1 // ignore-tidy-filelength
3 //! Slice management and manipulation.
5 //! For more details see [`std::slice`].
7 //! [`std::slice`]: ../../std/slice/index.html
9 #![stable(feature = "rust1", since = "1.0.0")]
11 use crate::cmp
::Ordering
::{self, Greater, Less}
;
12 use crate::marker
::Copy
;
14 use crate::num
::NonZeroUsize
;
15 use crate::ops
::{FnMut, Range, RangeBounds}
;
16 use crate::option
::Option
;
17 use crate::option
::Option
::{None, Some}
;
19 use crate::result
::Result
;
20 use crate::result
::Result
::{Err, Ok}
;
24 feature
= "slice_internals",
26 reason
= "exposed from core to be reused in std; use the memchr crate"
28 /// Pure rust memchr implementation, taken from rust-memchr
40 #[stable(feature = "rust1", since = "1.0.0")]
41 pub use iter
::{Chunks, ChunksMut, Windows}
;
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use iter
::{Iter, IterMut}
;
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use iter
::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut}
;
47 #[stable(feature = "slice_rsplit", since = "1.27.0")]
48 pub use iter
::{RSplit, RSplitMut}
;
50 #[stable(feature = "chunks_exact", since = "1.31.0")]
51 pub use iter
::{ChunksExact, ChunksExactMut}
;
53 #[stable(feature = "rchunks", since = "1.31.0")]
54 pub use iter
::{RChunks, RChunksExact, RChunksExactMut, RChunksMut}
;
56 #[unstable(feature = "array_chunks", issue = "74985")]
57 pub use iter
::{ArrayChunks, ArrayChunksMut}
;
59 #[unstable(feature = "array_windows", issue = "75027")]
60 pub use iter
::ArrayWindows
;
62 #[unstable(feature = "slice_group_by", issue = "80552")]
63 pub use iter
::{GroupBy, GroupByMut}
;
65 #[stable(feature = "split_inclusive", since = "1.51.0")]
66 pub use iter
::{SplitInclusive, SplitInclusiveMut}
;
68 #[stable(feature = "rust1", since = "1.0.0")]
69 pub use raw
::{from_raw_parts, from_raw_parts_mut}
;
71 #[stable(feature = "from_ref", since = "1.28.0")]
72 pub use raw
::{from_mut, from_ref}
;
74 // This function is public only because there is no other way to unit test heapsort.
75 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
76 pub use sort
::heapsort
;
78 #[stable(feature = "slice_get_slice", since = "1.28.0")]
79 pub use index
::SliceIndex
;
81 #[unstable(feature = "slice_range", issue = "76393")]
84 #[unstable(feature = "inherent_ascii_escape", issue = "77174")]
85 pub use ascii
::EscapeAscii
;
90 /// Returns the number of elements in the slice.
95 /// let a = [1, 2, 3];
96 /// assert_eq!(a.len(), 3);
98 #[cfg_attr(not(bootstrap), lang = "slice_len_fn")]
99 #[stable(feature = "rust1", since = "1.0.0")]
100 #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
102 // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
103 #[rustc_allow_const_fn_unstable(const_fn_union)]
104 pub const fn len(&self) -> usize {
105 // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
106 // As of this writing this causes a "Const-stable functions can only call other
107 // const-stable functions" error.
109 // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
110 // and PtrComponents<T> have the same memory layouts. Only std can make this
112 unsafe { crate::ptr::PtrRepr { const_ptr: self }
.components
.metadata
}
115 /// Returns `true` if the slice has a length of 0.
120 /// let a = [1, 2, 3];
121 /// assert!(!a.is_empty());
123 #[stable(feature = "rust1", since = "1.0.0")]
124 #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
126 pub const fn is_empty(&self) -> bool
{
130 /// Returns the first element of the slice, or `None` if it is empty.
135 /// let v = [10, 40, 30];
136 /// assert_eq!(Some(&10), v.first());
138 /// let w: &[i32] = &[];
139 /// assert_eq!(None, w.first());
141 #[stable(feature = "rust1", since = "1.0.0")]
142 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
144 pub const fn first(&self) -> Option
<&T
> {
145 if let [first
, ..] = self { Some(first) }
else { None }
148 /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
153 /// let x = &mut [0, 1, 2];
155 /// if let Some(first) = x.first_mut() {
158 /// assert_eq!(x, &[5, 1, 2]);
160 #[stable(feature = "rust1", since = "1.0.0")]
161 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
163 pub const fn first_mut(&mut self) -> Option
<&mut T
> {
164 if let [first
, ..] = self { Some(first) }
else { None }
167 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
172 /// let x = &[0, 1, 2];
174 /// if let Some((first, elements)) = x.split_first() {
175 /// assert_eq!(first, &0);
176 /// assert_eq!(elements, &[1, 2]);
179 #[stable(feature = "slice_splits", since = "1.5.0")]
180 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
182 pub const fn split_first(&self) -> Option
<(&T
, &[T
])> {
183 if let [first
, tail @
..] = self { Some((first, tail)) }
else { None }
186 /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
191 /// let x = &mut [0, 1, 2];
193 /// if let Some((first, elements)) = x.split_first_mut() {
198 /// assert_eq!(x, &[3, 4, 5]);
200 #[stable(feature = "slice_splits", since = "1.5.0")]
201 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
203 pub const fn split_first_mut(&mut self) -> Option
<(&mut T
, &mut [T
])> {
204 if let [first
, tail @
..] = self { Some((first, tail)) }
else { None }
207 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
212 /// let x = &[0, 1, 2];
214 /// if let Some((last, elements)) = x.split_last() {
215 /// assert_eq!(last, &2);
216 /// assert_eq!(elements, &[0, 1]);
219 #[stable(feature = "slice_splits", since = "1.5.0")]
220 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
222 pub const fn split_last(&self) -> Option
<(&T
, &[T
])> {
223 if let [init @
.., last
] = self { Some((last, init)) }
else { None }
226 /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
231 /// let x = &mut [0, 1, 2];
233 /// if let Some((last, elements)) = x.split_last_mut() {
238 /// assert_eq!(x, &[4, 5, 3]);
240 #[stable(feature = "slice_splits", since = "1.5.0")]
241 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
243 pub const fn split_last_mut(&mut self) -> Option
<(&mut T
, &mut [T
])> {
244 if let [init @
.., last
] = self { Some((last, init)) }
else { None }
247 /// Returns the last element of the slice, or `None` if it is empty.
252 /// let v = [10, 40, 30];
253 /// assert_eq!(Some(&30), v.last());
255 /// let w: &[i32] = &[];
256 /// assert_eq!(None, w.last());
258 #[stable(feature = "rust1", since = "1.0.0")]
259 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
261 pub const fn last(&self) -> Option
<&T
> {
262 if let [.., last
] = self { Some(last) }
else { None }
265 /// Returns a mutable pointer to the last item in the slice.
270 /// let x = &mut [0, 1, 2];
272 /// if let Some(last) = x.last_mut() {
275 /// assert_eq!(x, &[0, 1, 10]);
277 #[stable(feature = "rust1", since = "1.0.0")]
278 #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
280 pub const fn last_mut(&mut self) -> Option
<&mut T
> {
281 if let [.., last
] = self { Some(last) }
else { None }
284 /// Returns a reference to an element or subslice depending on the type of
287 /// - If given a position, returns a reference to the element at that
288 /// position or `None` if out of bounds.
289 /// - If given a range, returns the subslice corresponding to that range,
290 /// or `None` if out of bounds.
295 /// let v = [10, 40, 30];
296 /// assert_eq!(Some(&40), v.get(1));
297 /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
298 /// assert_eq!(None, v.get(3));
299 /// assert_eq!(None, v.get(0..4));
301 #[stable(feature = "rust1", since = "1.0.0")]
303 pub fn get
<I
>(&self, index
: I
) -> Option
<&I
::Output
>
310 /// Returns a mutable reference to an element or subslice depending on the
311 /// type of index (see [`get`]) or `None` if the index is out of bounds.
313 /// [`get`]: slice::get
318 /// let x = &mut [0, 1, 2];
320 /// if let Some(elem) = x.get_mut(1) {
323 /// assert_eq!(x, &[0, 42, 2]);
325 #[stable(feature = "rust1", since = "1.0.0")]
327 pub fn get_mut
<I
>(&mut self, index
: I
) -> Option
<&mut I
::Output
>
334 /// Returns a reference to an element or subslice, without doing bounds
337 /// For a safe alternative see [`get`].
341 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
342 /// even if the resulting reference is not used.
344 /// [`get`]: slice::get
345 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
350 /// let x = &[1, 2, 4];
353 /// assert_eq!(x.get_unchecked(1), &2);
356 #[stable(feature = "rust1", since = "1.0.0")]
358 pub unsafe fn get_unchecked
<I
>(&self, index
: I
) -> &I
::Output
362 // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
363 // the slice is dereferencable because `self` is a safe reference.
364 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
365 unsafe { &*index.get_unchecked(self) }
368 /// Returns a mutable reference to an element or subslice, without doing
371 /// For a safe alternative see [`get_mut`].
375 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
376 /// even if the resulting reference is not used.
378 /// [`get_mut`]: slice::get_mut
379 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
384 /// let x = &mut [1, 2, 4];
387 /// let elem = x.get_unchecked_mut(1);
390 /// assert_eq!(x, &[1, 13, 4]);
392 #[stable(feature = "rust1", since = "1.0.0")]
394 pub unsafe fn get_unchecked_mut
<I
>(&mut self, index
: I
) -> &mut I
::Output
398 // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
399 // the slice is dereferencable because `self` is a safe reference.
400 // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
401 unsafe { &mut *index.get_unchecked_mut(self) }
404 /// Returns a raw pointer to the slice's buffer.
406 /// The caller must ensure that the slice outlives the pointer this
407 /// function returns, or else it will end up pointing to garbage.
409 /// The caller must also ensure that the memory the pointer (non-transitively) points to
410 /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
411 /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
413 /// Modifying the container referenced by this slice may cause its buffer
414 /// to be reallocated, which would also make any pointers to it invalid.
419 /// let x = &[1, 2, 4];
420 /// let x_ptr = x.as_ptr();
423 /// for i in 0..x.len() {
424 /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
429 /// [`as_mut_ptr`]: slice::as_mut_ptr
430 #[stable(feature = "rust1", since = "1.0.0")]
431 #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
433 pub const fn as_ptr(&self) -> *const T
{
434 self as *const [T
] as *const T
437 /// Returns an unsafe mutable pointer to the slice's buffer.
439 /// The caller must ensure that the slice outlives the pointer this
440 /// function returns, or else it will end up pointing to garbage.
442 /// Modifying the container referenced by this slice may cause its buffer
443 /// to be reallocated, which would also make any pointers to it invalid.
448 /// let x = &mut [1, 2, 4];
449 /// let x_ptr = x.as_mut_ptr();
452 /// for i in 0..x.len() {
453 /// *x_ptr.add(i) += 2;
456 /// assert_eq!(x, &[3, 4, 6]);
458 #[stable(feature = "rust1", since = "1.0.0")]
459 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
461 pub const fn as_mut_ptr(&mut self) -> *mut T
{
462 self as *mut [T
] as *mut T
465 /// Returns the two raw pointers spanning the slice.
467 /// The returned range is half-open, which means that the end pointer
468 /// points *one past* the last element of the slice. This way, an empty
469 /// slice is represented by two equal pointers, and the difference between
470 /// the two pointers represents the size of the slice.
472 /// See [`as_ptr`] for warnings on using these pointers. The end pointer
473 /// requires extra caution, as it does not point to a valid element in the
476 /// This function is useful for interacting with foreign interfaces which
477 /// use two pointers to refer to a range of elements in memory, as is
480 /// It can also be useful to check if a pointer to an element refers to an
481 /// element of this slice:
484 /// let a = [1, 2, 3];
485 /// let x = &a[1] as *const _;
486 /// let y = &5 as *const _;
488 /// assert!(a.as_ptr_range().contains(&x));
489 /// assert!(!a.as_ptr_range().contains(&y));
492 /// [`as_ptr`]: slice::as_ptr
493 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
494 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
496 pub const fn as_ptr_range(&self) -> Range
<*const T
> {
497 let start
= self.as_ptr();
498 // SAFETY: The `add` here is safe, because:
500 // - Both pointers are part of the same object, as pointing directly
501 // past the object also counts.
