diff options
| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
| commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
| tree | 173a775858bd501c378080a10dca74132f05bc50 /library/core/src/slice/mod.rs | |
| parent | Initial commit. (diff) | |
| download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip | |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'library/core/src/slice/mod.rs')
| -rw-r--r-- | library/core/src/slice/mod.rs | 4244 |
1 files changed, 4244 insertions, 0 deletions
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs new file mode 100644 index 000000000..e6ca6ef82 --- /dev/null +++ b/library/core/src/slice/mod.rs @@ -0,0 +1,4244 @@ +//! Slice management and manipulation. +//! +//! For more details see [`std::slice`]. +//! +//! [`std::slice`]: ../../std/slice/index.html + +#![stable(feature = "rust1", since = "1.0.0")] + +use crate::cmp::Ordering::{self, Greater, Less}; +use crate::intrinsics::{assert_unsafe_precondition, exact_div}; +use crate::marker::Copy; +use crate::mem; +use crate::num::NonZeroUsize; +use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds}; +use crate::option::Option; +use crate::option::Option::{None, Some}; +use crate::ptr; +use crate::result::Result; +use crate::result::Result::{Err, Ok}; +use crate::simd::{self, Simd}; +use crate::slice; + +#[unstable( + feature = "slice_internals", + issue = "none", + reason = "exposed from core to be reused in std; use the memchr crate" +)] +/// Pure rust memchr implementation, taken from rust-memchr +pub mod memchr; + +mod ascii; +mod cmp; +mod index; +mod iter; +mod raw; +mod rotate; +mod sort; +mod specialize; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use iter::{Chunks, ChunksMut, Windows}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use iter::{Iter, IterMut}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut}; + +#[stable(feature = "slice_rsplit", since = "1.27.0")] +pub use iter::{RSplit, RSplitMut}; + +#[stable(feature = "chunks_exact", since = "1.31.0")] +pub use iter::{ChunksExact, ChunksExactMut}; + +#[stable(feature = "rchunks", since = "1.31.0")] +pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut}; + +#[unstable(feature = "array_chunks", issue = "74985")] +pub use iter::{ArrayChunks, ArrayChunksMut}; + +#[unstable(feature = "array_windows", issue = "75027")] +pub use iter::ArrayWindows; + +#[unstable(feature = "slice_group_by", issue = "80552")] +pub use iter::{GroupBy, GroupByMut}; + +#[stable(feature = "split_inclusive", since = "1.51.0")] +pub use iter::{SplitInclusive, SplitInclusiveMut}; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use raw::{from_raw_parts, from_raw_parts_mut}; + +#[stable(feature = "from_ref", since = "1.28.0")] +pub use raw::{from_mut, from_ref}; + +#[unstable(feature = "slice_from_ptr_range", issue = "89792")] +pub use raw::{from_mut_ptr_range, from_ptr_range}; + +// This function is public only because there is no other way to unit test heapsort. +#[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")] +pub use sort::heapsort; + +#[stable(feature = "slice_get_slice", since = "1.28.0")] +pub use index::SliceIndex; + +#[unstable(feature = "slice_range", issue = "76393")] +pub use index::range; + +#[stable(feature = "inherent_ascii_escape", since = "1.60.0")] +pub use ascii::EscapeAscii; + +/// Calculates the direction and split point of a one-sided range. +/// +/// This is a helper function for `take` and `take_mut` that returns +/// the direction of the split (front or back) as well as the index at +/// which to split. Returns `None` if the split index would overflow. +#[inline] +fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> { + use Bound::*; + + Some(match (range.start_bound(), range.end_bound()) { + (Unbounded, Excluded(i)) => (Direction::Front, *i), + (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?), + (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?), + (Included(i), Unbounded) => (Direction::Back, *i), + _ => unreachable!(), + }) +} + +enum Direction { + Front, + Back, +} + +#[cfg(not(test))] +impl<T> [T] { + /// Returns the number of elements in the slice. + /// + /// # Examples + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert_eq!(a.len(), 3); + /// ``` + #[lang = "slice_len_fn"] + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")] + #[inline] + #[must_use] + // SAFETY: const sound because we transmute out the length field as a usize (which it must be) + pub const fn len(&self) -> usize { + // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable. + // As of this writing this causes a "Const-stable functions can only call other + // const-stable functions" error. + + // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T + // and PtrComponents<T> have the same memory layouts. Only std can make this + // guarantee. + unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata } + } + + /// Returns `true` if the slice has a length of 0. + /// + /// # Examples + /// + /// ``` + /// let a = [1, 2, 3]; + /// assert!(!a.is_empty()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")] + #[inline] + #[must_use] + pub const fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// Returns the first element of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert_eq!(Some(&10), v.first()); + /// + /// let w: &[i32] = &[]; + /// assert_eq!(None, w.first()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")] + #[inline] + #[must_use] + pub const fn first(&self) -> Option<&T> { + if let [first, ..] = self { Some(first) } else { None } + } + + /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [0, 1, 2]; + /// + /// if let Some(first) = x.first_mut() { + /// *first = 5; + /// } + /// assert_eq!(x, &[5, 1, 2]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")] + #[inline] + #[must_use] + pub const fn first_mut(&mut self) -> Option<&mut T> { + if let [first, ..] = self { Some(first) } else { None } + } + + /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let x = &[0, 1, 2]; + /// + /// if let Some((first, elements)) = x.split_first() { + /// assert_eq!(first, &0); + /// assert_eq!(elements, &[1, 2]); + /// } + /// ``` + #[stable(feature = "slice_splits", since = "1.5.0")] + #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")] + #[inline] + #[must_use] + pub const fn split_first(&self) -> Option<(&T, &[T])> { + if let [first, tail @ ..] = self { Some((first, tail)) } else { None } + } + + /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [0, 1, 2]; + /// + /// if let Some((first, elements)) = x.split_first_mut() { + /// *first = 3; + /// elements[0] = 4; + /// elements[1] = 5; + /// } + /// assert_eq!(x, &[3, 4, 5]); + /// ``` + #[stable(feature = "slice_splits", since = "1.5.0")] + #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")] + #[inline] + #[must_use] + pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> { + if let [first, tail @ ..] = self { Some((first, tail)) } else { None } + } + + /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let x = &[0, 1, 2]; + /// + /// if let Some((last, elements)) = x.split_last() { + /// assert_eq!(last, &2); + /// assert_eq!(elements, &[0, 1]); + /// } + /// ``` + #[stable(feature = "slice_splits", since = "1.5.0")] + #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")] + #[inline] + #[must_use] + pub const fn split_last(&self) -> Option<(&T, &[T])> { + if let [init @ .., last] = self { Some((last, init)) } else { None } + } + + /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [0, 1, 2]; + /// + /// if let Some((last, elements)) = x.split_last_mut() { + /// *last = 3; + /// elements[0] = 4; + /// elements[1] = 5; + /// } + /// assert_eq!(x, &[4, 5, 3]); + /// ``` + #[stable(feature = "slice_splits", since = "1.5.0")] + #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")] + #[inline] + #[must_use] + pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> { + if let [init @ .., last] = self { Some((last, init)) } else { None } + } + + /// Returns the last element of the slice, or `None` if it is empty. + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert_eq!(Some(&30), v.last()); + /// + /// let w: &[i32] = &[]; + /// assert_eq!(None, w.last()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")] + #[inline] + #[must_use] + pub const fn last(&self) -> Option<&T> { + if let [.., last] = self { Some(last) } else { None } + } + + /// Returns a mutable pointer to the last item in the slice. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [0, 1, 2]; + /// + /// if let Some(last) = x.last_mut() { + /// *last = 10; + /// } + /// assert_eq!(x, &[0, 1, 10]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")] + #[inline] + #[must_use] + pub const fn last_mut(&mut self) -> Option<&mut T> { + if let [.., last] = self { Some(last) } else { None } + } + + /// Returns a reference to an element or subslice depending on the type of + /// index. + /// + /// - If given a position, returns a reference to the element at that + /// position or `None` if out of bounds. + /// - If given a range, returns the subslice corresponding to that range, + /// or `None` if out of bounds. + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert_eq!(Some(&40), v.get(1)); + /// assert_eq!(Some(&[10, 40][..]), v.get(0..2)); + /// assert_eq!(None, v.get(3)); + /// assert_eq!(None, v.get(0..4)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_index", issue = "none")] + #[inline] + #[must_use] + pub const fn get<I>(&self, index: I) -> Option<&I::Output> + where + I: ~const SliceIndex<Self>, + { + index.get(self) + } + + /// Returns a mutable reference to an element or subslice depending on the + /// type of index (see [`get`]) or `None` if the index is out of bounds. + /// + /// [`get`]: slice::get + /// + /// # Examples + /// + /// ``` + /// let x = &mut [0, 1, 2]; + /// + /// if let Some(elem) = x.get_mut(1) { + /// *elem = 42; + /// } + /// assert_eq!(x, &[0, 42, 2]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_index", issue = "none")] + #[inline] + #[must_use] + pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output> + where + I: ~const SliceIndex<Self>, + { + index.get_mut(self) + } + + /// Returns a reference to an element or subslice, without doing bounds + /// checking. + /// + /// For a safe alternative see [`get`]. + /// + /// # Safety + /// + /// Calling this method with an out-of-bounds index is *[undefined behavior]* + /// even if the resulting reference is not used. + /// + /// [`get`]: slice::get + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// let x = &[1, 2, 4]; + /// + /// unsafe { + /// assert_eq!(x.get_unchecked(1), &2); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_index", issue = "none")] + #[inline] + #[must_use] + pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output + where + I: ~const SliceIndex<Self>, + { + // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`; + // the slice is dereferenceable because `self` is a safe reference. + // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is. + unsafe { &*index.get_unchecked(self) } + } + + /// Returns a mutable reference to an element or subslice, without doing + /// bounds checking. + /// + /// For a safe alternative see [`get_mut`]. + /// + /// # Safety + /// + /// Calling this method with an out-of-bounds index is *[undefined behavior]* + /// even if the resulting reference is not used. + /// + /// [`get_mut`]: slice::get_mut + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// let x = &mut [1, 2, 4]; + /// + /// unsafe { + /// let elem = x.get_unchecked_mut(1); + /// *elem = 13; + /// } + /// assert_eq!(x, &[1, 13, 4]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_slice_index", issue = "none")] + #[inline] + #[must_use] + pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output + where + I: ~const SliceIndex<Self>, + { + // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`; + // the slice is dereferenceable because `self` is a safe reference. + // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is. + unsafe { &mut *index.get_unchecked_mut(self) } + } + + /// Returns a raw pointer to the slice's buffer. + /// + /// The caller must ensure that the slice outlives the pointer this + /// function returns, or else it will end up pointing to garbage. + /// + /// The caller must also ensure that the memory the pointer (non-transitively) points to + /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer + /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`]. + /// + /// Modifying the container referenced by this slice may cause its buffer + /// to be reallocated, which would also make any pointers to it invalid. + /// + /// # Examples + /// + /// ``` + /// let x = &[1, 2, 4]; + /// let x_ptr = x.as_ptr(); + /// + /// unsafe { + /// for i in 0..x.len() { + /// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i)); + /// } + /// } + /// ``` + /// + /// [`as_mut_ptr`]: slice::as_mut_ptr + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")] + #[inline] + #[must_use] + pub const fn as_ptr(&self) -> *const T { + self as *const [T] as *const T + } + + /// Returns an unsafe mutable pointer to the slice's buffer. + /// + /// The caller must ensure that the slice outlives the pointer this + /// function returns, or else it will end up pointing to garbage. + /// + /// Modifying the container referenced by this slice may cause its buffer + /// to be reallocated, which would also make any pointers to it invalid. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [1, 2, 4]; + /// let x_ptr = x.as_mut_ptr(); + /// + /// unsafe { + /// for i in 0..x.len() { + /// *x_ptr.add(i) += 2; + /// } + /// } + /// assert_eq!(x, &[3, 4, 6]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] + #[rustc_allow_const_fn_unstable(const_mut_refs)] + #[inline] + #[must_use] + pub const fn as_mut_ptr(&mut self) -> *mut T { + self as *mut [T] as *mut T + } + + /// Returns the two raw pointers spanning the slice. + /// + /// The returned range is half-open, which means that the end pointer + /// points *one past* the last element of the slice. This way, an empty + /// slice is represented by two equal pointers, and the difference between + /// the two pointers represents the size of the slice. + /// + /// See [`as_ptr`] for warnings on using these pointers. The end pointer + /// requires extra caution, as it does not point to a valid element in the + /// slice. + /// + /// This function is useful for interacting with foreign interfaces which + /// use two pointers to refer to a range of elements in memory, as is + /// common in C++. + /// + /// It can also be useful to check if a pointer to an element refers to an + /// element of this slice: + /// + /// ``` + /// let a = [1, 2, 3]; + /// let x = &a[1] as *const _; + /// let y = &5 as *const _; + /// + /// assert!(a.as_ptr_range().contains(&x)); + /// assert!