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, Equal, 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};
23 feature = "slice_internals",
25 reason = "exposed from core to be reused in std; use the memchr crate"
27 /// Pure rust memchr implementation, taken from rust-memchr
38 #[stable(feature = "rust1", since = "1.0.0")]
39 pub use iter::{Chunks, ChunksMut, Windows};
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter::{Iter, IterMut};
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
45 #[stable(feature = "slice_rsplit", since = "1.27.0")]
46 pub use iter::{RSplit, RSplitMut};
48 #[stable(feature = "chunks_exact", since = "1.31.0")]
49 pub use iter::{ChunksExact, ChunksExactMut};
51 #[stable(feature = "rchunks", since = "1.31.0")]
52 pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
54 #[unstable(feature = "array_chunks", issue = "74985")]
55 pub use iter::{ArrayChunks, ArrayChunksMut};
57 #[unstable(feature = "array_windows", issue = "75027")]
58 pub use iter::ArrayWindows;
60 #[unstable(feature = "split_inclusive", issue = "72360")]
61 pub use iter::{SplitInclusive, SplitInclusiveMut};
63 #[stable(feature = "rust1", since = "1.0.0")]
64 pub use raw::{from_raw_parts, from_raw_parts_mut};
66 #[stable(feature = "from_ref", since = "1.28.0")]
67 pub use raw::{from_mut, from_ref};
69 // This function is public only because there is no other way to unit test heapsort.
70 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
71 pub use sort::heapsort;
73 #[stable(feature = "slice_get_slice", since = "1.28.0")]
74 pub use index::SliceIndex;
79 /// Returns the number of elements in the slice.
84 /// let a = [1, 2, 3];
85 /// assert_eq!(a.len(), 3);
87 #[stable(feature = "rust1", since = "1.0.0")]
88 #[rustc_const_stable(feature = "const_slice_len", since = "1.32.0")]
90 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
91 #[cfg_attr(not(bootstrap), rustc_allow_const_fn_unstable(const_fn_union))]
92 #[cfg_attr(bootstrap, allow_internal_unstable(const_fn_union))]
93 pub const fn len(&self) -> usize {
94 // SAFETY: this is safe because `&[T]` and `FatPtr<T>` have the same layout.
95 // Only `std` can make this guarantee.
96 unsafe { crate::ptr::Repr { rust: self }.raw.len }
99 /// Returns `true` if the slice has a length of 0.
104 /// let a = [1, 2, 3];
105 /// assert!(!a.is_empty());
107 #[stable(feature = "rust1", since = "1.0.0")]
108 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.32.0")]
110 pub const fn is_empty(&self) -> bool {
114 /// Returns the first element of the slice, or `None` if it is empty.
119 /// let v = [10, 40, 30];
120 /// assert_eq!(Some(&10), v.first());
122 /// let w: &[i32] = &[];
123 /// assert_eq!(None, w.first());
125 #[stable(feature = "rust1", since = "1.0.0")]
127 pub fn first(&self) -> Option<&T> {
128 if let [first, ..] = self { Some(first) } else { None }
131 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
136 /// let x = &mut [0, 1, 2];
138 /// if let Some(first) = x.first_mut() {
141 /// assert_eq!(x, &[5, 1, 2]);
143 #[stable(feature = "rust1", since = "1.0.0")]
145 pub fn first_mut(&mut self) -> Option<&mut T> {
146 if let [first, ..] = self { Some(first) } else { None }
149 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
154 /// let x = &[0, 1, 2];
156 /// if let Some((first, elements)) = x.split_first() {
157 /// assert_eq!(first, &0);
158 /// assert_eq!(elements, &[1, 2]);
161 #[stable(feature = "slice_splits", since = "1.5.0")]
163 pub fn split_first(&self) -> Option<(&T, &[T])> {
164 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
167 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
172 /// let x = &mut [0, 1, 2];
174 /// if let Some((first, elements)) = x.split_first_mut() {
179 /// assert_eq!(x, &[3, 4, 5]);
181 #[stable(feature = "slice_splits", since = "1.5.0")]
183 pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
184 if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
187 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
192 /// let x = &[0, 1, 2];
194 /// if let Some((last, elements)) = x.split_last() {
195 /// assert_eq!(last, &2);
196 /// assert_eq!(elements, &[0, 1]);
199 #[stable(feature = "slice_splits", since = "1.5.0")]
201 pub fn split_last(&self) -> Option<(&T, &[T])> {
202 if let [init @ .., last] = self { Some((last, init)) } else { None }
205 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
210 /// let x = &mut [0, 1, 2];
212 /// if let Some((last, elements)) = x.split_last_mut() {
217 /// assert_eq!(x, &[4, 5, 3]);
219 #[stable(feature = "slice_splits", since = "1.5.0")]
221 pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
222 if let [init @ .., last] = self { Some((last, init)) } else { None }
225 /// Returns the last element of the slice, or `None` if it is empty.
230 /// let v = [10, 40, 30];
231 /// assert_eq!(Some(&30), v.last());
233 /// let w: &[i32] = &[];
234 /// assert_eq!(None, w.last());
236 #[stable(feature = "rust1", since = "1.0.0")]
238 pub fn last(&self) -> Option<&T> {
239 if let [.., last] = self { Some(last) } else { None }
242 /// Returns a mutable pointer to the last item in the slice.
247 /// let x = &mut [0, 1, 2];
249 /// if let Some(last) = x.last_mut() {
252 /// assert_eq!(x, &[0, 1, 10]);
254 #[stable(feature = "rust1", since = "1.0.0")]
256 pub fn last_mut(&mut self) -> Option<&mut T> {
257 if let [.., last] = self { Some(last) } else { None }
260 /// Returns a reference to an element or subslice depending on the type of
263 /// - If given a position, returns a reference to the element at that
264 /// position or `None` if out of bounds.
265 /// - If given a range, returns the subslice corresponding to that range,
266 /// or `None` if out of bounds.
271 /// let v = [10, 40, 30];
272 /// assert_eq!(Some(&40), v.get(1));
273 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
274 /// assert_eq!(None, v.get(3));
275 /// assert_eq!(None, v.get(0..4));
277 #[stable(feature = "rust1", since = "1.0.0")]
279 pub fn get<I>(&self, index: I) -> Option<&I::Output>
286 /// Returns a mutable reference to an element or subslice depending on the
287 /// type of index (see [`get`]) or `None` if the index is out of bounds.
289 /// [`get`]: #method.get
294 /// let x = &mut [0, 1, 2];
296 /// if let Some(elem) = x.get_mut(1) {
299 /// assert_eq!(x, &[0, 42, 2]);
301 #[stable(feature = "rust1", since = "1.0.0")]
303 pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
310 /// Returns a reference to an element or subslice, without doing bounds
313 /// For a safe alternative see [`get`].
317 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
318 /// even if the resulting reference is not used.
320 /// [`get`]: #method.get
321 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
326 /// let x = &[1, 2, 4];
329 /// assert_eq!(x.get_unchecked(1), &2);
332 #[stable(feature = "rust1", since = "1.0.0")]
334 pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
338 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
339 // the slice is dereferencable because `self` is a safe reference.
340 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
341 unsafe { &*index.get_unchecked(self) }
344 /// Returns a mutable reference to an element or subslice, without doing
347 /// For a safe alternative see [`get_mut`].
351 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
352 /// even if the resulting reference is not used.
354 /// [`get_mut`]: #method.get_mut
355 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
360 /// let x = &mut [1, 2, 4];
363 /// let elem = x.get_unchecked_mut(1);
366 /// assert_eq!(x, &[1, 13, 4]);
368 #[stable(feature = "rust1", since = "1.0.0")]
370 pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
374 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
375 // the slice is dereferencable because `self` is a safe reference.
376 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
377 unsafe { &mut *index.get_unchecked_mut(self) }
380 /// Returns a raw pointer to the slice's buffer.
382 /// The caller must ensure that the slice outlives the pointer this
383 /// function returns, or else it will end up pointing to garbage.
385 /// The caller must also ensure that the memory the pointer (non-transitively) points to
386 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
387 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
389 /// Modifying the container referenced by this slice may cause its buffer
390 /// to be reallocated, which would also make any pointers to it invalid.
395 /// let x = &[1, 2, 4];
396 /// let x_ptr = x.as_ptr();
399 /// for i in 0..x.len() {
400 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
405 /// [`as_mut_ptr`]: #method.as_mut_ptr
406 #[stable(feature = "rust1", since = "1.0.0")]
407 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
409 pub const fn as_ptr(&self) -> *const T {
410 self as *const [T] as *const T
413 /// Returns an unsafe mutable 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 /// Modifying the container referenced by this slice may cause its buffer
419 /// to be reallocated, which would also make any pointers to it invalid.
424 /// let x = &mut [1, 2, 4];
425 /// let x_ptr = x.as_mut_ptr();
428 /// for i in 0..x.len() {
429 /// *x_ptr.add(i) += 2;
432 /// assert_eq!(x, &[3, 4, 6]);
434 #[stable(feature = "rust1", since = "1.0.0")]
435 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
437 pub const fn as_mut_ptr(&mut self) -> *mut T {
438 self as *mut [T] as *mut T
441 /// Returns the two raw pointers spanning the slice.
443 /// The returned range is half-open, which means that the end pointer
444 /// points *one past* the last element of the slice. This way, an empty
445 /// slice is represented by two equal pointers, and the difference between
446 /// the two pointers represents the size of the slice.
