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
839 /// beginning of the slice.
841 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
842 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
843 /// from the `remainder` function of the iterator.
845 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
846 /// resulting code better than in the case of [`chunks`].
848 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
849 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
853 /// Panics if `chunk_size` is 0.
858 /// let slice = ['l', 'o', 'r', 'e', 'm'];
859 /// let mut iter = slice.chunks_exact(2);
860 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
861 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
862 /// assert!(iter.next().is_none());
863 /// assert_eq!(iter.remainder(), &['m']);
866 /// [`chunks`]: slice::chunks
867 /// [`rchunks_exact`]: slice::rchunks_exact
868 #[stable(feature = "chunks_exact", since = "1.31.0")]
870 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
871 assert_ne!(chunk_size, 0);
872 ChunksExact::new(self, chunk_size)
875 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
876 /// beginning of the slice.
878 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
879 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
880 /// retrieved from the `into_remainder` function of the iterator.
882 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
883 /// resulting code better than in the case of [`chunks_mut`].
885 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
886 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
891 /// Panics if `chunk_size` is 0.
896 /// let v = &mut [0, 0, 0, 0, 0];
897 /// let mut count = 1;
899 /// for chunk in v.chunks_exact_mut(2) {
900 /// for elem in chunk.iter_mut() {
905 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
908 /// [`chunks_mut`]: slice::chunks_mut
909 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
910 #[stable(feature = "chunks_exact", since = "1.31.0")]
912 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
913 assert_ne!(chunk_size, 0);
914 ChunksExactMut::new(self, chunk_size)
917 /// Splits the slice into a slice of `N`-element arrays,
918 /// assuming that there's no remainder.
922 /// This may only be called when
923 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
929 /// #![feature(slice_as_chunks)]
930 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
931 /// let chunks: &[[char; 1]] =
932 /// // SAFETY: 1-element chunks never have remainder
933 /// unsafe { slice.as_chunks_unchecked() };
934 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
935 /// let chunks: &[[char; 3]] =
936 /// // SAFETY: The slice length (6) is a multiple of 3
937 /// unsafe { slice.as_chunks_unchecked() };
938 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
940 /// // These would be unsound:
941 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
942 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
944 #[unstable(feature = "slice_as_chunks", issue = "74985")]
946 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
947 debug_assert_ne!(N, 0);
948 debug_assert_eq!(self.len() % N, 0);
950 // SAFETY: Our precondition is exactly what's needed to call this
951 unsafe { crate::intrinsics::exact_div(self.len(), N) };
952 // SAFETY: We cast a slice of `new_len * N` elements into
953 // a slice of `new_len` many `N` elements chunks.
954 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
957 /// Splits the slice into a slice of `N`-element arrays,
958 /// starting at the beginning of the slice,
959 /// and a remainder slice with length strictly less than `N`.
963 /// Panics if `N` is 0. This check will most probably get changed to a compile time
964 /// error before this method gets stabilized.
969 /// #![feature(slice_as_chunks)]
970 /// let slice = ['l', 'o', 'r', 'e', 'm'];
971 /// let (chunks, remainder) = slice.as_chunks();
972 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
973 /// assert_eq!(remainder, &['m']);
975 #[unstable(feature = "slice_as_chunks", issue = "74985")]
977 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
979 let len = self.len() / N;
980 let (multiple_of_n, remainder) = self.split_at(len * N);
981 // SAFETY: We already panicked for zero, and ensured by construction
982 // that the length of the subslice is a multiple of N.
983 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
984 (array_slice, remainder)
987 /// Splits the slice into a slice of `N`-element arrays,
988 /// starting at the end of the slice,
989 /// and a remainder slice with length strictly less than `N`.
993 /// Panics if `N` is 0. This check will most probably get changed to a compile time
994 /// error before this method gets stabilized.
999 /// #![feature(slice_as_chunks)]
1000 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1001 /// let (remainder, chunks) = slice.as_rchunks();
1002 /// assert_eq!(remainder, &['l']);
1003 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1005 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1007 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1009 let len = self.len() / N;
1010 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1011 // SAFETY: We already panicked for zero, and ensured by construction
1012 // that the length of the subslice is a multiple of N.
1013 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1014 (remainder, array_slice)
1017 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1018 /// beginning of the slice.
1020 /// The chunks are array references and do not overlap. If `N` does not divide the
1021 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1022 /// retrieved from the `remainder` function of the iterator.
1024 /// This method is the const generic equivalent of [`chunks_exact`].
1028 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1029 /// error before this method gets stabilized.
1034 /// #![feature(array_chunks)]
1035 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1036 /// let mut iter = slice.array_chunks();
1037 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1038 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1039 /// assert!(iter.next().is_none());
1040 /// assert_eq!(iter.remainder(), &['m']);
1043 /// [`chunks_exact`]: slice::chunks_exact
1044 #[unstable(feature = "array_chunks", issue = "74985")]
1046 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1048 ArrayChunks::new(self)
1051 /// Splits the slice into a slice of `N`-element arrays,
1052 /// assuming that there's no remainder.
1056 /// This may only be called when
1057 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1063 /// #![feature(slice_as_chunks)]
1064 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1065 /// let chunks: &mut [[char; 1]] =
1066 /// // SAFETY: 1-element chunks never have remainder
1067 /// unsafe { slice.as_chunks_unchecked_mut() };
1068 /// chunks[0] = ['L'];
1069 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1070 /// let chunks: &mut [[char; 3]] =
1071 /// // SAFETY: The slice length (6) is a multiple of 3
1072 /// unsafe { slice.as_chunks_unchecked_mut() };
1073 /// chunks[1] = ['a', 'x', '?'];
1074 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1076 /// // These would be unsound:
1077 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1078 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1080 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1082 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1083 debug_assert_ne!(N, 0);
1084 debug_assert_eq!(self.len() % N, 0);
1086 // SAFETY: Our precondition is exactly what's needed to call this
1087 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1088 // SAFETY: We cast a slice of `new_len * N` elements into
1089 // a slice of `new_len` many `N` elements chunks.
1090 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1093 /// Splits the slice into a slice of `N`-element arrays,
1094 /// starting at the beginning of the slice,
1095 /// and a remainder slice with length strictly less than `N`.
1099 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1100 /// error before this method gets stabilized.
1105 /// #![feature(slice_as_chunks)]
1106 /// let v = &mut [0, 0, 0, 0, 0];
1107 /// let mut count = 1;
1109 /// let (chunks, remainder) = v.as_chunks_mut();
1110 /// remainder[0] = 9;
1111 /// for chunk in chunks {
1112 /// *chunk = [count; 2];
1115 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1117 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1119 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1121 let len = self.len() / N;
1122 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1123 // SAFETY: We already panicked for zero, and ensured by construction
1124 // that the length of the subslice is a multiple of N.
1125 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1126 (array_slice, remainder)
1129 /// Splits the slice into a slice of `N`-element arrays,
1130 /// starting at the end of the slice,
1131 /// and a remainder slice with length strictly less than `N`.
1135 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1136 /// error before this method gets stabilized.
1141 /// #![feature(slice_as_chunks)]
1142 /// let v = &mut [0, 0, 0, 0, 0];
1143 /// let mut count = 1;
1145 /// let (remainder, chunks) = v.as_rchunks_mut();
1146 /// remainder[0] = 9;
1147 /// for chunk in chunks {
1148 /// *chunk = [count; 2];
1151 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1153 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1155 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1157 let len = self.len() / N;
1158 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1159 // SAFETY: We already panicked for zero, and ensured by construction
1160 // that the length of the subslice is a multiple of N.
1161 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1162 (remainder, array_slice)
1165 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1166 /// beginning of the slice.
