UFCS on forward reference

[Jens Mueller]

Timon Gehr wrote:
> On 05/15/2012 11:18 AM, Jens Mueller wrote:
> >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
> 
> This is a compile time error:
> struct S;
> struct S{}

Yes. But how does this relate to the issue?

Jens