Re: Compiled code in Emacs-26 will fail in Emacs-25 if use pcase [was: Add new bytecode op `switch' for implementing branch tables.]

[Kaushal Modi <kaushal.modi@gmail.com>]

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I have this in my emacs config for a while now.

It works pretty well. It also allows you to use an older emacs version
without have to mess up the compiled elpa dir of the current version. The
only side-effect is that when switching major versions the package
updates/installs will happen independently.

(setq package-user-dir (format "%selpa_%s/"
                               user-emacs-directory emacs-major-version))

On Thu, Feb 23, 2017 at 8:42 AM Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> > I) Compile under master branch.
> > II) Load the resultant .elc with Emacs-25
>
> As explained by Richard, this is usually considered acceptable.
> We don't really try to provide forward compatibility of byte-code files
> between major versions.
>
> This said, occasionally we try to reduce the pain a little: e.g. in
> Emacs-25 a similar incompatibility was introduced for the compilation of
> catch&condition-case, but the bytecodes were introduced a bit earlier.
> IOW the incompatibility was fundamentally introduced in 24.4 (IIRC), but
> the use of the this new feature was only enabled in Emacs-25.1, so files
> compiled with 25.1 will usually work in 24.5 as well.
>
>
>         Stefan
>
> --

Kaushal Modi

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