1168 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1169 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1170 /// can be retrieved from the `into_remainder` function of the iterator.
1172 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1176 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1177 /// error before this method gets stabilized.
1182 /// #![feature(array_chunks)]
1183 /// let v = &mut [0, 0, 0, 0, 0];
1184 /// let mut count = 1;
1186 /// for chunk in v.array_chunks_mut() {
1187 /// *chunk = [count; 2];
1190 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1193 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1194 #[unstable(feature = "array_chunks", issue = "74985")]
1196 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1198 ArrayChunksMut::new(self)
1201 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1202 /// starting at the beginning of the slice.
1204 /// This is the const generic equivalent of [`windows`].
1206 /// If `N` is greater than the size of the slice, it will return no windows.
1210 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1211 /// error before this method gets stabilized.
1216 /// #![feature(array_windows)]
1217 /// let slice = [0, 1, 2, 3];
1218 /// let mut iter = slice.array_windows();
1219 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1220 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1221 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1222 /// assert!(iter.next().is_none());
1225 /// [`windows`]: slice::windows
1226 #[unstable(feature = "array_windows", issue = "75027")]
1228 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1230 ArrayWindows::new(self)
1233 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1236 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1237 /// slice, then the last chunk will not have length `chunk_size`.
1239 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1240 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1245 /// Panics if `chunk_size` is 0.
1250 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1251 /// let mut iter = slice.rchunks(2);
1252 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1253 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1254 /// assert_eq!(iter.next().unwrap(), &['l']);
1255 /// assert!(iter.next().is_none());
1258 /// [`rchunks_exact`]: slice::rchunks_exact
1259 /// [`chunks`]: slice::chunks
1260 #[stable(feature = "rchunks", since = "1.31.0")]
1262 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1263 assert!(chunk_size != 0);
1264 RChunks::new(self, chunk_size)
1267 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1270 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1271 /// length of the slice, then the last chunk will not have length `chunk_size`.
1273 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1274 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1275 /// beginning of the slice.
1279 /// Panics if `chunk_size` is 0.
1284 /// let v = &mut [0, 0, 0, 0, 0];
1285 /// let mut count = 1;
1287 /// for chunk in v.rchunks_mut(2) {
1288 /// for elem in chunk.iter_mut() {
1293 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1296 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1297 /// [`chunks_mut`]: slice::chunks_mut
1298 #[stable(feature = "rchunks", since = "1.31.0")]
1300 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1301 assert!(chunk_size != 0);
1302 RChunksMut::new(self, chunk_size)
1305 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1306 /// end of the slice.
1308 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1309 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1310 /// from the `remainder` function of the iterator.
1312 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1313 /// resulting code better than in the case of [`chunks`].
1315 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1316 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1321 /// Panics if `chunk_size` is 0.
1326 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1327 /// let mut iter = slice.rchunks_exact(2);
1328 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1329 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1330 /// assert!(iter.next().is_none());
1331 /// assert_eq!(iter.remainder(), &['l']);
1334 /// [`chunks`]: slice::chunks
1335 /// [`rchunks`]: slice::rchunks
1336 /// [`chunks_exact`]: slice::chunks_exact
1337 #[stable(feature = "rchunks", since = "1.31.0")]
1339 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1340 assert!(chunk_size != 0);
1341 RChunksExact::new(self, chunk_size)
1344 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1347 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1348 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1349 /// retrieved from the `into_remainder` function of the iterator.
1351 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1352 /// resulting code better than in the case of [`chunks_mut`].
1354 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1355 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1360 /// Panics if `chunk_size` is 0.
1365 /// let v = &mut [0, 0, 0, 0, 0];
1366 /// let mut count = 1;
1368 /// for chunk in v.rchunks_exact_mut(2) {
1369 /// for elem in chunk.iter_mut() {
1374 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1377 /// [`chunks_mut`]: slice::chunks_mut
1378 /// [`rchunks_mut`]: slice::rchunks_mut
1379 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1380 #[stable(feature = "rchunks", since = "1.31.0")]
1382 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1383 assert!(chunk_size != 0);
1384 RChunksExactMut::new(self, chunk_size)
1387 /// Returns an iterator over the slice producing non-overlapping runs
1388 /// of elements using the predicate to separate them.
1390 /// The predicate is called on two elements following themselves,
1391 /// it means the predicate is called on `slice[0]` and `slice[1]`
1392 /// then on `slice[1]` and `slice[2]` and so on.
1397 /// #![feature(slice_group_by)]
1399 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1401 /// let mut iter = slice.group_by(|a, b| a == b);
1403 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1404 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1405 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1406 /// assert_eq!(iter.next(), None);
1409 /// This method can be used to extract the sorted subslices:
1412 /// #![feature(slice_group_by)]
1414 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1416 /// let mut iter = slice.group_by(|a, b| a <= b);
1418 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1419 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1420 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1421 /// assert_eq!(iter.next(), None);
1423 #[unstable(feature = "slice_group_by", issue = "80552")]
1425 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1427 F: FnMut(&T, &T) -> bool,
1429 GroupBy::new(self, pred)
1432 /// Returns an iterator over the slice producing non-overlapping mutable
1433 /// runs of elements using the predicate to separate them.
1435 /// The predicate is called on two elements following themselves,
1436 /// it means the predicate is called on `slice[0]` and `slice[1]`
1437 /// then on `slice[1]` and `slice[2]` and so on.
1442 /// #![feature(slice_group_by)]
1444 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1446 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1448 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1449 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1450 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1451 /// assert_eq!(iter.next(), None);
1454 /// This method can be used to extract the sorted subslices:
1457 /// #![feature(slice_group_by)]
1459 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1461 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1463 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1464 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1465 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1466 /// assert_eq!(iter.next(), None);
1468 #[unstable(feature = "slice_group_by", issue = "80552")]
1470 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1472 F: FnMut(&T, &T) -> bool,
1474 GroupByMut::new(self, pred)
1477 /// Divides one slice into two at an index.
1479 /// The first will contain all indices from `[0, mid)` (excluding
1480 /// the index `mid` itself) and the second will contain all
1481 /// indices from `[mid, len)` (excluding the index `len` itself).
1485 /// Panics if `mid > len`.
1490 /// let v = [1, 2, 3, 4, 5, 6];
1493 /// let (left, right) = v.split_at(0);
1494 /// assert_eq!(left, []);
1495 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1499 /// let (left, right) = v.split_at(2);
1500 /// assert_eq!(left, [1, 2]);
1501 /// assert_eq!(right, [3, 4, 5, 6]);
1505 /// let (left, right) = v.split_at(6);
1506 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1507 /// assert_eq!(right, []);
1510 #[stable(feature = "rust1", since = "1.0.0")]
1512 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1513 assert!(mid <= self.len());
1514 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1515 // fulfills the requirements of `from_raw_parts_mut`.
1516 unsafe { self.split_at_unchecked(mid) }
1519 /// Divides one mutable slice into two at an index.
1521 /// The first will contain all indices from `[0, mid)` (excluding
1522 /// the index `mid` itself) and the second will contain all
1523 /// indices from `[mid, len)` (excluding the index `len` itself).
1527 /// Panics if `mid > len`.
1532 /// let mut v = [1, 0, 3, 0, 5, 6];
1533 /// let (left, right) = v.split_at_mut(2);
1534 /// assert_eq!(left, [1, 0]);
1535 /// assert_eq!(right, [3, 0, 5, 6]);
1538 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1540 #[stable(feature = "rust1", since = "1.0.0")]
1542 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1543 assert!(mid <= self.len());
1544 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1545 // fulfills the requirements of `from_raw_parts_mut`.
1546 unsafe { self.split_at_mut_unchecked(mid) }
1549 /// Divides one slice into two at an index, without doing bounds checking.