(!a.as_ptr_range().contains(&y)); + /// ``` + /// + /// [`as_ptr`]: slice::as_ptr + #[stable(feature = "slice_ptr_range", since = "1.48.0")] + #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] + #[inline] + #[must_use] + pub const fn as_ptr_range(&self) -> Range<*const T> { + let start = self.as_ptr(); + // SAFETY: The `add` here is safe, because: + // + // - Both pointers are part of the same object, as pointing directly + // past the object also counts. + // + // - The size of the slice is never larger than isize::MAX bytes, as + // noted here: + // - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447 + // - https://doc.rust-lang.org/reference/behavior-considered-undefined.html + // - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety + // (This doesn't seem normative yet, but the very same assumption is + // made in many places, including the Index implementation of slices.) + // + // - There is no wrapping around involved, as slices do not wrap past + // the end of the address space. + // + // See the documentation of pointer::add. + let end = unsafe { start.add(self.len()) }; + start..end + } + + /// Returns the two unsafe mutable pointers spanning the slice. + /// + /// The returned range is half-open, which means that the end pointer + /// points *one past* the last element of the slice. This way, an empty + /// slice is represented by two equal pointers, and the difference between + /// the two pointers represents the size of the slice. + /// + /// See [`as_mut_ptr`] for warnings on using these pointers. The end + /// pointer requires extra caution, as it does not point to a valid element + /// in the slice. + /// + /// This function is useful for interacting with foreign interfaces which + /// use two pointers to refer to a range of elements in memory, as is + /// common in C++. + /// + /// [`as_mut_ptr`]: slice::as_mut_ptr + #[stable(feature = "slice_ptr_range", since = "1.48.0")] + #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] + #[rustc_allow_const_fn_unstable(const_mut_refs)] + #[inline] + #[must_use] + pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> { + let start = self.as_mut_ptr(); + // SAFETY: See as_ptr_range() above for why `add` here is safe. + let end = unsafe { start.add(self.len()) }; + start..end + } + + /// Swaps two elements in the slice. + /// + /// # Arguments + /// + /// * a - The index of the first element + /// * b - The index of the second element + /// + /// # Panics + /// + /// Panics if `a` or `b` are out of bounds. + /// + /// # Examples + /// + /// ``` + /// let mut v = ["a", "b", "c", "d", "e"]; + /// v.swap(2, 4); + /// assert!(v == ["a", "b", "e", "d", "c"]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_unstable(feature = "const_swap", issue = "83163")] + #[inline] + #[track_caller] + pub const fn swap(&mut self, a: usize, b: usize) { + // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343) + // Can't take two mutable loans from one vector, so instead use raw pointers. + let pa = ptr::addr_of_mut!(self[a]); + let pb = ptr::addr_of_mut!(self[b]); + // SAFETY: `pa` and `pb` have been created from safe mutable references and refer + // to elements in the slice and therefore are guaranteed to be valid and aligned. + // Note that accessing the elements behind `a` and `b` is checked and will + // panic when out of bounds. + unsafe { + ptr::swap(pa, pb); + } + } + + /// Swaps two elements in the slice, without doing bounds checking. + /// + /// For a safe alternative see [`swap`]. + /// + /// # Arguments + /// + /// * a - The index of the first element + /// * b - The index of the second element + /// + /// # Safety + /// + /// Calling this method with an out-of-bounds index is *[undefined behavior]*. + /// The caller has to ensure that `a < self.len()` and `b < self.len()`. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_swap_unchecked)] + /// + /// let mut v = ["a", "b", "c", "d"]; + /// // SAFETY: we know that 1 and 3 are both indices of the slice + /// unsafe { v.swap_unchecked(1, 3) }; + /// assert!(v == ["a", "d", "c", "b"]); + /// ``` + /// + /// [`swap`]: slice::swap + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + #[unstable(feature = "slice_swap_unchecked", issue = "88539")] + #[rustc_const_unstable(feature = "const_swap", issue = "83163")] + pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) { + let ptr = self.as_mut_ptr(); + // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()` + unsafe { + assert_unsafe_precondition!(a < self.len() && b < self.len()); + ptr::swap(ptr.add(a), ptr.add(b)); + } + } + + /// Reverses the order of elements in the slice, in place. + /// + /// # Examples + /// + /// ``` + /// let mut v = [1, 2, 3]; + /// v.reverse(); + /// assert!(v == [3, 2, 1]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn reverse(&mut self) { + let half_len = self.len() / 2; + let Range { start, end } = self.as_mut_ptr_range(); + + // These slices will skip the middle item for an odd length, + // since that one doesn't need to move. + let (front_half, back_half) = + // SAFETY: Both are subparts of the original slice, so the memory + // range is valid, and they don't overlap because they're each only + // half (or less) of the original slice. + unsafe { + ( + slice::from_raw_parts_mut(start, half_len), + slice::from_raw_parts_mut(end.sub(half_len), half_len), + ) + }; + + // Introducing a function boundary here means that the two halves + // get `noalias` markers, allowing better optimization as LLVM + // knows that they're disjoint, unlike in the original slice. + revswap(front_half, back_half, half_len); + + #[inline] + fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) { + debug_assert_eq!(a.len(), n); + debug_assert_eq!(b.len(), n); + + // Because this function is first compiled in isolation, + // this check tells LLVM that the indexing below is + // in-bounds. Then after inlining -- once the actual + // lengths of the slices are known -- it's removed. + let (a, b) = (&mut a[..n], &mut b[..n]); + + for i in 0..n { + mem::swap(&mut a[i], &mut b[n - 1 - i]); + } + } + } + + /// Returns an iterator over the slice. + /// + /// The iterator yields all items from start to end. + /// + /// # Examples + /// + /// ``` + /// let x = &[1, 2, 4]; + /// let mut iterator = x.iter(); + /// + /// assert_eq!(iterator.next(), Some(&1)); + /// assert_eq!(iterator.next(), Some(&2)); + /// assert_eq!(iterator.next(), Some(&4)); + /// assert_eq!(iterator.next(), None); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn iter(&self) -> Iter<'_, T> { + Iter::new(self) + } + + /// Returns an iterator that allows modifying each value. + /// + /// The iterator yields all items from start to end. + /// + /// # Examples + /// + /// ``` + /// let x = &mut [1, 2, 4]; + /// for elem in x.iter_mut() { + /// *elem += 2; + /// } + /// assert_eq!(x, &[3, 4, 6]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn iter_mut(&mut self) -> IterMut<'_, T> { + IterMut::new(self) + } + + /// Returns an iterator over all contiguous windows of length + /// `size`. The windows overlap. If the slice is shorter than + /// `size`, the iterator returns no values. + /// + /// # Panics + /// + /// Panics if `size` is 0. + /// + /// # Examples + /// + /// ``` + /// let slice = ['r', 'u', 's', 't']; + /// let mut iter = slice.windows(2); + /// assert_eq!(iter.next().unwrap(), &['r', 'u']); + /// assert_eq!(iter.next().unwrap(), &['u', 's']); + /// assert_eq!(iter.next().unwrap(), &['s', 't']); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// If the slice is shorter than `size`: + /// + /// ``` + /// let slice = ['f', 'o', 'o']; + /// let mut iter = slice.windows(4); + /// assert!(iter.next().is_none()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn windows(&self, size: usize) -> Windows<'_, T> { + let size = NonZeroUsize::new(size).expect("size is zero"); + Windows::new(self, size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the + /// slice, then the last chunk will not have length `chunk_size`. + /// + /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly + /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the + /// slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let mut iter = slice.chunks(2); + /// assert_eq!(iter.next().unwrap(), &['l', 'o']); + /// assert_eq!(iter.next().unwrap(), &['r', 'e']); + /// assert_eq!(iter.next().unwrap(), &['m']); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// [`chunks_exact`]: slice::chunks_exact + /// [`rchunks`]: slice::rchunks + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> { + assert_ne!(chunk_size, 0, "chunks cannot have a size of zero"); + Chunks::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the + /// length of the slice, then the last chunk will not have length `chunk_size`. + /// + /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always + /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at + /// the end of the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// for chunk in v.chunks_mut(2) { + /// for elem in chunk.iter_mut() { + /// *elem += count; + /// } + /// count += 1; + /// } + /// assert_eq!(v, &[1, 1, 2, 2, 3]); + /// ``` + /// + /// [`chunks_exact_mut`]: slice::chunks_exact_mut + /// [`rchunks_mut`]: slice::rchunks_mut + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> { + assert_ne!(chunk_size, 0, "chunks cannot have a size of zero"); + ChunksMut::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the + /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved + /// from the `remainder` function of the iterator. + /// + /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the + /// resulting code better than in the case of [`chunks`]. + /// + /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller + /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let mut iter = slice.chunks_exact(2); + /// assert_eq!(iter.next().unwrap(), &['l', 'o']); + /// assert_eq!(iter.next().unwrap(), &['r', 'e']); + /// assert!(iter.next().is_none()); + /// assert_eq!(iter.remainder(), &['m']); + /// ``` + /// + /// [`chunks`]: slice::chunks + /// [`rchunks_exact`]: slice::rchunks_exact + #[stable(feature = "chunks_exact", since = "1.31.0")] + #[inline] + pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> { + assert_ne!(chunk_size, 0); + ChunksExact::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the + /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be + /// retrieved from the `into_remainder` function of the iterator. + /// + /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the + /// resulting code better than in the case of [`chunks_mut`]. + /// + /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a + /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of + /// the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// for chunk in v.chunks_exact_mut(2) { + /// for elem in chunk.iter_mut() { + /// *elem += count; + /// } + /// count += 1; + /// } + /// assert_eq!(v, &[1, 1, 2, 2, 0]); + /// ``` + /// + /// [`chunks_mut`]: slice::chunks_mut + /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut + #[stable(feature = "chunks_exact", since = "1.31.0")] + #[inline] + pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> { + assert_ne!(chunk_size, 0); + ChunksExactMut::new(self, chunk_size) + } + + /// Splits the slice into a slice of `N`-element arrays, + /// assuming that there's no remainder. + /// + /// # Safety + /// + /// This may only be called when + /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`). + /// - `N != 0`. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!']; + /// let chunks: &[[char; 1]] = + /// // SAFETY: 1-element chunks never have remainder + /// unsafe { slice.as_chunks_unchecked() }; + /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]); + /// let chunks: &[[char; 3]] = + /// // SAFETY: The slice length (6) is a multiple of 3 + /// unsafe { slice.as_chunks_unchecked() }; + /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]); + /// + /// // These would be unsound: + /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5 + /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] { + // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length + let new_len = unsafe { + assert_unsafe_precondition!(N != 0 && self.len() % N == 0); + exact_div(self.len(), N) + }; + // SAFETY: We cast a slice of `new_len * N` elements into + // a slice of `new_len` many `N` elements chunks. + unsafe { from_raw_parts(self.as_ptr().cast(), new_len) } + } + + /// Splits the slice into a slice of `N`-element arrays, + /// starting at the beginning of the slice, + /// and a remainder slice with length strictly less than `N`. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let (chunks, remainder) = slice.as_chunks(); + /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]); + /// assert_eq!(remainder, &['m']); + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) { + assert_ne!(N, 0); + let len = self.len() / N; + let (multiple_of_n, remainder) = self.split_at(len * N); + // SAFETY: We already panicked for zero, and ensured by construction + // that the length of the subslice is a multiple of N. + let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() }; + (array_slice, remainder) + } + + /// Splits the slice into a slice of `N`-element arrays, + /// starting at the end of the slice, + /// and a remainder slice with length strictly less than `N`. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let (remainder, chunks) = slice.as_rchunks(); + /// assert_eq!(remainder, &['l']); + /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]); + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) { + assert_ne!(N, 0); + let len = self.len() / N; + let (remainder, multiple_of_n) = self.split_at(self.len() - len * N); + // SAFETY: We already panicked for zero, and ensured by construction + // that the length of the subslice is a multiple of N. + let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() }; + (remainder, array_slice) + } + + /// Returns an iterator over `N` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are array references and do not overlap. If `N` does not divide the + /// length of the slice, then the last up to `N-1` elements will be omitted and can be + /// retrieved from the `remainder` function of the iterator. + /// + /// This method is the const generic equivalent of [`chunks_exact`]. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_chunks)] + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let mut iter = slice.array_chunks(); + /// assert_eq!(iter.next().unwrap(), &['l', 'o']); + /// assert_eq!(iter.next().unwrap(), &['r', 'e']); + /// assert!(iter.next().is_none()); + /// assert_eq!(iter.remainder(), &['m']); + /// ``` + /// + /// [`chunks_exact`]: slice::chunks_exact + #[unstable(feature = "array_chunks", issue = "74985")] + #[inline] + pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> { + assert_ne!(N, 0); + ArrayChunks::new(self) + } + + /// Splits the slice into a slice of `N`-element arrays, + /// assuming that there's no remainder. + /// + /// # Safety + /// + /// This may only be called when + /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`). + /// - `N != 0`. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!']; + /// let chunks: &mut [[char; 1]] = + /// // SAFETY: 1-element chunks never have remainder + /// unsafe { slice.as_chunks_unchecked_mut() }; + /// chunks[0] = ['L']; + /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]); + /// let chunks: &mut [[char; 3]] = + /// // SAFETY: The slice length (6) is a multiple of 3 + /// unsafe { slice.as_chunks_unchecked_mut() }; + /// chunks[1] = ['a', 'x', '?']; + /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']); + /// + /// // These would be unsound: + /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5 + /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] { + // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length + let new_len = unsafe { + assert_unsafe_precondition!(N != 0 && self.len() % N == 0); + exact_div(self.len(), N) + }; + // SAFETY: We cast a slice of `new_len * N` elements into + // a slice of `new_len` many `N` elements chunks. + unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) } + } + + /// Splits the slice into a slice of `N`-element arrays, + /// starting at the beginning of the slice, + /// and a remainder slice with length strictly less than `N`. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// let (chunks, remainder) = v.as_chunks_mut(); + /// remainder[0] = 9; + /// for chunk in chunks { + /// *chunk = [count; 2]; + /// count += 1; + /// } + /// assert_eq!(v, &[1, 1, 2, 2, 9]); + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) { + assert_ne!(N, 0); + let len = self.len() / N; + let (multiple_of_n, remainder) = self.split_at_mut(len * N); + // SAFETY: We already panicked for zero, and ensured by construction + // that the length of the subslice is a multiple of N. + let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() }; + (array_slice, remainder) + } + + /// Splits the slice into a slice of `N`-element arrays, + /// starting at the end of the slice, + /// and a remainder slice with length strictly less than `N`. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_as_chunks)] + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// let (remainder, chunks) = v.as_rchunks_mut(); + /// remainder[0] = 9; + /// for chunk in chunks { + /// *chunk = [count; 2]; + /// count += 1; + /// } + /// assert_eq!(v, &[9, 1, 1, 2, 2]); + /// ``` + #[unstable(feature = "slice_as_chunks", issue = "74985")] + #[inline] + #[must_use] + pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) { + assert_ne!(N, 0); + let len = self.len() / N; + let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N); + // SAFETY: We already panicked for zero, and ensured by construction + // that the length of the subslice is a multiple of N. + let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() }; + (remainder, array_slice) + } + + /// Returns an iterator over `N` elements of the slice at a time, starting at the + /// beginning of the slice. + /// + /// The chunks are mutable array references and do not overlap. If `N` does not divide + /// the length of the slice, then the last up to `N-1` elements will be omitted and + /// can be retrieved from the `into_remainder` function of the iterator. + /// + /// This method is the const generic equivalent of [`chunks_exact_mut`]. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_chunks)] + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// for chunk in v.array_chunks_mut() { + /// *chunk = [count; 2]; + /// count += 1; + /// } + /// assert_eq!(v, &[1, 1, 2, 2, 0]); + /// ``` + /// + /// [`chunks_exact_mut`]: slice::chunks_exact_mut + #[unstable(feature = "array_chunks", issue = "74985")] + #[inline] + pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> { + assert_ne!(N, 0); + ArrayChunksMut::new(self) + } + + /// Returns an iterator over overlapping windows of `N` elements of a slice, + /// starting at the beginning of the slice. + /// + /// This is the const generic equivalent of [`windows`]. + /// + /// If `N` is greater than the size of the slice, it will return no windows. + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a compile time + /// error before this method gets stabilized. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_windows)] + /// let slice = [0, 1, 2, 3]; + /// let mut iter = slice.array_windows(); + /// assert_eq!(iter.next().unwrap(), &[0, 1]); + /// assert_eq!(iter.next().unwrap(), &[1, 2]); + /// assert_eq!(iter.next().unwrap(), &[2, 3]); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// [`windows`]: slice::windows + #[unstable(feature = "array_windows", issue = "75027")] + #[inline] + pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> { + assert_ne!(N, 0); + ArrayWindows::new(self) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end + /// of the slice. + /// + /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the + /// slice, then the last chunk will not have length `chunk_size`. + /// + /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly + /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning + /// of the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let mut iter = slice.rchunks(2); + /// assert_eq!(iter.next().unwrap(), &['e', 'm']); + /// assert_eq!(iter.next().unwrap(), &['o', 'r']); + /// assert_eq!(iter.next().unwrap(), &['l']); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// [`rchunks_exact`]: slice::rchunks_exact + /// [`chunks`]: slice::chunks + #[stable(feature = "rchunks", since = "1.31.0")] + #[inline] + pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> { + assert!(chunk_size != 0); + RChunks::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end + /// of the slice. + /// + /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the + /// length of the slice, then the last chunk will not have length `chunk_size`. + /// + /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always + /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the + /// beginning of the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// for chunk in v.rchunks_mut(2) { + /// for elem in chunk.iter_mut() { + /// *elem += count; + /// } + /// count += 1; + /// } + /// assert_eq!(v, &[3, 2, 2, 1, 1]); + /// ``` + /// + /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut + /// [`chunks_mut`]: slice::chunks_mut + #[stable(feature = "rchunks", since = "1.31.0")] + #[inline] + pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> { + assert!(chunk_size != 0); + RChunksMut::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the + /// end of the slice. + /// + /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the + /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved + /// from the `remainder` function of the iterator. + /// + /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the + /// resulting code better than in the case of [`rchunks`]. + /// + /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller + /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the + /// slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let slice = ['l', 'o', 'r', 'e', 'm']; + /// let mut iter = slice.rchunks_exact(2); + /// assert_eq!(iter.next().unwrap(), &['e', 'm']); + /// assert_eq!(iter.next().unwrap(), &['o', 'r']); + /// assert!(iter.next().is_none()); + /// assert_eq!(iter.remainder(), &['l']); + /// ``` + /// + /// [`chunks`]: slice::chunks + /// [`rchunks`]: slice::rchunks + /// [`chunks_exact`]: slice::chunks_exact + #[stable(feature = "rchunks", since = "1.31.0")] + #[inline] + pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> { + assert!(chunk_size != 0); + RChunksExact::new(self, chunk_size) + } + + /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end + /// of the slice. + /// + /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the + /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be + /// retrieved from the `into_remainder` function of the iterator. + /// + /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the + /// resulting code better than in the case of [`chunks_mut`]. + /// + /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a + /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning + /// of the slice. + /// + /// # Panics + /// + /// Panics if `chunk_size` is 0. + /// + /// # Examples + /// + /// ``` + /// let v = &mut [0, 0, 0, 0, 0]; + /// let mut count = 1; + /// + /// for chunk in v.rchunks_exact_mut(2) { + /// for elem in chunk.iter_mut() { + /// *elem += count; + /// } + /// count += 1; + /// } + /// assert_eq!(v, &[0, 2, 2, 1, 1]); + /// ``` + /// + /// [`chunks_mut`]: slice::chunks_mut + /// [`rchunks_mut`]: slice::rchunks_mut + /// [`chunks_exact_mut`]: slice::chunks_exact_mut + #[stable(feature = "rchunks", since = "1.31.0")] + #[inline] + pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> { + assert!(chunk_size != 0); + RChunksExactMut::new(self, chunk_size) + } + + /// Returns an iterator over the slice producing non-overlapping runs + /// of elements using the predicate to separate them. + /// + /// The predicate is called on two elements following themselves, + /// it means the predicate is called on `slice[0]` and `slice[1]` + /// then on `slice[1]` and `slice[2]` and so on. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_group_by)] + /// + /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2]; + /// + /// let mut iter = slice.group_by(|a, b| a == b); + /// + /// assert_eq!(iter.next(), Some(&[1, 1, 1][..])); + /// assert_eq!(iter.next(), Some(&[3, 3][..])); + /// assert_eq!(iter.next(), Some(&[2, 2, 2][..])); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// This method can be used to extract the sorted subslices: + /// + /// ``` + /// #![feature(slice_group_by)] + /// + /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4]; + /// + /// let mut iter = slice.group_by(|a, b| a <= b); + /// + /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..])); + /// assert_eq!(iter.next(), Some(&[2, 3][..])); + /// assert_eq!(iter.next(), Some(&[2, 3, 4][..])); + /// assert_eq!(iter.next(), None); + /// ``` + #[unstable(feature = "slice_group_by", issue = "80552")] + #[inline] + pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F> + where + F: FnMut(&T, &T) -> bool, + { + GroupBy::new(self, pred) + } + + /// Returns an iterator over the slice producing non-overlapping mutable + /// runs of elements using the predicate to separate them. + /// + /// The predicate is called on two elements following themselves, + /// it means the predicate is called on `slice[0]` and `slice[1]` + /// then on `slice[1]` and `slice[2]` and so on. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_group_by)] + /// + /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2]; + /// + /// let mut iter = slice.group_by_mut(|a, b| a == b); + /// + /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..])); + /// assert_eq!(iter.next(), Some(&mut [3, 3][..])); + /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..])); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// This method can be used to extract the sorted subslices: + /// + /// ``` + /// #![feature(slice_group_by)] + /// + /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4]; + /// + /// let mut iter = slice.group_by_mut(|a, b| a <= b); + /// + /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..])); + /// assert_eq!(iter.next(), Some(&mut [2, 3][..])); + /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..])); + /// assert_eq!(iter.next(), None); + /// ``` + #[unstable(feature = "slice_group_by", issue = "80552")] + #[inline] + pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F> + where + F: FnMut(&T, &T) -> bool, + { + GroupByMut::new(self, pred) + } + + /// Divides one slice into two at an index. + /// + /// The first will contain all indices from `[0, mid)` (excluding + /// the index `mid` itself) and the second will contain all + /// indices from `[mid, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `mid > len`. + /// + /// # Examples + /// + /// ``` + /// let v = [1, 2, 3, 4, 5, 6]; + /// + /// { + /// let (left, right) = v.split_at(0); + /// assert_eq!(left, []); + /// assert_eq!(right, [1, 2, 3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_at(2); + /// assert_eq!(left, [1, 2]); + /// assert_eq!(right, [3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_at(6); + /// assert_eq!(left, [1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, []); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + #[track_caller] + #[must_use] + pub fn split_at(&self, mid: usize) -> (&[T], &[T]) { + assert!(mid <= self.len()); + // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which + // fulfills the requirements of `from_raw_parts_mut`. + unsafe { self.split_at_unchecked(mid) } + } + + /// Divides one mutable slice into two at an index. + /// + /// The first will contain all indices from `[0, mid)` (excluding + /// the index `mid` itself) and the second will contain all + /// indices from `[mid, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `mid > len`. + /// + /// # Examples + /// + /// ``` + /// let mut v = [1, 0, 3, 0, 5, 6]; + /// let (left, right) = v.split_at_mut(2); + /// assert_eq!(left, [1, 0]); + /// assert_eq!(right, [3, 0, 5, 6]); + /// left[1] = 2; + /// right[1] = 4; + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + #[track_caller] + #[must_use] + pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) { + assert!(mid <= self.len()); + // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which + // fulfills the requirements of `from_raw_parts_mut`. + unsafe { self.split_at_mut_unchecked(mid) } + } + + /// Divides one slice into two at an index, without doing bounds checking. + /// + /// The first will contain all indices from `[0, mid)` (excluding + /// the index `mid` itself) and the second will contain all + /// indices from `[mid, len)` (excluding the index `len` itself). + /// + /// For a safe alternative see [`split_at`]. + /// + /// # Safety + /// + /// Calling this method with an out-of-bounds index is *[undefined behavior]* + /// even if the resulting reference is not used. The caller has to ensure that + /// `0 <= mid <= self.len()`. + /// + /// [`split_at`]: slice::split_at + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_split_at_unchecked)] + /// + /// let v = [1, 2, 3, 4, 5, 6]; + /// + /// unsafe { + /// let (left, right) = v.split_at_unchecked(0); + /// assert_eq!(left, []); + /// assert_eq!(right, [1, 2, 3, 4, 5, 6]); + /// } + /// + /// unsafe { + /// let (left, right) = v.split_at_unchecked(2); + /// assert_eq!(left, [1, 2]); + /// assert_eq!(right, [3, 4, 5, 6]); + /// } + /// + /// unsafe { + /// let (left, right) = v.split_at_unchecked(6); + /// assert_eq!(left, [1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, []); + /// } + /// ``` + #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")] + #[inline] + #[must_use] + pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) { + // SAFETY: Caller has to check that `0 <= mid <= self.len()` + unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) } + } + + /// Divides one mutable slice into two at an index, without doing bounds checking. + /// + /// The first will contain all indices from `[0, mid)` (excluding + /// the index `mid` itself) and the second will contain all + /// indices from `[mid, len)` (excluding the index `len` itself). + /// + /// For a safe alternative see [`split_at_mut`]. + /// + /// # Safety + /// + /// Calling this method with an out-of-bounds index is *[undefined behavior]* + /// even if the resulting reference is not used. The caller has to ensure that + /// `0 <= mid <= self.len()`. + /// + /// [`split_at_mut`]: slice::split_at_mut + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_split_at_unchecked)] + /// + /// let mut v = [1, 0, 3, 0, 5, 6]; + /// // scoped to restrict the lifetime of the borrows + /// unsafe { + /// let (left, right) = v.split_at_mut_unchecked(2); + /// assert_eq!(left, [1, 0]); + /// assert_eq!(right, [3, 0, 5, 6]); + /// left[1] = 2; + /// right[1] = 4; + /// } + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")] + #[inline] + #[must_use] + pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) { + let len = self.len(); + let ptr = self.as_mut_ptr(); + + // SAFETY: Caller has to check that `0 <= mid <= self.len()`. + // + // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference + // is fine. + unsafe { + assert_unsafe_precondition!(mid <= len); + (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) + } + } + + /// Divides one slice into an array and a remainder slice at an index. + /// + /// The array will contain all indices from `[0, N)` (excluding + /// the index `N` itself) and the slice will contain all + /// indices from `[N, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `N > len`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let v = &[1, 2, 3, 4, 5, 6][..]; + /// + /// { + /// let (left, right) = v.split_array_ref::<0>(); + /// assert_eq!