503 // - The size of the slice is never larger than isize::MAX bytes, as
505 // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
506 // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
507 // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
508 // (This doesn't seem normative yet, but the very same assumption is
509 // made in many places, including the Index implementation of slices.)
511 // - There is no wrapping around involved, as slices do not wrap past
512 // the end of the address space.
514 // See the documentation of pointer::add.
515 let end
= unsafe { start.add(self.len()) }
;
519 /// Returns the two unsafe mutable pointers spanning the slice.
521 /// The returned range is half-open, which means that the end pointer
522 /// points *one past* the last element of the slice. This way, an empty
523 /// slice is represented by two equal pointers, and the difference between
524 /// the two pointers represents the size of the slice.
526 /// See [`as_mut_ptr`] for warnings on using these pointers. The end
527 /// pointer requires extra caution, as it does not point to a valid element
530 /// This function is useful for interacting with foreign interfaces which
531 /// use two pointers to refer to a range of elements in memory, as is
534 /// [`as_mut_ptr`]: slice::as_mut_ptr
535 #[stable(feature = "slice_ptr_range", since = "1.48.0")]
536 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
538 pub const fn as_mut_ptr_range(&mut self) -> Range
<*mut T
> {
539 let start
= self.as_mut_ptr();
540 // SAFETY: See as_ptr_range() above for why `add` here is safe.
541 let end
= unsafe { start.add(self.len()) }
;
545 /// Swaps two elements in the slice.
549 /// * a - The index of the first element
550 /// * b - The index of the second element
554 /// Panics if `a` or `b` are out of bounds.
559 /// let mut v = ["a", "b", "c", "d"];
561 /// assert!(v == ["a", "d", "c", "b"]);
563 #[stable(feature = "rust1", since = "1.0.0")]
565 pub fn swap(&mut self, a
: usize, b
: usize) {
566 // Can't take two mutable loans from one vector, so instead use raw pointers.
567 let pa
= ptr
::addr_of_mut
!(self[a
]);
568 let pb
= ptr
::addr_of_mut
!(self[b
]);
569 // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
570 // to elements in the slice and therefore are guaranteed to be valid and aligned.
571 // Note that accessing the elements behind `a` and `b` is checked and will
572 // panic when out of bounds.
578 /// Reverses the order of elements in the slice, in place.
583 /// let mut v = [1, 2, 3];
585 /// assert!(v == [3, 2, 1]);
587 #[stable(feature = "rust1", since = "1.0.0")]
589 pub fn reverse(&mut self) {
590 let mut i
: usize = 0;
593 // For very small types, all the individual reads in the normal
594 // path perform poorly. We can do better, given efficient unaligned
595 // load/store, by loading a larger chunk and reversing a register.
597 // Ideally LLVM would do this for us, as it knows better than we do
598 // whether unaligned reads are efficient (since that changes between
599 // different ARM versions, for example) and what the best chunk size
600 // would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
601 // the loop, so we need to do this ourselves. (Hypothesis: reverse
602 // is troublesome because the sides can be aligned differently --
603 // will be, when the length is odd -- so there's no way of emitting
604 // pre- and postludes to use fully-aligned SIMD in the middle.)
606 let fast_unaligned
= cfg
!(any(target_arch
= "x86", target_arch
= "x86_64"));
608 if fast_unaligned
&& mem
::size_of
::<T
>() == 1 {
609 // Use the llvm.bswap intrinsic to reverse u8s in a usize
610 let chunk
= mem
::size_of
::<usize>();
611 while i
+ chunk
- 1 < ln
/ 2 {
612 // SAFETY: There are several things to check here:
614 // - Note that `chunk` is either 4 or 8 due to the cfg check
615 // above. So `chunk - 1` is positive.
616 // - Indexing with index `i` is fine as the loop check guarantees
617 // `i + chunk - 1 < ln / 2`
618 // <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
619 // - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
620 // - `i + chunk > 0` is trivially true.
621 // - The loop check guarantees:
622 // `i + chunk - 1 < ln / 2`
623 // <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
624 // - The `read_unaligned` and `write_unaligned` calls are fine:
625 // - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
626 // (see above) and `pb` points to index `ln - i - chunk`, so
627 // both are at least `chunk`
628 // many bytes away from the end of `self`.
629 // - Any initialized memory is valid `usize`.
631 let ptr
= self.as_mut_ptr();
633 let pb
= ptr
.add(ln
- i
- chunk
);
634 let va
= ptr
::read_unaligned(pa
as *mut usize);
635 let vb
= ptr
::read_unaligned(pb
as *mut usize);
636 ptr
::write_unaligned(pa
as *mut usize, vb
.swap_bytes());
637 ptr
::write_unaligned(pb
as *mut usize, va
.swap_bytes());
643 if fast_unaligned
&& mem
::size_of
::<T
>() == 2 {
644 // Use rotate-by-16 to reverse u16s in a u32
645 let chunk
= mem
::size_of
::<u32>() / 2;
646 while i
+ chunk
- 1 < ln
/ 2 {
647 // SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
648 // (and obviously `i < ln`), because each element is 2 bytes and
651 // `i + chunk - 1 < ln / 2` # while condition
652 // `i + 2 - 1 < ln / 2`
655 // Since it's less than the length divided by 2, then it must be
658 // This also means that the condition `0 < i + chunk <= ln` is
659 // always respected, ensuring the `pb` pointer can be used
662 let ptr
= self.as_mut_ptr();
664 let pb
= ptr
.add(ln
- i
- chunk
);
665 let va
= ptr
::read_unaligned(pa
as *mut u32);
666 let vb
= ptr
::read_unaligned(pb
as *mut u32);
667 ptr
::write_unaligned(pa
as *mut u32, vb
.rotate_left(16));
668 ptr
::write_unaligned(pb
as *mut u32, va
.rotate_left(16));
675 // SAFETY: `i` is inferior to half the length of the slice so
676 // accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
677 // will not go further than `ln / 2 - 1`).
678 // The resulting pointers `pa` and `pb` are therefore valid and
679 // aligned, and can be read from and written to.
681 // Unsafe swap to avoid the bounds check in safe swap.
682 let ptr
= self.as_mut_ptr();
684 let pb
= ptr
.add(ln
- i
- 1);
691 /// Returns an iterator over the slice.
696 /// let x = &[1, 2, 4];
697 /// let mut iterator = x.iter();
699 /// assert_eq!(iterator.next(), Some(&1));
700 /// assert_eq!(iterator.next(), Some(&2));
701 /// assert_eq!(iterator.next(), Some(&4));
702 /// assert_eq!(iterator.next(), None);
704 #[stable(feature = "rust1", since = "1.0.0")]
706 pub fn iter(&self) -> Iter
<'_
, T
> {
710 /// Returns an iterator that allows modifying each value.
715 /// let x = &mut [1, 2, 4];
716 /// for elem in x.iter_mut() {
719 /// assert_eq!(x, &[3, 4, 6]);
721 #[stable(feature = "rust1", since = "1.0.0")]
723 pub fn iter_mut(&mut self) -> IterMut
<'_
, T
> {
727 /// Returns an iterator over all contiguous windows of length
728 /// `size`. The windows overlap. If the slice is shorter than
729 /// `size`, the iterator returns no values.
733 /// Panics if `size` is 0.
738 /// let slice = ['r', 'u', 's', 't'];
739 /// let mut iter = slice.windows(2);
740 /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
741 /// assert_eq!(iter.next().unwrap(), &['u', 's']);
742 /// assert_eq!(iter.next().unwrap(), &['s', 't']);
743 /// assert!(iter.next().is_none());
746 /// If the slice is shorter than `size`:
749 /// let slice = ['f', 'o', 'o'];
750 /// let mut iter = slice.windows(4);
751 /// assert!(iter.next().is_none());
753 #[stable(feature = "rust1", since = "1.0.0")]
755 pub fn windows(&self, size
: usize) -> Windows
<'_
, T
> {
756 let size
= NonZeroUsize
::new(size
).expect("size is zero");
757 Windows
::new(self, size
)
760 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
761 /// beginning of the slice.
763 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
764 /// slice, then the last chunk will not have length `chunk_size`.
766 /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
767 /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
772 /// Panics if `chunk_size` is 0.
777 /// let slice = ['l', 'o', 'r', 'e', 'm'];
778 /// let mut iter = slice.chunks(2);
779 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
780 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
781 /// assert_eq!(iter.next().unwrap(), &['m']);
782 /// assert!(iter.next().is_none());
785 /// [`chunks_exact`]: slice::chunks_exact
786 /// [`rchunks`]: slice::rchunks
787 #[stable(feature = "rust1", since = "1.0.0")]
789 pub fn chunks(&self, chunk_size
: usize) -> Chunks
<'_
, T
> {
790 assert_ne
!(chunk_size
, 0);
791 Chunks
::new(self, chunk_size
)
794 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
795 /// beginning of the slice.
797 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
798 /// length of the slice, then the last chunk will not have length `chunk_size`.
800 /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
801 /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
802 /// the end of the slice.
806 /// Panics if `chunk_size` is 0.
811 /// let v = &mut [0, 0, 0, 0, 0];
812 /// let mut count = 1;
814 /// for chunk in v.chunks_mut(2) {
815 /// for elem in chunk.iter_mut() {
820 /// assert_eq!(v, &[1, 1, 2, 2, 3]);
823 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
824 /// [`rchunks_mut`]: slice::rchunks_mut
825 #[stable(feature = "rust1", since = "1.0.0")]
827 pub fn chunks_mut(&mut self, chunk_size
: usize) -> ChunksMut
<'_
, T
> {
828 assert_ne
!(chunk_size
, 0);
829 ChunksMut
::new(self, chunk_size
)
832 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
833 /// beginning of the slice.
835 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
836 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
837 /// from the `remainder` function of the iterator.
839 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
840 /// resulting code better than in the case of [`chunks`].
842 /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
843 /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
847 /// Panics if `chunk_size` is 0.
852 /// let slice = ['l', 'o', 'r', 'e', 'm'];
853 /// let mut iter = slice.chunks_exact(2);
854 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
855 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
856 /// assert!(iter.next().is_none());
857 /// assert_eq!(iter.remainder(), &['m']);
860 /// [`chunks`]: slice::chunks
861 /// [`rchunks_exact`]: slice::rchunks_exact
862 #[stable(feature = "chunks_exact", since = "1.31.0")]
864 pub fn chunks_exact(&self, chunk_size
: usize) -> ChunksExact
<'_
, T
> {
865 assert_ne
!(chunk_size
, 0);
866 ChunksExact
::new(self, chunk_size
)
869 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
870 /// beginning of the slice.
872 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
873 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
874 /// retrieved from the `into_remainder` function of the iterator.
876 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
877 /// resulting code better than in the case of [`chunks_mut`].
879 /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
880 /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
885 /// Panics if `chunk_size` is 0.
890 /// let v = &mut [0, 0, 0, 0, 0];
891 /// let mut count = 1;
893 /// for chunk in v.chunks_exact_mut(2) {
894 /// for elem in chunk.iter_mut() {
899 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
902 /// [`chunks_mut`]: slice::chunks_mut
903 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
904 #[stable(feature = "chunks_exact", since = "1.31.0")]
906 pub fn chunks_exact_mut(&mut self, chunk_size
: usize) -> ChunksExactMut
<'_
, T
> {
907 assert_ne
!(chunk_size
, 0);
908 ChunksExactMut
::new(self, chunk_size
)
911 /// Splits the slice into a slice of `N`-element arrays,
912 /// assuming that there's no remainder.
916 /// This may only be called when
917 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
923 /// #![feature(slice_as_chunks)]
924 /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
925 /// let chunks: &[[char; 1]] =
926 /// // SAFETY: 1-element chunks never have remainder
927 /// unsafe { slice.as_chunks_unchecked() };
928 /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
929 /// let chunks: &[[char; 3]] =
930 /// // SAFETY: The slice length (6) is a multiple of 3
931 /// unsafe { slice.as_chunks_unchecked() };
932 /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
934 /// // These would be unsound:
935 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
936 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
938 #[unstable(feature = "slice_as_chunks", issue = "74985")]
940 pub unsafe fn as_chunks_unchecked
<const N
: usize>(&self) -> &[[T
; N
]] {
941 debug_assert_ne
!(N
, 0);
942 debug_assert_eq
!(self.len() % N
, 0);
944 // SAFETY: Our precondition is exactly what's needed to call this
945 unsafe { crate::intrinsics::exact_div(self.len(), N) }
;
946 // SAFETY: We cast a slice of `new_len * N` elements into
947 // a slice of `new_len` many `N` elements chunks.
