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android / toolchain / rustc / 32f7835b4f844d645621e83c89a3178ef87b0d69 / . / library / core / src / slice / mod.rs
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// ignore-tidy-filelength
//! Slice management and manipulation.
//!
//! For more details see [`std::slice`].
//!
//! [`std::slice`]: ../../std/slice/index.html
#![stable(feature = "rust1", since = "1.0.0")]
use crate::cmp::Ordering::{self, Greater, Less};
use crate::marker::Copy;
use crate::mem;
use crate::num::NonZeroUsize;
use crate::ops::{FnMut, Range, RangeBounds};
use crate::option::Option;
use crate::option::Option::{None, Some};
use crate::ptr;
use crate::result::Result;
use crate::result::Result::{Err, Ok};
use crate::slice;
#[unstable(
feature = "slice_internals",
issue = "none",
reason = "exposed from core to be reused in std; use the memchr crate"
)]
/// Pure rust memchr implementation, taken from rust-memchr
pub mod memchr;
mod ascii;
mod cmp;
mod index;
mod iter;
mod raw;
mod rotate;
mod sort;
mod specialize;
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{Chunks, ChunksMut, Windows};
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{Iter, IterMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
#[stable(feature = "slice_rsplit", since = "1.27.0")]
pub use iter::{RSplit, RSplitMut};
#[stable(feature = "chunks_exact", since = "1.31.0")]
pub use iter::{ChunksExact, ChunksExactMut};
#[stable(feature = "rchunks", since = "1.31.0")]
pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
#[unstable(feature = "array_chunks", issue = "74985")]
pub use iter::{ArrayChunks, ArrayChunksMut};
#[unstable(feature = "array_windows", issue = "75027")]
pub use iter::ArrayWindows;
#[unstable(feature = "slice_group_by", issue = "80552")]
pub use iter::{GroupBy, GroupByMut};
#[stable(feature = "split_inclusive", since = "1.51.0")]
pub use iter::{SplitInclusive, SplitInclusiveMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use raw::{from_raw_parts, from_raw_parts_mut};
#[stable(feature = "from_ref", since = "1.28.0")]
pub use raw::{from_mut, from_ref};
// 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;
#[unstable(feature = "inherent_ascii_escape", issue = "77174")]
pub use ascii::EscapeAscii;
#[lang = "slice"]
#[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);
/// ```
#[doc(alias = "length")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
#[inline]
// SAFETY: const sound because we transmute out the length field as a usize (which it must be)
#[rustc_allow_const_fn_unstable(const_fn_union)]
pub const fn len(&self) -> usize {
// FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
// As of this writing this causes a "Const-stable functions can only call other
// const-stable functions" error.
// SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
// and PtrComponents<T> have the same memory layouts. Only std can make this
// guarantee.
unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
}
/// Returns `true` if the slice has a length of 0.
///
/// # Examples
///
/// ```
/// let a = [1, 2, 3];
/// assert!(!a.is_empty());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
#[inline]
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_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub const fn first(&self) -> Option<&T> {
if let [first, ..] = self { Some(first) } else { None }
}
/// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(first) = x.first_mut() {
/// *first = 5;
/// }
/// assert_eq!(x, &[5, 1, 2]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
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_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
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]
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_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
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]
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_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub const fn last(&self) -> Option<&T> {
if let [.., last] = self { Some(last) } else { None }
}
/// Returns a mutable pointer to the last item in the slice.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_mut() {
/// *last = 10;
/// }
/// assert_eq!(x, &[0, 1, 10]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
#[inline]
pub const fn last_mut(&mut self) -> Option<&mut T> {
if let [.., last] = self { Some(last) } else { None }
}
/// Returns a reference to an element or subslice depending on the type of
/// index.
///
/// - If given a position, returns a reference to the element at that
/// position or `None` if out of bounds.
/// - If given a range, returns the subslice corresponding to that range,
/// or `None` if out of bounds.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&40), v.get(1));
/// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
/// assert_eq!(None, v.get(3));
/// assert_eq!(None, v.get(0..4));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
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]
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.
///
/// [`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]
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 dereferencable because `self` is a safe reference.
// The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
unsafe { &*index.get_unchecked(self) }
}
/// Returns a mutable reference to an element or subslice, without doing
/// bounds checking.
///
/// For a safe alternative see [`get_mut`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used.
///
/// [`get_mut`]: slice::get_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
///
/// unsafe {
/// let elem = x.get_unchecked_mut(1);
/// *elem = 13;
/// }
/// assert_eq!(x, &[1, 13, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
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 dereferencable because `self` is a safe reference.
// The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
unsafe { &mut *index.get_unchecked_mut(self) }
}
/// Returns a raw pointer to the slice's buffer.
///
/// The caller must ensure that the slice outlives the pointer this
/// function returns, or else it will end up pointing to garbage.
///
/// The caller must also ensure that the memory the pointer (non-transitively) points to
/// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
/// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
///
/// Modifying the container referenced by this slice may cause its buffer
/// to be reallocated, which would also make any pointers to it invalid.
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
/// let x_ptr = x.as_ptr();
///
/// unsafe {
/// for i in 0..x.len() {
/// assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
/// }
/// }
/// ```
///
/// [`as_mut_ptr`]: slice::as_mut_ptr
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
#[inline]
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_unstable(feature = "const_ptr_offset", issue = "71499")]
#[inline]
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_unstable(feature = "const_ptr_offset", issue = "71499")]
#[inline]
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_unstable(feature = "const_ptr_offset", issue = "71499")]
#[inline]
pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
let start = self.as_mut_ptr();
// SAFETY: See as_ptr_range() above for why `add` here is safe.
let end = unsafe { start.add(self.len()) };
start..end
}
/// Swaps two elements in the slice.
///
/// # Arguments
///
/// * a - The index of the first element
/// * b - The index of the second element
///
/// # Panics
///
/// Panics if `a` or `b` are out of bounds.
///
/// # Examples
///
/// ```
/// let mut v = ["a", "b", "c", "d"];
/// v.swap(1, 3);
/// assert!(v == ["a", "d", "c", "b"]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn swap(&mut self, a: usize, b: usize) {
// 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);
}
}
/// 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 mut i: usize = 0;
let ln = self.len();
// For very small types, all the individual reads in the normal
// path perform poorly. We can do better, given efficient unaligned
// load/store, by loading a larger chunk and reversing a register.
// Ideally LLVM would do this for us, as it knows better than we do
// whether unaligned reads are efficient (since that changes between
// different ARM versions, for example) and what the best chunk size
// would be. Unfortunately, as of LLVM 4.0 (2017-05) it only unrolls
// the loop, so we need to do this ourselves. (Hypothesis: reverse
// is troublesome because the sides can be aligned differently --
// will be, when the length is odd -- so there's no way of emitting
// pre- and postludes to use fully-aligned SIMD in the middle.)
let fast_unaligned = cfg!(any(target_arch = "x86", target_arch = "x86_64"));
if fast_unaligned && mem::size_of::<T>() == 1 {
// Use the llvm.bswap intrinsic to reverse u8s in a usize
let chunk = mem::size_of::<usize>();
while i + chunk - 1 < ln / 2 {
// SAFETY: There are several things to check here:
//
// - Note that `chunk` is either 4 or 8 due to the cfg check
// above. So `chunk - 1` is positive.
