//! Utilities for the array primitive type.
//!
//! *[See also the array primitive type](array).*
#![stable(feature = "core_array", since = "1.36.0")]
use crate::borrow::{Borrow, BorrowMut};
use crate::cmp::Ordering;
use crate::convert::{Infallible, TryFrom};
use crate::error::Error;
use crate::fmt;
use crate::hash::{self, Hash};
use crate::iter::UncheckedIterator;
use crate::mem::{self, MaybeUninit};
use crate::ops::{
ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
};
use crate::slice::{Iter, IterMut};
mod ascii;
mod drain;
mod equality;
mod iter;
pub(crate) use drain::drain_array_with;
#[stable(feature = "array_value_iter", since = "1.51.0")]
pub use iter::IntoIter;
/// Creates an array of type [T; N], where each element `T` is the returned value from `cb`
/// using that element's index.
///
/// # Arguments
///
/// * `cb`: Callback where the passed argument is the current array index.
///
/// # Example
///
/// ```rust
/// // type inference is helping us here, the way `from_fn` knows how many
/// // elements to produce is the length of array down there: only arrays of
/// // equal lengths can be compared, so the const generic parameter `N` is
/// // inferred to be 5, thus creating array of 5 elements.
///
/// let array = core::array::from_fn(|i| i);
/// // indexes are: 0 1 2 3 4
/// assert_eq!(array, [0, 1, 2, 3, 4]);
///
/// let array2: [usize; 8] = core::array::from_fn(|i| i * 2);
/// // indexes are: 0 1 2 3 4 5 6 7
/// assert_eq!(array2, [0, 2, 4, 6, 8, 10, 12, 14]);
///
/// let bool_arr = core::array::from_fn::<_, 5, _>(|i| i % 2 == 0);
/// // indexes are: 0 1 2 3 4
/// assert_eq!(bool_arr, [true, false, true, false, true]);
/// ```
#[inline]
#[stable(feature = "array_from_fn", since = "1.63.0")]
pub fn from_fn<T, const N: usize, F>(cb: F) -> [T; N]
where
F: FnMut(usize) -> T,
{
try_from_fn(NeverShortCircuit::wrap_mut_1(cb)).0
}
/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error
/// if any element creation was unsuccessful.
///
/// The return type of this function depends on the return type of the closure.
/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
///
/// # Arguments
///
/// * `cb`: Callback where the passed argument is the current array index.
///
/// # Example
///
/// ```rust
/// #![feature(array_try_from_fn)]
///
/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into());
/// assert_eq!(array, Ok([0, 1, 2, 3, 4]));
///
/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into());
/// assert!(array.is_err());
///
/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100));
/// assert_eq!(array, Some([100, 101, 102, 103]));
///
/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100));
/// assert_eq!(array, None);
/// ```
#[inline]
#[unstable(feature = "array_try_from_fn", issue = "89379")]
pub fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]>
where
F: FnMut(usize) -> R,
R: Try,
R::Residual: Residual<[R::Output; N]>,
{
let mut array = MaybeUninit::uninit_array::<N>();
match try_from_fn_erased(&mut array, cb) {
ControlFlow::Break(r) => FromResidual::from_residual(r),
ControlFlow::Continue(()) => {
// SAFETY: All elements of the array were populated.
try { unsafe { MaybeUninit::array_assume_init(array) } }
}
}
}
/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
#[stable(feature = "array_from_ref", since = "1.53.0")]
#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
pub const fn from_ref<T>(s: &T) -> &[T; 1] {
// SAFETY: Converting `&T` to `&[T; 1]` is sound.
unsafe { &*(s as *const T).cast::<[T; 1]>() }
}
/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
#[stable(feature = "array_from_ref", since = "1.53.0")]
#[rustc_const_unstable(feature = "const_array_from_ref", issue = "90206")]
pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
// SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
}
/// The error type returned when a conversion from a slice to an array fails.