448 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
449 /// requires extra caution, as it does not point to a valid element in the
452 /// This function is useful for interacting with foreign interfaces which
453 /// use two pointers to refer to a range of elements in memory, as is
456 /// It can also be useful to check if a pointer to an element refers to an
457 /// element of this slice:
460 /// let a = [1, 2, 3];
461 /// let x = &a[1] as *const _;
462 /// let y = &5 as *const _;
464 /// assert!(a.as_ptr_range().contains(&x));
465 /// assert!(!a.as_ptr_range().contains(&y));
468 /// [`as_ptr`]: #method.as_ptr
469 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
470 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
472 pub const fn as_ptr_range(&self) -> Range<*const T> {
473 let start = self.as_ptr();
474 // SAFETY: The `add` here is safe, because:
476 // - Both pointers are part of the same object, as pointing directly
477 // past the object also counts.
479 // - The size of the slice is never larger than isize::MAX bytes, as
481 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
482 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
483 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
484 // (This doesn't seem normative yet, but the very same assumption is
485 // made in many places, including the Index implementation of slices.)
487 // - There is no wrapping around involved, as slices do not wrap past
488 // the end of the address space.
490 // See the documentation of pointer::add.
491 let end = unsafe { start.add(self.len()) };
495 /// Returns the two unsafe mutable pointers spanning the slice.
497 /// The returned range is half-open, which means that the end pointer
498 /// points *one past* the last element of the slice. This way, an empty
499 /// slice is represented by two equal pointers, and the difference between
500 /// the two pointers represents the size of the slice.
502 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
503 /// pointer requires extra caution, as it does not point to a valid element
506 /// This function is useful for interacting with foreign interfaces which
507 /// use two pointers to refer to a range of elements in memory, as is
510 /// [`as_mut_ptr`]: #method.as_mut_ptr
511 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
512 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
514 pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
515 let start = self.as_mut_ptr();
516 // SAFETY: See as_ptr_range() above for why `add` here is safe.
517 let end = unsafe { start.add(self.len()) };
521 /// Swaps two elements in the slice.
525 /// * a - The index of the first element
526 /// * b - The index of the second element
530 /// Panics if `a` or `b` are out of bounds.
535 /// let mut v = ["a", "b", "c", "d"];
537 /// assert!(v == ["a", "d", "c", "b"]);
539 #[stable(feature = "rust1", since = "1.0.0")]
541 pub fn swap(&mut self, a: usize, b: usize) {
542 // Can't take two mutable loans from one vector, so instead just cast
543 // them to their raw pointers to do the swap.
544 let pa: *mut T = &mut self[a];
545 let pb: *mut T = &mut self[b];
546 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
547 // to elements in the slice and therefore are guaranteed to be valid and aligned.
548 // Note that accessing the elements behind `a` and `b` is checked and will
549 // panic when out of bounds.
555 /// Reverses the order of elements in the slice, in place.
560 /// let mut v = [1, 2, 3];
562 /// assert!(v == [3, 2, 1]);
564 #[stable(feature = "rust1", since = "1.0.0")]
566 pub fn reverse(&mut self) {
567 let mut i: usize = 0;
570 // For very small types, all the individual reads in the normal
571 // path perform poorly. We can do better, given efficient unaligned
572 // load/store, by loading a larger chunk and reversing a register.
574 // Ideally LLVM would do this for us, as it knows better than we do
575 // whether unaligned reads are efficient (since that changes between
576 // different ARM versions, for example) and what the best chunk size
577 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
578 // the loop, so we need to do this ourselves. (Hypothesis: reverse
579 // is troublesome because the sides can be aligned differently --
580 // will be, when the length is odd -- so there's no way of emitting
581 // pre- and postludes to use fully-aligned SIMD in the middle.)
583 let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
585 if fast_unaligned && mem::size_of::<T>() == 1 {
586 // Use the llvm.bswap intrinsic to reverse u8s in a usize
587 let chunk = mem::size_of::<usize>();
588 while i + chunk - 1 < ln / 2 {
589 // SAFETY: There are several things to check here:
591 // - Note that `chunk` is either 4 or 8 due to the cfg check
592 // above. So `chunk - 1` is positive.
593 // - Indexing with index `i` is fine as the loop check guarantees
594 // `i + chunk - 1 < ln / 2`
595 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
596 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
597 // - `i + chunk > 0` is trivially true.
598 // - The loop check guarantees:
599 // `i + chunk - 1 < ln / 2`
600 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
601 // - The `read_unaligned` and `write_unaligned` calls are fine:
602 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
603 // (see above) and `pb` points to index `ln - i - chunk`, so
604 // both are at least `chunk`
605 // many bytes away from the end of `self`.
606 // - Any initialized memory is valid `usize`.
608 let ptr = self.as_mut_ptr();
610 let pb = ptr.add(ln - i - chunk);
611 let va = ptr::read_unaligned(pa as *mut usize);
612 let vb = ptr::read_unaligned(pb as *mut usize);
613 ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
614 ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
620 if fast_unaligned && mem::size_of::<T>() == 2 {
621 // Use rotate-by-16 to reverse u16s in a u32
622 let chunk = mem::size_of::<u32>() / 2;
623 while i + chunk - 1 < ln / 2 {
624 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
625 // (and obviously `i < ln`), because each element is 2 bytes and
628 // `i + chunk - 1 < ln / 2` # while condition
629 // `i + 2 - 1 < ln / 2`
632 // Since it's less than the length divided by 2, then it must be
635 // This also means that the condition `0 < i + chunk <= ln` is
636 // always respected, ensuring the `pb` pointer can be used
639 let ptr = self.as_mut_ptr();
641 let pb = ptr.add(ln - i - chunk);
642 let va = ptr::read_unaligned(pa as *mut u32);
643 let vb = ptr::read_unaligned(pb as *mut u32);
644 ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
645 ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
652 // SAFETY: `i` is inferior to half the length of the slice so
653 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
654 // will not go further than `ln / 2 - 1`).
655 // The resulting pointers `pa` and `pb` are therefore valid and
656 // aligned, and can be read from and written to.
658 // Unsafe swap to avoid the bounds check in safe swap.
659 let ptr = self.as_mut_ptr();
661 let pb = ptr.add(ln - i - 1);
668 /// Returns an iterator over the slice.
673 /// let x = &[1, 2, 4];
674 /// let mut iterator = x.iter();
676 /// assert_eq!(iterator.next(), Some(&1));
677 /// assert_eq!(iterator.next(), Some(&2));
678 /// assert_eq!(iterator.next(), Some(&4));
679 /// assert_eq!(iterator.next(), None);
681 #[stable(feature = "rust1", since = "1.0.0")]
683 pub fn iter(&self) -> Iter<'_, T> {
687 /// Returns an iterator that allows modifying each value.
692 /// let x = &mut [1, 2, 4];
693 /// for elem in x.iter_mut() {
696 /// assert_eq!(x, &[3, 4, 6]);
698 #[stable(feature = "rust1", since = "1.0.0")]
700 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
704 /// Returns an iterator over all contiguous windows of length
705 /// `size`. The windows overlap. If the slice is shorter than
706 /// `size`, the iterator returns no values.
710 /// Panics if `size` is 0.
715 /// let slice = ['r', 'u', 's', 't'];
716 /// let mut iter = slice.windows(2);
717 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
718 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
719 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
720 /// assert!(iter.next().is_none());
723 /// If the slice is shorter than `size`:
726 /// let slice = ['f', 'o', 'o'];
727 /// let mut iter = slice.windows(4);
728 /// assert!(iter.next().is_none());
730 #[stable(feature = "rust1", since = "1.0.0")]
732 pub fn windows(&self, size: usize) -> Windows<'_, T> {
733 let size = NonZeroUsize::new(size).expect("size is zero");
734 Windows::new(self, size)
737 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
738 /// beginning of the slice.
740 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
741 /// slice, then the last chunk will not have length `chunk_size`.
743 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
744 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
749 /// Panics if `chunk_size` is 0.
754 /// let slice = ['l', 'o', 'r', 'e', 'm'];
755 /// let mut iter = slice.chunks(2);
756 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
757 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
758 /// assert_eq!(iter.next().unwrap(), &['m']);
759 /// assert!(iter.next().is_none());
762 /// [`chunks_exact`]: #method.chunks_exact
763 /// [`rchunks`]: #method.rchunks
764 #[stable(feature = "rust1", since = "1.0.0")]
766 pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
767 assert_ne!(chunk_size, 0);
768 Chunks::new(self, chunk_size)
771 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
772 /// beginning of the slice.
774 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
775 /// length of the slice, then the last chunk will not have length `chunk_size`.
777 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
778 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
779 /// the end of the slice.
783 /// Panics if `chunk_size` is 0.
788 /// let v = &mut [0, 0, 0, 0, 0];
789 /// let mut count = 1;
791 /// for chunk in v.chunks_mut(2) {
792 /// for elem in chunk.iter_mut() {
797 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
800 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
801 /// [`rchunks_mut`]: #method.rchunks_mut
802 #[stable(feature = "rust1", since = "1.0.0")]
804 pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
805 assert_ne!(chunk_size, 0);
806 ChunksMut::new(self, chunk_size)
809 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
810 /// beginning of the slice.
812 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
813 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
814 /// from the `remainder` function of the iterator.
816 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
817 /// resulting code better than in the case of [`chunks`].
819 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
820 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
824 /// Panics if `chunk_size` is 0.
