Re: [RFC] Using a display_info union instead of a typedef Display_Info

[Eli Zaretskii <eliz@gnu.org>]

> From: Alex Gramiak <agrambot@gmail.com>
> Cc: emacs-devel@gnu.org,  monnier@iro.umontreal.ca
> Date: Fri, 12 Apr 2019 12:40:45 -0600
> 
> > Looks to me like replacing one set of window-system specific code with
> > another: still the same #ifdef's and the same window-system specific
> > code fragments.  Maybe I'm missing something, but it doesn't look to
> > me like a change for the better.
> 
> There will always have to be window-system specific code somewhere. The
> difference with this patch is that the changed parts of the code will be
> able to be used by multiple different window systems. That is to say, I
> believe this is a necessary step towards Stefan's goal of using multiple
> window systems simultaneously.
> 
> Note how before there was the implicit conditional compilation regarding
> the definition of check_x_display_info and x_get_arg that allowed the
> procedure to be used by _only_ 1 window system, but decode_display_info
> and gui_display_get_arg would be able to handle _all_ graphical window
> systems that Emacs is built with.
> 
> This currently doesn't mean any functional change as that number can
> currently only be 1, but it would be nice for that to change. Again, I
> believe this is (part of) the way to do so.

We've been through this before: if these changes don't come together
with, or closely followed by, the code to support using several
window-systems in the same session, I'd prefer not to make these
changes at this time.  The advantages you describe are at this point
theoretical, whereas the disadvantage -- making the code less familiar
for veteran Emacs hackers -- is very real.

Let's invest our time and energy in making changes that are useful
today, not in some distant future.

> To show how it's used, I've included a diff that uses
> decode_display_info to simplify all 3 check_x_display_info
> implementations into a single conditional. (I could remove that
> conditional with another terminal hook, but I'm not sure that's worth
> it).

There's a way to attain that without the massive changes you propose:
just make a single function which dispatches by the type of
output_data.  We won't be able to judge which alternative is better
until and unless we have real code which implements this feature.

Thanks.