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 = "1.32.0")]
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 = "1.32.0")]
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")]
149 pub fn first(&self) -> Option<&T> {
150 if let [first, ..] = self { Some(first) } else { None }
153 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
158 /// let x = &mut [0, 1, 2];
160 /// if let Some(first) = x.first_mut() {
163 /// assert_eq!(x, &[5, 1, 2]);
165 #[stable(feature = "rust1", since = "1.0.0")]
167 pub fn first_mut(&mut self) -> Option<&mut T> {
168 if let [first, ..] = self { Some(first) } else { None }
171 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
176 /// let x = &[0, 1, 2];
178 /// if let Some((first, elements)) = x.split_first() {
179 /// assert_eq!(first, &0);
180 /// assert_eq!(elements, &[1, 2]);
183 #[stable(feature = "slice_splits", since = "1.5.0")]
185 pub fn split_first(&self) -> Option<(&T, &[T])> {
186 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
189 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
194 /// let x = &mut [0, 1, 2];
196 /// if let Some((first, elements)) = x.split_first_mut() {
201 /// assert_eq!(x, &[3, 4, 5]);
203 #[stable(feature = "slice_splits", since = "1.5.0")]
205 pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
206 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
209 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
214 /// let x = &[0, 1, 2];
216 /// if let Some((last, elements)) = x.split_last() {
217 /// assert_eq!(last, &2);
218 /// assert_eq!(elements, &[0, 1]);
221 #[stable(feature = "slice_splits", since = "1.5.0")]
223 pub fn split_last(&self) -> Option<(&T, &[T])> {
224 if let [init @ .., last] = self { Some((last, init)) } else { None }
227 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
232 /// let x = &mut [0, 1, 2];
234 /// if let Some((last, elements)) = x.split_last_mut() {
239 /// assert_eq!(x, &[4, 5, 3]);
241 #[stable(feature = "slice_splits", since = "1.5.0")]
243 pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
244 if let [init @ .., last] = self { Some((last, init)) } else { None }
247 /// Returns the last element of the slice, or `None` if it is empty.
252 /// let v = [10, 40, 30];
253 /// assert_eq!(Some(&30), v.last());
255 /// let w: &[i32] = &[];
256 /// assert_eq!(None, w.last());
258 #[stable(feature = "rust1", since = "1.0.0")]
260 pub fn last(&self) -> Option<&T> {
261 if let [.., last] = self { Some(last) } else { None }
264 /// Returns a mutable pointer to the last item in the slice.
269 /// let x = &mut [0, 1, 2];
271 /// if let Some(last) = x.last_mut() {
274 /// assert_eq!(x, &[0, 1, 10]);
276 #[stable(feature = "rust1", since = "1.0.0")]
278 pub fn last_mut(&mut self) -> Option<&mut T> {
279 if let [.., last] = self { Some(last) } else { None }
282 /// Returns a reference to an element or subslice depending on the type of
285 /// - If given a position, returns a reference to the element at that
286 /// position or `None` if out of bounds.
287 /// - If given a range, returns the subslice corresponding to that range,
288 /// or `None` if out of bounds.
293 /// let v = [10, 40, 30];
294 /// assert_eq!(Some(&40), v.get(1));
295 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
296 /// assert_eq!(None, v.get(3));
297 /// assert_eq!(None, v.get(0..4));
299 #[stable(feature = "rust1", since = "1.0.0")]
301 pub fn get<I>(&self, index: I) -> Option<&I::Output>
308 /// Returns a mutable reference to an element or subslice depending on the
309 /// type of index (see [`get`]) or `None` if the index is out of bounds.
311 /// [`get`]: #method.get
316 /// let x = &mut [0, 1, 2];
318 /// if let Some(elem) = x.get_mut(1) {
321 /// assert_eq!(x, &[0, 42, 2]);
323 #[stable(feature = "rust1", since = "1.0.0")]
325 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
332 /// Returns a reference to an element or subslice, without doing bounds
335 /// For a safe alternative see [`get`].
339 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
340 /// even if the resulting reference is not used.
342 /// [`get`]: #method.get
343 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
348 /// let x = &[1, 2, 4];
351 /// assert_eq!(x.get_unchecked(1), &2);
354 #[stable(feature = "rust1", since = "1.0.0")]
356 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
360 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
361 // the slice is dereferencable because `self` is a safe reference.
362 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
363 unsafe { &*index.get_unchecked(self) }
366 /// Returns a mutable reference to an element or subslice, without doing
369 /// For a safe alternative see [`get_mut`].
373 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
374 /// even if the resulting reference is not used.
376 /// [`get_mut`]: #method.get_mut
377 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
382 /// let x = &mut [1, 2, 4];
385 /// let elem = x.get_unchecked_mut(1);
388 /// assert_eq!(x, &[1, 13, 4]);
390 #[stable(feature = "rust1", since = "1.0.0")]
392 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
396 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
397 // the slice is dereferencable because `self` is a safe reference.
398 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
399 unsafe { &mut *index.get_unchecked_mut(self) }
402 /// Returns a raw pointer to the slice's buffer.
404 /// The caller must ensure that the slice outlives the pointer this
405 /// function returns, or else it will end up pointing to garbage.
407 /// The caller must also ensure that the memory the pointer (non-transitively) points to
408 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
409 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
411 /// Modifying the container referenced by this slice may cause its buffer
412 /// to be reallocated, which would also make any pointers to it invalid.
417 /// let x = &[1, 2, 4];
418 /// let x_ptr = x.as_ptr();
421 /// for i in 0..x.len() {
422 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
427 /// [`as_mut_ptr`]: #method.as_mut_ptr
428 #[stable(feature = "rust1", since = "1.0.0")]
429 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
431 pub const fn as_ptr(&self) -> *const T {
432 self as *const [T] as *const T
435 /// Returns an unsafe mutable pointer to the slice's buffer.
437 /// The caller must ensure that the slice outlives the pointer this
438 /// function returns, or else it will end up pointing to garbage.
440 /// Modifying the container referenced by this slice may cause its buffer
441 /// to be reallocated, which would also make any pointers to it invalid.
446 /// let x = &mut [1, 2, 4];
447 /// let x_ptr = x.as_mut_ptr();
450 /// for i in 0..x.len() {
451 /// *x_ptr.add(i) += 2;
454 /// assert_eq!(x, &[3, 4, 6]);
456 #[stable(feature = "rust1", since = "1.0.0")]
457 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
459 pub const fn as_mut_ptr(&mut self) -> *mut T {
460 self as *mut [T] as *mut T
463 /// Returns the two raw pointers spanning the slice.
465 /// The returned range is half-open, which means that the end pointer
466 /// points *one past* the last element of the slice. This way, an empty
467 /// slice is represented by two equal pointers, and the difference between
468 /// the two pointers represents the size of the slice.
470 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
471 /// requires extra caution, as it does not point to a valid element in the
474 /// This function is useful for interacting with foreign interfaces which
475 /// use two pointers to refer to a range of elements in memory, as is
478 /// It can also be useful to check if a pointer to an element refers to an
479 /// element of this slice:
482 /// let a = [1, 2, 3];
483 /// let x = &a[1] as *const _;
484 /// let y = &5 as *const _;
486 /// assert!(a.as_ptr_range().contains(&x));
487 /// assert!(!a.as_ptr_range().contains(&y));
490 /// [`as_ptr`]: #method.as_ptr
491 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
492 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
494 pub const fn as_ptr_range(&self) -> Range<*const T> {
495 let start = self.as_ptr();
496 // SAFETY: The `add` here is safe, because:
498 // - Both pointers are part of the same object, as pointing directly
499 // past the object also counts.
501 // - The size of the slice is never larger than isize::MAX bytes, as
503 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
504 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
505 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
506 // (This doesn't seem normative yet, but the very same assumption is
507 // made in many places, including the Index implementation of slices.)
509 // - There is no wrapping around involved, as slices do not wrap past
510 // the end of the address space.
512 // See the documentation of pointer::add.
513 let end = unsafe { start.add(self.len()) };
517 /// Returns the two unsafe mutable pointers spanning the slice.
519 /// The returned range is half-open, which means that the end pointer
520 /// points *one past* the last element of the slice. This way, an empty
521 /// slice is represented by two equal pointers, and the difference between
522 /// the two pointers represents the size of the slice.
524 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
525 /// pointer requires extra caution, as it does not point to a valid element
528 /// This function is useful for interacting with foreign interfaces which
529 /// use two pointers to refer to a range of elements in memory, as is
532 /// [`as_mut_ptr`]: #method.as_mut_ptr
533 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
534 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
536 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
537 let start = self.as_mut_ptr();
538 // SAFETY: See as_ptr_range() above for why `add` here is safe.
539 let end = unsafe { start.add(self.len()) };
543 /// Swaps two elements in the slice.
547 /// * a - The index of the first element
548 /// * b - The index of the second element
552 /// Panics if `a` or `b` are out of bounds.
557 /// let mut v = ["a", "b", "c", "d"];
559 /// assert!(v == ["a", "d", "c", "b"]);
561 #[stable(feature = "rust1", since = "1.0.0")]
563 pub fn swap(&mut self, a: usize, b: usize) {
564 // Can't take two mutable loans from one vector, so instead use raw pointers.
565 let pa = ptr::addr_of_mut!(self[a]);
566 let pb = ptr::addr_of_mut!(self[b]);
567 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
568 // to elements in the slice and therefore are guaranteed to be valid and aligned.
569 // Note that accessing the elements behind `a` and `b` is checked and will
570 // panic when out of bounds.
576 /// Reverses the order of elements in the slice, in place.
