Add CanSend impls for reference types too (#442)

Summary:
Pull Request resolved: #442

This makes it easier to use a generic to represent either `&Context<>` (borrowed),
`&Mailbox` (borrowed), or `Mailbox` (owned).

Reviewed By: mariusae

Differential Revision: D77868301

fbshipit-source-id: 8544fed8321804f24e312af47609eac4b7188240

Author: andrewjcg

hyperactor/src/mailbox.rs

@@ -1323,6 +1323,17 @@ impl cap::sealed::CanSend for Mailbox {
         MailboxSender::post(self, envelope, return_handle);
     }
 }
+impl cap::sealed::CanSend for &Mailbox {
+    fn post(&self, dest: PortId, headers: Attrs, data: Serialized) {
+        cap::sealed::CanSend::post(*self, dest, headers, data)
+    }
+}
+
+impl cap::sealed::CanOpenPort for &Mailbox {
+    fn mailbox(&self) -> &Mailbox {
+        self
+    }
+}
 
 impl cap::sealed::CanOpenPort for Mailbox {
     fn mailbox(&self) -> &Mailbox {

hyperactor/src/proc.rs

@@ -1195,12 +1195,24 @@ impl<A: Actor> cap::sealed::CanSend for Instance<A> {
     }
 }
 
+impl<A: Actor> cap::sealed::CanSend for &Instance<A> {
+    fn post(&self, dest: PortId, headers: Attrs, data: Serialized) {
+        (*self).post(dest, headers, data)
+    }
+}
+
 impl<A: Actor> cap::sealed::CanOpenPort for Instance<A> {
     fn mailbox(&self) -> &Mailbox {
         &self.mailbox
     }
 }
 
+impl<A: Actor> cap::sealed::CanOpenPort for &Instance<A> {
+    fn mailbox(&self) -> &Mailbox {
+        &self.mailbox
+    }
+}
+
 impl<A: Actor> cap::sealed::CanSplitPort for Instance<A> {
     fn split(&self, port_id: PortId, reducer_spec: Option<ReducerSpec>) -> anyhow::Result<PortId> {
         self.mailbox.split(port_id, reducer_spec)
@@ -1234,12 +1246,24 @@ impl<A: Actor> cap::sealed::CanSend for Context<'_, A> {
     }
 }
 
+impl<A: Actor> cap::sealed::CanSend for &Context<'_, A> {
+    fn post(&self, dest: PortId, headers: Attrs, data: Serialized) {
+        <Instance<A> as cap::sealed::CanSend>::post(self, dest, headers, data)
+    }
+}
+
 impl<A: Actor> cap::sealed::CanOpenPort for Context<'_, A> {
     fn mailbox(&self) -> &Mailbox {
         <Instance<A> as cap::sealed::CanOpenPort>::mailbox(self)
     }
 }
 
+impl<A: Actor> cap::sealed::CanOpenPort for &Context<'_, A> {
+    fn mailbox(&self) -> &Mailbox {
+        <Instance<A> as cap::sealed::CanOpenPort>::mailbox(self)
+    }
+}
+
 impl<A: Actor> cap::sealed::CanSplitPort for Context<'_, A> {
     fn split(&self, port_id: PortId, reducer_spec: Option<ReducerSpec>) -> anyhow::Result<PortId> {
         <Instance<A> as cap::sealed::CanSplitPort>::split(self, port_id, reducer_spec)