1 // ignore-tidy-filelength
3 //! Slice management and manipulation.
5 //! For more details see [`std::slice`].
7 //! [`std::slice`]: ../../std/slice/index.html
9 #![stable(feature = "rust1", since = "1.0.0")]
11 use crate::cmp::Ordering::{self, Greater, Less};
12 use crate::marker::Copy;
14 use crate::num::NonZeroUsize;
15 use crate::ops::{FnMut, Range, RangeBounds};
16 use crate::option::Option;
17 use crate::option::Option::{None, Some};
19 use crate::result::Result;
20 use crate::result::Result::{Err, Ok};
24 feature = "slice_internals",
26 reason = "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Chunks, ChunksMut, Windows};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{Iter, IterMut};
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter::{RSplit, RSplitMut};
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter::{ChunksExact, ChunksExactMut};
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter::{ArrayChunks, ArrayChunksMut};
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter::ArrayWindows;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter::{GroupBy, GroupByMut};
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter::{SplitInclusive, SplitInclusiveMut};
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw::{from_raw_parts, from_raw_parts_mut};
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw::{from_mut, from_ref};
74 // This function is public only because there is no other way to unit test heapsort.
75 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
76 pub use sort::heapsort;
78 #[stable(feature = "slice_get_slice", since = "1.28.0")]
79 pub use index::SliceIndex;
81 #[unstable(feature = "slice_range", issue = "76393")]
84 #[unstable(feature = "inherent_ascii_escape", issue = "77174")]
85 pub use ascii::EscapeAscii;
90 /// Returns the number of elements in the slice.
95 /// let a = [1, 2, 3];
96 /// assert_eq!(a.len(), 3);
98 #[doc(alias = "length")]
99 #[stable(feature = "rust1", since = "1.0.0")]
100 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
102 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
103 #[rustc_allow_const_fn_unstable(const_fn_union)]
104 pub const fn len(&self) -> usize {
107 // SAFETY: this is safe because `&[T]` and `FatPtr<T>` have the same layout.
108 // Only `std` can make this guarantee.
109 unsafe { crate::ptr::Repr { rust: self }.raw.len }
111 #[cfg(not(bootstrap))]
113 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
114 // As of this writing this causes a "Const-stable functions can only call other
115 // const-stable functions" error.
117 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
118 // and PtrComponents<T> have the same memory layouts. Only std can make this
120 unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
124 /// Returns `true` if the slice has a length of 0.
129 /// let a = [1, 2, 3];
130 /// assert!(!a.is_empty());
132 #[stable(feature = "rust1", since = "1.0.0")]
133 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
135 pub const fn is_empty(&self) -> bool {
139 /// Returns the first element of the slice, or `None` if it is empty.
144 /// let v = [10, 40, 30];
145 /// assert_eq!(Some(&10), v.first());
147 /// let w: &[i32] = &[];
148 /// assert_eq!(None, w.first());
150 #[stable(feature = "rust1", since = "1.0.0")]
151 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
153 pub const fn first(&self) -> Option<&T> {
154 if let [first, ..] = self { Some(first) } else { None }
157 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
162 /// let x = &mut [0, 1, 2];
164 /// if let Some(first) = x.first_mut() {
167 /// assert_eq!(x, &[5, 1, 2]);
169 #[stable(feature = "rust1", since = "1.0.0")]
170 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
172 pub const fn first_mut(&mut self) -> Option<&mut T> {
173 if let [first, ..] = self { Some(first) } else { None }
176 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
181 /// let x = &[0, 1, 2];
183 /// if let Some((first, elements)) = x.split_first() {
184 /// assert_eq!(first, &0);
185 /// assert_eq!(elements, &[1, 2]);
188 #[stable(feature = "slice_splits", since = "1.5.0")]
189 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
191 pub const fn split_first(&self) -> Option<(&T, &[T])> {
192 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
195 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
200 /// let x = &mut [0, 1, 2];
202 /// if let Some((first, elements)) = x.split_first_mut() {
207 /// assert_eq!(x, &[3, 4, 5]);
209 #[stable(feature = "slice_splits", since = "1.5.0")]
210 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
212 pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
213 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
216 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
221 /// let x = &[0, 1, 2];
223 /// if let Some((last, elements)) = x.split_last() {
224 /// assert_eq!(last, &2);
225 /// assert_eq!(elements, &[0, 1]);
228 #[stable(feature = "slice_splits", since = "1.5.0")]
229 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
231 pub const fn split_last(&self) -> Option<(&T, &[T])> {
232 if let [init @ .., last] = self { Some((last, init)) } else { None }
235 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
240 /// let x = &mut [0, 1, 2];
242 /// if let Some((last, elements)) = x.split_last_mut() {
247 /// assert_eq!(x, &[4, 5, 3]);
249 #[stable(feature = "slice_splits", since = "1.5.0")]
250 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
252 pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
253 if let [init @ .., last] = self { Some((last, init)) } else { None }
256 /// Returns the last element of the slice, or `None` if it is empty.
261 /// let v = [10, 40, 30];
262 /// assert_eq!(Some(&30), v.last());
264 /// let w: &[i32] = &[];
265 /// assert_eq!(None, w.last());
267 #[stable(feature = "rust1", since = "1.0.0")]
268 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
270 pub const fn last(&self) -> Option<&T> {
271 if let [.., last] = self { Some(last) } else { None }
274 /// Returns a mutable pointer to the last item in the slice.
279 /// let x = &mut [0, 1, 2];
281 /// if let Some(last) = x.last_mut() {
284 /// assert_eq!(x, &[0, 1, 10]);
286 #[stable(feature = "rust1", since = "1.0.0")]
287 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
289 pub const fn last_mut(&mut self) -> Option<&mut T> {
290 if let [.., last] = self { Some(last) } else { None }
293 /// Returns a reference to an element or subslice depending on the type of
296 /// - If given a position, returns a reference to the element at that
297 /// position or `None` if out of bounds.
298 /// - If given a range, returns the subslice corresponding to that range,
299 /// or `None` if out of bounds.
304 /// let v = [10, 40, 30];
305 /// assert_eq!(Some(&40), v.get(1));
306 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
307 /// assert_eq!(None, v.get(3));
308 /// assert_eq!(None, v.get(0..4));
310 #[stable(feature = "rust1", since = "1.0.0")]
312 pub fn get<I>(&self, index: I) -> Option<&I::Output>
319 /// Returns a mutable reference to an element or subslice depending on the
320 /// type of index (see [`get`]) or `None` if the index is out of bounds.
322 /// [`get`]: slice::get
327 /// let x = &mut [0, 1, 2];
329 /// if let Some(elem) = x.get_mut(1) {
332 /// assert_eq!(x, &[0, 42, 2]);
334 #[stable(feature = "rust1", since = "1.0.0")]
336 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
343 /// Returns a reference to an element or subslice, without doing bounds
346 /// For a safe alternative see [`get`].
350 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
351 /// even if the resulting reference is not used.
353 /// [`get`]: slice::get
354 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
359 /// let x = &[1, 2, 4];
362 /// assert_eq!(x.get_unchecked(1), &2);
365 #[stable(feature = "rust1", since = "1.0.0")]
367 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
371 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
372 // the slice is dereferencable because `self` is a safe reference.
373 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
374 unsafe { &*index.get_unchecked(self) }
377 /// Returns a mutable reference to an element or subslice, without doing
380 /// For a safe alternative see [`get_mut`].
384 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
385 /// even if the resulting reference is not used.
387 /// [`get_mut`]: slice::get_mut
388 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
393 /// let x = &mut [1, 2, 4];
396 /// let elem = x.get_unchecked_mut(1);
399 /// assert_eq!(x, &[1, 13, 4]);
401 #[stable(feature = "rust1", since = "1.0.0")]
403 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
407 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
408 // the slice is dereferencable because `self` is a safe reference.
409 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
410 unsafe { &mut *index.get_unchecked_mut(self) }
413 /// Returns a raw pointer to the slice's buffer.
415 /// The caller must ensure that the slice outlives the pointer this
416 /// function returns, or else it will end up pointing to garbage.
418 /// The caller must also ensure that the memory the pointer (non-transitively) points to
419 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
420 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
422 /// Modifying the container referenced by this slice may cause its buffer
423 /// to be reallocated, which would also make any pointers to it invalid.
428 /// let x = &[1, 2, 4];
429 /// let x_ptr = x.as_ptr();
432 /// for i in 0..x.len() {
433 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
438 /// [`as_mut_ptr`]: slice::as_mut_ptr
439 #[stable(feature = "rust1", since = "1.0.0")]
440 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
442 pub const fn as_ptr(&self) -> *const T {
443 self as *const [T] as *const T
446 /// Returns an unsafe mutable pointer to the slice's buffer.
448 /// The caller must ensure that the slice outlives the pointer this
449 /// function returns, or else it will end up pointing to garbage.
451 /// Modifying the container referenced by this slice may cause its buffer
452 /// to be reallocated, which would also make any pointers to it invalid.
457 /// let x = &mut [1, 2, 4];
458 /// let x_ptr = x.as_mut_ptr();
461 /// for i in 0..x.len() {
462 /// *x_ptr.add(i) += 2;
465 /// assert_eq!(x, &[3, 4, 6]);
467 #[stable(feature = "rust1", since = "1.0.0")]
468 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
470 pub const fn as_mut_ptr(&mut self) -> *mut T {
471 self as *mut [T] as *mut T
474 /// Returns the two raw pointers spanning the slice.
476 /// The returned range is half-open, which means that the end pointer
477 /// points *one past* the last element of the slice. This way, an empty
478 /// slice is represented by two equal pointers, and the difference between
479 /// the two pointers represents the size of the slice.