581 /// let mut v = [1, 2, 3];
583 /// assert!(v == [3, 2, 1]);
585 #[stable(feature = "rust1", since = "1.0.0")]
587 pub fn reverse(&mut self) {
588 let mut i: usize = 0;
591 // For very small types, all the individual reads in the normal
592 // path perform poorly. We can do better, given efficient unaligned
593 // load/store, by loading a larger chunk and reversing a register.
595 // Ideally LLVM would do this for us, as it knows better than we do
596 // whether unaligned reads are efficient (since that changes between
597 // different ARM versions, for example) and what the best chunk size
598 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
599 // the loop, so we need to do this ourselves. (Hypothesis: reverse
600 // is troublesome because the sides can be aligned differently --
601 // will be, when the length is odd -- so there's no way of emitting
602 // pre- and postludes to use fully-aligned SIMD in the middle.)
604 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
606 if fast_unaligned && mem::size_of::<T>() == 1 {
607 // Use the llvm.bswap intrinsic to reverse u8s in a usize
608 let chunk = mem::size_of::<usize>();
609 while i + chunk - 1 < ln / 2 {
610 // SAFETY: There are several things to check here:
612 // - Note that `chunk` is either 4 or 8 due to the cfg check
613 // above. So `chunk - 1` is positive.
614 // - Indexing with index `i` is fine as the loop check guarantees
615 // `i + chunk - 1 < ln / 2`
616 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
617 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
618 // - `i + chunk > 0` is trivially true.
619 // - The loop check guarantees:
620 // `i + chunk - 1 < ln / 2`
621 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
622 // - The `read_unaligned` and `write_unaligned` calls are fine:
623 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
624 // (see above) and `pb` points to index `ln - i - chunk`, so
625 // both are at least `chunk`
626 // many bytes away from the end of `self`.
627 // - Any initialized memory is valid `usize`.
629 let ptr = self.as_mut_ptr();
631 let pb = ptr.add(ln - i - chunk);
632 let va = ptr::read_unaligned(pa as *mut usize);
633 let vb = ptr::read_unaligned(pb as *mut usize);
634 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
635 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
641 if fast_unaligned && mem::size_of::<T>() == 2 {
642 // Use rotate-by-16 to reverse u16s in a u32
643 let chunk = mem::size_of::<u32>() / 2;
644 while i + chunk - 1 < ln / 2 {
645 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
646 // (and obviously `i < ln`), because each element is 2 bytes and
649 // `i + chunk - 1 < ln / 2` # while condition
650 // `i + 2 - 1 < ln / 2`
653 // Since it's less than the length divided by 2, then it must be
656 // This also means that the condition `0 < i + chunk <= ln` is
657 // always respected, ensuring the `pb` pointer can be used
660 let ptr = self.as_mut_ptr();
662 let pb = ptr.add(ln - i - chunk);
663 let va = ptr::read_unaligned(pa as *mut u32);
664 let vb = ptr::read_unaligned(pb as *mut u32);
665 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
666 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
673 // SAFETY: `i` is inferior to half the length of the slice so
674 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
675 // will not go further than `ln / 2 - 1`).
676 // The resulting pointers `pa` and `pb` are therefore valid and
677 // aligned, and can be read from and written to.
679 // Unsafe swap to avoid the bounds check in safe swap.
680 let ptr = self.as_mut_ptr();
682 let pb = ptr.add(ln - i - 1);
689 /// Returns an iterator over the slice.
694 /// let x = &[1, 2, 4];
695 /// let mut iterator = x.iter();
697 /// assert_eq!(iterator.next(), Some(&1));
698 /// assert_eq!(iterator.next(), Some(&2));
699 /// assert_eq!(iterator.next(), Some(&4));
700 /// assert_eq!(iterator.next(), None);
702 #[stable(feature = "rust1", since = "1.0.0")]
704 pub fn iter(&self) -> Iter<'_, T> {
708 /// Returns an iterator that allows modifying each value.
713 /// let x = &mut [1, 2, 4];
714 /// for elem in x.iter_mut() {
717 /// assert_eq!(x, &[3, 4, 6]);
719 #[stable(feature = "rust1", since = "1.0.0")]
721 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
725 /// Returns an iterator over all contiguous windows of length
726 /// `size`. The windows overlap. If the slice is shorter than
727 /// `size`, the iterator returns no values.
731 /// Panics if `size` is 0.
736 /// let slice = ['r', 'u', 's', 't'];
737 /// let mut iter = slice.windows(2);
738 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
739 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
740 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
741 /// assert!(iter.next().is_none());
744 /// If the slice is shorter than `size`:
747 /// let slice = ['f', 'o', 'o'];
748 /// let mut iter = slice.windows(4);
749 /// assert!(iter.next().is_none());
751 #[stable(feature = "rust1", since = "1.0.0")]
753 pub fn windows(&self, size: usize) -> Windows<'_, T> {
754 let size = NonZeroUsize::new(size).expect("size is zero");
755 Windows::new(self, size)
758 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
759 /// beginning of the slice.
761 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
762 /// slice, then the last chunk will not have length `chunk_size`.
764 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
765 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
770 /// Panics if `chunk_size` is 0.
775 /// let slice = ['l', 'o', 'r', 'e', 'm'];
776 /// let mut iter = slice.chunks(2);
777 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
778 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
779 /// assert_eq!(iter.next().unwrap(), &['m']);
780 /// assert!(iter.next().is_none());
783 /// [`chunks_exact`]: #method.chunks_exact
784 /// [`rchunks`]: #method.rchunks
785 #[stable(feature = "rust1", since = "1.0.0")]
787 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
788 assert_ne!(chunk_size, 0);
789 Chunks::new(self, chunk_size)
792 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
793 /// beginning of the slice.
795 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
796 /// length of the slice, then the last chunk will not have length `chunk_size`.
798 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
799 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
800 /// the end of the slice.
804 /// Panics if `chunk_size` is 0.
809 /// let v = &mut [0, 0, 0, 0, 0];
810 /// let mut count = 1;
812 /// for chunk in v.chunks_mut(2) {
813 /// for elem in chunk.iter_mut() {
818 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
821 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
822 /// [`rchunks_mut`]: #method.rchunks_mut
823 #[stable(feature = "rust1", since = "1.0.0")]
825 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
826 assert_ne!(chunk_size, 0);
827 ChunksMut::new(self, chunk_size)
830 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
831 /// beginning of the slice.
833 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
834 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
835 /// from the `remainder` function of the iterator.
837 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
838 /// resulting code better than in the case of [`chunks`].
840 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
841 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
845 /// Panics if `chunk_size` is 0.
850 /// let slice = ['l', 'o', 'r', 'e', 'm'];
851 /// let mut iter = slice.chunks_exact(2);
852 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
853 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
854 /// assert!(iter.next().is_none());
855 /// assert_eq!(iter.remainder(), &['m']);
858 /// [`chunks`]: #method.chunks
859 /// [`rchunks_exact`]: #method.rchunks_exact
860 #[stable(feature = "chunks_exact", since = "1.31.0")]
862 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
863 assert_ne!(chunk_size, 0);
864 ChunksExact::new(self, chunk_size)
867 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
868 /// beginning of the slice.
870 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
871 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
872 /// retrieved from the `into_remainder` function of the iterator.
874 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
875 /// resulting code better than in the case of [`chunks_mut`].
877 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
878 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
883 /// Panics if `chunk_size` is 0.
888 /// let v = &mut [0, 0, 0, 0, 0];
889 /// let mut count = 1;
891 /// for chunk in v.chunks_exact_mut(2) {
892 /// for elem in chunk.iter_mut() {
897 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
900 /// [`chunks_mut`]: #method.chunks_mut
901 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
902 #[stable(feature = "chunks_exact", since = "1.31.0")]
904 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
905 assert_ne!(chunk_size, 0);
906 ChunksExactMut::new(self, chunk_size)
909 /// Splits the slice into a slice of `N`-element arrays,
910 /// assuming that there's no remainder.
914 /// This may only be called when
915 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
921 /// #![feature(slice_as_chunks)]
922 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
923 /// let chunks: &[[char; 1]] =
924 /// // SAFETY: 1-element chunks never have remainder
925 /// unsafe { slice.as_chunks_unchecked() };
926 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
927 /// let chunks: &[[char; 3]] =
928 /// // SAFETY: The slice length (6) is a multiple of 3
929 /// unsafe { slice.as_chunks_unchecked() };
930 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
932 /// // These would be unsound:
933 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
934 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
936 #[unstable(feature = "slice_as_chunks", issue = "74985")]
938 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
939 debug_assert_ne!(N, 0);
940 debug_assert_eq!(self.len() % N, 0);
942 // SAFETY: Our precondition is exactly what's needed to call this
943 unsafe { crate::intrinsics::exact_div(self.len(), N) };
944 // SAFETY: We cast a slice of `new_len * N` elements into
945 // a slice of `new_len` many `N` elements chunks.
946 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
949 /// Splits the slice into a slice of `N`-element arrays,
950 /// starting at the beginning of the slice,
951 /// and a remainder slice with length strictly less than `N`.
955 /// Panics if `N` is 0. This check will most probably get changed to a compile time
956 /// error before this method gets stabilized.
961 /// #![feature(slice_as_chunks)]
962 /// let slice = ['l', 'o', 'r', 'e', 'm'];
963 /// let (chunks, remainder) = slice.as_chunks();
964 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
965 /// assert_eq!(remainder, &['m']);
967 #[unstable(feature = "slice_as_chunks", issue = "74985")]
969 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
971 let len = self.len() / N;
972 let (multiple_of_n, remainder) = self.split_at(len * N);
973 // SAFETY: We already panicked for zero, and ensured by construction
974 // that the length of the subslice is a multiple of N.