(left, &[]); + /// assert_eq!(right, [1, 2, 3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_array_ref::<2>(); + /// assert_eq!(left, &[1, 2]); + /// assert_eq!(right, [3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_array_ref::<6>(); + /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, []); + /// } + /// ``` + #[unstable(feature = "split_array", reason = "new API", issue = "90091")] + #[inline] + #[track_caller] + #[must_use] + pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) { + let (a, b) = self.split_at(N); + // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at) + unsafe { (&*(a.as_ptr() as *const [T; N]), b) } + } + + /// Divides one mutable slice into an array and a remainder slice at an index. + /// + /// The array will contain all indices from `[0, N)` (excluding + /// the index `N` itself) and the slice will contain all + /// indices from `[N, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `N > len`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let mut v = &mut [1, 0, 3, 0, 5, 6][..]; + /// let (left, right) = v.split_array_mut::<2>(); + /// assert_eq!(left, &mut [1, 0]); + /// assert_eq!(right, [3, 0, 5, 6]); + /// left[1] = 2; + /// right[1] = 4; + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable(feature = "split_array", reason = "new API", issue = "90091")] + #[inline] + #[track_caller] + #[must_use] + pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) { + let (a, b) = self.split_at_mut(N); + // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut) + unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) } + } + + /// Divides one slice into an array and a remainder slice at an index from + /// the end. + /// + /// The slice will contain all indices from `[0, len - N)` (excluding + /// the index `len - N` itself) and the array will contain all + /// indices from `[len - N, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `N > len`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let v = &[1, 2, 3, 4, 5, 6][..]; + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<0>(); + /// assert_eq!(left, [1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, &[]); + /// } + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<2>(); + /// assert_eq!(left, [1, 2, 3, 4]); + /// assert_eq!(right, &[5, 6]); + /// } + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<6>(); + /// assert_eq!(left, []); + /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]); + /// } + /// ``` + #[unstable(feature = "split_array", reason = "new API", issue = "90091")] + #[inline] + #[must_use] + pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) { + assert!(N <= self.len()); + let (a, b) = self.split_at(self.len() - N); + // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at) + unsafe { (a, &*(b.as_ptr() as *const [T; N])) } + } + + /// Divides one mutable slice into an array and a remainder slice at an + /// index from the end. + /// + /// The slice will contain all indices from `[0, len - N)` (excluding + /// the index `N` itself) and the array will contain all + /// indices from `[len - N, len)` (excluding the index `len` itself). + /// + /// # Panics + /// + /// Panics if `N > len`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let mut v = &mut [1, 0, 3, 0, 5, 6][..]; + /// let (left, right) = v.rsplit_array_mut::<4>(); + /// assert_eq!(left, [1, 0]); + /// assert_eq!(right, &mut [3, 0, 5, 6]); + /// left[1] = 2; + /// right[1] = 4; + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable(feature = "split_array", reason = "new API", issue = "90091")] + #[inline] + #[must_use] + pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) { + assert!(N <= self.len()); + let (a, b) = self.split_at_mut(self.len() - N); + // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut) + unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) } + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred`. The matched element is not contained in the subslices. + /// + /// # Examples + /// + /// ``` + /// let slice = [10, 40, 33, 20]; + /// let mut iter = slice.split(|num| num % 3 == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[10, 40]); + /// assert_eq!(iter.next().unwrap(), &[20]); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// If the first element is matched, an empty slice will be the first item + /// returned by the iterator. Similarly, if the last element in the slice + /// is matched, an empty slice will be the last item returned by the + /// iterator: + /// + /// ``` + /// let slice = [10, 40, 33]; + /// let mut iter = slice.split(|num| num % 3 == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[10, 40]); + /// assert_eq!(iter.next().unwrap(), &[]); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// If two matched elements are directly adjacent, an empty slice will be + /// present between them: + /// + /// ``` + /// let slice = [10, 6, 33, 20]; + /// let mut iter = slice.split(|num| num % 3 == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[10]); + /// assert_eq!(iter.next().unwrap(), &[]); + /// assert_eq!(iter.next().unwrap(), &[20]); + /// assert!(iter.next().is_none()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn split<F>(&self, pred: F) -> Split<'_, T, F> + where + F: FnMut(&T) -> bool, + { + Split::new(self, pred) + } + + /// Returns an iterator over mutable subslices separated by elements that + /// match `pred`. The matched element is not contained in the subslices. + /// + /// # Examples + /// + /// ``` + /// let mut v = [10, 40, 30, 20, 60, 50]; + /// + /// for group in v.split_mut(|num| *num % 3 == 0) { + /// group[0] = 1; + /// } + /// assert_eq!(v, [1, 40, 30, 1, 60, 1]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F> + where + F: FnMut(&T) -> bool, + { + SplitMut::new(self, pred) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred`. The matched element is contained in the end of the previous + /// subslice as a terminator. + /// + /// # Examples + /// + /// ``` + /// let slice = [10, 40, 33, 20]; + /// let mut iter = slice.split_inclusive(|num| num % 3 == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]); + /// assert_eq!(iter.next().unwrap(), &[20]); + /// assert!(iter.next().is_none()); + /// ``` + /// + /// If the last element of the slice is matched, + /// that element will be considered the terminator of the preceding slice. + /// That slice will be the last item returned by the iterator. + /// + /// ``` + /// let slice = [3, 10, 40, 33]; + /// let mut iter = slice.split_inclusive(|num| num % 3 == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[3]); + /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]); + /// assert!(iter.next().is_none()); + /// ``` + #[stable(feature = "split_inclusive", since = "1.51.0")] + #[inline] + pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F> + where + F: FnMut(&T) -> bool, + { + SplitInclusive::new(self, pred) + } + + /// Returns an iterator over mutable subslices separated by elements that + /// match `pred`. The matched element is contained in the previous + /// subslice as a terminator. + /// + /// # Examples + /// + /// ``` + /// let mut v = [10, 40, 30, 20, 60, 50]; + /// + /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) { + /// let terminator_idx = group.len()-1; + /// group[terminator_idx] = 1; + /// } + /// assert_eq!(v, [10, 40, 1, 20, 1, 1]); + /// ``` + #[stable(feature = "split_inclusive", since = "1.51.0")] + #[inline] + pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F> + where + F: FnMut(&T) -> bool, + { + SplitInclusiveMut::new(self, pred) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred`, starting at the end of the slice and working backwards. + /// The matched element is not contained in the subslices. + /// + /// # Examples + /// + /// ``` + /// let slice = [11, 22, 33, 0, 44, 55]; + /// let mut iter = slice.rsplit(|num| *num == 0); + /// + /// assert_eq!(iter.next().unwrap(), &[44, 55]); + /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]); + /// assert_eq!(iter.next(), None); + /// ``` + /// + /// As with `split()`, if the first or last element is matched, an empty + /// slice will be the first (or last) item returned by the iterator. + /// + /// ``` + /// let v = &[0, 1, 1, 2, 3, 5, 8]; + /// let mut it = v.rsplit(|n| *n % 2 == 0); + /// assert_eq!(it.next().unwrap(), &[]); + /// assert_eq!(it.next().unwrap(), &[3, 5]); + /// assert_eq!(it.next().unwrap(), &[1, 1]); + /// assert_eq!(it.next().unwrap(), &[]); + /// assert_eq!(it.next(), None); + /// ``` + #[stable(feature = "slice_rsplit", since = "1.27.0")] + #[inline] + pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F> + where + F: FnMut(&T) -> bool, + { + RSplit::new(self, pred) + } + + /// Returns an iterator over mutable subslices separated by elements that + /// match `pred`, starting at the end of the slice and working + /// backwards. The matched element is not contained in the subslices. + /// + /// # Examples + /// + /// ``` + /// let mut v = [100, 400, 300, 200, 600, 500]; + /// + /// let mut count = 0; + /// for group in v.rsplit_mut(|num| *num % 3 == 0) { + /// count += 1; + /// group[0] = count; + /// } + /// assert_eq!(v, [3, 400, 300, 2, 600, 1]); + /// ``` + /// + #[stable(feature = "slice_rsplit", since = "1.27.0")] + #[inline] + pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F> + where + F: FnMut(&T) -> bool, + { + RSplitMut::new(self, pred) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred`, limited to returning at most `n` items. The matched element is + /// not contained in the subslices. + /// + /// The last element returned, if any, will contain the remainder of the + /// slice. + /// + /// # Examples + /// + /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`, + /// `[20, 60, 50]`): + /// + /// ``` + /// let v = [10, 40, 30, 20, 60, 50]; + /// + /// for group in v.splitn(2, |num| *num % 3 == 0) { + /// println!("{group:?}"); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F> + where + F: FnMut(&T) -> bool, + { + SplitN::new(self.split(pred), n) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred`, limited to returning at most `n` items. The matched element is + /// not contained in the subslices. + /// + /// The last element returned, if any, will contain the remainder of the + /// slice. + /// + /// # Examples + /// + /// ``` + /// let mut v = [10, 40, 30, 20, 60, 50]; + /// + /// for group in v.splitn_mut(2, |num| *num % 3 == 0) { + /// group[0] = 1; + /// } + /// assert_eq!(v, [1, 40, 30, 1, 60, 50]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F> + where + F: FnMut(&T) -> bool, + { + SplitNMut::new(self.split_mut(pred), n) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred` limited to returning at most `n` items. This starts at the end of + /// the slice and works backwards. The matched element is not contained in + /// the subslices. + /// + /// The last element returned, if any, will contain the remainder of the + /// slice. + /// + /// # Examples + /// + /// Print the slice split once, starting from the end, by numbers divisible + /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`): + /// + /// ``` + /// let v = [10, 40, 30, 20, 60, 50]; + /// + /// for group in v.rsplitn(2, |num| *num % 3 == 0) { + /// println!("{group:?}"); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F> + where + F: FnMut(&T) -> bool, + { + RSplitN::new(self.rsplit(pred), n) + } + + /// Returns an iterator over subslices separated by elements that match + /// `pred` limited to returning at most `n` items. This starts at the end of + /// the slice and works backwards. The matched element is not contained in + /// the subslices. + /// + /// The last element returned, if any, will contain the remainder of the + /// slice. + /// + /// # Examples + /// + /// ``` + /// let mut s = [10, 40, 30, 20, 60, 50]; + /// + /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) { + /// group[0] = 1; + /// } + /// assert_eq!(s, [1, 40, 30, 20, 60, 1]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F> + where + F: FnMut(&T) -> bool, + { + RSplitNMut::new(self.rsplit_mut(pred), n) + } + + /// Returns `true` if the slice contains an element with the given value. + /// + /// This operation is *O*(*n*). + /// + /// Note that if you have a sorted slice, [`binary_search`] may be faster. + /// + /// [`binary_search`]: slice::binary_search + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert!(v.contains(&30)); + /// assert!(!v.contains(&50)); + /// ``` + /// + /// If you do not have a `&T`, but some other value that you can compare + /// with one (for example, `String` implements `PartialEq<str>`), you can + /// use `iter().any`: + /// + /// ``` + /// let v = [String::from("hello"), String::from("world")]; // slice of `String` + /// assert!(v.iter().any(|e| e == "hello")); // search with `&str` + /// assert!(!v.iter().any(|e| e == "hi")); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + #[must_use] + pub fn contains(&self, x: &T) -> bool + where + T: PartialEq, + { + cmp::SliceContains::slice_contains(x, self) + } + + /// Returns `true` if `needle` is a prefix of the slice. + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert!(v.starts_with(&[10])); + /// assert!(v.starts_with(&[10, 40])); + /// assert!(!v.starts_with(&[50])); + /// assert!(!v.starts_with(&[10, 50])); + /// ``` + /// + /// Always returns `true` if `needle` is an empty slice: + /// + /// ``` + /// let v = &[10, 40, 30]; + /// assert!(v.starts_with(&[])); + /// let v: &[u8] = &[]; + /// assert!(v.starts_with(&[])); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn starts_with(&self, needle: &[T]) -> bool + where + T: PartialEq, + { + let n = needle.len(); + self.len() >= n && needle == &self[..n] + } + + /// Returns `true` if `needle` is a suffix of the slice. + /// + /// # Examples + /// + /// ``` + /// let v = [10, 40, 30]; + /// assert!(v.ends_with(&[30])); + /// assert!(v.ends_with(&[40, 30])); + /// assert!(!v.ends_with(&[50])); + /// assert!(!v.ends_with(&[50, 30])); + /// ``` + /// + /// Always returns `true` if `needle` is an empty slice: + /// + /// ``` + /// let v = &[10, 40, 30]; + /// assert!(v.ends_with(&[])); + /// let v: &[u8] = &[]; + /// assert!(v.ends_with(&[])); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn ends_with(&self, needle: &[T]) -> bool + where + T: PartialEq, + { + let (m, n) = (self.len(), needle.len()); + m >= n && needle == &self[m - n..] + } + + /// Returns a subslice with the prefix removed. + /// + /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`. + /// If `prefix` is empty, simply returns the original slice. + /// + /// If the slice does not start with `prefix`, returns `None`. + /// + /// # Examples + /// + /// ``` + /// let v = &[10, 40, 30]; + /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..])); + /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..])); + /// assert_eq!(v.strip_prefix(&[50]), None); + /// assert_eq!