948 unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
951 /// Splits the slice into a slice of `N`-element arrays,
952 /// starting at the beginning of the slice,
953 /// and a remainder slice with length strictly less than `N`.
957 /// Panics if `N` is 0. This check will most probably get changed to a compile time
958 /// error before this method gets stabilized.
963 /// #![feature(slice_as_chunks)]
964 /// let slice = ['l', 'o', 'r', 'e', 'm'];
965 /// let (chunks, remainder) = slice.as_chunks();
966 /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
967 /// assert_eq!(remainder, &['m']);
969 #[unstable(feature = "slice_as_chunks", issue = "74985")]
971 pub fn as_chunks
<const N
: usize>(&self) -> (&[[T
; N
]], &[T
]) {
973 let len
= self.len() / N
;
974 let (multiple_of_n
, remainder
) = self.split_at(len
* N
);
975 // SAFETY: We already panicked for zero, and ensured by construction
976 // that the length of the subslice is a multiple of N.
977 let array_slice
= unsafe { multiple_of_n.as_chunks_unchecked() }
;
978 (array_slice
, remainder
)
981 /// Splits the slice into a slice of `N`-element arrays,
982 /// starting at the end of the slice,
983 /// and a remainder slice with length strictly less than `N`.
987 /// Panics if `N` is 0. This check will most probably get changed to a compile time
988 /// error before this method gets stabilized.
993 /// #![feature(slice_as_chunks)]
994 /// let slice = ['l', 'o', 'r', 'e', 'm'];
995 /// let (remainder, chunks) = slice.as_rchunks();
996 /// assert_eq!(remainder, &['l']);
997 /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
999 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1001 pub fn as_rchunks
<const N
: usize>(&self) -> (&[T
], &[[T
; N
]]) {
1003 let len
= self.len() / N
;
1004 let (remainder
, multiple_of_n
) = self.split_at(self.len() - len
* N
);
1005 // SAFETY: We already panicked for zero, and ensured by construction
1006 // that the length of the subslice is a multiple of N.
1007 let array_slice
= unsafe { multiple_of_n.as_chunks_unchecked() }
;
1008 (remainder
, array_slice
)
1011 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1012 /// beginning of the slice.
1014 /// The chunks are array references and do not overlap. If `N` does not divide the
1015 /// length of the slice, then the last up to `N-1` elements will be omitted and can be
1016 /// retrieved from the `remainder` function of the iterator.
1018 /// This method is the const generic equivalent of [`chunks_exact`].
1022 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1023 /// error before this method gets stabilized.
1028 /// #![feature(array_chunks)]
1029 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1030 /// let mut iter = slice.array_chunks();
1031 /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
1032 /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
1033 /// assert!(iter.next().is_none());
1034 /// assert_eq!(iter.remainder(), &['m']);
1037 /// [`chunks_exact`]: slice::chunks_exact
1038 #[unstable(feature = "array_chunks", issue = "74985")]
1040 pub fn array_chunks
<const N
: usize>(&self) -> ArrayChunks
<'_
, T
, N
> {
1042 ArrayChunks
::new(self)
1045 /// Splits the slice into a slice of `N`-element arrays,
1046 /// assuming that there's no remainder.
1050 /// This may only be called when
1051 /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
1057 /// #![feature(slice_as_chunks)]
1058 /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
1059 /// let chunks: &mut [[char; 1]] =
1060 /// // SAFETY: 1-element chunks never have remainder
1061 /// unsafe { slice.as_chunks_unchecked_mut() };
1062 /// chunks[0] = ['L'];
1063 /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
1064 /// let chunks: &mut [[char; 3]] =
1065 /// // SAFETY: The slice length (6) is a multiple of 3
1066 /// unsafe { slice.as_chunks_unchecked_mut() };
1067 /// chunks[1] = ['a', 'x', '?'];
1068 /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
1070 /// // These would be unsound:
1071 /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
1072 /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
1074 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1076 pub unsafe fn as_chunks_unchecked_mut
<const N
: usize>(&mut self) -> &mut [[T
; N
]] {
1077 debug_assert_ne
!(N
, 0);
1078 debug_assert_eq
!(self.len() % N
, 0);
1080 // SAFETY: Our precondition is exactly what's needed to call this
1081 unsafe { crate::intrinsics::exact_div(self.len(), N) }
;
1082 // SAFETY: We cast a slice of `new_len * N` elements into
1083 // a slice of `new_len` many `N` elements chunks.
1084 unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
1087 /// Splits the slice into a slice of `N`-element arrays,
1088 /// starting at the beginning of the slice,
1089 /// and a remainder slice with length strictly less than `N`.
1093 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1094 /// error before this method gets stabilized.
1099 /// #![feature(slice_as_chunks)]
1100 /// let v = &mut [0, 0, 0, 0, 0];
1101 /// let mut count = 1;
1103 /// let (chunks, remainder) = v.as_chunks_mut();
1104 /// remainder[0] = 9;
1105 /// for chunk in chunks {
1106 /// *chunk = [count; 2];
1109 /// assert_eq!(v, &[1, 1, 2, 2, 9]);
1111 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1113 pub fn as_chunks_mut
<const N
: usize>(&mut self) -> (&mut [[T
; N
]], &mut [T
]) {
1115 let len
= self.len() / N
;
1116 let (multiple_of_n
, remainder
) = self.split_at_mut(len
* N
);
1117 // SAFETY: We already panicked for zero, and ensured by construction
1118 // that the length of the subslice is a multiple of N.
1119 let array_slice
= unsafe { multiple_of_n.as_chunks_unchecked_mut() }
;
1120 (array_slice
, remainder
)
1123 /// Splits the slice into a slice of `N`-element arrays,
1124 /// starting at the end of the slice,
1125 /// and a remainder slice with length strictly less than `N`.
1129 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1130 /// error before this method gets stabilized.
1135 /// #![feature(slice_as_chunks)]
1136 /// let v = &mut [0, 0, 0, 0, 0];
1137 /// let mut count = 1;
1139 /// let (remainder, chunks) = v.as_rchunks_mut();
1140 /// remainder[0] = 9;
1141 /// for chunk in chunks {
1142 /// *chunk = [count; 2];
1145 /// assert_eq!(v, &[9, 1, 1, 2, 2]);
1147 #[unstable(feature = "slice_as_chunks", issue = "74985")]
1149 pub fn as_rchunks_mut
<const N
: usize>(&mut self) -> (&mut [T
], &mut [[T
; N
]]) {
1151 let len
= self.len() / N
;
1152 let (remainder
, multiple_of_n
) = self.split_at_mut(self.len() - len
* N
);
1153 // SAFETY: We already panicked for zero, and ensured by construction
1154 // that the length of the subslice is a multiple of N.
1155 let array_slice
= unsafe { multiple_of_n.as_chunks_unchecked_mut() }
;
1156 (remainder
, array_slice
)
1159 /// Returns an iterator over `N` elements of the slice at a time, starting at the
1160 /// beginning of the slice.
1162 /// The chunks are mutable array references and do not overlap. If `N` does not divide
1163 /// the length of the slice, then the last up to `N-1` elements will be omitted and
1164 /// can be retrieved from the `into_remainder` function of the iterator.
1166 /// This method is the const generic equivalent of [`chunks_exact_mut`].
1170 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1171 /// error before this method gets stabilized.
1176 /// #![feature(array_chunks)]
1177 /// let v = &mut [0, 0, 0, 0, 0];
1178 /// let mut count = 1;
1180 /// for chunk in v.array_chunks_mut() {
1181 /// *chunk = [count; 2];
1184 /// assert_eq!(v, &[1, 1, 2, 2, 0]);
1187 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1188 #[unstable(feature = "array_chunks", issue = "74985")]
1190 pub fn array_chunks_mut
<const N
: usize>(&mut self) -> ArrayChunksMut
<'_
, T
, N
> {
1192 ArrayChunksMut
::new(self)
1195 /// Returns an iterator over overlapping windows of `N` elements of a slice,
1196 /// starting at the beginning of the slice.
1198 /// This is the const generic equivalent of [`windows`].
1200 /// If `N` is greater than the size of the slice, it will return no windows.
1204 /// Panics if `N` is 0. This check will most probably get changed to a compile time
1205 /// error before this method gets stabilized.
1210 /// #![feature(array_windows)]
1211 /// let slice = [0, 1, 2, 3];
1212 /// let mut iter = slice.array_windows();
1213 /// assert_eq!(iter.next().unwrap(), &[0, 1]);
1214 /// assert_eq!(iter.next().unwrap(), &[1, 2]);
1215 /// assert_eq!(iter.next().unwrap(), &[2, 3]);
1216 /// assert!(iter.next().is_none());
1219 /// [`windows`]: slice::windows
1220 #[unstable(feature = "array_windows", issue = "75027")]
1222 pub fn array_windows
<const N
: usize>(&self) -> ArrayWindows
<'_
, T
, N
> {
1224 ArrayWindows
::new(self)
1227 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1230 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1231 /// slice, then the last chunk will not have length `chunk_size`.
1233 /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
1234 /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
1239 /// Panics if `chunk_size` is 0.
1244 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1245 /// let mut iter = slice.rchunks(2);
1246 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1247 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1248 /// assert_eq!(iter.next().unwrap(), &['l']);
1249 /// assert!(iter.next().is_none());
1252 /// [`rchunks_exact`]: slice::rchunks_exact
1253 /// [`chunks`]: slice::chunks
1254 #[stable(feature = "rchunks", since = "1.31.0")]
1256 pub fn rchunks(&self, chunk_size
: usize) -> RChunks
<'_
, T
> {
1257 assert
!(chunk_size
!= 0);
1258 RChunks
::new(self, chunk_size
)
1261 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1264 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1265 /// length of the slice, then the last chunk will not have length `chunk_size`.
1267 /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
1268 /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
1269 /// beginning of the slice.
1273 /// Panics if `chunk_size` is 0.
1278 /// let v = &mut [0, 0, 0, 0, 0];
1279 /// let mut count = 1;
1281 /// for chunk in v.rchunks_mut(2) {
1282 /// for elem in chunk.iter_mut() {
1287 /// assert_eq!(v, &[3, 2, 2, 1, 1]);
1290 /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
1291 /// [`chunks_mut`]: slice::chunks_mut
1292 #[stable(feature = "rchunks", since = "1.31.0")]
1294 pub fn rchunks_mut(&mut self, chunk_size
: usize) -> RChunksMut
<'_
, T
> {
1295 assert
!(chunk_size
!= 0);
1296 RChunksMut
::new(self, chunk_size
)
1299 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
1300 /// end of the slice.
1302 /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
1303 /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
1304 /// from the `remainder` function of the iterator.
1306 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1307 /// resulting code better than in the case of [`chunks`].
1309 /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
1310 /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
1315 /// Panics if `chunk_size` is 0.
1320 /// let slice = ['l', 'o', 'r', 'e', 'm'];
1321 /// let mut iter = slice.rchunks_exact(2);
1322 /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
1323 /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
1324 /// assert!(iter.next().is_none());
1325 /// assert_eq!(iter.remainder(), &['l']);
1328 /// [`chunks`]: slice::chunks
1329 /// [`rchunks`]: slice::rchunks
1330 /// [`chunks_exact`]: slice::chunks_exact
1331 #[stable(feature = "rchunks", since = "1.31.0")]
1333 pub fn rchunks_exact(&self, chunk_size
: usize) -> RChunksExact
<'_
, T
> {
1334 assert
!(chunk_size
!= 0);
1335 RChunksExact
::new(self, chunk_size
)
1338 /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
1341 /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
1342 /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
1343 /// retrieved from the `into_remainder` function of the iterator.
1345 /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
1346 /// resulting code better than in the case of [`chunks_mut`].
1348 /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
1349 /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
1354 /// Panics if `chunk_size` is 0.