829 /// let slice = ['l', 'o', 'r', 'e', 'm'];
830 /// let mut iter = slice.chunks_exact(2);
831 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
832 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
833 /// assert!(iter.next().is_none());
834 /// assert_eq!(iter.remainder(), &['m']);
837 /// [`chunks`]: #method.chunks
838 /// [`rchunks_exact`]: #method.rchunks_exact
839 #[stable(feature = "chunks_exact", since = "1.31.0")]
841 pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
842 assert_ne!(chunk_size, 0);
843 ChunksExact::new(self, chunk_size)
846 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
847 /// beginning of the slice.
849 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
850 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
851 /// retrieved from the `into_remainder` function of the iterator.
853 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
854 /// resulting code better than in the case of [`chunks_mut`].
856 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
857 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
862 /// Panics if `chunk_size` is 0.
867 /// let v = &mut [0, 0, 0, 0, 0];
868 /// let mut count = 1;
870 /// for chunk in v.chunks_exact_mut(2) {
871 /// for elem in chunk.iter_mut() {
876 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
879 /// [`chunks_mut`]: #method.chunks_mut
880 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
881 #[stable(feature = "chunks_exact", since = "1.31.0")]
883 pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
884 assert_ne!(chunk_size, 0);
885 ChunksExactMut::new(self, chunk_size)
888 /// Splits the slice into a slice of `N`-element arrays,
889 /// starting at the beginning of the slice,
890 /// and a remainder slice with length strictly less than `N`.
894 /// Panics if `N` is 0. This check will most probably get changed to a compile time
895 /// error before this method gets stabilized.
900 /// #![feature(slice_as_chunks)]
901 /// let slice = ['l', 'o', 'r', 'e', 'm'];
902 /// let (chunks, remainder) = slice.as_chunks();
903 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
904 /// assert_eq!(remainder, &['m']);
906 #[unstable(feature = "slice_as_chunks", issue = "74985")]
908 pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
910 let len = self.len() / N;
911 let (multiple_of_n, remainder) = self.split_at(len * N);
912 // SAFETY: We cast a slice of `len * N` elements into
913 // a slice of `len` many `N` elements chunks.
914 let array_slice: &[[T; N]] = unsafe { from_raw_parts(multiple_of_n.as_ptr().cast(), len) };
915 (array_slice, remainder)
918 /// Returns an iterator over `N` elements of the slice at a time, starting at the
919 /// beginning of the slice.
921 /// The chunks are array references and do not overlap. If `N` does not divide the
922 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
923 /// retrieved from the `remainder` function of the iterator.
925 /// This method is the const generic equivalent of [`chunks_exact`].
929 /// Panics if `N` is 0. This check will most probably get changed to a compile time
930 /// error before this method gets stabilized.
935 /// #![feature(array_chunks)]
936 /// let slice = ['l', 'o', 'r', 'e', 'm'];
937 /// let mut iter = slice.array_chunks();
938 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
939 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
940 /// assert!(iter.next().is_none());
941 /// assert_eq!(iter.remainder(), &['m']);
944 /// [`chunks_exact`]: #method.chunks_exact
945 #[unstable(feature = "array_chunks", issue = "74985")]
947 pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
949 ArrayChunks::new(self)
952 /// Splits the slice into a slice of `N`-element arrays,
953 /// starting at the beginning of the slice,
954 /// and a remainder slice with length strictly less than `N`.
958 /// Panics if `N` is 0. This check will most probably get changed to a compile time
959 /// error before this method gets stabilized.
964 /// #![feature(slice_as_chunks)]
965 /// let v = &mut [0, 0, 0, 0, 0];
966 /// let mut count = 1;
968 /// let (chunks, remainder) = v.as_chunks_mut();
969 /// remainder[0] = 9;
970 /// for chunk in chunks {
971 /// *chunk = [count; 2];
974 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
976 #[unstable(feature = "slice_as_chunks", issue = "74985")]
978 pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
980 let len = self.len() / N;
981 let (multiple_of_n, remainder) = self.split_at_mut(len * N);
982 let array_slice: &mut [[T; N]] =
983 // SAFETY: We cast a slice of `len * N` elements into
984 // a slice of `len` many `N` elements chunks.
985 unsafe { from_raw_parts_mut(multiple_of_n.as_mut_ptr().cast(), len) };
986 (array_slice, remainder)
989 /// Returns an iterator over `N` elements of the slice at a time, starting at the
990 /// beginning of the slice.
992 /// The chunks are mutable array references and do not overlap. If `N` does not divide
993 /// the length of the slice, then the last up to `N-1` elements will be omitted and
994 /// can be retrieved from the `into_remainder` function of the iterator.
996 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1000 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1001 /// error before this method gets stabilized.
1006 /// #![feature(array_chunks)]
1007 /// let v = &mut [0, 0, 0, 0, 0];
1008 /// let mut count = 1;
1010 /// for chunk in v.array_chunks_mut() {
1011 /// *chunk = [count; 2];
1014 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1017 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1018 #[unstable(feature = "array_chunks", issue = "74985")]
1020 pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
1022 ArrayChunksMut::new(self)
1025 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1026 /// starting at the beginning of the slice.
1028 /// This is the const generic equivalent of [`windows`].
1030 /// If `N` is greater than the size of the slice, it will return no windows.
1034 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1035 /// error before this method gets stabilized.
1040 /// #![feature(array_windows)]
1041 /// let slice = [0, 1, 2, 3];
1042 /// let mut iter = slice.array_windows();
1043 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1044 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1045 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1046 /// assert!(iter.next().is_none());
1049 /// [`windows`]: #method.windows
1050 #[unstable(feature = "array_windows", issue = "75027")]
1052 pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
1054 ArrayWindows::new(self)
1057 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1060 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1061 /// slice, then the last chunk will not have length `chunk_size`.
1063 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1064 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1069 /// Panics if `chunk_size` is 0.
1074 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1075 /// let mut iter = slice.rchunks(2);
1076 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1077 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1078 /// assert_eq!(iter.next().unwrap(), &['l']);
1079 /// assert!(iter.next().is_none());
1082 /// [`rchunks_exact`]: #method.rchunks_exact
1083 /// [`chunks`]: #method.chunks
1084 #[stable(feature = "rchunks", since = "1.31.0")]
1086 pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
1087 assert!(chunk_size != 0);
1088 RChunks::new(self, chunk_size)
1091 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1094 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1095 /// length of the slice, then the last chunk will not have length `chunk_size`.
1097 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1098 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1099 /// beginning of the slice.
1103 /// Panics if `chunk_size` is 0.
1108 /// let v = &mut [0, 0, 0, 0, 0];
1109 /// let mut count = 1;
1111 /// for chunk in v.rchunks_mut(2) {
1112 /// for elem in chunk.iter_mut() {
1117 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1120 /// [`rchunks_exact_mut`]: #method.rchunks_exact_mut
1121 /// [`chunks_mut`]: #method.chunks_mut
1122 #[stable(feature = "rchunks", since = "1.31.0")]
1124 pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
1125 assert!(chunk_size != 0);
1126 RChunksMut::new(self, chunk_size)
1129 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1130 /// end of the slice.
1132 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1133 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1134 /// from the `remainder` function of the iterator.
1136 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1137 /// resulting code better than in the case of [`chunks`].
1139 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1140 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1145 /// Panics if `chunk_size` is 0.
1150 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1151 /// let mut iter = slice.rchunks_exact(2);
1152 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1153 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1154 /// assert!(iter.next().is_none());
1155 /// assert_eq!(iter.remainder(), &['l']);
1158 /// [`chunks`]: #method.chunks
1159 /// [`rchunks`]: #method.rchunks
1160 /// [`chunks_exact`]: #method.chunks_exact
1161 #[stable(feature = "rchunks", since = "1.31.0")]
1163 pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
1164 assert!(chunk_size != 0);
1165 RChunksExact::new(self, chunk_size)
1168 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1171 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1172 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1173 /// retrieved from the `into_remainder` function of the iterator.
1175 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1176 /// resulting code better than in the case of [`chunks_mut`].
1178 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1179 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1184 /// Panics if `chunk_size` is 0.
1189 /// let v = &mut [0, 0, 0, 0, 0];
1190 /// let mut count = 1;
1192 /// for chunk in v.rchunks_exact_mut(2) {
1193 /// for elem in chunk.iter_mut() {
1198 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1201 /// [`chunks_mut`]: #method.chunks_mut
1202 /// [`rchunks_mut`]: #method.rchunks_mut
1203 /// [`chunks_exact_mut`]: #method.chunks_exact_mut
1204 #[stable(feature = "rchunks", since = "1.31.0")]
1206 pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
1207 assert!(chunk_size != 0);
1208 RChunksExactMut::new(self, chunk_size)
1211 /// Divides one slice into two at an index.
1213 /// The first will contain all indices from `[0, mid)` (excluding
1214 /// the index `mid` itself) and the second will contain all
1215 /// indices from `[mid, len)` (excluding the index `len` itself).
1219 /// Panics if `mid > len`.
1224 /// let v = [1, 2, 3, 4, 5, 6];
1227 /// let (left, right) = v.split_at(0);
1228 /// assert_eq!(left, []);
1229 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1233 /// let (left, right) = v.split_at(2);
1234 /// assert_eq!(left, [1, 2]);
1235 /// assert_eq!(right, [3, 4, 5, 6]);
1239 /// let (left, right) = v.split_at(6);
1240 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1241 /// assert_eq!(right, []);
1244 #[stable(feature = "rust1", since = "1.0.0")]
1246 pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
1247 assert!(mid <= self.len());
1248 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1249 // fulfills the requirements of `from_raw_parts_mut`.
