[PATCH] Abstract out a display-table-specific API (2)

[Stephen J. Turnbull]

Aidan Kehoe writes:
 > 
 >  Ar an séú lá is fiche de mí na Nollaig, scríobh Stephen J. Turnbull: 
 > 
 >  > Aidan Kehoe writes:
 >  > 
 >  >  >  Ar an ceathrú lá is fiche de mí na Nollaig, scríobh
 >  >  >  mike.kupfer at xemacs.org:
 >  > 
 >  >  >  > First, I'm nervous about XEmacs-specific patches that I would have
 >  >  >  > to apply every time I resync with upstream.
 >  >  > 
 >  >  > Yeah; I need to ask the Gnus people to apply it too.
 >  > 
 >  > That's the best solution, but IIRC Gnus currently aims at supporting
 >  > Emacs 21, 22, and 23, as well as multiple XEmacsen---spanning about
 >  > four different redisplay mechanisms.  Expect difficulties in getting
 >  > it right. :-(
 > 
 > Hmm? Historically, in both XEmacs and GNU Emacs display tables were vectors. 

Sure.  Ben moans about that in disp-table.el, does he not?

 > I want to move to a reasonably clean implementation that uses char
 > tables.

Which is going to require maintaing two APIs unless you can convince
GNU to go to a char-table-based implementation.  As long as things
like `(length display-table)' are available, you can bet that someone
(probably a Gnus developer ;-) will find a use for it.  All I mean by
"difficulties" is that this is likely to become one of those recurring
points where you have to pay attention.

Gnus will undoubtedly DTRT (define an internal API that works with
both XEmacs and GNU Emacs), but I doubt that will be universal.