On 06/12/2019 19:56, Brian Goetz wrote:
If we have an inline class:
inline class V {
public void m() { }
}
then, at least for the public members of V (if not more), we would like to lift
these onto the reference projection:
V.ref vr = …
vr.m() // succeeds
One way to get there is to simply have the compiler desugar these members onto
the reference projection. This is simple for the VM, in that these become
ordinary interface calls and no additional VM help is needed, but on the other
hand, we are now duplicating members between V and V.ref, which VM folks don’t
like. The VM folks would prefer that V.ref be an “empty” interface.
Is there a way to do this by appealing to delegation? E.g. rather than
completely duplicating the V member in V.ref, can we use the cast trick
below to add a "bridge" from V.ref to V?
I'm not too worried about having a V.ref with its own members - after
all, V.ref should be a language fiction (for the VM, the only real thing
is V). So, in my mental model, it will be javac, not the VM, to do most
of the lifting here. Am I wrong in my assumption?
Maurizio
Another would be to appeal to casting; desugar `vr.m()` as `((V) vr).m()` in
the static compiler. This works, until we want to make V private (and the
combination of public reference projection and private implementation is
expected to be a common one.) If we do this, we’ll get a linkage error trying
to resolve the cast, since it names a class not accessible to the client.
A third way is to soften up the linkage requirements for `invokeinterface` when
in the presence of a reference projection. Here, when called upon to link an
invocation, if the method is not present in the interface, and the interface is
a reference projection for V, we can try to link to the corresponding method on
V, _ignoring access control for V itself but still doing access control for the
method_. (This also has the benefit of working for non-public members too.)
