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//! Helper functions and types for fixed-length arrays.
//!
//! *[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::fmt;
use crate::hash::{self, Hash};
use crate::iter::TrustedLen;
use crate::mem::{self, MaybeUninit};
use crate::ops::{
ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
};
use crate::slice::{Iter, IterMut};
mod equality;
mod iter;
#[stable(feature = "array_value_iter", since = "1.51.0")]
pub use iter::IntoIter;
/// Creates an array `[T; N]` where each array element `T` is returned by the `cb` call.
///
/// # Arguments
///
/// * `cb`: Callback where the passed argument is the current array index.
///
/// # Example
///
/// ```rust
/// let array = core::array::from_fn(|i| i);
/// assert_eq!(array, [0, 1, 2, 3, 4]);
/// ```
#[inline]
#[stable(feature = "array_from_fn", since = "1.63.0")]
pub fn from_fn<T, const N: usize, F>(mut cb: F) -> [T; N]
where
F: FnMut(usize) -> T,
{
let mut idx = 0;
[(); N].map(|_| {
let res = cb(idx);
idx += 1;
res
})
}
/// 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]>,
{
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { try_collect_into_array_unchecked(&mut (0..N).map(cb)) }
}
/// 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 {
fmt::Display::fmt(self.__description(), f)
}
}
impl TryFromSliceError {
#[unstable(
feature = "array_error_internals",
reason = "available through Error trait and this method should not \
be exposed publicly",
issue = "none"
)]
#[inline]
#[doc(hidden)]
pub fn __description(&self) -> &str {
"could not convert slice to array"
}
}
#[stable(feature = "try_from_slice_error", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
impl const 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")]
#[rustc_const_unstable(feature = "const_borrow", issue = "91522")]
impl<T, const N: usize> const Borrow<[T]> for [T; N] {
fn borrow(&self) -> &[T] {
self
}
}
#[stable(feature = "array_borrow", since = "1.4.0")]
#[rustc_const_unstable(feature = "const_borrow", issue = "91522")]
impl<T, const N: usize> const BorrowMut<[T]> for [T; N] {
fn borrow_mut(&mut self) -> &mut [T] {
self
}
}
#[stable(feature = "try_from", since = "1.34.0")]
impl<T, const N: usize> TryFrom<&[T]> for [T; N]
where
T: Copy,
{
type Error = TryFromSliceError;
fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> {
<&Self>::try_from(slice).map(|r| *r)
}
}
#[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;
fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> {
<Self>::try_from(&*slice)
}
}
#[stable(feature = "try_from", since = "1.34.0")]
impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
type Error = TryFromSliceError;
fn try_from(slice: &[T]) -> Result<&[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(()))
}
}
}
#[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;
fn try_from(slice: &mut [T]) -> Result<&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.
///
/// ```
/// #![feature(build_hasher_simple_hash_one)]
/// 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")]
#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
impl<T, I, const N: usize> const Index<I> for [T; N]
where
[T]: ~const 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")]
#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
impl<T, I, const N: usize> const IndexMut<I> for [T; N]
where
[T]: ~const 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] {
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { collect_into_array_unchecked(&mut 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, $t:ident $($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(), $($ts::default()),*]
}
}
array_impl_default!{($n - 1), $($ts)*}
};
{$n:expr,} => {
#[stable(since = "1.4.0", feature = "array_default")]
#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
impl<T> const 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,
{
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) }
}
/// 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]>,
{
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { try_collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) }
}
/// 'Zips up' two arrays into a single array of pairs.
///
/// `zip()` returns a new array where every element is a tuple where the
/// first element comes from the first array, and the second element comes
/// from the second array. In other words, it zips two arrays together,
/// into a single one.
///
/// # Examples
///
/// ```
/// #![feature(array_zip)]
/// let x = [1, 2, 3];
/// let y = [4, 5, 6];
/// let z = x.zip(y);
/// assert_eq!(z, [(1, 4), (2, 5), (3, 6)]);
/// ```
#[unstable(feature = "array_zip", issue = "80094")]
pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N] {
let mut iter = IntoIterator::into_iter(self).zip(rhs);
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { collect_into_array_unchecked(&mut iter) }
}
/// 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] {
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { collect_into_array_unchecked(&mut 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] {
// SAFETY: we know for certain that this iterator will yield exactly `N`
// items.
unsafe { collect_into_array_unchecked(&mut 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>()
}
}
/// Pulls `N` items from `iter` and returns them as an array. If the iterator
/// yields fewer than `N` items, this function exhibits undefined behavior.