#[stable(feature = "try_from", since = "1.34.0")]
#[derive(Debug, Copy, Clone)]
pub struct TryFromSliceError(());
#[stable(feature = "core_array", since = "1.36.0")]
impl fmt::Display for TryFromSliceError {
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
#[allow(deprecated)]
self.description().fmt(f)
}
}
#[stable(feature = "try_from", since = "1.34.0")]
impl Error for TryFromSliceError {
#[allow(deprecated)]
fn description(&self) -> &str {
"could not convert slice to array"
}
}
#[stable(feature = "try_from_slice_error", since = "1.36.0")]
impl From<Infallible> for TryFromSliceError {
fn from(x: Infallible) -> TryFromSliceError {
match x {}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, const N: usize> AsRef<[T]> for [T; N] {
#[inline]
fn as_ref(&self) -> &[T] {
&self[..]
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, const N: usize> AsMut<[T]> for [T; N] {
#[inline]
fn as_mut(&mut self) -> &mut [T] {
&mut self[..]
}
}
#[stable(feature = "array_borrow", since = "1.4.0")]
impl<T, const N: usize> Borrow<[T]> for [T; N] {
fn borrow(&self) -> &[T] {
self
}
}
#[stable(feature = "array_borrow", since = "1.4.0")]
impl<T, const N: usize> BorrowMut<[T]> for [T; N] {
fn borrow_mut(&mut self) -> &mut [T] {
self
}
}
/// Tries to create an array `[T; N]` by copying from a slice `&[T]`. Succeeds if
/// `slice.len() == N`.
///
/// ```
/// let bytes: [u8; 3] = [1, 0, 2];
///
/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
/// assert_eq!(1, u16::from_le_bytes(bytes_head));
///
/// let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<T, const N: usize> TryFrom<&[T]> for [T; N]
where
T: Copy,
{
type Error = TryFromSliceError;
#[inline]
fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
<&Self>::try_from(slice).map(|r| *r)
}
}
/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
/// Succeeds if `slice.len() == N`.
///
/// ```
/// let mut bytes: [u8; 3] = [1, 0, 2];
///
/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
/// assert_eq!(1, u16::from_le_bytes(bytes_head));
///
/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
/// ```
#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]
where
T: Copy,
{
type Error = TryFromSliceError;
#[inline]
fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
<Self>::try_from(&*slice)
}
}
/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
/// `slice.len() == N`.
///
/// ```
/// let bytes: [u8; 3] = [1, 0, 2];
///
/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
///
/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
type Error = TryFromSliceError;
#[inline]
fn try_from(slice: &'a [T]) -> Result<&'a [T; N], TryFromSliceError> {
if slice.len() == N {
let ptr = slice.as_ptr() as *const [T; N];
// SAFETY: ok because we just checked that the length fits
unsafe { Ok(&*ptr) }
} else {
Err(TryFromSliceError(()))
}
}
}
/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
/// `&mut [T]`. Succeeds if `slice.len() == N`.
///
/// ```
/// let mut bytes: [u8; 3] = [1, 0, 2];
///
/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
///
/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] {
type Error = TryFromSliceError;
#[inline]
fn try_from(slice: &'a mut [T]) -> Result<&'a mut [T; N], TryFromSliceError> {
if slice.len() == N {
let ptr = slice.as_mut_ptr() as *mut [T; N];
// SAFETY: ok because we just checked that the length fits
unsafe { Ok(&mut *ptr) }
} else {
Err(TryFromSliceError(()))
}
}
}
/// The hash of an array is the same as that of the corresponding slice,
/// as required by the `Borrow` implementation.
///
/// ```
/// use std::hash::BuildHasher;
///
/// let b = std::collections::hash_map::RandomState::new();
/// let a: [u8; 3] = [0xa8, 0x3c, 0x09];
/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
/// assert_eq!(b.hash_one(a), b.hash_one(s));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Hash, const N: usize> Hash for [T; N] {
fn hash<H: hash::Hasher>(&self, state: &mut H) {
Hash::hash(&self[..], state)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&&self[..], f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
type Item = &'a T;
type IntoIter = Iter<'a, T>;
fn into_iter(self) -> Iter<'a, T> {
self.iter()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
type Item = &'a mut T;
type IntoIter = IterMut<'a, T>;
fn into_iter(self) -> IterMut<'a, T> {
self.iter_mut()
}
}
#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
impl<T, I, const N: usize> Index<I> for [T; N]
where
[T]: Index<I>,
{
type Output = <[T] as Index<I>>::Output;
#[inline]
fn index(&self, index: I) -> &Self::Output {
Index::index(self as &[T], index)
}
}
#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]
impl<T, I, const N: usize> IndexMut<I> for [T; N]
where
[T]: IndexMut<I>,
{
#[inline]
fn index_mut(&mut self, index: I) -> &mut Self::Output {
IndexMut::index_mut(self as &mut [T], index)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] {
#[inline]
fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> {
PartialOrd::partial_cmp(&&self[..], &&other[..])