481 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
482 /// requires extra caution, as it does not point to a valid element in the
485 /// This function is useful for interacting with foreign interfaces which
486 /// use two pointers to refer to a range of elements in memory, as is
489 /// It can also be useful to check if a pointer to an element refers to an
490 /// element of this slice:
493 /// let a = [1, 2, 3];
494 /// let x = &a[1] as *const _;
495 /// let y = &5 as *const _;
497 /// assert!(a.as_ptr_range().contains(&x));
498 /// assert!(!a.as_ptr_range().contains(&y));
501 /// [`as_ptr`]: slice::as_ptr
502 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
503 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
505 pub const fn as_ptr_range(&self) -> Range<*const T> {
506 let start = self.as_ptr();
507 // SAFETY: The `add` here is safe, because:
509 // - Both pointers are part of the same object, as pointing directly
510 // past the object also counts.
512 // - The size of the slice is never larger than isize::MAX bytes, as
514 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
515 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
516 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
517 // (This doesn't seem normative yet, but the very same assumption is
518 // made in many places, including the Index implementation of slices.)
520 // - There is no wrapping around involved, as slices do not wrap past
521 // the end of the address space.
523 // See the documentation of pointer::add.
524 let end = unsafe { start.add(self.len()) };
528 /// Returns the two unsafe mutable pointers spanning the slice.
530 /// The returned range is half-open, which means that the end pointer
531 /// points *one past* the last element of the slice. This way, an empty
532 /// slice is represented by two equal pointers, and the difference between
533 /// the two pointers represents the size of the slice.
535 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
536 /// pointer requires extra caution, as it does not point to a valid element
539 /// This function is useful for interacting with foreign interfaces which
540 /// use two pointers to refer to a range of elements in memory, as is
543 /// [`as_mut_ptr`]: slice::as_mut_ptr
544 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
545 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
547 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
548 let start = self.as_mut_ptr();
549 // SAFETY: See as_ptr_range() above for why `add` here is safe.
550 let end = unsafe { start.add(self.len()) };
554 /// Swaps two elements in the slice.
558 /// * a - The index of the first element
559 /// * b - The index of the second element
563 /// Panics if `a` or `b` are out of bounds.
568 /// let mut v = ["a", "b", "c", "d"];
570 /// assert!(v == ["a", "d", "c", "b"]);
572 #[stable(feature = "rust1", since = "1.0.0")]
574 pub fn swap(&mut self, a: usize, b: usize) {
575 // Can't take two mutable loans from one vector, so instead use raw pointers.
576 let pa = ptr::addr_of_mut!(self[a]);
577 let pb = ptr::addr_of_mut!(self[b]);
578 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
579 // to elements in the slice and therefore are guaranteed to be valid and aligned.
580 // Note that accessing the elements behind `a` and `b` is checked and will
581 // panic when out of bounds.
587 /// Reverses the order of elements in the slice, in place.
592 /// let mut v = [1, 2, 3];
594 /// assert!(v == [3, 2, 1]);
596 #[stable(feature = "rust1", since = "1.0.0")]
598 pub fn reverse(&mut self) {
599 let mut i: usize = 0;
602 // For very small types, all the individual reads in the normal
603 // path perform poorly. We can do better, given efficient unaligned
604 // load/store, by loading a larger chunk and reversing a register.
606 // Ideally LLVM would do this for us, as it knows better than we do
607 // whether unaligned reads are efficient (since that changes between
608 // different ARM versions, for example) and what the best chunk size
609 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
610 // the loop, so we need to do this ourselves. (Hypothesis: reverse
611 // is troublesome because the sides can be aligned differently --
612 // will be, when the length is odd -- so there's no way of emitting
613 // pre- and postludes to use fully-aligned SIMD in the middle.)
615 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
617 if fast_unaligned && mem::size_of::<T>() == 1 {
618 // Use the llvm.bswap intrinsic to reverse u8s in a usize
619 let chunk = mem::size_of::<usize>();
620 while i + chunk - 1 < ln / 2 {
621 // SAFETY: There are several things to check here:
623 // - Note that `chunk` is either 4 or 8 due to the cfg check
624 // above. So `chunk - 1` is positive.
625 // - Indexing with index `i` is fine as the loop check guarantees
626 // `i + chunk - 1 < ln / 2`
627 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
628 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
629 // - `i + chunk > 0` is trivially true.
630 // - The loop check guarantees:
631 // `i + chunk - 1 < ln / 2`
632 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
633 // - The `read_unaligned` and `write_unaligned` calls are fine:
634 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
635 // (see above) and `pb` points to index `ln - i - chunk`, so
636 // both are at least `chunk`
637 // many bytes away from the end of `self`.
638 // - Any initialized memory is valid `usize`.
640 let ptr = self.as_mut_ptr();
642 let pb = ptr.add(ln - i - chunk);
643 let va = ptr::read_unaligned(pa as *mut usize);
644 let vb = ptr::read_unaligned(pb as *mut usize);
645 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
646 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
652 if fast_unaligned && mem::size_of::<T>() == 2 {
653 // Use rotate-by-16 to reverse u16s in a u32
654 let chunk = mem::size_of::<u32>() / 2;
655 while i + chunk - 1 < ln / 2 {
656 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
657 // (and obviously `i < ln`), because each element is 2 bytes and
660 // `i + chunk - 1 < ln / 2` # while condition
661 // `i + 2 - 1 < ln / 2`
664 // Since it's less than the length divided by 2, then it must be
667 // This also means that the condition `0 < i + chunk <= ln` is
668 // always respected, ensuring the `pb` pointer can be used
671 let ptr = self.as_mut_ptr();
673 let pb = ptr.add(ln - i - chunk);
674 let va = ptr::read_unaligned(pa as *mut u32);
675 let vb = ptr::read_unaligned(pb as *mut u32);
676 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
677 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
684 // SAFETY: `i` is inferior to half the length of the slice so
685 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
686 // will not go further than `ln / 2 - 1`).
687 // The resulting pointers `pa` and `pb` are therefore valid and
688 // aligned, and can be read from and written to.
690 // Unsafe swap to avoid the bounds check in safe swap.
691 let ptr = self.as_mut_ptr();
693 let pb = ptr.add(ln - i - 1);
700 /// Returns an iterator over the slice.
705 /// let x = &[1, 2, 4];
706 /// let mut iterator = x.iter();
708 /// assert_eq!(iterator.next(), Some(&1));
709 /// assert_eq!(iterator.next(), Some(&2));
710 /// assert_eq!(iterator.next(), Some(&4));
711 /// assert_eq!(iterator.next(), None);
713 #[stable(feature = "rust1", since = "1.0.0")]
715 pub fn iter(&self) -> Iter<'_, T> {
719 /// Returns an iterator that allows modifying each value.
724 /// let x = &mut [1, 2, 4];
725 /// for elem in x.iter_mut() {
728 /// assert_eq!(x, &[3, 4, 6]);
730 #[stable(feature = "rust1", since = "1.0.0")]
732 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
736 /// Returns an iterator over all contiguous windows of length
737 /// `size`. The windows overlap. If the slice is shorter than
738 /// `size`, the iterator returns no values.
742 /// Panics if `size` is 0.
747 /// let slice = ['r', 'u', 's', 't'];
748 /// let mut iter = slice.windows(2);
749 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
750 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
751 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
752 /// assert!(iter.next().is_none());
755 /// If the slice is shorter than `size`:
758 /// let slice = ['f', 'o', 'o'];
759 /// let mut iter = slice.windows(4);
760 /// assert!(iter.next().is_none());
762 #[stable(feature = "rust1", since = "1.0.0")]
764 pub fn windows(&self, size: usize) -> Windows<'_, T> {
765 let size = NonZeroUsize::new(size).expect("size is zero");
766 Windows::new(self, size)
769 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
770 /// beginning of the slice.
772 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
773 /// slice, then the last chunk will not have length `chunk_size`.
775 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
776 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
781 /// Panics if `chunk_size` is 0.
786 /// let slice = ['l', 'o', 'r', 'e', 'm'];
787 /// let mut iter = slice.chunks(2);
788 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
789 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
790 /// assert_eq!(iter.next().unwrap(), &['m']);
791 /// assert!(iter.next().is_none());
794 /// [`chunks_exact`]: slice::chunks_exact
795 /// [`rchunks`]: slice::rchunks
796 #[stable(feature = "rust1", since = "1.0.0")]
798 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
799 assert_ne!(chunk_size, 0);
800 Chunks::new(self, chunk_size)
803 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
804 /// beginning of the slice.
806 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
807 /// length of the slice, then the last chunk will not have length `chunk_size`.
809 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
810 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
811 /// the end of the slice.
815 /// Panics if `chunk_size` is 0.
820 /// let v = &mut [0, 0, 0, 0, 0];
821 /// let mut count = 1;
823 /// for chunk in v.chunks_mut(2) {
824 /// for elem in chunk.iter_mut() {
829 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
832 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
833 /// [`rchunks_mut`]: slice::rchunks_mut
834 #[stable(feature = "rust1", since = "1.0.0")]
836 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
837 assert_ne!(chunk_size, 0);
838 ChunksMut::new(self, chunk_size)
841 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
842 /// beginning of the slice.
844 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
845 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
846 /// from the `remainder` function of the iterator.
848 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
849 /// resulting code better than in the case of [`chunks`].
851 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
852 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
856 /// Panics if `chunk_size` is 0.
861 /// let slice = ['l', 'o', 'r', 'e', 'm'];
862 /// let mut iter = slice.chunks_exact(2);
863 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
864 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
865 /// assert!(iter.next().is_none());
866 /// assert_eq!(iter.remainder(), &['m']);
869 /// [`chunks`]: slice::chunks
870 /// [`rchunks_exact`]: slice::rchunks_exact
871 #[stable(feature = "chunks_exact", since = "1.31.0")]
873 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
874 assert_ne!(chunk_size, 0);
875 ChunksExact::new(self, chunk_size)
878 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
879 /// beginning of the slice.
881 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
882 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
883 /// retrieved from the `into_remainder` function of the iterator.
885 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
886 /// resulting code better than in the case of [`chunks_mut`].
888 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
889 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
894 /// Panics if `chunk_size` is 0.