///
/// See [`try_collect_into_array`] for more information.
///
///
/// # Safety
///
/// It is up to the caller to guarantee that `iter` yields at least `N` items.
/// Violating this condition causes undefined behavior.
unsafe fn try_collect_into_array_unchecked<I, T, R, const N: usize>(iter: &mut I) -> R::TryType
where
// Note: `TrustedLen` here is somewhat of an experiment. This is just an
// internal function, so feel free to remove if this bound turns out to be a
// bad idea. In that case, remember to also remove the lower bound
// `debug_assert!` below!
I: Iterator + TrustedLen,
I::Item: Try<Output = T, Residual = R>,
R: Residual<[T; N]>,
{
debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX));
debug_assert!(N <= iter.size_hint().0);
// SAFETY: covered by the function contract.
unsafe { try_collect_into_array(iter).unwrap_unchecked() }
}
// Infallible version of `try_collect_into_array_unchecked`.
unsafe fn collect_into_array_unchecked<I, const N: usize>(iter: &mut I) -> [I::Item; N]
where
I: Iterator + TrustedLen,
{
let mut map = iter.map(NeverShortCircuit);
// SAFETY: The same safety considerations w.r.t. the iterator length
// apply for `try_collect_into_array_unchecked` as for
// `collect_into_array_unchecked`
match unsafe { try_collect_into_array_unchecked(&mut map) } {
NeverShortCircuit(array) => array,
}
}
/// 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.
#[inline]
fn try_collect_into_array<I, T, R, const N: usize>(
iter: &mut I,
) -> Result<R::TryType, IntoIter<T, N>>
where
I: Iterator,
I::Item: Try<Output = T, Residual = R>,
R: Residual<[T; N]>,
{
if N == 0 {
// SAFETY: An empty array is always inhabited and has no validity invariants.
return Ok(Try::from_output(unsafe { mem::zeroed() }));
}
struct Guard<'a, T, const N: usize> {
array_mut: &'a mut [MaybeUninit<T>; N],
initialized: usize,
}
impl<T, const N: usize> Drop for Guard<'_, T, N> {
fn drop(&mut self) {
debug_assert!(self.initialized <= N);
// SAFETY: this slice will contain only initialized objects.
unsafe {
crate::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
&mut self.array_mut.get_unchecked_mut(..self.initialized),
));
}
}
}
let mut array = MaybeUninit::uninit_array::<N>();
let mut guard = Guard { array_mut: &mut array, initialized: 0 };
for _ in 0..N {
match iter.next() {
Some(item_rslt) => {
let item = match item_rslt.branch() {
ControlFlow::Break(r) => {
return Ok(FromResidual::from_residual(r));
}
ControlFlow::Continue(elem) => elem,
};
// SAFETY: `guard.initialized` starts at 0, is increased by one in the
// loop and the loop is aborted once it reaches N (which is
// `array.len()`).
unsafe {
guard.array_mut.get_unchecked_mut(guard.initialized).write(item);
}
guard.initialized += 1;
}
None => {
let alive = 0..guard.initialized;
mem::forget(guard);
// SAFETY: `array` was initialized with exactly `initialized`
// number of elements.
return Err(unsafe { IntoIter::new_unchecked(array, alive) });
}
}
}
mem::forget(guard);
// SAFETY: All elements of the array were populated in the loop above.
let output = unsafe { MaybeUninit::array_assume_init(array) };
Ok(Try::from_output(output))
}
/// Returns the next chunk of `N` items from the iterator or errors with an
/// iterator over the remainder. Used for `Iterator::next_chunk`.
#[inline]
pub(crate) fn iter_next_chunk<I, const N: usize>(
iter: &mut I,
) -> Result<[I::Item; N], IntoIter<I::Item, N>>
where
I: Iterator,
{
let mut map = iter.map(NeverShortCircuit);
try_collect_into_array(&mut map).map(|NeverShortCircuit(arr)| arr)
}