Re: running multiple Emacs versions

[nchubrich]

Tim---

Thanks, initz sounds like what I am looking for---do you happen to
know how to access the source without a debian package manager, since
I am on Mac OS X?  The download link is here: 
http://packages.debian.org/sid/initz

Drew---

Regarding .elc files, aren't most of these placed in the individual
App directories on Mac OS X, i.e. Aquamacs.app, Emacs.app?  When you
refer to "byte compiling", do you mean Emacs LISP packages you have
written, or are you talking about installing external packages say
from Elpa?

Thanks for all your help!

On Feb 12, 8:04 pm, "Drew Adams" <drew.ad...@oracle.com> wrote:
> > Using one .emacs file is probably not going to be the big issue. Your
> > problem is likely to be byte code incompatibility, especially as emacs
> > 23 moved to utf-8 encoding, which makes the *.elc files incompatible
> > with versions prior to 23. Emacs 23 can read older *.elc files, but it
> > does a translation/conversion process 'on the fly' which can
> > substantially slow down file loading etc.
>
> > There are ways around all of this, but take a bit of work. As an
> > example, you cold look at how Debian/Ubuntu handle running multiple
> > emacs versions at the same time. For your init file, look at
> > initz (see emacs wiki). I htink there is some other info on this
> > in the wiki as well.
>
> > For your .emacs, you may be able to just get by using simple 'when'
> > blocks for the version specific stuff i.e.
>
> > (when (= emacs-major-version 23)
> >   ;; do 23 specific stuff
> > )
>
> Everything Tim said is true, I believe.
>
> But as (only) one data point (FWIW), I routinely byte-compile in Emacs 20 (or 
> in
> 22, if the library isn't designed for 20/21), and then use the *.elc in more
> recent versions, including Emacs 23. I haven't particularly noticed any 
> slowdown
> (but I don't doubt that there is one, at least theoretically).
>
> However, some Emacs 23-specific features are available only if you 
> byte-compile
> the code in Emacs 23. Likewise, some Emacs 22-specific features need to be
> compiled using Emacs 22 (or 23). So while byte-compiling using an older 
> release
> generally works and I haven't noticed a slowdown, you might lose some features
> that are specific to more recent releases. In practice, this is pretty rare,
> however (IMO/experience).
>
> Wrt version testing, to protect/expose various code sections (e.g. in your 
> init
> file): Yes, `emacs-major-version' is your friend.
>
> But if you know something more specific about the code that is needed from 
> that
> release, then it's often better to test for the presence of that specific
> object.  Testing the Emacs version is generally a last resort, but sometimes 
> it
> is the most appropriate thing to do.
>
> You can test for a given feature (library) using (require... nil t) - or
> `featurep' if already loaded. You can test for the presence of a specific
> function using `fboundp'. You can test for the presence of a specific variable
> using `boundp'.
>
> (What's not so easy to test for is a specific function signature. If a 
> function
> has a different number of arguments in different releases, then about the only
> way to test which is which is to use `condition-case' and tempt an error.)
>
> HTH.