1250 unsafe { self.split_at_unchecked(mid) }
1253 /// Divides one mutable slice into two at an index.
1255 /// The first will contain all indices from `[0, mid)` (excluding
1256 /// the index `mid` itself) and the second will contain all
1257 /// indices from `[mid, len)` (excluding the index `len` itself).
1261 /// Panics if `mid > len`.
1266 /// let mut v = [1, 0, 3, 0, 5, 6];
1267 /// // scoped to restrict the lifetime of the borrows
1269 /// let (left, right) = v.split_at_mut(2);
1270 /// assert_eq!(left, [1, 0]);
1271 /// assert_eq!(right, [3, 0, 5, 6]);
1275 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1277 #[stable(feature = "rust1", since = "1.0.0")]
1279 pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1280 assert!(mid <= self.len());
1281 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1282 // fulfills the requirements of `from_raw_parts_mut`.
1283 unsafe { self.split_at_mut_unchecked(mid) }
1286 /// Divides one slice into two at an index, without doing bounds checking.
1288 /// The first will contain all indices from `[0, mid)` (excluding
1289 /// the index `mid` itself) and the second will contain all
1290 /// indices from `[mid, len)` (excluding the index `len` itself).
1292 /// For a safe alternative see [`split_at`].
1296 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1297 /// even if the resulting reference is not used. The caller has to ensure that
1298 /// `0 <= mid <= self.len()`.
1300 /// [`split_at`]: #method.split_at
1301 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1306 /// #![feature(slice_split_at_unchecked)]
1308 /// let v = [1, 2, 3, 4, 5, 6];
1311 /// let (left, right) = v.split_at_unchecked(0);
1312 /// assert_eq!(left, []);
1313 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1317 /// let (left, right) = v.split_at_unchecked(2);
1318 /// assert_eq!(left, [1, 2]);
1319 /// assert_eq!(right, [3, 4, 5, 6]);
1323 /// let (left, right) = v.split_at_unchecked(6);
1324 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1325 /// assert_eq!(right, []);
1328 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1330 unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
1331 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1332 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1335 /// Divides one mutable slice into two at an index, without doing bounds checking.
1337 /// The first will contain all indices from `[0, mid)` (excluding
1338 /// the index `mid` itself) and the second will contain all
1339 /// indices from `[mid, len)` (excluding the index `len` itself).
1341 /// For a safe alternative see [`split_at_mut`].
1345 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1346 /// even if the resulting reference is not used. The caller has to ensure that
1347 /// `0 <= mid <= self.len()`.
1349 /// [`split_at_mut`]: #method.split_at_mut
1350 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1355 /// #![feature(slice_split_at_unchecked)]
1357 /// let mut v = [1, 0, 3, 0, 5, 6];
1358 /// // scoped to restrict the lifetime of the borrows
1360 /// let (left, right) = v.split_at_mut_unchecked(2);
1361 /// assert_eq!(left, [1, 0]);
1362 /// assert_eq!(right, [3, 0, 5, 6]);
1366 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1368 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1370 unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
1371 let len = self.len();
1372 let ptr = self.as_mut_ptr();
1374 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1376 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1378 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1381 /// Returns an iterator over subslices separated by elements that match
1382 /// `pred`. The matched element is not contained in the subslices.
1387 /// let slice = [10, 40, 33, 20];
1388 /// let mut iter = slice.split(|num| num % 3 == 0);
1390 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1391 /// assert_eq!(iter.next().unwrap(), &[20]);
1392 /// assert!(iter.next().is_none());
1395 /// If the first element is matched, an empty slice will be the first item
1396 /// returned by the iterator. Similarly, if the last element in the slice
1397 /// is matched, an empty slice will be the last item returned by the
1401 /// let slice = [10, 40, 33];
1402 /// let mut iter = slice.split(|num| num % 3 == 0);
1404 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1405 /// assert_eq!(iter.next().unwrap(), &[]);
1406 /// assert!(iter.next().is_none());
1409 /// If two matched elements are directly adjacent, an empty slice will be
1410 /// present between them:
1413 /// let slice = [10, 6, 33, 20];
1414 /// let mut iter = slice.split(|num| num % 3 == 0);
1416 /// assert_eq!(iter.next().unwrap(), &[10]);
1417 /// assert_eq!(iter.next().unwrap(), &[]);
1418 /// assert_eq!(iter.next().unwrap(), &[20]);
1419 /// assert!(iter.next().is_none());
1421 #[stable(feature = "rust1", since = "1.0.0")]
1423 pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
1425 F: FnMut(&T) -> bool,
1427 Split::new(self, pred)
1430 /// Returns an iterator over mutable subslices separated by elements that
1431 /// match `pred`. The matched element is not contained in the subslices.
1436 /// let mut v = [10, 40, 30, 20, 60, 50];
1438 /// for group in v.split_mut(|num| *num % 3 == 0) {
1441 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1443 #[stable(feature = "rust1", since = "1.0.0")]
1445 pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
1447 F: FnMut(&T) -> bool,
1449 SplitMut::new(self, pred)
1452 /// Returns an iterator over subslices separated by elements that match
1453 /// `pred`. The matched element is contained in the end of the previous
1454 /// subslice as a terminator.
1459 /// #![feature(split_inclusive)]
1460 /// let slice = [10, 40, 33, 20];
1461 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1463 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1464 /// assert_eq!(iter.next().unwrap(), &[20]);
1465 /// assert!(iter.next().is_none());
1468 /// If the last element of the slice is matched,
1469 /// that element will be considered the terminator of the preceding slice.
1470 /// That slice will be the last item returned by the iterator.
1473 /// #![feature(split_inclusive)]
1474 /// let slice = [3, 10, 40, 33];
1475 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1477 /// assert_eq!(iter.next().unwrap(), &[3]);
1478 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1479 /// assert!(iter.next().is_none());
1481 #[unstable(feature = "split_inclusive", issue = "72360")]
1483 pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
1485 F: FnMut(&T) -> bool,
1487 SplitInclusive::new(self, pred)
1490 /// Returns an iterator over mutable subslices separated by elements that
1491 /// match `pred`. The matched element is contained in the previous
1492 /// subslice as a terminator.
1497 /// #![feature(split_inclusive)]
1498 /// let mut v = [10, 40, 30, 20, 60, 50];
1500 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1501 /// let terminator_idx = group.len()-1;
1502 /// group[terminator_idx] = 1;
1504 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1506 #[unstable(feature = "split_inclusive", issue = "72360")]
1508 pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
1510 F: FnMut(&T) -> bool,
1512 SplitInclusiveMut::new(self, pred)
1515 /// Returns an iterator over subslices separated by elements that match
1516 /// `pred`, starting at the end of the slice and working backwards.
1517 /// The matched element is not contained in the subslices.
1522 /// let slice = [11, 22, 33, 0, 44, 55];
1523 /// let mut iter = slice.rsplit(|num| *num == 0);
1525 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1526 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1527 /// assert_eq!(iter.next(), None);
1530 /// As with `split()`, if the first or last element is matched, an empty
1531 /// slice will be the first (or last) item returned by the iterator.
1534 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1535 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1536 /// assert_eq!(it.next().unwrap(), &[]);
1537 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1538 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1539 /// assert_eq!(it.next().unwrap(), &[]);
1540 /// assert_eq!(it.next(), None);
1542 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1544 pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
1546 F: FnMut(&T) -> bool,
1548 RSplit::new(self, pred)
1551 /// Returns an iterator over mutable subslices separated by elements that
1552 /// match `pred`, starting at the end of the slice and working
1553 /// backwards. The matched element is not contained in the subslices.
1558 /// let mut v = [100, 400, 300, 200, 600, 500];
1560 /// let mut count = 0;
1561 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1563 /// group[0] = count;
1565 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1568 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1570 pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
1572 F: FnMut(&T) -> bool,
1574 RSplitMut::new(self, pred)
1577 /// Returns an iterator over subslices separated by elements that match
1578 /// `pred`, limited to returning at most `n` items. The matched element is
1579 /// not contained in the subslices.
1581 /// The last element returned, if any, will contain the remainder of the
1586 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1587 /// `[20, 60, 50]`):
1590 /// let v = [10, 40, 30, 20, 60, 50];
1592 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1593 /// println!("{:?}", group);
1596 #[stable(feature = "rust1", since = "1.0.0")]
1598 pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
1600 F: FnMut(&T) -> bool,
1602 SplitN::new(self.split(pred), n)
1605 /// Returns an iterator over subslices separated by elements that match
1606 /// `pred`, limited to returning at most `n` items. The matched element is
1607 /// not contained in the subslices.
