Why don't you just use "normal c userdata", if you want metafunctions?
(I assume that in this case your userdata quite sure is anyway somehow
"more important" / more "heavy"?).
userdata is a GC object , and we don’t need lua manage the lifespan of objects.
For example, we have a game scene graph in C side, only a few objects (when needed) export into lua side. So,not all C object has the lua proxy.
Userdata is only a reference to scene node. We need another (weak) table to cache them. (Scene node pointer-> userdata)
Another usecase is fixed-point number or complex number library. A value type is much cheaper than GC object.
