[slime-devel] Re: Clicky things in the REPL.

[Brian Downing]

On Wed, Dec 17, 2003 at 04:22:13PM +0100, Luke Gorrie wrote:
> Brian Downing <bdowning at lavos.net> writes:
> > One question I would have is, how is the object accessed once it's
> > clicked on?  I imagine CLIM just holds a (weak?) pointer to the object
> > in its presentation.  From emacs, you may see "#<FOO {40541D01}>", and
> > even know the address more concretely if its passed in some sort of
> > object-info, but as soon as GC happens, you're likely screwed.
> 
> If CLIM used weak references, it would have the same trouble. I would
> guess they use normal references and normal GC, but I don't know.

Not the way I was thinking about it.  What I meant is that the GC would
probably move the object, not collect it, and if your reference to it
was based on address, it would be broken even though the object still
existed.

Weak references make sense to me, even for CLIM, because I really
wouldn't want all the objects I've created in the REPL to persist just
because their presentations still exist in my scrollback.  That
completely changes the semantics of working at the REPL.  Maybe somebody
who has worked on the LispM could explain what semantics presentations
in its listener had with respect to garbage collection.

If I print a piece of data that is part of a larger structure, and not
garbage, I'd want the presentation to still be able to access it after
it has been moved by the GC.  But I'd also like to be able to do 
(progn (print (make-instance 'two-hundred-megabyte-object)) nil) 
at the REPL and not saddle the GC with any limitations on how to collect
this data that nobody else is using, like waiting for it to "time out"
or having another 200 presentations created after it.

All IMHO, of course.

-bcd