// - Indexing with index `i` is fine as the loop check guarantees
// `i + chunk - 1 < ln / 2`
// <=> `i < ln / 2 - (chunk - 1) < ln / 2 < ln`.
// - Indexing with index `ln - i - chunk = ln - (i + chunk)` is fine:
// - `i + chunk > 0` is trivially true.
// - The loop check guarantees:
// `i + chunk - 1 < ln / 2`
// <=> `i + chunk ≤ ln / 2 ≤ ln`, thus subtraction does not underflow.
// - The `read_unaligned` and `write_unaligned` calls are fine:
// - `pa` points to index `i` where `i < ln / 2 - (chunk - 1)`
// (see above) and `pb` points to index `ln - i - chunk`, so
// both are at least `chunk`
// many bytes away from the end of `self`.
// - Any initialized memory is valid `usize`.
unsafe {
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - chunk);
let va = ptr::read_unaligned(pa as *mut usize);
let vb = ptr::read_unaligned(pb as *mut usize);
ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
ptr::write_unaligned(pb as *mut usize, va.swap_bytes());
}
i += chunk;
}
}
if fast_unaligned && mem::size_of::<T>() == 2 {
// Use rotate-by-16 to reverse u16s in a u32
let chunk = mem::size_of::<u32>() / 2;
while i + chunk - 1 < ln / 2 {
// SAFETY: An unaligned u32 can be read from `i` if `i + 1 < ln`
// (and obviously `i < ln`), because each element is 2 bytes and
// we're reading 4.
//
// `i + chunk - 1 < ln / 2` # while condition
// `i + 2 - 1 < ln / 2`
// `i + 1 < ln / 2`
//
// Since it's less than the length divided by 2, then it must be
// in bounds.
//
// This also means that the condition `0 < i + chunk <= ln` is
// always respected, ensuring the `pb` pointer can be used
// safely.
unsafe {
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - chunk);
let va = ptr::read_unaligned(pa as *mut u32);
let vb = ptr::read_unaligned(pb as *mut u32);
ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
ptr::write_unaligned(pb as *mut u32, va.rotate_left(16));
}
i += chunk;
}
}
while i < ln / 2 {
// SAFETY: `i` is inferior to half the length of the slice so
// accessing `i` and `ln - i - 1` is safe (`i` starts at 0 and
// will not go further than `ln / 2 - 1`).
// The resulting pointers `pa` and `pb` are therefore valid and
// aligned, and can be read from and written to.
unsafe {
// Unsafe swap to avoid the bounds check in safe swap.
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - 1);
ptr::swap(pa, pb);
}
i += 1;
}
}
/// Returns an iterator over the slice.
///
/// # 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.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
/// for elem in x.iter_mut() {
/// *elem += 2;
/// }
/// assert_eq!(x, &[3, 4, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn iter_mut(&mut self) -> IterMut<'_, T> {
IterMut::new(self)
}
/// Returns an iterator over all contiguous windows of length
/// `size`. The windows overlap. If the slice is shorter than
/// `size`, the iterator returns no values.
///
/// # Panics
///
/// Panics if `size` is 0.
///
/// # Examples
///
/// ```
/// let slice = ['r', 'u', 's', 't'];
/// let mut iter = slice.windows(2);
/// assert_eq!(iter.next().unwrap(), &['r', 'u']);
/// assert_eq!(iter.next().unwrap(), &['u', 's']);
/// assert_eq!(iter.next().unwrap(), &['s', 't']);
/// assert!(iter.next().is_none());
/// ```
///
/// If the slice is shorter than `size`:
///
/// ```
/// let slice = ['f', 'o', 'o'];
/// let mut iter = slice.windows(4);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn windows(&self, size: usize) -> Windows<'_, T> {
let size = NonZeroUsize::new(size).expect("size is zero");
Windows::new(self, size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last chunk will not have length `chunk_size`.
///
/// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
/// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
/// slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.chunks(2);
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert_eq!(iter.next().unwrap(), &['m']);
/// assert!(iter.next().is_none());
/// ```
///
/// [`chunks_exact`]: slice::chunks_exact
/// [`rchunks`]: slice::rchunks
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
assert_ne!(chunk_size, 0);
Chunks::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last chunk will not have length `chunk_size`.
///
/// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
/// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
/// the end of the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.chunks_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 3]);
/// ```
///
/// [`chunks_exact_mut`]: slice::chunks_exact_mut
/// [`rchunks_mut`]: slice::rchunks_mut
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
assert_ne!(chunk_size, 0);
ChunksMut::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
/// from the `remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks`].
///
/// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
/// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.chunks_exact(2);
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert!(iter.next().is_none());
/// assert_eq!(iter.remainder(), &['m']);
/// ```
///
/// [`chunks`]: slice::chunks
/// [`rchunks_exact`]: slice::rchunks_exact
#[stable(feature = "chunks_exact", since = "1.31.0")]
#[inline]
pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
assert_ne!(chunk_size, 0);
ChunksExact::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
/// retrieved from the `into_remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks_mut`].
///
/// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
/// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
/// the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.chunks_exact_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 0]);
/// ```
///
/// [`chunks_mut`]: slice::chunks_mut
/// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
#[stable(feature = "chunks_exact", since = "1.31.0")]
#[inline]
pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
assert_ne!(chunk_size, 0);
ChunksExactMut::new(self, chunk_size)
}
/// Splits the slice into a slice of `N`-element arrays,
/// assuming that there's no remainder.
///
/// # Safety
///
/// This may only be called when
/// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
/// - `N != 0`.
///
/// # Examples
///
/// ```
/// #![feature(slice_as_chunks)]
/// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
/// let chunks: &[[char; 1]] =
/// // SAFETY: 1-element chunks never have remainder
/// unsafe { slice.as_chunks_unchecked() };
/// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
/// let chunks: &[[char; 3]] =
/// // SAFETY: The slice length (6) is a multiple of 3
/// unsafe { slice.as_chunks_unchecked() };
/// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
///
/// // These would be unsound:
/// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
/// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
debug_assert_ne!(N, 0);
debug_assert_eq!(self.len() % N, 0);
let new_len =
// SAFETY: Our precondition is exactly what's needed to call this
unsafe { crate::intrinsics::exact_div(self.len(), N) };
// SAFETY: We cast a slice of `new_len * N` elements into
// a slice of `new_len` many `N` elements chunks.
unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the beginning of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(slice_as_chunks)]
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let (chunks, remainder) = slice.as_chunks();
/// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
/// assert_eq!(remainder, &['m']);
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
assert_ne!(N, 0);
let len = self.len() / N;
let (multiple_of_n, remainder) = self.split_at(len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
(array_slice, remainder)
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the end of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(slice_as_chunks)]
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let (remainder, chunks) = slice.as_rchunks();
/// assert_eq!(remainder, &['l']);
/// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
assert_ne!(N, 0);
let len = self.len() / N;
let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
(remainder, array_slice)
}
/// Returns an iterator over `N` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are array references and do not overlap. If `N` does not divide the
/// length of the slice, then the last up to `N-1` elements will be omitted and can be
/// retrieved from the `remainder` function of the iterator.