1551 /// The first will contain all indices from `[0, mid)` (excluding
1552 /// the index `mid` itself) and the second will contain all
1553 /// indices from `[mid, len)` (excluding the index `len` itself).
1555 /// For a safe alternative see [`split_at`].
1559 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1560 /// even if the resulting reference is not used. The caller has to ensure that
1561 /// `0 <= mid <= self.len()`.
1563 /// [`split_at`]: slice::split_at
1564 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1569 /// #![feature(slice_split_at_unchecked)]
1571 /// let v = [1, 2, 3, 4, 5, 6];
1574 /// let (left, right) = v.split_at_unchecked(0);
1575 /// assert_eq!(left, []);
1576 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1580 /// let (left, right) = v.split_at_unchecked(2);
1581 /// assert_eq!(left, [1, 2]);
1582 /// assert_eq!(right, [3, 4, 5, 6]);
1586 /// let (left, right) = v.split_at_unchecked(6);
1587 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1588 /// assert_eq!(right, []);
1591 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1593 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1594 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1595 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1598 /// Divides one mutable slice into two at an index, without doing bounds checking.
1600 /// The first will contain all indices from `[0, mid)` (excluding
1601 /// the index `mid` itself) and the second will contain all
1602 /// indices from `[mid, len)` (excluding the index `len` itself).
1604 /// For a safe alternative see [`split_at_mut`].
1608 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1609 /// even if the resulting reference is not used. The caller has to ensure that
1610 /// `0 <= mid <= self.len()`.
1612 /// [`split_at_mut`]: slice::split_at_mut
1613 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1618 /// #![feature(slice_split_at_unchecked)]
1620 /// let mut v = [1, 0, 3, 0, 5, 6];
1621 /// // scoped to restrict the lifetime of the borrows
1623 /// let (left, right) = v.split_at_mut_unchecked(2);
1624 /// assert_eq!(left, [1, 0]);
1625 /// assert_eq!(right, [3, 0, 5, 6]);
1629 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1631 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1633 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1634 let len = self.len();
1635 let ptr = self.as_mut_ptr();
1637 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1639 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1641 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1644 /// Returns an iterator over subslices separated by elements that match
1645 /// `pred`. The matched element is not contained in the subslices.
1650 /// let slice = [10, 40, 33, 20];
1651 /// let mut iter = slice.split(|num| num % 3 == 0);
1653 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1654 /// assert_eq!(iter.next().unwrap(), &[20]);
1655 /// assert!(iter.next().is_none());
1658 /// If the first element is matched, an empty slice will be the first item
1659 /// returned by the iterator. Similarly, if the last element in the slice
1660 /// is matched, an empty slice will be the last item returned by the
1664 /// let slice = [10, 40, 33];
1665 /// let mut iter = slice.split(|num| num % 3 == 0);
1667 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1668 /// assert_eq!(iter.next().unwrap(), &[]);
1669 /// assert!(iter.next().is_none());
1672 /// If two matched elements are directly adjacent, an empty slice will be
1673 /// present between them:
1676 /// let slice = [10, 6, 33, 20];
1677 /// let mut iter = slice.split(|num| num % 3 == 0);
1679 /// assert_eq!(iter.next().unwrap(), &[10]);
1680 /// assert_eq!(iter.next().unwrap(), &[]);
1681 /// assert_eq!(iter.next().unwrap(), &[20]);
1682 /// assert!(iter.next().is_none());
1684 #[stable(feature = "rust1", since = "1.0.0")]
1686 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1688 F: FnMut(&T) -> bool,
1690 Split::new(self, pred)
1693 /// Returns an iterator over mutable subslices separated by elements that
1694 /// match `pred`. The matched element is not contained in the subslices.
1699 /// let mut v = [10, 40, 30, 20, 60, 50];
1701 /// for group in v.split_mut(|num| *num % 3 == 0) {
1704 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1706 #[stable(feature = "rust1", since = "1.0.0")]
1708 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1710 F: FnMut(&T) -> bool,
1712 SplitMut::new(self, pred)
1715 /// Returns an iterator over subslices separated by elements that match
1716 /// `pred`. The matched element is contained in the end of the previous
1717 /// subslice as a terminator.
1722 /// let slice = [10, 40, 33, 20];
1723 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1725 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1726 /// assert_eq!(iter.next().unwrap(), &[20]);
1727 /// assert!(iter.next().is_none());
1730 /// If the last element of the slice is matched,
1731 /// that element will be considered the terminator of the preceding slice.
1732 /// That slice will be the last item returned by the iterator.
1735 /// let slice = [3, 10, 40, 33];
1736 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1738 /// assert_eq!(iter.next().unwrap(), &[3]);
1739 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1740 /// assert!(iter.next().is_none());
1742 #[stable(feature = "split_inclusive", since = "1.51.0")]
1744 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1746 F: FnMut(&T) -> bool,
1748 SplitInclusive::new(self, pred)
1751 /// Returns an iterator over mutable subslices separated by elements that
1752 /// match `pred`. The matched element is contained in the previous
1753 /// subslice as a terminator.
1758 /// let mut v = [10, 40, 30, 20, 60, 50];
1760 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1761 /// let terminator_idx = group.len()-1;
1762 /// group[terminator_idx] = 1;
1764 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1766 #[stable(feature = "split_inclusive", since = "1.51.0")]
1768 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1770 F: FnMut(&T) -> bool,
1772 SplitInclusiveMut::new(self, pred)
1775 /// Returns an iterator over subslices separated by elements that match
1776 /// `pred`, starting at the end of the slice and working backwards.
1777 /// The matched element is not contained in the subslices.
1782 /// let slice = [11, 22, 33, 0, 44, 55];
1783 /// let mut iter = slice.rsplit(|num| *num == 0);
1785 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1786 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1787 /// assert_eq!(iter.next(), None);
1790 /// As with `split()`, if the first or last element is matched, an empty
1791 /// slice will be the first (or last) item returned by the iterator.
1794 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1795 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1796 /// assert_eq!(it.next().unwrap(), &[]);
1797 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1798 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1799 /// assert_eq!(it.next().unwrap(), &[]);
1800 /// assert_eq!(it.next(), None);
1802 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1804 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1806 F: FnMut(&T) -> bool,
1808 RSplit::new(self, pred)
1811 /// Returns an iterator over mutable subslices separated by elements that
1812 /// match `pred`, starting at the end of the slice and working
1813 /// backwards. The matched element is not contained in the subslices.
1818 /// let mut v = [100, 400, 300, 200, 600, 500];
1820 /// let mut count = 0;
1821 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1823 /// group[0] = count;
1825 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1828 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1830 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1832 F: FnMut(&T) -> bool,
1834 RSplitMut::new(self, pred)
1837 /// Returns an iterator over subslices separated by elements that match
1838 /// `pred`, limited to returning at most `n` items. The matched element is
1839 /// not contained in the subslices.
1841 /// The last element returned, if any, will contain the remainder of the
1846 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1847 /// `[20, 60, 50]`):
1850 /// let v = [10, 40, 30, 20, 60, 50];
1852 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1853 /// println!("{:?}", group);
1856 #[stable(feature = "rust1", since = "1.0.0")]
1858 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1860 F: FnMut(&T) -> bool,
1862 SplitN::new(self.split(pred), n)
1865 /// Returns an iterator over subslices separated by elements that match
1866 /// `pred`, limited to returning at most `n` items. The matched element is
1867 /// not contained in the subslices.
