Messages in this thread | | | Date | Fri, 27 Jan 2023 14:03:19 +0000 | From | Gary Guo <> | Subject | Re: [PATCH 4/5] rust: types: implement `ForeignOwnable` for the unit type |
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On Thu, 19 Jan 2023 14:40:35 -0300 Wedson Almeida Filho <wedsonaf@gmail.com> wrote:
> This allows us to use the unit type `()` when we have no object whose > ownership must be managed but one implementing the `ForeignOwnable` > trait is needed. > > Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com> > --- > rust/kernel/types.rs | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index e037c262f23e..8f80cffbff59 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -85,6 +85,19 @@ impl<T: 'static> ForeignOwnable for Box<T> { > } > } > > +impl ForeignOwnable for () { > + type Borrowed<'a> = (); > + > + fn into_foreign(self) -> *const core::ffi::c_void { > + // We use 1 to be different from a null pointer. > + 1usize as _
this should really be `core::ptr::invalid(1)`. That's currently unstable, but can be equivalently written as `NonNull::<()>::dangling().as_ptr()`.
This has a different semantic meaning from `as` since it explicitly suggests an invalid provenance and thus will not alias with other pointers. (Although I don't think compiler currently can take advantage of this fact yet)
> + } > + > + unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {} > + > + unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {} > +} > + > /// Runs a cleanup function/closure when dropped. > /// > /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
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