Il mar 17 dic 2024, 16:55 Zhao Liu <zhao1....@intel.com> ha scritto: > On Mon, Dec 09, 2024 at 01:37:17PM +0100, Paolo Bonzini wrote: > > Date: Mon, 9 Dec 2024 13:37:17 +0100 > > From: Paolo Bonzini <pbonz...@redhat.com> > > Subject: [PATCH 26/26] rust: callbacks: allow passing optional callbacks > as > > () > > X-Mailer: git-send-email 2.47.1 > > > > In some cases, callbacks are optional. Using "Some(function)" and "None" > > does not work well, because when someone writes "None" the compiler does > > not know what to use for "F" in "Option<F>". > > I understand the direct use case is MemoryRegionOps, which has optional > callbacks. However, I'm not quite sure how exactly it should be applied > to C bindings and how it will play with Option<callback>. >
You wouldn't use Option<callback> at all, using () instead of None; the difference is that () does not have a parameter while None does (and the compiler cannot infer it). But I am okay with leaving this patch behind until there's a need. Paolo Could u pls provide a simple example? > > > Therefore, adopt () to mean a "null" callback. It is possible to enforce > > that a callback is valid by adding a "let _: () = F::ASSERT_IS_SOME" > before > > the invocation of F::call. > > > > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > > --- > > rust/qemu-api/src/callbacks.rs | 97 ++++++++++++++++++++++++++++++++++ > > 1 file changed, 97 insertions(+) > > > > diff --git a/rust/qemu-api/src/callbacks.rs b/rust/qemu-api/src/ > callbacks.rs > > index 6401d807198..83c681d6478 100644 > > --- a/rust/qemu-api/src/callbacks.rs > > +++ b/rust/qemu-api/src/callbacks.rs > > @@ -76,6 +76,31 @@ > > /// call_it(&move |_| String::from(x), "hello workd"); > > typo: s/workd/word/ (in previous patch :-)) > >