1869 /// The last element returned, if any, will contain the remainder of the
1875 /// let mut v = [10, 40, 30, 20, 60, 50];
1877 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1880 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1882 #[stable(feature = "rust1", since = "1.0.0")]
1884 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1886 F: FnMut(&T) -> bool,
1888 SplitNMut::new(self.split_mut(pred), n)
1891 /// Returns an iterator over subslices separated by elements that match
1892 /// `pred` limited to returning at most `n` items. This starts at the end of
1893 /// the slice and works backwards. The matched element is not contained in
1896 /// The last element returned, if any, will contain the remainder of the
1901 /// Print the slice split once, starting from the end, by numbers divisible
1902 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1905 /// let v = [10, 40, 30, 20, 60, 50];
1907 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1908 /// println!("{:?}", group);
1911 #[stable(feature = "rust1", since = "1.0.0")]
1913 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1915 F: FnMut(&T) -> bool,
1917 RSplitN::new(self.rsplit(pred), n)
1920 /// Returns an iterator over subslices separated by elements that match
1921 /// `pred` limited to returning at most `n` items. This starts at the end of
1922 /// the slice and works backwards. The matched element is not contained in
1925 /// The last element returned, if any, will contain the remainder of the
1931 /// let mut s = [10, 40, 30, 20, 60, 50];
1933 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1936 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1938 #[stable(feature = "rust1", since = "1.0.0")]
1940 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1942 F: FnMut(&T) -> bool,
1944 RSplitNMut::new(self.rsplit_mut(pred), n)
1947 /// Returns `true` if the slice contains an element with the given value.
1952 /// let v = [10, 40, 30];
1953 /// assert!(v.contains(&30));
1954 /// assert!(!v.contains(&50));
1957 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1958 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1961 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1962 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1963 /// assert!(!v.iter().any(|e| e == "hi"));
1965 #[stable(feature = "rust1", since = "1.0.0")]
1967 pub fn contains(&self, x: &T) -> bool
1971 cmp::SliceContains::slice_contains(x, self)
1974 /// Returns `true` if `needle` is a prefix of the slice.
1979 /// let v = [10, 40, 30];
1980 /// assert!(v.starts_with(&[10]));
1981 /// assert!(v.starts_with(&[10, 40]));
1982 /// assert!(!v.starts_with(&[50]));
1983 /// assert!(!v.starts_with(&[10, 50]));
1986 /// Always returns `true` if `needle` is an empty slice:
1989 /// let v = &[10, 40, 30];
1990 /// assert!(v.starts_with(&[]));
1991 /// let v: &[u8] = &[];
1992 /// assert!(v.starts_with(&[]));
1994 #[stable(feature = "rust1", since = "1.0.0")]
1995 pub fn starts_with(&self, needle: &[T]) -> bool
1999 let n = needle.len();
2000 self.len() >= n && needle == &self[..n]
2003 /// Returns `true` if `needle` is a suffix of the slice.
2008 /// let v = [10, 40, 30];
2009 /// assert!(v.ends_with(&[30]));
2010 /// assert!(v.ends_with(&[40, 30]));
2011 /// assert!(!v.ends_with(&[50]));
2012 /// assert!(!v.ends_with(&[50, 30]));
2015 /// Always returns `true` if `needle` is an empty slice:
2018 /// let v = &[10, 40, 30];
2019 /// assert!(v.ends_with(&[]));
2020 /// let v: &[u8] = &[];
2021 /// assert!(v.ends_with(&[]));
2023 #[stable(feature = "rust1", since = "1.0.0")]
2024 pub fn ends_with(&self, needle: &[T]) -> bool
2028 let (m, n) = (self.len(), needle.len());
2029 m >= n && needle == &self[m - n..]
2032 /// Returns a subslice with the prefix removed.
2034 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2035 /// If `prefix` is empty, simply returns the original slice.
2037 /// If the slice does not start with `prefix`, returns `None`.
2042 /// let v = &[10, 40, 30];
2043 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2044 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2045 /// assert_eq!(v.strip_prefix(&[50]), None);
2046 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2048 /// let prefix : &str = "he";
2049 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2050 /// Some(b"llo".as_ref()));
2052 #[must_use = "returns the subslice without modifying the original"]
2053 #[stable(feature = "slice_strip", since = "1.51.0")]
2054 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2058 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2059 let prefix = prefix.as_slice();
2060 let n = prefix.len();
2061 if n <= self.len() {
2062 let (head, tail) = self.split_at(n);
2070 /// Returns a subslice with the suffix removed.
2072 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2073 /// If `suffix` is empty, simply returns the original slice.
2075 /// If the slice does not end with `suffix`, returns `None`.
2080 /// let v = &[10, 40, 30];
2081 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2082 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2083 /// assert_eq!(v.strip_suffix(&[50]), None);
2084 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2086 #[must_use = "returns the subslice without modifying the original"]
2087 #[stable(feature = "slice_strip", since = "1.51.0")]
2088 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2092 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2093 let suffix = suffix.as_slice();
2094 let (len, n) = (self.len(), suffix.len());
2096 let (head, tail) = self.split_at(len - n);
2104 /// Binary searches this sorted slice for a given element.
2106 /// If the value is found then [`Result::Ok`] is returned, containing the
2107 /// index of the matching element. If there are multiple matches, then any
2108 /// one of the matches could be returned. If the value is not found then
2109 /// [`Result::Err`] is returned, containing the index where a matching
2110 /// element could be inserted while maintaining sorted order.
2112 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2114 /// [`binary_search_by`]: slice::binary_search_by
2115 /// [`binary_search_by_key`]: slice::binary_search_by_key
2116 /// [`partition_point`]: slice::partition_point
2120 /// Looks up a series of four elements. The first is found, with a
2121 /// uniquely determined position; the second and third are not
2122 /// found; the fourth could match any position in `[1, 4]`.
2125 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2127 /// assert_eq!(s.binary_search(&13), Ok(9));
2128 /// assert_eq!(s.binary_search(&4), Err(7));
2129 /// assert_eq!(s.binary_search(&100), Err(13));
2130 /// let r = s.binary_search(&1);
2131 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2134 /// If you want to insert an item to a sorted vector, while maintaining
2138 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2140 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2141 /// s.insert(idx, num);
2142 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2144 #[stable(feature = "rust1", since = "1.0.0")]
2145 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2149 self.binary_search_by(|p| p.cmp(x))
2152 /// Binary searches this sorted slice with a comparator function.
2154 /// The comparator function should implement an order consistent
2155 /// with the sort order of the underlying slice, returning an
2156 /// order code that indicates whether its argument is `Less`,
2157 /// `Equal` or `Greater` the desired target.
2159 /// If the value is found then [`Result::Ok`] is returned, containing the
2160 /// index of the matching element. If there are multiple matches, then any
2161 /// one of the matches could be returned. If the value is not found then
2162 /// [`Result::Err`] is returned, containing the index where a matching
2163 /// element could be inserted while maintaining sorted order.
2165 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2167 /// [`binary_search`]: slice::binary_search
2168 /// [`binary_search_by_key`]: slice::binary_search_by_key
2169 /// [`partition_point`]: slice::partition_point
2173 /// Looks up a series of four elements. The first is found, with a
2174 /// uniquely determined position; the second and third are not
2175 /// found; the fourth could match any position in `[1, 4]`.
2178 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2181 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2183 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2185 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2187 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2188 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2190 #[stable(feature = "rust1", since = "1.0.0")]
2192 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2194 F: FnMut(&'a T) -> Ordering,
2196 let mut size = self.len();
2198 let mut right = size;
2199 while left < right {
2200 let mid = left + size / 2;
2202 // SAFETY: the call is made safe by the following invariants:
2204 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2205 let cmp = f(unsafe { self.get_unchecked(mid) });
2207 // The reason why we use if/else control flow rather than match
2208 // is because match reorders comparison operations, which is perf sensitive.
2209 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2212 } else if cmp == Greater {
2218 size = right - left;
2223 /// Binary searches this sorted slice with a key extraction function.
