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Rollup merge of #90162 - WaffleLapkin:const_array_slice_from_ref_mut, r=oli-obk

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Mark `{array, slice}::{from_ref, from_mut}` as const fn

This PR marks the following APIs as `const`:
```rust
// core::array
pub const fn from_ref<T>(s: &T) -> &[T; 1];
pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1];

// core::slice
pub const fn from_ref<T>(s: &T) -> &[T];
pub const fn from_mut<T>(s: &mut T) -> &mut [T];
```

Note that `from_ref` methods require `const_raw_ptr_deref` feature (which seems totally fine, since it's being stabilized, see #89551), `from_mut` methods require `const_mut_refs` (which seems fine too since this PR marks `from_mut` functions as const unstable).

r? ````@oli-obk````
This commit is contained in:
Matthias Krüger 2021-10-24 15:48:44 +02:00 • committed by GitHub
commit c16ee19dd4
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6 changed files with 25 additions and 4 deletions
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5
library/core/tests/array.rs
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@ -7,6 +7,11 @@ fn array_from_ref() {
let value: String = "Hello World!".into();
let arr: &[String; 1] = array::from_ref(&value);
assert_eq!(&[value.clone()], arr);
const VALUE: &&str = &"Hello World!";
const ARR: &[&str; 1] = array::from_ref(VALUE);
assert_eq!(&[*VALUE], ARR);
assert!(core::ptr::eq(VALUE, &ARR[0]));
}
#[test]