Functors

[mfichman]

Basic idea:

• Generate vtables in the final executable only (link)
• Put operator functions in vtable
• Direct jump to operator function using operator dispatch
• Autogen for some operator funcs?

JsonOutput < Functor {
    @dispatch(obj Starship)
    @dispatch(obj Asteroid)
}

Render < Functor {
    @dispatch(obj Mesh)
    @dispatch(obj Particles)
    @dispatch(obj Quads)
    @dispatch(obj Material)
    @dispatch(obj Light)
}

[mfichman]

To make this work, a special "hidden" interface must be created by the compiler:

Render < Functor {
    @case(obj Mesh)
    @case(obj Particles)
    @call(intf _RenderIntf)
    # Anything that doesn't match is ignored
}

_RenderIntf < Interface {
    Render__apply(f Render)
    # In this case, 'self' actually referse to the RenderIntf so we will need to 
    # swap 'self' and 'obj'
}

V-Tables are extended w/ the apply function:

Mesh_vtable:
   Mesh_Render__apply # Found at the index for Render__apply

[mfichman]

As an optimization, the Render__call function can use a switch-based if-else chain instead of doing an indirection through the object's vtable. This may actually be good enough for an initial implementation.

[mfichman]

Functors should be "open" types, i.e., the following should be allowed:

Render < Functor {
   @case(obj Mesh)
   @case(obj Particles)
}

... different source file ...

Render < Functor {
    @case(obj Material)
}

Under this implementation, the @call method of the functor must be generated in the main executable, b/c only then will all the @case methods be known.