899 /// let v = &mut [0, 0, 0, 0, 0];
900 /// let mut count = 1;
902 /// for chunk in v.chunks_exact_mut(2) {
903 /// for elem in chunk.iter_mut() {
908 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
911 /// [`chunks_mut`]: slice::chunks_mut
912 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
913 #[stable(feature = "chunks_exact", since = "1.31.0")]
915 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
916 assert_ne!(chunk_size, 0);
917 ChunksExactMut::new(self, chunk_size)
920 /// Splits the slice into a slice of `N`-element arrays,
921 /// assuming that there's no remainder.
925 /// This may only be called when
926 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
932 /// #![feature(slice_as_chunks)]
933 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
934 /// let chunks: &[[char; 1]] =
935 /// // SAFETY: 1-element chunks never have remainder
936 /// unsafe { slice.as_chunks_unchecked() };
937 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
938 /// let chunks: &[[char; 3]] =
939 /// // SAFETY: The slice length (6) is a multiple of 3
940 /// unsafe { slice.as_chunks_unchecked() };
941 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
943 /// // These would be unsound:
944 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
945 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
947 #[unstable(feature = "slice_as_chunks", issue = "74985")]
949 pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
950 debug_assert_ne!(N, 0);
951 debug_assert_eq!(self.len() % N, 0);
953 // SAFETY: Our precondition is exactly what's needed to call this
954 unsafe { crate::intrinsics::exact_div(self.len(), N) };
955 // SAFETY: We cast a slice of `new_len * N` elements into
956 // a slice of `new_len` many `N` elements chunks.
957 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
960 /// Splits the slice into a slice of `N`-element arrays,
961 /// starting at the beginning of the slice,
962 /// and a remainder slice with length strictly less than `N`.
966 /// Panics if `N` is 0. This check will most probably get changed to a compile time
967 /// error before this method gets stabilized.
972 /// #![feature(slice_as_chunks)]
973 /// let slice = ['l', 'o', 'r', 'e', 'm'];
974 /// let (chunks, remainder) = slice.as_chunks();
975 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
976 /// assert_eq!(remainder, &['m']);
978 #[unstable(feature = "slice_as_chunks", issue = "74985")]
980 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
982 let len = self.len() / N;
983 let (multiple_of_n, remainder) = self.split_at(len * N);
984 // SAFETY: We already panicked for zero, and ensured by construction
985 // that the length of the subslice is a multiple of N.
986 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
987 (array_slice, remainder)
990 /// Splits the slice into a slice of `N`-element arrays,
991 /// starting at the end of the slice,
992 /// and a remainder slice with length strictly less than `N`.
996 /// Panics if `N` is 0. This check will most probably get changed to a compile time
997 /// error before this method gets stabilized.
1002 /// #![feature(slice_as_chunks)]
1003 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1004 /// let (remainder, chunks) = slice.as_rchunks();
1005 /// assert_eq!(remainder, &['l']);
1006 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
1008 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1010 pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
1012 let len = self.len() / N;
1013 let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
1014 // SAFETY: We already panicked for zero, and ensured by construction
1015 // that the length of the subslice is a multiple of N.
1016 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
1017 (remainder, array_slice)
1020 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1021 /// beginning of the slice.
1023 /// The chunks are array references and do not overlap. If `N` does not divide the
1024 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1025 /// retrieved from the `remainder` function of the iterator.
1027 /// This method is the const generic equivalent of [`chunks_exact`].
1031 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1032 /// error before this method gets stabilized.
1037 /// #![feature(array_chunks)]
1038 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1039 /// let mut iter = slice.array_chunks();
1040 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1041 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1042 /// assert!(iter.next().is_none());
1043 /// assert_eq!(iter.remainder(), &['m']);
1046 /// [`chunks_exact`]: slice::chunks_exact
1047 #[unstable(feature = "array_chunks", issue = "74985")]
1049 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
1051 ArrayChunks::new(self)
1054 /// Splits the slice into a slice of `N`-element arrays,
1055 /// assuming that there's no remainder.
1059 /// This may only be called when
1060 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1066 /// #![feature(slice_as_chunks)]
1067 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1068 /// let chunks: &mut [[char; 1]] =
1069 /// // SAFETY: 1-element chunks never have remainder
1070 /// unsafe { slice.as_chunks_unchecked_mut() };
1071 /// chunks[0] = ['L'];
1072 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1073 /// let chunks: &mut [[char; 3]] =
1074 /// // SAFETY: The slice length (6) is a multiple of 3
1075 /// unsafe { slice.as_chunks_unchecked_mut() };
1076 /// chunks[1] = ['a', 'x', '?'];
1077 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1079 /// // These would be unsound:
1080 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1081 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1083 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1085 pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
1086 debug_assert_ne!(N, 0);
1087 debug_assert_eq!(self.len() % N, 0);
1089 // SAFETY: Our precondition is exactly what's needed to call this
1090 unsafe { crate::intrinsics::exact_div(self.len(), N) };
1091 // SAFETY: We cast a slice of `new_len * N` elements into
1092 // a slice of `new_len` many `N` elements chunks.
1093 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1096 /// Splits the slice into a slice of `N`-element arrays,
1097 /// starting at the beginning of the slice,
1098 /// and a remainder slice with length strictly less than `N`.
1102 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1103 /// error before this method gets stabilized.
1108 /// #![feature(slice_as_chunks)]
1109 /// let v = &mut [0, 0, 0, 0, 0];
1110 /// let mut count = 1;
1112 /// let (chunks, remainder) = v.as_chunks_mut();
1113 /// remainder[0] = 9;
1114 /// for chunk in chunks {
1115 /// *chunk = [count; 2];
1118 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1120 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1122 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
1124 let len = self.len() / N;
1125 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
1126 // SAFETY: We already panicked for zero, and ensured by construction
1127 // that the length of the subslice is a multiple of N.
1128 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1129 (array_slice, remainder)
1132 /// Splits the slice into a slice of `N`-element arrays,
1133 /// starting at the end of the slice,
1134 /// and a remainder slice with length strictly less than `N`.
1138 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1139 /// error before this method gets stabilized.
1144 /// #![feature(slice_as_chunks)]
1145 /// let v = &mut [0, 0, 0, 0, 0];
1146 /// let mut count = 1;
1148 /// let (remainder, chunks) = v.as_rchunks_mut();
1149 /// remainder[0] = 9;
1150 /// for chunk in chunks {
1151 /// *chunk = [count; 2];
1154 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1156 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1158 pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
1160 let len = self.len() / N;
1161 let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
1162 // SAFETY: We already panicked for zero, and ensured by construction
1163 // that the length of the subslice is a multiple of N.
1164 let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
1165 (remainder, array_slice)
1168 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1169 /// beginning of the slice.
1171 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1172 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1173 /// can be retrieved from the `into_remainder` function of the iterator.
1175 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1179 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1180 /// error before this method gets stabilized.
1185 /// #![feature(array_chunks)]
1186 /// let v = &mut [0, 0, 0, 0, 0];
1187 /// let mut count = 1;
1189 /// for chunk in v.array_chunks_mut() {
1190 /// *chunk = [count; 2];
1193 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1196 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1197 #[unstable(feature = "array_chunks", issue = "74985")]
1199 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1201 ArrayChunksMut::new(self)
1204 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1205 /// starting at the beginning of the slice.
1207 /// This is the const generic equivalent of [`windows`].
1209 /// If `N` is greater than the size of the slice, it will return no windows.
1213 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1214 /// error before this method gets stabilized.
1219 /// #![feature(array_windows)]
1220 /// let slice = [0, 1, 2, 3];
1221 /// let mut iter = slice.array_windows();
1222 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1223 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1224 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1225 /// assert!(iter.next().is_none());
1228 /// [`windows`]: slice::windows
1229 #[unstable(feature = "array_windows", issue = "75027")]
1231 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1233 ArrayWindows::new(self)
1236 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1239 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1240 /// slice, then the last chunk will not have length `chunk_size`.
1242 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1243 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1248 /// Panics if `chunk_size` is 0.
1253 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1254 /// let mut iter = slice.rchunks(2);
1255 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1256 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1257 /// assert_eq!(iter.next().unwrap(), &['l']);
1258 /// assert!(iter.next().is_none());
1261 /// [`rchunks_exact`]: slice::rchunks_exact
1262 /// [`chunks`]: slice::chunks
1263 #[stable(feature = "rchunks", since = "1.31.0")]
1265 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1266 assert!(chunk_size != 0);
1267 RChunks::new(self, chunk_size)
1270 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1273 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1274 /// length of the slice, then the last chunk will not have length `chunk_size`.
1276 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1277 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1278 /// beginning of the slice.
1282 /// Panics if `chunk_size` is 0.
1287 /// let v = &mut [0, 0, 0, 0, 0];
1288 /// let mut count = 1;
1290 /// for chunk in v.rchunks_mut(2) {
1291 /// for elem in chunk.iter_mut() {
1296 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1299 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1300 /// [`chunks_mut`]: slice::chunks_mut
1301 #[stable(feature = "rchunks", since = "1.31.0")]
1303 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1304 assert!(chunk_size != 0);
1305 RChunksMut::new(self, chunk_size)
1308 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1309 /// end of the slice.
1311 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1312 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1313 /// from the `remainder` function of the iterator.
1315 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1316 /// resulting code better than in the case of [`chunks`].
1318 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1319 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1324 /// Panics if `chunk_size` is 0.
1329 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1330 /// let mut iter = slice.rchunks_exact(2);
1331 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1332 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1333 /// assert!(iter.next().is_none());
1334 /// assert_eq!(iter.remainder(), &['l']);
1337 /// [`chunks`]: slice::chunks
1338 /// [`rchunks`]: slice::rchunks
1339 /// [`chunks_exact`]: slice::chunks_exact
1340 #[stable(feature = "rchunks", since = "1.31.0")]
1342 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1343 assert!(chunk_size != 0);
1344 RChunksExact::new(self, chunk_size)
1347 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1350 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1351 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1352 /// retrieved from the `into_remainder` function of the iterator.
1354 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1355 /// resulting code better than in the case of [`chunks_mut`].
1357 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1358 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1363 /// Panics if `chunk_size` is 0.
