Re: rmsbolt.el [Was: Colorful line numbers]

[Eli Zaretskii <eliz@gnu.org>]

> From: João Távora <joaotavora@gmail.com>
> Cc: emacs-devel@gnu.org
> Date: Sat, 23 Jul 2022 10:35:07 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Aaanyway, I think I'm happy with the current implementation that _doesn't_ 
> >> use line numbers at all. I think this discussion has been productive (to some
> >> degree).  If I ever need this again (or someone else, like Dmitry), I'll be sure
> >> to ping here again. 
> >
> > OK.  Let me just say, for the future, that basing this on text
> > properties is IMO not the best idea.  I think a better idea is to have
> > some buffer-local (or window-local) variable whose value is an
> > appropriate data structure that specifies faces for ranges of line
> > numbers.  Of course that value will need to be updated at suitable
> > times, which in itself is not a trivial task.
> 
> OK.  Since we're in speculation territory, I don't see a big difference
> between that and using text properties, which are also a buffer-local
> structure.

The big difference from my POV is that text properties slow down
redisplay code in general, whereas buffer-local variables only slow
down (somewhat) the code which examines their values and uses them.

> Looking up the line we're iterating in that hypothetical
> Lisp structure would seem to amount to about the same work as looking
> for a particulr text property in a known place of that same line.

No, referencing a variable is much faster, because it doesn't involve
finding the correct interval for a buffer position.