RE: character folding future [was: Questions about isearch]

[Drew Adams <drew.adams@oracle.com>]

> > 1. An option, `char-fold-ad-hoc', for the ad hoc char foldings.
> >    Default value: the same ad hoc foldings as vanilla Emacs
> >    (quotation marks).
> 
> Thanks for the code again. A list of ad-hoc foldings for the user to
> customize (your `char-fold-ad-hoc') is something I want too (ideally,
> as soon as 25.1). The reason I didn't include it initially is that the
> character-fold-table can take many seconds to generate, so it's pretty
> important that it be generated at compile time.
> 
> I suppose one solution is to make it a defcustom with a :set property
> that updates the char-fold-table, and clearly state in the docstring
> that editing this variable can add several seconds to emacs startup
> time.

1. Do you really see that "character-fold-table can take many
   seconds to generate"?  I don't see that, AFAICT.

2. Have you tried it?  What difference do you see in the
   generation time?  Did you really see that it "can add
   several seconds"?

3. I do it now in `character-fold+.el'.  (Did it for
   `char-fold-symmetric' from the outset, but just now added
   it also for `char-fold-ad-hoc'.)  And AFAICT there is no
   noticeable time difference in initializing, and none for
   updating `character-fold-table' after a user customizes
   `char-fold-ad-hoc'.

   Not noticeable is quite different from "many seconds" or
   "several seconds".  Maybe this is platform dependent?
   I'm using MS Windows 7 on an average laptop that is a
   few years old (nothing special wrt memory or CPU).

   Do you see the same thing I see, in terms of time, if
   you try `character-fold+.el'?

4. There _is_ a noticeable delay when a user customizes
   `char-fold-symmetric', of course - that does a lot more
   work.  But there is no delay for that initially.  It is
   off by default, so `update-char-fold-table' does nothing
   with it, except when a user customizes or toggles it on.

5. I think it makes sense in any case to factor out the
   code that creates/updates the table (as in my function
   `update-char-fold-table').