1368 /// let v = &mut [0, 0, 0, 0, 0];
1369 /// let mut count = 1;
1371 /// for chunk in v.rchunks_exact_mut(2) {
1372 /// for elem in chunk.iter_mut() {
1377 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1380 /// [`chunks_mut`]: slice::chunks_mut
1381 /// [`rchunks_mut`]: slice::rchunks_mut
1382 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1383 #[stable(feature = "rchunks", since = "1.31.0")]
1385 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1386 assert!(chunk_size != 0);
1387 RChunksExactMut::new(self, chunk_size)
1390 /// Returns an iterator over the slice producing non-overlapping runs
1391 /// of elements using the predicate to separate them.
1393 /// The predicate is called on two elements following themselves,
1394 /// it means the predicate is called on `slice[0]` and `slice[1]`
1395 /// then on `slice[1]` and `slice[2]` and so on.
1400 /// #![feature(slice_group_by)]
1402 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1404 /// let mut iter = slice.group_by(|a, b| a == b);
1406 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1407 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1408 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1409 /// assert_eq!(iter.next(), None);
1412 /// This method can be used to extract the sorted subslices:
1415 /// #![feature(slice_group_by)]
1417 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1419 /// let mut iter = slice.group_by(|a, b| a <= b);
1421 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1422 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1423 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1424 /// assert_eq!(iter.next(), None);
1426 #[unstable(feature = "slice_group_by", issue = "80552")]
1428 pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
1430 F: FnMut(&T, &T) -> bool,
1432 GroupBy::new(self, pred)
1435 /// Returns an iterator over the slice producing non-overlapping mutable
1436 /// runs of elements using the predicate to separate them.
1438 /// The predicate is called on two elements following themselves,
1439 /// it means the predicate is called on `slice[0]` and `slice[1]`
1440 /// then on `slice[1]` and `slice[2]` and so on.
1445 /// #![feature(slice_group_by)]
1447 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1449 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1451 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1452 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1453 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1454 /// assert_eq!(iter.next(), None);
1457 /// This method can be used to extract the sorted subslices:
1460 /// #![feature(slice_group_by)]
1462 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1464 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1466 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1467 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1468 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1469 /// assert_eq!(iter.next(), None);
1471 #[unstable(feature = "slice_group_by", issue = "80552")]
1473 pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
1475 F: FnMut(&T, &T) -> bool,
1477 GroupByMut::new(self, pred)
1480 /// Divides one slice into two at an index.
1482 /// The first will contain all indices from `[0, mid)` (excluding
1483 /// the index `mid` itself) and the second will contain all
1484 /// indices from `[mid, len)` (excluding the index `len` itself).
1488 /// Panics if `mid > len`.
1493 /// let v = [1, 2, 3, 4, 5, 6];
1496 /// let (left, right) = v.split_at(0);
1497 /// assert_eq!(left, []);
1498 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1502 /// let (left, right) = v.split_at(2);
1503 /// assert_eq!(left, [1, 2]);
1504 /// assert_eq!(right, [3, 4, 5, 6]);
1508 /// let (left, right) = v.split_at(6);
1509 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1510 /// assert_eq!(right, []);
1513 #[stable(feature = "rust1", since = "1.0.0")]
1515 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1516 assert!(mid <= self.len());
1517 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1518 // fulfills the requirements of `from_raw_parts_mut`.
1519 unsafe { self.split_at_unchecked(mid) }
1522 /// Divides one mutable slice into two at an index.
1524 /// The first will contain all indices from `[0, mid)` (excluding
1525 /// the index `mid` itself) and the second will contain all
1526 /// indices from `[mid, len)` (excluding the index `len` itself).
1530 /// Panics if `mid > len`.
1535 /// let mut v = [1, 0, 3, 0, 5, 6];
1536 /// let (left, right) = v.split_at_mut(2);
1537 /// assert_eq!(left, [1, 0]);
1538 /// assert_eq!(right, [3, 0, 5, 6]);
1541 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1543 #[stable(feature = "rust1", since = "1.0.0")]
1545 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1546 assert!(mid <= self.len());
1547 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1548 // fulfills the requirements of `from_raw_parts_mut`.
1549 unsafe { self.split_at_mut_unchecked(mid) }
1552 /// Divides one slice into two at an index, without doing bounds checking.
1554 /// The first will contain all indices from `[0, mid)` (excluding
1555 /// the index `mid` itself) and the second will contain all
1556 /// indices from `[mid, len)` (excluding the index `len` itself).
1558 /// For a safe alternative see [`split_at`].
1562 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1563 /// even if the resulting reference is not used. The caller has to ensure that
1564 /// `0 <= mid <= self.len()`.
1566 /// [`split_at`]: slice::split_at
1567 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1572 /// #![feature(slice_split_at_unchecked)]
1574 /// let v = [1, 2, 3, 4, 5, 6];
1577 /// let (left, right) = v.split_at_unchecked(0);
1578 /// assert_eq!(left, []);
1579 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1583 /// let (left, right) = v.split_at_unchecked(2);
1584 /// assert_eq!(left, [1, 2]);
1585 /// assert_eq!(right, [3, 4, 5, 6]);
1589 /// let (left, right) = v.split_at_unchecked(6);
1590 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1591 /// assert_eq!(right, []);
1594 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1596 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1597 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1598 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1601 /// Divides one mutable slice into two at an index, without doing bounds checking.
1603 /// The first will contain all indices from `[0, mid)` (excluding
1604 /// the index `mid` itself) and the second will contain all
1605 /// indices from `[mid, len)` (excluding the index `len` itself).
1607 /// For a safe alternative see [`split_at_mut`].
1611 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1612 /// even if the resulting reference is not used. The caller has to ensure that
1613 /// `0 <= mid <= self.len()`.
1615 /// [`split_at_mut`]: slice::split_at_mut
1616 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1621 /// #![feature(slice_split_at_unchecked)]
1623 /// let mut v = [1, 0, 3, 0, 5, 6];
1624 /// // scoped to restrict the lifetime of the borrows
1626 /// let (left, right) = v.split_at_mut_unchecked(2);
1627 /// assert_eq!(left, [1, 0]);
1628 /// assert_eq!(right, [3, 0, 5, 6]);
1632 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1634 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1636 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1637 let len = self.len();
1638 let ptr = self.as_mut_ptr();
1640 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1642 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1644 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1647 /// Returns an iterator over subslices separated by elements that match
1648 /// `pred`. The matched element is not contained in the subslices.
1653 /// let slice = [10, 40, 33, 20];
1654 /// let mut iter = slice.split(|num| num % 3 == 0);
1656 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1657 /// assert_eq!(iter.next().unwrap(), &[20]);
1658 /// assert!(iter.next().is_none());
1661 /// If the first element is matched, an empty slice will be the first item
1662 /// returned by the iterator. Similarly, if the last element in the slice
1663 /// is matched, an empty slice will be the last item returned by the
1667 /// let slice = [10, 40, 33];
1668 /// let mut iter = slice.split(|num| num % 3 == 0);
1670 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1671 /// assert_eq!(iter.next().unwrap(), &[]);
1672 /// assert!(iter.next().is_none());
1675 /// If two matched elements are directly adjacent, an empty slice will be
1676 /// present between them:
1679 /// let slice = [10, 6, 33, 20];
1680 /// let mut iter = slice.split(|num| num % 3 == 0);
1682 /// assert_eq!(iter.next().unwrap(), &[10]);
1683 /// assert_eq!(iter.next().unwrap(), &[]);
1684 /// assert_eq!(iter.next().unwrap(), &[20]);
1685 /// assert!(iter.next().is_none());
1687 #[stable(feature = "rust1", since = "1.0.0")]
1689 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1691 F: FnMut(&T) -> bool,
1693 Split::new(self, pred)
1696 /// Returns an iterator over mutable subslices separated by elements that
1697 /// match `pred`. The matched element is not contained in the subslices.
1702 /// let mut v = [10, 40, 30, 20, 60, 50];
1704 /// for group in v.split_mut(|num| *num % 3 == 0) {
1707 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1709 #[stable(feature = "rust1", since = "1.0.0")]
1711 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1713 F: FnMut(&T) -> bool,
1715 SplitMut::new(self, pred)
1718 /// Returns an iterator over subslices separated by elements that match
1719 /// `pred`. The matched element is contained in the end of the previous
1720 /// subslice as a terminator.
1725 /// let slice = [10, 40, 33, 20];
1726 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1728 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1729 /// assert_eq!(iter.next().unwrap(), &[20]);
1730 /// assert!(iter.next().is_none());
1733 /// If the last element of the slice is matched,
1734 /// that element will be considered the terminator of the preceding slice.
1735 /// That slice will be the last item returned by the iterator.
1738 /// let slice = [3, 10, 40, 33];
1739 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1741 /// assert_eq!(iter.next().unwrap(), &[3]);
1742 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1743 /// assert!(iter.next().is_none());
1745 #[stable(feature = "split_inclusive", since = "1.51.0")]
1747 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1749 F: FnMut(&T) -> bool,
1751 SplitInclusive::new(self, pred)
1754 /// Returns an iterator over mutable subslices separated by elements that
1755 /// match `pred`. The matched element is contained in the previous
1756 /// subslice as a terminator.
1761 /// let mut v = [10, 40, 30, 20, 60, 50];
1763 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1764 /// let terminator_idx = group.len()-1;
1765 /// group[terminator_idx] = 1;
1767 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1769 #[stable(feature = "split_inclusive", since = "1.51.0")]
1771 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1773 F: FnMut(&T) -> bool,
1775 SplitInclusiveMut::new(self, pred)
1778 /// Returns an iterator over subslices separated by elements that match
1779 /// `pred`, starting at the end of the slice and working backwards.
1780 /// The matched element is not contained in the subslices.
1785 /// let slice = [11, 22, 33, 0, 44, 55];
1786 /// let mut iter = slice.rsplit(|num| *num == 0);
1788 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1789 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1790 /// assert_eq!(iter.next(), None);
1793 /// As with `split()`, if the first or last element is matched, an empty
1794 /// slice will be the first (or last) item returned by the iterator.
