Only one signal per object?

[Andrej Mitrovic]

Yeah, if I change the two function types in Signal to this:
        alias bool delegate(ref Types) slot_t;
        alias void delegate(ref Types) void_slot_t;

then I can connect functions with ref arguments. But then I'll get
exceptions thrown if the functions have non-ref arguments.

This seems like a difficult problem to solve. How can you
(efficiently) store a dynamic list of function pointers which could
have arbitrary storage classes for its parameters? Hmm..