(v.strip_prefix(&[10, 50]), None); + /// + /// let prefix : &str = "he"; + /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()), + /// Some(b"llo".as_ref())); + /// ``` + #[must_use = "returns the subslice without modifying the original"] + #[stable(feature = "slice_strip", since = "1.51.0")] + pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]> + where + T: PartialEq, + { + // This function will need rewriting if and when SlicePattern becomes more sophisticated. + let prefix = prefix.as_slice(); + let n = prefix.len(); + if n <= self.len() { + let (head, tail) = self.split_at(n); + if head == prefix { + return Some(tail); + } + } + None + } + + /// Returns a subslice with the suffix removed. + /// + /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`. + /// If `suffix` is empty, simply returns the original slice. + /// + /// If the slice does not end with `suffix`, returns `None`. + /// + /// # Examples + /// + /// ``` + /// let v = &[10, 40, 30]; + /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..])); + /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..])); + /// assert_eq!(v.strip_suffix(&[50]), None); + /// assert_eq!(v.strip_suffix(&[50, 30]), None); + /// ``` + #[must_use = "returns the subslice without modifying the original"] + #[stable(feature = "slice_strip", since = "1.51.0")] + pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]> + where + T: PartialEq, + { + // This function will need rewriting if and when SlicePattern becomes more sophisticated. + let suffix = suffix.as_slice(); + let (len, n) = (self.len(), suffix.len()); + if n <= len { + let (head, tail) = self.split_at(len - n); + if tail == suffix { + return Some(head); + } + } + None + } + + /// Binary searches this slice for a given element. + /// This behaves similary to [`contains`] if this slice is sorted. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. The index is chosen + /// deterministically, but is subject to change in future versions of Rust. + /// If the value is not found then [`Result::Err`] is returned, containing + /// the index where a matching element could be inserted while maintaining + /// sorted order. + /// + /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`]. + /// + /// [`contains`]: slice::contains + /// [`binary_search_by`]: slice::binary_search_by + /// [`binary_search_by_key`]: slice::binary_search_by_key + /// [`partition_point`]: slice::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements. The first is found, with a + /// uniquely determined position; the second and third are not + /// found; the fourth could match any position in `[1, 4]`. + /// + /// ``` + /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; + /// + /// assert_eq!(s.binary_search(&13), Ok(9)); + /// assert_eq!(s.binary_search(&4), Err(7)); + /// assert_eq!(s.binary_search(&100), Err(13)); + /// let r = s.binary_search(&1); + /// assert!(match r { Ok(1..=4) => true, _ => false, }); + /// ``` + /// + /// If you want to insert an item to a sorted vector, while maintaining + /// sort order, consider using [`partition_point`]: + /// + /// ``` + /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; + /// let num = 42; + /// let idx = s.partition_point(|&x| x < num); + /// // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);` + /// s.insert(idx, num); + /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn binary_search(&self, x: &T) -> Result<usize, usize> + where + T: Ord, + { + self.binary_search_by(|p| p.cmp(x)) + } + + /// Binary searches this slice with a comparator function. + /// This behaves similarly to [`contains`] if this slice is sorted. + /// + /// The comparator function should implement an order consistent + /// with the sort order of the underlying slice, returning an + /// order code that indicates whether its argument is `Less`, + /// `Equal` or `Greater` the desired target. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. The index is chosen + /// deterministically, but is subject to change in future versions of Rust. + /// If the value is not found then [`Result::Err`] is returned, containing + /// the index where a matching element could be inserted while maintaining + /// sorted order. + /// + /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`]. + /// + /// [`contains`]: slice::contains + /// [`binary_search`]: slice::binary_search + /// [`binary_search_by_key`]: slice::binary_search_by_key + /// [`partition_point`]: slice::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements. The first is found, with a + /// uniquely determined position; the second and third are not + /// found; the fourth could match any position in `[1, 4]`. + /// + /// ``` + /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; + /// + /// let seek = 13; + /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9)); + /// let seek = 4; + /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7)); + /// let seek = 100; + /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13)); + /// let seek = 1; + /// let r = s.binary_search_by(|probe| probe.cmp(&seek)); + /// assert!(match r { Ok(1..=4) => true, _ => false, }); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize> + where + F: FnMut(&'a T) -> Ordering, + { + let mut size = self.len(); + let mut left = 0; + let mut right = size; + while left < right { + let mid = left + size / 2; + + // SAFETY: the call is made safe by the following invariants: + // - `mid >= 0` + // - `mid < size`: `mid` is limited by `[left; right)` bound. + let cmp = f(unsafe { self.get_unchecked(mid) }); + + // The reason why we use if/else control flow rather than match + // is because match reorders comparison operations, which is perf sensitive. + // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra. + if cmp == Less { + left = mid + 1; + } else if cmp == Greater { + right = mid; + } else { + // SAFETY: same as the `get_unchecked` above + unsafe { crate::intrinsics::assume(mid < self.len()) }; + return Ok(mid); + } + + size = right - left; + } + Err(left) + } + + /// Binary searches this slice with a key extraction function. + /// This behaves similarly to [`contains`] if this slice is sorted. + /// + /// Assumes that the slice is sorted by the key, for instance with + /// [`sort_by_key`] using the same key extraction function. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. The index is chosen + /// deterministically, but is subject to change in future versions of Rust. + /// If the value is not found then [`Result::Err`] is returned, containing + /// the index where a matching element could be inserted while maintaining + /// sorted order. + /// + /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`]. + /// + /// [`contains`]: slice::contains + /// [`sort_by_key`]: slice::sort_by_key + /// [`binary_search`]: slice::binary_search + /// [`binary_search_by`]: slice::binary_search_by + /// [`partition_point`]: slice::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements in a slice of pairs sorted by + /// their second elements. The first is found, with a uniquely + /// determined position; the second and third are not found; the + /// fourth could match any position in `[1, 4]`. + /// + /// ``` + /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1), + /// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13), + /// (1, 21), (2, 34), (4, 55)]; + /// + /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b), Ok(9)); + /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b), Err(7)); + /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13)); + /// let r = s.binary_search_by_key(&1, |&(a, b)| b); + /// assert!(match r { Ok(1..=4) => true, _ => false, }); + /// ``` + // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is + // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481. + // This breaks links when slice is displayed in core, but changing it to use relative links + // would break when the item is re-exported. So allow the core links to be broken for now. + #[allow(rustdoc::broken_intra_doc_links)] + #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")] + #[inline] + pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize> + where + F: FnMut(&'a T) -> B, + B: Ord, + { + self.binary_search_by(|k| f(k).cmp(b)) + } + + /// Sorts the slice, but might not preserve the order of equal elements. + /// + /// This sort is unstable (i.e., may reorder equal elements), in-place + /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case. + /// + /// # Current implementation + /// + /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters, + /// which combines the fast average case of randomized quicksort with the fast worst case of + /// heapsort, while achieving linear time on slices with certain patterns. It uses some + /// randomization to avoid degenerate cases, but with a fixed seed to always provide + /// deterministic behavior. + /// + /// It is typically faster than stable sorting, except in a few special cases, e.g., when the + /// slice consists of several concatenated sorted sequences. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5, 4, 1, -3, 2]; + /// + /// v.sort_unstable(); + /// assert!(v == [-5, -3, 1, 2, 4]); + /// ``` + /// + /// [pdqsort]: https://github.com/orlp/pdqsort + #[stable(feature = "sort_unstable", since = "1.20.0")] + #[inline] + pub fn sort_unstable(&mut self) + where + T: Ord, + { + sort::quicksort(self, |a, b| a.lt(b)); + } + + /// Sorts the slice with a comparator function, but might not preserve the order of equal + /// elements. + /// + /// This sort is unstable (i.e., may reorder equal elements), in-place + /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case. + /// + /// The comparator function must define a total ordering for the elements in the slice. If + /// the ordering is not total, the order of the elements is unspecified. An order is a + /// total order if it is (for all `a`, `b` and `c`): + /// + /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and + /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. + /// + /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use + /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`. + /// + /// ``` + /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0]; + /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap()); + /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]); + /// ``` + /// + /// # Current implementation + /// + /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters, + /// which combines the fast average case of randomized quicksort with the fast worst case of + /// heapsort, while achieving linear time on slices with certain patterns. It uses some + /// randomization to avoid degenerate cases, but with a fixed seed to always provide + /// deterministic behavior. + /// + /// It is typically faster than stable sorting, except in a few special cases, e.g., when the + /// slice consists of several concatenated sorted sequences. + /// + /// # Examples + /// + /// ``` + /// let mut v = [5, 4, 1, 3, 2]; + /// v.sort_unstable_by(|a, b| a.cmp(b)); + /// assert!(v == [1, 2, 3, 4, 5]); + /// + /// // reverse sorting + /// v.sort_unstable_by(|a, b| b.cmp(a)); + /// assert!(v == [5, 4, 3, 2, 1]); + /// ``` + /// + /// [pdqsort]: https://github.com/orlp/pdqsort + #[stable(feature = "sort_unstable", since = "1.20.0")] + #[inline] + pub fn sort_unstable_by<F>(&mut self, mut compare: F) + where + F: FnMut(&T, &T) -> Ordering, + { + sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less); + } + + /// Sorts the slice with a key extraction function, but might not preserve the order of equal + /// elements. + /// + /// This sort is unstable (i.e., may reorder equal elements), in-place + /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is + /// *O*(*m*). + /// + /// # Current implementation + /// + /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters, + /// which combines the fast average case of randomized quicksort with the fast worst case of + /// heapsort, while achieving linear time on slices with certain patterns. It uses some + /// randomization to avoid degenerate cases, but with a fixed seed to always provide + /// deterministic behavior. + /// + /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key) + /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in + /// cases where the key function is expensive. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5i32, 4, 1, -3, 2]; + /// + /// v.sort_unstable_by_key(|k| k.abs()); + /// assert!(v == [1, 2, -3, 4, -5]); + /// ``` + /// + /// [pdqsort]: https://github.com/orlp/pdqsort + #[stable(feature = "sort_unstable", since = "1.20.0")] + #[inline] + pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F) + where + F: FnMut(&T) -> K, + K: Ord, + { + sort::quicksort(self, |a, b| f(a).lt(&f(b))); + } + + /// Reorder the slice such that the element at `index` is at its final sorted position. + /// + /// This reordering has the additional property that any value at position `i < index` will be + /// less than or equal to any value at a position `j > index`. Additionally, this reordering is + /// unstable (i.e. any number of equal elements may end up at position `index`), in-place + /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth + /// element" in other libraries. It returns a triplet of the following values: all elements less + /// than the one at the given index, the value at the given index, and all elements greater than + /// the one at the given index. + /// + /// # Current implementation + /// + /// The current algorithm is based on the quickselect portion of the same quicksort algorithm + /// used for [`sort_unstable`]. + /// + /// [`sort_unstable`]: slice::sort_unstable + /// + /// # Panics + /// + /// Panics when `index >= len()`, meaning it always panics on empty slices. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5i32, 4, 1, -3, 2]; + /// + /// // Find the median + /// v.select_nth_unstable(2); + /// + /// // We are only guaranteed the slice will be one of the following, based on the way we sort + /// // about the specified index. + /// assert!(v == [-3, -5, 1, 2, 4] || + /// v == [-5, -3, 1, 2, 4] || + /// v == [-3, -5, 1, 4, 2] || + /// v == [-5, -3, 1, 4, 2]); + /// ``` + #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")] + #[inline] + pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T]) + where + T: Ord, + { + let mut f = |a: &T, b: &T| a.lt(b); + sort::partition_at_index(self, index, &mut f) + } + + /// Reorder the slice with a comparator function such that the element at `index` is at its + /// final sorted position. + /// + /// This reordering has the additional property that any value at position `i < index` will be + /// less than or equal to any value at a position `j > index` using the comparator function. + /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at + /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function + /// is also known as "kth element" in other libraries. It returns a triplet of the following + /// values: all elements less than the one at the given index, the value at the given index, + /// and all elements greater than the one at the given index, using the provided comparator + /// function. + /// + /// # Current implementation + /// + /// The current algorithm is based on the quickselect portion of the same quicksort algorithm + /// used for [`sort_unstable`]. + /// + /// [`sort_unstable`]: slice::sort_unstable + /// + /// # Panics + /// + /// Panics when `index >= len()`, meaning it always panics on empty slices. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5i32, 4, 1, -3, 2]; + /// + /// // Find the median as if the slice were sorted in descending order. + /// v.select_nth_unstable_by(2, |a, b| b.cmp(a)); + /// + /// // We are only guaranteed the slice will be one of the following, based on the way we sort + /// // about the specified index. + /// assert!