1797 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1798 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1799 /// assert_eq!(it.next().unwrap(), &[]);
1800 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1801 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1802 /// assert_eq!(it.next().unwrap(), &[]);
1803 /// assert_eq!(it.next(), None);
1805 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1807 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1809 F: FnMut(&T) -> bool,
1811 RSplit::new(self, pred)
1814 /// Returns an iterator over mutable subslices separated by elements that
1815 /// match `pred`, starting at the end of the slice and working
1816 /// backwards. The matched element is not contained in the subslices.
1821 /// let mut v = [100, 400, 300, 200, 600, 500];
1823 /// let mut count = 0;
1824 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1826 /// group[0] = count;
1828 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1831 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1833 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1835 F: FnMut(&T) -> bool,
1837 RSplitMut::new(self, pred)
1840 /// Returns an iterator over subslices separated by elements that match
1841 /// `pred`, limited to returning at most `n` items. The matched element is
1842 /// not contained in the subslices.
1844 /// The last element returned, if any, will contain the remainder of the
1849 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1850 /// `[20, 60, 50]`):
1853 /// let v = [10, 40, 30, 20, 60, 50];
1855 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1856 /// println!("{:?}", group);
1859 #[stable(feature = "rust1", since = "1.0.0")]
1861 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1863 F: FnMut(&T) -> bool,
1865 SplitN::new(self.split(pred), n)
1868 /// Returns an iterator over subslices separated by elements that match
1869 /// `pred`, limited to returning at most `n` items. The matched element is
1870 /// not contained in the subslices.
1872 /// The last element returned, if any, will contain the remainder of the
1878 /// let mut v = [10, 40, 30, 20, 60, 50];
1880 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1883 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1885 #[stable(feature = "rust1", since = "1.0.0")]
1887 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1889 F: FnMut(&T) -> bool,
1891 SplitNMut::new(self.split_mut(pred), n)
1894 /// Returns an iterator over subslices separated by elements that match
1895 /// `pred` limited to returning at most `n` items. This starts at the end of
1896 /// the slice and works backwards. The matched element is not contained in
1899 /// The last element returned, if any, will contain the remainder of the
1904 /// Print the slice split once, starting from the end, by numbers divisible
1905 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1908 /// let v = [10, 40, 30, 20, 60, 50];
1910 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1911 /// println!("{:?}", group);
1914 #[stable(feature = "rust1", since = "1.0.0")]
1916 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1918 F: FnMut(&T) -> bool,
1920 RSplitN::new(self.rsplit(pred), n)
1923 /// Returns an iterator over subslices separated by elements that match
1924 /// `pred` limited to returning at most `n` items. This starts at the end of
1925 /// the slice and works backwards. The matched element is not contained in
1928 /// The last element returned, if any, will contain the remainder of the
1934 /// let mut s = [10, 40, 30, 20, 60, 50];
1936 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1939 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1941 #[stable(feature = "rust1", since = "1.0.0")]
1943 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1945 F: FnMut(&T) -> bool,
1947 RSplitNMut::new(self.rsplit_mut(pred), n)
1950 /// Returns `true` if the slice contains an element with the given value.
1955 /// let v = [10, 40, 30];
1956 /// assert!(v.contains(&30));
1957 /// assert!(!v.contains(&50));
1960 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1961 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1964 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1965 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1966 /// assert!(!v.iter().any(|e| e == "hi"));
1968 #[stable(feature = "rust1", since = "1.0.0")]
1970 pub fn contains(&self, x: &T) -> bool
1974 cmp::SliceContains::slice_contains(x, self)
1977 /// Returns `true` if `needle` is a prefix of the slice.
1982 /// let v = [10, 40, 30];
1983 /// assert!(v.starts_with(&[10]));
1984 /// assert!(v.starts_with(&[10, 40]));
1985 /// assert!(!v.starts_with(&[50]));
1986 /// assert!(!v.starts_with(&[10, 50]));
1989 /// Always returns `true` if `needle` is an empty slice:
1992 /// let v = &[10, 40, 30];
1993 /// assert!(v.starts_with(&[]));
1994 /// let v: &[u8] = &[];
1995 /// assert!(v.starts_with(&[]));
1997 #[stable(feature = "rust1", since = "1.0.0")]
1998 pub fn starts_with(&self, needle: &[T]) -> bool
2002 let n = needle.len();
2003 self.len() >= n && needle == &self[..n]
2006 /// Returns `true` if `needle` is a suffix of the slice.
2011 /// let v = [10, 40, 30];
2012 /// assert!(v.ends_with(&[30]));
2013 /// assert!(v.ends_with(&[40, 30]));
2014 /// assert!(!v.ends_with(&[50]));
2015 /// assert!(!v.ends_with(&[50, 30]));
2018 /// Always returns `true` if `needle` is an empty slice:
2021 /// let v = &[10, 40, 30];
2022 /// assert!(v.ends_with(&[]));
2023 /// let v: &[u8] = &[];
2024 /// assert!(v.ends_with(&[]));
2026 #[stable(feature = "rust1", since = "1.0.0")]
2027 pub fn ends_with(&self, needle: &[T]) -> bool
2031 let (m, n) = (self.len(), needle.len());
2032 m >= n && needle == &self[m - n..]
2035 /// Returns a subslice with the prefix removed.
2037 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2038 /// If `prefix` is empty, simply returns the original slice.
2040 /// If the slice does not start with `prefix`, returns `None`.
2045 /// let v = &[10, 40, 30];
2046 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2047 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2048 /// assert_eq!(v.strip_prefix(&[50]), None);
2049 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2051 /// let prefix : &str = "he";
2052 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2053 /// Some(b"llo".as_ref()));
2055 #[must_use = "returns the subslice without modifying the original"]
2056 #[stable(feature = "slice_strip", since = "1.51.0")]
2057 pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
2061 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2062 let prefix = prefix.as_slice();
2063 let n = prefix.len();
2064 if n <= self.len() {
2065 let (head, tail) = self.split_at(n);
2073 /// Returns a subslice with the suffix removed.
2075 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2076 /// If `suffix` is empty, simply returns the original slice.
2078 /// If the slice does not end with `suffix`, returns `None`.
2083 /// let v = &[10, 40, 30];
2084 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2085 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2086 /// assert_eq!(v.strip_suffix(&[50]), None);
2087 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2089 #[must_use = "returns the subslice without modifying the original"]
2090 #[stable(feature = "slice_strip", since = "1.51.0")]
2091 pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
2095 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2096 let suffix = suffix.as_slice();
2097 let (len, n) = (self.len(), suffix.len());
2099 let (head, tail) = self.split_at(len - n);
2107 /// Binary searches this sorted slice for a given element.
2109 /// If the value is found then [`Result::Ok`] is returned, containing the
2110 /// index of the matching element. If there are multiple matches, then any
2111 /// one of the matches could be returned. If the value is not found then
2112 /// [`Result::Err`] is returned, containing the index where a matching
2113 /// element could be inserted while maintaining sorted order.
2115 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2117 /// [`binary_search_by`]: slice::binary_search_by
2118 /// [`binary_search_by_key`]: slice::binary_search_by_key
2119 /// [`partition_point`]: slice::partition_point
2123 /// Looks up a series of four elements. The first is found, with a
2124 /// uniquely determined position; the second and third are not
2125 /// found; the fourth could match any position in `[1, 4]`.
2128 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2130 /// assert_eq!(s.binary_search(&13), Ok(9));
2131 /// assert_eq!(s.binary_search(&4), Err(7));
2132 /// assert_eq!(s.binary_search(&100), Err(13));
2133 /// let r = s.binary_search(&1);
2134 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2137 /// If you want to insert an item to a sorted vector, while maintaining
2141 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2143 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2144 /// s.insert(idx, num);
2145 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2147 #[stable(feature = "rust1", since = "1.0.0")]
2148 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2152 self.binary_search_by(|p| p.cmp(x))
2155 /// Binary searches this sorted slice with a comparator function.
2157 /// The comparator function should implement an order consistent
2158 /// with the sort order of the underlying slice, returning an
2159 /// order code that indicates whether its argument is `Less`,
2160 /// `Equal` or `Greater` the desired target.
2162 /// If the value is found then [`Result::Ok`] is returned, containing the
2163 /// index of the matching element. If there are multiple matches, then any
2164 /// one of the matches could be returned. If the value is not found then
2165 /// [`Result::Err`] is returned, containing the index where a matching
2166 /// element could be inserted while maintaining sorted order.
2168 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2170 /// [`binary_search`]: slice::binary_search
2171 /// [`binary_search_by_key`]: slice::binary_search_by_key
2172 /// [`partition_point`]: slice::partition_point
2176 /// Looks up a series of four elements. The first is found, with a
2177 /// uniquely determined position; the second and third are not
2178 /// found; the fourth could match any position in `[1, 4]`.
2181 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2184 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2186 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2188 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2190 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2191 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2193 #[stable(feature = "rust1", since = "1.0.0")]
2195 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2197 F: FnMut(&'a T) -> Ordering,
2199 let mut size = self.len();
2201 let mut right = size;
2202 while left < right {
2203 let mid = left + size / 2;
2205 // SAFETY: the call is made safe by the following invariants:
2207 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2208 let cmp = f(unsafe { self.get_unchecked(mid) });
2210 // The reason why we use if/else control flow rather than match
2211 // is because match reorders comparison operations, which is perf sensitive.
2212 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2215 } else if cmp == Greater {
2218 // SAFETY: same as the `get_unchecked` above
2219 unsafe { crate::intrinsics::assume(mid < self.len()) };
2223 size = right - left;
2228 /// Binary searches this sorted slice with a key extraction function.
2230 /// Assumes that the slice is sorted by the key, for instance with
2231 /// [`sort_by_key`] using the same key extraction function.
2233 /// If the value is found then [`Result::Ok`] is returned, containing the
2234 /// index of the matching element. If there are multiple matches, then any
2235 /// one of the matches could be returned. If the value is not found then
2236 /// [`Result::Err`] is returned, containing the index where a matching
2237 /// element could be inserted while maintaining sorted order.