///
/// This method is the const generic equivalent of [`chunks_exact`].
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(array_chunks)]
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.array_chunks();
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert!(iter.next().is_none());
/// assert_eq!(iter.remainder(), &['m']);
/// ```
///
/// [`chunks_exact`]: slice::chunks_exact
#[unstable(feature = "array_chunks", issue = "74985")]
#[inline]
pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
assert_ne!(N, 0);
ArrayChunks::new(self)
}
/// Splits the slice into a slice of `N`-element arrays,
/// assuming that there's no remainder.
///
/// # Safety
///
/// This may only be called when
/// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
/// - `N != 0`.
///
/// # Examples
///
/// ```
/// #![feature(slice_as_chunks)]
/// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
/// let chunks: &mut [[char; 1]] =
/// // SAFETY: 1-element chunks never have remainder
/// unsafe { slice.as_chunks_unchecked_mut() };
/// chunks[0] = ['L'];
/// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
/// let chunks: &mut [[char; 3]] =
/// // SAFETY: The slice length (6) is a multiple of 3
/// unsafe { slice.as_chunks_unchecked_mut() };
/// chunks[1] = ['a', 'x', '?'];
/// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
///
/// // These would be unsound:
/// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
/// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
debug_assert_ne!(N, 0);
debug_assert_eq!(self.len() % N, 0);
let new_len =
// SAFETY: Our precondition is exactly what's needed to call this
unsafe { crate::intrinsics::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]
pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
assert_ne!(N, 0);
let len = self.len() / N;
let (multiple_of_n, remainder) = self.split_at_mut(len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
(array_slice, remainder)
}
/// Splits the slice into a slice of `N`-element arrays,
/// starting at the end of the slice,
/// and a remainder slice with length strictly less than `N`.
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(slice_as_chunks)]
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// let (remainder, chunks) = v.as_rchunks_mut();
/// remainder[0] = 9;
/// for chunk in chunks {
/// *chunk = [count; 2];
/// count += 1;
/// }
/// assert_eq!(v, &[9, 1, 1, 2, 2]);
/// ```
#[unstable(feature = "slice_as_chunks", issue = "74985")]
#[inline]
pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
assert_ne!(N, 0);
let len = self.len() / N;
let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
// SAFETY: We already panicked for zero, and ensured by construction
// that the length of the subslice is a multiple of N.
let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
(remainder, array_slice)
}
/// Returns an iterator over `N` elements of the slice at a time, starting at the
/// beginning of the slice.
///
/// The chunks are mutable array references and do not overlap. If `N` does not divide
/// the length of the slice, then the last up to `N-1` elements will be omitted and
/// can be retrieved from the `into_remainder` function of the iterator.
///
/// This method is the const generic equivalent of [`chunks_exact_mut`].
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(array_chunks)]
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.array_chunks_mut() {
/// *chunk = [count; 2];
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 0]);
/// ```
///
/// [`chunks_exact_mut`]: slice::chunks_exact_mut
#[unstable(feature = "array_chunks", issue = "74985")]
#[inline]
pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
assert_ne!(N, 0);
ArrayChunksMut::new(self)
}
/// Returns an iterator over overlapping windows of `N` elements of a slice,
/// starting at the beginning of the slice.
///
/// This is the const generic equivalent of [`windows`].
///
/// If `N` is greater than the size of the slice, it will return no windows.
///
/// # Panics
///
/// Panics if `N` is 0. This check will most probably get changed to a compile time
/// error before this method gets stabilized.
///
/// # Examples
///
/// ```
/// #![feature(array_windows)]
/// let slice = [0, 1, 2, 3];
/// let mut iter = slice.array_windows();
/// assert_eq!(iter.next().unwrap(), &[0, 1]);
/// assert_eq!(iter.next().unwrap(), &[1, 2]);
/// assert_eq!(iter.next().unwrap(), &[2, 3]);
/// assert!(iter.next().is_none());
/// ```
///
/// [`windows`]: slice::windows
#[unstable(feature = "array_windows", issue = "75027")]
#[inline]
pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
assert_ne!(N, 0);
ArrayWindows::new(self)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last chunk will not have length `chunk_size`.
///
/// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
/// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
/// of the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.rchunks(2);
/// assert_eq!(iter.next().unwrap(), &['e', 'm']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r']);
/// assert_eq!(iter.next().unwrap(), &['l']);
/// assert!(iter.next().is_none());
/// ```
///
/// [`rchunks_exact`]: slice::rchunks_exact
/// [`chunks`]: slice::chunks
#[stable(feature = "rchunks", since = "1.31.0")]
#[inline]
pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
assert!(chunk_size != 0);
RChunks::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last chunk will not have length `chunk_size`.
///
/// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
/// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
/// beginning of the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.rchunks_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[3, 2, 2, 1, 1]);
/// ```
///
/// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
/// [`chunks_mut`]: slice::chunks_mut
#[stable(feature = "rchunks", since = "1.31.0")]
#[inline]
pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
assert!(chunk_size != 0);
RChunksMut::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
/// end of the slice.
///
/// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
/// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
/// from the `remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks`].
///
/// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
/// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
/// slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.rchunks_exact(2);
/// assert_eq!(iter.next().unwrap(), &['e', 'm']);
/// assert_eq!(iter.next().unwrap(), &['o', 'r']);
/// assert!(iter.next().is_none());
/// assert_eq!(iter.remainder(), &['l']);
/// ```
///
/// [`chunks`]: slice::chunks
/// [`rchunks`]: slice::rchunks
/// [`chunks_exact`]: slice::chunks_exact
#[stable(feature = "rchunks", since = "1.31.0")]
#[inline]
pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
assert!(chunk_size != 0);
RChunksExact::new(self, chunk_size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
/// of the slice.
///
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
/// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
/// retrieved from the `into_remainder` function of the iterator.
///
/// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
/// resulting code better than in the case of [`chunks_mut`].
///
/// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
/// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
/// of the slice.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.rchunks_exact_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[0, 2, 2, 1, 1]);
/// ```
///
/// [`chunks_mut`]: slice::chunks_mut
/// [`rchunks_mut`]: slice::rchunks_mut
/// [`chunks_exact_mut`]: slice::chunks_exact_mut
#[stable(feature = "rchunks", since = "1.31.0")]
#[inline]
pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
assert!(chunk_size != 0);
RChunksExactMut::new(self, chunk_size)
}
/// Returns an iterator over the slice producing non-overlapping runs
/// of elements using the predicate to separate them.