1359 /// let v = &mut [0, 0, 0, 0, 0];
1360 /// let mut count = 1;
1362 /// for chunk in v.rchunks_exact_mut(2) {
1363 /// for elem in chunk.iter_mut() {
1368 /// assert_eq!(v, &[0, 2, 2, 1, 1]);
1371 /// [`chunks_mut`]: slice::chunks_mut
1372 /// [`rchunks_mut`]: slice::rchunks_mut
1373 /// [`chunks_exact_mut`]: slice::chunks_exact_mut
1374 #[stable(feature = "rchunks", since = "1.31.0")]
1376 pub fn rchunks_exact_mut(&mut self, chunk_size
: usize) -> RChunksExactMut
<'_
, T
> {
1377 assert
!(chunk_size
!= 0);
1378 RChunksExactMut
::new(self, chunk_size
)
1381 /// Returns an iterator over the slice producing non-overlapping runs
1382 /// of elements using the predicate to separate them.
1384 /// The predicate is called on two elements following themselves,
1385 /// it means the predicate is called on `slice[0]` and `slice[1]`
1386 /// then on `slice[1]` and `slice[2]` and so on.
1391 /// #![feature(slice_group_by)]
1393 /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
1395 /// let mut iter = slice.group_by(|a, b| a == b);
1397 /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
1398 /// assert_eq!(iter.next(), Some(&[3, 3][..]));
1399 /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
1400 /// assert_eq!(iter.next(), None);
1403 /// This method can be used to extract the sorted subslices:
1406 /// #![feature(slice_group_by)]
1408 /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
1410 /// let mut iter = slice.group_by(|a, b| a <= b);
1412 /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
1413 /// assert_eq!(iter.next(), Some(&[2, 3][..]));
1414 /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
1415 /// assert_eq!(iter.next(), None);
1417 #[unstable(feature = "slice_group_by", issue = "80552")]
1419 pub fn group_by
<F
>(&self, pred
: F
) -> GroupBy
<'_
, T
, F
>
1421 F
: FnMut(&T
, &T
) -> bool
,
1423 GroupBy
::new(self, pred
)
1426 /// Returns an iterator over the slice producing non-overlapping mutable
1427 /// runs of elements using the predicate to separate them.
1429 /// The predicate is called on two elements following themselves,
1430 /// it means the predicate is called on `slice[0]` and `slice[1]`
1431 /// then on `slice[1]` and `slice[2]` and so on.
1436 /// #![feature(slice_group_by)]
1438 /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
1440 /// let mut iter = slice.group_by_mut(|a, b| a == b);
1442 /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
1443 /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
1444 /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
1445 /// assert_eq!(iter.next(), None);
1448 /// This method can be used to extract the sorted subslices:
1451 /// #![feature(slice_group_by)]
1453 /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
1455 /// let mut iter = slice.group_by_mut(|a, b| a <= b);
1457 /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
1458 /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
1459 /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
1460 /// assert_eq!(iter.next(), None);
1462 #[unstable(feature = "slice_group_by", issue = "80552")]
1464 pub fn group_by_mut
<F
>(&mut self, pred
: F
) -> GroupByMut
<'_
, T
, F
>
1466 F
: FnMut(&T
, &T
) -> bool
,
1468 GroupByMut
::new(self, pred
)
1471 /// Divides one slice into two at an index.
1473 /// The first will contain all indices from `[0, mid)` (excluding
1474 /// the index `mid` itself) and the second will contain all
1475 /// indices from `[mid, len)` (excluding the index `len` itself).
1479 /// Panics if `mid > len`.
1484 /// let v = [1, 2, 3, 4, 5, 6];
1487 /// let (left, right) = v.split_at(0);
1488 /// assert_eq!(left, []);
1489 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1493 /// let (left, right) = v.split_at(2);
1494 /// assert_eq!(left, [1, 2]);
1495 /// assert_eq!(right, [3, 4, 5, 6]);
1499 /// let (left, right) = v.split_at(6);
1500 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1501 /// assert_eq!(right, []);
1504 #[stable(feature = "rust1", since = "1.0.0")]
1506 pub fn split_at(&self, mid
: usize) -> (&[T
], &[T
]) {
1507 assert
!(mid
<= self.len());
1508 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1509 // fulfills the requirements of `from_raw_parts_mut`.
1510 unsafe { self.split_at_unchecked(mid) }
1513 /// Divides one mutable slice into two at an index.
1515 /// The first will contain all indices from `[0, mid)` (excluding
1516 /// the index `mid` itself) and the second will contain all
1517 /// indices from `[mid, len)` (excluding the index `len` itself).
1521 /// Panics if `mid > len`.
1526 /// let mut v = [1, 0, 3, 0, 5, 6];
1527 /// let (left, right) = v.split_at_mut(2);
1528 /// assert_eq!(left, [1, 0]);
1529 /// assert_eq!(right, [3, 0, 5, 6]);
1532 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1534 #[stable(feature = "rust1", since = "1.0.0")]
1536 pub fn split_at_mut(&mut self, mid
: usize) -> (&mut [T
], &mut [T
]) {
1537 assert
!(mid
<= self.len());
1538 // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
1539 // fulfills the requirements of `from_raw_parts_mut`.
1540 unsafe { self.split_at_mut_unchecked(mid) }
1543 /// Divides one slice into two at an index, without doing bounds checking.
1545 /// The first will contain all indices from `[0, mid)` (excluding
1546 /// the index `mid` itself) and the second will contain all
1547 /// indices from `[mid, len)` (excluding the index `len` itself).
1549 /// For a safe alternative see [`split_at`].
1553 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1554 /// even if the resulting reference is not used. The caller has to ensure that
1555 /// `0 <= mid <= self.len()`.
1557 /// [`split_at`]: slice::split_at
1558 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1563 /// #![feature(slice_split_at_unchecked)]
1565 /// let v = [1, 2, 3, 4, 5, 6];
1568 /// let (left, right) = v.split_at_unchecked(0);
1569 /// assert_eq!(left, []);
1570 /// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
1574 /// let (left, right) = v.split_at_unchecked(2);
1575 /// assert_eq!(left, [1, 2]);
1576 /// assert_eq!(right, [3, 4, 5, 6]);
1580 /// let (left, right) = v.split_at_unchecked(6);
1581 /// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
1582 /// assert_eq!(right, []);
1585 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1587 unsafe fn split_at_unchecked(&self, mid
: usize) -> (&[T
], &[T
]) {
1588 // SAFETY: Caller has to check that `0 <= mid <= self.len()`
1589 unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
1592 /// Divides one mutable slice into two at an index, without doing bounds checking.
1594 /// The first will contain all indices from `[0, mid)` (excluding
1595 /// the index `mid` itself) and the second will contain all
1596 /// indices from `[mid, len)` (excluding the index `len` itself).
1598 /// For a safe alternative see [`split_at_mut`].
1602 /// Calling this method with an out-of-bounds index is *[undefined behavior]*
1603 /// even if the resulting reference is not used. The caller has to ensure that
1604 /// `0 <= mid <= self.len()`.
1606 /// [`split_at_mut`]: slice::split_at_mut
1607 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1612 /// #![feature(slice_split_at_unchecked)]
1614 /// let mut v = [1, 0, 3, 0, 5, 6];
1615 /// // scoped to restrict the lifetime of the borrows
1617 /// let (left, right) = v.split_at_mut_unchecked(2);
1618 /// assert_eq!(left, [1, 0]);
1619 /// assert_eq!(right, [3, 0, 5, 6]);
1623 /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1625 #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
1627 unsafe fn split_at_mut_unchecked(&mut self, mid
: usize) -> (&mut [T
], &mut [T
]) {
1628 let len
= self.len();
1629 let ptr
= self.as_mut_ptr();
1631 // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
1633 // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
1635 unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
1638 /// Returns an iterator over subslices separated by elements that match
1639 /// `pred`. The matched element is not contained in the subslices.
1644 /// let slice = [10, 40, 33, 20];
1645 /// let mut iter = slice.split(|num| num % 3 == 0);
1647 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1648 /// assert_eq!(iter.next().unwrap(), &[20]);
1649 /// assert!(iter.next().is_none());
1652 /// If the first element is matched, an empty slice will be the first item
1653 /// returned by the iterator. Similarly, if the last element in the slice
1654 /// is matched, an empty slice will be the last item returned by the
1658 /// let slice = [10, 40, 33];
1659 /// let mut iter = slice.split(|num| num % 3 == 0);
1661 /// assert_eq!(iter.next().unwrap(), &[10, 40]);
1662 /// assert_eq!(iter.next().unwrap(), &[]);
1663 /// assert!(iter.next().is_none());
1666 /// If two matched elements are directly adjacent, an empty slice will be
1667 /// present between them:
1670 /// let slice = [10, 6, 33, 20];
1671 /// let mut iter = slice.split(|num| num % 3 == 0);
1673 /// assert_eq!(iter.next().unwrap(), &[10]);
1674 /// assert_eq!(iter.next().unwrap(), &[]);
1675 /// assert_eq!(iter.next().unwrap(), &[20]);
1676 /// assert!(iter.next().is_none());
1678 #[stable(feature = "rust1", since = "1.0.0")]
1680 pub fn split
<F
>(&self, pred
: F
) -> Split
<'_
, T
, F
>
1682 F
: FnMut(&T
) -> bool
,
1684 Split
::new(self, pred
)
1687 /// Returns an iterator over mutable subslices separated by elements that
1688 /// match `pred`. The matched element is not contained in the subslices.
1693 /// let mut v = [10, 40, 30, 20, 60, 50];
1695 /// for group in v.split_mut(|num| *num % 3 == 0) {
1698 /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
1700 #[stable(feature = "rust1", since = "1.0.0")]
1702 pub fn split_mut
<F
>(&mut self, pred
: F
) -> SplitMut
<'_
, T
, F
>
1704 F
: FnMut(&T
) -> bool
,
1706 SplitMut
::new(self, pred
)
1709 /// Returns an iterator over subslices separated by elements that match
1710 /// `pred`. The matched element is contained in the end of the previous
1711 /// subslice as a terminator.
1716 /// let slice = [10, 40, 33, 20];
1717 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1719 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1720 /// assert_eq!(iter.next().unwrap(), &[20]);
1721 /// assert!(iter.next().is_none());
1724 /// If the last element of the slice is matched,
1725 /// that element will be considered the terminator of the preceding slice.
1726 /// That slice will be the last item returned by the iterator.
1729 /// let slice = [3, 10, 40, 33];
1730 /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
1732 /// assert_eq!(iter.next().unwrap(), &[3]);
1733 /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
1734 /// assert!(iter.next().is_none());
1736 #[stable(feature = "split_inclusive", since = "1.51.0")]
1738 pub fn split_inclusive
<F
>(&self, pred
: F
) -> SplitInclusive
<'_
, T
, F
>
1740 F
: FnMut(&T
) -> bool
,
1742 SplitInclusive
::new(self, pred
)
1745 /// Returns an iterator over mutable subslices separated by elements that
1746 /// match `pred`. The matched element is contained in the previous
1747 /// subslice as a terminator.
1752 /// let mut v = [10, 40, 30, 20, 60, 50];
1754 /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
1755 /// let terminator_idx = group.len()-1;
1756 /// group[terminator_idx] = 1;
1758 /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
1760 #[stable(feature = "split_inclusive", since = "1.51.0")]
1762 pub fn split_inclusive_mut
<F
>(&mut self, pred
: F
) -> SplitInclusiveMut
<'_
, T
, F
>
1764 F
: FnMut(&T
) -> bool
,
1766 SplitInclusiveMut
::new(self, pred
)
1769 /// Returns an iterator over subslices separated by elements that match
1770 /// `pred`, starting at the end of the slice and working backwards.
1771 /// The matched element is not contained in the subslices.
1776 /// let slice = [11, 22, 33, 0, 44, 55];
1777 /// let mut iter = slice.rsplit(|num| *num == 0);
1779 /// assert_eq!(iter.next().unwrap(), &[44, 55]);
1780 /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
1781 /// assert_eq!(iter.next(), None);
1784 /// As with `split()`, if the first or last element is matched, an empty
1785 /// slice will be the first (or last) item returned by the iterator.
