Commit 2dde1c8b authored by Tamir Duberstein's avatar Tamir Duberstein Committed by Miguel Ojeda
Browse files

rust: sync: document `PhantomData` in `Arc` 



Add a comment explaining the relevant semantics of `PhantomData`. This
should help future readers who may, as I did, assume that this field is
redundant at first glance.

Signed-off-by: default avatarTamir Duberstein <tamird@gmail.com>
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241107-simplify-arc-v2-1-7256e638aac1@gmail.com


Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 3f4223c0

rust/kernel/sync/arc.rs

+8 −0
Original line number Diff line number Diff line
@@ -127,6 +127,14 @@ 
/// ```

pub struct Arc<T: ?Sized> {

    ptr: NonNull<ArcInner<T>>,

    // NB: this informs dropck that objects of type `ArcInner<T>` may be used in `<Arc<T> as

    // Drop>::drop`. Note that dropck already assumes that objects of type `T` may be used in

    // `<Arc<T> as Drop>::drop` and the distinction between `T` and `ArcInner<T>` is not presently

    // meaningful with respect to dropck - but this may change in the future so this is left here

    // out of an abundance of caution.

    //

    // See https://doc.rust-lang.org/nomicon/phantom-data.html#generic-parameters-and-drop-checking

    // for more detail on the semantics of dropck in the presence of `PhantomData`.

    _p: PhantomData<ArcInner<T>>,

}