///
/// The predicate is called on two elements following themselves,
/// it means the predicate is called on `slice[0]` and `slice[1]`
/// then on `slice[1]` and `slice[2]` and so on.
///
/// # Examples
///
/// ```
/// #![feature(slice_group_by)]
///
/// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.group_by(|a, b| a == b);
///
/// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
/// assert_eq!(iter.next(), Some(&[3, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
/// assert_eq!(iter.next(), None);
/// ```
///
/// This method can be used to extract the sorted subslices:
///
/// ```
/// #![feature(slice_group_by)]
///
/// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.group_by(|a, b| a <= b);
///
/// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 3][..]));
/// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
/// assert_eq!(iter.next(), None);
/// ```
#[unstable(feature = "slice_group_by", issue = "80552")]
#[inline]
pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
GroupBy::new(self, pred)
}
/// Returns an iterator over the slice producing non-overlapping mutable
/// runs of elements using the predicate to separate them.
///
/// The predicate is called on two elements following themselves,
/// it means the predicate is called on `slice[0]` and `slice[1]`
/// then on `slice[1]` and `slice[2]` and so on.
///
/// # Examples
///
/// ```
/// #![feature(slice_group_by)]
///
/// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
///
/// let mut iter = slice.group_by_mut(|a, b| a == b);
///
/// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
/// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
/// assert_eq!(iter.next(), None);
/// ```
///
/// This method can be used to extract the sorted subslices:
///
/// ```
/// #![feature(slice_group_by)]
///
/// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
///
/// let mut iter = slice.group_by_mut(|a, b| a <= b);
///
/// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
/// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
/// assert_eq!(iter.next(), None);
/// ```
#[unstable(feature = "slice_group_by", issue = "80552")]
#[inline]
pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
where
F: FnMut(&T, &T) -> bool,
{
GroupByMut::new(self, pred)
}
/// Divides one slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`.
///
/// # Examples
///
/// ```
/// let v = [1, 2, 3, 4, 5, 6];
///
/// {
/// let (left, right) = v.split_at(0);
/// assert_eq!(left, []);
/// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_at(2);
/// assert_eq!(left, [1, 2]);
/// assert_eq!(right, [3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_at(6);
/// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
/// assert_eq!(right, []);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
assert!(mid <= self.len());
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `from_raw_parts_mut`.
unsafe { self.split_at_unchecked(mid) }
}
/// Divides one mutable slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`.
///
/// # Examples
///
/// ```
/// let mut v = [1, 0, 3, 0, 5, 6];
/// let (left, right) = v.split_at_mut(2);
/// assert_eq!(left, [1, 0]);
/// assert_eq!(right, [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
assert!(mid <= self.len());
// SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
// fulfills the requirements of `from_raw_parts_mut`.
unsafe { self.split_at_mut_unchecked(mid) }
}
/// Divides one slice into two at an index, without doing bounds checking.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// For a safe alternative see [`split_at`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used. The caller has to ensure that
/// `0 <= mid <= self.len()`.
///
/// [`split_at`]: slice::split_at
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```compile_fail
/// #![feature(slice_split_at_unchecked)]
///
/// let v = [1, 2, 3, 4, 5, 6];
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(0);
/// assert_eq!(left, []);
/// assert_eq!(right, [1, 2, 3, 4, 5, 6]);
/// }
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(2);
/// assert_eq!(left, [1, 2]);
/// assert_eq!(right, [3, 4, 5, 6]);
/// }
///
/// unsafe {
/// let (left, right) = v.split_at_unchecked(6);
/// assert_eq!(left, [1, 2, 3, 4, 5, 6]);
/// assert_eq!(right, []);
/// }
/// ```
#[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
#[inline]
unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
// SAFETY: Caller has to check that `0 <= mid <= self.len()`
unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
}
/// Divides one mutable slice into two at an index, without doing bounds checking.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// For a safe alternative see [`split_at_mut`].
///
/// # Safety
///
/// Calling this method with an out-of-bounds index is *[undefined behavior]*
/// even if the resulting reference is not used. The caller has to ensure that
/// `0 <= mid <= self.len()`.
///
/// [`split_at_mut`]: slice::split_at_mut
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```compile_fail
/// #![feature(slice_split_at_unchecked)]
///
/// let mut v = [1, 0, 3, 0, 5, 6];
/// // scoped to restrict the lifetime of the borrows
/// unsafe {
/// let (left, right) = v.split_at_mut_unchecked(2);
/// assert_eq!(left, [1, 0]);
/// assert_eq!(right, [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// }
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
#[inline]
unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
let len = self.len();
let ptr = self.as_mut_ptr();
// SAFETY: Caller has to check that `0 <= mid <= self.len()`.
//
// `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
// is fine.
unsafe { (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid)) }
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let slice = [10, 40, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
///
/// If the first element is matched, an empty slice will be the first item
/// returned by the iterator. Similarly, if the last element in the slice
/// is matched, an empty slice will be the last item returned by the
/// iterator:
///
/// ```
/// let slice = [10, 40, 33];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert!(iter.next().is_none());
/// ```
///
/// If two matched elements are directly adjacent, an empty slice will be
/// present between them:
///
/// ```
/// let slice = [10, 6, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
where
F: FnMut(&T) -> bool,
{
Split::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.split_mut(|num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`. The matched element is contained in the end of the previous
/// subslice as a terminator.
///
/// # Examples
///
/// ```
/// let slice = [10, 40, 33, 20];
/// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
///
/// If the last element of the slice is matched,
/// that element will be considered the terminator of the preceding slice.
/// That slice will be the last item returned by the iterator.
///
/// ```
/// let slice = [3, 10, 40, 33];
/// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[3]);
/// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "split_inclusive", since = "1.51.0")]
#[inline]
pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitInclusive::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`. The matched element is contained in the previous
/// subslice as a terminator.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
/// let terminator_idx = group.len()-1;
/// group[terminator_idx] = 1;
/// }
/// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
/// ```
#[stable(feature = "split_inclusive", since = "1.51.0")]
#[inline]
pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitInclusiveMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, starting at the end of the slice and working backwards.
/// The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let slice = [11, 22, 33, 0, 44, 55];
/// let mut iter = slice.rsplit(|num| *num == 0);
///
/// assert_eq!(iter.next().unwrap(), &[44, 55]);
/// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
/// assert_eq!(iter.next(), None);
/// ```
///
/// As with `split()`, if the first or last element is matched, an empty
/// slice will be the first (or last) item returned by the iterator.