(v == [2, 4, 1, -5, -3] || + /// v == [2, 4, 1, -3, -5] || + /// v == [4, 2, 1, -5, -3] || + /// v == [4, 2, 1, -3, -5]); + /// ``` + #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")] + #[inline] + pub fn select_nth_unstable_by<F>( + &mut self, + index: usize, + mut compare: F, + ) -> (&mut [T], &mut T, &mut [T]) + where + F: FnMut(&T, &T) -> Ordering, + { + let mut f = |a: &T, b: &T| compare(a, b) == Less; + sort::partition_at_index(self, index, &mut f) + } + + /// Reorder the slice with a key extraction function such that the element at `index` is at its + /// final sorted position. + /// + /// This reordering has the additional property that any value at position `i < index` will be + /// less than or equal to any value at a position `j > index` using the key extraction function. + /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at + /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function + /// is also known as "kth element" in other libraries. It returns a triplet of the following + /// values: all elements less than the one at the given index, the value at the given index, and + /// all elements greater than the one at the given index, using the provided key extraction + /// function. + /// + /// # Current implementation + /// + /// The current algorithm is based on the quickselect portion of the same quicksort algorithm + /// used for [`sort_unstable`]. + /// + /// [`sort_unstable`]: slice::sort_unstable + /// + /// # Panics + /// + /// Panics when `index >= len()`, meaning it always panics on empty slices. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5i32, 4, 1, -3, 2]; + /// + /// // Return the median as if the array were sorted according to absolute value. + /// v.select_nth_unstable_by_key(2, |a| a.abs()); + /// + /// // We are only guaranteed the slice will be one of the following, based on the way we sort + /// // about the specified index. + /// assert!(v == [1, 2, -3, 4, -5] || + /// v == [1, 2, -3, -5, 4] || + /// v == [2, 1, -3, 4, -5] || + /// v == [2, 1, -3, -5, 4]); + /// ``` + #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")] + #[inline] + pub fn select_nth_unstable_by_key<K, F>( + &mut self, + index: usize, + mut f: F, + ) -> (&mut [T], &mut T, &mut [T]) + where + F: FnMut(&T) -> K, + K: Ord, + { + let mut g = |a: &T, b: &T| f(a).lt(&f(b)); + sort::partition_at_index(self, index, &mut g) + } + + /// Moves all consecutive repeated elements to the end of the slice according to the + /// [`PartialEq`] trait implementation. + /// + /// Returns two slices. The first contains no consecutive repeated elements. + /// The second contains all the duplicates in no specified order. + /// + /// If the slice is sorted, the first returned slice contains no duplicates. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_partition_dedup)] + /// + /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1]; + /// + /// let (dedup, duplicates) = slice.partition_dedup(); + /// + /// assert_eq!(dedup, [1, 2, 3, 2, 1]); + /// assert_eq!(duplicates, [2, 3, 1]); + /// ``` + #[unstable(feature = "slice_partition_dedup", issue = "54279")] + #[inline] + pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T]) + where + T: PartialEq, + { + self.partition_dedup_by(|a, b| a == b) + } + + /// Moves all but the first of consecutive elements to the end of the slice satisfying + /// a given equality relation. + /// + /// Returns two slices. The first contains no consecutive repeated elements. + /// The second contains all the duplicates in no specified order. + /// + /// The `same_bucket` function is passed references to two elements from the slice and + /// must determine if the elements compare equal. The elements are passed in opposite order + /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved + /// at the end of the slice. + /// + /// If the slice is sorted, the first returned slice contains no duplicates. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_partition_dedup)] + /// + /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"]; + /// + /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b)); + /// + /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]); + /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]); + /// ``` + #[unstable(feature = "slice_partition_dedup", issue = "54279")] + #[inline] + pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T]) + where + F: FnMut(&mut T, &mut T) -> bool, + { + // Although we have a mutable reference to `self`, we cannot make + // *arbitrary* changes. The `same_bucket` calls could panic, so we + // must ensure that the slice is in a valid state at all times. + // + // The way that we handle this is by using swaps; we iterate + // over all the elements, swapping as we go so that at the end + // the elements we wish to keep are in the front, and those we + // wish to reject are at the back. We can then split the slice. + // This operation is still `O(n)`. + // + // Example: We start in this state, where `r` represents "next + // read" and `w` represents "next_write`. + // + // r + // +---+---+---+---+---+---+ + // | 0 | 1 | 1 | 2 | 3 | 3 | + // +---+---+---+---+---+---+ + // w + // + // Comparing self[r] against self[w-1], this is not a duplicate, so + // we swap self[r] and self[w] (no effect as r==w) and then increment both + // r and w, leaving us with: + // + // r + // +---+---+---+---+---+---+ + // | 0 | 1 | 1 | 2 | 3 | 3 | + // +---+---+---+---+---+---+ + // w + // + // Comparing self[r] against self[w-1], this value is a duplicate, + // so we increment `r` but leave everything else unchanged: + // + // r + // +---+---+---+---+---+---+ + // | 0 | 1 | 1 | 2 | 3 | 3 | + // +---+---+---+---+---+---+ + // w + // + // Comparing self[r] against self[w-1], this is not a duplicate, + // so swap self[r] and self[w] and advance r and w: + // + // r + // +---+---+---+---+---+---+ + // | 0 | 1 | 2 | 1 | 3 | 3 | + // +---+---+---+---+---+---+ + // w + // + // Not a duplicate, repeat: + // + // r + // +---+---+---+---+---+---+ + // | 0 | 1 | 2 | 3 | 1 | 3 | + // +---+---+---+---+---+---+ + // w + // + // Duplicate, advance r. End of slice. Split at w. + + let len = self.len(); + if len <= 1 { + return (self, &mut []); + } + + let ptr = self.as_mut_ptr(); + let mut next_read: usize = 1; + let mut next_write: usize = 1; + + // SAFETY: the `while` condition guarantees `next_read` and `next_write` + // are less than `len`, thus are inside `self`. `prev_ptr_write` points to + // one element before `ptr_write`, but `next_write` starts at 1, so + // `prev_ptr_write` is never less than 0 and is inside the slice. + // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write` + // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)` + // and `prev_ptr_write.offset(1)`. + // + // `next_write` is also incremented at most once per loop at most meaning + // no element is skipped when it may need to be swapped. + // + // `ptr_read` and `prev_ptr_write` never point to the same element. This + // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe. + // The explanation is simply that `next_read >= next_write` is always true, + // thus `next_read > next_write - 1` is too. + unsafe { + // Avoid bounds checks by using raw pointers. + while next_read < len { + let ptr_read = ptr.add(next_read); + let prev_ptr_write = ptr.add(next_write - 1); + if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) { + if next_read != next_write { + let ptr_write = prev_ptr_write.offset(1); + mem::swap(&mut *ptr_read, &mut *ptr_write); + } + next_write += 1; + } + next_read += 1; + } + } + + self.split_at_mut(next_write) + } + + /// Moves all but the first of consecutive elements to the end of the slice that resolve + /// to the same key. + /// + /// Returns two slices. The first contains no consecutive repeated elements. + /// The second contains all the duplicates in no specified order. + /// + /// If the slice is sorted, the first returned slice contains no duplicates. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_partition_dedup)] + /// + /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13]; + /// + /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10); + /// + /// assert_eq!(dedup, [10, 20, 30, 20, 11]); + /// assert_eq!(duplicates, [21, 30, 13]); + /// ``` + #[unstable(feature = "slice_partition_dedup", issue = "54279")] + #[inline] + pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T]) + where + F: FnMut(&mut T) -> K, + K: PartialEq, + { + self.partition_dedup_by(|a, b| key(a) == key(b)) + } + + /// Rotates the slice in-place such that the first `mid` elements of the + /// slice move to the end while the last `self.len() - mid` elements move to + /// the front. After calling `rotate_left`, the element previously at index + /// `mid` will become the first element in the slice. + /// + /// # Panics + /// + /// This function will panic if `mid` is greater than the length of the + /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op + /// rotation. + /// + /// # Complexity + /// + /// Takes linear (in `self.len()`) time. + /// + /// # Examples + /// + /// ``` + /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f']; + /// a.rotate_left(2); + /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']); + /// ``` + /// + /// Rotating a subslice: + /// + /// ``` + /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f']; + /// a[1..5].rotate_left(1); + /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']); + /// ``` + #[stable(feature = "slice_rotate", since = "1.26.0")] + pub fn rotate_left(&mut self, mid: usize) { + assert!(mid <= self.len()); + let k = self.len() - mid; + let p = self.as_mut_ptr(); + + // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially + // valid for reading and writing, as required by `ptr_rotate`. + unsafe { + rotate::ptr_rotate(mid, p.add(mid), k); + } + } + + /// Rotates the slice in-place such that the first `self.len() - k` + /// elements of the slice move to the end while the last `k` elements move + /// to the front. After calling `rotate_right`, the element previously at + /// index `self.len() - k` will become the first element in the slice. + /// + /// # Panics + /// + /// This function will panic if `k` is greater than the length of the + /// slice. Note that `k == self.len()` does _not_ panic and is a no-op + /// rotation. + /// + /// # Complexity + /// + /// Takes linear (in `self.len()`) time. + /// + /// # Examples + /// + /// ``` + /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f']; + /// a.rotate_right(2); + /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']); + /// ``` + /// + /// Rotate a subslice: + /// + /// ``` + /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f']; + /// a[1..5].rotate_right(1); + /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']); + /// ``` + #[stable(feature = "slice_rotate", since = "1.26.0")] + pub fn rotate_right(&mut self, k: usize) { + assert!(k <= self.len()); + let mid = self.len() - k; + let p = self.as_mut_ptr(); + + // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially + // valid for reading and writing, as required by `ptr_rotate`. + unsafe { + rotate::ptr_rotate(mid, p.add(mid), k); + } + } + + /// Fills `self` with elements by cloning `value`. + /// + /// # Examples + /// + /// ``` + /// let mut buf = vec![0; 10]; + /// buf.fill(1); + /// assert_eq!(buf, vec![1; 10]); + /// ``` + #[doc(alias = "memset")] + #[stable(feature = "slice_fill", since = "1.50.0")] + pub fn fill(&mut self, value: T) + where + T: Clone, + { + specialize::SpecFill::spec_fill(self, value); + } + + /// Fills `self` with elements returned by calling a closure repeatedly. + /// + /// This method uses a closure to create new values. If you'd rather + /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`] + /// trait to generate values, you can pass [`Default::default`] as the + /// argument. + /// + /// [`fill`]: slice::fill + /// + /// # Examples + /// + /// ``` + /// let mut buf = vec![1; 10]; + /// buf.fill_with(Default::default); + /// assert_eq!(buf, vec![0; 10]); + /// ``` + #[stable(feature = "slice_fill_with", since = "1.51.0")] + pub fn fill_with<F>(&mut self, mut f: F) + where + F: FnMut() -> T, + { + for el in self { + *el = f(); + } + } + + /// Copies the elements from `src` into `self`. + /// + /// The length of `src` must be the same as `self`. + /// + /// # Panics + /// + /// This function will panic if the two slices have different lengths. + /// + /// # Examples + /// + /// Cloning two elements from a slice into another: + /// + /// ``` + /// let src = [1, 2, 3, 4]; + /// let mut dst = [0, 0]; + /// + /// // Because the slices have to be the same length, + /// // we slice the source slice from four elements + /// // to two. It will panic if we don't do this. + /// dst.clone_from_slice(&src[2..]); + /// + /// assert_eq!(src, [1, 2, 3, 4]); + /// assert_eq!(dst, [3, 4]); + /// ``` + /// + /// Rust enforces that there can only be one mutable reference with no + /// immutable references to a particular piece of data in a particular + /// scope. Because of this, attempting to use `clone_from_slice` on a + /// single slice will result in a compile failure: + /// + /// ```compile_fail + /// let mut slice = [1, 2, 3, 4, 5]; + /// + /// slice[..2].clone_from_slice(&slice[3..]); // compile fail! + /// ``` + /// + /// To work around this, we can use [`split_at_mut`] to create two distinct + /// sub-slices from a slice: + /// + /// ``` + /// let mut slice = [1, 2, 3, 4, 5]; + /// + /// { + /// let (left, right) = slice.split_at_mut(2); + /// left.clone_from_slice(&right[1..]); + /// } + /// + /// assert_eq!(slice, [4, 5, 3, 4, 5]); + /// ``` + /// + /// [`copy_from_slice`]: slice::copy_from_slice + /// [`split_at_mut`]: slice::split_at_mut + #[stable(feature = "clone_from_slice", since = "1.7.0")] + #[track_caller] + pub fn clone_from_slice(&mut self, src: &[T]) + where + T: Clone, + { + self.spec_clone_from(src); + } + + /// Copies all elements from `src` into `self`, using a memcpy. + /// + /// The length of `src` must be the same as `self`. + /// + /// If `T` does not implement `Copy`, use [`clone_from_slice`]. + /// + /// # Panics + /// + /// This function will panic if the two slices have different lengths. + /// + /// # Examples + /// + /// Copying two elements from a slice into another: + /// + /// ``` + /// let src = [1, 2, 3, 4]; + /// let mut dst = [0, 0]; + /// + /// // Because the slices have to be the same length, + /// // we slice the source slice from four elements + /// // to two. It will panic if we don't do this. + /// dst.copy_from_slice(&src[2..]); + /// + /// assert_eq!(src, [1, 2, 3, 4]); + /// assert_eq!(dst, [3, 4]); + /// ``` + /// + /// Rust enforces that there can only be one mutable reference with no + /// immutable references to a particular piece of data in a particular + /// scope. Because of this, attempting to use `copy_from_slice` on a + /// single slice will result in a compile failure: + /// + /// ```compile_fail + /// let mut slice = [1, 2, 3, 4, 5]; + /// + /// slice[..2].copy_from_slice(&slice[3..]); // compile fail! + /// ``` + /// + /// To work around this, we can use [`split_at_mut`] to create two distinct + /// sub-slices from a slice: + /// + /// ``` + /// let mut slice = [1, 2, 3, 4, 5]; + /// + /// { + /// let (left, right) = slice.split_at_mut(2); + /// left.copy_from_slice(&right[1..]); + /// } + /// + /// assert_eq!(slice, [4, 5, 3, 4, 5]); + /// ``` + /// + /// [`clone_from_slice`]: slice::clone_from_slice + /// [`split_at_mut`]: slice::split_at_mut + #[doc(alias = "memcpy")] + #[stable(feature = "copy_from_slice", since = "1.9.0")] + #[track_caller] + pub fn copy_from_slice(&mut self, src: &[T]) + where + T: Copy, + { + // The panic code path was put into a cold function to not bloat the + // call site. + #[inline(never)] + #[cold] + #[track_caller] + fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! { + panic!