2239 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2241 /// [`sort_by_key`]: slice::sort_by_key
2242 /// [`binary_search`]: slice::binary_search
2243 /// [`binary_search_by`]: slice::binary_search_by
2244 /// [`partition_point`]: slice::partition_point
2248 /// Looks up a series of four elements in a slice of pairs sorted by
2249 /// their second elements. The first is found, with a uniquely
2250 /// determined position; the second and third are not found; the
2251 /// fourth could match any position in `[1, 4]`.
2254 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2255 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2256 /// (1, 21), (2, 34), (4, 55)];
2258 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2259 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2260 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2261 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2262 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2264 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2265 // in crate `alloc`, and as such doesn't exists yet when building `core`.
2266 // links to downstream crate: #74481. Since primitives are only documented in
2267 // libstd (#73423), this never leads to broken links in practice.
2268 #[cfg_attr(not(bootstrap), allow(rustdoc::broken_intra_doc_links))]
2269 #[cfg_attr(bootstrap, allow(broken_intra_doc_links))]
2270 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2272 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2274 F: FnMut(&'a T) -> B,
2277 self.binary_search_by(|k| f(k).cmp(b))
2280 /// Sorts the slice, but may not preserve the order of equal elements.
2282 /// This sort is unstable (i.e., may reorder equal elements), in-place
2283 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2285 /// # Current implementation
2287 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2288 /// which combines the fast average case of randomized quicksort with the fast worst case of
2289 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2290 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2291 /// deterministic behavior.
2293 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2294 /// slice consists of several concatenated sorted sequences.
2299 /// let mut v = [-5, 4, 1, -3, 2];
2301 /// v.sort_unstable();
2302 /// assert!(v == [-5, -3, 1, 2, 4]);
2305 /// [pdqsort]: https://github.com/orlp/pdqsort
2306 #[stable(feature = "sort_unstable", since = "1.20.0")]
2308 pub fn sort_unstable(&mut self)
2312 sort::quicksort(self, |a, b| a.lt(b));
2315 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2318 /// This sort is unstable (i.e., may reorder equal elements), in-place
2319 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2321 /// The comparator function must define a total ordering for the elements in the slice. If
2322 /// the ordering is not total, the order of the elements is unspecified. An order is a
2323 /// total order if it is (for all `a`, `b` and `c`):
2325 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2326 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2328 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2329 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2332 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2333 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2334 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2337 /// # Current implementation
2339 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2340 /// which combines the fast average case of randomized quicksort with the fast worst case of
2341 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2342 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2343 /// deterministic behavior.
2345 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2346 /// slice consists of several concatenated sorted sequences.
2351 /// let mut v = [5, 4, 1, 3, 2];
2352 /// v.sort_unstable_by(|a, b| a.cmp(b));
2353 /// assert!(v == [1, 2, 3, 4, 5]);
2355 /// // reverse sorting
2356 /// v.sort_unstable_by(|a, b| b.cmp(a));
2357 /// assert!(v == [5, 4, 3, 2, 1]);
2360 /// [pdqsort]: https://github.com/orlp/pdqsort
2361 #[stable(feature = "sort_unstable", since = "1.20.0")]
2363 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2365 F: FnMut(&T, &T) -> Ordering,
2367 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2370 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2373 /// This sort is unstable (i.e., may reorder equal elements), in-place
2374 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2377 /// # Current implementation
2379 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2380 /// which combines the fast average case of randomized quicksort with the fast worst case of
2381 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2382 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2383 /// deterministic behavior.
2385 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2386 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2387 /// cases where the key function is expensive.
2392 /// let mut v = [-5i32, 4, 1, -3, 2];
2394 /// v.sort_unstable_by_key(|k| k.abs());
2395 /// assert!(v == [1, 2, -3, 4, -5]);
2398 /// [pdqsort]: https://github.com/orlp/pdqsort
2399 #[stable(feature = "sort_unstable", since = "1.20.0")]
2401 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2406 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2409 /// Reorder the slice such that the element at `index` is at its final sorted position.
2410 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2411 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2413 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2417 self.select_nth_unstable(index)
2420 /// Reorder the slice with a comparator function such that the element at `index` is at its
2421 /// final sorted position.
2422 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2423 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2425 pub fn partition_at_index_by<F>(
2429 ) -> (&mut [T], &mut T, &mut [T])
2431 F: FnMut(&T, &T) -> Ordering,
2433 self.select_nth_unstable_by(index, compare)
2436 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2437 /// final sorted position.
2438 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2439 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2441 pub fn partition_at_index_by_key<K, F>(
2445 ) -> (&mut [T], &mut T, &mut [T])
2450 self.select_nth_unstable_by_key(index, f)
2453 /// Reorder the slice such that the element at `index` is at its final sorted position.
2455 /// This reordering has the additional property that any value at position `i < index` will be
2456 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2457 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2458 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2459 /// element" in other libraries. It returns a triplet of the following values: all elements less
2460 /// than the one at the given index, the value at the given index, and all elements greater than
2461 /// the one at the given index.
2463 /// # Current implementation
2465 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2466 /// used for [`sort_unstable`].
2468 /// [`sort_unstable`]: slice::sort_unstable
2472 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2477 /// let mut v = [-5i32, 4, 1, -3, 2];
2479 /// // Find the median
2480 /// v.select_nth_unstable(2);
2482 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2483 /// // about the specified index.
2484 /// assert!(v == [-3, -5, 1, 2, 4] ||
2485 /// v == [-5, -3, 1, 2, 4] ||
2486 /// v == [-3, -5, 1, 4, 2] ||
2487 /// v == [-5, -3, 1, 4, 2]);
2489 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2491 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2495 let mut f = |a: &T, b: &T| a.lt(b);
2496 sort::partition_at_index(self, index, &mut f)
2499 /// Reorder the slice with a comparator function such that the element at `index` is at its
2500 /// final sorted position.
2502 /// This reordering has the additional property that any value at position `i < index` will be
2503 /// less than or equal to any value at a position `j > index` using the comparator function.
2504 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2505 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2506 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2507 /// values: all elements less than the one at the given index, the value at the given index,
2508 /// and all elements greater than the one at the given index, using the provided comparator
2511 /// # Current implementation
2513 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2514 /// used for [`sort_unstable`].
2516 /// [`sort_unstable`]: slice::sort_unstable
2520 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2525 /// let mut v = [-5i32, 4, 1, -3, 2];
2527 /// // Find the median as if the slice were sorted in descending order.
2528 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2530 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2531 /// // about the specified index.
2532 /// assert!(v == [2, 4, 1, -5, -3] ||
2533 /// v == [2, 4, 1, -3, -5] ||
2534 /// v == [4, 2, 1, -5, -3] ||
2535 /// v == [4, 2, 1, -3, -5]);
2537 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2539 pub fn select_nth_unstable_by<F>(
2543 ) -> (&mut [T], &mut T, &mut [T])
2545 F: FnMut(&T, &T) -> Ordering,
2547 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2548 sort::partition_at_index(self, index, &mut f)
2551 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2552 /// final sorted position.
2554 /// This reordering has the additional property that any value at position `i < index` will be
2555 /// less than or equal to any value at a position `j > index` using the key extraction function.
2556 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2557 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2558 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2559 /// values: all elements less than the one at the given index, the value at the given index, and
2560 /// all elements greater than the one at the given index, using the provided key extraction
2563 /// # Current implementation
2565 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2566 /// used for [`sort_unstable`].
2568 /// [`sort_unstable`]: slice::sort_unstable
2572 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2577 /// let mut v = [-5i32, 4, 1, -3, 2];
2579 /// // Return the median as if the array were sorted according to absolute value.
2580 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2582 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2583 /// // about the specified index.
2584 /// assert!(v == [1, 2, -3, 4, -5] ||
2585 /// v == [1, 2, -3, -5, 4] ||
2586 /// v == [2, 1, -3, 4, -5] ||
2587 /// v == [2, 1, -3, -5, 4]);
2589 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2591 pub fn select_nth_unstable_by_key<K, F>(
2595 ) -> (&mut [T], &mut T, &mut [T])
2600 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2601 sort::partition_at_index(self, index, &mut g)
2604 /// Moves all consecutive repeated elements to the end of the slice according to the
2605 /// [`PartialEq`] trait implementation.
2607 /// Returns two slices. The first contains no consecutive repeated elements.
2608 /// The second contains all the duplicates in no specified order.
2610 /// If the slice is sorted, the first returned slice contains no duplicates.
2615 /// #![feature(slice_partition_dedup)]
2617 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2619 /// let (dedup, duplicates) = slice.partition_dedup();
2621 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2622 /// assert_eq!(duplicates, [2, 3, 1]);
2624 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2626 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2630 self.partition_dedup_by(|a, b| a == b)
2633 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2634 /// a given equality relation.
2636 /// Returns two slices. The first contains no consecutive repeated elements.
2637 /// The second contains all the duplicates in no specified order.
2639 /// The `same_bucket` function is passed references to two elements from the slice and
2640 /// must determine if the elements compare equal. The elements are passed in opposite order
2641 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2642 /// at the end of the slice.
2644 /// If the slice is sorted, the first returned slice contains no duplicates.
2649 /// #![feature(slice_partition_dedup)]
2651 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2653 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2655 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2656 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2658 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2660 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2662 F: FnMut(&mut T, &mut T) -> bool,
2664 // Although we have a mutable reference to `self`, we cannot make
2665 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2666 // must ensure that the slice is in a valid state at all times.
2668 // The way that we handle this is by using swaps; we iterate
2669 // over all the elements, swapping as we go so that at the end
2670 // the elements we wish to keep are in the front, and those we
2671 // wish to reject are at the back. We can then split the slice.
2672 // This operation is still `O(n)`.
2674 // Example: We start in this state, where `r` represents "next
2675 // read" and `w` represents "next_write`.