///
/// ```
/// let v = &[0, 1, 1, 2, 3, 5, 8];
/// let mut it = v.rsplit(|n| *n % 2 == 0);
/// assert_eq!(it.next().unwrap(), &[]);
/// assert_eq!(it.next().unwrap(), &[3, 5]);
/// assert_eq!(it.next().unwrap(), &[1, 1]);
/// assert_eq!(it.next().unwrap(), &[]);
/// assert_eq!(it.next(), None);
/// ```
#[stable(feature = "slice_rsplit", since = "1.27.0")]
#[inline]
pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplit::new(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`, starting at the end of the slice and working
/// backwards. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let mut v = [100, 400, 300, 200, 600, 500];
///
/// let mut count = 0;
/// for group in v.rsplit_mut(|num| *num % 3 == 0) {
/// count += 1;
/// group[0] = count;
/// }
/// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
/// ```
///
#[stable(feature = "slice_rsplit", since = "1.27.0")]
#[inline]
pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitMut::new(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
/// `[20, 60, 50]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn(2, |num| *num % 3 == 0) {
/// println!("{:?}", group);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitN::new(self.split(pred), n)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
SplitNMut::new(self.split_mut(pred), n)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once, starting from the end, by numbers divisible
/// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.rsplitn(2, |num| *num % 3 == 0) {
/// println!("{:?}", group);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitN::new(self.rsplit(pred), n)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut s = [10, 40, 30, 20, 60, 50];
///
/// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
where
F: FnMut(&T) -> bool,
{
RSplitNMut::new(self.rsplit_mut(pred), n)
}
/// Returns `true` if the slice contains an element with the given value.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.contains(&30));
/// assert!(!v.contains(&50));
/// ```
///
/// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
/// (e.g. `String: Borrow<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]
pub fn contains(&self, x: &T) -> bool
where
T: PartialEq,
{
cmp::SliceContains::slice_contains(x, self)
}
/// Returns `true` if `needle` is a prefix of the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.starts_with(&[10]));
/// assert!(v.starts_with(&[10, 40]));
/// assert!(!v.starts_with(&[50]));
/// assert!(!v.starts_with(&[10, 50]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.starts_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.starts_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn starts_with(&self, needle: &[T]) -> bool
where
T: PartialEq,
{
let n = needle.len();
self.len() >= n && needle == &self[..n]
}
/// Returns `true` if `needle` is a suffix of the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.ends_with(&[30]));
/// assert!(v.ends_with(&[40, 30]));
/// assert!(!v.ends_with(&[50]));
/// assert!(!v.ends_with(&[50, 30]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.ends_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.ends_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn ends_with(&self, needle: &[T]) -> bool
where
T: PartialEq,
{
let (m, n) = (self.len(), needle.len());
m >= n && needle == &self[m - n..]
}
/// Returns a subslice with the prefix removed.
///
/// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
/// If `prefix` is empty, simply returns the original slice.
///
/// If the slice does not start with `prefix`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = &[10, 40, 30];
/// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
/// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
/// assert_eq!(v.strip_prefix(&[50]), None);
/// assert_eq!(v.strip_prefix(&[10, 50]), None);
///
/// let prefix : &str = "he";
/// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
/// Some(b"llo".as_ref()));
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[stable(feature = "slice_strip", since = "1.51.0")]
pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let prefix = prefix.as_slice();
let n = prefix.len();
if n <= self.len() {
let (head, tail) = self.split_at(n);
if head == prefix {
return Some(tail);
}
}
None
}
/// Returns a subslice with the suffix removed.
///
/// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
/// If `suffix` is empty, simply returns the original slice.
///
/// If the slice does not end with `suffix`, returns `None`.
///
/// # Examples
///
/// ```
/// let v = &[10, 40, 30];
/// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
/// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
/// assert_eq!(v.strip_suffix(&[50]), None);
/// assert_eq!(v.strip_suffix(&[50, 30]), None);
/// ```
#[must_use = "returns the subslice without modifying the original"]
#[stable(feature = "slice_strip", since = "1.51.0")]
pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
where
T: PartialEq,
{
// This function will need rewriting if and when SlicePattern becomes more sophisticated.
let suffix = suffix.as_slice();
let (len, n) = (self.len(), suffix.len());
if n <= len {
let (head, tail) = self.split_at(len - n);
if tail == suffix {
return Some(head);
}
}
None
}
/// Binary searches this sorted slice for a given element.
///
/// 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. 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 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.binary_search(&num).unwrap_or_else(|x| x);
/// s.insert(idx, num);
/// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn binary_search(&self, x: &T) -> Result<usize, usize>
where
T: Ord,
{
self.binary_search_by(|p| p.cmp(x))
}
/// Binary searches this sorted slice with a comparator function.
///
/// The comparator function should implement an order consistent
/// with the sort order of the underlying slice, returning an
/// order code that indicates whether its argument is `Less`,
/// `Equal` or `Greater` the desired target.
///
/// If the value is found then [`Result::Ok`] is returned, containing the
/// index of the matching element. If there are multiple matches, then any
/// one of the matches could be returned. 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,
{
let mut size = self.len();
let mut left = 0;
let mut right = size;
while left < right {
let mid = left + size / 2;
// SAFETY: the call is made safe by the following invariants:
// - `mid >= 0`
// - `mid < size`: `mid` is limited by `[left; right)` bound.
let cmp = f(unsafe { self.get_unchecked(mid) });
// The reason why we use if/else control flow rather than match
// is because match reorders comparison operations, which is perf sensitive.
// This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
if cmp == Less {
left = mid + 1;
} else if cmp == Greater {
right = mid;
} else {
// SAFETY: same as the `get_unchecked` above
unsafe { crate::intrinsics::assume(mid < self.len()) };
return Ok(mid);
}
size = right - left;
}
Err(left)
}
/// Binary searches this sorted 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 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. 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`.
// links to downstream crate: #74481. Since primitives are only documented in
// libstd (#73423), this never leads to broken links in practice.
#[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 may not preserve the order of equal elements.
///
/// This sort is unstable (i.e., may reorder equal elements), in-place
/// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
///
/// # Current implementation
///
/// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
/// which combines the fast average case of randomized quicksort with the fast worst case of
/// heapsort, while achieving linear time on slices with certain patterns. It uses some
/// randomization to avoid degenerate cases, but with a fixed seed to always provide
/// deterministic behavior.
///
/// It is typically faster than stable sorting, except in a few special cases, e.g., when the
/// slice consists of several concatenated sorted sequences.
///
/// # Examples
///
/// ```
/// let mut v = [-5, 4, 1, -3, 2];
///
/// v.sort_unstable();
/// assert!(v == [-5, -3, 1, 2, 4]);
/// ```
///
/// [pdqsort]: https://github.com/orlp/pdqsort
#[stable(feature = "sort_unstable", since = "1.20.0")]
#[inline]
pub fn sort_unstable(&mut self)
where
T: Ord,
{
sort::quicksort(self, |a, b| a.lt(b));
}
/// Sorts the slice with a comparator function, but may 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 may not preserve the order of equal
/// elements.
///
/// This sort is unstable (i.e., may reorder equal elements), in-place
/// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
/// *O*(*m*).
