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//! 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, Equal, Greater, Less};
use crate::fmt;
use crate::hint;
use crate::intrinsics::{exact_div, unchecked_sub};
use crate::mem::{self, SizedTypeProperties};
use crate::num::NonZero;
use crate::ops::{Bound, OneSidedRange, Range, RangeBounds};
use crate::ptr;
use crate::simd::{self, Simd};
use crate::slice;
use crate::ub_checks::assert_unsafe_precondition;
#[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;
#[unstable(
feature = "slice_internals",
issue = "none",
reason = "exposed from core to be reused in std;"
)]
pub mod sort;
mod ascii;
mod cmp;
pub(crate) mod index;
mod iter;
mod raw;
mod rotate;
mod select;
mod specialize;
#[unstable(feature = "str_internals", issue = "none")]
#[doc(hidden)]
pub use ascii::is_ascii_simple;
#[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;
#[stable(feature = "slice_group_by", since = "1.77.0")]
pub use iter::{ChunkBy, ChunkByMut};
#[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, try_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")]
#[rustc_allow_const_fn_unstable(ptr_metadata)]
#[inline]
#[must_use]
pub const fn len(&self) -> usize {
ptr::metadata(self)
}
/// Returns `true` if the slice has a length of 0.
///
/// # Examples
///
/// ```
/// let a = [1, 2, 3];
/// assert!(!a.is_empty());
///
/// let b: &[i32] = &[];
/// assert!(b.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]);
///
/// let y: &mut [i32] = &mut [];
/// assert_eq!(None, y.first_mut());
/// ```
#[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 reference to the last item in the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_mut() {
/// *last = 10;
/// }
/// assert_eq!(x, &[0, 1, 10]);
///
/// let y: &mut [i32] = &mut [];
/// assert_eq!(None, y.last_mut());
/// ```
#[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 }
}
/// Return an array reference to the first `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let u = [10, 40, 30];
/// assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());
///
/// let v: &[i32] = &[10];
/// assert_eq!(None, v.first_chunk::<2>());
///
/// let w: &[i32] = &[];
/// assert_eq!(Some(&[]), w.first_chunk::<0>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the reference outlive the slice.
Some(unsafe { &*(self.as_ptr().cast::<[T; N]>()) })
}
}
/// Return a mutable array reference to the first `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(first) = x.first_chunk_mut::<2>() {
/// first[0] = 5;
/// first[1] = 4;
/// }
/// assert_eq!(x, &[5, 4, 2]);
///
/// assert_eq!(None, x.first_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
pub const fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and require exclusive access to the entire slice to mutate the chunk.
Some(unsafe { &mut *(self.as_mut_ptr().cast::<[T; N]>()) })
}
}
/// Return an array reference to the first `N` items in the slice and the remaining slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_chunk::<2>() {
/// assert_eq!(first, &[0, 1]);
/// assert_eq!(elements, &[2]);
/// }
///
/// assert_eq!(None, x.split_first_chunk::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the split.
let (first, tail) = unsafe { self.split_at_unchecked(N) };
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some((unsafe { &*(first.as_ptr().cast::<[T; N]>()) }, tail))
}
}
/// Return a mutable array reference to the first `N` items in the slice and the remaining
/// slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
/// first[0] = 3;
/// first[1] = 4;
/// elements[0] = 5;
/// }
/// assert_eq!(x, &[3, 4, 5]);
///
/// assert_eq!(None, x.split_first_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
pub const fn split_first_chunk_mut<const N: usize>(
&mut self,
) -> Option<(&mut [T; N], &mut [T])> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the split.
let (first, tail) = unsafe { self.split_at_mut_unchecked(N) };
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and enforce exclusive mutability of the chunk by the split.