2225 /// Assumes that the slice is sorted by the key, for instance with
2226 /// [`sort_by_key`] using the same key extraction function.
2228 /// If the value is found then [`Result::Ok`] is returned, containing the
2229 /// index of the matching element. If there are multiple matches, then any
2230 /// one of the matches could be returned. If the value is not found then
2231 /// [`Result::Err`] is returned, containing the index where a matching
2232 /// element could be inserted while maintaining sorted order.
2234 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2236 /// [`sort_by_key`]: slice::sort_by_key
2237 /// [`binary_search`]: slice::binary_search
2238 /// [`binary_search_by`]: slice::binary_search_by
2239 /// [`partition_point`]: slice::partition_point
2243 /// Looks up a series of four elements in a slice of pairs sorted by
2244 /// their second elements. The first is found, with a uniquely
2245 /// determined position; the second and third are not found; the
2246 /// fourth could match any position in `[1, 4]`.
2249 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2250 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2251 /// (1, 21), (2, 34), (4, 55)];
2253 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2254 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2255 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2256 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2257 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2259 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2260 // in crate `alloc`, and as such doesn't exists yet when building `core`.
2261 // links to downstream crate: #74481. Since primitives are only documented in
2262 // libstd (#73423), this never leads to broken links in practice.
2263 #[cfg_attr(not(bootstrap), allow(rustdoc::broken_intra_doc_links))]
2264 #[cfg_attr(bootstrap, allow(broken_intra_doc_links))]
2265 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2267 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2269 F: FnMut(&'a T) -> B,
2272 self.binary_search_by(|k| f(k).cmp(b))
2275 /// Sorts the slice, but may not preserve the order of equal elements.
2277 /// This sort is unstable (i.e., may reorder equal elements), in-place
2278 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2280 /// # Current implementation
2282 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2283 /// which combines the fast average case of randomized quicksort with the fast worst case of
2284 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2285 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2286 /// deterministic behavior.
2288 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2289 /// slice consists of several concatenated sorted sequences.
2294 /// let mut v = [-5, 4, 1, -3, 2];
2296 /// v.sort_unstable();
2297 /// assert!(v == [-5, -3, 1, 2, 4]);
2300 /// [pdqsort]: https://github.com/orlp/pdqsort
2301 #[stable(feature = "sort_unstable", since = "1.20.0")]
2303 pub fn sort_unstable(&mut self)
2307 sort::quicksort(self, |a, b| a.lt(b));
2310 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2313 /// This sort is unstable (i.e., may reorder equal elements), in-place
2314 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2316 /// The comparator function must define a total ordering for the elements in the slice. If
2317 /// the ordering is not total, the order of the elements is unspecified. An order is a
2318 /// total order if it is (for all `a`, `b` and `c`):
2320 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2321 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2323 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2324 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2327 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2328 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2329 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2332 /// # Current implementation
2334 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2335 /// which combines the fast average case of randomized quicksort with the fast worst case of
2336 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2337 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2338 /// deterministic behavior.
2340 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2341 /// slice consists of several concatenated sorted sequences.
2346 /// let mut v = [5, 4, 1, 3, 2];
2347 /// v.sort_unstable_by(|a, b| a.cmp(b));
2348 /// assert!(v == [1, 2, 3, 4, 5]);
2350 /// // reverse sorting
2351 /// v.sort_unstable_by(|a, b| b.cmp(a));
2352 /// assert!(v == [5, 4, 3, 2, 1]);
2355 /// [pdqsort]: https://github.com/orlp/pdqsort
2356 #[stable(feature = "sort_unstable", since = "1.20.0")]
2358 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2360 F: FnMut(&T, &T) -> Ordering,
2362 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2365 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2368 /// This sort is unstable (i.e., may reorder equal elements), in-place
2369 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2372 /// # Current implementation
2374 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2375 /// which combines the fast average case of randomized quicksort with the fast worst case of
2376 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2377 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2378 /// deterministic behavior.
2380 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2381 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2382 /// cases where the key function is expensive.
2387 /// let mut v = [-5i32, 4, 1, -3, 2];
2389 /// v.sort_unstable_by_key(|k| k.abs());
2390 /// assert!(v == [1, 2, -3, 4, -5]);
2393 /// [pdqsort]: https://github.com/orlp/pdqsort
2394 #[stable(feature = "sort_unstable", since = "1.20.0")]
2396 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2401 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2404 /// Reorder the slice such that the element at `index` is at its final sorted position.
2405 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2406 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2408 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2412 self.select_nth_unstable(index)
2415 /// Reorder the slice with a comparator function such that the element at `index` is at its
2416 /// final sorted position.
2417 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2418 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2420 pub fn partition_at_index_by<F>(
2424 ) -> (&mut [T], &mut T, &mut [T])
2426 F: FnMut(&T, &T) -> Ordering,
2428 self.select_nth_unstable_by(index, compare)
2431 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2432 /// final sorted position.
2433 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2434 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2436 pub fn partition_at_index_by_key<K, F>(
2440 ) -> (&mut [T], &mut T, &mut [T])
2445 self.select_nth_unstable_by_key(index, f)
2448 /// Reorder the slice such that the element at `index` is at its final sorted position.
2450 /// This reordering has the additional property that any value at position `i < index` will be
2451 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2452 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2453 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2454 /// element" in other libraries. It returns a triplet of the following values: all elements less
2455 /// than the one at the given index, the value at the given index, and all elements greater than
2456 /// the one at the given index.
2458 /// # Current implementation
2460 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2461 /// used for [`sort_unstable`].
2463 /// [`sort_unstable`]: slice::sort_unstable
2467 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2472 /// let mut v = [-5i32, 4, 1, -3, 2];
2474 /// // Find the median
2475 /// v.select_nth_unstable(2);
2477 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2478 /// // about the specified index.
2479 /// assert!(v == [-3, -5, 1, 2, 4] ||
2480 /// v == [-5, -3, 1, 2, 4] ||
2481 /// v == [-3, -5, 1, 4, 2] ||
2482 /// v == [-5, -3, 1, 4, 2]);
2484 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2486 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2490 let mut f = |a: &T, b: &T| a.lt(b);
2491 sort::partition_at_index(self, index, &mut f)
2494 /// Reorder the slice with a comparator function such that the element at `index` is at its
2495 /// final sorted position.
2497 /// This reordering has the additional property that any value at position `i < index` will be
2498 /// less than or equal to any value at a position `j > index` using the comparator function.
2499 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2500 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2501 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2502 /// values: all elements less than the one at the given index, the value at the given index,
2503 /// and all elements greater than the one at the given index, using the provided comparator
2506 /// # Current implementation
2508 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2509 /// used for [`sort_unstable`].
2511 /// [`sort_unstable`]: slice::sort_unstable
2515 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2520 /// let mut v = [-5i32, 4, 1, -3, 2];
2522 /// // Find the median as if the slice were sorted in descending order.
2523 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2525 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2526 /// // about the specified index.
2527 /// assert!(v == [2, 4, 1, -5, -3] ||
2528 /// v == [2, 4, 1, -3, -5] ||
2529 /// v == [4, 2, 1, -5, -3] ||
2530 /// v == [4, 2, 1, -3, -5]);
2532 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2534 pub fn select_nth_unstable_by<F>(
2538 ) -> (&mut [T], &mut T, &mut [T])
2540 F: FnMut(&T, &T) -> Ordering,
2542 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2543 sort::partition_at_index(self, index, &mut f)
2546 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2547 /// final sorted position.
2549 /// This reordering has the additional property that any value at position `i < index` will be
2550 /// less than or equal to any value at a position `j > index` using the key extraction function.