}
#[inline]
fn lt(&self, other: &[T; N]) -> bool {
PartialOrd::lt(&&self[..], &&other[..])
}
#[inline]
fn le(&self, other: &[T; N]) -> bool {
PartialOrd::le(&&self[..], &&other[..])
}
#[inline]
fn ge(&self, other: &[T; N]) -> bool {
PartialOrd::ge(&&self[..], &&other[..])
}
#[inline]
fn gt(&self, other: &[T; N]) -> bool {
PartialOrd::gt(&&self[..], &&other[..])
}
}
/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord, const N: usize> Ord for [T; N] {
#[inline]
fn cmp(&self, other: &[T; N]) -> Ordering {
Ord::cmp(&&self[..], &&other[..])
}
}
#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
impl<T: Copy, const N: usize> Copy for [T; N] {}
#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
impl<T: Clone, const N: usize> Clone for [T; N] {
#[inline]
fn clone(&self) -> Self {
SpecArrayClone::clone(self)
}
#[inline]
fn clone_from(&mut self, other: &Self) {
self.clone_from_slice(other);
}
}
trait SpecArrayClone: Clone {
fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];
}
impl<T: Clone> SpecArrayClone for T {
#[inline]
default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
from_trusted_iterator(array.iter().cloned())
}
}
impl<T: Copy> SpecArrayClone for T {
#[inline]
fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
*array
}
}
// The Default impls cannot be done with const generics because `[T; 0]` doesn't
// require Default to be implemented, and having different impl blocks for
// different numbers isn't supported yet.
macro_rules! array_impl_default {
{$n:expr, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mo>:</mo><mi>i</mi><mi>d</mi><mi>e</mi><mi>n</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">t:ident </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6151em;"></span><span class="mord mathnormal">t</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">:</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">i</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mord mathnormal">t</span></span></span></span>($ts:ident)*} => {
#[stable(since = "1.4.0", feature = "array_default")]
impl<T> Default for [T; $n] where T: Default {
fn default() -> [T; $n] {
[$t::default(), <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span></span></span></span>ts::default()),*]
}
}
array_impl_default!{($n - 1), <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span></span></span></span>ts)*}
};
{$n:expr,} => {
#[stable(since = "1.4.0", feature = "array_default")]
impl<T> Default for [T; $n] {
fn default() -> [T; $n] { [] }
}
};
}
array_impl_default! {32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T}
impl<T, const N: usize> [T; N] {
/// Returns an array of the same size as `self`, with function `f` applied to each element
/// in order.
///
/// If you don't necessarily need a new fixed-size array, consider using
/// [`Iterator::map`] instead.
///
///
/// # Note on performance and stack usage
///
/// Unfortunately, usages of this method are currently not always optimized
/// as well as they could be. This mainly concerns large arrays, as mapping
/// over small arrays seem to be optimized just fine. Also note that in
/// debug mode (i.e. without any optimizations), this method can use a lot
/// of stack space (a few times the size of the array or more).
///
/// Therefore, in performance-critical code, try to avoid using this method
/// on large arrays or check the emitted code. Also try to avoid chained
/// maps (e.g. `arr.map(...).map(...)`).
///
/// In many cases, you can instead use [`Iterator::map`] by calling `.iter()`
/// or `.into_iter()` on your array. `[T; N]::map` is only necessary if you
/// really need a new array of the same size as the result. Rust's lazy
/// iterators tend to get optimized very well.