///
/// # Current implementation
///
/// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
/// which combines the fast average case of randomized quicksort with the fast worst case of
/// heapsort, while achieving linear time on slices with certain patterns. It uses some
/// randomization to avoid degenerate cases, but with a fixed seed to always provide
/// deterministic behavior.
///
/// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
/// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
/// cases where the key function is expensive.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// v.sort_unstable_by_key(|k| k.abs());
/// assert!(v == [1, 2, -3, 4, -5]);
/// ```
///
/// [pdqsort]: https://github.com/orlp/pdqsort
#[stable(feature = "sort_unstable", since = "1.20.0")]
#[inline]
pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
where
F: FnMut(&T) -> K,
K: Ord,
{
sort::quicksort(self, |a, b| f(a).lt(&f(b)));
}
/// Reorder the slice such that the element at `index` is at its final sorted position.
#[unstable(feature = "slice_partition_at_index", issue = "55300")]
#[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable() instead")]
#[inline]
pub fn partition_at_index(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
where
T: Ord,
{
self.select_nth_unstable(index)
}
/// Reorder the slice with a comparator function such that the element at `index` is at its
/// final sorted position.
#[unstable(feature = "slice_partition_at_index", issue = "55300")]
#[rustc_deprecated(since = "1.49.0", reason = "use select_nth_unstable_by() instead")]
#[inline]
pub fn partition_at_index_by<F>(
&mut self,
index: usize,
compare: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T, &T) -> Ordering,
{
self.select_nth_unstable_by(index, compare)
}
/// Reorder the slice with a key extraction function such that the element at `index` is at its
/// final sorted position.
#[unstable(feature = "slice_partition_at_index", issue = "55300")]
#[rustc_deprecated(since = "1.49.0", reason = "use the select_nth_unstable_by_key() instead")]
#[inline]
pub fn partition_at_index_by_key<K, F>(
&mut self,
index: usize,
f: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T) -> K,
K: Ord,
{
self.select_nth_unstable_by_key(index, f)
}
/// Reorder the slice such that the element at `index` is at its final sorted position.
///
/// This reordering has the additional property that any value at position `i < index` will be
/// less than or equal to any value at a position `j > index`. Additionally, this reordering is
/// unstable (i.e. any number of equal elements may end up at position `index`), in-place
/// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
/// element" in other libraries. It returns a triplet of the following values: all elements less
/// than the one at the given index, the value at the given index, and all elements greater than
/// the one at the given index.
///
/// # Current implementation
///
/// The current algorithm is based on the quickselect portion of the same quicksort algorithm
/// used for [`sort_unstable`].
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// // Find the median
/// v.select_nth_unstable(2);
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [-3, -5, 1, 2, 4] ||
/// v == [-5, -3, 1, 2, 4] ||
/// v == [-3, -5, 1, 4, 2] ||
/// v == [-5, -3, 1, 4, 2]);
/// ```
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
where
T: Ord,
{
let mut f = |a: &T, b: &T| a.lt(b);
sort::partition_at_index(self, index, &mut f)
}
/// Reorder the slice with a comparator function such that the element at `index` is at its
/// final sorted position.
///
/// This reordering has the additional property that any value at position `i < index` will be
/// less than or equal to any value at a position `j > index` using the comparator function.
/// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
/// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
/// is also known as "kth element" in other libraries. It returns a triplet of the following
/// values: all elements less than the one at the given index, the value at the given index,
/// and all elements greater than the one at the given index, using the provided comparator
/// function.
///
/// # Current implementation
///
/// The current algorithm is based on the quickselect portion of the same quicksort algorithm
/// used for [`sort_unstable`].
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// // Find the median as if the slice were sorted in descending order.
/// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [2, 4, 1, -5, -3] ||
/// v == [2, 4, 1, -3, -5] ||
/// v == [4, 2, 1, -5, -3] ||
/// v == [4, 2, 1, -3, -5]);
/// ```
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable_by<F>(
&mut self,
index: usize,
mut compare: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T, &T) -> Ordering,
{
let mut f = |a: &T, b: &T| compare(a, b) == Less;
sort::partition_at_index(self, index, &mut f)
}
/// Reorder the slice with a key extraction function such that the element at `index` is at its
/// final sorted position.
///
/// This reordering has the additional property that any value at position `i < index` will be
/// less than or equal to any value at a position `j > index` using the key extraction function.
/// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
/// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
/// is also known as "kth element" in other libraries. It returns a triplet of the following
/// values: all elements less than the one at the given index, the value at the given index, and
/// all elements greater than the one at the given index, using the provided key extraction
/// function.
///
/// # Current implementation
///
/// The current algorithm is based on the quickselect portion of the same quicksort algorithm
/// used for [`sort_unstable`].
///
/// [`sort_unstable`]: slice::sort_unstable
///
/// # Panics
///
/// Panics when `index >= len()`, meaning it always panics on empty slices.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// // Return the median as if the array were sorted according to absolute value.
/// v.select_nth_unstable_by_key(2, |a| a.abs());
///
/// // We are only guaranteed the slice will be one of the following, based on the way we sort
/// // about the specified index.
/// assert!(v == [1, 2, -3, 4, -5] ||
/// v == [1, 2, -3, -5, 4] ||
/// v == [2, 1, -3, 4, -5] ||
/// v == [2, 1, -3, -5, 4]);
/// ```
#[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
#[inline]
pub fn select_nth_unstable_by_key<K, F>(
&mut self,
index: usize,
mut f: F,
) -> (&mut [T], &mut T, &mut [T])
where
F: FnMut(&T) -> K,
K: Ord,
{
let mut g = |a: &T, b: &T| f(a).lt(&f(b));
sort::partition_at_index(self, index, &mut g)
}
/// Moves all consecutive repeated elements to the end of the slice according to the
/// [`PartialEq`] trait implementation.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
///
/// let (dedup, duplicates) = slice.partition_dedup();
///
/// assert_eq!(dedup, [1, 2, 3, 2, 1]);
/// assert_eq!(duplicates, [2, 3, 1]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
where
T: PartialEq,
{
self.partition_dedup_by(|a, b| a == b)
}
/// Moves all but the first of consecutive elements to the end of the slice satisfying
/// a given equality relation.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// The `same_bucket` function is passed references to two elements from the slice and
/// must determine if the elements compare equal. The elements are passed in opposite order
/// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
/// at the end of the slice.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
///
/// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
///
/// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
/// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
where
F: FnMut(&mut T, &mut T) -> bool,
{
// Although we have a mutable reference to `self`, we cannot make
// *arbitrary* changes. The `same_bucket` calls could panic, so we
// must ensure that the slice is in a valid state at all times.
//
// The way that we handle this is by using swaps; we iterate
// over all the elements, swapping as we go so that at the end
// the elements we wish to keep are in the front, and those we
// wish to reject are at the back. We can then split the slice.
// This operation is still `O(n)`.
//
// Example: We start in this state, where `r` represents "next
// read" and `w` represents "next_write`.