Some((unsafe { &mut *(first.as_mut_ptr().cast::<[T; N]>()) }, tail))
}
}
/// Return an array reference to the last `N` items in the slice and the remaining slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((elements, last)) = x.split_last_chunk::<2>() {
/// assert_eq!(elements, &[0]);
/// assert_eq!(last, &[1, 2]);
/// }
///
/// assert_eq!(None, x.split_last_chunk::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the split.
let (init, last) = unsafe { self.split_at_unchecked(self.len() - N) };
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some((init, unsafe { &*(last.as_ptr().cast::<[T; N]>()) }))
}
}
/// Return a mutable array reference to the last `N` items in the slice and the remaining
/// slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((elements, last)) = x.split_last_chunk_mut::<2>() {
/// last[0] = 3;
/// last[1] = 4;
/// elements[0] = 5;
/// }
/// assert_eq!(x, &[5, 3, 4]);
///
/// assert_eq!(None, x.split_last_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
pub const fn split_last_chunk_mut<const N: usize>(
&mut self,
) -> Option<(&mut [T], &mut [T; N])> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the split.
let (init, last) = unsafe { self.split_at_mut_unchecked(self.len() - N) };
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and enforce exclusive mutability of the chunk by the split.
Some((init, unsafe { &mut *(last.as_mut_ptr().cast::<[T; N]>()) }))
}
}
/// Return an array reference to the last `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let u = [10, 40, 30];
/// assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());
///
/// let v: &[i32] = &[10];
/// assert_eq!(None, v.last_chunk::<2>());
///
/// let w: &[i32] = &[];
/// assert_eq!(Some(&[]), w.last_chunk::<0>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_stable(feature = "slice_first_last_chunk", since = "1.77.0")]
pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the slice.
// FIXME: Without const traits, we need this instead of `get_unchecked`.
let last = unsafe { self.split_at_unchecked(self.len() - N).1 };
// SAFETY: We explicitly check for the correct number of elements,
// and do not let the references outlive the slice.
Some(unsafe { &*(last.as_ptr().cast::<[T; N]>()) })
}
}
/// Return a mutable array reference to the last `N` items in the slice.
///
/// If the slice is not at least `N` in length, this will return `None`.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_chunk_mut::<2>() {
/// last[0] = 10;
/// last[1] = 20;
/// }
/// assert_eq!(x, &[0, 10, 20]);
///
/// assert_eq!(None, x.last_chunk_mut::<4>());
/// ```
#[inline]
#[stable(feature = "slice_first_last_chunk", since = "1.77.0")]
#[rustc_const_unstable(feature = "const_slice_first_last_chunk", issue = "111774")]
pub const fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
if self.len() < N {
None
} else {
// SAFETY: We manually verified the bounds of the slice.
// FIXME: Without const traits, we need this instead of `get_unchecked`.
let last = unsafe { self.split_at_mut_unchecked(self.len() - N).1 };
// SAFETY: We explicitly check for the correct number of elements,
// do not let the reference outlive the slice,
// and require exclusive access to the entire slice to mutate the chunk.
Some(unsafe { &mut *(last.as_mut_ptr().cast::<[T; N]>()) })
}
}
/// 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")]
#[inline]
#[must_use]
pub fn get<I>(&self, index: I) -> Option<&I::Output>
where
I: 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")]
#[inline]
#[must_use]
pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
where
I: 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.
///
/// You can think of this like `.get(index).unwrap_unchecked()`. It's UB
/// to call `.get_unchecked(len)`, even if you immediately convert to a
/// pointer. And it's UB to call `.get_unchecked(..len + 1)`,
/// `.get_unchecked(..=len)`, or similar.
///
/// [`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")]
#[inline]
#[must_use]
pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
where
I: 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.
///
/// You can think of this like `.get_mut(index).unwrap_unchecked()`. It's
/// UB to call `.get_unchecked_mut(len)`, even if you immediately convert
/// to a pointer. And it's UB to call `.get_unchecked_mut(..len + 1)`,
/// `.get_unchecked_mut(..=len)`, or similar.
///
/// [`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")]
#[inline]
#[must_use]
pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
where
I: 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")]
#[rustc_never_returns_null_ptr]
#[inline(always)]
#[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)]
#[rustc_never_returns_null_ptr]
#[inline(always)]
#[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.
///
/// If `a` equals to `b`, it's guaranteed that elements won't change value.
