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> > This is the impression I'm under as well, but I was wondering:      
> > since these entries in the metatable (the metamethods that is)      
> > are used by the VM it wouldn't be too ugly to keep a number of      
> > flags with each table/userdata for storing wich (of the "standard") 
> > metamethods have been set in it's metatable. Then every time, say,  
> > an index operation takes place all you have to do is check if the   
> > index flag is set (a very cheap operation) instead of looking up    
> > the metatable and indexing it.                                      

> Actually I think this is roughly how it's implemented in reality.

The metatable itself has these bits. When we modify a table there
is no way to know which objects use it as a metatable, so there would
be no way to reset their bits.

-- Roberto