Re: cons cells for Lua

["Jay Carlson" <nop@...>]

"Mark Hamburg" <mhamburg@adobe.com> writes:

> on 3/25/04 8:45 AM, Jay Carlson at nop@nop.com wrote:
>
> > The reason to use [0] and [1] is they take advantage of the "small
integer
> > keys are stored in an array" optimization in Lua 5.0.  For clarity you
could
> > use .car and .cdr instead.  Note that all strings in Lua are interned,
so
> > the performance penalty is not that great.
>
> Do you want to use 0 and 1 or 1 and 2?

Argh, yes.  Use 1 and 2.  I misread the C code.

> > On the other hand, it might be a fun exercise to implement this as a C
> > extension.  The car would be stored as a ref, which is something the
> > reference manual doesn't emphasize enough.  (Somebody might wanna write
a
> > tutorial for the wiki on references).  If you allow improper lists,
you'll
> > have to store the cdr as a ref as well.
>
> Beware of what amount to reference-counting cycles when creating refs.
It's
> actually a bit of a pain to get userdata to refer safely to other Lua data
> objects and seems to require the use of per-object metatables rather than
> sharing the metatables across a type.

The whole discussion of this made my brain hurt, so I filed it away under
"reread this thread when I'm on a trans-pacific plane" :-)

But refs are important for many bindings, especially when dealing with
callbacks specific to particular C-library objects.  From the reference
manual alone, it is unclear how to bind such things at all, unless you read
very carefully.

Jay