2551 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2552 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2553 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2554 /// values: all elements less than the one at the given index, the value at the given index, and
2555 /// all elements greater than the one at the given index, using the provided key extraction
2558 /// # Current implementation
2560 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2561 /// used for [`sort_unstable`].
2563 /// [`sort_unstable`]: slice::sort_unstable
2567 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2572 /// let mut v = [-5i32, 4, 1, -3, 2];
2574 /// // Return the median as if the array were sorted according to absolute value.
2575 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2577 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2578 /// // about the specified index.
2579 /// assert!(v == [1, 2, -3, 4, -5] ||
2580 /// v == [1, 2, -3, -5, 4] ||
2581 /// v == [2, 1, -3, 4, -5] ||
2582 /// v == [2, 1, -3, -5, 4]);
2584 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2586 pub fn select_nth_unstable_by_key<K, F>(
2590 ) -> (&mut [T], &mut T, &mut [T])
2595 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2596 sort::partition_at_index(self, index, &mut g)
2599 /// Moves all consecutive repeated elements to the end of the slice according to the
2600 /// [`PartialEq`] trait implementation.
2602 /// Returns two slices. The first contains no consecutive repeated elements.
2603 /// The second contains all the duplicates in no specified order.
2605 /// If the slice is sorted, the first returned slice contains no duplicates.
2610 /// #![feature(slice_partition_dedup)]
2612 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2614 /// let (dedup, duplicates) = slice.partition_dedup();
2616 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2617 /// assert_eq!(duplicates, [2, 3, 1]);
2619 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2621 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2625 self.partition_dedup_by(|a, b| a == b)
2628 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2629 /// a given equality relation.
2631 /// Returns two slices. The first contains no consecutive repeated elements.
2632 /// The second contains all the duplicates in no specified order.
2634 /// The `same_bucket` function is passed references to two elements from the slice and
2635 /// must determine if the elements compare equal. The elements are passed in opposite order
2636 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2637 /// at the end of the slice.
2639 /// If the slice is sorted, the first returned slice contains no duplicates.
2644 /// #![feature(slice_partition_dedup)]
2646 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2648 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2650 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2651 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2653 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2655 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2657 F: FnMut(&mut T, &mut T) -> bool,
2659 // Although we have a mutable reference to `self`, we cannot make
2660 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2661 // must ensure that the slice is in a valid state at all times.
2663 // The way that we handle this is by using swaps; we iterate
2664 // over all the elements, swapping as we go so that at the end
2665 // the elements we wish to keep are in the front, and those we
2666 // wish to reject are at the back. We can then split the slice.
2667 // This operation is still `O(n)`.
2669 // Example: We start in this state, where `r` represents "next
2670 // read" and `w` represents "next_write`.
2673 // +---+---+---+---+---+---+
2674 // | 0 | 1 | 1 | 2 | 3 | 3 |
2675 // +---+---+---+---+---+---+
2678 // Comparing self[r] against self[w-1], this is not a duplicate, so
2679 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2680 // r and w, leaving us with:
2683 // +---+---+---+---+---+---+
2684 // | 0 | 1 | 1 | 2 | 3 | 3 |
2685 // +---+---+---+---+---+---+
2688 // Comparing self[r] against self[w-1], this value is a duplicate,
2689 // so we increment `r` but leave everything else unchanged:
2692 // +---+---+---+---+---+---+
2693 // | 0 | 1 | 1 | 2 | 3 | 3 |
2694 // +---+---+---+---+---+---+
2697 // Comparing self[r] against self[w-1], this is not a duplicate,
2698 // so swap self[r] and self[w] and advance r and w:
2701 // +---+---+---+---+---+---+
2702 // | 0 | 1 | 2 | 1 | 3 | 3 |
2703 // +---+---+---+---+---+---+
2706 // Not a duplicate, repeat:
2709 // +---+---+---+---+---+---+
2710 // | 0 | 1 | 2 | 3 | 1 | 3 |
2711 // +---+---+---+---+---+---+
2714 // Duplicate, advance r. End of slice. Split at w.
2716 let len = self.len();
2718 return (self, &mut []);
2721 let ptr = self.as_mut_ptr();
2722 let mut next_read: usize = 1;
2723 let mut next_write: usize = 1;
2725 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2726 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2727 // one element before `ptr_write`, but `next_write` starts at 1, so
2728 // `prev_ptr_write` is never less than 0 and is inside the slice.
2729 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2730 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2731 // and `prev_ptr_write.offset(1)`.
2733 // `next_write` is also incremented at most once per loop at most meaning
2734 // no element is skipped when it may need to be swapped.
2736 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2737 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2738 // The explanation is simply that `next_read >= next_write` is always true,
2739 // thus `next_read > next_write - 1` is too.
2741 // Avoid bounds checks by using raw pointers.
2742 while next_read < len {
2743 let ptr_read = ptr.add(next_read);
2744 let prev_ptr_write = ptr.add(next_write - 1);
2745 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2746 if next_read != next_write {
2747 let ptr_write = prev_ptr_write.offset(1);
2748 mem::swap(&mut *ptr_read, &mut *ptr_write);
2756 self.split_at_mut(next_write)
2759 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2760 /// to the same key.
2762 /// Returns two slices. The first contains no consecutive repeated elements.
2763 /// The second contains all the duplicates in no specified order.
2765 /// If the slice is sorted, the first returned slice contains no duplicates.
2770 /// #![feature(slice_partition_dedup)]
2772 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2774 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2776 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2777 /// assert_eq!(duplicates, [21, 30, 13]);
2779 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2781 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2783 F: FnMut(&mut T) -> K,
2786 self.partition_dedup_by(|a, b| key(a) == key(b))
2789 /// Rotates the slice in-place such that the first `mid` elements of the
2790 /// slice move to the end while the last `self.len() - mid` elements move to
2791 /// the front. After calling `rotate_left`, the element previously at index
2792 /// `mid` will become the first element in the slice.
2796 /// This function will panic if `mid` is greater than the length of the
2797 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2802 /// Takes linear (in `self.len()`) time.
2807 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2808 /// a.rotate_left(2);
2809 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2812 /// Rotating a subslice:
2815 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2816 /// a[1..5].rotate_left(1);
2817 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2819 #[stable(feature = "slice_rotate", since = "1.26.0")]
2820 pub fn rotate_left(&mut self, mid: usize) {
2821 assert!(mid <= self.len());
2822 let k = self.len() - mid;
2823 let p = self.as_mut_ptr();
2825 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2826 // valid for reading and writing, as required by `ptr_rotate`.
2828 rotate::ptr_rotate(mid, p.add(mid), k);
2832 /// Rotates the slice in-place such that the first `self.len() - k`
2833 /// elements of the slice move to the end while the last `k` elements move
2834 /// to the front. After calling `rotate_right`, the element previously at
2835 /// index `self.len() - k` will become the first element in the slice.
2839 /// This function will panic if `k` is greater than the length of the
2840 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2845 /// Takes linear (in `self.len()`) time.
2850 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2851 /// a.rotate_right(2);
2852 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2855 /// Rotate a subslice:
2858 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2859 /// a[1..5].rotate_right(1);
2860 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2862 #[stable(feature = "slice_rotate", since = "1.26.0")]
2863 pub fn rotate_right(&mut self, k: usize) {
2864 assert!(k <= self.len());
2865 let mid = self.len() - k;
2866 let p = self.as_mut_ptr();
2868 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2869 // valid for reading and writing, as required by `ptr_rotate`.
2871 rotate::ptr_rotate(mid, p.add(mid), k);
2875 /// Fills `self` with elements by cloning `value`.
