Rollup merge of #77074 - lcnr:array-from-ref, r=SimonSapin
add array::from_ref mirrors the methods in `std::slice` with the same name. I guess this method previously didn't exist as there was close to no reason to create an array of size `1`. This will change due to const generics in the near future.
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09b0bd6022
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@ -19,6 +19,20 @@ mod iter;
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#[unstable(feature = "array_value_iter", issue = "65798")]
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pub use iter::IntoIter;
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/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
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#[unstable(feature = "array_from_ref", issue = "77101")]
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pub fn from_ref<T>(s: &T) -> &[T; 1] {
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// SAFETY: Converting `&T` to `&[T; 1]` is sound.
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unsafe { &*(s as *const T).cast::<[T; 1]>() }
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}
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/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
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#[unstable(feature = "array_from_ref", issue = "77101")]
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pub fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
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// SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
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unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
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}
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/// Utility trait implemented only on arrays of fixed size
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///
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/// This trait can be used to implement other traits on fixed-size arrays
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@ -1,5 +1,6 @@
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//! Free functions to create `&[T]` and `&mut [T]`.
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use crate::array;
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use crate::intrinsics::is_aligned_and_not_null;
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use crate::mem;
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use crate::ptr;
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@ -140,19 +141,11 @@ pub unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T]
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/// Converts a reference to T into a slice of length 1 (without copying).
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#[stable(feature = "from_ref", since = "1.28.0")]
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pub fn from_ref<T>(s: &T) -> &[T] {
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// SAFETY: a reference is guaranteed to be valid for reads. The returned
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// reference cannot be mutated as it is an immutable reference.
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// `mem::size_of::<T>()` cannot be larger than `isize::MAX`.
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// Thus the call to `from_raw_parts` is safe.
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unsafe { from_raw_parts(s, 1) }
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array::from_ref(s)
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}
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/// Converts a reference to T into a slice of length 1 (without copying).
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#[stable(feature = "from_ref", since = "1.28.0")]
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pub fn from_mut<T>(s: &mut T) -> &mut [T] {
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// SAFETY: a mutable reference is guaranteed to be valid for writes.
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// The reference cannot be accessed by another pointer as it is an mutable reference.
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// `mem::size_of::<T>()` cannot be larger than `isize::MAX`.
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// Thus the call to `from_raw_parts_mut` is safe.
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unsafe { from_raw_parts_mut(s, 1) }
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array::from_mut(s)
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}
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@ -1,4 +1,4 @@
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use core::array::{FixedSizeArray, IntoIter};
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use core::array::{self, FixedSizeArray, IntoIter};
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use core::convert::TryFrom;
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#[test]
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@ -19,6 +19,21 @@ fn fixed_size_array() {
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assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_zero_sized).len(), 0);
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}
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#[test]
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fn array_from_ref() {
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let value: String = "Hello World!".into();
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let arr: &[String; 1] = array::from_ref(&value);
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assert_eq!(&[value.clone()], arr);
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}
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#[test]
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fn array_from_mut() {
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let mut value: String = "Hello World".into();
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let arr: &mut [String; 1] = array::from_mut(&mut value);
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arr[0].push_str("!");
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assert_eq!(&value, "Hello World!");
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}
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#[test]
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fn array_try_from() {
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macro_rules! test {
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@ -1,5 +1,6 @@
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#![feature(alloc_layout_extra)]
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#![feature(array_chunks)]
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#![feature(array_from_ref)]
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#![feature(array_methods)]
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#![feature(array_map)]
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#![feature(array_windows)]
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