1788 /// let v = &[0, 1, 1, 2, 3, 5, 8];
1789 /// let mut it = v.rsplit(|n| *n % 2 == 0);
1790 /// assert_eq!(it.next().unwrap(), &[]);
1791 /// assert_eq!(it.next().unwrap(), &[3, 5]);
1792 /// assert_eq!(it.next().unwrap(), &[1, 1]);
1793 /// assert_eq!(it.next().unwrap(), &[]);
1794 /// assert_eq!(it.next(), None);
1796 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1798 pub fn rsplit
<F
>(&self, pred
: F
) -> RSplit
<'_
, T
, F
>
1800 F
: FnMut(&T
) -> bool
,
1802 RSplit
::new(self, pred
)
1805 /// Returns an iterator over mutable subslices separated by elements that
1806 /// match `pred`, starting at the end of the slice and working
1807 /// backwards. The matched element is not contained in the subslices.
1812 /// let mut v = [100, 400, 300, 200, 600, 500];
1814 /// let mut count = 0;
1815 /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
1817 /// group[0] = count;
1819 /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
1822 #[stable(feature = "slice_rsplit", since = "1.27.0")]
1824 pub fn rsplit_mut
<F
>(&mut self, pred
: F
) -> RSplitMut
<'_
, T
, F
>
1826 F
: FnMut(&T
) -> bool
,
1828 RSplitMut
::new(self, pred
)
1831 /// Returns an iterator over subslices separated by elements that match
1832 /// `pred`, limited to returning at most `n` items. The matched element is
1833 /// not contained in the subslices.
1835 /// The last element returned, if any, will contain the remainder of the
1840 /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
1841 /// `[20, 60, 50]`):
1844 /// let v = [10, 40, 30, 20, 60, 50];
1846 /// for group in v.splitn(2, |num| *num % 3 == 0) {
1847 /// println!("{:?}", group);
1850 #[stable(feature = "rust1", since = "1.0.0")]
1852 pub fn splitn
<F
>(&self, n
: usize, pred
: F
) -> SplitN
<'_
, T
, F
>
1854 F
: FnMut(&T
) -> bool
,
1856 SplitN
::new(self.split(pred
), n
)
1859 /// Returns an iterator over subslices separated by elements that match
1860 /// `pred`, limited to returning at most `n` items. The matched element is
1861 /// not contained in the subslices.
1863 /// The last element returned, if any, will contain the remainder of the
1869 /// let mut v = [10, 40, 30, 20, 60, 50];
1871 /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
1874 /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
1876 #[stable(feature = "rust1", since = "1.0.0")]
1878 pub fn splitn_mut
<F
>(&mut self, n
: usize, pred
: F
) -> SplitNMut
<'_
, T
, F
>
1880 F
: FnMut(&T
) -> bool
,
1882 SplitNMut
::new(self.split_mut(pred
), n
)
1885 /// Returns an iterator over subslices separated by elements that match
1886 /// `pred` limited to returning at most `n` items. This starts at the end of
1887 /// the slice and works backwards. The matched element is not contained in
1890 /// The last element returned, if any, will contain the remainder of the
1895 /// Print the slice split once, starting from the end, by numbers divisible
1896 /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
1899 /// let v = [10, 40, 30, 20, 60, 50];
1901 /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
1902 /// println!("{:?}", group);
1905 #[stable(feature = "rust1", since = "1.0.0")]
1907 pub fn rsplitn
<F
>(&self, n
: usize, pred
: F
) -> RSplitN
<'_
, T
, F
>
1909 F
: FnMut(&T
) -> bool
,
1911 RSplitN
::new(self.rsplit(pred
), n
)
1914 /// Returns an iterator over subslices separated by elements that match
1915 /// `pred` limited to returning at most `n` items. This starts at the end of
1916 /// the slice and works backwards. The matched element is not contained in
1919 /// The last element returned, if any, will contain the remainder of the
1925 /// let mut s = [10, 40, 30, 20, 60, 50];
1927 /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
1930 /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
1932 #[stable(feature = "rust1", since = "1.0.0")]
1934 pub fn rsplitn_mut
<F
>(&mut self, n
: usize, pred
: F
) -> RSplitNMut
<'_
, T
, F
>
1936 F
: FnMut(&T
) -> bool
,
1938 RSplitNMut
::new(self.rsplit_mut(pred
), n
)
1941 /// Returns `true` if the slice contains an element with the given value.
1946 /// let v = [10, 40, 30];
1947 /// assert!(v.contains(&30));
1948 /// assert!(!v.contains(&50));
1951 /// If you do not have a `&T`, but some other value that you can compare
1952 /// with one (for example, `String` implements `PartialEq<str>`), you can
1953 /// use `iter().any`:
1956 /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
1957 /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
1958 /// assert!(!v.iter().any(|e| e == "hi"));
1960 #[stable(feature = "rust1", since = "1.0.0")]
1962 pub fn contains(&self, x
: &T
) -> bool
1966 cmp
::SliceContains
::slice_contains(x
, self)
1969 /// Returns `true` if `needle` is a prefix of the slice.
1974 /// let v = [10, 40, 30];
1975 /// assert!(v.starts_with(&[10]));
1976 /// assert!(v.starts_with(&[10, 40]));
1977 /// assert!(!v.starts_with(&[50]));
1978 /// assert!(!v.starts_with(&[10, 50]));
1981 /// Always returns `true` if `needle` is an empty slice:
1984 /// let v = &[10, 40, 30];
1985 /// assert!(v.starts_with(&[]));
1986 /// let v: &[u8] = &[];
1987 /// assert!(v.starts_with(&[]));
1989 #[stable(feature = "rust1", since = "1.0.0")]
1990 pub fn starts_with(&self, needle
: &[T
]) -> bool
1994 let n
= needle
.len();
1995 self.len() >= n
&& needle
== &self[..n
]
1998 /// Returns `true` if `needle` is a suffix of the slice.
2003 /// let v = [10, 40, 30];
2004 /// assert!(v.ends_with(&[30]));
2005 /// assert!(v.ends_with(&[40, 30]));
2006 /// assert!(!v.ends_with(&[50]));
2007 /// assert!(!v.ends_with(&[50, 30]));
2010 /// Always returns `true` if `needle` is an empty slice:
2013 /// let v = &[10, 40, 30];
2014 /// assert!(v.ends_with(&[]));
2015 /// let v: &[u8] = &[];
2016 /// assert!(v.ends_with(&[]));
2018 #[stable(feature = "rust1", since = "1.0.0")]
2019 pub fn ends_with(&self, needle
: &[T
]) -> bool
2023 let (m
, n
) = (self.len(), needle
.len());
2024 m
>= n
&& needle
== &self[m
- n
..]
2027 /// Returns a subslice with the prefix removed.
2029 /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
2030 /// If `prefix` is empty, simply returns the original slice.
2032 /// If the slice does not start with `prefix`, returns `None`.
2037 /// let v = &[10, 40, 30];
2038 /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
2039 /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
2040 /// assert_eq!(v.strip_prefix(&[50]), None);
2041 /// assert_eq!(v.strip_prefix(&[10, 50]), None);
2043 /// let prefix : &str = "he";
2044 /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
2045 /// Some(b"llo".as_ref()));
2047 #[must_use = "returns the subslice without modifying the original"]
2048 #[stable(feature = "slice_strip", since = "1.51.0")]
2049 pub fn strip_prefix
<P
: SlicePattern
<Item
= T
> + ?Sized
>(&self, prefix
: &P
) -> Option
<&[T
]>
2053 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2054 let prefix
= prefix
.as_slice();
2055 let n
= prefix
.len();
2056 if n
<= self.len() {
2057 let (head
, tail
) = self.split_at(n
);
2065 /// Returns a subslice with the suffix removed.
2067 /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
2068 /// If `suffix` is empty, simply returns the original slice.
2070 /// If the slice does not end with `suffix`, returns `None`.
2075 /// let v = &[10, 40, 30];
2076 /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
2077 /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
2078 /// assert_eq!(v.strip_suffix(&[50]), None);
2079 /// assert_eq!(v.strip_suffix(&[50, 30]), None);
2081 #[must_use = "returns the subslice without modifying the original"]
2082 #[stable(feature = "slice_strip", since = "1.51.0")]
2083 pub fn strip_suffix
<P
: SlicePattern
<Item
= T
> + ?Sized
>(&self, suffix
: &P
) -> Option
<&[T
]>
2087 // This function will need rewriting if and when SlicePattern becomes more sophisticated.
2088 let suffix
= suffix
.as_slice();
2089 let (len
, n
) = (self.len(), suffix
.len());
2091 let (head
, tail
) = self.split_at(len
- n
);
2099 /// Binary searches this sorted slice for a given element.
2101 /// If the value is found then [`Result::Ok`] is returned, containing the
2102 /// index of the matching element. If there are multiple matches, then any
2103 /// one of the matches could be returned. The index is chosen
2104 /// deterministically, but is subject to change in future versions of Rust.
2105 /// If the value is not found then [`Result::Err`] is returned, containing
2106 /// the index where a matching element could be inserted while maintaining
2109 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2111 /// [`binary_search_by`]: slice::binary_search_by
2112 /// [`binary_search_by_key`]: slice::binary_search_by_key
2113 /// [`partition_point`]: slice::partition_point
2117 /// Looks up a series of four elements. The first is found, with a
2118 /// uniquely determined position; the second and third are not
2119 /// found; the fourth could match any position in `[1, 4]`.
2122 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2124 /// assert_eq!(s.binary_search(&13), Ok(9));
2125 /// assert_eq!(s.binary_search(&4), Err(7));
2126 /// assert_eq!(s.binary_search(&100), Err(13));
2127 /// let r = s.binary_search(&1);
2128 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2131 /// If you want to insert an item to a sorted vector, while maintaining
2135 /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2137 /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
2138 /// s.insert(idx, num);
2139 /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2141 #[stable(feature = "rust1", since = "1.0.0")]
2142 pub fn binary_search(&self, x
: &T
) -> Result
<usize, usize>
2146 self.binary_search_by(|p
| p
.cmp(x
))
2149 /// Binary searches this sorted slice with a comparator function.
2151 /// The comparator function should implement an order consistent
2152 /// with the sort order of the underlying slice, returning an
2153 /// order code that indicates whether its argument is `Less`,
2154 /// `Equal` or `Greater` the desired target.
2156 /// If the value is found then [`Result::Ok`] is returned, containing the
2157 /// index of the matching element. If there are multiple matches, then any
2158 /// one of the matches could be returned. The index is chosen
2159 /// deterministically, but is subject to change in future versions of Rust.
2160 /// If the value is not found then [`Result::Err`] is returned, containing
2161 /// the index where a matching element could be inserted while maintaining
2164 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2166 /// [`binary_search`]: slice::binary_search
2167 /// [`binary_search_by_key`]: slice::binary_search_by_key
2168 /// [`partition_point`]: slice::partition_point
2172 /// Looks up a series of four elements. The first is found, with a
2173 /// uniquely determined position; the second and third are not
2174 /// found; the fourth could match any position in `[1, 4]`.
2177 /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
2180 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
2182 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
2184 /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
2186 /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
2187 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2189 #[stable(feature = "rust1", since = "1.0.0")]
2191 pub fn binary_search_by
<'a
, F
>(&'a
self, mut f
: F
) -> Result
<usize, usize>
2193 F
: FnMut(&'a T
) -> Ordering
,
2195 let mut size
= self.len();
2197 let mut right
= size
;
2198 while left
< right
{
2199 let mid
= left
+ size
/ 2;
2201 // SAFETY: the call is made safe by the following invariants:
2203 // - `mid < size`: `mid` is limited by `[left; right)` bound.
2204 let cmp
= f(unsafe { self.get_unchecked(mid) }
);
2206 // The reason why we use if/else control flow rather than match
2207 // is because match reorders comparison operations, which is perf sensitive.
2208 // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
2211 } else if cmp
== Greater
{
2214 // SAFETY: same as the `get_unchecked` above
2215 unsafe { crate::intrinsics::assume(mid < self.len()) }
;
2219 size
= right
- left
;
2224 /// Binary searches this sorted slice with a key extraction function.
2226 /// Assumes that the slice is sorted by the key, for instance with
2227 /// [`sort_by_key`] using the same key extraction function.
2229 /// If the value is found then [`Result::Ok`] is returned, containing the
2230 /// index of the matching element. If there are multiple matches, then any
2231 /// one of the matches could be returned. The index is chosen
2232 /// deterministically, but is subject to change in future versions of Rust.
