UFCS on forward reference

[Jens Mueller]

Timon Gehr wrote:
> On 05/15/2012 07:44 AM, Ali Çehreli wrote:
> >On 05/14/2012 10:02 PM, Timon Gehr wrote:
> > > On 05/15/2012 04:28 AM, John Belmonte wrote:
> > >> C API's often use a opaque struct pointer as a handle. Mapping such a
> > >> struct to D using a forward declaration, I noticed that UFCS doesn't
> > >> work:
> > >>
> > >> struct State;
> > >> ...
> > >> State* s = new_state();
> > >> foo(s); // ok
> > >> s.foo(); // compile error
> > >>
> > >> Error detail:
> > >>
> > >> Error: struct State is forward referenced when looking for 'foo'
> > >> Error: struct State is forward referenced when looking for 'opDot'
> > >> Error: struct State is forward referenced when looking for 'opDispatch'
> > >>
> > >> I'm wondering if anything would be harmed by removing this restriction.
> > >>
> > >> As a workaround I can use "struct State {}", but that feels wrong.
> > >>
> > >
> > > This is a compiler bug. You can report it here:
> > > http://d.puremagic.com/issues/
> >
> >I would expect the compiler to need to see the definition of S to know
> >that it really does not have a matching foo() member function.
> >
> >Ali
> >
> 
> S is opaque. It does not have any visible member functions.

How should the compiler infer that S is opaque? How does it know when
you write "struct State;" that State has no members? Is opaqueness
implied when I do a forward declaration?

Jens