Skip to content

ManuallyDrop != MaybeUninit #58780

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Mar 3, 2019
Merged

ManuallyDrop != MaybeUninit #58780

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
4e7d4c7
ManuallyDrop != MaybeUninit
RalfJung Feb 27, 2019
f92c204
improve readability
RalfJung Feb 27, 2019
0c1a38c
Update src/libcore/mem.rs
Centril Feb 28, 2019
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 8 additions & 0 deletions src/libcore/mem.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -900,10 +900,16 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
}
}

// FIXME: Reference `MaybeUninit` from these docs, once that is stable.
/// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
///
/// This wrapper is 0-cost.
///
/// `ManuallyDrop<T>` is subject to the same layout optimizations as `T`.
/// As a consequence, it has *no effect* on the assumptions that the compiler makes
/// about all values being initialized at their type. In particular, initializing
/// a `ManuallyDrop<&mut T>` with [`mem::zeroed`] is undefined behavior.
///
/// # Examples
///
/// This wrapper helps with explicitly documenting the drop order dependencies between fields of
Expand Down Expand Up @@ -935,6 +941,8 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
/// }
/// }
/// ```
///
/// [`mem::zeroed`]: fn.zeroed.html
#[stable(feature = "manually_drop", since = "1.20.0")]
#[lang = "manually_drop"]
#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
Expand Down