The most insulting thing about _Generic is the name. Really? _Generic? For a type-based switch with horrific syntax? What were they thinking...

That said, generic programming in C isn't that bad, just very annoying.

To me the best approach is to write the code for a concrete type (like Vec_int), make sure everything is working, and then do the following:

A macro Vec(T) sets up the struct. It can then be wrapped in a typedef like typedef Vec(int) Vec_i;

For each function, like vec_append(...), copy the body into a macro VEC_APPEND(...).

Then for each relevant type T: copy paste all the function declarations, then do a manual find/replace to give them some suffix and fill in the body with a call to the macro (to avoid any issues with expressions being executed multiple times in a macro body).

Is it annoying? Definitely. Is it unmanageable? Not really. Some people don't even bother with this last bit and just use the macros to inline the code everywhere.

Some macros can delegate to void*-based helpers to minimize the bloating.

EDIT: I almost dread to suggest this but CMake's configure_file command works great to implement generic files...