975 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
976 (array_slice, remainder)
979 /// Splits the slice into a slice of `N`-element arrays,
980 /// starting at the end of the slice,
981 /// and a remainder slice with length strictly less than `N`.
985 /// Panics if `N` is 0. This check will most probably get changed to a compile time
986 /// error before this method gets stabilized.
991 /// #![feature(slice_as_chunks)]
992 /// let slice = ['l', 'o', 'r', 'e', 'm'];
993 /// let (remainder, chunks) = slice.as_rchunks();
994 /// assert_eq!(remainder, &['l']);
995 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
997 #[unstable(feature = "slice_as_chunks", issue = "74985")]
999 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1001 let len = self.len() / N;
1002 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1003 // SAFETY: We already panicked for zero, and ensured by construction
1004 // that the length of the subslice is a multiple of N.
1005 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1006 (remainder, array_slice)
1009 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1010 /// beginning of the slice.
1012 /// The chunks are array references and do not overlap. If `N` does not divide the
1013 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1014 /// retrieved from the `remainder` function of the iterator.
1016 /// This method is the const generic equivalent of [`chunks_exact`].
1020 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1021 /// error before this method gets stabilized.
1026 /// #![feature(array_chunks)]
1027 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1028 /// let mut iter = slice.array_chunks();
1029 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1030 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1031 /// assert!(iter.next().is_none());
1032 /// assert_eq!(iter.remainder(), &['m']);
1035 /// [`chunks_exact`]: #method.chunks_exact
1036 #[unstable(feature = "array_chunks", issue = "74985")]
1038 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1040 ArrayChunks::new(self)
1043 /// Splits the slice into a slice of `N`-element arrays,
1044 /// assuming that there's no remainder.
1048 /// This may only be called when
1049 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1055 /// #![feature(slice_as_chunks)]
1056 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1057 /// let chunks: &mut [[char; 1]] =
1058 /// // SAFETY: 1-element chunks never have remainder
1059 /// unsafe { slice.as_chunks_unchecked_mut() };
1060 /// chunks[0] = ['L'];
1061 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1062 /// let chunks: &mut [[char; 3]] =
1063 /// // SAFETY: The slice length (6) is a multiple of 3
1064 /// unsafe { slice.as_chunks_unchecked_mut() };
1065 /// chunks[1] = ['a', 'x', '?'];
1066 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1068 /// // These would be unsound:
1069 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1070 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1072 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1074 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1075 debug_assert_ne!(N, 0);
1076 debug_assert_eq!(self.len() % N, 0);
1078 // SAFETY: Our precondition is exactly what's needed to call this
1079 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1080 // SAFETY: We cast a slice of `new_len * N` elements into
1081 // a slice of `new_len` many `N` elements chunks.
1082 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1085 /// Splits the slice into a slice of `N`-element arrays,
1086 /// starting at the beginning of the slice,
1087 /// and a remainder slice with length strictly less than `N`.
1091 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1092 /// error before this method gets stabilized.
1097 /// #![feature(slice_as_chunks)]
1098 /// let v = &mut [0, 0, 0, 0, 0];
1099 /// let mut count = 1;
1101 /// let (chunks, remainder) = v.as_chunks_mut();
1102 /// remainder[0] = 9;
1103 /// for chunk in chunks {
1104 /// *chunk = [count; 2];
1107 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1109 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1111 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1113 let len = self.len() / N;
1114 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1115 // SAFETY: We already panicked for zero, and ensured by construction
1116 // that the length of the subslice is a multiple of N.
1117 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1118 (array_slice, remainder)
1121 /// Splits the slice into a slice of `N`-element arrays,
1122 /// starting at the end of the slice,
1123 /// and a remainder slice with length strictly less than `N`.
1127 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1128 /// error before this method gets stabilized.
1133 /// #![feature(slice_as_chunks)]
1134 /// let v = &mut [0, 0, 0, 0, 0];
1135 /// let mut count = 1;
1137 /// let (remainder, chunks) = v.as_rchunks_mut();
1138 /// remainder[0] = 9;
1139 /// for chunk in chunks {
1140 /// *chunk = [count; 2];
1143 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1145 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1147 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1149 let len = self.len() / N;
1150 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1151 // SAFETY: We already panicked for zero, and ensured by construction
1152 // that the length of the subslice is a multiple of N.
1153 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1154 (remainder, array_slice)
1157 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1158 /// beginning of the slice.
1160 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1161 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1162 /// can be retrieved from the `into_remainder` function of the iterator.
1164 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1168 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1169 /// error before this method gets stabilized.
1174 /// #![feature(array_chunks)]
1175 /// let v = &mut [0, 0, 0, 0, 0];
1176 /// let mut count = 1;
1178 /// for chunk in v.array_chunks_mut() {
1179 /// *chunk = [count; 2];
1182 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1185 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1186 #[unstable(feature = "array_chunks", issue = "74985")]
1188 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1190 ArrayChunksMut::new(self)
1193 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1194 /// starting at the beginning of the slice.
1196 /// This is the const generic equivalent of [`windows`].
1198 /// If `N` is greater than the size of the slice, it will return no windows.
1202 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1203 /// error before this method gets stabilized.
1208 /// #![feature(array_windows)]
1209 /// let slice = [0, 1, 2, 3];
1210 /// let mut iter = slice.array_windows();
1211 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1212 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1213 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1214 /// assert!(iter.next().is_none());
1217 /// [`windows`]: #method.windows
1218 #[unstable(feature = "array_windows", issue = "75027")]
1220 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1222 ArrayWindows::new(self)
1225 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1228 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1229 /// slice, then the last chunk will not have length `chunk_size`.
1231 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1232 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1237 /// Panics if `chunk_size` is 0.
1242 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1243 /// let mut iter = slice.rchunks(2);
1244 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1245 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1246 /// assert_eq!(iter.next().unwrap(), &['l']);
1247 /// assert!(iter.next().is_none());
1250 /// [`rchunks_exact`]: #method.rchunks_exact
1251 /// [`chunks`]: #method.chunks
1252 #[stable(feature = "rchunks", since = "1.31.0")]
1254 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1255 assert!(chunk_size != 0);
1256 RChunks::new(self, chunk_size)
1259 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1262 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1263 /// length of the slice, then the last chunk will not have length `chunk_size`.
1265 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1266 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1267 /// beginning of the slice.
1271 /// Panics if `chunk_size` is 0.
1276 /// let v = &mut [0, 0, 0, 0, 0];
1277 /// let mut count = 1;
1279 /// for chunk in v.rchunks_mut(2) {
1280 /// for elem in chunk.iter_mut() {
1285 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1288 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
1289 /// [`chunks_mut`]: #method.chunks_mut
1290 #[stable(feature = "rchunks", since = "1.31.0")]
1292 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1293 assert!(chunk_size != 0);
1294 RChunksMut::new(self, chunk_size)
1297 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1298 /// end of the slice.
1300 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1301 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1302 /// from the `remainder` function of the iterator.
1304 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1305 /// resulting code better than in the case of [`chunks`].
1307 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1308 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1313 /// Panics if `chunk_size` is 0.
1318 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1319 /// let mut iter = slice.rchunks_exact(2);
1320 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1321 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1322 /// assert!(iter.next().is_none());
1323 /// assert_eq!(iter.remainder(), &['l']);
1326 /// [`chunks`]: #method.chunks
1327 /// [`rchunks`]: #method.rchunks
1328 /// [`chunks_exact`]: #method.chunks_exact
1329 #[stable(feature = "rchunks", since = "1.31.0")]
1331 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1332 assert!(chunk_size != 0);
1333 RChunksExact::new(self, chunk_size)
1336 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1339 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1340 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1341 /// retrieved from the `into_remainder` function of the iterator.
1343 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1344 /// resulting code better than in the case of [`chunks_mut`].
1346 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1347 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1352 /// Panics if `chunk_size` is 0.
1357 /// let v = &mut [0, 0, 0, 0, 0];
1358 /// let mut count = 1;
1360 /// for chunk in v.rchunks_exact_mut(2) {
1361 /// for elem in chunk.iter_mut() {
1366 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1369 /// [`chunks_mut`]: #method.chunks_mut
1370 /// [`rchunks_mut`]: #method.rchunks_mut
1371 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1372 #[stable(feature = "rchunks", since = "1.31.0")]
1374 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1375 assert!(chunk_size != 0);
1376 RChunksExactMut::new(self, chunk_size)
1379 /// Returns an iterator over the slice producing non-overlapping runs
1380 /// of elements using the predicate to separate them.
1382 /// The predicate is called on two elements following themselves,
1383 /// it means the predicate is called on `slice[0]` and `slice[1]`
1384 /// then on `slice[1]` and `slice[2]` and so on.
1389 /// #![feature(slice_group_by)]
1391 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1393 /// let mut iter = slice.group_by(|a, b| a == b);
1395 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1396 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1397 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1398 /// assert_eq!(iter.next(), None);
1401 /// This method can be used to extract the sorted subslices:
1404 /// #![feature(slice_group_by)]
1406 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1408 /// let mut iter = slice.group_by(|a, b| a <= b);
1410 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1411 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1412 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1413 /// assert_eq!(iter.next(), None);
1415 #[unstable(feature = "slice_group_by", issue = "80552")]
1417 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1419 F: FnMut(&T, &T) -> bool,
1421 GroupBy::new(self, pred)
1424 /// Returns an iterator over the slice producing non-overlapping mutable
1425 /// runs of elements using the predicate to separate them.