2678 // +---+---+---+---+---+---+
2679 // | 0 | 1 | 1 | 2 | 3 | 3 |
2680 // +---+---+---+---+---+---+
2683 // Comparing self[r] against self[w-1], this is not a duplicate, so
2684 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2685 // r and w, leaving us with:
2688 // +---+---+---+---+---+---+
2689 // | 0 | 1 | 1 | 2 | 3 | 3 |
2690 // +---+---+---+---+---+---+
2693 // Comparing self[r] against self[w-1], this value is a duplicate,
2694 // so we increment `r` but leave everything else unchanged:
2697 // +---+---+---+---+---+---+
2698 // | 0 | 1 | 1 | 2 | 3 | 3 |
2699 // +---+---+---+---+---+---+
2702 // Comparing self[r] against self[w-1], this is not a duplicate,
2703 // so swap self[r] and self[w] and advance r and w:
2706 // +---+---+---+---+---+---+
2707 // | 0 | 1 | 2 | 1 | 3 | 3 |
2708 // +---+---+---+---+---+---+
2711 // Not a duplicate, repeat:
2714 // +---+---+---+---+---+---+
2715 // | 0 | 1 | 2 | 3 | 1 | 3 |
2716 // +---+---+---+---+---+---+
2719 // Duplicate, advance r. End of slice. Split at w.
2721 let len = self.len();
2723 return (self, &mut []);
2726 let ptr = self.as_mut_ptr();
2727 let mut next_read: usize = 1;
2728 let mut next_write: usize = 1;
2730 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2731 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2732 // one element before `ptr_write`, but `next_write` starts at 1, so
2733 // `prev_ptr_write` is never less than 0 and is inside the slice.
2734 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2735 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2736 // and `prev_ptr_write.offset(1)`.
2738 // `next_write` is also incremented at most once per loop at most meaning
2739 // no element is skipped when it may need to be swapped.
2741 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2742 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2743 // The explanation is simply that `next_read >= next_write` is always true,
2744 // thus `next_read > next_write - 1` is too.
2746 // Avoid bounds checks by using raw pointers.
2747 while next_read < len {
2748 let ptr_read = ptr.add(next_read);
2749 let prev_ptr_write = ptr.add(next_write - 1);
2750 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2751 if next_read != next_write {
2752 let ptr_write = prev_ptr_write.offset(1);
2753 mem::swap(&mut *ptr_read, &mut *ptr_write);
2761 self.split_at_mut(next_write)
2764 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2765 /// to the same key.
2767 /// Returns two slices. The first contains no consecutive repeated elements.
2768 /// The second contains all the duplicates in no specified order.
2770 /// If the slice is sorted, the first returned slice contains no duplicates.
2775 /// #![feature(slice_partition_dedup)]
2777 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2779 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2781 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2782 /// assert_eq!(duplicates, [21, 30, 13]);
2784 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2786 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2788 F: FnMut(&mut T) -> K,
2791 self.partition_dedup_by(|a, b| key(a) == key(b))
2794 /// Rotates the slice in-place such that the first `mid` elements of the
2795 /// slice move to the end while the last `self.len() - mid` elements move to
2796 /// the front. After calling `rotate_left`, the element previously at index
2797 /// `mid` will become the first element in the slice.
2801 /// This function will panic if `mid` is greater than the length of the
2802 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2807 /// Takes linear (in `self.len()`) time.
2812 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2813 /// a.rotate_left(2);
2814 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2817 /// Rotating a subslice:
2820 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2821 /// a[1..5].rotate_left(1);
2822 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2824 #[stable(feature = "slice_rotate", since = "1.26.0")]
2825 pub fn rotate_left(&mut self, mid: usize) {
2826 assert!(mid <= self.len());
2827 let k = self.len() - mid;
2828 let p = self.as_mut_ptr();
2830 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2831 // valid for reading and writing, as required by `ptr_rotate`.
2833 rotate::ptr_rotate(mid, p.add(mid), k);
2837 /// Rotates the slice in-place such that the first `self.len() - k`
2838 /// elements of the slice move to the end while the last `k` elements move
2839 /// to the front. After calling `rotate_right`, the element previously at
2840 /// index `self.len() - k` will become the first element in the slice.
2844 /// This function will panic if `k` is greater than the length of the
2845 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2850 /// Takes linear (in `self.len()`) time.
2855 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2856 /// a.rotate_right(2);
2857 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2860 /// Rotate a subslice:
2863 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2864 /// a[1..5].rotate_right(1);
2865 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2867 #[stable(feature = "slice_rotate", since = "1.26.0")]
2868 pub fn rotate_right(&mut self, k: usize) {
2869 assert!(k <= self.len());
2870 let mid = self.len() - k;
2871 let p = self.as_mut_ptr();
2873 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2874 // valid for reading and writing, as required by `ptr_rotate`.
2876 rotate::ptr_rotate(mid, p.add(mid), k);
2880 /// Fills `self` with elements by cloning `value`.
2885 /// let mut buf = vec![0; 10];
2887 /// assert_eq!(buf, vec![1; 10]);
2889 #[doc(alias = "memset")]
2890 #[stable(feature = "slice_fill", since = "1.50.0")]
2891 pub fn fill(&mut self, value: T)
2895 specialize::SpecFill::spec_fill(self, value);
2898 /// Fills `self` with elements returned by calling a closure repeatedly.
2900 /// This method uses a closure to create new values. If you'd rather
2901 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2902 /// trait to generate values, you can pass [`Default::default`] as the
2905 /// [`fill`]: slice::fill
2910 /// let mut buf = vec![1; 10];
2911 /// buf.fill_with(Default::default);
2912 /// assert_eq!(buf, vec![0; 10]);
2914 #[doc(alias = "memset")]
2915 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2916 pub fn fill_with<F>(&mut self, mut f: F)
2925 /// Copies the elements from `src` into `self`.
2927 /// The length of `src` must be the same as `self`.
2929 /// If `T` implements `Copy`, it can be more performant to use
2930 /// [`copy_from_slice`].
2934 /// This function will panic if the two slices have different lengths.
2938 /// Cloning two elements from a slice into another:
2941 /// let src = [1, 2, 3, 4];
2942 /// let mut dst = [0, 0];
2944 /// // Because the slices have to be the same length,
2945 /// // we slice the source slice from four elements
2946 /// // to two. It will panic if we don't do this.
2947 /// dst.clone_from_slice(&src[2..]);
2949 /// assert_eq!(src, [1, 2, 3, 4]);
2950 /// assert_eq!(dst, [3, 4]);
2953 /// Rust enforces that there can only be one mutable reference with no
2954 /// immutable references to a particular piece of data in a particular
2955 /// scope. Because of this, attempting to use `clone_from_slice` on a
2956 /// single slice will result in a compile failure:
2959 /// let mut slice = [1, 2, 3, 4, 5];
2961 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2964 /// To work around this, we can use [`split_at_mut`] to create two distinct
2965 /// sub-slices from a slice:
2968 /// let mut slice = [1, 2, 3, 4, 5];
2971 /// let (left, right) = slice.split_at_mut(2);
2972 /// left.clone_from_slice(&right[1..]);
2975 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2978 /// [`copy_from_slice`]: slice::copy_from_slice
2979 /// [`split_at_mut`]: slice::split_at_mut
2980 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2981 pub fn clone_from_slice(&mut self, src: &[T])
2985 self.spec_clone_from(src);
2988 /// Copies all elements from `src` into `self`, using a memcpy.
2990 /// The length of `src` must be the same as `self`.
2992 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2996 /// This function will panic if the two slices have different lengths.
3000 /// Copying two elements from a slice into another:
3003 /// let src = [1, 2, 3, 4];
3004 /// let mut dst = [0, 0];
3006 /// // Because the slices have to be the same length,
3007 /// // we slice the source slice from four elements
3008 /// // to two. It will panic if we don't do this.
3009 /// dst.copy_from_slice(&src[2..]);
3011 /// assert_eq!(src, [1, 2, 3, 4]);
3012 /// assert_eq!(dst, [3, 4]);
3015 /// Rust enforces that there can only be one mutable reference with no
3016 /// immutable references to a particular piece of data in a particular
3017 /// scope. Because of this, attempting to use `copy_from_slice` on a
3018 /// single slice will result in a compile failure:
3021 /// let mut slice = [1, 2, 3, 4, 5];
3023 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3026 /// To work around this, we can use [`split_at_mut`] to create two distinct
3027 /// sub-slices from a slice:
3030 /// let mut slice = [1, 2, 3, 4, 5];
3033 /// let (left, right) = slice.split_at_mut(2);
3034 /// left.copy_from_slice(&right[1..]);
3037 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3040 /// [`clone_from_slice`]: slice::clone_from_slice
3041 /// [`split_at_mut`]: slice::split_at_mut
3042 #[doc(alias = "memcpy")]
3043 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3044 pub fn copy_from_slice(&mut self, src: &[T])
3048 // The panic code path was put into a cold function to not bloat the
3053 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
3055 "source slice length ({}) does not match destination slice length ({})",
3060 if self.len() != src.len() {
3061 len_mismatch_fail(self.len(), src.len());
3064 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3065 // checked to have the same length. The slices cannot overlap because
3066 // mutable references are exclusive.
3068 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
3072 /// Copies elements from one part of the slice to another part of itself,
3073 /// using a memmove.
3075 /// `src` is the range within `self` to copy from. `dest` is the starting
3076 /// index of the range within `self` to copy to, which will have the same
3077 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3078 /// must be less than or equal to `self.len()`.
3082 /// This function will panic if either range exceeds the end of the slice,
3083 /// or if the end of `src` is before the start.
3087 /// Copying four bytes within a slice:
3090 /// let mut bytes = *b"Hello, World!";
3092 /// bytes.copy_within(1..5, 8);
3094 /// assert_eq!(&bytes, b"Hello, Wello!");
3096 #[stable(feature = "copy_within", since = "1.37.0")]
3098 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
3102 let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
3103 let count = src_end - src_start;
3104 assert!(dest <= self.len() - count, "dest is out of bounds");
3105 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3106 // as have those for `ptr::add`.
3108 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
3112 /// Swaps all elements in `self` with those in `other`.
3114 /// The length of `other` must be the same as `self`.
3118 /// This function will panic if the two slices have different lengths.
