On 10/01/2019 00.55, Nick Desaulniers wrote: > I agree that something like builtin_types_compatible_p() in a macro > could help make these functions more "generic" in the sense of being > able to accept either a `struct xarray*` or `struct xarray_cyclic*`.
An alternative to implementing all the generic functions as macros is transparent_union: https://godbolt.org/z/TK_SJD If there is an interface that takes a "const xarray *" one would define another union type union __transparent_union const_xarray_any { const struct xarray *xa; const struct xarray_cyclic *xac; }; The obvious implementation using _Generic fails since all expressions must be valid: https://godbolt.org/z/X0bvwO and _Generic is gcc >= 4.9 anyway. I think an implementation based on choose_expr/types_compatible might have the same problem, but maybe there's some clever way around that. Rasmus