1427 /// The predicate is called on two elements following themselves,
1428 /// it means the predicate is called on `slice[0]` and `slice[1]`
1429 /// then on `slice[1]` and `slice[2]` and so on.
1434 /// #![feature(slice_group_by)]
1436 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1438 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1440 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1441 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1442 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1443 /// assert_eq!(iter.next(), None);
1446 /// This method can be used to extract the sorted subslices:
1449 /// #![feature(slice_group_by)]
1451 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1453 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1455 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1456 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1457 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1458 /// assert_eq!(iter.next(), None);
1460 #[unstable(feature = "slice_group_by", issue = "80552")]
1462 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1464 F: FnMut(&T, &T) -> bool,
1466 GroupByMut::new(self, pred)
1469 /// Divides one slice into two at an index.
1471 /// The first will contain all indices from `[0, mid)` (excluding
1472 /// the index `mid` itself) and the second will contain all
1473 /// indices from `[mid, len)` (excluding the index `len` itself).
1477 /// Panics if `mid > len`.
1482 /// let v = [1, 2, 3, 4, 5, 6];
1485 /// let (left, right) = v.split_at(0);
1486 /// assert_eq!(left, []);
1487 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1491 /// let (left, right) = v.split_at(2);
1492 /// assert_eq!(left, [1, 2]);
1493 /// assert_eq!(right, [3, 4, 5, 6]);
1497 /// let (left, right) = v.split_at(6);
1498 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1499 /// assert_eq!(right, []);
1502 #[stable(feature = "rust1", since = "1.0.0")]
1504 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1505 assert!(mid <= self.len());
1506 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1507 // fulfills the requirements of `from_raw_parts_mut`.
1508 unsafe { self.split_at_unchecked(mid) }
1511 /// Divides one mutable slice into two at an index.
1513 /// The first will contain all indices from `[0, mid)` (excluding
1514 /// the index `mid` itself) and the second will contain all
1515 /// indices from `[mid, len)` (excluding the index `len` itself).
1519 /// Panics if `mid > len`.
1524 /// let mut v = [1, 0, 3, 0, 5, 6];
1525 /// let (left, right) = v.split_at_mut(2);
1526 /// assert_eq!(left, [1, 0]);
1527 /// assert_eq!(right, [3, 0, 5, 6]);
1530 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1532 #[stable(feature = "rust1", since = "1.0.0")]
1534 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1535 assert!(mid <= self.len());
1536 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1537 // fulfills the requirements of `from_raw_parts_mut`.
1538 unsafe { self.split_at_mut_unchecked(mid) }
1541 /// Divides one slice into two at an index, without doing bounds checking.
1543 /// The first will contain all indices from `[0, mid)` (excluding
1544 /// the index `mid` itself) and the second will contain all
1545 /// indices from `[mid, len)` (excluding the index `len` itself).
1547 /// For a safe alternative see [`split_at`].
1551 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1552 /// even if the resulting reference is not used. The caller has to ensure that
1553 /// `0 <= mid <= self.len()`.
1555 /// [`split_at`]: #method.split_at
1556 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1561 /// #![feature(slice_split_at_unchecked)]
1563 /// let v = [1, 2, 3, 4, 5, 6];
1566 /// let (left, right) = v.split_at_unchecked(0);
1567 /// assert_eq!(left, []);
1568 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1572 /// let (left, right) = v.split_at_unchecked(2);
1573 /// assert_eq!(left, [1, 2]);
1574 /// assert_eq!(right, [3, 4, 5, 6]);
1578 /// let (left, right) = v.split_at_unchecked(6);
1579 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1580 /// assert_eq!(right, []);
1583 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1585 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1586 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1587 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1590 /// Divides one mutable slice into two at an index, without doing bounds checking.
1592 /// The first will contain all indices from `[0, mid)` (excluding
1593 /// the index `mid` itself) and the second will contain all
1594 /// indices from `[mid, len)` (excluding the index `len` itself).
1596 /// For a safe alternative see [`split_at_mut`].
1600 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1601 /// even if the resulting reference is not used. The caller has to ensure that
1602 /// `0 <= mid <= self.len()`.
1604 /// [`split_at_mut`]: #method.split_at_mut
1605 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1610 /// #![feature(slice_split_at_unchecked)]
1612 /// let mut v = [1, 0, 3, 0, 5, 6];
1613 /// // scoped to restrict the lifetime of the borrows
1615 /// let (left, right) = v.split_at_mut_unchecked(2);
1616 /// assert_eq!(left, [1, 0]);
1617 /// assert_eq!(right, [3, 0, 5, 6]);
1621 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1623 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1625 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1626 let len = self.len();
1627 let ptr = self.as_mut_ptr();
1629 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1631 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1633 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1636 /// Returns an iterator over subslices separated by elements that match
1637 /// `pred`. The matched element is not contained in the subslices.
1642 /// let slice = [10, 40, 33, 20];
1643 /// let mut iter = slice.split(|num| num % 3 == 0);
1645 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1646 /// assert_eq!(iter.next().unwrap(), &[20]);
1647 /// assert!(iter.next().is_none());
1650 /// If the first element is matched, an empty slice will be the first item
1651 /// returned by the iterator. Similarly, if the last element in the slice
1652 /// is matched, an empty slice will be the last item returned by the
1656 /// let slice = [10, 40, 33];
1657 /// let mut iter = slice.split(|num| num % 3 == 0);
1659 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1660 /// assert_eq!(iter.next().unwrap(), &[]);
1661 /// assert!(iter.next().is_none());
1664 /// If two matched elements are directly adjacent, an empty slice will be
1665 /// present between them:
1668 /// let slice = [10, 6, 33, 20];
1669 /// let mut iter = slice.split(|num| num % 3 == 0);
1671 /// assert_eq!(iter.next().unwrap(), &[10]);
1672 /// assert_eq!(iter.next().unwrap(), &[]);
1673 /// assert_eq!(iter.next().unwrap(), &[20]);
1674 /// assert!(iter.next().is_none());
1676 #[stable(feature = "rust1", since = "1.0.0")]
1678 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1680 F: FnMut(&T) -> bool,
1682 Split::new(self, pred)
1685 /// Returns an iterator over mutable subslices separated by elements that
1686 /// match `pred`. The matched element is not contained in the subslices.
1691 /// let mut v = [10, 40, 30, 20, 60, 50];
1693 /// for group in v.split_mut(|num| *num % 3 == 0) {
1696 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1698 #[stable(feature = "rust1", since = "1.0.0")]
1700 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1702 F: FnMut(&T) -> bool,
1704 SplitMut::new(self, pred)
1707 /// Returns an iterator over subslices separated by elements that match
1708 /// `pred`. The matched element is contained in the end of the previous
1709 /// subslice as a terminator.
1714 /// let slice = [10, 40, 33, 20];
1715 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1717 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1718 /// assert_eq!(iter.next().unwrap(), &[20]);
1719 /// assert!(iter.next().is_none());
1722 /// If the last element of the slice is matched,
1723 /// that element will be considered the terminator of the preceding slice.
1724 /// That slice will be the last item returned by the iterator.
1727 /// let slice = [3, 10, 40, 33];
1728 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1730 /// assert_eq!(iter.next().unwrap(), &[3]);
1731 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1732 /// assert!(iter.next().is_none());
1734 #[stable(feature = "split_inclusive", since = "1.51.0")]
1736 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1738 F: FnMut(&T) -> bool,
1740 SplitInclusive::new(self, pred)
1743 /// Returns an iterator over mutable subslices separated by elements that
1744 /// match `pred`. The matched element is contained in the previous
1745 /// subslice as a terminator.
1750 /// let mut v = [10, 40, 30, 20, 60, 50];
1752 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1753 /// let terminator_idx = group.len()-1;
1754 /// group[terminator_idx] = 1;
1756 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1758 #[stable(feature = "split_inclusive", since = "1.51.0")]
1760 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1762 F: FnMut(&T) -> bool,
1764 SplitInclusiveMut::new(self, pred)
1767 /// Returns an iterator over subslices separated by elements that match
1768 /// `pred`, starting at the end of the slice and working backwards.
1769 /// The matched element is not contained in the subslices.
1774 /// let slice = [11, 22, 33, 0, 44, 55];
1775 /// let mut iter = slice.rsplit(|num| *num == 0);
1777 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1778 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1779 /// assert_eq!(iter.next(), None);
1782 /// As with `split()`, if the first or last element is matched, an empty
1783 /// slice will be the first (or last) item returned by the iterator.
1786 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1787 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1788 /// assert_eq!(it.next().unwrap(), &[]);
1789 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1790 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1791 /// assert_eq!(it.next().unwrap(), &[]);
1792 /// assert_eq!(it.next(), None);
1794 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1796 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1798 F: FnMut(&T) -> bool,
1800 RSplit::new(self, pred)
1803 /// Returns an iterator over mutable subslices separated by elements that
1804 /// match `pred`, starting at the end of the slice and working
1805 /// backwards. The matched element is not contained in the subslices.
1810 /// let mut v = [100, 400, 300, 200, 600, 500];
1812 /// let mut count = 0;
1813 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1815 /// group[0] = count;
1817 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1820 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1822 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1824 F: FnMut(&T) -> bool,
1826 RSplitMut::new(self, pred)
1829 /// Returns an iterator over subslices separated by elements that match
1830 /// `pred`, limited to returning at most `n` items. The matched element is
1831 /// not contained in the subslices.
1833 /// The last element returned, if any, will contain the remainder of the
1838 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1839 /// `[20, 60, 50]`):
1842 /// let v = [10, 40, 30, 20, 60, 50];
1844 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1845 /// println!("{:?}", group);
1848 #[stable(feature = "rust1", since = "1.0.0")]
1850 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1852 F: FnMut(&T) -> bool,
1854 SplitN::new(self.split(pred), n)
1857 /// Returns an iterator over subslices separated by elements that match
1858 /// `pred`, limited to returning at most `n` items. The matched element is
1859 /// not contained in the subslices.