2233 /// If the value is not found then [`Result::Err`] is returned, containing
2234 /// the index where a matching element could be inserted while maintaining
2237 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2239 /// [`sort_by_key`]: slice::sort_by_key
2240 /// [`binary_search`]: slice::binary_search
2241 /// [`binary_search_by`]: slice::binary_search_by
2242 /// [`partition_point`]: slice::partition_point
2246 /// Looks up a series of four elements in a slice of pairs sorted by
2247 /// their second elements. The first is found, with a uniquely
2248 /// determined position; the second and third are not found; the
2249 /// fourth could match any position in `[1, 4]`.
2252 /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
2253 /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2254 /// (1, 21), (2, 34), (4, 55)];
2256 /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2257 /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2258 /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2259 /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
2260 /// assert!(match r { Ok(1..=4) => true, _ => false, });
2262 // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
2263 // in crate `alloc`, and as such doesn't exists yet when building `core`.
2264 // links to downstream crate: #74481. Since primitives are only documented in
2265 // libstd (#73423), this never leads to broken links in practice.
2266 #[allow(rustdoc::broken_intra_doc_links)]
2267 #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
2269 pub fn binary_search_by_key
<'a
, B
, F
>(&'a
self, b
: &B
, mut f
: F
) -> Result
<usize, usize>
2271 F
: FnMut(&'a T
) -> B
,
2274 self.binary_search_by(|k
| f(k
).cmp(b
))
2277 /// Sorts the slice, but may not preserve the order of equal elements.
2279 /// This sort is unstable (i.e., may reorder equal elements), in-place
2280 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2282 /// # Current implementation
2284 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2285 /// which combines the fast average case of randomized quicksort with the fast worst case of
2286 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2287 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2288 /// deterministic behavior.
2290 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2291 /// slice consists of several concatenated sorted sequences.
2296 /// let mut v = [-5, 4, 1, -3, 2];
2298 /// v.sort_unstable();
2299 /// assert!(v == [-5, -3, 1, 2, 4]);
2302 /// [pdqsort]: https://github.com/orlp/pdqsort
2303 #[stable(feature = "sort_unstable", since = "1.20.0")]
2305 pub fn sort_unstable(&mut self)
2309 sort
::quicksort(self, |a
, b
| a
.lt(b
));
2312 /// Sorts the slice with a comparator function, but may not preserve the order of equal
2315 /// This sort is unstable (i.e., may reorder equal elements), in-place
2316 /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
2318 /// The comparator function must define a total ordering for the elements in the slice. If
2319 /// the ordering is not total, the order of the elements is unspecified. An order is a
2320 /// total order if it is (for all `a`, `b` and `c`):
2322 /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
2323 /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
2325 /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
2326 /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
2329 /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
2330 /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
2331 /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
2334 /// # Current implementation
2336 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2337 /// which combines the fast average case of randomized quicksort with the fast worst case of
2338 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2339 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2340 /// deterministic behavior.
2342 /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
2343 /// slice consists of several concatenated sorted sequences.
2348 /// let mut v = [5, 4, 1, 3, 2];
2349 /// v.sort_unstable_by(|a, b| a.cmp(b));
2350 /// assert!(v == [1, 2, 3, 4, 5]);
2352 /// // reverse sorting
2353 /// v.sort_unstable_by(|a, b| b.cmp(a));
2354 /// assert!(v == [5, 4, 3, 2, 1]);
2357 /// [pdqsort]: https://github.com/orlp/pdqsort
2358 #[stable(feature = "sort_unstable", since = "1.20.0")]
2360 pub fn sort_unstable_by
<F
>(&mut self, mut compare
: F
)
2362 F
: FnMut(&T
, &T
) -> Ordering
,
2364 sort
::quicksort(self, |a
, b
| compare(a
, b
) == Ordering
::Less
);
2367 /// Sorts the slice with a key extraction function, but may not preserve the order of equal
2370 /// This sort is unstable (i.e., may reorder equal elements), in-place
2371 /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
2374 /// # Current implementation
2376 /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
2377 /// which combines the fast average case of randomized quicksort with the fast worst case of
2378 /// heapsort, while achieving linear time on slices with certain patterns. It uses some
2379 /// randomization to avoid degenerate cases, but with a fixed seed to always provide
2380 /// deterministic behavior.
2382 /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
2383 /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
2384 /// cases where the key function is expensive.
2389 /// let mut v = [-5i32, 4, 1, -3, 2];
2391 /// v.sort_unstable_by_key(|k| k.abs());
2392 /// assert!(v == [1, 2, -3, 4, -5]);
2395 /// [pdqsort]: https://github.com/orlp/pdqsort
2396 #[stable(feature = "sort_unstable", since = "1.20.0")]
2398 pub fn sort_unstable_by_key
<K
, F
>(&mut self, mut f
: F
)
2403 sort
::quicksort(self, |a
, b
| f(a
).lt(&f(b
)));
2406 /// Reorder the slice such that the element at `index` is at its final sorted position.
2407 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2408 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
2410 pub fn partition_at_index(&mut self, index
: usize) -> (&mut [T
], &mut T
, &mut [T
])
2414 self.select_nth_unstable(index
)
2417 /// Reorder the slice with a comparator function such that the element at `index` is at its
2418 /// final sorted position.
2419 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2420 #[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
2422 pub fn partition_at_index_by
<F
>(
2426 ) -> (&mut [T
], &mut T
, &mut [T
])
2428 F
: FnMut(&T
, &T
) -> Ordering
,
2430 self.select_nth_unstable_by(index
, compare
)
2433 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2434 /// final sorted position.
2435 #[unstable(feature = "slice_partition_at_index", issue = "55300")]
2436 #[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
2438 pub fn partition_at_index_by_key
<K
, F
>(
2442 ) -> (&mut [T
], &mut T
, &mut [T
])
2447 self.select_nth_unstable_by_key(index
, f
)
2450 /// Reorder the slice such that the element at `index` is at its final sorted position.
2452 /// This reordering has the additional property that any value at position `i < index` will be
2453 /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
2454 /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
2455 /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
2456 /// element" in other libraries. It returns a triplet of the following values: all elements less
2457 /// than the one at the given index, the value at the given index, and all elements greater than
2458 /// the one at the given index.
2460 /// # Current implementation
2462 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2463 /// used for [`sort_unstable`].
2465 /// [`sort_unstable`]: slice::sort_unstable
2469 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2474 /// let mut v = [-5i32, 4, 1, -3, 2];
2476 /// // Find the median
2477 /// v.select_nth_unstable(2);
2479 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2480 /// // about the specified index.
2481 /// assert!(v == [-3, -5, 1, 2, 4] ||
2482 /// v == [-5, -3, 1, 2, 4] ||
2483 /// v == [-3, -5, 1, 4, 2] ||
2484 /// v == [-5, -3, 1, 4, 2]);
2486 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2488 pub fn select_nth_unstable(&mut self, index
: usize) -> (&mut [T
], &mut T
, &mut [T
])
2492 let mut f
= |a
: &T
, b
: &T
| a
.lt(b
);
2493 sort
::partition_at_index(self, index
, &mut f
)
2496 /// Reorder the slice with a comparator function such that the element at `index` is at its
2497 /// final sorted position.
2499 /// This reordering has the additional property that any value at position `i < index` will be
2500 /// less than or equal to any value at a position `j > index` using the comparator function.
2501 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2502 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2503 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2504 /// values: all elements less than the one at the given index, the value at the given index,
2505 /// and all elements greater than the one at the given index, using the provided comparator
2508 /// # Current implementation
2510 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2511 /// used for [`sort_unstable`].
2513 /// [`sort_unstable`]: slice::sort_unstable
2517 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2522 /// let mut v = [-5i32, 4, 1, -3, 2];
2524 /// // Find the median as if the slice were sorted in descending order.
2525 /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
2527 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2528 /// // about the specified index.
2529 /// assert!(v == [2, 4, 1, -5, -3] ||
2530 /// v == [2, 4, 1, -3, -5] ||
2531 /// v == [4, 2, 1, -5, -3] ||
2532 /// v == [4, 2, 1, -3, -5]);
2534 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2536 pub fn select_nth_unstable_by
<F
>(
2540 ) -> (&mut [T
], &mut T
, &mut [T
])
2542 F
: FnMut(&T
, &T
) -> Ordering
,
2544 let mut f
= |a
: &T
, b
: &T
| compare(a
, b
) == Less
;
2545 sort
::partition_at_index(self, index
, &mut f
)
2548 /// Reorder the slice with a key extraction function such that the element at `index` is at its
2549 /// final sorted position.
2551 /// This reordering has the additional property that any value at position `i < index` will be
2552 /// less than or equal to any value at a position `j > index` using the key extraction function.
2553 /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
2554 /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
2555 /// is also known as "kth element" in other libraries. It returns a triplet of the following
2556 /// values: all elements less than the one at the given index, the value at the given index, and
2557 /// all elements greater than the one at the given index, using the provided key extraction
2560 /// # Current implementation
2562 /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
2563 /// used for [`sort_unstable`].
2565 /// [`sort_unstable`]: slice::sort_unstable
2569 /// Panics when `index >= len()`, meaning it always panics on empty slices.
2574 /// let mut v = [-5i32, 4, 1, -3, 2];
2576 /// // Return the median as if the array were sorted according to absolute value.
2577 /// v.select_nth_unstable_by_key(2, |a| a.abs());
2579 /// // We are only guaranteed the slice will be one of the following, based on the way we sort
2580 /// // about the specified index.
2581 /// assert!(v == [1, 2, -3, 4, -5] ||
2582 /// v == [1, 2, -3, -5, 4] ||
2583 /// v == [2, 1, -3, 4, -5] ||
2584 /// v == [2, 1, -3, -5, 4]);
2586 #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
2588 pub fn select_nth_unstable_by_key
<K
, F
>(
2592 ) -> (&mut [T
], &mut T
, &mut [T
])
2597 let mut g
= |a
: &T
, b
: &T
| f(a
).lt(&f(b
));
2598 sort
::partition_at_index(self, index
, &mut g
)
2601 /// Moves all consecutive repeated elements to the end of the slice according to the
2602 /// [`PartialEq`] trait implementation.
2604 /// Returns two slices. The first contains no consecutive repeated elements.
2605 /// The second contains all the duplicates in no specified order.
2607 /// If the slice is sorted, the first returned slice contains no duplicates.
2612 /// #![feature(slice_partition_dedup)]
2614 /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
2616 /// let (dedup, duplicates) = slice.partition_dedup();
2618 /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
2619 /// assert_eq!(duplicates, [2, 3, 1]);
2621 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2623 pub fn partition_dedup(&mut self) -> (&mut [T
], &mut [T
])
2627 self.partition_dedup_by(|a
, b
| a
== b
)
2630 /// Moves all but the first of consecutive elements to the end of the slice satisfying
2631 /// a given equality relation.
2633 /// Returns two slices. The first contains no consecutive repeated elements.
2634 /// The second contains all the duplicates in no specified order.
2636 /// The `same_bucket` function is passed references to two elements from the slice and
2637 /// must determine if the elements compare equal. The elements are passed in opposite order
2638 /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
2639 /// at the end of the slice.
2641 /// If the slice is sorted, the first returned slice contains no duplicates.
2646 /// #![feature(slice_partition_dedup)]
2648 /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
2650 /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
2652 /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
2653 /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
2655 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2657 pub fn partition_dedup_by
<F
>(&mut self, mut same_bucket
: F
) -> (&mut [T
], &mut [T
])
2659 F
: FnMut(&mut T
, &mut T
) -> bool
,
2661 // Although we have a mutable reference to `self`, we cannot make
2662 // *arbitrary* changes. The `same_bucket` calls could panic, so we
2663 // must ensure that the slice is in a valid state at all times.
2665 // The way that we handle this is by using swaps; we iterate
2666 // over all the elements, swapping as we go so that at the end
2667 // the elements we wish to keep are in the front, and those we
2668 // wish to reject are at the back. We can then split the slice.
2669 // This operation is still `O(n)`.
2671 // Example: We start in this state, where `r` represents "next
2672 // read" and `w` represents "next_write`.
