//! Utilities for the array primitive type.

//!

//! *[See also the array primitive type](array).*

#![stable(feature = "core_array", since = "1.35.0")]

#[cfg(not(feature = "ferrocene_certified"))]

use crate::borrow::{Borrow, BorrowMut};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::cmp::Ordering;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::convert::Infallible;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::error::Error;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::fmt;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::hash::{self, Hash};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::intrinsics::transmute_unchecked;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::iter::{UncheckedIterator, repeat_n};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::mem::{self, MaybeUninit};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::ops::{

    ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,

};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::ptr::{null, null_mut};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::slice::{Iter, IterMut};

#[cfg(not(feature = "ferrocene_certified"))]

mod ascii;

#[cfg(not(feature = "ferrocene_certified"))]

mod drain;

#[cfg(not(feature = "ferrocene_certified"))]

mod equality;

#[cfg(not(feature = "ferrocene_certified"))]

mod iter;

#[cfg(not(feature = "ferrocene_certified"))]

pub(crate) use drain::drain_array_with;

#[stable(feature = "array_value_iter", since = "1.51.0")]

// blocked by IntoIter

#[cfg(not(feature = "ferrocene_certified"))]

pub use iter::IntoIter;

/// Creates an array of type `[T; N]` by repeatedly cloning a value.

///

/// This is the same as `[val; N]`, but it also works for types that do not

/// implement [`Copy`].

///

/// The provided value will be used as an element of the resulting array and

/// will be cloned N - 1 times to fill up the rest. If N is zero, the value

/// will be dropped.

///

/// # Example

///

/// Creating multiple copies of a `String`:

/// ```rust

/// use std::array;

///

/// let string = "Hello there!".to_string();

/// let strings = array::repeat(string);

/// assert_eq!(strings, ["Hello there!", "Hello there!"]);

/// ```

#[inline]

#[must_use = "cloning is often expensive and is not expected to have side effects"]

#[stable(feature = "array_repeat", since = "CURRENT_RUSTC_VERSION")]

#[cfg(not(feature = "ferrocene_certified"))]

pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {

    from_trusted_iterator(repeat_n(val, N))

}

/// Creates an array where each element is produced by calling `f` with

/// that element's index while walking forward through the array.

///

/// This is essentially the same as writing

/// ```text

/// [f(0), f(1), f(2), …, f(N - 2), f(N - 1)]

/// ```

/// and is similar to `(0..i).map(f)`, just for arrays not iterators.

///

/// If `N == 0`, this produces an empty array without ever calling `f`.

///

/// # 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]);

/// ```

///

/// You can also capture things, for example to create an array full of clones

/// where you can't just use `[item; N]` because it's not `Copy`:

/// ```

/// # // TBH `array::repeat` would be better for this, but it's not stable yet.

/// let my_string = String::from("Hello");

/// let clones: [String; 42] = std::array::from_fn(|_| my_string.clone());

/// assert!(clones.iter().all(|x| *x == my_string));

/// ```

///

/// The array is generated in ascending index order, starting from the front

/// and going towards the back, so you can use closures with mutable state:

/// ```

/// let mut state = 1;

/// let a = std::array::from_fn(|_| { let x = state; state *= 2; x });

/// assert_eq!(a, [1, 2, 4, 8, 16, 32]);

/// ```

#[inline]

#[stable(feature = "array_from_fn", since = "1.63.0")]

#[cfg(not(feature = "ferrocene_certified"))]

pub fn from_fn<T, const N: usize, F>(f: F) -> [T; N]

where

    F: FnMut(usize) -> T,

{

    try_from_fn(NeverShortCircuit::wrap_mut_1(f)).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")]

#[cfg(not(feature = "ferrocene_certified"))]

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 = [const { MaybeUninit::uninit() }; 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")]

#[cfg(not(feature = "ferrocene_certified"))]

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_stable(feature = "const_array_from_ref", since = "1.83.0")]

#[cfg(not(feature = "ferrocene_certified"))]

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)]

#[cfg(not(feature = "ferrocene_certified"))]

pub struct TryFromSliceError(());

#[stable(feature = "core_array", since = "1.35.0")]

#[cfg(not(feature = "ferrocene_certified"))]

impl fmt::Display for TryFromSliceError {

    #[inline]

    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

        "could not convert slice to array".fmt(f)

    }

}

#[stable(feature = "try_from", since = "1.34.0")]

#[cfg(not(feature = "ferrocene_certified"))]

impl Error for TryFromSliceError {}

#[stable(feature = "try_from_slice_error", since = "1.36.0")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl const From<Infallible> for TryFromSliceError {

    fn from(x: Infallible) -> TryFromSliceError {

        match x {}

    }

}

#[stable(feature = "rust1", since = "1.0.0")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, const N: usize> const AsRef<[T]> for [T; N] {

    #[inline]

    fn as_ref(&self) -> &[T] {

        &self[..]

    }

}

#[stable(feature = "rust1", since = "1.0.0")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, const N: usize> const 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_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

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_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, const N: usize> const 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")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, const N: usize> const TryFrom<&[T]> for [T; N]

where

    T: Copy,

{

    type Error = TryFromSliceError;

    #[inline]

}

/// 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")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, const N: usize> const 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")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<'a, T, const N: usize> const TryFrom<&'a [T]> for &'a [T; N] {

    type Error = TryFromSliceError;

    #[inline]

}

/// 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")]

#[rustc_const_unstable(feature = "const_convert", issue = "143773")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<'a, T, const N: usize> const 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> {

        slice.as_mut_array().ok_or(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::hash::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")]

#[cfg(not(feature = "ferrocene_certified"))]

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")]

#[cfg(not(feature = "ferrocene_certified"))]

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")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {

    type Item = &'a T;

    type IntoIter = Iter<'a, T>;

}

#[stable(feature = "rust1", since = "1.0.0")]

#[cfg(not(feature = "ferrocene_certified"))]

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_index", issue = "143775")]

#[cfg(not(feature = "ferrocene_certified"))]

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]

}

#[stable(feature = "index_trait_on_arrays", since = "1.50.0")]

#[rustc_const_unstable(feature = "const_index", issue = "143775")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T, I, const N: usize> const IndexMut<I> for [T; N]

where

    [T]: [const] IndexMut<I>,

{

    #[inline]

}

/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison).

