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core: simplify implementation of array::repeat, address other nits

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joboet 2023-12-20 00:14:25 +01:00
parent 8aa24572f0
commit 39a918002e
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GPG Key ID: 704E0149B0194B3C
1 changed files with 9 additions and 18 deletions
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27
library/core/src/array/mod.rs
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@ -10,8 +10,7 @@ use crate::convert::Infallible;
use crate::error::Error; use crate::error::Error;
use crate::fmt; use crate::fmt;
use crate::hash::{self, Hash}; use crate::hash::{self, Hash};
use crate::intrinsics::transmute_unchecked; use crate::iter::{repeat_n, UncheckedIterator};
use crate::iter::UncheckedIterator;
use crate::mem::{self, MaybeUninit}; use crate::mem::{self, MaybeUninit};
use crate::ops::{ use crate::ops::{
ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try, ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
@ -30,12 +29,16 @@ pub use iter::IntoIter;
/// Creates an array of type `[T; N]` by repeatedly cloning a value. /// Creates an array of type `[T; N]` by repeatedly cloning a value.
/// ///
/// The value will be used as the last element of the resulting array, so it /// This is the same as `[val; N]`, but it also works for types that do not
/// will be cloned N - 1 times. If N is zero, the value will be dropped. /// 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 /// # Example
/// ///
/// Creating muliple copies of a string: /// Creating muliple copies of a `String`:
/// ```rust /// ```rust
/// #![feature(array_repeat)] /// #![feature(array_repeat)]
/// ///
@ -48,19 +51,7 @@ pub use iter::IntoIter;
#[inline] #[inline]
#[unstable(feature = "array_repeat", issue = "none")] #[unstable(feature = "array_repeat", issue = "none")]
pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] { pub fn repeat<T: Clone, const N: usize>(val: T) -> [T; N] {
match N { from_trusted_iterator(repeat_n(val, N))
// SAFETY: we know N to be 0 at this point.
0 => unsafe { transmute_unchecked::<[T; 0], [T; N]>([]) },
// SAFETY: we know N to be 1 at this point.
1 => unsafe { transmute_unchecked::<[T; 1], [T; N]>([val]) },
_ => {
let mut array = MaybeUninit::uninit_array::<N>();
try_from_fn_erased(&mut array[..N - 1], NeverShortCircuit::wrap_mut_1(|_| val.clone()));
array[N - 1].write(val);
// SAFETY: all elements were initialized.
unsafe { MaybeUninit::array_assume_init(array) }
}
}
} }
/// Creates an array of type [T; N], where each element `T` is the returned value from `cb` /// Creates an array of type [T; N], where each element `T` is the returned value from `cb`