///
/// # 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) {
assert_unsafe_precondition!(
check_library_ub,
"slice::swap_unchecked requires that the indices are within the slice",
(
len: usize = self.len(),
a: usize = a,
b: usize = b,
) => a < len && b < len,
);
let ptr = self.as_mut_ptr();
// SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
unsafe {
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!(a.len() == n);
debug_assert!(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]);
let mut i = 0;
while i < n {
mem::swap(&mut a[i], &mut b[n - 1 - i]);
i += 1;
}
}
}
/// 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 = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.windows(3);
/// assert_eq!(iter.next().unwrap(), &['l', 'o', 'r']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r', 'e']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e', 'm']);
/// 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());
/// ```
///
/// There's no `windows_mut`, as that existing would let safe code violate the
/// "only one `&mut` at a time to the same thing" rule. However, you can sometimes
/// use [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
/// conjunction with `windows` to accomplish something similar:
/// ```
/// use std::cell::Cell;
///
/// let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
/// let slice = &mut array[..];
/// let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
/// for w in slice_of_cells.windows(3) {
/// Cell::swap(&w[0], &w[2]);
/// }
/// assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
#[track_caller]
pub fn windows(&self, size: usize) -> Windows<'_, T> {
let size = NonZero::new(size).expect("window size must be non-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]
#[track_caller]
pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-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]
#[track_caller]
pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-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]
#[track_caller]
pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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 const unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
assert_unsafe_precondition!(
check_language_ub,
"slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
(n: usize = N, len: usize = self.len()) => n != 0 && len % n == 0,
);
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe { 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']);
/// ```
///
/// If you expect the slice to be an exact multiple, you can combine
/// `let`-`else` with an empty slice pattern:
/// ```
/// #![feature(slice_as_chunks)]
/// let slice = ['R', 'u', 's', 't'];
/// let (chunks, []) = slice.as_chunks::<2>() else {
/// panic!("slice didn't have even length")
/// };
/// assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
#[track_caller]
#[must_use]
pub const fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
assert!(N != 0, "chunk size must be non-zero");
let len_rounded_down = self.len() / N * N;
// SAFETY: The rounded-down value is always the same or smaller than the
// original length, and thus must be in-bounds of the slice.
let (multiple_of_n, remainder) = unsafe { self.split_at_unchecked(len_rounded_down) };
// 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]
#[track_caller]
#[must_use]
pub const fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
assert!(N != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
assert!(N != 0, "chunk size must be non-zero");
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 const unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
assert_unsafe_precondition!(
check_language_ub,
"slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
(n: usize = N, len: usize = self.len()) => n != 0 && len % n == 0
);
// SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
let new_len = unsafe { 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]
#[track_caller]
#[must_use]
pub const fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
assert!(N != 0, "chunk size must be non-zero");
let len_rounded_down = self.len() / N * N;
// SAFETY: The rounded-down value is always the same or smaller than the
// original length, and thus must be in-bounds of the slice.
let (multiple_of_n, remainder) = unsafe { self.split_at_mut_unchecked(len_rounded_down) };
// 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]
#[track_caller]
#[must_use]
pub const fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
assert!(N != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
assert!(N != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
assert!(N != 0, "window size must be non-zero");
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]
#[track_caller]
pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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]
#[track_caller]
pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
assert!(chunk_size != 0, "chunk size must be non-zero");
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 for every pair of consecutive elements,
/// meaning that it is called on `slice[0]` and `slice[1]`,
/// followed by `slice[1]` and `slice[2]`, and so on.
///
/// # Examples
///
/// ```
/// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.chunk_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:
///
/// ```
/// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.chunk_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);
/// ```
#[stable(feature = "slice_group_by", since = "1.77.0")]
#[inline]
pub fn chunk_by<F>(&self, pred: F) -> ChunkBy<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
ChunkBy::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 for every pair of consecutive elements,
/// meaning that it is called on `slice[0]` and `slice[1]`,
/// followed by `slice[1]` and `slice[2]`, and so on.
///
/// # Examples
///
/// ```
/// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.chunk_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:
///
/// ```
/// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.chunk_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);
/// ```
#[stable(feature = "slice_group_by", since = "1.77.0")]
#[inline]
pub fn chunk_by_mut<F>(&mut self, pred: F) -> ChunkByMut<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
ChunkByMut::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`. For a non-panicking alternative see
/// [`split_at_checked`](slice::split_at_checked).