#[stable(feature = "rust1", since = "1.0.0")]

// blocked by PartialOrd

#[cfg(not(feature = "ferrocene_certified"))]

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")]

#[cfg(not(feature = "ferrocene_certified"))]

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")]

#[cfg(not(feature = "ferrocene_certified"))]

impl<T: Copy, const N: usize> Copy for [T; N] {}

#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]

#[cfg(not(feature = "ferrocene_certified"))]

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);

    }

}

#[cfg(not(feature = "ferrocene_certified"))]

trait SpecArrayClone: Clone {

    fn clone<const N: usize>(array: &[Self; N]) -> [Self; N];

}

#[cfg(not(feature = "ferrocene_certified"))]

impl<T: Clone> SpecArrayClone for T {

    #[inline]

    default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {

        from_trusted_iterator(array.iter().cloned())

    }

}

#[cfg(not(feature = "ferrocene_certified"))]

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.

#[cfg(not(feature = "ferrocene_certified"))]

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")]

        impl<T> Default for [T; $n] {

            fn default() -> [T; $n] { [] }

        }

    };

}

#[cfg(not(feature = "ferrocene_certified"))]

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]);

    /// ```

    #[must_use]

    #[stable(feature = "array_map", since = "1.55.0")]

    #[cfg(not(feature = "ferrocene_certified"))]

    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::NonZero;

    ///

    /// let z = [1, 2, 0, 3, 4];

    /// assert_eq!(z.try_map(NonZero::new), None);

    ///

    /// let a = [1, 2, 3];

    /// let b = a.try_map(NonZero::new);

    /// let c = b.map(|x| x.map(NonZero::get));

    /// assert_eq!(c, Some(a));

    /// ```

    #[unstable(feature = "array_try_map", issue = "79711")]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub fn try_map<R>(self, f: impl FnMut(T) -> R) -> ChangeOutputType<R, [R::Output; N]>

    where

        R: Try<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")]

    #[rustc_const_stable(feature = "const_array_as_mut_slice", since = "1.89.0")]

    /// Borrows each element and returns an array of references with the same

    /// size as `self`.

    ///

    ///

    /// # Example

    ///

    /// ```

    /// 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`].

    ///

    /// ```

    /// 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);

    /// ```

    #[stable(feature = "array_methods", since = "1.77.0")]

    #[rustc_const_stable(feature = "const_array_each_ref", since = "CURRENT_RUSTC_VERSION")]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn each_ref(&self) -> [&T; N] {

        let mut buf = [null::<T>(); N];

        // FIXME(const_trait_impl): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.

        let mut i = 0;

        while i < N {

            buf[i] = &raw const self[i];

            i += 1;

        }

        // SAFETY: `*const T` has the same layout as `&T`, and we've also initialised each pointer as a valid reference.

        unsafe { transmute_unchecked(buf) }

    }

    /// Borrows each element mutably and returns an array of mutable references

    /// with the same size as `self`.

    ///

    ///

    /// # Example

    ///

    /// ```

    ///

    /// 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]);

    /// ```

    #[stable(feature = "array_methods", since = "1.77.0")]

    #[rustc_const_stable(feature = "const_array_each_ref", since = "CURRENT_RUSTC_VERSION")]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn each_mut(&mut self) -> [&mut T; N] {

        let mut buf = [null_mut::<T>(); N];

        // FIXME(const_trait_impl): We would like to simply use iterators for this (as in the original implementation), but this is not allowed in constant expressions.

        let mut i = 0;

        while i < N {

            buf[i] = &raw mut self[i];

            i += 1;

        }

        // SAFETY: `*mut T` has the same layout as `&mut T`, and we've also initialised each pointer as a valid reference.

        unsafe { transmute_unchecked(buf) }

    }

    /// 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]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) {

        self.split_first_chunk::<M>().unwrap()

    }

    /// 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]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) {

        self.split_first_chunk_mut::<M>().unwrap()

    }

    /// 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]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) {

        self.split_last_chunk::<M>().unwrap()

    }

    /// 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]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) {

        self.split_last_chunk_mut::<M>().unwrap()

    }

}

/// 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]

#[cfg(not(feature = "ferrocene_certified"))]

fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {

    try_from_trusted_iterator(iter.map(NeverShortCircuit)).0

}

#[inline]

#[cfg(not(feature = "ferrocene_certified"))]

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]

#[cfg(not(feature = "ferrocene_certified"))]

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.

#[cfg(not(feature = "ferrocene_certified"))]

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,

}

#[cfg(not(feature = "ferrocene_certified"))]

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]

        // 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.

}

#[cfg(not(feature = "ferrocene_certified"))]

impl<T> Drop for Guard<'_, T> {

    #[inline]

        // SAFETY: this slice will contain only initialized objects.

}

/// 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]

#[cfg(not(feature = "ferrocene_certified"))]

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 = [const { MaybeUninit::uninit() }; 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]

#[cfg(not(feature = "ferrocene_certified"))]

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(())

}