1861 /// The last element returned, if any, will contain the remainder of the
1867 /// let mut v = [10, 40, 30, 20, 60, 50];
1869 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1872 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1874 #[stable(feature = "rust1", since = "1.0.0")]
1876 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1878 F: FnMut(&T) -> bool,
1880 SplitNMut::new(self.split_mut(pred), n)
1883 /// Returns an iterator over subslices separated by elements that match
1884 /// `pred` limited to returning at most `n` items. This starts at the end of
1885 /// the slice and works backwards. The matched element is not contained in
1888 /// The last element returned, if any, will contain the remainder of the
1893 /// Print the slice split once, starting from the end, by numbers divisible
1894 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1897 /// let v = [10, 40, 30, 20, 60, 50];
1899 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1900 /// println!("{:?}", group);
1903 #[stable(feature = "rust1", since = "1.0.0")]
1905 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1907 F: FnMut(&T) -> bool,
1909 RSplitN::new(self.rsplit(pred), n)
1912 /// Returns an iterator over subslices separated by elements that match
1913 /// `pred` limited to returning at most `n` items. This starts at the end of
1914 /// the slice and works backwards. The matched element is not contained in
1917 /// The last element returned, if any, will contain the remainder of the
1923 /// let mut s = [10, 40, 30, 20, 60, 50];
1925 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1928 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1930 #[stable(feature = "rust1", since = "1.0.0")]
1932 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1934 F: FnMut(&T) -> bool,
1936 RSplitNMut::new(self.rsplit_mut(pred), n)
1939 /// Returns `true` if the slice contains an element with the given value.
1944 /// let v = [10, 40, 30];
1945 /// assert!(v.contains(&30));
1946 /// assert!(!v.contains(&50));
1949 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1950 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1953 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1954 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1955 /// assert!(!v.iter().any(|e| e == "hi"));
1957 #[stable(feature = "rust1", since = "1.0.0")]
1959 pub fn contains(&self, x: &T) -> bool
1963 cmp::SliceContains::slice_contains(x, self)
1966 /// Returns `true` if `needle` is a prefix of the slice.
1971 /// let v = [10, 40, 30];
1972 /// assert!(v.starts_with(&[10]));
1973 /// assert!(v.starts_with(&[10, 40]));
1974 /// assert!(!v.starts_with(&[50]));
1975 /// assert!(!v.starts_with(&[10, 50]));
1978 /// Always returns `true` if `needle` is an empty slice:
1981 /// let v = &[10, 40, 30];
1982 /// assert!(v.starts_with(&[]));
1983 /// let v: &[u8] = &[];
1984 /// assert!(v.starts_with(&[]));
1986 #[stable(feature = "rust1", since = "1.0.0")]
1987 pub fn starts_with(&self, needle: &[T]) -> bool
1991 let n = needle.len();
1992 self.len() >= n && needle == &self[..n]
1995 /// Returns `true` if `needle` is a suffix of the slice.
2000 /// let v = [10, 40, 30];
2001 /// assert!(v.ends_with(&[30]));
2002 /// assert!(v.ends_with(&[40, 30]));
2003 /// assert!(!v.ends_with(&[50]));
2004 /// assert!(!v.ends_with(&[50, 30]));
2007 /// Always returns `true` if `needle` is an empty slice:
2010 /// let v = &[10, 40, 30];
2011 /// assert!(v.ends_with(&[]));
2012 /// let v: &[u8] = &[];
2013 /// assert!(v.ends_with(&[]));
2015 #[stable(feature = "rust1", since = "1.0.0")]
2016 pub fn ends_with(&self, needle: &[T]) -> bool
2020 let (m, n) = (self.len(), needle.len());
2021 m >= n && needle == &self[m - n..]
2024 /// Returns a subslice with the prefix removed.
2026 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2027 /// If `prefix` is empty, simply returns the original slice.
2029 /// If the slice does not start with `prefix`, returns `None`.
2034 /// let v = &[10, 40, 30];
2035 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2036 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2037 /// assert_eq!(v.strip_prefix(&[50]), None);
2038 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2040 /// let prefix : &str = "he";
2041 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2042 /// Some(b"llo".as_ref()));
2044 #[must_use = "returns the subslice without modifying the original"]
2045 #[stable(feature = "slice_strip", since = "1.51.0")]
2046 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2050 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2051 let prefix = prefix.as_slice();
2052 let n = prefix.len();
2053 if n <= self.len() {
2054 let (head, tail) = self.split_at(n);
2062 /// Returns a subslice with the suffix removed.
2064 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2065 /// If `suffix` is empty, simply returns the original slice.
2067 /// If the slice does not end with `suffix`, returns `None`.
2072 /// let v = &[10, 40, 30];
2073 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2074 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2075 /// assert_eq!(v.strip_suffix(&[50]), None);
2076 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2078 #[must_use = "returns the subslice without modifying the original"]
2079 #[stable(feature = "slice_strip", since = "1.51.0")]
2080 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2084 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2085 let suffix = suffix.as_slice();
2086 let (len, n) = (self.len(), suffix.len());
2088 let (head, tail) = self.split_at(len - n);
2096 /// Binary searches this sorted slice for a given element.
2098 /// If the value is found then [`Result::Ok`] is returned, containing the
2099 /// index of the matching element. If there are multiple matches, then any
2100 /// one of the matches could be returned. If the value is not found then
2101 /// [`Result::Err`] is returned, containing the index where a matching
2102 /// element could be inserted while maintaining sorted order.
2104 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2106 /// [`binary_search_by`]: #method.binary_search_by
2107 /// [`binary_search_by_key`]: #method.binary_search_by_key
2108 /// [`partition_point`]: #method.partition_point
2112 /// Looks up a series of four elements. The first is found, with a
2113 /// uniquely determined position; the second and third are not
2114 /// found; the fourth could match any position in `[1, 4]`.
2117 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2119 /// assert_eq!(s.binary_search(&13), Ok(9));
2120 /// assert_eq!(s.binary_search(&4), Err(7));
2121 /// assert_eq!(s.binary_search(&100), Err(13));
2122 /// let r = s.binary_search(&1);
2123 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2126 /// If you want to insert an item to a sorted vector, while maintaining
2130 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2132 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2133 /// s.insert(idx, num);
2134 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2136 #[stable(feature = "rust1", since = "1.0.0")]
2137 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2141 self.binary_search_by(|p| p.cmp(x))
2144 /// Binary searches this sorted slice with a comparator function.
2146 /// The comparator function should implement an order consistent
2147 /// with the sort order of the underlying slice, returning an
2148 /// order code that indicates whether its argument is `Less`,
2149 /// `Equal` or `Greater` the desired target.
2151 /// If the value is found then [`Result::Ok`] is returned, containing the
2152 /// index of the matching element. If there are multiple matches, then any
2153 /// one of the matches could be returned. If the value is not found then
2154 /// [`Result::Err`] is returned, containing the index where a matching
2155 /// element could be inserted while maintaining sorted order.
2157 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2159 /// [`binary_search`]: #method.binary_search
2160 /// [`binary_search_by_key`]: #method.binary_search_by_key
2161 /// [`partition_point`]: #method.partition_point
2165 /// Looks up a series of four elements. The first is found, with a
2166 /// uniquely determined position; the second and third are not
2167 /// found; the fourth could match any position in `[1, 4]`.
2170 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2173 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2175 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2177 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2179 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2180 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2182 #[stable(feature = "rust1", since = "1.0.0")]
2184 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2186 F: FnMut(&'a T) -> Ordering,
2188 let mut size = self.len();
2190 let mut right = size;
2191 while left < right {
2192 let mid = left + size / 2;
2194 // SAFETY: the call is made safe by the following invariants:
2196 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2197 let cmp = f(unsafe { self.get_unchecked(mid) });
2199 // The reason why we use if/else control flow rather than match
2200 // is because match reorders comparison operations, which is perf sensitive.
2201 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2204 } else if cmp == Greater {
2210 size = right - left;
2215 /// Binary searches this sorted slice with a key extraction function.
2217 /// Assumes that the slice is sorted by the key, for instance with
2218 /// [`sort_by_key`] using the same key extraction function.
2220 /// If the value is found then [`Result::Ok`] is returned, containing the
2221 /// index of the matching element. If there are multiple matches, then any
2222 /// one of the matches could be returned. If the value is not found then
2223 /// [`Result::Err`] is returned, containing the index where a matching
2224 /// element could be inserted while maintaining sorted order.
2226 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2228 /// [`sort_by_key`]: #method.sort_by_key
2229 /// [`binary_search`]: #method.binary_search
2230 /// [`binary_search_by`]: #method.binary_search_by
2231 /// [`partition_point`]: #method.partition_point
2235 /// Looks up a series of four elements in a slice of pairs sorted by
2236 /// their second elements. The first is found, with a uniquely
2237 /// determined position; the second and third are not found; the
2238 /// fourth could match any position in `[1, 4]`.
2241 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2242 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2243 /// (1, 21), (2, 34), (4, 55)];
2245 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2246 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2247 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2248 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2249 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2251 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2253 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2255 F: FnMut(&'a T) -> B,
2258 self.binary_search_by(|k| f(k).cmp(b))
2261 /// Sorts the slice, but may not preserve the order of equal elements.