///
/// # 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")]
#[rustc_const_stable(feature = "const_slice_split_at_not_mut", since = "1.71.0")]
#[rustc_allow_const_fn_unstable(split_at_checked)]
#[inline]
#[track_caller]
#[must_use]
pub const fn split_at(&self, mid: usize) -> (&[T], &[T]) {
match self.split_at_checked(mid) {
Some(pair) => pair,
None => panic!("mid > len"),
}
}
/// 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`. For a non-panicking alternative see
/// [`split_at_mut_checked`](slice::split_at_mut_checked).
///
/// # 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]
#[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
match self.split_at_mut_checked(mid) {
Some(pair) => pair,
None => panic!("mid > len"),
}
}
/// 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
///
/// ```
/// 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, []);
/// }
/// ```
#[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
#[rustc_const_stable(feature = "const_slice_split_at_unchecked", since = "1.77.0")]
#[inline]
#[must_use]
pub const unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
// HACK: the const function `from_raw_parts` is used to make this
// function const; previously the implementation used
// `(self.get_unchecked(..mid), self.get_unchecked(mid..))`
let len = self.len();
let ptr = self.as_ptr();
assert_unsafe_precondition!(
check_library_ub,
"slice::split_at_unchecked requires the index to be within the slice",
(mid: usize = mid, len: usize = len) => mid <= len,
);
// SAFETY: Caller has to check that `0 <= mid <= self.len()`
unsafe { (from_raw_parts(ptr, mid), from_raw_parts(ptr.add(mid), unchecked_sub(len, 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
///
/// ```
/// 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]);
/// ```
#[stable(feature = "slice_split_at_unchecked", since = "1.79.0")]
#[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
#[inline]
#[must_use]
pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
let len = self.len();
let ptr = self.as_mut_ptr();
assert_unsafe_precondition!(
check_library_ub,
"slice::split_at_mut_unchecked requires the index to be within the slice",
(mid: usize = mid, len: usize = len) => mid <= len,
);
// 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 {
(
from_raw_parts_mut(ptr, mid),
from_raw_parts_mut(ptr.add(mid), unchecked_sub(len, mid)),
)
}
}
/// Divides one slice into two at an index, returning `None` if the slice is
/// too short.
///
/// If `mid ≤ len` returns a pair of slices where 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).
///
/// Otherwise, if `mid > len`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = [1, -2, 3, -4, 5, -6];
///
/// {
/// let (left, right) = v.split_at_checked(0).unwrap();
/// assert_eq!(left, []);
/// assert_eq!(right, [1, -2, 3, -4, 5, -6]);
/// }
///
/// {
/// let (left, right) = v.split_at_checked(2).unwrap();
/// assert_eq!(left, [1, -2]);
/// assert_eq!(right, [3, -4, 5, -6]);
/// }
///
/// {
/// let (left, right) = v.split_at_checked(6).unwrap();
/// assert_eq!(left, [1, -2, 3, -4, 5, -6]);
/// assert_eq!(right, []);
/// }
///
/// assert_eq!(None, v.split_at_checked(7));
/// ```
#[stable(feature = "split_at_checked", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_stable(feature = "split_at_checked", since = "CURRENT_RUSTC_VERSION")]
#[inline]
#[must_use]
pub const fn split_at_checked(&self, mid: usize) -> Option<(&[T], &[T])> {
if mid <= self.len() {
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `split_at_unchecked`.
Some(unsafe { self.split_at_unchecked(mid) })
} else {
None
}
}
/// Divides one mutable slice into two at an index, returning `None` if the
/// slice is too short.
///
/// If `mid ≤ len` returns a pair of slices where 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).
///
/// Otherwise, if `mid > len`, returns `None`.
