[luabind] About make_function definition in make_function.hpp

[Baojiang S. <sho...@gm...>]

Hi guys, I have an question in reading luabind code. At the bottom of file
make_function.hpp is the definitions of two function:

template <class F, class Signature, class Policies>
object make_function(lua_State* L, F f, Signature, Policies)
{
typedef typename detail::as_vector<Signature>::type signature;

return detail::make_function_aux(
    L
  , new detail::function_object_impl&lt;F, signature, Policies&gt;(
        f, Policies()
    )
);

}

template <class F>
object make_function(lua_State* L, F f)
{
return make_function(L, detail::deduce_signature(f), detail::null_type());
}

In the statement make_function(L, detail::deduce_signature(f),
detail::null_type()) which only provide three args, but the above
make_function need four args. Why?