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate, so
// we swap self[r] and self[w] (no effect as r==w) and then increment both
// r and w, leaving us with:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this value is a duplicate,
// so we increment `r` but leave everything else unchanged:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate,
// so swap self[r] and self[w] and advance r and w:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 1 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Not a duplicate, repeat:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 3 | 1 | 3 |
// +---+---+---+---+---+---+
// w
//
// Duplicate, advance r. End of slice. Split at w.
let len = self.len();
if len <= 1 {
return (self, &mut []);
}
let ptr = self.as_mut_ptr();
let mut next_read: usize = 1;
let mut next_write: usize = 1;
// SAFETY: the `while` condition guarantees `next_read` and `next_write`
// are less than `len`, thus are inside `self`. `prev_ptr_write` points to
// one element before `ptr_write`, but `next_write` starts at 1, so
// `prev_ptr_write` is never less than 0 and is inside the slice.
// This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
// and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
// and `prev_ptr_write.offset(1)`.
//
// `next_write` is also incremented at most once per loop at most meaning
// no element is skipped when it may need to be swapped.
//
// `ptr_read` and `prev_ptr_write` never point to the same element. This
// is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
// The explanation is simply that `next_read >= next_write` is always true,
// thus `next_read > next_write - 1` is too.
unsafe {
// Avoid bounds checks by using raw pointers.
while next_read < len {
let ptr_read = ptr.add(next_read);
let prev_ptr_write = ptr.add(next_write - 1);
if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
if next_read != next_write {
let ptr_write = prev_ptr_write.offset(1);
mem::swap(&mut *ptr_read, &mut *ptr_write);
}
next_write += 1;
}
next_read += 1;
}
}
self.split_at_mut(next_write)
}
/// Moves all but the first of consecutive elements to the end of the slice that resolve
/// to the same key.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
///
/// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
///
/// assert_eq!(dedup, [10, 20, 30, 20, 11]);
/// assert_eq!(duplicates, [21, 30, 13]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
where
F: FnMut(&mut T) -> K,
K: PartialEq,
{
self.partition_dedup_by(|a, b| key(a) == key(b))
}
/// Rotates the slice in-place such that the first `mid` elements of the
/// slice move to the end while the last `self.len() - mid` elements move to
/// the front. After calling `rotate_left`, the element previously at index
/// `mid` will become the first element in the slice.
///
/// # Panics
///
/// This function will panic if `mid` is greater than the length of the
/// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
/// rotation.
///
/// # Complexity
///
/// Takes linear (in `self.len()`) time.
///
/// # Examples
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a.rotate_left(2);
/// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
/// ```
///
/// Rotating a subslice:
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a[1..5].rotate_left(1);
/// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
/// ```
#[stable(feature = "slice_rotate", since = "1.26.0")]
pub fn rotate_left(&mut self, mid: usize) {
assert!(mid <= self.len());
let k = self.len() - mid;
let p = self.as_mut_ptr();
// SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
// valid for reading and writing, as required by `ptr_rotate`.
unsafe {
rotate::ptr_rotate(mid, p.add(mid), k);
}
}
/// Rotates the slice in-place such that the first `self.len() - k`
/// elements of the slice move to the end while the last `k` elements move
/// to the front. After calling `rotate_right`, the element previously at
/// index `self.len() - k` will become the first element in the slice.
///
/// # Panics
///
/// This function will panic if `k` is greater than the length of the
/// slice. Note that `k == self.len()` does _not_ panic and is a no-op
/// rotation.
///
/// # Complexity
///
/// Takes linear (in `self.len()`) time.
///
/// # Examples
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a.rotate_right(2);
/// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
/// ```
///
/// Rotate a subslice:
///
/// ```
/// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
/// a[1..5].rotate_right(1);
/// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
/// ```
#[stable(feature = "slice_rotate", since = "1.26.0")]
pub fn rotate_right(&mut self, k: usize) {
assert!(k <= self.len());
let mid = self.len() - k;
let p = self.as_mut_ptr();
// SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
// valid for reading and writing, as required by `ptr_rotate`.
unsafe {
rotate::ptr_rotate(mid, p.add(mid), k);
}
}
/// Fills `self` with elements by cloning `value`.
///
/// # Examples
///
/// ```
/// let mut buf = vec![0; 10];
/// buf.fill(1);
/// assert_eq!(buf, vec![1; 10]);
/// ```
#[doc(alias = "memset")]
#[stable(feature = "slice_fill", since = "1.50.0")]
pub fn fill(&mut self, value: T)
where
T: Clone,
{
specialize::SpecFill::spec_fill(self, value);
}
/// Fills `self` with elements returned by calling a closure repeatedly.
///
/// This method uses a closure to create new values. If you'd rather
/// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
/// trait to generate values, you can pass [`Default::default`] as the
/// argument.
///
/// [`fill`]: slice::fill
///
/// # Examples
///
/// ```
/// let mut buf = vec![1; 10];
/// buf.fill_with(Default::default);
/// assert_eq!(buf, vec![0; 10]);
/// ```
#[doc(alias = "memset")]
#[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`.
///
/// If `T` implements `Copy`, it can be more performant to use
/// [`copy_from_slice`].
///
/// # 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")]
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")]
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 {
ptr::copy(self.as_ptr().add(src_start), self.as_mut_ptr().add(dest), 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")]
pub fn swap_with_slice(&mut self, other: &mut [T]) {
assert!(self.len() == other.len(), "destination and source slices have different lengths");
// SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
// checked to have the same length. The slices cannot overlap because
// mutable references are exclusive.
unsafe {
ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
}
}
/// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
fn align_to_offsets<U>(&self) -> (usize, usize) {
// What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
// lowest number of `T`s. And how many `T`s we need for each such "multiple".
//
// Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
// for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
// place of every 3 Ts in the `rest` slice. A bit more complicated.
//
// Formula to calculate this is:
//
// Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
// Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
//
// Expanded and simplified:
//
// Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
// Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
//
// Luckily since all this is constant-evaluated... performance here matters not!
#[inline]
fn gcd(a: usize, b: usize) -> usize {
use crate::intrinsics;
// iterative stein’s algorithm
// We should still make this `const fn` (and revert to recursive algorithm if we do)
// because relying on llvm to consteval all this is… well, it makes me uncomfortable.
// SAFETY: `a` and `b` are checked to be non-zero values.
let (ctz_a, mut ctz_b) = unsafe {
if a == 0 {
return b;
}
if b == 0 {
return a;
}
(intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
};
let k = ctz_a.min(ctz_b);
let mut a = a >> ctz_a;
let mut b = b;
loop {
// remove all factors of 2 from b
b >>= ctz_b;
if a > b {
mem::swap(&mut a, &mut b);
}
b = b - a;
// SAFETY: `b` is checked to be non-zero.
unsafe {
if b == 0 {
break;
}
ctz_b = intrinsics::cttz_nonzero(b);
}
}
a << k
}
let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
let ts: usize = mem::size_of::<U>() / gcd;
let us: usize = mem::size_of::<T>() / gcd;
// Armed with this knowledge, we can find how many `U`s we can fit!
let us_len = self.len() / ts * us;
// And how many `T`s will be in the trailing slice!
let ts_len = self.len() % ts;
(us_len, ts_len)
}
/// Transmute the slice to a slice of another type, ensuring alignment of the types is
/// maintained.