///
///
/// # Examples
///
/// ```
/// let x = [1, 2, 3];
/// let y = x.map(|v| v + 1);
/// assert_eq!(y, [2, 3, 4]);
///
/// let x = [1, 2, 3];
/// let mut temp = 0;
/// let y = x.map(|v| { temp += 1; v * temp });
/// assert_eq!(y, [1, 4, 9]);
///
/// let x = ["Ferris", "Bueller's", "Day", "Off"];
/// let y = x.map(|v| v.len());
/// assert_eq!(y, [6, 9, 3, 3]);
/// ```
#[stable(feature = "array_map", since = "1.55.0")]
pub fn map<F, U>(self, f: F) -> [U; N]
where
F: FnMut(T) -> U,
{
self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
}
/// A fallible function `f` applied to each element on array `self` in order to
/// return an array the same size as `self` or the first error encountered.
///
/// The return type of this function depends on the return type of the closure.
/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N], E>`.
/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`.
///
/// # Examples
///
/// ```
/// #![feature(array_try_map)]
/// let a = ["1", "2", "3"];
/// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1);
/// assert_eq!(b, [2, 3, 4]);
///
/// let a = ["1", "2a", "3"];
/// let b = a.try_map(|v| v.parse::<u32>());
/// assert!(b.is_err());
///
/// use std::num::NonZeroU32;
/// let z = [1, 2, 0, 3, 4];
/// assert_eq!(z.try_map(NonZeroU32::new), None);
/// let a = [1, 2, 3];
/// let b = a.try_map(NonZeroU32::new);
/// let c = b.map(|x| x.map(NonZeroU32::get));
/// assert_eq!(c, Some(a));
/// ```
#[unstable(feature = "array_try_map", issue = "79711")]
pub fn try_map<F, R>(self, f: F) -> ChangeOutputType<R, [R::Output; N]>
where
F: FnMut(T) -> R,
R: Try,
R::Residual: Residual<[R::Output; N]>,
{
drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f)))
}
/// Returns a slice containing the entire array. Equivalent to `&s[..]`.
#[stable(feature = "array_as_slice", since = "1.57.0")]
#[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
pub const fn as_slice(&self) -> &[T] {
self
}
/// Returns a mutable slice containing the entire array. Equivalent to
/// `&mut s[..]`.
#[stable(feature = "array_as_slice", since = "1.57.0")]
pub fn as_mut_slice(&mut self) -> &mut [T] {
self
}
/// Borrows each element and returns an array of references with the same
/// size as `self`.
///
///
/// # Example
///
/// ```
/// #![feature(array_methods)]
///
/// let floats = [3.1, 2.7, -1.0];
/// let float_refs: [&f64; 3] = floats.each_ref();
/// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]);
/// ```
///
/// This method is particularly useful if combined with other methods, like
/// [`map`](#method.map). This way, you can avoid moving the original
/// array if its elements are not [`Copy`].
///
/// ```
/// #![feature(array_methods)]
///
/// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()];
/// let is_ascii = strings.each_ref().map(|s| s.is_ascii());
/// assert_eq!(is_ascii, [true, false, true]);
///
/// // We can still access the original array: it has not been moved.
/// assert_eq!(strings.len(), 3);
/// ```
#[unstable(feature = "array_methods", issue = "76118")]
pub fn each_ref(&self) -> [&T; N] {
from_trusted_iterator(self.iter())
}
/// Borrows each element mutably and returns an array of mutable references
/// with the same size as `self`.
///
///
/// # Example
///
/// ```
/// #![feature(array_methods)]
///
/// let mut floats = [3.1, 2.7, -1.0];
/// let float_refs: [&mut f64; 3] = floats.each_mut();
/// *float_refs[0] = 0.0;
/// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]);
/// assert_eq!(floats, [0.0, 2.7, -1.0]);
/// ```
#[unstable(feature = "array_methods", issue = "76118")]
pub fn each_mut(&mut self) -> [&mut T; N] {
from_trusted_iterator(self.iter_mut())
}
/// Divides one array reference into two at an index.
///
/// The first will contain all indices from `[0, M)` (excluding
/// the index `M` itself) and the second will contain all
/// indices from `[M, N)` (excluding the index `N` itself).
///
/// # Panics
///
/// Panics if `M > N`.