2263 /// This sort is unstable (i.e., may reorder equal elements), in-place
2264 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2266 /// # Current implementation
2268 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2269 /// which combines the fast average case of randomized quicksort with the fast worst case of
2270 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2271 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2272 /// deterministic behavior.
2274 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2275 /// slice consists of several concatenated sorted sequences.
2280 /// let mut v = [-5, 4, 1, -3, 2];
2282 /// v.sort_unstable();
2283 /// assert!(v == [-5, -3, 1, 2, 4]);
2286 /// [pdqsort]: https://github.com/orlp/pdqsort
2287 #[stable(feature = "sort_unstable", since = "1.20.0")]
2289 pub fn sort_unstable(&mut self)
2293 sort::quicksort(self, |a, b| a.lt(b));
2296 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2299 /// This sort is unstable (i.e., may reorder equal elements), in-place
2300 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2302 /// The comparator function must define a total ordering for the elements in the slice. If
2303 /// the ordering is not total, the order of the elements is unspecified. An order is a
2304 /// total order if it is (for all `a`, `b` and `c`):
2306 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2307 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2309 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2310 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2313 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2314 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2315 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2318 /// # Current implementation
2320 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2321 /// which combines the fast average case of randomized quicksort with the fast worst case of
2322 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2323 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2324 /// deterministic behavior.
2326 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2327 /// slice consists of several concatenated sorted sequences.
2332 /// let mut v = [5, 4, 1, 3, 2];
2333 /// v.sort_unstable_by(|a, b| a.cmp(b));
2334 /// assert!(v == [1, 2, 3, 4, 5]);
2336 /// // reverse sorting
2337 /// v.sort_unstable_by(|a, b| b.cmp(a));
2338 /// assert!(v == [5, 4, 3, 2, 1]);
2341 /// [pdqsort]: https://github.com/orlp/pdqsort
2342 #[stable(feature = "sort_unstable", since = "1.20.0")]
2344 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2346 F: FnMut(&T, &T) -> Ordering,
2348 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2351 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2354 /// This sort is unstable (i.e., may reorder equal elements), in-place
2355 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2358 /// # Current implementation
2360 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2361 /// which combines the fast average case of randomized quicksort with the fast worst case of
2362 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2363 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2364 /// deterministic behavior.
2366 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2367 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2368 /// cases where the key function is expensive.
2373 /// let mut v = [-5i32, 4, 1, -3, 2];
2375 /// v.sort_unstable_by_key(|k| k.abs());
2376 /// assert!(v == [1, 2, -3, 4, -5]);
2379 /// [pdqsort]: https://github.com/orlp/pdqsort
2380 #[stable(feature = "sort_unstable", since = "1.20.0")]
2382 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2387 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2390 /// Reorder the slice such that the element at `index` is at its final sorted position.
2391 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2392 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2394 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2398 self.select_nth_unstable(index)
2401 /// Reorder the slice with a comparator function such that the element at `index` is at its
2402 /// final sorted position.
2403 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2404 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2406 pub fn partition_at_index_by<F>(
2410 ) -> (&mut [T], &mut T, &mut [T])
2412 F: FnMut(&T, &T) -> Ordering,
2414 self.select_nth_unstable_by(index, compare)
2417 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2418 /// final sorted position.
2419 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2420 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2422 pub fn partition_at_index_by_key<K, F>(
2426 ) -> (&mut [T], &mut T, &mut [T])
2431 self.select_nth_unstable_by_key(index, f)
2434 /// Reorder the slice such that the element at `index` is at its final sorted position.
2436 /// This reordering has the additional property that any value at position `i < index` will be
2437 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2438 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2439 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2440 /// element" in other libraries. It returns a triplet of the following values: all elements less
2441 /// than the one at the given index, the value at the given index, and all elements greater than
2442 /// the one at the given index.
2444 /// # Current implementation
2446 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2447 /// used for [`sort_unstable`].
2449 /// [`sort_unstable`]: #method.sort_unstable
2453 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2458 /// let mut v = [-5i32, 4, 1, -3, 2];
2460 /// // Find the median
2461 /// v.select_nth_unstable(2);
2463 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2464 /// // about the specified index.
2465 /// assert!(v == [-3, -5, 1, 2, 4] ||
2466 /// v == [-5, -3, 1, 2, 4] ||
2467 /// v == [-3, -5, 1, 4, 2] ||
2468 /// v == [-5, -3, 1, 4, 2]);
2470 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2472 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2476 let mut f = |a: &T, b: &T| a.lt(b);
2477 sort::partition_at_index(self, index, &mut f)
2480 /// Reorder the slice with a comparator function such that the element at `index` is at its
2481 /// final sorted position.
2483 /// This reordering has the additional property that any value at position `i < index` will be
2484 /// less than or equal to any value at a position `j > index` using the comparator function.
2485 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2486 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2487 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2488 /// values: all elements less than the one at the given index, the value at the given index,
2489 /// and all elements greater than the one at the given index, using the provided comparator
2492 /// # Current implementation
2494 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2495 /// used for [`sort_unstable`].
2497 /// [`sort_unstable`]: #method.sort_unstable
2501 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2506 /// let mut v = [-5i32, 4, 1, -3, 2];
2508 /// // Find the median as if the slice were sorted in descending order.
2509 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2511 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2512 /// // about the specified index.
2513 /// assert!(v == [2, 4, 1, -5, -3] ||
2514 /// v == [2, 4, 1, -3, -5] ||
2515 /// v == [4, 2, 1, -5, -3] ||
2516 /// v == [4, 2, 1, -3, -5]);
2518 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2520 pub fn select_nth_unstable_by<F>(
2524 ) -> (&mut [T], &mut T, &mut [T])
2526 F: FnMut(&T, &T) -> Ordering,
2528 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2529 sort::partition_at_index(self, index, &mut f)
2532 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2533 /// final sorted position.
2535 /// This reordering has the additional property that any value at position `i < index` will be
2536 /// less than or equal to any value at a position `j > index` using the key extraction function.
2537 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2538 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2539 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2540 /// values: all elements less than the one at the given index, the value at the given index, and
2541 /// all elements greater than the one at the given index, using the provided key extraction
2544 /// # Current implementation
2546 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2547 /// used for [`sort_unstable`].
2549 /// [`sort_unstable`]: #method.sort_unstable
2553 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2558 /// let mut v = [-5i32, 4, 1, -3, 2];
2560 /// // Return the median as if the array were sorted according to absolute value.
2561 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2563 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2564 /// // about the specified index.
2565 /// assert!(v == [1, 2, -3, 4, -5] ||
2566 /// v == [1, 2, -3, -5, 4] ||
2567 /// v == [2, 1, -3, 4, -5] ||
2568 /// v == [2, 1, -3, -5, 4]);
2570 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2572 pub fn select_nth_unstable_by_key<K, F>(
2576 ) -> (&mut [T], &mut T, &mut [T])
2581 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2582 sort::partition_at_index(self, index, &mut g)
2585 /// Moves all consecutive repeated elements to the end of the slice according to the
2586 /// [`PartialEq`] trait implementation.
2588 /// Returns two slices. The first contains no consecutive repeated elements.
2589 /// The second contains all the duplicates in no specified order.
2591 /// If the slice is sorted, the first returned slice contains no duplicates.
2596 /// #![feature(slice_partition_dedup)]
2598 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2600 /// let (dedup, duplicates) = slice.partition_dedup();
2602 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2603 /// assert_eq!(duplicates, [2, 3, 1]);
2605 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2607 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2611 self.partition_dedup_by(|a, b| a == b)
2614 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2615 /// a given equality relation.
2617 /// Returns two slices. The first contains no consecutive repeated elements.
2618 /// The second contains all the duplicates in no specified order.
2620 /// The `same_bucket` function is passed references to two elements from the slice and
2621 /// must determine if the elements compare equal. The elements are passed in opposite order
2622 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2623 /// at the end of the slice.
2625 /// If the slice is sorted, the first returned slice contains no duplicates.
2630 /// #![feature(slice_partition_dedup)]
2632 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2634 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2636 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2637 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2639 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2641 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2643 F: FnMut(&mut T, &mut T) -> bool,
2645 // Although we have a mutable reference to `self`, we cannot make
2646 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2647 // must ensure that the slice is in a valid state at all times.
2649 // The way that we handle this is by using swaps; we iterate
2650 // over all the elements, swapping as we go so that at the end
2651 // the elements we wish to keep are in the front, and those we
2652 // wish to reject are at the back. We can then split the slice.
2653 // This operation is still `O(n)`.
2655 // Example: We start in this state, where `r` represents "next
2656 // read" and `w` represents "next_write`.
2659 // +---+---+---+---+---+---+
2660 // | 0 | 1 | 1 | 2 | 3 | 3 |
2661 // +---+---+---+---+---+---+
2664 // Comparing self[r] against self[w-1], this is not a duplicate, so
2665 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2666 // r and w, leaving us with:
2669 // +---+---+---+---+---+---+
2670 // | 0 | 1 | 1 | 2 | 3 | 3 |
2671 // +---+---+---+---+---+---+
2674 // Comparing self[r] against self[w-1], this value is a duplicate,
2675 // so we increment `r` but leave everything else unchanged:
2678 // +---+---+---+---+---+---+
2679 // | 0 | 1 | 1 | 2 | 3 | 3 |
2680 // +---+---+---+---+---+---+
2683 // Comparing self[r] against self[w-1], this is not a duplicate,
2684 // so swap self[r] and self[w] and advance r and w:
2687 // +---+---+---+---+---+---+
2688 // | 0 | 1 | 2 | 1 | 3 | 3 |
2689 // +---+---+---+---+---+---+
2692 // Not a duplicate, repeat:
2695 // +---+---+---+---+---+---+
2696 // | 0 | 1 | 2 | 3 | 1 | 3 |
2697 // +---+---+---+---+---+---+
2700 // Duplicate, advance r. End of slice. Split at w.