1609 /// The last element returned, if any, will contain the remainder of the
1615 /// let mut v = [10, 40, 30, 20, 60, 50];
1617 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1620 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1622 #[stable(feature = "rust1", since = "1.0.0")]
1624 pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
1626 F: FnMut(&T) -> bool,
1628 SplitNMut::new(self.split_mut(pred), n)
1631 /// Returns an iterator over subslices separated by elements that match
1632 /// `pred` limited to returning at most `n` items. This starts at the end of
1633 /// the slice and works backwards. The matched element is not contained in
1636 /// The last element returned, if any, will contain the remainder of the
1641 /// Print the slice split once, starting from the end, by numbers divisible
1642 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1645 /// let v = [10, 40, 30, 20, 60, 50];
1647 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1648 /// println!("{:?}", group);
1651 #[stable(feature = "rust1", since = "1.0.0")]
1653 pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
1655 F: FnMut(&T) -> bool,
1657 RSplitN::new(self.rsplit(pred), n)
1660 /// Returns an iterator over subslices separated by elements that match
1661 /// `pred` limited to returning at most `n` items. This starts at the end of
1662 /// the slice and works backwards. The matched element is not contained in
1665 /// The last element returned, if any, will contain the remainder of the
1671 /// let mut s = [10, 40, 30, 20, 60, 50];
1673 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1676 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1678 #[stable(feature = "rust1", since = "1.0.0")]
1680 pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
1682 F: FnMut(&T) -> bool,
1684 RSplitNMut::new(self.rsplit_mut(pred), n)
1687 /// Returns `true` if the slice contains an element with the given value.
1692 /// let v = [10, 40, 30];
1693 /// assert!(v.contains(&30));
1694 /// assert!(!v.contains(&50));
1697 /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
1698 /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
1701 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1702 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1703 /// assert!(!v.iter().any(|e| e == "hi"));
1705 #[stable(feature = "rust1", since = "1.0.0")]
1707 pub fn contains(&self, x: &T) -> bool
1711 cmp::SliceContains::slice_contains(x, self)
1714 /// Returns `true` if `needle` is a prefix of the slice.
1719 /// let v = [10, 40, 30];
1720 /// assert!(v.starts_with(&[10]));
1721 /// assert!(v.starts_with(&[10, 40]));
1722 /// assert!(!v.starts_with(&[50]));
1723 /// assert!(!v.starts_with(&[10, 50]));
1726 /// Always returns `true` if `needle` is an empty slice:
1729 /// let v = &[10, 40, 30];
1730 /// assert!(v.starts_with(&[]));
1731 /// let v: &[u8] = &[];
1732 /// assert!(v.starts_with(&[]));
1734 #[stable(feature = "rust1", since = "1.0.0")]
1735 pub fn starts_with(&self, needle: &[T]) -> bool
1739 let n = needle.len();
1740 self.len() >= n && needle == &self[..n]
1743 /// Returns `true` if `needle` is a suffix of the slice.
1748 /// let v = [10, 40, 30];
1749 /// assert!(v.ends_with(&[30]));
1750 /// assert!(v.ends_with(&[40, 30]));
1751 /// assert!(!v.ends_with(&[50]));
1752 /// assert!(!v.ends_with(&[50, 30]));
1755 /// Always returns `true` if `needle` is an empty slice:
1758 /// let v = &[10, 40, 30];
1759 /// assert!(v.ends_with(&[]));
1760 /// let v: &[u8] = &[];
1761 /// assert!(v.ends_with(&[]));
1763 #[stable(feature = "rust1", since = "1.0.0")]
1764 pub fn ends_with(&self, needle: &[T]) -> bool
1768 let (m, n) = (self.len(), needle.len());
1769 m >= n && needle == &self[m - n..]
1772 /// Returns a subslice with the prefix removed.
1774 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
1775 /// If `prefix` is empty, simply returns the original slice.
1777 /// If the slice does not start with `prefix`, returns `None`.
1782 /// #![feature(slice_strip)]
1783 /// let v = &[10, 40, 30];
1784 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
1785 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
1786 /// assert_eq!(v.strip_prefix(&[50]), None);
1787 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
1789 #[must_use = "returns the subslice without modifying the original"]
1790 #[unstable(feature = "slice_strip", issue = "73413")]
1791 pub fn strip_prefix(&self, prefix: &[T]) -> Option<&[T]>
1795 let n = prefix.len();
1796 if n <= self.len() {
1797 let (head, tail) = self.split_at(n);
1805 /// Returns a subslice with the suffix removed.
1807 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
1808 /// If `suffix` is empty, simply returns the original slice.
1810 /// If the slice does not end with `suffix`, returns `None`.
1815 /// #![feature(slice_strip)]
1816 /// let v = &[10, 40, 30];
1817 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
1818 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
1819 /// assert_eq!(v.strip_suffix(&[50]), None);
1820 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
1822 #[must_use = "returns the subslice without modifying the original"]
1823 #[unstable(feature = "slice_strip", issue = "73413")]
1824 pub fn strip_suffix(&self, suffix: &[T]) -> Option<&[T]>
1828 let (len, n) = (self.len(), suffix.len());
1830 let (head, tail) = self.split_at(len - n);
1838 /// Binary searches this sorted slice for a given element.
1840 /// If the value is found then [`Result::Ok`] is returned, containing the
1841 /// index of the matching element. If there are multiple matches, then any
1842 /// one of the matches could be returned. If the value is not found then
1843 /// [`Result::Err`] is returned, containing the index where a matching
1844 /// element could be inserted while maintaining sorted order.
1848 /// Looks up a series of four elements. The first is found, with a
1849 /// uniquely determined position; the second and third are not
1850 /// found; the fourth could match any position in `[1, 4]`.
1853 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1855 /// assert_eq!(s.binary_search(&13), Ok(9));
1856 /// assert_eq!(s.binary_search(&4), Err(7));
1857 /// assert_eq!(s.binary_search(&100), Err(13));
1858 /// let r = s.binary_search(&1);
1859 /// assert!(match r { Ok(1..=4) => true, _ => false, });
1862 /// If you want to insert an item to a sorted vector, while maintaining
1866 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1868 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
1869 /// s.insert(idx, num);
1870 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
1872 #[stable(feature = "rust1", since = "1.0.0")]
1873 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
1877 self.binary_search_by(|p| p.cmp(x))
1880 /// Binary searches this sorted slice with a comparator function.
1882 /// The comparator function should implement an order consistent
1883 /// with the sort order of the underlying slice, returning an
1884 /// order code that indicates whether its argument is `Less`,
1885 /// `Equal` or `Greater` the desired target.
1887 /// If the value is found then [`Result::Ok`] is returned, containing the
1888 /// index of the matching element. If there are multiple matches, then any
1889 /// one of the matches could be returned. If the value is not found then
1890 /// [`Result::Err`] is returned, containing the index where a matching
1891 /// element could be inserted while maintaining sorted order.
1895 /// Looks up a series of four elements. The first is found, with a
1896 /// uniquely determined position; the second and third are not
1897 /// found; the fourth could match any position in `[1, 4]`.
1900 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
1903 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
1905 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
1907 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
1909 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
1910 /// assert!(match r { Ok(1..=4) => true, _ => false, });
1912 #[stable(feature = "rust1", since = "1.0.0")]
1914 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
1916 F: FnMut(&'a T) -> Ordering,
1919 let mut size = s.len();
1923 let mut base = 0usize;
1925 let half = size / 2;
1926 let mid = base + half;
1927 // SAFETY: the call is made safe by the following inconstants:
1928 // - `mid >= 0`: by definition
1929 // - `mid < size`: `mid = size / 2 + size / 4 + size / 8 ...`
1930 let cmp = f(unsafe { s.get_unchecked(mid) });
1931 base = if cmp == Greater { base } else { mid };
1934 // SAFETY: base is always in [0, size) because base <= mid.
1935 let cmp = f(unsafe { s.get_unchecked(base) });
1936 if cmp == Equal { Ok(base) } else { Err(base + (cmp == Less) as usize) }
1939 /// Binary searches this sorted slice with a key extraction function.
1941 /// Assumes that the slice is sorted by the key, for instance with
1942 /// [`sort_by_key`] using the same key extraction function.
1944 /// If the value is found then [`Result::Ok`] is returned, containing the
1945 /// index of the matching element. If there are multiple matches, then any
1946 /// one of the matches could be returned. If the value is not found then
1947 /// [`Result::Err`] is returned, containing the index where a matching
1948 /// element could be inserted while maintaining sorted order.
1950 /// [`sort_by_key`]: #method.sort_by_key
1954 /// Looks up a series of four elements in a slice of pairs sorted by
1955 /// their second elements. The first is found, with a uniquely
1956 /// determined position; the second and third are not found; the
1957 /// fourth could match any position in `[1, 4]`.
1960 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
1961 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
1962 /// (1, 21), (2, 34), (4, 55)];
1964 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
1965 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
1966 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
1967 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
1968 /// assert!(match r { Ok(1..=4) => true, _ => false, });
1970 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
1972 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
1974 F: FnMut(&'a T) -> B,
1977 self.binary_search_by(|k| f(k).cmp(b))
1980 /// Sorts the slice, but may not preserve the order of equal elements.
1982 /// This sort is unstable (i.e., may reorder equal elements), in-place
1983 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
1985 /// # Current implementation
1987 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
1988 /// which combines the fast average case of randomized quicksort with the fast worst case of
1989 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
1990 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
1991 /// deterministic behavior.
1993 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
1994 /// slice consists of several concatenated sorted sequences.
1999 /// let mut v = [-5, 4, 1, -3, 2];
2001 /// v.sort_unstable();
2002 /// assert!(v == [-5, -3, 1, 2, 4]);
2005 /// [pdqsort]: https://github.com/orlp/pdqsort
2006 #[stable(feature = "sort_unstable", since = "1.20.0")]
2008 pub fn sort_unstable(&mut self)
2012 sort::quicksort(self, |a, b| a.lt(b));
2015 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2018 /// This sort is unstable (i.e., may reorder equal elements), in-place
2019 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2021 /// The comparator function must define a total ordering for the elements in the slice. If
2022 /// the ordering is not total, the order of the elements is unspecified. An order is a
2023 /// total order if it is (for all `a`, `b` and `c`):
2025 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2026 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2028 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2029 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2032 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2033 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2034 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2037 /// # Current implementation
2039 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2040 /// which combines the fast average case of randomized quicksort with the fast worst case of
2041 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2042 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2043 /// deterministic behavior.
