I've found that most libraries implement the wrapper around C++ functions in the most terrible way. It ranges from userdata types wrapping std::function objects to wrapping the lua_State, which the users have to interact with themselfs.

Luwra uses inlinable functions and templates almost exclusively. That way (best-case scenario), each wrapped field/method/constructor/function implies only one generated lua_CFunction, which invokes the Lua API to retrieve the values and finally call the wrapped function with them. And all that, during compile-time, which in my opinion is the best part about it.