2880 /// let mut buf = vec![0; 10];
2882 /// assert_eq!(buf, vec![1; 10]);
2884 #[doc(alias = "memset")]
2885 #[stable(feature = "slice_fill", since = "1.50.0")]
2886 pub fn fill(&mut self, value: T)
2890 specialize::SpecFill::spec_fill(self, value);
2893 /// Fills `self` with elements returned by calling a closure repeatedly.
2895 /// This method uses a closure to create new values. If you'd rather
2896 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2897 /// trait to generate values, you can pass [`Default::default`] as the
2900 /// [`fill`]: slice::fill
2905 /// let mut buf = vec![1; 10];
2906 /// buf.fill_with(Default::default);
2907 /// assert_eq!(buf, vec![0; 10]);
2909 #[doc(alias = "memset")]
2910 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2911 pub fn fill_with<F>(&mut self, mut f: F)
2920 /// Copies the elements from `src` into `self`.
2922 /// The length of `src` must be the same as `self`.
2924 /// If `T` implements `Copy`, it can be more performant to use
2925 /// [`copy_from_slice`].
2929 /// This function will panic if the two slices have different lengths.
2933 /// Cloning two elements from a slice into another:
2936 /// let src = [1, 2, 3, 4];
2937 /// let mut dst = [0, 0];
2939 /// // Because the slices have to be the same length,
2940 /// // we slice the source slice from four elements
2941 /// // to two. It will panic if we don't do this.
2942 /// dst.clone_from_slice(&src[2..]);
2944 /// assert_eq!(src, [1, 2, 3, 4]);
2945 /// assert_eq!(dst, [3, 4]);
2948 /// Rust enforces that there can only be one mutable reference with no
2949 /// immutable references to a particular piece of data in a particular
2950 /// scope. Because of this, attempting to use `clone_from_slice` on a
2951 /// single slice will result in a compile failure:
2954 /// let mut slice = [1, 2, 3, 4, 5];
2956 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2959 /// To work around this, we can use [`split_at_mut`] to create two distinct
2960 /// sub-slices from a slice:
2963 /// let mut slice = [1, 2, 3, 4, 5];
2966 /// let (left, right) = slice.split_at_mut(2);
2967 /// left.clone_from_slice(&right[1..]);
2970 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2973 /// [`copy_from_slice`]: slice::copy_from_slice
2974 /// [`split_at_mut`]: slice::split_at_mut
2975 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2976 pub fn clone_from_slice(&mut self, src: &[T])
2980 self.spec_clone_from(src);
2983 /// Copies all elements from `src` into `self`, using a memcpy.
2985 /// The length of `src` must be the same as `self`.
2987 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2991 /// This function will panic if the two slices have different lengths.
2995 /// Copying two elements from a slice into another:
2998 /// let src = [1, 2, 3, 4];
2999 /// let mut dst = [0, 0];
3001 /// // Because the slices have to be the same length,
3002 /// // we slice the source slice from four elements
3003 /// // to two. It will panic if we don't do this.
3004 /// dst.copy_from_slice(&src[2..]);
3006 /// assert_eq!(src, [1, 2, 3, 4]);
3007 /// assert_eq!(dst, [3, 4]);
3010 /// Rust enforces that there can only be one mutable reference with no
3011 /// immutable references to a particular piece of data in a particular
3012 /// scope. Because of this, attempting to use `copy_from_slice` on a
3013 /// single slice will result in a compile failure:
3016 /// let mut slice = [1, 2, 3, 4, 5];
3018 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3021 /// To work around this, we can use [`split_at_mut`] to create two distinct
3022 /// sub-slices from a slice:
3025 /// let mut slice = [1, 2, 3, 4, 5];
3028 /// let (left, right) = slice.split_at_mut(2);
3029 /// left.copy_from_slice(&right[1..]);
3032 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3035 /// [`clone_from_slice`]: slice::clone_from_slice
3036 /// [`split_at_mut`]: slice::split_at_mut
3037 #[doc(alias = "memcpy")]
3038 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3039 pub fn copy_from_slice(&mut self, src: &[T])
3043 // The panic code path was put into a cold function to not bloat the
3048 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3050 "source slice length ({}) does not match destination slice length ({})",
3055 if self.len() != src.len() {
3056 len_mismatch_fail(self.len(), src.len());
3059 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3060 // checked to have the same length. The slices cannot overlap because
3061 // mutable references are exclusive.
3063 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3067 /// Copies elements from one part of the slice to another part of itself,
3068 /// using a memmove.
3070 /// `src` is the range within `self` to copy from. `dest` is the starting
3071 /// index of the range within `self` to copy to, which will have the same
3072 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3073 /// must be less than or equal to `self.len()`.
3077 /// This function will panic if either range exceeds the end of the slice,
3078 /// or if the end of `src` is before the start.
3082 /// Copying four bytes within a slice:
3085 /// let mut bytes = *b"Hello, World!";
3087 /// bytes.copy_within(1..5, 8);
3089 /// assert_eq!(&bytes, b"Hello, Wello!");
3091 #[stable(feature = "copy_within", since = "1.37.0")]
3093 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3097 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3098 let count = src_end - src_start;
3099 assert!(dest <= self.len() - count, "dest is out of bounds");
3100 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3101 // as have those for `ptr::add`.
3103 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3107 /// Swaps all elements in `self` with those in `other`.
3109 /// The length of `other` must be the same as `self`.
3113 /// This function will panic if the two slices have different lengths.
3117 /// Swapping two elements across slices:
3120 /// let mut slice1 = [0, 0];
3121 /// let mut slice2 = [1, 2, 3, 4];
3123 /// slice1.swap_with_slice(&mut slice2[2..]);
3125 /// assert_eq!(slice1, [3, 4]);
3126 /// assert_eq!(slice2, [1, 2, 0, 0]);
3129 /// Rust enforces that there can only be one mutable reference to a
3130 /// particular piece of data in a particular scope. Because of this,
3131 /// attempting to use `swap_with_slice` on a single slice will result in
3132 /// a compile failure:
3135 /// let mut slice = [1, 2, 3, 4, 5];
3136 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3139 /// To work around this, we can use [`split_at_mut`] to create two distinct
3140 /// mutable sub-slices from a slice:
3143 /// let mut slice = [1, 2, 3, 4, 5];
3146 /// let (left, right) = slice.split_at_mut(2);
3147 /// left.swap_with_slice(&mut right[1..]);
3150 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3153 /// [`split_at_mut`]: slice::split_at_mut
3154 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3155 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3156 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3157 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3158 // checked to have the same length. The slices cannot overlap because
3159 // mutable references are exclusive.
3161 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3165 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3166 fn align_to_offsets<U>(&self) -> (usize, usize) {
3167 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3168 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3170 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3171 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3172 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3174 // Formula to calculate this is:
3176 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3177 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3179 // Expanded and simplified:
3181 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3182 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3184 // Luckily since all this is constant-evaluated... performance here matters not!
3186 fn gcd(a: usize, b: usize) -> usize {
3187 use crate::intrinsics;
3188 // iterative stein’s algorithm
3189 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3190 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3192 // SAFETY: `a` and `b` are checked to be non-zero values.
3193 let (ctz_a, mut ctz_b) = unsafe {
3200 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3202 let k = ctz_a.min(ctz_b);
3203 let mut a = a >> ctz_a;
3206 // remove all factors of 2 from b
3209 mem::swap(&mut a, &mut b);
3212 // SAFETY: `b` is checked to be non-zero.
3217 ctz_b = intrinsics::cttz_nonzero(b);
3222 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3223 let ts: usize = mem::size_of::<U>() / gcd;
3224 let us: usize = mem::size_of::<T>() / gcd;
3226 // Armed with this knowledge, we can find how many `U`s we can fit!
3227 let us_len = self.len() / ts * us;
3228 // And how many `T`s will be in the trailing slice!