2045 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2046 /// slice consists of several concatenated sorted sequences.
2051 /// let mut v = [5, 4, 1, 3, 2];
2052 /// v.sort_unstable_by(|a, b| a.cmp(b));
2053 /// assert!(v == [1, 2, 3, 4, 5]);
2055 /// // reverse sorting
2056 /// v.sort_unstable_by(|a, b| b.cmp(a));
2057 /// assert!(v == [5, 4, 3, 2, 1]);
2060 /// [pdqsort]: https://github.com/orlp/pdqsort
2061 #[stable(feature = "sort_unstable", since = "1.20.0")]
2063 pub fn sort_unstable_by<F>(&mut self, mut compare: F)
2065 F: FnMut(&T, &T) -> Ordering,
2067 sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
2070 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2073 /// This sort is unstable (i.e., may reorder equal elements), in-place
2074 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2077 /// # Current implementation
2079 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2080 /// which combines the fast average case of randomized quicksort with the fast worst case of
2081 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2082 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2083 /// deterministic behavior.
2085 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2086 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2087 /// cases where the key function is expensive.
2092 /// let mut v = [-5i32, 4, 1, -3, 2];
2094 /// v.sort_unstable_by_key(|k| k.abs());
2095 /// assert!(v == [1, 2, -3, 4, -5]);
2098 /// [pdqsort]: https://github.com/orlp/pdqsort
2099 #[stable(feature = "sort_unstable", since = "1.20.0")]
2101 pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
2106 sort::quicksort(self, |a, b| f(a).lt(&f(b)));
2109 /// Reorder the slice such that the element at `index` is at its final sorted position.
2110 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2111 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2113 pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2117 self.select_nth_unstable(index)
2120 /// Reorder the slice with a comparator function such that the element at `index` is at its
2121 /// final sorted position.
2122 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2123 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2125 pub fn partition_at_index_by<F>(
2129 ) -> (&mut [T], &mut T, &mut [T])
2131 F: FnMut(&T, &T) -> Ordering,
2133 self.select_nth_unstable_by(index, compare)
2136 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2137 /// final sorted position.
2138 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2139 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2141 pub fn partition_at_index_by_key<K, F>(
2145 ) -> (&mut [T], &mut T, &mut [T])
2150 self.select_nth_unstable_by_key(index, f)
2153 /// Reorder the slice such that the element at `index` is at its final sorted position.
2155 /// This reordering has the additional property that any value at position `i < index` will be
2156 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2157 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2158 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2159 /// element" in other libraries. It returns a triplet of the following values: all elements less
2160 /// than the one at the given index, the value at the given index, and all elements greater than
2161 /// the one at the given index.
2163 /// # Current implementation
2165 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2166 /// used for [`sort_unstable`].
2168 /// [`sort_unstable`]: #method.sort_unstable
2172 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2177 /// let mut v = [-5i32, 4, 1, -3, 2];
2179 /// // Find the median
2180 /// v.select_nth_unstable(2);
2182 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2183 /// // about the specified index.
2184 /// assert!(v == [-3, -5, 1, 2, 4] ||
2185 /// v == [-5, -3, 1, 2, 4] ||
2186 /// v == [-3, -5, 1, 4, 2] ||
2187 /// v == [-5, -3, 1, 4, 2]);
2189 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2191 pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
2195 let mut f = |a: &T, b: &T| a.lt(b);
2196 sort::partition_at_index(self, index, &mut f)
2199 /// Reorder the slice with a comparator function such that the element at `index` is at its
2200 /// final sorted position.
2202 /// This reordering has the additional property that any value at position `i < index` will be
2203 /// less than or equal to any value at a position `j > index` using the comparator function.
2204 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2205 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2206 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2207 /// values: all elements less than the one at the given index, the value at the given index,
2208 /// and all elements greater than the one at the given index, using the provided comparator
2211 /// # Current implementation
2213 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2214 /// used for [`sort_unstable`].
2216 /// [`sort_unstable`]: #method.sort_unstable
2220 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2225 /// let mut v = [-5i32, 4, 1, -3, 2];
2227 /// // Find the median as if the slice were sorted in descending order.
2228 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2230 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2231 /// // about the specified index.
2232 /// assert!(v == [2, 4, 1, -5, -3] ||
2233 /// v == [2, 4, 1, -3, -5] ||
2234 /// v == [4, 2, 1, -5, -3] ||
2235 /// v == [4, 2, 1, -3, -5]);
2237 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2239 pub fn select_nth_unstable_by<F>(
2243 ) -> (&mut [T], &mut T, &mut [T])
2245 F: FnMut(&T, &T) -> Ordering,
2247 let mut f = |a: &T, b: &T| compare(a, b) == Less;
2248 sort::partition_at_index(self, index, &mut f)
2251 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2252 /// final sorted position.
2254 /// This reordering has the additional property that any value at position `i < index` will be
2255 /// less than or equal to any value at a position `j > index` using the key extraction function.
2256 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2257 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2258 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2259 /// values: all elements less than the one at the given index, the value at the given index, and
2260 /// all elements greater than the one at the given index, using the provided key extraction
2263 /// # Current implementation
2265 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2266 /// used for [`sort_unstable`].
2268 /// [`sort_unstable`]: #method.sort_unstable
2272 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2277 /// let mut v = [-5i32, 4, 1, -3, 2];
2279 /// // Return the median as if the array were sorted according to absolute value.
2280 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2282 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2283 /// // about the specified index.
2284 /// assert!(v == [1, 2, -3, 4, -5] ||
2285 /// v == [1, 2, -3, -5, 4] ||
2286 /// v == [2, 1, -3, 4, -5] ||
2287 /// v == [2, 1, -3, -5, 4]);
2289 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2291 pub fn select_nth_unstable_by_key<K, F>(
2295 ) -> (&mut [T], &mut T, &mut [T])
2300 let mut g = |a: &T, b: &T| f(a).lt(&f(b));
2301 sort::partition_at_index(self, index, &mut g)
2304 /// Moves all consecutive repeated elements to the end of the slice according to the
2305 /// [`PartialEq`] trait implementation.
2307 /// Returns two slices. The first contains no consecutive repeated elements.
2308 /// The second contains all the duplicates in no specified order.
2310 /// If the slice is sorted, the first returned slice contains no duplicates.
2315 /// #![feature(slice_partition_dedup)]
2317 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2319 /// let (dedup, duplicates) = slice.partition_dedup();
2321 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2322 /// assert_eq!(duplicates, [2, 3, 1]);
2324 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2326 pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
2330 self.partition_dedup_by(|a, b| a == b)
2333 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2334 /// a given equality relation.
2336 /// Returns two slices. The first contains no consecutive repeated elements.
2337 /// The second contains all the duplicates in no specified order.
2339 /// The `same_bucket` function is passed references to two elements from the slice and
2340 /// must determine if the elements compare equal. The elements are passed in opposite order
2341 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2342 /// at the end of the slice.
2344 /// If the slice is sorted, the first returned slice contains no duplicates.
2349 /// #![feature(slice_partition_dedup)]
2351 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2353 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2355 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2356 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2358 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2360 pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
2362 F: FnMut(&mut T, &mut T) -> bool,
2364 // Although we have a mutable reference to `self`, we cannot make
2365 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2366 // must ensure that the slice is in a valid state at all times.
2368 // The way that we handle this is by using swaps; we iterate
2369 // over all the elements, swapping as we go so that at the end
2370 // the elements we wish to keep are in the front, and those we
2371 // wish to reject are at the back. We can then split the slice.
2372 // This operation is still `O(n)`.
2374 // Example: We start in this state, where `r` represents "next
2375 // read" and `w` represents "next_write`.
2378 // +---+---+---+---+---+---+
2379 // | 0 | 1 | 1 | 2 | 3 | 3 |
2380 // +---+---+---+---+---+---+
2383 // Comparing self[r] against self[w-1], this is not a duplicate, so
2384 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2385 // r and w, leaving us with:
2388 // +---+---+---+---+---+---+
2389 // | 0 | 1 | 1 | 2 | 3 | 3 |
2390 // +---+---+---+---+---+---+
2393 // Comparing self[r] against self[w-1], this value is a duplicate,
2394 // so we increment `r` but leave everything else unchanged:
2397 // +---+---+---+---+---+---+
2398 // | 0 | 1 | 1 | 2 | 3 | 3 |
2399 // +---+---+---+---+---+---+
2402 // Comparing self[r] against self[w-1], this is not a duplicate,
2403 // so swap self[r] and self[w] and advance r and w:
2406 // +---+---+---+---+---+---+
2407 // | 0 | 1 | 2 | 1 | 3 | 3 |
2408 // +---+---+---+---+---+---+
2411 // Not a duplicate, repeat:
2414 // +---+---+---+---+---+---+
2415 // | 0 | 1 | 2 | 3 | 1 | 3 |
2416 // +---+---+---+---+---+---+
2419 // Duplicate, advance r. End of slice. Split at w.