///
/// # Examples
///
/// ```
/// let mut v = [1, 0, 3, 0, 5, 6];
///
/// if let Some((left, right)) = v.split_at_mut_checked(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]);
///
/// assert_eq!(None, v.split_at_mut_checked(7));
/// ```
#[stable(feature = "split_at_checked", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
#[inline]
#[must_use]
pub const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut [T], &mut [T])> {
if mid <= self.len() {
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `split_at_unchecked`.
Some(unsafe { self.split_at_mut_unchecked(mid) })
} else {
None
}
}
/// 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 mutable 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)
}
/// Splits the slice on the first element that matches the specified
/// predicate.
///
/// If any matching elements are present in the slice, returns the prefix
/// before the match and suffix after. The matching element itself is not
/// included. If no elements match, returns `None`.
///
/// # Examples
///
/// ```
/// #![feature(slice_split_once)]
/// let s = [1, 2, 3, 2, 4];
/// assert_eq!(s.split_once(|&x| x == 2), Some((
/// &[1][..],
/// &[3, 2, 4][..]
/// )));
/// assert_eq!(s.split_once(|&x| x == 0), None);
/// ```
#[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
#[inline]
pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
where
F: FnMut(&T) -> bool,
{
let index = self.iter().position(pred)?;
Some((&self[..index], &self[index + 1..]))
}
/// Splits the slice on the last element that matches the specified
/// predicate.
///
/// If any matching elements are present in the slice, returns the prefix
/// before the match and suffix after. The matching element itself is not
/// included. If no elements match, returns `None`.
///
/// # Examples
///
/// ```
/// #![feature(slice_split_once)]
/// let s = [1, 2, 3, 2, 4];
/// assert_eq!(s.rsplit_once(|&x| x == 2), Some((
/// &[1, 2, 3][..],
/// &[4][..]
/// )));
/// assert_eq!(s.rsplit_once(|&x| x == 0), None);
/// ```
#[unstable(feature = "slice_split_once", reason = "newly added", issue = "112811")]
#[inline]
pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>
where
F: FnMut(&T) -> bool,
{
let index = self.iter().rposition(pred)?;
Some((&self[..index], &self[index + 1..]))
}
/// 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 or equal to the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.starts_with(&[10]));
/// assert!(v.starts_with(&[10, 40]));
/// assert!(v.starts_with(&v));
/// 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 or equal to the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.ends_with(&[30]));
/// assert!(v.ends_with(&[40, 30]));
/// assert!(v.ends_with(&v));
/// 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 `prefix` is equal to the
/// original slice, returns an empty 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(&[10, 40, 30]), Some(&[][..]));
/// 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 `suffix` is equal to the
/// original slice, returns an empty 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(&[10, 40, 30]), Some(&[][..]));
/// 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.
/// If the slice is not sorted, the returned result is unspecified and
/// meaningless.
///
/// 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`].
///
/// [`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 find that whole *range* of matching items, rather than
/// an arbitrary matching one, that can be done using [`partition_point`]:
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// let low = s.partition_point(|x| x < &1);
/// assert_eq!(low, 1);
/// let high = s.partition_point(|x| x <= &1);
/// assert_eq!(high, 5);
/// let r = s.binary_search(&1);
/// assert!((low..high).contains(&r.unwrap()));
///
/// assert!(s[..low].iter().all(|&x| x < 1));
/// assert!(s[low..high].iter().all(|&x| x == 1));
/// assert!(s[high..].iter().all(|&x| x > 1));
///
/// // For something not found, the "range" of equal items is empty
/// assert_eq!(s.partition_point(|x| x < &11), 9);
/// assert_eq!(s.partition_point(|x| x <= &11), 9);
/// assert_eq!(s.binary_search(&11), Err(9));
/// ```
///
/// 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);
/// // If `num` is unique, `s.partition_point(|&x| x < num)` (with `<`) is equivalent to
/// // `s.binary_search(&num).unwrap_or_else(|x| x)`, but using `<=` will allow `insert`
/// // to shift less elements.
/// 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.
///
/// The comparator function should return an order code that indicates
/// whether its argument is `Less`, `Equal` or `Greater` the desired
/// target.
/// If the slice is not sorted or if the comparator function does not
/// implement an order consistent with the sort order of the underlying
/// slice, the returned result is unspecified and meaningless.
