Adding converters for user defined types

It is possible to get luabind to handle user defined types like it does the built in types by specializing luabind::default_converter<>:

struct int_wrapper
{
    int_wrapper(int value)
      : value(value)
    {}

    int value;
};

namespace luabind
{
    template <>
    struct default_converter<X>
      : native_converter_base<X>
    {
        static int compute_score(lua_State* L, int index)
        {
            return lua_type(L, index) == LUA_TNUMBER ? 0 : -1;
        }

        X from(lua_State* L, int index)
        {
            return X(lua_tonumber(L, index));
        }

        void to(lua_State* L, X const& x)
        {
            lua_pushnumber(L, x.value);
        }
    };

    template <>
    struct default_converter<X const&>
      : default_converter<X>
    {};
}

Note that default_converter<> is instantiated for the actual argument and return types of the bound functions. In the above example, we add a specialization for X const& that simply forwards to the X converter. This lets us export functions which accept X by const reference.

native_converter_base<> should be used as the base class for the specialized converters. It simplifies the converter interface, and provides a mean for backward compatibility since the underlying interface is in flux.