Re: __gc visible to lua code...

[Michael Broughton <mbobowik@...>]

Graham,

I have been working on a library this last week, and I just did some 
experimenting with separating my metatable and method table, as 
suggested by Rici Lake. It made my library a few lines longer, but it is 
mostly unchanged.

As expected, none of the metamethods are accessible from the Lua side 
anymore. For example, you can do these:

#udata
udata:close()
u3 = u1 + u2

But not these:

udata:__len()
udata:__gc()
u3 = u1:__add(u2)

This is the behavior you want, right? I'll post my library, if you want 
an example. I just need to write some documentation first.

Mike


Graham Wakefield wrote:
> Having a close() method may be a good idea for many uses of userdata, 
> where freeing resources referred by the userdata can be independent of 
> the userdata lifetime.  In such cases, it makes sense to test against 
> NULL for the userdata contents, etc.  Calling udata:close() won't set 
> the udata to nil, won't free the userdata itself, since this is under 
> the control of the garbage collector.
>
> But this is irrelevant to __gc.  The __gc metamethod, as far as I 
> understand, is supposed to be a kind of callback into C to let you 
> know that the userdata has been collected, so you can free additional 
> resources if necessary.  It makes no sense to expose this method to 
> Lua code.   
>
> Using __gc as a close() method confuses two distinct purposes.