///
/// # Examples
///
/// ```
/// #![feature(split_array)]
///
/// let v = [1, 2, 3, 4, 5, 6];
///
/// {
/// let (left, right) = v.split_array_ref::<0>();
/// assert_eq!(left, &[]);
/// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_array_ref::<2>();
/// assert_eq!(left, &[1, 2]);
/// assert_eq!(right, &[3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_array_ref::<6>();
/// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
/// assert_eq!(right, &[]);
/// }
/// ```
#[unstable(
feature = "split_array",
reason = "return type should have array as 2nd element",
issue = "90091"
)]
#[inline]
pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {
(&self[..]).split_array_ref::<M>()
}
/// Divides one mutable array reference into two at an index.
///
/// The first will contain all indices from `[0, M)` (excluding
/// the index `M` itself) and the second will contain all
/// indices from `[M, N)` (excluding the index `N` itself).
///
/// # Panics
///
/// Panics if `M > N`.
///
/// # Examples
///
/// ```
/// #![feature(split_array)]
///
/// let mut v = [1, 0, 3, 0, 5, 6];
/// let (left, right) = v.split_array_mut::<2>();
/// assert_eq!(left, &mut [1, 0][..]);
/// assert_eq!(right, &mut [3, 0, 5, 6]);
/// left[1] = 2;
/// right[1] = 4;
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[unstable(
feature = "split_array",
reason = "return type should have array as 2nd element",
issue = "90091"
)]
#[inline]
pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {
(&mut self[..]).split_array_mut::<M>()
}
/// Divides one array reference into two at an index from the end.
///
/// The first will contain all indices from `[0, N - M)` (excluding
/// the index `N - M` itself) and the second will contain all
/// indices from `[N - M, N)` (excluding the index `N` itself).
///
/// # Panics
///
/// Panics if `M > N`.
///
/// # Examples
///
/// ```
/// #![feature(split_array)]
///
/// let v = [1, 2, 3, 4, 5, 6];
///
/// {
/// let (left, right) = v.rsplit_array_ref::<0>();
/// assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
/// assert_eq!(right, &[]);
/// }
///
/// {
/// let (left, right) = v.rsplit_array_ref::<2>();
/// assert_eq!(left, &[1, 2, 3, 4]);
/// assert_eq!(right, &[5, 6]);
/// }
///
/// {
/// let (left, right) = v.rsplit_array_ref::<6>();
/// assert_eq!(left, &[]);
/// assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
/// }
/// ```
#[unstable(
feature = "split_array",
reason = "return type should have array as 2nd element",
issue = "90091"
)]
#[inline]
pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {
(&self[..]).rsplit_array_ref::<M>()
}
/// Divides one mutable array reference into two at an index from the end.
///
/// The first will contain all indices from `[0, N - M)` (excluding
/// the index `N - M` itself) and the second will contain all
/// indices from `[N - M, N)` (excluding the index `N` itself).
///
/// # Panics
///
/// Panics if `M > N`.
///
/// # Examples
///
/// ```
/// #![feature(split_array)]
///
/// let mut v = [1, 0, 3, 0, 5, 6];
/// let (left, right) = v.rsplit_array_mut::<4>();
/// assert_eq!(left, &mut [1, 0]);
/// assert_eq!(right, &mut [3, 0, 5, 6][..]);
/// left[1] = 2;
/// right[1] = 4;
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[unstable(
feature = "split_array",
reason = "return type should have array as 2nd element",
issue = "90091"
)]
#[inline]
pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {
(&mut self[..]).rsplit_array_mut::<M>()
}
}
/// Populate an array from the first `N` elements of `iter`
///
/// # Panics
///
/// If the iterator doesn't actually have enough items.
///
/// By depending on `TrustedLen`, however, we can do that check up-front (where
/// it easily optimizes away) so it doesn't impact the loop that fills the array.
#[inline]
fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
}
#[inline]
fn try_from_trusted_iterator<T, R, const N: usize>(
iter: impl UncheckedIterator<Item = R>,
) -> ChangeOutputType<R, [T; N]>
where
R: Try<Output = T>,
R::Residual: Residual<[T; N]>,
{
assert!(iter.size_hint().0 >= N);
fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
move |_| {
// SAFETY: We know that `from_fn` will call this at most N times,
// and we checked to ensure that we have at least that many items.
unsafe { iter.next_unchecked() }
}
}
try_from_fn(next(iter))
}
/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
/// needing to monomorphize for every array length.
///
/// This takes a generator rather than an iterator so that *at the type level*
/// it never needs to worry about running out of items. When combined with
/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
/// it to optimize well.
