Function is_valid_metatable

library/LuaWrapper.cpp:402–419

* Check if the object and metatable are a valid DF reference or type. */

 * Check if the object and metatable are a valid DF reference or type.
 */
static bool is_valid_metatable(lua_State *state, int objidx, int metaidx)
{
    // Verify object type validity
    if (lua_isuserdata(state, objidx))
    {
        lua_pushvalue(state, metaidx);
        lua_rawget(state, UPVAL_TYPETABLE);
    }
    else
    {
        lua_pushvalue(state, objidx);
        LookupInTable(state, &DFHACK_TYPEID_TABLE_TOKEN);
    }

    bool ok = !lua_isnil(state, -1);
    lua_pop(state, 1);
    return ok;
}

bool Lua::IsDFNull(lua_State *state, int val_index)
{