///
/// 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`].
///
/// [`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,
{
// INVARIANTS:
// - 0 <= left <= left + size = right <= self.len()
// - f returns Less for everything in self[..left]
// - f returns Greater for everything in self[right..]
let mut size = self.len();
let mut left = 0;
let mut right = size;
while left < right {
let mid = left + size / 2;
// SAFETY: the while condition means `size` is strictly positive, so
// `size/2 < size`. Thus `left + size/2 < left + size`, which
// coupled with the `left + size <= self.len()` invariant means
// we have `left + size/2 < self.len()`, and this is in-bounds.
let cmp = f(unsafe { self.get_unchecked(mid) });
// This control flow produces conditional moves, which results in
// fewer branches and instructions than if/else or matching on
// cmp::Ordering.
// This is x86 asm for u8: https://rust.godbolt.org/z/698eYffTx.
left = if cmp == Less { mid + 1 } else { left };
right = if cmp == Greater { mid } else { right };
if cmp == Equal {
// SAFETY: same as the `get_unchecked` above
unsafe { hint::assert_unchecked(mid < self.len()) };
return Ok(mid);
}
size = right - left;
}
// SAFETY: directly true from the overall invariant.
// Note that this is `<=`, unlike the assume in the `Ok` path.
unsafe { hint::assert_unchecked(left <= self.len()) };
Err(left)
}
/// Binary searches this slice with a key extraction function.
///
/// Assumes that the slice is sorted by the key, for instance with
/// [`sort_by_key`] using the same key extraction function.
/// If the slice is not sorted by the key, the returned result is
/// unspecified and meaningless.
///
/// 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`].
///
/// [`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, T::lt);
}
/// 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` after the reordering 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 runs in *O*(*n*) time.
/// This function is also known as "kth element" in other libraries.
///
/// It returns a triplet of the following from the reordered slice:
/// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
/// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
/// and greater-than-or-equal-to the value of the element at `index`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
/// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
/// pivot selection, which guarantees linear runtime for all inputs.
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 2, -3, 1];
///
/// // Find the items less than or equal to the median, the median, and greater than or equal to
/// // the median.
/// let (lesser, median, greater) = v.select_nth_unstable(2);
///
/// assert!(lesser == [-3, -5] || lesser == [-5, -3]);
/// assert_eq!(median, &mut 1);
/// assert!(greater == [4, 2] || greater == [2, 4]);
///
/// // 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,
{
select::partition_at_index(self, index, T::lt)
}
/// Reorder the slice with a comparator function such that the element at `index` after the reordering 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 runs in *O*(*n*) time.
/// This function is also known as "kth element" in other libraries.
///
/// It returns a triplet of the following from
/// the slice reordered according to the provided comparator function: the subslice prior to
/// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
/// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
/// the value of the element at `index`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
/// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
/// pivot selection, which guarantees linear runtime for all inputs.
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 2, -3, 1];
///
/// // Find the items less than or equal to the median, the median, and greater than or equal to
/// // the median as if the slice were sorted in descending order.
/// let (lesser, median, greater) = v.select_nth_unstable_by(2, |a, b| b.cmp(a));
///
/// assert!(lesser == [4, 2] || lesser == [2, 4]);
/// assert_eq!(median, &mut 1);
/// assert!(greater == [-3, -5] || greater == [-5, -3]);
///
/// // 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,
{
select::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
}
/// Reorder the slice with a key extraction function such that the element at `index` after the reordering 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 runs in *O*(*n*) time.
/// This function is also known as "kth element" in other libraries.
///
/// It returns a triplet of the following from
/// the slice reordered according to the provided key extraction function: the subslice prior to
/// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
/// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
/// the value of the element at `index`.
///
/// # Current implementation
///
/// The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also
/// the basis for [`sort_unstable`]. The fallback algorithm is Median of Medians using Tukey's Ninther for
/// pivot selection, which guarantees linear runtime for all inputs.
///
/// [`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 items less than or equal to the median, the median, and greater than or equal to
/// // the median as if the slice were sorted according to absolute value.