( + "source slice length ({}) does not match destination slice length ({})", + src_len, dst_len, + ); + } + + if self.len() != src.len() { + len_mismatch_fail(self.len(), src.len()); + } + + // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was + // checked to have the same length. The slices cannot overlap because + // mutable references are exclusive. + unsafe { + ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len()); + } + } + + /// Copies elements from one part of the slice to another part of itself, + /// using a memmove. + /// + /// `src` is the range within `self` to copy from. `dest` is the starting + /// index of the range within `self` to copy to, which will have the same + /// length as `src`. The two ranges may overlap. The ends of the two ranges + /// must be less than or equal to `self.len()`. + /// + /// # Panics + /// + /// This function will panic if either range exceeds the end of the slice, + /// or if the end of `src` is before the start. + /// + /// # Examples + /// + /// Copying four bytes within a slice: + /// + /// ``` + /// let mut bytes = *b"Hello, World!"; + /// + /// bytes.copy_within(1..5, 8); + /// + /// assert_eq!(&bytes, b"Hello, Wello!"); + /// ``` + #[stable(feature = "copy_within", since = "1.37.0")] + #[track_caller] + pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize) + where + T: Copy, + { + let Range { start: src_start, end: src_end } = slice::range(src, ..self.len()); + let count = src_end - src_start; + assert!(dest <= self.len() - count, "dest is out of bounds"); + // SAFETY: the conditions for `ptr::copy` have all been checked above, + // as have those for `ptr::add`. + unsafe { + // Derive both `src_ptr` and `dest_ptr` from the same loan + let ptr = self.as_mut_ptr(); + let src_ptr = ptr.add(src_start); + let dest_ptr = ptr.add(dest); + ptr::copy(src_ptr, dest_ptr, count); + } + } + + /// Swaps all elements in `self` with those in `other`. + /// + /// The length of `other` must be the same as `self`. + /// + /// # Panics + /// + /// This function will panic if the two slices have different lengths. + /// + /// # Example + /// + /// Swapping two elements across slices: + /// + /// ``` + /// let mut slice1 = [0, 0]; + /// let mut slice2 = [1, 2, 3, 4]; + /// + /// slice1.swap_with_slice(&mut slice2[2..]); + /// + /// assert_eq!(slice1, [3, 4]); + /// assert_eq!(slice2, [1, 2, 0, 0]); + /// ``` + /// + /// Rust enforces that there can only be one mutable reference to a + /// particular piece of data in a particular scope. Because of this, + /// attempting to use `swap_with_slice` on a single slice will result in + /// a compile failure: + /// + /// ```compile_fail + /// let mut slice = [1, 2, 3, 4, 5]; + /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail! + /// ``` + /// + /// To work around this, we can use [`split_at_mut`] to create two distinct + /// mutable sub-slices from a slice: + /// + /// ``` + /// let mut slice = [1, 2, 3, 4, 5]; + /// + /// { + /// let (left, right) = slice.split_at_mut(2); + /// left.swap_with_slice(&mut right[1..]); + /// } + /// + /// assert_eq!(slice, [4, 5, 3, 1, 2]); + /// ``` + /// + /// [`split_at_mut`]: slice::split_at_mut + #[stable(feature = "swap_with_slice", since = "1.27.0")] + #[track_caller] + pub fn swap_with_slice(&mut self, other: &mut [T]) { + assert!(self.len() == other.len(), "destination and source slices have different lengths"); + // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was + // checked to have the same length. The slices cannot overlap because + // mutable references are exclusive. + unsafe { + ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len()); + } + } + + /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`. + fn align_to_offsets<U>(&self) -> (usize, usize) { + // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a + // lowest number of `T`s. And how many `T`s we need for each such "multiple". + // + // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider + // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in + // place of every 3 Ts in the `rest` slice. A bit more complicated. + // + // Formula to calculate this is: + // + // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U> + // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T> + // + // Expanded and simplified: + // + // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>) + // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>) + // + // Luckily since all this is constant-evaluated... performance here matters not! + #[inline] + fn gcd(a: usize, b: usize) -> usize { + use crate::intrinsics; + // iterative stein’s algorithm + // We should still make this `const fn` (and revert to recursive algorithm if we do) + // because relying on llvm to consteval all this is… well, it makes me uncomfortable. + + // SAFETY: `a` and `b` are checked to be non-zero values. + let (ctz_a, mut ctz_b) = unsafe { + if a == 0 { + return b; + } + if b == 0 { + return a; + } + (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b)) + }; + let k = ctz_a.min(ctz_b); + let mut a = a >> ctz_a; + let mut b = b; + loop { + // remove all factors of 2 from b + b >>= ctz_b; + if a > b { + mem::swap(&mut a, &mut b); + } + b = b - a; + // SAFETY: `b` is checked to be non-zero. + unsafe { + if b == 0 { + break; + } + ctz_b = intrinsics::cttz_nonzero(b); + } + } + a << k + } + let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>()); + let ts: usize = mem::size_of::<U>() / gcd; + let us: usize = mem::size_of::<T>() / gcd; + + // Armed with this knowledge, we can find how many `U`s we can fit! + let us_len = self.len() / ts * us; + // And how many `T`s will be in the trailing slice! + let ts_len = self.len() % ts; + (us_len, ts_len) + } + + /// Transmute the slice to a slice of another type, ensuring alignment of the types is + /// maintained. + /// + /// This method splits the slice into three distinct slices: prefix, correctly aligned middle + /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest + /// length possible for a given type and input slice, but only your algorithm's performance + /// should depend on that, not its correctness. It is permissible for all of the input data to + /// be returned as the prefix or suffix slice. + /// + /// This method has no purpose when either input element `T` or output element `U` are + /// zero-sized and will return the original slice without splitting anything. + /// + /// # Safety + /// + /// This method is essentially a `transmute` with respect to the elements in the returned + /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// unsafe { + /// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7]; + /// let (prefix, shorts, suffix) = bytes.align_to::<u16>(); + /// // less_efficient_algorithm_for_bytes(prefix); + /// // more_efficient_algorithm_for_aligned_shorts(shorts); + /// // less_efficient_algorithm_for_bytes(suffix); + /// } + /// ``` + #[stable(feature = "slice_align_to", since = "1.30.0")] + #[must_use] + pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) { + // Note that most of this function will be constant-evaluated, + if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 { + // handle ZSTs specially, which is – don't handle them at all. + return (self, &[], &[]); + } + + // First, find at what point do we split between the first and 2nd slice. Easy with + // ptr.align_offset. + let ptr = self.as_ptr(); + // SAFETY: See the `align_to_mut` method for the detailed safety comment. + let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) }; + if offset > self.len() { + (self, &[], &[]) + } else { + let (left, rest) = self.split_at(offset); + let (us_len, ts_len) = rest.align_to_offsets::<U>(); + // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay, + // since the caller guarantees that we can transmute `T` to `U` safely. + unsafe { + ( + left, + from_raw_parts(rest.as_ptr() as *const U, us_len), + from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len), + ) + } + } + } + + /// Transmute the slice to a slice of another type, ensuring alignment of the types is + /// maintained. + /// + /// This method splits the slice into three distinct slices: prefix, correctly aligned middle + /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest + /// length possible for a given type and input slice, but only your algorithm's performance + /// should depend on that, not its correctness. It is permissible for all of the input data to + /// be returned as the prefix or suffix slice. + /// + /// This method has no purpose when either input element `T` or output element `U` are + /// zero-sized and will return the original slice without splitting anything. + /// + /// # Safety + /// + /// This method is essentially a `transmute` with respect to the elements in the returned + /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// unsafe { + /// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7]; + /// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>(); + /// // less_efficient_algorithm_for_bytes(prefix); + /// // more_efficient_algorithm_for_aligned_shorts(shorts); + /// // less_efficient_algorithm_for_bytes(suffix); + /// } + /// ``` + #[stable(feature = "slice_align_to", since = "1.30.0")] + #[must_use] + pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) { + // Note that most of this function will be constant-evaluated, + if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 { + // handle ZSTs specially, which is – don't handle them at all. + return (self, &mut [], &mut []); + } + + // First, find at what point do we split between the first and 2nd slice. Easy with + // ptr.align_offset. + let ptr = self.as_ptr(); + // SAFETY: Here we are ensuring we will use aligned pointers for U for the + // rest of the method. This is done by passing a pointer to &[T] with an + // alignment targeted for U. + // `crate::ptr::align_offset` is called with a correctly aligned and + // valid pointer `ptr` (it comes from a reference to `self`) and with + // a size that is a power of two (since it comes from the alignement for U), + // satisfying its safety constraints. + let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) }; + if offset > self.len() { + (self, &mut [], &mut []) + } else { + let (left, rest) = self.split_at_mut(offset); + let (us_len, ts_len) = rest.align_to_offsets::<U>(); + let rest_len = rest.len(); + let mut_ptr = rest.as_mut_ptr(); + // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`! + // SAFETY: see comments for `align_to`. + unsafe { + ( + left, + from_raw_parts_mut(mut_ptr as *mut U, us_len), + from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len), + ) + } + } + } + + /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix. + /// + /// This is a safe wrapper around [`slice::align_to`], so has the same weak + /// postconditions as that method. You're only assured that + /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`. + /// + /// Notably, all of the following are possible: + /// - `prefix.len() >= LANES`. + /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`. + /// - `suffix.len() >= LANES`. + /// + /// That said, this is a safe method, so if you're only writing safe code, + /// then this can at most cause incorrect logic, not unsoundness. + /// + /// # Panics + /// + /// This will panic if the size of the SIMD type is different from + /// `LANES` times that of the scalar. + /// + /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps + /// that from ever happening, as only power-of-two numbers of lanes are + /// supported. It's possible that, in the future, those restrictions might + /// be lifted in a way that would make it possible to see panics from this + /// method for something like `LANES == 3`. + /// + /// # Examples + /// + /// ``` + /// #![feature(portable_simd)] + /// use core::simd::SimdFloat; + /// + /// let short = &[1, 2, 3]; + /// let (prefix, middle, suffix) = short.as_simd::<4>(); + /// assert_eq!(middle, []); // Not enough elements for anything in the middle + /// + /// // They might be split in any possible way between prefix and suffix + /// let it = prefix.iter().chain(suffix).copied(); + /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]); + /// + /// fn basic_simd_sum(x: &[f32]) -> f32 { + /// use std::ops::Add; + /// use std::simd::f32x4; + /// let (prefix, middle, suffix) = x.as_simd(); + /// let sums = f32x4::from_array([ + /// prefix.iter().copied().sum(), + /// 0.0, + /// 0.0, + /// suffix.iter().copied().sum(), + /// ]); + /// let sums = middle.iter().copied().fold(sums, f32x4::add); + /// sums.reduce_sum() + /// } + /// + /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect(); + /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0); + /// ``` + #[unstable(feature = "portable_simd", issue = "86656")] + #[must_use] + pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T]) + where + Simd<T, LANES>: AsRef<[T; LANES]>, + T: simd::SimdElement, + simd::LaneCount<LANES>: simd::SupportedLaneCount, + { + // These are expected to always match, as vector types are laid out like + // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we + // might as well double-check since it'll optimize away anyhow. + assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>()); + + // SAFETY: The simd types have the same layout as arrays, just with + // potentially-higher alignment, so the de-facto transmutes are sound. + unsafe { self.align_to() } + } + + /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix. + /// + /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak + /// postconditions as that method. You're only assured that + /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`. + /// + /// Notably, all of the following are possible: + /// - `prefix.len() >= LANES`. + /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`. + /// - `suffix.len() >= LANES`. + /// + /// That said, this is a safe method, so if you're only writing safe code, + /// then this can at most cause incorrect logic, not unsoundness. + /// + /// This is the mutable version of [`slice::as_simd`]; see that for examples. + /// + /// # Panics + /// + /// This will panic if the size of the SIMD type is different from + /// `LANES` times that of the scalar. + /// + /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps + /// that from ever happening, as only power-of-two numbers of lanes are + /// supported. It's possible that, in the future, those restrictions might + /// be lifted in a way that would make it possible to see panics from this + /// method for something like `LANES == 3`. + #[unstable(feature = "portable_simd", issue = "86656")] + #[must_use] + pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T]) + where + Simd<T, LANES>: AsMut<[T; LANES]>, + T: simd::SimdElement, + simd::LaneCount<LANES>: simd::SupportedLaneCount, + { + // These are expected to always match, as vector types are laid out like + // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we + // might as well double-check since it'll optimize away anyhow. + assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>()); + + // SAFETY: The simd types have the same layout as arrays, just with + // potentially-higher alignment, so the de-facto transmutes are sound. + unsafe { self.align_to_mut() } + } + + /// Checks if the elements of this slice are sorted. + /// + /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the + /// slice yields exactly zero or one element, `true` is returned. + /// + /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition + /// implies that this function returns `false` if any two consecutive items are not + /// comparable. + /// + /// # Examples + /// + /// ``` + /// #![feature(is_sorted)] + /// let empty: [i32; 0] = []; + /// + /// assert!