2421 let len = self.len();
2423 return (self, &mut []);
2426 let ptr = self.as_mut_ptr();
2427 let mut next_read: usize = 1;
2428 let mut next_write: usize = 1;
2430 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2431 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2432 // one element before `ptr_write`, but `next_write` starts at 1, so
2433 // `prev_ptr_write` is never less than 0 and is inside the slice.
2434 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2435 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2436 // and `prev_ptr_write.offset(1)`.
2438 // `next_write` is also incremented at most once per loop at most meaning
2439 // no element is skipped when it may need to be swapped.
2441 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2442 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2443 // The explanation is simply that `next_read >= next_write` is always true,
2444 // thus `next_read > next_write - 1` is too.
2446 // Avoid bounds checks by using raw pointers.
2447 while next_read < len {
2448 let ptr_read = ptr.add(next_read);
2449 let prev_ptr_write = ptr.add(next_write - 1);
2450 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
2451 if next_read != next_write {
2452 let ptr_write = prev_ptr_write.offset(1);
2453 mem::swap(&mut *ptr_read, &mut *ptr_write);
2461 self.split_at_mut(next_write)
2464 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2465 /// to the same key.
2467 /// Returns two slices. The first contains no consecutive repeated elements.
2468 /// The second contains all the duplicates in no specified order.
2470 /// If the slice is sorted, the first returned slice contains no duplicates.
2475 /// #![feature(slice_partition_dedup)]
2477 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2479 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2481 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2482 /// assert_eq!(duplicates, [21, 30, 13]);
2484 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2486 pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
2488 F: FnMut(&mut T) -> K,
2491 self.partition_dedup_by(|a, b| key(a) == key(b))
2494 /// Rotates the slice in-place such that the first `mid` elements of the
2495 /// slice move to the end while the last `self.len() - mid` elements move to
2496 /// the front. After calling `rotate_left`, the element previously at index
2497 /// `mid` will become the first element in the slice.
2501 /// This function will panic if `mid` is greater than the length of the
2502 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2507 /// Takes linear (in `self.len()`) time.
2512 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2513 /// a.rotate_left(2);
2514 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2517 /// Rotating a subslice:
2520 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2521 /// a[1..5].rotate_left(1);
2522 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2524 #[stable(feature = "slice_rotate", since = "1.26.0")]
2525 pub fn rotate_left(&mut self, mid: usize) {
2526 assert!(mid <= self.len());
2527 let k = self.len() - mid;
2528 let p = self.as_mut_ptr();
2530 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2531 // valid for reading and writing, as required by `ptr_rotate`.
2533 rotate::ptr_rotate(mid, p.add(mid), k);
2537 /// Rotates the slice in-place such that the first `self.len() - k`
2538 /// elements of the slice move to the end while the last `k` elements move
2539 /// to the front. After calling `rotate_right`, the element previously at
2540 /// index `self.len() - k` will become the first element in the slice.
2544 /// This function will panic if `k` is greater than the length of the
2545 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2550 /// Takes linear (in `self.len()`) time.
2555 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2556 /// a.rotate_right(2);
2557 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2560 /// Rotate a subslice:
2563 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2564 /// a[1..5].rotate_right(1);
2565 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2567 #[stable(feature = "slice_rotate", since = "1.26.0")]
2568 pub fn rotate_right(&mut self, k: usize) {
2569 assert!(k <= self.len());
2570 let mid = self.len() - k;
2571 let p = self.as_mut_ptr();
2573 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2574 // valid for reading and writing, as required by `ptr_rotate`.
2576 rotate::ptr_rotate(mid, p.add(mid), k);
2580 /// Fills `self` with elements by cloning `value`.
2585 /// #![feature(slice_fill)]
2587 /// let mut buf = vec![0; 10];
2589 /// assert_eq!(buf, vec![1; 10]);
2591 #[doc(alias = "memset")]
2592 #[unstable(feature = "slice_fill", issue = "70758")]
2593 pub fn fill(&mut self, value: T)
2597 if let Some((last, elems)) = self.split_last_mut() {
2599 el.clone_from(&value);
2606 /// Fills `self` with elements returned by calling a closure repeatedly.
2608 /// This method uses a closure to create new values. If you'd rather
2609 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2610 /// trait to generate values, you can pass [`Default::default`] as the
2613 /// [`fill`]: #method.fill
2618 /// #![feature(slice_fill_with)]
2620 /// let mut buf = vec![1; 10];
2621 /// buf.fill_with(Default::default);
2622 /// assert_eq!(buf, vec![0; 10]);
2624 #[unstable(feature = "slice_fill_with", issue = "79221")]
2625 pub fn fill_with<F>(&mut self, mut f: F)
2634 /// Copies the elements from `src` into `self`.
2636 /// The length of `src` must be the same as `self`.
2638 /// If `T` implements `Copy`, it can be more performant to use
2639 /// [`copy_from_slice`].
2643 /// This function will panic if the two slices have different lengths.
2647 /// Cloning two elements from a slice into another:
2650 /// let src = [1, 2, 3, 4];
2651 /// let mut dst = [0, 0];
2653 /// // Because the slices have to be the same length,
2654 /// // we slice the source slice from four elements
2655 /// // to two. It will panic if we don't do this.
2656 /// dst.clone_from_slice(&src[2..]);
2658 /// assert_eq!(src, [1, 2, 3, 4]);
2659 /// assert_eq!(dst, [3, 4]);
2662 /// Rust enforces that there can only be one mutable reference with no
2663 /// immutable references to a particular piece of data in a particular
2664 /// scope. Because of this, attempting to use `clone_from_slice` on a
2665 /// single slice will result in a compile failure:
2668 /// let mut slice = [1, 2, 3, 4, 5];
2670 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2673 /// To work around this, we can use [`split_at_mut`] to create two distinct
2674 /// sub-slices from a slice:
2677 /// let mut slice = [1, 2, 3, 4, 5];
2680 /// let (left, right) = slice.split_at_mut(2);
2681 /// left.clone_from_slice(&right[1..]);
2684 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2687 /// [`copy_from_slice`]: #method.copy_from_slice
2688 /// [`split_at_mut`]: #method.split_at_mut
2689 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2690 pub fn clone_from_slice(&mut self, src: &[T])
2694 assert!(self.len() == src.len(), "destination and source slices have different lengths");
2695 // NOTE: We need to explicitly slice them to the same length
2696 // for bounds checking to be elided, and the optimizer will
2697 // generate memcpy for simple cases (for example T = u8).
2698 let len = self.len();
2699 let src = &src[..len];
2701 self[i].clone_from(&src[i]);
2705 /// Copies all elements from `src` into `self`, using a memcpy.
2707 /// The length of `src` must be the same as `self`.
2709 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2713 /// This function will panic if the two slices have different lengths.
2717 /// Copying two elements from a slice into another:
2720 /// let src = [1, 2, 3, 4];
2721 /// let mut dst = [0, 0];
2723 /// // Because the slices have to be the same length,
2724 /// // we slice the source slice from four elements
2725 /// // to two. It will panic if we don't do this.
2726 /// dst.copy_from_slice(&src[2..]);
2728 /// assert_eq!(src, [1, 2, 3, 4]);
2729 /// assert_eq!(dst, [3, 4]);
2732 /// Rust enforces that there can only be one mutable reference with no
2733 /// immutable references to a particular piece of data in a particular
2734 /// scope. Because of this, attempting to use `copy_from_slice` on a
2735 /// single slice will result in a compile failure:
2738 /// let mut slice = [1, 2, 3, 4, 5];
2740 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
2743 /// To work around this, we can use [`split_at_mut`] to create two distinct
2744 /// sub-slices from a slice:
2747 /// let mut slice = [1, 2, 3, 4, 5];
2750 /// let (left, right) = slice.split_at_mut(2);
2751 /// left.copy_from_slice(&right[1..]);
2754 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2757 /// [`clone_from_slice`]: #method.clone_from_slice
2758 /// [`split_at_mut`]: #method.split_at_mut
2759 #[doc(alias = "memcpy")]
2760 #[stable(feature = "copy_from_slice", since = "1.9.0")]
2761 pub fn copy_from_slice(&mut self, src: &[T])
2765 // The panic code path was put into a cold function to not bloat the
2770 fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
2772 "source slice length ({}) does not match destination slice length ({})",
2777 if self.len() != src.len() {
2778 len_mismatch_fail(self.len(), src.len());
2781 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
2782 // checked to have the same length. The slices cannot overlap because
2783 // mutable references are exclusive.
2785 ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
2789 /// Copies elements from one part of the slice to another part of itself,
2790 /// using a memmove.
2792 /// `src` is the range within `self` to copy from. `dest` is the starting
2793 /// index of the range within `self` to copy to, which will have the same
2794 /// length as `src`. The two ranges may overlap. The ends of the two ranges
2795 /// must be less than or equal to `self.len()`.
2799 /// This function will panic if either range exceeds the end of the slice,
2800 /// or if the end of `src` is before the start.
2804 /// Copying four bytes within a slice:
2807 /// let mut bytes = *b"Hello, World!";
2809 /// bytes.copy_within(1..5, 8);
2811 /// assert_eq!(&bytes, b"Hello, Wello!");
2813 #[stable(feature = "copy_within", since = "1.37.0")]
2815 pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
2819 let Range { start: src_start, end: src_end } = src.assert_len(self.len());
2820 let count = src_end - src_start;
2821 assert!(dest <= self.len() - count, "dest is out of bounds");
2822 // SAFETY: the conditions for `ptr::copy` have all been checked above,
2823 // as have those for `ptr::add`.
