Wrap any Lua function with a sigc++ slot

class LuaSlot {
public:
    static inline sigc::slot<void> Wrap(lua_State *l) {
        lua_getfield(l, LUA_REGISTRYINDEX, "_slot");
        if (lua_isnil(l, -1)) {
            lua_newtable(l);
            lua_pushvalue(l, -1);
            lua_setfield(l, LUA_REGISTRYINDEX, "_slot");
        }
        lua_pushvalue(l, -2);
        int ref = luaL_ref(l, -2);
        lua_pop(l, 1);
        return sigc::bind(sigc::ptr_fun(&trampoline), l, ref);
    }

private:
    static inline void trampoline(lua_State *l, int ref) {
        lua_getfield(l, LUA_REGISTRYINDEX, "_slot");
        lua_rawgeti(l, -1, ref);
        luaL_unref(l, -2, ref);
        lua_remove(l, -2);
        lua_call(l, -1, 0);
    }
};