public void SetMetatable(int idx)
{
var val = _stack.Get(idx);
var mtVal = _stack.Pop();
switch (mtVal)
{
case null:
LuaValue.SetMetatable(val, null, this);
break;
case LuaTable mtl:
LuaValue.SetMetatable(val, mtl, this);
break;
default:
throw new Exception("table expected!"); // todo
}
}