2702 let len = self.len();
2704 return (self, &mut []);
2707 let ptr = self.as_mut_ptr();
2708 let mut next_read: usize = 1;
2709 let mut next_write: usize = 1;
2711 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2712 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2713 // one element before `ptr_write`, but `next_write` starts at 1, so
2714 // `prev_ptr_write` is never less than 0 and is inside the slice.
2715 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2716 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2717 // and `prev_ptr_write.offset(1)`.
2719 // `next_write` is also incremented at most once per loop at most meaning
2720 // no element is skipped when it may need to be swapped.
2722 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2723 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2724 // The explanation is simply that `next_read >= next_write` is always true,
2725 // thus `next_read > next_write - 1` is too.
2727 // Avoid bounds checks by using raw pointers.
2728 while next_read < len {
2729 let ptr_read = ptr.add(next_read);
2730 let prev_ptr_write = ptr.add(next_write - 1);
2731 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2732 if next_read != next_write {
2733 let ptr_write = prev_ptr_write.offset(1);
2734 mem::swap(&mut *ptr_read, &mut *ptr_write);
2742 self.split_at_mut(next_write)
2745 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2746 /// to the same key.
2748 /// Returns two slices. The first contains no consecutive repeated elements.
2749 /// The second contains all the duplicates in no specified order.
2751 /// If the slice is sorted, the first returned slice contains no duplicates.
2756 /// #![feature(slice_partition_dedup)]
2758 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2760 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2762 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2763 /// assert_eq!(duplicates, [21, 30, 13]);
2765 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2767 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2769 F: FnMut(&mut T) -> K,
2772 self.partition_dedup_by(|a, b| key(a) == key(b))
2775 /// Rotates the slice in-place such that the first `mid` elements of the
2776 /// slice move to the end while the last `self.len() - mid` elements move to
2777 /// the front. After calling `rotate_left`, the element previously at index
2778 /// `mid` will become the first element in the slice.
2782 /// This function will panic if `mid` is greater than the length of the
2783 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2788 /// Takes linear (in `self.len()`) time.
2793 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2794 /// a.rotate_left(2);
2795 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2798 /// Rotating a subslice:
2801 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2802 /// a[1..5].rotate_left(1);
2803 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2805 #[stable(feature = "slice_rotate", since = "1.26.0")]
2806 pub fn rotate_left(&mut self, mid: usize) {
2807 assert!(mid <= self.len());
2808 let k = self.len() - mid;
2809 let p = self.as_mut_ptr();
2811 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2812 // valid for reading and writing, as required by `ptr_rotate`.
2814 rotate::ptr_rotate(mid, p.add(mid), k);
2818 /// Rotates the slice in-place such that the first `self.len() - k`
2819 /// elements of the slice move to the end while the last `k` elements move
2820 /// to the front. After calling `rotate_right`, the element previously at
2821 /// index `self.len() - k` will become the first element in the slice.
2825 /// This function will panic if `k` is greater than the length of the
2826 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2831 /// Takes linear (in `self.len()`) time.
2836 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2837 /// a.rotate_right(2);
2838 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2841 /// Rotate a subslice:
2844 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2845 /// a[1..5].rotate_right(1);
2846 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2848 #[stable(feature = "slice_rotate", since = "1.26.0")]
2849 pub fn rotate_right(&mut self, k: usize) {
2850 assert!(k <= self.len());
2851 let mid = self.len() - k;
2852 let p = self.as_mut_ptr();
2854 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2855 // valid for reading and writing, as required by `ptr_rotate`.
2857 rotate::ptr_rotate(mid, p.add(mid), k);
2861 /// Fills `self` with elements by cloning `value`.
2866 /// let mut buf = vec![0; 10];
2868 /// assert_eq!(buf, vec![1; 10]);
2870 #[doc(alias = "memset")]
2871 #[stable(feature = "slice_fill", since = "1.50.0")]
2872 pub fn fill(&mut self, value: T)
2876 specialize::SpecFill::spec_fill(self, value);
2879 /// Fills `self` with elements returned by calling a closure repeatedly.
2881 /// This method uses a closure to create new values. If you'd rather
2882 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2883 /// trait to generate values, you can pass [`Default::default`] as the
2886 /// [`fill`]: #method.fill
2891 /// let mut buf = vec![1; 10];
2892 /// buf.fill_with(Default::default);
2893 /// assert_eq!(buf, vec![0; 10]);
2895 #[doc(alias = "memset")]
2896 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2897 pub fn fill_with<F>(&mut self, mut f: F)
2906 /// Copies the elements from `src` into `self`.
2908 /// The length of `src` must be the same as `self`.
2910 /// If `T` implements `Copy`, it can be more performant to use
2911 /// [`copy_from_slice`].
2915 /// This function will panic if the two slices have different lengths.
2919 /// Cloning two elements from a slice into another:
2922 /// let src = [1, 2, 3, 4];
2923 /// let mut dst = [0, 0];
2925 /// // Because the slices have to be the same length,
2926 /// // we slice the source slice from four elements
2927 /// // to two. It will panic if we don't do this.
2928 /// dst.clone_from_slice(&src[2..]);
2930 /// assert_eq!(src, [1, 2, 3, 4]);
2931 /// assert_eq!(dst, [3, 4]);
2934 /// Rust enforces that there can only be one mutable reference with no
2935 /// immutable references to a particular piece of data in a particular
2936 /// scope. Because of this, attempting to use `clone_from_slice` on a
2937 /// single slice will result in a compile failure:
2940 /// let mut slice = [1, 2, 3, 4, 5];
2942 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2945 /// To work around this, we can use [`split_at_mut`] to create two distinct
2946 /// sub-slices from a slice:
2949 /// let mut slice = [1, 2, 3, 4, 5];
2952 /// let (left, right) = slice.split_at_mut(2);
2953 /// left.clone_from_slice(&right[1..]);
2956 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2959 /// [`copy_from_slice`]: #method.copy_from_slice
2960 /// [`split_at_mut`]: #method.split_at_mut
2961 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2962 pub fn clone_from_slice(&mut self, src: &[T])
2966 self.spec_clone_from(src);
2969 /// Copies all elements from `src` into `self`, using a memcpy.
2971 /// The length of `src` must be the same as `self`.
2973 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2977 /// This function will panic if the two slices have different lengths.
2981 /// Copying two elements from a slice into another:
2984 /// let src = [1, 2, 3, 4];
2985 /// let mut dst = [0, 0];
2987 /// // Because the slices have to be the same length,
2988 /// // we slice the source slice from four elements
2989 /// // to two. It will panic if we don't do this.
2990 /// dst.copy_from_slice(&src[2..]);
2992 /// assert_eq!(src, [1, 2, 3, 4]);
2993 /// assert_eq!(dst, [3, 4]);
2996 /// Rust enforces that there can only be one mutable reference with no
2997 /// immutable references to a particular piece of data in a particular
2998 /// scope. Because of this, attempting to use `copy_from_slice` on a
2999 /// single slice will result in a compile failure:
3002 /// let mut slice = [1, 2, 3, 4, 5];
3004 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3007 /// To work around this, we can use [`split_at_mut`] to create two distinct
3008 /// sub-slices from a slice:
3011 /// let mut slice = [1, 2, 3, 4, 5];
3014 /// let (left, right) = slice.split_at_mut(2);
3015 /// left.copy_from_slice(&right[1..]);
3018 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3021 /// [`clone_from_slice`]: #method.clone_from_slice
3022 /// [`split_at_mut`]: #method.split_at_mut
3023 #[doc(alias = "memcpy")]
3024 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3025 pub fn copy_from_slice(&mut self, src: &[T])
3029 // The panic code path was put into a cold function to not bloat the
3034 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3036 "source slice length ({}) does not match destination slice length ({})",
3041 if self.len() != src.len() {
3042 len_mismatch_fail(self.len(), src.len());
3045 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3046 // checked to have the same length. The slices cannot overlap because
3047 // mutable references are exclusive.
3049 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3053 /// Copies elements from one part of the slice to another part of itself,
3054 /// using a memmove.
3056 /// `src` is the range within `self` to copy from. `dest` is the starting
3057 /// index of the range within `self` to copy to, which will have the same
3058 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3059 /// must be less than or equal to `self.len()`.
3063 /// This function will panic if either range exceeds the end of the slice,
3064 /// or if the end of `src` is before the start.
3068 /// Copying four bytes within a slice:
3071 /// let mut bytes = *b"Hello, World!";
3073 /// bytes.copy_within(1..5, 8);
3075 /// assert_eq!(&bytes, b"Hello, Wello!");
3077 #[stable(feature = "copy_within", since = "1.37.0")]
3079 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3083 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3084 let count = src_end - src_start;
3085 assert!(dest <= self.len() - count, "dest is out of bounds");
3086 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3087 // as have those for `ptr::add`.
3089 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3093 /// Swaps all elements in `self` with those in `other`.
3095 /// The length of `other` must be the same as `self`.
3099 /// This function will panic if the two slices have different lengths.