3229 let ts_len = self.len() % ts;
3233 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3236 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3237 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3238 /// length possible for a given type and input slice, but only your algorithm's performance
3239 /// should depend on that, not its correctness. It is permissible for all of the input data to
3240 /// be returned as the prefix or suffix slice.
3242 /// This method has no purpose when either input element `T` or output element `U` are
3243 /// zero-sized and will return the original slice without splitting anything.
3247 /// This method is essentially a `transmute` with respect to the elements in the returned
3248 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3256 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3257 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3258 /// // less_efficient_algorithm_for_bytes(prefix);
3259 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3260 /// // less_efficient_algorithm_for_bytes(suffix);
3263 #[stable(feature = "slice_align_to", since = "1.30.0")]
3264 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3265 // Note that most of this function will be constant-evaluated,
3266 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3267 // handle ZSTs specially, which is – don't handle them at all.
3268 return (self, &[], &[]);
3271 // First, find at what point do we split between the first and 2nd slice. Easy with
3272 // ptr.align_offset.
3273 let ptr = self.as_ptr();
3274 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3275 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3276 if offset > self.len() {
3279 let (left, rest) = self.split_at(offset);
3280 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3281 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3282 // since the caller guarantees that we can transmute `T` to `U` safely.
3286 from_raw_parts(rest.as_ptr() as *const U, us_len),
3287 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3293 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3296 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3297 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3298 /// length possible for a given type and input slice, but only your algorithm's performance
3299 /// should depend on that, not its correctness. It is permissible for all of the input data to
3300 /// be returned as the prefix or suffix slice.
3302 /// This method has no purpose when either input element `T` or output element `U` are
3303 /// zero-sized and will return the original slice without splitting anything.
3307 /// This method is essentially a `transmute` with respect to the elements in the returned
3308 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3316 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3317 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3318 /// // less_efficient_algorithm_for_bytes(prefix);
3319 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3320 /// // less_efficient_algorithm_for_bytes(suffix);
3323 #[stable(feature = "slice_align_to", since = "1.30.0")]
3324 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3325 // Note that most of this function will be constant-evaluated,
3326 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3327 // handle ZSTs specially, which is – don't handle them at all.
3328 return (self, &mut [], &mut []);
3331 // First, find at what point do we split between the first and 2nd slice. Easy with
3332 // ptr.align_offset.
3333 let ptr = self.as_ptr();
3334 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3335 // rest of the method. This is done by passing a pointer to &[T] with an
3336 // alignment targeted for U.
3337 // `crate::ptr::align_offset` is called with a correctly aligned and
3338 // valid pointer `ptr` (it comes from a reference to `self`) and with
3339 // a size that is a power of two (since it comes from the alignement for U),
3340 // satisfying its safety constraints.
3341 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3342 if offset > self.len() {
3343 (self, &mut [], &mut [])
3345 let (left, rest) = self.split_at_mut(offset);
3346 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3347 let rest_len = rest.len();
3348 let mut_ptr = rest.as_mut_ptr();
3349 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3350 // SAFETY: see comments for `align_to`.
3354 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3355 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3361 /// Checks if the elements of this slice are sorted.
3363 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3364 /// slice yields exactly zero or one element, `true` is returned.
3366 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3367 /// implies that this function returns `false` if any two consecutive items are not
3373 /// #![feature(is_sorted)]
3374 /// let empty: [i32; 0] = [];
3376 /// assert!([1, 2, 2, 9].is_sorted());
3377 /// assert!(![1, 3, 2, 4].is_sorted());
3378 /// assert!([0].is_sorted());
3379 /// assert!(empty.is_sorted());
3380 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3383 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3384 pub fn is_sorted(&self) -> bool
3388 self.is_sorted_by(|a, b| a.partial_cmp(b))
3391 /// Checks if the elements of this slice are sorted using the given comparator function.
3393 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3394 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3395 /// [`is_sorted`]; see its documentation for more information.
3397 /// [`is_sorted`]: slice::is_sorted
3398 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3399 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3401 F: FnMut(&T, &T) -> Option<Ordering>,
3403 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3406 /// Checks if the elements of this slice are sorted using the given key extraction function.
3408 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3409 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3410 /// documentation for more information.
3412 /// [`is_sorted`]: slice::is_sorted
3417 /// #![feature(is_sorted)]
3419 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3420 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3423 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3424 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3429 self.iter().is_sorted_by_key(f)
3432 /// Returns the index of the partition point according to the given predicate
3433 /// (the index of the first element of the second partition).
3435 /// The slice is assumed to be partitioned according to the given predicate.
3436 /// This means that all elements for which the predicate returns true are at the start of the slice
3437 /// and all elements for which the predicate returns false are at the end.
3438 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3439 /// (all odd numbers are at the start, all even at the end).
3441 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3442 /// as this method performs a kind of binary search.
3444 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3446 /// [`binary_search`]: slice::binary_search
3447 /// [`binary_search_by`]: slice::binary_search_by
3448 /// [`binary_search_by_key`]: slice::binary_search_by_key
3453 /// let v = [1, 2, 3, 3, 5, 6, 7];
3454 /// let i = v.partition_point(|&x| x < 5);
3456 /// assert_eq!(i, 4);
3457 /// assert!(v[..i].iter().all(|&x| x < 5));
3458 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3460 #[stable(feature = "partition_point", since = "1.52.0")]
3461 pub fn partition_point<P>(&self, mut pred: P) -> usize
3463 P: FnMut(&T) -> bool,
3466 let mut right = self.len();
3468 while left != right {
3469 let mid = left + (right - left) / 2;
3470 // SAFETY: When `left < right`, `left <= mid < right`.
3471 // Therefore `left` always increases and `right` always decreases,
3472 // and either of them is selected. In both cases `left <= right` is
3473 // satisfied. Therefore if `left < right` in a step, `left <= right`
3474 // is satisfied in the next step. Therefore as long as `left != right`,
3475 // `0 <= left < right <= len` is satisfied and if this case
3476 // `0 <= mid < len` is satisfied too.
3477 let value = unsafe { self.get_unchecked(mid) };
3489 trait CloneFromSpec<T> {
3490 fn spec_clone_from(&mut self, src: &[T]);
3493 impl<T> CloneFromSpec<T> for [T]
3497 default fn spec_clone_from(&mut self, src: &[T]) {
3498 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3499 // NOTE: We need to explicitly slice them to the same length
3500 // to make it easier for the optimizer to elide bounds checking.
3501 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3502 let len = self.len();
3503 let src = &src[..len];
3505 self[i].clone_from(&src[i]);
3510 impl<T> CloneFromSpec<T> for [T]
3514 fn spec_clone_from(&mut self, src: &[T]) {
3515 self.copy_from_slice(src);
3519 #[stable(feature = "rust1", since = "1.0.0")]
3520 impl<T> Default for &[T] {
3521 /// Creates an empty slice.
3522 fn default() -> Self {
3527 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3528 impl<T> Default for &mut [T] {
3529 /// Creates a mutable empty slice.
3530 fn default() -> Self {
3535 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3536 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3537 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3538 /// `str`) to slices, and then this trait will be replaced or abolished.
3539 pub trait SlicePattern {
3540 /// The element type of the slice being matched on.
3543 /// Currently, the consumers of `SlicePattern` need a slice.
3544 fn as_slice(&self) -> &[Self::Item];
3547 #[stable(feature = "slice_strip", since = "1.51.0")]
3548 impl<T> SlicePattern for [T] {
3552 fn as_slice(&self) -> &[Self::Item] {
3557 #[stable(feature = "slice_strip", since = "1.51.0")]
3558 impl<T, const N: usize> SlicePattern for [T; N] {
3562 fn as_slice(&self) -> &[Self::Item] {