/// let (lesser, median, greater) = v.select_nth_unstable_by_key(2, |a| a.abs());
///
/// assert!(lesser == [1, 2] || lesser == [2, 1]);
/// assert_eq!(median, &mut -3);
/// assert!(greater == [4, -5] || greater == [-5, 4]);
///
/// // 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,
{
select::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
}
/// 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.add(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']);
/// ```
///
/// Rotating 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!
const fn gcd(a: usize, b: usize) -> usize {
if b == 0 { a } else { gcd(b, a % b) }
}
// Explicitly wrap the function call in a const block so it gets
// constant-evaluated even in debug mode.
let gcd: usize = const { 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 middle part will be as big as possible under
/// the given alignment constraint and element size.
///
/// 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 U::IS_ZST || T::IS_ZST {
// 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>();
// Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
#[cfg(miri)]
crate::intrinsics::miri_promise_symbolic_alignment(
rest.as_ptr().cast(),
mem::align_of::<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 mutable slice to a mutable 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 middle part will be as big as possible under
/// the given alignment constraint and element size.
///
/// 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 U::IS_ZST || T::IS_ZST {
// 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 alignment 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();
// Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
#[cfg(miri)]
crate::intrinsics::miri_promise_symbolic_alignment(
mut_ptr.cast() as *const (),
mem::align_of::<U>(),
);
// 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::prelude::*;
///
/// 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;
/// 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 mutable slice into a mutable prefix, a middle of aligned SIMD types,
/// and a mutable 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 <= 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 whether two elements are to be considered in sorted order.
///
/// # Examples
///
/// ```
/// #![feature(is_sorted)]
///
/// assert!([1, 2, 2, 9].is_sorted_by(|a, b| a <= b));
/// assert!(![1, 2, 2, 9].is_sorted_by(|a, b| a < b));
///
/// assert!([0].is_sorted_by(|a, b| true));
/// assert!([0].is_sorted_by(|a, b| false));
///
/// let empty: [i32; 0] = [];
/// assert!(empty.is_sorted_by(|a, b| false));
/// assert!(empty.is_sorted_by(|a, b| true));
/// ```
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
#[must_use]
pub fn is_sorted_by<'a, F>(&'a self, mut compare: F) -> bool
where
F: FnMut(&'a T, &'a T) -> bool,
{
self.array_windows().all(|[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<'a, F, K>(&'a self, f: F) -> bool
where
F: FnMut(&'a 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 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 all elements of the slice match the predicate, including if the slice
/// is empty, then the length of the slice will be returned:
///
/// ```
/// let a = [2, 4, 8];
/// assert_eq!(a.partition_point(|x| x < &100), a.len());
/// let a: [i32; 0] = [];
/// assert_eq!(a.partition_point(|x| x < &100), 0);
/// ```
///
/// 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)
}
/// Returns mutable references to many indices at once, without doing any checks.
///
/// For a safe alternative see [`get_many_mut`].
///
/// # Safety
///
/// Calling this method with overlapping or out-of-bounds indices is *[undefined behavior]*
/// even if the resulting references are not used.
///
/// # Examples
///
/// ```
/// #![feature(get_many_mut)]
///
/// let x = &mut [1, 2, 4];
///
/// unsafe {
/// let [a, b] = x.get_many_unchecked_mut([0, 2]);
/// *a *= 10;
/// *b *= 100;
/// }
/// assert_eq!(x, &[10, 2, 400]);
/// ```
///
/// [`get_many_mut`]: slice::get_many_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[unstable(feature = "get_many_mut", issue = "104642")]
#[inline]
pub unsafe fn get_many_unchecked_mut<const N: usize>(
&mut self,
indices: [usize; N],
) -> [&mut T; N] {
// NB: This implementation is written as it is because any variation of
// `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
// or generate worse code otherwise. This is also why we need to go
// through a raw pointer here.
let slice: *mut [T] = self;
let mut arr: mem::MaybeUninit<[&mut T; N]> = mem::MaybeUninit::uninit();
let arr_ptr = arr.as_mut_ptr();
// SAFETY: We expect `indices` to contain disjunct values that are
// in bounds of `self`.
unsafe {
for i in 0..N {
let idx = *indices.get_unchecked(i);
*(*arr_ptr).get_unchecked_mut(i) = &mut *slice.get_unchecked_mut(idx);
}
arr.assume_init()
}
}
/// Returns mutable references to many indices at once.