///
/// This method splits the slice into three distinct slices: prefix, correctly aligned middle
/// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
/// length possible for a given type and input slice, but only your algorithm's performance
/// should depend on that, not its correctness. It is permissible for all of the input data to
/// be returned as the prefix or suffix slice.
///
/// This method has no purpose when either input element `T` or output element `U` are
/// zero-sized and will return the original slice without splitting anything.
///
/// # Safety
///
/// This method is essentially a `transmute` with respect to the elements in the returned
/// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// unsafe {
/// let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
/// let (prefix, shorts, suffix) = bytes.align_to::<u16>();
/// // less_efficient_algorithm_for_bytes(prefix);
/// // more_efficient_algorithm_for_aligned_shorts(shorts);
/// // less_efficient_algorithm_for_bytes(suffix);
/// }
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
// Note that most of this function will be constant-evaluated,
if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &[], &[]);
}
// First, find at what point do we split between the first and 2nd slice. Easy with
// ptr.align_offset.
let ptr = self.as_ptr();
// SAFETY: See the `align_to_mut` method for the detailed safety comment.
let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
if offset > self.len() {
(self, &[], &[])
} else {
let (left, rest) = self.split_at(offset);
let (us_len, ts_len) = rest.align_to_offsets::<U>();
// SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
// since the caller guarantees that we can transmute `T` to `U` safely.
unsafe {
(
left,
from_raw_parts(rest.as_ptr() as *const U, us_len),
from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
)
}
}
}
/// Transmute the slice to a slice of another type, ensuring alignment of the types is
/// maintained.
///
/// This method splits the slice into three distinct slices: prefix, correctly aligned middle
/// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
/// length possible for a given type and input slice, but only your algorithm's performance
/// should depend on that, not its correctness. It is permissible for all of the input data to
/// be returned as the prefix or suffix slice.
///
/// This method has no purpose when either input element `T` or output element `U` are
/// zero-sized and will return the original slice without splitting anything.
///
/// # Safety
///
/// This method is essentially a `transmute` with respect to the elements in the returned
/// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// unsafe {
/// let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
/// let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
/// // less_efficient_algorithm_for_bytes(prefix);
/// // more_efficient_algorithm_for_aligned_shorts(shorts);
/// // less_efficient_algorithm_for_bytes(suffix);
/// }
/// ```
#[stable(feature = "slice_align_to", since = "1.30.0")]
pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
// Note that most of this function will be constant-evaluated,
if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
// handle ZSTs specially, which is – don't handle them at all.
return (self, &mut [], &mut []);
}
// First, find at what point do we split between the first and 2nd slice. Easy with
// ptr.align_offset.
let ptr = self.as_ptr();
// SAFETY: Here we are ensuring we will use aligned pointers for U for the
// rest of the method. This is done by passing a pointer to &[T] with an
// alignment targeted for U.
// `crate::ptr::align_offset` is called with a correctly aligned and
// valid pointer `ptr` (it comes from a reference to `self`) and with
// a size that is a power of two (since it comes from the alignement for U),
// satisfying its safety constraints.
let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
if offset > self.len() {
(self, &mut [], &mut [])
} else {
let (left, rest) = self.split_at_mut(offset);
let (us_len, ts_len) = rest.align_to_offsets::<U>();
let rest_len = rest.len();
let mut_ptr = rest.as_mut_ptr();
// We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
// SAFETY: see comments for `align_to`.
unsafe {
(
left,
from_raw_parts_mut(mut_ptr as *mut U, us_len),
from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
)
}
}
}
/// 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")]
pub fn is_sorted(&self) -> bool
where
T: PartialOrd,
{
self.is_sorted_by(|a, b| a.partial_cmp(b))
}
/// Checks if the elements of this slice are sorted using the given comparator function.
///
/// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
/// function to determine the ordering of two elements. Apart from that, it's equivalent to
/// [`is_sorted`]; see its documentation for more information.
///
/// [`is_sorted`]: slice::is_sorted
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
where
F: FnMut(&T, &T) -> Option<Ordering>,
{
self.iter().is_sorted_by(|a, b| compare(*a, *b))
}
/// Checks if the elements of this slice are sorted using the given key extraction function.
///
/// Instead of comparing the slice's elements directly, this function compares the keys of the
/// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
/// documentation for more information.
///
/// [`is_sorted`]: slice::is_sorted
///
/// # Examples
///
/// ```
/// #![feature(is_sorted)]
///
/// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
/// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
/// ```
#[inline]
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
where
F: FnMut(&T) -> K,
K: PartialOrd,
{
self.iter().is_sorted_by_key(f)
}
/// Returns the index of the partition point according to the given predicate
/// (the index of the first element of the second partition).
///
/// The slice is assumed to be partitioned according to the given predicate.
/// This means that all elements for which the predicate returns true are at the start of the slice
/// and all elements for which the predicate returns false are at the end.
/// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
/// (all odd numbers are at the start, all even at the end).
///
/// If this slice is not partitioned, the returned result is unspecified and meaningless,
/// as this method performs a kind of binary search.
///
/// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
///
/// [`binary_search`]: slice::binary_search
/// [`binary_search_by`]: slice::binary_search_by
/// [`binary_search_by_key`]: slice::binary_search_by_key
///
/// # Examples
///
/// ```
/// let v = [1, 2, 3, 3, 5, 6, 7];
/// let i = v.partition_point(|&x| x < 5);
///
/// assert_eq!(i, 4);
/// assert!(v[..i].iter().all(|&x| x < 5));
/// assert!(v[i..].iter().all(|&x| !(x < 5)));
/// ```
#[stable(feature = "partition_point", since = "1.52.0")]
pub fn partition_point<P>(&self, mut pred: P) -> usize
where
P: FnMut(&T) -> bool,
{
let mut left = 0;
let mut right = self.len();
while left != right {
let mid = left + (right - left) / 2;
// SAFETY: When `left < right`, `left <= mid < right`.
// Therefore `left` always increases and `right` always decreases,
// and either of them is selected. In both cases `left <= right` is
// satisfied. Therefore if `left < right` in a step, `left <= right`
// is satisfied in the next step. Therefore as long as `left != right`,
// `0 <= left < right <= len` is satisfied and if this case
// `0 <= mid < len` is satisfied too.
let value = unsafe { self.get_unchecked(mid) };
if pred(value) {
left = mid + 1;
} else {
right = mid;
}
}
left
}
}
trait CloneFromSpec<T> {
fn spec_clone_from(&mut self, src: &[T]);
}
impl<T> CloneFromSpec<T> for [T]
where
T: Clone,
{
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,
{
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
}
}