///
/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
/// function that does the union of both things, but last time it was that way
/// it resulted in poor codegen from the "are there enough source items?" checks
/// not optimizing away. So if you give it a shot, make sure to watch what
/// happens in the codegen tests.
#[inline]
fn try_from_fn_erased<T, R>(
buffer: &mut [MaybeUninit<T>],
mut generator: impl FnMut(usize) -> R,
) -> ControlFlow<R::Residual>
where
R: Try<Output = T>,
{
let mut guard = Guard { array_mut: buffer, initialized: 0 };
while guard.initialized < guard.array_mut.len() {
let item = generator(guard.initialized).branch()?;
// SAFETY: The loop condition ensures we have space to push the item
unsafe { guard.push_unchecked(item) };
}
mem::forget(guard);
ControlFlow::Continue(())
}
/// Panic guard for incremental initialization of arrays.
///
/// Disarm the guard with `mem::forget` once the array has been initialized.
///
/// # Safety
///
/// All write accesses to this structure are unsafe and must maintain a correct
/// count of `initialized` elements.
///
/// To minimize indirection fields are still pub but callers should at least use
/// `push_unchecked` to signal that something unsafe is going on.
struct Guard<'a, T> {
/// The array to be initialized.
pub array_mut: &'a mut [MaybeUninit<T>],
/// The number of items that have been initialized so far.
pub initialized: usize,
}
impl<T> Guard<'_, T> {
/// Adds an item to the array and updates the initialized item counter.
///
/// # Safety
///
/// No more than N elements must be initialized.
#[inline]
pub unsafe fn push_unchecked(&mut self, item: T) {
// SAFETY: If `initialized` was correct before and the caller does not
// invoke this method more than N times then writes will be in-bounds
// and slots will not be initialized more than once.
unsafe {
self.array_mut.get_unchecked_mut(self.initialized).write(item);
self.initialized = self.initialized.unchecked_add(1);
}
}
}
impl<T> Drop for Guard<'_, T> {
fn drop(&mut self) {
debug_assert!(self.initialized <= self.array_mut.len());
// SAFETY: this slice will contain only initialized objects.
unsafe {
crate::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
self.array_mut.get_unchecked_mut(..self.initialized),
));
}
}
}
/// Pulls `N` items from `iter` and returns them as an array. If the iterator
/// yields fewer than `N` items, `Err` is returned containing an iterator over
/// the already yielded items.
///
/// Since the iterator is passed as a mutable reference and this function calls
/// `next` at most `N` times, the iterator can still be used afterwards to
/// retrieve the remaining items.
///
/// If `iter.next()` panicks, all items already yielded by the iterator are
/// dropped.
///
/// Used for [`Iterator::next_chunk`].
#[inline]
pub(crate) fn iter_next_chunk<T, const N: usize>(
iter: &mut impl Iterator<Item = T>,
) -> Result<[T; N], IntoIter<T, N>> {
let mut array = MaybeUninit::uninit_array::<N>();
let r = iter_next_chunk_erased(&mut array, iter);
match r {
Ok(()) => {
// SAFETY: All elements of `array` were populated.
Ok(unsafe { MaybeUninit::array_assume_init(array) })
}
Err(initialized) => {
// SAFETY: Only the first `initialized` elements were populated
Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
}
}
}
/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
/// needing to monomorphize for every array length.
///
/// Unfortunately this loop has two exit conditions, the buffer filling up
/// or the iterator running out of items, making it tend to optimize poorly.
#[inline]
fn iter_next_chunk_erased<T>(
buffer: &mut [MaybeUninit<T>],
iter: &mut impl Iterator<Item = T>,
) -> Result<(), usize> {
let mut guard = Guard { array_mut: buffer, initialized: 0 };
while guard.initialized < guard.array_mut.len() {
let Some(item) = iter.next() else {
// Unlike `try_from_fn_erased`, we want to keep the partial results,
// so we need to defuse the guard instead of using `?`.
let initialized = guard.initialized;
mem::forget(guard);
return Err(initialized);
};
// SAFETY: The loop condition ensures we have space to push the item
unsafe { guard.push_unchecked(item) };
}
mem::forget(guard);
Ok(())
}