Under new metaclass format, no way to __generate base classes

[davrec72]

I gather you are experimenting with defining metaclasses via a constexpr function, and relying on the user to __generate members via that function. I like it, it's more straightforward to do powerful manipulations, but the problem is there is nowhere to __generate base classes, and so the user-specified bases are being omitted from the outputted class instance.

//Given an "interface" metaclass definition:
template constexpr void interface(T source) { ... }
//...and an interface instance with a base class:
class(interface) Rectangle : public Shape { ... }
//...the following test will fail:
static_assert(std::is_base_of<Shape, Rectangle>::value, "Base class lost in meta-processing!");