> SDS is a string library for C [...]

Function overloading does not exist in C.

C99 doesn't support function overloading. I guess that style is used by everything that wants to expose a C compatible API.

Come to think of it, it might be possible to do that with C11 _Generic.

And... SDS and plain strings are both char pointers so even with _Generic it is probably not possible to do that.