Re: Multiple M-x shells sharing input ring

[Michael Heerdegen]

Drew Adams <drew.adams@oracle.com> writes:

> There are not only two alternatives: permanent-local and global.
> The normal way to handle what you describe is to make the variable
> local in each buffer where it should be local.  It can even be made
> automatically local everywhere (`make-variable-buffer-local').
>
> And any mode derived from comint mode that happens to want a separate
> history can easily obtain that, even if the variable is not declared
> automatically local.  Nothing prevents scheme mode or whatever from
> doing `make-buffer-local' in its buffers.  That's the usual way these
> things are done.

Yes, but if you want to have a shared input history for all shell
buffers, and another shared history for all interactive scheme buffers,
using a global var is not good enough either.

> AFAICT, `permanent-local' is for a different purpose.  At least its
> doc claims that.  It speaks specifically of "the file".  Again:
>
>  Permanent locals are appropriate for data pertaining to where the
>  file came from or how to save it, rather than with how to edit the
>  contents.
>
> I don't see how anything in that description applies here.

It doesn't say that it's inappropriate for all other cases ;-)

> > It's not that easy, since `comint-mode' does a lot of explicit
> > `make-local-variable' calls including for `comint-input-ring'.
>
> Why would it do that, if the variable is already permanent-local?
> Doesn't permanent-local imply buffer-local?

I think no:

  (put 'foo 'permanent-local t)
  
  (setq foo 1)
  
  (local-variable-p 'foo)
    ==> nil
  
  (make-local-variable 'foo)
  
  (setq foo 2)
  
  (local-variable-p 'foo)
    ==> t

  (kill-all-local-variables)
  
  (local-variable-p 'foo)
    ==> t

> And even if it does that, that just makes the variable buffer-local.
> What prevents one from then killing that local variable and using
> the global one instead?

Nothing, but I just think a per-mode input history could be more useful.

Michael.