создание новой метатаблицы

int l_getsize(lua_State* L)
{
    auto const grid_ptr = checkgrid(L);
    if (!grid_ptr)
        return 0;
    lua_newtable(L);//size
    lua_pushinteger(L, grid_ptr->Size.x);
    lua_setfield(L, -2, "x");
    lua_pushinteger(L, grid_ptr->Size.y);
    lua_setfield(L, -2, "y");
    return 1;
}
/*эту функцию просто взял с интернета, в 5.1 такой функции нет*/
static void luaL_setfuncs(lua_State* L, const luaL_Reg* l, int nup) {
    luaL_checkstack(L, nup + 1, "too many upvalues");
    for (; l->name != NULL; l++) {  /* fill the table with given functions */
        int i;
        lua_pushstring(L, l->name);
        for (i = 0; i < nup; i++)  /* copy upvalues to the top */
            lua_pushvalue(L, -(nup + 1));
        lua_pushcclosure(L, l->func, nup);  /* closure with those upvalues */
        lua_settable(L, -(nup + 3));
    }
    lua_pop(L, nup);  /* remove upvalues */
}

CORONA_EXPORT int luaopen_plugin_helloplug (lua_State* L)
{
    using namespace Corona;

    luaL_newmetatable(L, GRID_META);
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    luaL_Reg arraylib_m[] = {
        {
            "size", l_getsize
        },
        { nullptr, nullptr }
    };

    luaL_setfuncs(L, arraylib_m, 0);

    lua_newtable(L); // helloplug

    luaL_Reg arraylib_f[] = {
        {
            "sin_from_c", l_sin
        },
        {
            "GenerateAndCalculateCorridors", l_GenerateAndCalculateCorridors
        },
        { nullptr, nullptr }
    };

    luaL_register(L, nullptr, arraylib_f);

    return 1;
}