2675 // +---+---+---+---+---+---+
2676 // | 0 | 1 | 1 | 2 | 3 | 3 |
2677 // +---+---+---+---+---+---+
2680 // Comparing self[r] against self[w-1], this is not a duplicate, so
2681 // we swap self[r] and self[w] (no effect as r==w) and then increment both
2682 // r and w, leaving us with:
2685 // +---+---+---+---+---+---+
2686 // | 0 | 1 | 1 | 2 | 3 | 3 |
2687 // +---+---+---+---+---+---+
2690 // Comparing self[r] against self[w-1], this value is a duplicate,
2691 // so we increment `r` but leave everything else unchanged:
2694 // +---+---+---+---+---+---+
2695 // | 0 | 1 | 1 | 2 | 3 | 3 |
2696 // +---+---+---+---+---+---+
2699 // Comparing self[r] against self[w-1], this is not a duplicate,
2700 // so swap self[r] and self[w] and advance r and w:
2703 // +---+---+---+---+---+---+
2704 // | 0 | 1 | 2 | 1 | 3 | 3 |
2705 // +---+---+---+---+---+---+
2708 // Not a duplicate, repeat:
2711 // +---+---+---+---+---+---+
2712 // | 0 | 1 | 2 | 3 | 1 | 3 |
2713 // +---+---+---+---+---+---+
2716 // Duplicate, advance r. End of slice. Split at w.
2718 let len
= self.len();
2720 return (self, &mut []);
2723 let ptr
= self.as_mut_ptr();
2724 let mut next_read
: usize = 1;
2725 let mut next_write
: usize = 1;
2727 // SAFETY: the `while` condition guarantees `next_read` and `next_write`
2728 // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
2729 // one element before `ptr_write`, but `next_write` starts at 1, so
2730 // `prev_ptr_write` is never less than 0 and is inside the slice.
2731 // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
2732 // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
2733 // and `prev_ptr_write.offset(1)`.
2735 // `next_write` is also incremented at most once per loop at most meaning
2736 // no element is skipped when it may need to be swapped.
2738 // `ptr_read` and `prev_ptr_write` never point to the same element. This
2739 // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
2740 // The explanation is simply that `next_read >= next_write` is always true,
2741 // thus `next_read > next_write - 1` is too.
2743 // Avoid bounds checks by using raw pointers.
2744 while next_read
< len
{
2745 let ptr_read
= ptr
.add(next_read
);
2746 let prev_ptr_write
= ptr
.add(next_write
- 1);
2747 if !same_bucket(&mut *ptr_read
, &mut *prev_ptr_write
) {
2748 if next_read
!= next_write
{
2749 let ptr_write
= prev_ptr_write
.offset(1);
2750 mem
::swap(&mut *ptr_read
, &mut *ptr_write
);
2758 self.split_at_mut(next_write
)
2761 /// Moves all but the first of consecutive elements to the end of the slice that resolve
2762 /// to the same key.
2764 /// Returns two slices. The first contains no consecutive repeated elements.
2765 /// The second contains all the duplicates in no specified order.
2767 /// If the slice is sorted, the first returned slice contains no duplicates.
2772 /// #![feature(slice_partition_dedup)]
2774 /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
2776 /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
2778 /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
2779 /// assert_eq!(duplicates, [21, 30, 13]);
2781 #[unstable(feature = "slice_partition_dedup", issue = "54279")]
2783 pub fn partition_dedup_by_key
<K
, F
>(&mut self, mut key
: F
) -> (&mut [T
], &mut [T
])
2785 F
: FnMut(&mut T
) -> K
,
2788 self.partition_dedup_by(|a
, b
| key(a
) == key(b
))
2791 /// Rotates the slice in-place such that the first `mid` elements of the
2792 /// slice move to the end while the last `self.len() - mid` elements move to
2793 /// the front. After calling `rotate_left`, the element previously at index
2794 /// `mid` will become the first element in the slice.
2798 /// This function will panic if `mid` is greater than the length of the
2799 /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
2804 /// Takes linear (in `self.len()`) time.
2809 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2810 /// a.rotate_left(2);
2811 /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
2814 /// Rotating a subslice:
2817 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2818 /// a[1..5].rotate_left(1);
2819 /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
2821 #[stable(feature = "slice_rotate", since = "1.26.0")]
2822 pub fn rotate_left(&mut self, mid
: usize) {
2823 assert
!(mid
<= self.len());
2824 let k
= self.len() - mid
;
2825 let p
= self.as_mut_ptr();
2827 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2828 // valid for reading and writing, as required by `ptr_rotate`.
2830 rotate
::ptr_rotate(mid
, p
.add(mid
), k
);
2834 /// Rotates the slice in-place such that the first `self.len() - k`
2835 /// elements of the slice move to the end while the last `k` elements move
2836 /// to the front. After calling `rotate_right`, the element previously at
2837 /// index `self.len() - k` will become the first element in the slice.
2841 /// This function will panic if `k` is greater than the length of the
2842 /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
2847 /// Takes linear (in `self.len()`) time.
2852 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2853 /// a.rotate_right(2);
2854 /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
2857 /// Rotate a subslice:
2860 /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
2861 /// a[1..5].rotate_right(1);
2862 /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
2864 #[stable(feature = "slice_rotate", since = "1.26.0")]
2865 pub fn rotate_right(&mut self, k
: usize) {
2866 assert
!(k
<= self.len());
2867 let mid
= self.len() - k
;
2868 let p
= self.as_mut_ptr();
2870 // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
2871 // valid for reading and writing, as required by `ptr_rotate`.
2873 rotate
::ptr_rotate(mid
, p
.add(mid
), k
);
2877 /// Fills `self` with elements by cloning `value`.
2882 /// let mut buf = vec![0; 10];
2884 /// assert_eq!(buf, vec![1; 10]);
2886 #[doc(alias = "memset")]
2887 #[stable(feature = "slice_fill", since = "1.50.0")]
2888 pub fn fill(&mut self, value
: T
)
2892 specialize
::SpecFill
::spec_fill(self, value
);
2895 /// Fills `self` with elements returned by calling a closure repeatedly.
2897 /// This method uses a closure to create new values. If you'd rather
2898 /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
2899 /// trait to generate values, you can pass [`Default::default`] as the
2902 /// [`fill`]: slice::fill
2907 /// let mut buf = vec![1; 10];
2908 /// buf.fill_with(Default::default);
2909 /// assert_eq!(buf, vec![0; 10]);
2911 #[doc(alias = "memset")]
2912 #[stable(feature = "slice_fill_with", since = "1.51.0")]
2913 pub fn fill_with
<F
>(&mut self, mut f
: F
)
2922 /// Copies the elements from `src` into `self`.
2924 /// The length of `src` must be the same as `self`.
2926 /// If `T` implements `Copy`, it can be more performant to use
2927 /// [`copy_from_slice`].
2931 /// This function will panic if the two slices have different lengths.
2935 /// Cloning two elements from a slice into another:
2938 /// let src = [1, 2, 3, 4];
2939 /// let mut dst = [0, 0];
2941 /// // Because the slices have to be the same length,
2942 /// // we slice the source slice from four elements
2943 /// // to two. It will panic if we don't do this.
2944 /// dst.clone_from_slice(&src[2..]);
2946 /// assert_eq!(src, [1, 2, 3, 4]);
2947 /// assert_eq!(dst, [3, 4]);
2950 /// Rust enforces that there can only be one mutable reference with no
2951 /// immutable references to a particular piece of data in a particular
2952 /// scope. Because of this, attempting to use `clone_from_slice` on a
2953 /// single slice will result in a compile failure:
2956 /// let mut slice = [1, 2, 3, 4, 5];
2958 /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
2961 /// To work around this, we can use [`split_at_mut`] to create two distinct
2962 /// sub-slices from a slice:
2965 /// let mut slice = [1, 2, 3, 4, 5];
2968 /// let (left, right) = slice.split_at_mut(2);
2969 /// left.clone_from_slice(&right[1..]);
2972 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
2975 /// [`copy_from_slice`]: slice::copy_from_slice
2976 /// [`split_at_mut`]: slice::split_at_mut
2977 #[stable(feature = "clone_from_slice", since = "1.7.0")]
2978 pub fn clone_from_slice(&mut self, src
: &[T
])
2982 self.spec_clone_from(src
);
2985 /// Copies all elements from `src` into `self`, using a memcpy.
2987 /// The length of `src` must be the same as `self`.
2989 /// If `T` does not implement `Copy`, use [`clone_from_slice`].
2993 /// This function will panic if the two slices have different lengths.
2997 /// Copying two elements from a slice into another:
3000 /// let src = [1, 2, 3, 4];
3001 /// let mut dst = [0, 0];
3003 /// // Because the slices have to be the same length,
3004 /// // we slice the source slice from four elements
3005 /// // to two. It will panic if we don't do this.
3006 /// dst.copy_from_slice(&src[2..]);
3008 /// assert_eq!(src, [1, 2, 3, 4]);
3009 /// assert_eq!(dst, [3, 4]);
3012 /// Rust enforces that there can only be one mutable reference with no
3013 /// immutable references to a particular piece of data in a particular
3014 /// scope. Because of this, attempting to use `copy_from_slice` on a
3015 /// single slice will result in a compile failure:
3018 /// let mut slice = [1, 2, 3, 4, 5];
3020 /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
3023 /// To work around this, we can use [`split_at_mut`] to create two distinct
3024 /// sub-slices from a slice:
3027 /// let mut slice = [1, 2, 3, 4, 5];
3030 /// let (left, right) = slice.split_at_mut(2);
3031 /// left.copy_from_slice(&right[1..]);
3034 /// assert_eq!(slice, [4, 5, 3, 4, 5]);
3037 /// [`clone_from_slice`]: slice::clone_from_slice
3038 /// [`split_at_mut`]: slice::split_at_mut
3039 #[doc(alias = "memcpy")]
3040 #[stable(feature = "copy_from_slice", since = "1.9.0")]
3041 pub fn copy_from_slice(&mut self, src
: &[T
])
3045 // The panic code path was put into a cold function to not bloat the
3050 fn len_mismatch_fail(dst_len
: usize, src_len
: usize) -> ! {
3052 "source slice length ({}) does not match destination slice length ({})",
3057 if self.len() != src
.len() {
3058 len_mismatch_fail(self.len(), src
.len());
3061 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3062 // checked to have the same length. The slices cannot overlap because
3063 // mutable references are exclusive.
3065 ptr
::copy_nonoverlapping(src
.as_ptr(), self.as_mut_ptr(), self.len());
3069 /// Copies elements from one part of the slice to another part of itself,
3070 /// using a memmove.
3072 /// `src` is the range within `self` to copy from. `dest` is the starting
3073 /// index of the range within `self` to copy to, which will have the same
3074 /// length as `src`. The two ranges may overlap. The ends of the two ranges
3075 /// must be less than or equal to `self.len()`.
3079 /// This function will panic if either range exceeds the end of the slice,
3080 /// or if the end of `src` is before the start.
3084 /// Copying four bytes within a slice:
3087 /// let mut bytes = *b"Hello, World!";
3089 /// bytes.copy_within(1..5, 8);
3091 /// assert_eq!(&bytes, b"Hello, Wello!");
3093 #[stable(feature = "copy_within", since = "1.37.0")]
3095 pub fn copy_within
<R
: RangeBounds
<usize>>(&mut self, src
: R
, dest
: usize)
3099 let Range { start: src_start, end: src_end }
= slice
::range(src
, ..self.len());
3100 let count
= src_end
- src_start
;
3101 assert
!(dest
<= self.len() - count
, "dest is out of bounds");
3102 // SAFETY: the conditions for `ptr::copy` have all been checked above,
3103 // as have those for `ptr::add`.
3105 // Derive both `src_ptr` and `dest_ptr` from the same loan
3106 let ptr
= self.as_mut_ptr();
3107 let src_ptr
= ptr
.add(src_start
);
3108 let dest_ptr
= ptr
.add(dest
);
3109 ptr
::copy(src_ptr
, dest_ptr
, count
);
3113 /// Swaps all elements in `self` with those in `other`.
3115 /// The length of `other` must be the same as `self`.
3119 /// This function will panic if the two slices have different lengths.