([1, 2, 2, 9].is_sorted()); + /// assert!(![1, 3, 2, 4].is_sorted()); + /// assert!([0].is_sorted()); + /// assert!(empty.is_sorted()); + /// assert!(![0.0, 1.0, f32::NAN].is_sorted()); + /// ``` + #[inline] + #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] + #[must_use] + pub fn is_sorted(&self) -> bool + where + T: PartialOrd, + { + self.is_sorted_by(|a, b| a.partial_cmp(b)) + } + + /// Checks if the elements of this slice are sorted using the given comparator function. + /// + /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` + /// function to determine the ordering of two elements. Apart from that, it's equivalent to + /// [`is_sorted`]; see its documentation for more information. + /// + /// [`is_sorted`]: slice::is_sorted + #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] + #[must_use] + pub fn is_sorted_by<F>(&self, mut compare: F) -> bool + where + F: FnMut(&T, &T) -> Option<Ordering>, + { + self.iter().is_sorted_by(|a, b| compare(*a, *b)) + } + + /// Checks if the elements of this slice are sorted using the given key extraction function. + /// + /// Instead of comparing the slice's elements directly, this function compares the keys of the + /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its + /// documentation for more information. + /// + /// [`is_sorted`]: slice::is_sorted + /// + /// # Examples + /// + /// ``` + /// #![feature(is_sorted)] + /// + /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len())); + /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs())); + /// ``` + #[inline] + #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] + #[must_use] + pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool + where + F: FnMut(&T) -> K, + K: PartialOrd, + { + self.iter().is_sorted_by_key(f) + } + + /// Returns the index of the partition point according to the given predicate + /// (the index of the first element of the second partition). + /// + /// The slice is assumed to be partitioned according to the given predicate. + /// This means that all elements for which the predicate returns true are at the start of the slice + /// and all elements for which the predicate returns false are at the end. + /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0 + /// (all odd numbers are at the start, all even at the end). + /// + /// If this slice is not partitioned, the returned result is unspecified and meaningless, + /// as this method performs a kind of binary search. + /// + /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`]. + /// + /// [`binary_search`]: slice::binary_search + /// [`binary_search_by`]: slice::binary_search_by + /// [`binary_search_by_key`]: slice::binary_search_by_key + /// + /// # Examples + /// + /// ``` + /// let v = [1, 2, 3, 3, 5, 6, 7]; + /// let i = v.partition_point(|&x| x < 5); + /// + /// assert_eq!(i, 4); + /// assert!(v[..i].iter().all(|&x| x < 5)); + /// assert!(v[i..].iter().all(|&x| !(x < 5))); + /// ``` + /// + /// If you want to insert an item to a sorted vector, while maintaining + /// sort order: + /// + /// ``` + /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]; + /// let num = 42; + /// let idx = s.partition_point(|&x| x < num); + /// s.insert(idx, num); + /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]); + /// ``` + #[stable(feature = "partition_point", since = "1.52.0")] + #[must_use] + pub fn partition_point<P>(&self, mut pred: P) -> usize + where + P: FnMut(&T) -> bool, + { + self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i) + } + + /// Removes the subslice corresponding to the given range + /// and returns a reference to it. + /// + /// Returns `None` and does not modify the slice if the given + /// range is out of bounds. + /// + /// Note that this method only accepts one-sided ranges such as + /// `2..` or `..6`, but not `2..6`. + /// + /// # Examples + /// + /// Taking the first three elements of a slice: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &[_] = &['a', 'b', 'c', 'd']; + /// let mut first_three = slice.take(..3).unwrap(); + /// + /// assert_eq!(slice, &['d']); + /// assert_eq!(first_three, &['a', 'b', 'c']); + /// ``` + /// + /// Taking the last two elements of a slice: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &[_] = &['a', 'b', 'c', 'd']; + /// let mut tail = slice.take(2..).unwrap(); + /// + /// assert_eq!(slice, &['a', 'b']); + /// assert_eq!(tail, &['c', 'd']); + /// ``` + /// + /// Getting `None` when `range` is out of bounds: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &[_] = &['a', 'b', 'c', 'd']; + /// + /// assert_eq!(None, slice.take(5..)); + /// assert_eq!(None, slice.take(..5)); + /// assert_eq!(None, slice.take(..=4)); + /// let expected: &[char] = &['a', 'b', 'c', 'd']; + /// assert_eq!(Some(expected), slice.take(..4)); + /// ``` + #[inline] + #[must_use = "method does not modify the slice if the range is out of bounds"] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> { + let (direction, split_index) = split_point_of(range)?; + if split_index > self.len() { + return None; + } + let (front, back) = self.split_at(split_index); + match direction { + Direction::Front => { + *self = back; + Some(front) + } + Direction::Back => { + *self = front; + Some(back) + } + } + } + + /// Removes the subslice corresponding to the given range + /// and returns a mutable reference to it. + /// + /// Returns `None` and does not modify the slice if the given + /// range is out of bounds. + /// + /// Note that this method only accepts one-sided ranges such as + /// `2..` or `..6`, but not `2..6`. + /// + /// # Examples + /// + /// Taking the first three elements of a slice: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd']; + /// let mut first_three = slice.take_mut(..3).unwrap(); + /// + /// assert_eq!(slice, &mut ['d']); + /// assert_eq!(first_three, &mut ['a', 'b', 'c']); + /// ``` + /// + /// Taking the last two elements of a slice: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd']; + /// let mut tail = slice.take_mut(2..).unwrap(); + /// + /// assert_eq!(slice, &mut ['a', 'b']); + /// assert_eq!(tail, &mut ['c', 'd']); + /// ``` + /// + /// Getting `None` when `range` is out of bounds: + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd']; + /// + /// assert_eq!(None, slice.take_mut(5..)); + /// assert_eq!(None, slice.take_mut(..5)); + /// assert_eq!(None, slice.take_mut(..=4)); + /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd']; + /// assert_eq!(Some(expected), slice.take_mut(..4)); + /// ``` + #[inline] + #[must_use = "method does not modify the slice if the range is out of bounds"] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take_mut<'a, R: OneSidedRange<usize>>( + self: &mut &'a mut Self, + range: R, + ) -> Option<&'a mut Self> { + let (direction, split_index) = split_point_of(range)?; + if split_index > self.len() { + return None; + } + let (front, back) = mem::take(self).split_at_mut(split_index); + match direction { + Direction::Front => { + *self = back; + Some(front) + } + Direction::Back => { + *self = front; + Some(back) + } + } + } + + /// Removes the first element of the slice and returns a reference + /// to it. + /// + /// Returns `None` if the slice is empty. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &[_] = &['a', 'b', 'c']; + /// let first = slice.take_first().unwrap(); + /// + /// assert_eq!(slice, &['b', 'c']); + /// assert_eq!(first, &'a'); + /// ``` + #[inline] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> { + let (first, rem) = self.split_first()?; + *self = rem; + Some(first) + } + + /// Removes the first element of the slice and returns a mutable + /// reference to it. + /// + /// Returns `None` if the slice is empty. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &mut [_] = &mut ['a', 'b', 'c']; + /// let first = slice.take_first_mut().unwrap(); + /// *first = 'd'; + /// + /// assert_eq!(slice, &['b', 'c']); + /// assert_eq!(first, &'d'); + /// ``` + #[inline] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> { + let (first, rem) = mem::take(self).split_first_mut()?; + *self = rem; + Some(first) + } + + /// Removes the last element of the slice and returns a reference + /// to it. + /// + /// Returns `None` if the slice is empty. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &[_] = &['a', 'b', 'c']; + /// let last = slice.take_last().unwrap(); + /// + /// assert_eq!(slice, &['a', 'b']); + /// assert_eq!(last, &'c'); + /// ``` + #[inline] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> { + let (last, rem) = self.split_last()?; + *self = rem; + Some(last) + } + + /// Removes the last element of the slice and returns a mutable + /// reference to it. + /// + /// Returns `None` if the slice is empty. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_take)] + /// + /// let mut slice: &mut [_] = &mut ['a', 'b', 'c']; + /// let last = slice.take_last_mut().unwrap(); + /// *last = 'd'; + /// + /// assert_eq!(slice, &['a', 'b']); + /// assert_eq!(last, &'d'); + /// ``` + #[inline] + #[unstable(feature = "slice_take", issue = "62280")] + pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> { + let (last, rem) = mem::take(self).split_last_mut()?; + *self = rem; + Some(last) + } +} + +impl<T, const N: usize> [[T; N]] { + /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`. + /// + /// # Panics + /// + /// This panics if the length of the resulting slice would overflow a `usize`. + /// + /// This is only possible when flattening a slice of arrays of zero-sized + /// types, and thus tends to be irrelevant in practice. If + /// `size_of::<T>() > 0`, this will never panic. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_flatten)] + /// + /// assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]); + /// + /// assert_eq!( + /// [[1, 2, 3], [4, 5, 6]].flatten(), + /// [[1, 2], [3, 4], [5, 6]].flatten(), + /// ); + /// + /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []]; + /// assert!(slice_of_empty_arrays.flatten().is_empty()); + /// + /// let empty_slice_of_arrays: &[[u32; 10]] = &[]; + /// assert!(empty_slice_of_arrays.flatten().is_empty()); + /// ``` + #[unstable(feature = "slice_flatten", issue = "95629")] + pub fn flatten(&self) -> &[T] { + let len = if crate::mem::size_of::<T>() == 0 { + self.len().checked_mul(N).expect("slice len overflow") + } else { + // SAFETY: `self.len() * N` cannot overflow because `self` is + // already in the address space. + unsafe { self.len().unchecked_mul(N) } + }; + // SAFETY: `[T]` is layout-identical to `[T; N]` + unsafe { from_raw_parts(self.as_ptr().cast(), len) } + } + + /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`. + /// + /// # Panics + /// + /// This panics if the length of the resulting slice would overflow a `usize`. + /// + /// This is only possible when flattening a slice of arrays of zero-sized + /// types, and thus tends to be irrelevant in practice. If + /// `size_of::<T>() > 0`, this will never panic. + /// + /// # Examples + /// + /// ``` + /// #![feature(slice_flatten)] + /// + /// fn add_5_to_all(slice: &mut [i32]) { + /// for i in slice { + /// *i += 5; + /// } + /// } + /// + /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]; + /// add_5_to_all(array.flatten_mut()); + /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]); + /// ``` + #[unstable(feature = "slice_flatten", issue = "95629")] + pub fn flatten_mut(&mut self) -> &mut [T] { + let len = if crate::mem::size_of::<T>() == 0 { + self.len().checked_mul(N).expect("slice len overflow") + } else { + // SAFETY: `self.len() * N` cannot overflow because `self` is + // already in the address space. + unsafe { self.len().unchecked_mul(N) } + }; + // SAFETY: `[T]` is layout-identical to `[T; N]` + unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) } + } +} + +#[cfg(not(bootstrap))] +#[cfg(not(test))] +impl [f32] { + /// Sorts the slice of floats. + /// + /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses + /// the ordering defined by [`f32::total_cmp`]. + /// + /// # Current implementation + /// + /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by). + /// + /// # Examples + /// + /// ``` + /// #![feature(sort_floats)] + /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0]; + /// + /// v.sort_floats(); + /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN]; + /// assert_eq!(&v[..8], &sorted[..8]); + /// assert!(v[8].is_nan()); + /// ``` + #[unstable(feature = "sort_floats", issue = "93396")] + #[inline] + pub fn sort_floats(&mut self) { + self.sort_unstable_by(f32::total_cmp); + } +} + +#[cfg(not(bootstrap))] +#[cfg(not(test))] +impl [f64] { + /// Sorts the slice of floats. + /// + /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses + /// the ordering defined by [`f64::total_cmp`]. + /// + /// # Current implementation + /// + /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by). + /// + /// # Examples + /// + /// ``` + /// #![feature(sort_floats)] + /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0]; + /// + /// v.sort_floats(); + /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN]; + /// assert_eq!(&v[..8], &sorted[..8]); + /// assert!(v[8].is_nan()); + /// ``` + #[unstable(feature = "sort_floats", issue = "93396")] + #[inline] + pub fn sort_floats(&mut self) { + self.sort_unstable_by(f64::total_cmp); + } +} + +trait CloneFromSpec<T> { + fn spec_clone_from(&mut self, src: &[T]); +} + +impl<T> CloneFromSpec<T> for [T] +where + T: Clone, +{ + #[track_caller] + default fn spec_clone_from(&mut self, src: &[T]) { + assert!(self.len() == src.len(), "destination and source slices have different lengths"); + // NOTE: We need to explicitly slice them to the same length + // to make it easier for the optimizer to elide bounds checking. + // But since it can't be relied on we also have an explicit specialization for T: Copy. + let len = self.len(); + let src = &src[..len]; + for i in 0..len { + self[i].clone_from(&src[i]); + } + } +} + +impl<T> CloneFromSpec<T> for [T] +where + T: Copy, +{ + #[track_caller] + fn spec_clone_from(&mut self, src: &[T]) { + self.copy_from_slice(src); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")] +impl<T> const Default for &[T] { + /// Creates an empty slice. + fn default() -> Self { + &[] + } +} + +#[stable(feature = "mut_slice_default", since = "1.5.0")] +#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")] +impl<T> const Default for &mut [T] { + /// Creates a mutable empty slice. + fn default() -> Self { + &mut [] + } +} + +#[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")] +/// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`. At a future +/// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to +/// `str`) to slices, and then this trait will be replaced or abolished. +pub trait SlicePattern { + /// The element type of the slice being matched on. + type Item; + + /// Currently, the consumers of `SlicePattern` need a slice. + fn as_slice(&self) -> &[Self::Item]; +} + +#[stable(feature = "slice_strip", since = "1.51.0")] +impl<T> SlicePattern for [T] { + type Item = T; + + #[inline] + fn as_slice(&self) -> &[Self::Item] { + self + } +} + +#[stable(feature = "slice_strip", since = "1.51.0")] +impl<T, const N: usize> SlicePattern for [T; N] { + type Item = T; + + #[inline] + fn as_slice(&self) -> &[Self::Item] { + self + } +} |