bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Implement write() method for Box<MaybeUninit<T>>

Browse source 
This adds method similar to `MaybeUninit::write` main difference being
it returns owned `Box`. This can be used to elide copy from stack
safely, however it's not currently tested that the optimization actually
occurs.

Analogous methods are not provided for `Rc` and `Arc` as those need to
handle the possibility of sharing. Some version of them may be added in
the future.

This was discussed in #63291 which this change extends.
This commit is contained in:
Martin Habovstiak 2021-09-13 15:44:27 +02:00
parent 18bb8c61a9
commit 41e21aa1c2
2 changed files with 38 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

6
compiler/rustc_data_structures/src/functor.rs
View file

@ -31,11 +31,9 @@ impl<T> IdFunctor for Box<T> {
let value = raw.read();
// SAFETY: Converts `Box<T>` to `Box<MaybeUninit<T>>` which is the
// inverse of `Box::assume_init()` and should be safe.
let mut raw: Box<mem::MaybeUninit<T>> = Box::from_raw(raw.cast());
let raw: Box<mem::MaybeUninit<T>> = Box::from_raw(raw.cast());
// SAFETY: Write the mapped value back into the `Box`.
raw.write(f(value)?);
// SAFETY: We just initialized `raw`.
raw.assume_init()
Box::write(raw, f(value)?)
})
}
}