2825 ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), count);
2829 /// Swaps all elements in `self` with those in `other`.
2831 /// The length of `other` must be the same as `self`.
2835 /// This function will panic if the two slices have different lengths.
2839 /// Swapping two elements across slices:
2842 /// let mut slice1 = [0, 0];
2843 /// let mut slice2 = [1, 2, 3, 4];
2845 /// slice1.swap_with_slice(&mut slice2[2..]);
2847 /// assert_eq!(slice1, [3, 4]);
2848 /// assert_eq!(slice2, [1, 2, 0, 0]);
2851 /// Rust enforces that there can only be one mutable reference to a
2852 /// particular piece of data in a particular scope. Because of this,
2853 /// attempting to use `swap_with_slice` on a single slice will result in
2854 /// a compile failure:
2857 /// let mut slice = [1, 2, 3, 4, 5];
2858 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
2861 /// To work around this, we can use [`split_at_mut`] to create two distinct
2862 /// mutable sub-slices from a slice:
2865 /// let mut slice = [1, 2, 3, 4, 5];
2868 /// let (left, right) = slice.split_at_mut(2);
2869 /// left.swap_with_slice(&mut right[1..]);
2872 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
2875 /// [`split_at_mut`]: #method.split_at_mut
2876 #[stable(feature = "swap_with_slice", since = "1.27.0")]
2877 pub fn swap_with_slice(&mut self, other: &mut [T]) {
2878 assert!(self.len() == other.len(), "destination and source slices have different lengths");
2879 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
2880 // checked to have the same length. The slices cannot overlap because
2881 // mutable references are exclusive.
2883 ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
2887 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
2888 fn align_to_offsets<U>(&self) -> (usize, usize) {
2889 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
2890 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
2892 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
2893 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
2894 // place of every 3 Ts in the `rest` slice. A bit more complicated.
2896 // Formula to calculate this is:
2898 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
2899 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
2901 // Expanded and simplified:
2903 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
2904 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
2906 // Luckily since all this is constant-evaluated... performance here matters not!
2908 fn gcd(a: usize, b: usize) -> usize {
2909 use crate::intrinsics;
2910 // iterative stein’s algorithm
2911 // We should still make this `const fn` (and revert to recursive algorithm if we do)
2912 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
2914 // SAFETY: `a` and `b` are checked to be non-zero values.
2915 let (ctz_a, mut ctz_b) = unsafe {
2922 (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
2924 let k = ctz_a.min(ctz_b);
2925 let mut a = a >> ctz_a;
2928 // remove all factors of 2 from b
2931 mem::swap(&mut a, &mut b);
2934 // SAFETY: `b` is checked to be non-zero.
2939 ctz_b = intrinsics::cttz_nonzero(b);
2944 let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
2945 let ts: usize = mem::size_of::<U>() / gcd;
2946 let us: usize = mem::size_of::<T>() / gcd;
2948 // Armed with this knowledge, we can find how many `U`s we can fit!
2949 let us_len = self.len() / ts * us;
2950 // And how many `T`s will be in the trailing slice!
2951 let ts_len = self.len() % ts;
2955 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
2958 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
2959 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
2960 /// length possible for a given type and input slice, but only your algorithm's performance
2961 /// should depend on that, not its correctness. It is permissible for all of the input data to
2962 /// be returned as the prefix or suffix slice.
2964 /// This method has no purpose when either input element `T` or output element `U` are
2965 /// zero-sized and will return the original slice without splitting anything.
2969 /// This method is essentially a `transmute` with respect to the elements in the returned
2970 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
2978 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
2979 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
2980 /// // less_efficient_algorithm_for_bytes(prefix);
2981 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
2982 /// // less_efficient_algorithm_for_bytes(suffix);
2985 #[stable(feature = "slice_align_to", since = "1.30.0")]
2986 pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
2987 // Note that most of this function will be constant-evaluated,
2988 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
2989 // handle ZSTs specially, which is – don't handle them at all.
2990 return (self, &[], &[]);
2993 // First, find at what point do we split between the first and 2nd slice. Easy with
2994 // ptr.align_offset.
2995 let ptr = self.as_ptr();
2996 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
2997 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
2998 if offset > self.len() {
3001 let (left, rest) = self.split_at(offset);
3002 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3003 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3004 // since the caller guarantees that we can transmute `T` to `U` safely.
3008 from_raw_parts(rest.as_ptr() as *const U, us_len),
3009 from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
3015 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3018 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3019 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3020 /// length possible for a given type and input slice, but only your algorithm's performance
3021 /// should depend on that, not its correctness. It is permissible for all of the input data to
3022 /// be returned as the prefix or suffix slice.
3024 /// This method has no purpose when either input element `T` or output element `U` are
3025 /// zero-sized and will return the original slice without splitting anything.
3029 /// This method is essentially a `transmute` with respect to the elements in the returned
3030 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3038 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3039 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3040 /// // less_efficient_algorithm_for_bytes(prefix);
3041 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3042 /// // less_efficient_algorithm_for_bytes(suffix);
3045 #[stable(feature = "slice_align_to", since = "1.30.0")]
3046 pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
3047 // Note that most of this function will be constant-evaluated,
3048 if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
3049 // handle ZSTs specially, which is – don't handle them at all.
3050 return (self, &mut [], &mut []);
3053 // First, find at what point do we split between the first and 2nd slice. Easy with
3054 // ptr.align_offset.
3055 let ptr = self.as_ptr();
3056 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3057 // rest of the method. This is done by passing a pointer to &[T] with an
3058 // alignment targeted for U.
3059 // `crate::ptr::align_offset` is called with a correctly aligned and
3060 // valid pointer `ptr` (it comes from a reference to `self`) and with
3061 // a size that is a power of two (since it comes from the alignement for U),
3062 // satisfying its safety constraints.
3063 let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
3064 if offset > self.len() {
3065 (self, &mut [], &mut [])
3067 let (left, rest) = self.split_at_mut(offset);
3068 let (us_len, ts_len) = rest.align_to_offsets::<U>();
3069 let rest_len = rest.len();
3070 let mut_ptr = rest.as_mut_ptr();
3071 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3072 // SAFETY: see comments for `align_to`.
3076 from_raw_parts_mut(mut_ptr as *mut U, us_len),
3077 from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
3083 /// Checks if the elements of this slice are sorted.
3085 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3086 /// slice yields exactly zero or one element, `true` is returned.
3088 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3089 /// implies that this function returns `false` if any two consecutive items are not
3095 /// #![feature(is_sorted)]
3096 /// let empty: [i32; 0] = [];
3098 /// assert!([1, 2, 2, 9].is_sorted());
3099 /// assert!(![1, 3, 2, 4].is_sorted());
3100 /// assert!([0].is_sorted());
3101 /// assert!(empty.is_sorted());
3102 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3105 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3106 pub fn is_sorted(&self) -> bool
3110 self.is_sorted_by(|a, b| a.partial_cmp(b))
3113 /// Checks if the elements of this slice are sorted using the given comparator function.
3115 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3116 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3117 /// [`is_sorted`]; see its documentation for more information.
3119 /// [`is_sorted`]: #method.is_sorted
3120 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3121 pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
3123 F: FnMut(&T, &T) -> Option<Ordering>,
3125 self.iter().is_sorted_by(|a, b| compare(*a, *b))
3128 /// Checks if the elements of this slice are sorted using the given key extraction function.
3130 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3131 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3132 /// documentation for more information.
3134 /// [`is_sorted`]: #method.is_sorted
3139 /// #![feature(is_sorted)]
3141 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3142 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3145 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3146 pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
3151 self.iter().is_sorted_by_key(f)
3154 /// Returns the index of the partition point according to the given predicate
3155 /// (the index of the first element of the second partition).
3157 /// The slice is assumed to be partitioned according to the given predicate.
3158 /// This means that all elements for which the predicate returns true are at the start of the slice
3159 /// and all elements for which the predicate returns false are at the end.
3160 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3161 /// (all odd numbers are at the start, all even at the end).
3163 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3164 /// as this method performs a kind of binary search.
3169 /// #![feature(partition_point)]
3171 /// let v = [1, 2, 3, 3, 5, 6, 7];
3172 /// let i = v.partition_point(|&x| x < 5);
3174 /// assert_eq!(i, 4);
3175 /// assert!(v[..i].iter().all(|&x| x < 5));
3176 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3178 #[unstable(feature = "partition_point", reason = "new API", issue = "73831")]
3179 pub fn partition_point<P>(&self, mut pred: P) -> usize
3181 P: FnMut(&T) -> bool,
3184 let mut right = self.len();
3186 while left != right {
3187 let mid = left + (right - left) / 2;
3188 // SAFETY: When `left < right`, `left <= mid < right`.
3189 // Therefore `left` always increases and `right` always decreases,
3190 // and either of them is selected. In both cases `left <= right` is
3191 // satisfied. Therefore if `left < right` in a step, `left <= right`
3192 // is satisfied in the next step. Therefore as long as `left != right`,
3193 // `0 <= left < right <= len` is satisfied and if this case
3194 // `0 <= mid < len` is satisfied too.
3195 let value = unsafe { self.get_unchecked(mid) };
3207 #[stable(feature = "rust1", since = "1.0.0")]
3208 impl<T> Default for &[T] {
3209 /// Creates an empty slice.
3210 fn default() -> Self {
3215 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3216 impl<T> Default for &mut [T] {
3217 /// Creates a mutable empty slice.
3218 fn default() -> Self {