///
/// Returns an error if any index is out-of-bounds, or if the same index was
/// passed more than once.
///
/// # Examples
///
/// ```
/// #![feature(get_many_mut)]
///
/// let v = &mut [1, 2, 3];
/// if let Ok([a, b]) = v.get_many_mut([0, 2]) {
/// *a = 413;
/// *b = 612;
/// }
/// assert_eq!(v, &[413, 2, 612]);
/// ```
#[unstable(feature = "get_many_mut", issue = "104642")]
#[inline]
pub fn get_many_mut<const N: usize>(
&mut self,
indices: [usize; N],
) -> Result<[&mut T; N], GetManyMutError<N>> {
if !get_many_check_valid(&indices, self.len()) {
return Err(GetManyMutError { _private: () });
}
// SAFETY: The `get_many_check_valid()` call checked that all indices
// are disjunct and in bounds.
unsafe { Ok(self.get_many_unchecked_mut(indices)) }
}
}
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
///
/// ```
/// assert_eq!([[1, 2, 3], [4, 5, 6]].as_flattened(), &[1, 2, 3, 4, 5, 6]);
///
/// assert_eq!(
/// [[1, 2, 3], [4, 5, 6]].as_flattened(),
/// [[1, 2], [3, 4], [5, 6]].as_flattened(),
/// );
///
/// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
/// assert!(slice_of_empty_arrays.as_flattened().is_empty());
///
/// let empty_slice_of_arrays: &[[u32; 10]] = &[];
/// assert!(empty_slice_of_arrays.as_flattened().is_empty());
/// ```
#[stable(feature = "slice_flatten", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_unstable(feature = "const_slice_flatten", issue = "95629")]
pub const fn as_flattened(&self) -> &[T] {
let len = if T::IS_ZST {
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
///
/// ```
/// 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.as_flattened_mut());
/// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
/// ```
#[stable(feature = "slice_flatten", since = "CURRENT_RUSTC_VERSION")]
pub fn as_flattened_mut(&mut self) -> &mut [T] {
let len = if T::IS_ZST {
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(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(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")]
impl<T> Default for &[T] {
/// Creates an empty slice.
fn default() -> Self {
&[]
}
}
#[stable(feature = "mut_slice_default", since = "1.5.0")]
impl<T> 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
}
}
/// This checks every index against each other, and against `len`.
///
/// This will do `binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, ..`
/// comparison operations.
fn get_many_check_valid<const N: usize>(indices: &[usize; N], len: usize) -> bool {
// NB: The optimizer should inline the loops into a sequence
// of instructions without additional branching.
let mut valid = true;
for (i, &idx) in indices.iter().enumerate() {
valid &= idx < len;
for &idx2 in &indices[..i] {
valid &= idx != idx2;
}
}
valid
}
/// The error type returned by [`get_many_mut<N>`][`slice::get_many_mut`].
///
/// It indicates one of two possible errors:
/// - An index is out-of-bounds.
/// - The same index appeared multiple times in the array.
///
/// # Examples
///
/// ```
/// #![feature(get_many_mut)]
///
/// let v = &mut [1, 2, 3];
/// assert!(v.get_many_mut([0, 999]).is_err());
/// assert!(v.get_many_mut([1, 1]).is_err());
/// ```
#[unstable(feature = "get_many_mut", issue = "104642")]
// NB: The N here is there to be forward-compatible with adding more details
// to the error type at a later point
pub struct GetManyMutError<const N: usize> {
_private: (),
}
#[unstable(feature = "get_many_mut", issue = "104642")]
impl<const N: usize> fmt::Debug for GetManyMutError<N> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("GetManyMutError").finish_non_exhaustive()
}
}
#[unstable(feature = "get_many_mut", issue = "104642")]
impl<const N: usize> fmt::Display for GetManyMutError<N> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt("an index is out of bounds or appeared multiple times in the array", f)
}
}
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