Re: GC method for objects

["Adam D. Moss" <adam@...>]

Roberto Ierusalimschy wrote:
> > In short, what you do is create a weak-valued table which maps
> > from dummy created-on-demant heavyuserdata to your {}s - the __gc
> > sits on the userdata and thus indirectly gets called when the {}
> > becomes collectable.
>
> A simpler way is to store the dummy created-on-demant heavyuserdata
> directly in your {}, using a reserved key (e.g., __userdata).

That's possible but pollutes the original table (but that
might not be a problem for objects, where you wouldn't
usually for example want to do a pairs() over the table).

> > You then need a way to map back from the userdata to the table
>
> Since this userdata is dummy anyway, you can store the table as the
> userdata's metatable.

That's a very nice idea (though then, surely, the __gc field has
to go into the table itself and the same pollution occurs as above).

> Lua 5.1 offers a more proper way to do this mapping.

Neat.  Any examples?

--Adam
--
Adam D. Moss   -   adam@gimp.org