3103 /// Swapping two elements across slices:
3106 /// let mut slice1 = [0, 0];
3107 /// let mut slice2 = [1, 2, 3, 4];
3109 /// slice1.swap_with_slice(&mut slice2[2..]);
3111 /// assert_eq!(slice1, [3, 4]);
3112 /// assert_eq!(slice2, [1, 2, 0, 0]);
3115 /// Rust enforces that there can only be one mutable reference to a
3116 /// particular piece of data in a particular scope. Because of this,
3117 /// attempting to use `swap_with_slice` on a single slice will result in
3118 /// a compile failure:
3121 /// let mut slice = [1, 2, 3, 4, 5];
3122 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3125 /// To work around this, we can use [`split_at_mut`] to create two distinct
3126 /// mutable sub-slices from a slice:
3129 /// let mut slice = [1, 2, 3, 4, 5];
3132 /// let (left, right) = slice.split_at_mut(2);
3133 /// left.swap_with_slice(&mut right[1..]);
3136 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3139 /// [`split_at_mut`]: #method.split_at_mut
3140 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3141 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3142 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3143 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3144 // checked to have the same length. The slices cannot overlap because
3145 // mutable references are exclusive.
3147 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3151 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3152 fn align_to_offsets<U>(&self) -> (usize, usize) {
3153 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3154 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3156 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3157 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3158 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3160 // Formula to calculate this is:
3162 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3163 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3165 // Expanded and simplified:
3167 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3168 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3170 // Luckily since all this is constant-evaluated... performance here matters not!
3172 fn gcd(a: usize, b: usize) -> usize {
3173 use crate::intrinsics;
3174 // iterative stein’s algorithm
3175 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3176 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3178 // SAFETY: `a` and `b` are checked to be non-zero values.
3179 let (ctz_a, mut ctz_b) = unsafe {
3186 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3188 let k = ctz_a.min(ctz_b);
3189 let mut a = a >> ctz_a;
3192 // remove all factors of 2 from b
3195 mem::swap(&mut a, &mut b);
3198 // SAFETY: `b` is checked to be non-zero.
3203 ctz_b = intrinsics::cttz_nonzero(b);
3208 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3209 let ts: usize = mem::size_of::<U>() / gcd;
3210 let us: usize = mem::size_of::<T>() / gcd;
3212 // Armed with this knowledge, we can find how many `U`s we can fit!
3213 let us_len = self.len() / ts * us;
3214 // And how many `T`s will be in the trailing slice!
3215 let ts_len = self.len() % ts;
3219 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3222 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3223 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3224 /// length possible for a given type and input slice, but only your algorithm's performance
3225 /// should depend on that, not its correctness. It is permissible for all of the input data to
3226 /// be returned as the prefix or suffix slice.
3228 /// This method has no purpose when either input element `T` or output element `U` are
3229 /// zero-sized and will return the original slice without splitting anything.
3233 /// This method is essentially a `transmute` with respect to the elements in the returned
3234 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3242 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3243 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3244 /// // less_efficient_algorithm_for_bytes(prefix);
3245 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3246 /// // less_efficient_algorithm_for_bytes(suffix);
3249 #[stable(feature = "slice_align_to", since = "1.30.0")]
3250 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3251 // Note that most of this function will be constant-evaluated,
3252 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3253 // handle ZSTs specially, which is – don't handle them at all.
3254 return (self, &[], &[]);
3257 // First, find at what point do we split between the first and 2nd slice. Easy with
3258 // ptr.align_offset.
3259 let ptr = self.as_ptr();
3260 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3261 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3262 if offset > self.len() {
3265 let (left, rest) = self.split_at(offset);
3266 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3267 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3268 // since the caller guarantees that we can transmute `T` to `U` safely.
3272 from_raw_parts(rest.as_ptr() as *const U, us_len),
3273 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3279 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3282 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3283 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3284 /// length possible for a given type and input slice, but only your algorithm's performance
3285 /// should depend on that, not its correctness. It is permissible for all of the input data to
3286 /// be returned as the prefix or suffix slice.
3288 /// This method has no purpose when either input element `T` or output element `U` are
3289 /// zero-sized and will return the original slice without splitting anything.
3293 /// This method is essentially a `transmute` with respect to the elements in the returned
3294 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3302 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3303 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3304 /// // less_efficient_algorithm_for_bytes(prefix);
3305 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3306 /// // less_efficient_algorithm_for_bytes(suffix);
3309 #[stable(feature = "slice_align_to", since = "1.30.0")]
3310 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3311 // Note that most of this function will be constant-evaluated,
3312 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3313 // handle ZSTs specially, which is – don't handle them at all.
3314 return (self, &mut [], &mut []);
3317 // First, find at what point do we split between the first and 2nd slice. Easy with
3318 // ptr.align_offset.
3319 let ptr = self.as_ptr();
3320 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3321 // rest of the method. This is done by passing a pointer to &[T] with an
3322 // alignment targeted for U.
3323 // `crate::ptr::align_offset` is called with a correctly aligned and
3324 // valid pointer `ptr` (it comes from a reference to `self`) and with
3325 // a size that is a power of two (since it comes from the alignement for U),
3326 // satisfying its safety constraints.
3327 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3328 if offset > self.len() {
3329 (self, &mut [], &mut [])
3331 let (left, rest) = self.split_at_mut(offset);
3332 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3333 let rest_len = rest.len();
3334 let mut_ptr = rest.as_mut_ptr();
3335 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3336 // SAFETY: see comments for `align_to`.
3340 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3341 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3347 /// Checks if the elements of this slice are sorted.
3349 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3350 /// slice yields exactly zero or one element, `true` is returned.
3352 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3353 /// implies that this function returns `false` if any two consecutive items are not
3359 /// #![feature(is_sorted)]
3360 /// let empty: [i32; 0] = [];
3362 /// assert!([1, 2, 2, 9].is_sorted());
3363 /// assert!(![1, 3, 2, 4].is_sorted());
3364 /// assert!([0].is_sorted());
3365 /// assert!(empty.is_sorted());
3366 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3369 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3370 pub fn is_sorted(&self) -> bool
3374 self.is_sorted_by(|a, b| a.partial_cmp(b))
3377 /// Checks if the elements of this slice are sorted using the given comparator function.
3379 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3380 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3381 /// [`is_sorted`]; see its documentation for more information.
3383 /// [`is_sorted`]: #method.is_sorted
3384 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3385 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3387 F: FnMut(&T, &T) -> Option<Ordering>,
3389 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3392 /// Checks if the elements of this slice are sorted using the given key extraction function.
3394 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3395 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3396 /// documentation for more information.
3398 /// [`is_sorted`]: #method.is_sorted
3403 /// #![feature(is_sorted)]
3405 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3406 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3409 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3410 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3415 self.iter().is_sorted_by_key(f)
3418 /// Returns the index of the partition point according to the given predicate
3419 /// (the index of the first element of the second partition).
3421 /// The slice is assumed to be partitioned according to the given predicate.
3422 /// This means that all elements for which the predicate returns true are at the start of the slice
3423 /// and all elements for which the predicate returns false are at the end.
3424 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3425 /// (all odd numbers are at the start, all even at the end).
3427 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3428 /// as this method performs a kind of binary search.
3430 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3432 /// [`binary_search`]: #method.binary_search
3433 /// [`binary_search_by`]: #method.binary_search_by
3434 /// [`binary_search_by_key`]: #method.binary_search_by_key
3439 /// let v = [1, 2, 3, 3, 5, 6, 7];
3440 /// let i = v.partition_point(|&x| x < 5);
3442 /// assert_eq!(i, 4);
3443 /// assert!(v[..i].iter().all(|&x| x < 5));
3444 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3446 #[stable(feature = "partition_point", since = "1.52.0")]
3447 pub fn partition_point<P>(&self, mut pred: P) -> usize
3449 P: FnMut(&T) -> bool,
3452 let mut right = self.len();
3454 while left != right {
3455 let mid = left + (right - left) / 2;
3456 // SAFETY: When `left < right`, `left <= mid < right`.
3457 // Therefore `left` always increases and `right` always decreases,
3458 // and either of them is selected. In both cases `left <= right` is
3459 // satisfied. Therefore if `left < right` in a step, `left <= right`
3460 // is satisfied in the next step. Therefore as long as `left != right`,
3461 // `0 <= left < right <= len` is satisfied and if this case
3462 // `0 <= mid < len` is satisfied too.
3463 let value = unsafe { self.get_unchecked(mid) };
3475 trait CloneFromSpec<T> {
3476 fn spec_clone_from(&mut self, src: &[T]);
3479 impl<T> CloneFromSpec<T> for [T]
3483 default fn spec_clone_from(&mut self, src: &[T]) {
3484 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3485 // NOTE: We need to explicitly slice them to the same length
3486 // to make it easier for the optimizer to elide bounds checking.
3487 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3488 let len = self.len();
3489 let src = &src[..len];
3491 self[i].clone_from(&src[i]);
3496 impl<T> CloneFromSpec<T> for [T]
3500 fn spec_clone_from(&mut self, src: &[T]) {
3501 self.copy_from_slice(src);
3505 #[stable(feature = "rust1", since = "1.0.0")]
3506 impl<T> Default for &[T] {
3507 /// Creates an empty slice.
3508 fn default() -> Self {
3513 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3514 impl<T> Default for &mut [T] {
3515 /// Creates a mutable empty slice.
3516 fn default() -> Self {
3521 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3522 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3523 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3524 /// `str`) to slices, and then this trait will be replaced or abolished.
3525 pub trait SlicePattern {
3526 /// The element type of the slice being matched on.
3529 /// Currently, the consumers of `SlicePattern` need a slice.
3530 fn as_slice(&self) -> &[Self::Item];
3533 #[stable(feature = "slice_strip", since = "1.51.0")]
3534 impl<T> SlicePattern for [T] {
3538 fn as_slice(&self) -> &[Self::Item] {
3543 #[stable(feature = "slice_strip", since = "1.51.0")]
3544 impl<T, const N: usize> SlicePattern for [T; N] {
3548 fn as_slice(&self) -> &[Self::Item] {