3122 /// Swapping two elements across slices:
3125 /// let mut slice1 = [0, 0];
3126 /// let mut slice2 = [1, 2, 3, 4];
3128 /// slice1.swap_with_slice(&mut slice2[2..]);
3130 /// assert_eq!(slice1, [3, 4]);
3131 /// assert_eq!(slice2, [1, 2, 0, 0]);
3134 /// Rust enforces that there can only be one mutable reference to a
3135 /// particular piece of data in a particular scope. Because of this,
3136 /// attempting to use `swap_with_slice` on a single slice will result in
3137 /// a compile failure:
3140 /// let mut slice = [1, 2, 3, 4, 5];
3141 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3144 /// To work around this, we can use [`split_at_mut`] to create two distinct
3145 /// mutable sub-slices from a slice:
3148 /// let mut slice = [1, 2, 3, 4, 5];
3151 /// let (left, right) = slice.split_at_mut(2);
3152 /// left.swap_with_slice(&mut right[1..]);
3155 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3158 /// [`split_at_mut`]: slice::split_at_mut
3159 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3160 pub fn swap_with_slice(&mut self, other: &mut [T]) {
3161 assert!(self.len() == other.len(), "destination and source slices have different lengths");
3162 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3163 // checked to have the same length. The slices cannot overlap because
3164 // mutable references are exclusive.
3166 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
3170 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3171 fn align_to_offsets<U>(&self) -> (usize, usize) {
3172 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3173 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3175 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3176 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3177 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3179 // Formula to calculate this is:
3181 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3182 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3184 // Expanded and simplified:
3186 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3187 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3189 // Luckily since all this is constant-evaluated... performance here matters not!
3191 fn gcd(a: usize, b: usize) -> usize {
3192 use crate::intrinsics;
3193 // iterative stein’s algorithm
3194 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3195 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3197 // SAFETY: `a` and `b` are checked to be non-zero values.
3198 let (ctz_a, mut ctz_b) = unsafe {
3205 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
3207 let k = ctz_a.min(ctz_b);
3208 let mut a = a >> ctz_a;
3211 // remove all factors of 2 from b
3214 mem::swap(&mut a, &mut b);
3217 // SAFETY: `b` is checked to be non-zero.
3222 ctz_b = intrinsics::cttz_nonzero(b);
3227 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
3228 let ts: usize = mem::size_of::<U>() / gcd;
3229 let us: usize = mem::size_of::<T>() / gcd;
3231 // Armed with this knowledge, we can find how many `U`s we can fit!
3232 let us_len = self.len() / ts * us;
3233 // And how many `T`s will be in the trailing slice!
3234 let ts_len = self.len() % ts;
3238 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3241 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3242 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3243 /// length possible for a given type and input slice, but only your algorithm's performance
3244 /// should depend on that, not its correctness. It is permissible for all of the input data to
3245 /// be returned as the prefix or suffix slice.
3247 /// This method has no purpose when either input element `T` or output element `U` are
3248 /// zero-sized and will return the original slice without splitting anything.
3252 /// This method is essentially a `transmute` with respect to the elements in the returned
3253 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3261 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3262 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3263 /// // less_efficient_algorithm_for_bytes(prefix);
3264 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3265 /// // less_efficient_algorithm_for_bytes(suffix);
3268 #[stable(feature = "slice_align_to", since = "1.30.0")]
3269 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
3270 // Note that most of this function will be constant-evaluated,
3271 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3272 // handle ZSTs specially, which is – don't handle them at all.
3273 return (self, &[], &[]);
3276 // First, find at what point do we split between the first and 2nd slice. Easy with
3277 // ptr.align_offset.
3278 let ptr = self.as_ptr();
3279 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3280 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3281 if offset > self.len() {
3284 let (left, rest) = self.split_at(offset);
3285 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3286 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3287 // since the caller guarantees that we can transmute `T` to `U` safely.
3291 from_raw_parts(rest.as_ptr() as *const U, us_len),
3292 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3298 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3301 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3302 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3303 /// length possible for a given type and input slice, but only your algorithm's performance
3304 /// should depend on that, not its correctness. It is permissible for all of the input data to
3305 /// be returned as the prefix or suffix slice.
3307 /// This method has no purpose when either input element `T` or output element `U` are
3308 /// zero-sized and will return the original slice without splitting anything.
3312 /// This method is essentially a `transmute` with respect to the elements in the returned
3313 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3321 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3322 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3323 /// // less_efficient_algorithm_for_bytes(prefix);
3324 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3325 /// // less_efficient_algorithm_for_bytes(suffix);
3328 #[stable(feature = "slice_align_to", since = "1.30.0")]
3329 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3330 // Note that most of this function will be constant-evaluated,
3331 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3332 // handle ZSTs specially, which is – don't handle them at all.
3333 return (self, &mut [], &mut []);
3336 // First, find at what point do we split between the first and 2nd slice. Easy with
3337 // ptr.align_offset.
3338 let ptr = self.as_ptr();
3339 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3340 // rest of the method. This is done by passing a pointer to &[T] with an
3341 // alignment targeted for U.
3342 // `crate::ptr::align_offset` is called with a correctly aligned and
3343 // valid pointer `ptr` (it comes from a reference to `self`) and with
3344 // a size that is a power of two (since it comes from the alignement for U),
3345 // satisfying its safety constraints.
3346 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3347 if offset > self.len() {
3348 (self, &mut [], &mut [])
3350 let (left, rest) = self.split_at_mut(offset);
3351 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3352 let rest_len = rest.len();
3353 let mut_ptr = rest.as_mut_ptr();
3354 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3355 // SAFETY: see comments for `align_to`.
3359 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3360 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3366 /// Checks if the elements of this slice are sorted.
3368 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3369 /// slice yields exactly zero or one element, `true` is returned.
3371 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3372 /// implies that this function returns `false` if any two consecutive items are not
3378 /// #![feature(is_sorted)]
3379 /// let empty: [i32; 0] = [];
3381 /// assert!([1, 2, 2, 9].is_sorted());
3382 /// assert!(![1, 3, 2, 4].is_sorted());
3383 /// assert!([0].is_sorted());
3384 /// assert!(empty.is_sorted());
3385 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3388 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3389 pub fn is_sorted(&self) -> bool
3393 self.is_sorted_by(|a, b| a.partial_cmp(b))
3396 /// Checks if the elements of this slice are sorted using the given comparator function.
3398 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3399 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3400 /// [`is_sorted`]; see its documentation for more information.
3402 /// [`is_sorted`]: slice::is_sorted
3403 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3404 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3406 F: FnMut(&T, &T) -> Option<Ordering>,
3408 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3411 /// Checks if the elements of this slice are sorted using the given key extraction function.
3413 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3414 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3415 /// documentation for more information.
3417 /// [`is_sorted`]: slice::is_sorted
3422 /// #![feature(is_sorted)]
3424 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3425 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3428 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3429 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3434 self.iter().is_sorted_by_key(f)
3437 /// Returns the index of the partition point according to the given predicate
3438 /// (the index of the first element of the second partition).
3440 /// The slice is assumed to be partitioned according to the given predicate.
3441 /// This means that all elements for which the predicate returns true are at the start of the slice
3442 /// and all elements for which the predicate returns false are at the end.
3443 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3444 /// (all odd numbers are at the start, all even at the end).
3446 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3447 /// as this method performs a kind of binary search.
3449 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3451 /// [`binary_search`]: slice::binary_search
3452 /// [`binary_search_by`]: slice::binary_search_by
3453 /// [`binary_search_by_key`]: slice::binary_search_by_key
3458 /// let v = [1, 2, 3, 3, 5, 6, 7];
3459 /// let i = v.partition_point(|&x| x < 5);
3461 /// assert_eq!(i, 4);
3462 /// assert!(v[..i].iter().all(|&x| x < 5));
3463 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3465 #[stable(feature = "partition_point", since = "1.52.0")]
3466 pub fn partition_point<P>(&self, mut pred: P) -> usize
3468 P: FnMut(&T) -> bool,
3471 let mut right = self.len();
3473 while left != right {
3474 let mid = left + (right - left) / 2;
3475 // SAFETY: When `left < right`, `left <= mid < right`.
3476 // Therefore `left` always increases and `right` always decreases,
3477 // and either of them is selected. In both cases `left <= right` is
3478 // satisfied. Therefore if `left < right` in a step, `left <= right`
3479 // is satisfied in the next step. Therefore as long as `left != right`,
3480 // `0 <= left < right <= len` is satisfied and if this case
3481 // `0 <= mid < len` is satisfied too.
3482 let value = unsafe { self.get_unchecked(mid) };
3494 trait CloneFromSpec<T> {
3495 fn spec_clone_from(&mut self, src: &[T]);
3498 impl<T> CloneFromSpec<T> for [T]
3502 default fn spec_clone_from(&mut self, src: &[T]) {
3503 assert!(self.len() == src.len(), "destination and source slices have different lengths");
3504 // NOTE: We need to explicitly slice them to the same length
3505 // to make it easier for the optimizer to elide bounds checking.
3506 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3507 let len = self.len();
3508 let src = &src[..len];
3510 self[i].clone_from(&src[i]);
3515 impl<T> CloneFromSpec<T> for [T]
3519 fn spec_clone_from(&mut self, src: &[T]) {
3520 self.copy_from_slice(src);
3524 #[stable(feature = "rust1", since = "1.0.0")]
3525 impl<T> Default for &[T] {
3526 /// Creates an empty slice.
3527 fn default() -> Self {
3532 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3533 impl<T> Default for &mut [T] {
3534 /// Creates a mutable empty slice.
3535 fn default() -> Self {
3540 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3541 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3542 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3543 /// `str`) to slices, and then this trait will be replaced or abolished.
3544 pub trait SlicePattern {
3545 /// The element type of the slice being matched on.
3548 /// Currently, the consumers of `SlicePattern` need a slice.
3549 fn as_slice(&self) -> &[Self::Item];
3552 #[stable(feature = "slice_strip", since = "1.51.0")]
3553 impl<T> SlicePattern for [T] {
3557 fn as_slice(&self) -> &[Self::Item] {
3562 #[stable(feature = "slice_strip", since = "1.51.0")]
3563 impl<T, const N: usize> SlicePattern for [T; N] {
3567 fn as_slice(&self) -> &[Self::Item] {