3123 /// Swapping two elements across slices:
3126 /// let mut slice1 = [0, 0];
3127 /// let mut slice2 = [1, 2, 3, 4];
3129 /// slice1.swap_with_slice(&mut slice2[2..]);
3131 /// assert_eq!(slice1, [3, 4]);
3132 /// assert_eq!(slice2, [1, 2, 0, 0]);
3135 /// Rust enforces that there can only be one mutable reference to a
3136 /// particular piece of data in a particular scope. Because of this,
3137 /// attempting to use `swap_with_slice` on a single slice will result in
3138 /// a compile failure:
3141 /// let mut slice = [1, 2, 3, 4, 5];
3142 /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
3145 /// To work around this, we can use [`split_at_mut`] to create two distinct
3146 /// mutable sub-slices from a slice:
3149 /// let mut slice = [1, 2, 3, 4, 5];
3152 /// let (left, right) = slice.split_at_mut(2);
3153 /// left.swap_with_slice(&mut right[1..]);
3156 /// assert_eq!(slice, [4, 5, 3, 1, 2]);
3159 /// [`split_at_mut`]: slice::split_at_mut
3160 #[stable(feature = "swap_with_slice", since = "1.27.0")]
3161 pub fn swap_with_slice(&mut self, other
: &mut [T
]) {
3162 assert
!(self.len() == other
.len(), "destination and source slices have different lengths");
3163 // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
3164 // checked to have the same length. The slices cannot overlap because
3165 // mutable references are exclusive.
3167 ptr
::swap_nonoverlapping(self.as_mut_ptr(), other
.as_mut_ptr(), self.len());
3171 /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
3172 fn align_to_offsets
<U
>(&self) -> (usize, usize) {
3173 // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
3174 // lowest number of `T`s. And how many `T`s we need for each such "multiple".
3176 // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
3177 // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
3178 // place of every 3 Ts in the `rest` slice. A bit more complicated.
3180 // Formula to calculate this is:
3182 // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
3183 // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
3185 // Expanded and simplified:
3187 // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
3188 // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
3190 // Luckily since all this is constant-evaluated... performance here matters not!
3192 fn gcd(a
: usize, b
: usize) -> usize {
3193 use crate::intrinsics
;
3194 // iterative stein’s algorithm
3195 // We should still make this `const fn` (and revert to recursive algorithm if we do)
3196 // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
3198 // SAFETY: `a` and `b` are checked to be non-zero values.
3199 let (ctz_a
, mut ctz_b
) = unsafe {
3206 (intrinsics
::cttz_nonzero(a
), intrinsics
::cttz_nonzero(b
))
3208 let k
= ctz_a
.min(ctz_b
);
3209 let mut a
= a
>> ctz_a
;
3212 // remove all factors of 2 from b
3215 mem
::swap(&mut a
, &mut b
);
3218 // SAFETY: `b` is checked to be non-zero.
3223 ctz_b
= intrinsics
::cttz_nonzero(b
);
3228 let gcd
: usize = gcd(mem
::size_of
::<T
>(), mem
::size_of
::<U
>());
3229 let ts
: usize = mem
::size_of
::<U
>() / gcd
;
3230 let us
: usize = mem
::size_of
::<T
>() / gcd
;
3232 // Armed with this knowledge, we can find how many `U`s we can fit!
3233 let us_len
= self.len() / ts
* us
;
3234 // And how many `T`s will be in the trailing slice!
3235 let ts_len
= self.len() % ts
;
3239 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3242 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3243 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3244 /// length possible for a given type and input slice, but only your algorithm's performance
3245 /// should depend on that, not its correctness. It is permissible for all of the input data to
3246 /// be returned as the prefix or suffix slice.
3248 /// This method has no purpose when either input element `T` or output element `U` are
3249 /// zero-sized and will return the original slice without splitting anything.
3253 /// This method is essentially a `transmute` with respect to the elements in the returned
3254 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3262 /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3263 /// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
3264 /// // less_efficient_algorithm_for_bytes(prefix);
3265 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3266 /// // less_efficient_algorithm_for_bytes(suffix);
3269 #[stable(feature = "slice_align_to", since = "1.30.0")]
3270 pub unsafe fn align_to
<U
>(&self) -> (&[T
], &[U
], &[T
]) {
3271 // Note that most of this function will be constant-evaluated,
3272 if mem
::size_of
::<U
>() == 0 || mem
::size_of
::<T
>() == 0 {
3273 // handle ZSTs specially, which is – don't handle them at all.
3274 return (self, &[], &[]);
3277 // First, find at what point do we split between the first and 2nd slice. Easy with
3278 // ptr.align_offset.
3279 let ptr
= self.as_ptr();
3280 // SAFETY: See the `align_to_mut` method for the detailed safety comment.
3281 let offset
= unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) }
;
3282 if offset
> self.len() {
3285 let (left
, rest
) = self.split_at(offset
);
3286 let (us_len
, ts_len
) = rest
.align_to_offsets
::<U
>();
3287 // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
3288 // since the caller guarantees that we can transmute `T` to `U` safely.
3292 from_raw_parts(rest
.as_ptr() as *const U
, us_len
),
3293 from_raw_parts(rest
.as_ptr().add(rest
.len() - ts_len
), ts_len
),
3299 /// Transmute the slice to a slice of another type, ensuring alignment of the types is
3302 /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
3303 /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
3304 /// length possible for a given type and input slice, but only your algorithm's performance
3305 /// should depend on that, not its correctness. It is permissible for all of the input data to
3306 /// be returned as the prefix or suffix slice.
3308 /// This method has no purpose when either input element `T` or output element `U` are
3309 /// zero-sized and will return the original slice without splitting anything.
3313 /// This method is essentially a `transmute` with respect to the elements in the returned
3314 /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
3322 /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
3323 /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
3324 /// // less_efficient_algorithm_for_bytes(prefix);
3325 /// // more_efficient_algorithm_for_aligned_shorts(shorts);
3326 /// // less_efficient_algorithm_for_bytes(suffix);
3329 #[stable(feature = "slice_align_to", since = "1.30.0")]
3330 pub unsafe fn align_to_mut
<U
>(&mut self) -> (&mut [T
], &mut [U
], &mut [T
]) {
3331 // Note that most of this function will be constant-evaluated,
3332 if mem
::size_of
::<U
>() == 0 || mem
::size_of
::<T
>() == 0 {
3333 // handle ZSTs specially, which is – don't handle them at all.
3334 return (self, &mut [], &mut []);
3337 // First, find at what point do we split between the first and 2nd slice. Easy with
3338 // ptr.align_offset.
3339 let ptr
= self.as_ptr();
3340 // SAFETY: Here we are ensuring we will use aligned pointers for U for the
3341 // rest of the method. This is done by passing a pointer to &[T] with an
3342 // alignment targeted for U.
3343 // `crate::ptr::align_offset` is called with a correctly aligned and
3344 // valid pointer `ptr` (it comes from a reference to `self`) and with
3345 // a size that is a power of two (since it comes from the alignement for U),
3346 // satisfying its safety constraints.
3347 let offset
= unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) }
;
3348 if offset
> self.len() {
3349 (self, &mut [], &mut [])
3351 let (left
, rest
) = self.split_at_mut(offset
);
3352 let (us_len
, ts_len
) = rest
.align_to_offsets
::<U
>();
3353 let rest_len
= rest
.len();
3354 let mut_ptr
= rest
.as_mut_ptr();
3355 // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
3356 // SAFETY: see comments for `align_to`.
3360 from_raw_parts_mut(mut_ptr
as *mut U
, us_len
),
3361 from_raw_parts_mut(mut_ptr
.add(rest_len
- ts_len
), ts_len
),
3367 /// Checks if the elements of this slice are sorted.
3369 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3370 /// slice yields exactly zero or one element, `true` is returned.
3372 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3373 /// implies that this function returns `false` if any two consecutive items are not
3379 /// #![feature(is_sorted)]
3380 /// let empty: [i32; 0] = [];
3382 /// assert!([1, 2, 2, 9].is_sorted());
3383 /// assert!(![1, 3, 2, 4].is_sorted());
3384 /// assert!([0].is_sorted());
3385 /// assert!(empty.is_sorted());
3386 /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
3389 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3390 pub fn is_sorted(&self) -> bool
3394 self.is_sorted_by(|a
, b
| a
.partial_cmp(b
))
3397 /// Checks if the elements of this slice are sorted using the given comparator function.
3399 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3400 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3401 /// [`is_sorted`]; see its documentation for more information.
3403 /// [`is_sorted`]: slice::is_sorted
3404 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3405 pub fn is_sorted_by
<F
>(&self, mut compare
: F
) -> bool
3407 F
: FnMut(&T
, &T
) -> Option
<Ordering
>,
3409 self.iter().is_sorted_by(|a
, b
| compare(*a
, *b
))
3412 /// Checks if the elements of this slice are sorted using the given key extraction function.
3414 /// Instead of comparing the slice's elements directly, this function compares the keys of the
3415 /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
3416 /// documentation for more information.
3418 /// [`is_sorted`]: slice::is_sorted
3423 /// #![feature(is_sorted)]
3425 /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
3426 /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
3429 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3430 pub fn is_sorted_by_key
<F
, K
>(&self, f
: F
) -> bool
3435 self.iter().is_sorted_by_key(f
)
3438 /// Returns the index of the partition point according to the given predicate
3439 /// (the index of the first element of the second partition).
3441 /// The slice is assumed to be partitioned according to the given predicate.
3442 /// This means that all elements for which the predicate returns true are at the start of the slice
3443 /// and all elements for which the predicate returns false are at the end.
3444 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
3445 /// (all odd numbers are at the start, all even at the end).
3447 /// If this slice is not partitioned, the returned result is unspecified and meaningless,
3448 /// as this method performs a kind of binary search.
3450 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
3452 /// [`binary_search`]: slice::binary_search
3453 /// [`binary_search_by`]: slice::binary_search_by
3454 /// [`binary_search_by_key`]: slice::binary_search_by_key
3459 /// let v = [1, 2, 3, 3, 5, 6, 7];
3460 /// let i = v.partition_point(|&x| x < 5);
3462 /// assert_eq!(i, 4);
3463 /// assert!(v[..i].iter().all(|&x| x < 5));
3464 /// assert!(v[i..].iter().all(|&x| !(x < 5)));
3466 #[stable(feature = "partition_point", since = "1.52.0")]
3467 pub fn partition_point
<P
>(&self, mut pred
: P
) -> usize
3469 P
: FnMut(&T
) -> bool
,
3471 self.binary_search_by(|x
| if pred(x
) { Less }
else { Greater }
).unwrap_or_else(|i
| i
)
3475 trait CloneFromSpec
<T
> {
3476 fn spec_clone_from(&mut self, src
: &[T
]);
3479 impl<T
> CloneFromSpec
<T
> for [T
]
3483 default fn spec_clone_from(&mut self, src
: &[T
]) {
3484 assert
!(self.len() == src
.len(), "destination and source slices have different lengths");
3485 // NOTE: We need to explicitly slice them to the same length
3486 // to make it easier for the optimizer to elide bounds checking.
3487 // But since it can't be relied on we also have an explicit specialization for T: Copy.
3488 let len
= self.len();
3489 let src
= &src
[..len
];
3491 self[i
].clone_from(&src
[i
]);
3496 impl<T
> CloneFromSpec
<T
> for [T
]
3500 fn spec_clone_from(&mut self, src
: &[T
]) {
3501 self.copy_from_slice(src
);
3505 #[stable(feature = "rust1", since = "1.0.0")]
3506 impl<T
> Default
for &[T
] {
3507 /// Creates an empty slice.
3508 fn default() -> Self {
3513 #[stable(feature = "mut_slice_default", since = "1.5.0")]
3514 impl<T
> Default
for &mut [T
] {
3515 /// Creates a mutable empty slice.
3516 fn default() -> Self {
3521 #[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
3522 /// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future
3523 /// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
3524 /// `str`) to slices, and then this trait will be replaced or abolished.
3525 pub trait SlicePattern
{
3526 /// The element type of the slice being matched on.
3529 /// Currently, the consumers of `SlicePattern` need a slice.
3530 fn as_slice(&self) -> &[Self::Item
];
3533 #[stable(feature = "slice_strip", since = "1.51.0")]
3534 impl<T
> SlicePattern
for [T
] {
3538 fn as_slice(&self) -> &[Self::Item
] {
3543 #[stable(feature = "slice_strip", since = "1.51.0")]
3544 impl<T
, const N
: usize> SlicePattern
for [T
; N
] {
3548 fn as_slice(&self) -> &[Self::Item
] {