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Re: Condider adding buffer-mode

From: Stefan Monnier
Subject: Re: Condider adding buffer-mode
Date: Tue, 29 Oct 2013 12:36:44 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

>> > I’ve seen the following code used hundreds of times:
>> > (buffer-local-value 'major-mode buffer)
>> > or
>> > (with-current-buffer buffer ‘major-mode)
>> Where?
> One example would be packages like SLIME and CIDER which feature commands
> that operate in a different manner when invoked in a REPL or a lisp buffer.
> Obviously one could have written different commands for the different
> modes, but that doesn't change the fact that people write code like this.

This sounds like they check `major-mode', but in the current buffer, so
they wouldn't need something like `buffer-mode'.

> Another example would be selecting all buffers that have some major mode -
> maybe you want to enable something in all active elisp buffers, etc.

Can you point out actual code?
I'm not saying it doesn't exist, I'm just failing to understand why
`buffer-mode' would be useful for those cases.

E.g. using buffer-mode, I guess I'd write a loop like:

   (dolist (buf (cl-remove-if-not (lambda (x) (eq 'foo-mode (buffer-mode x)))
     (with-current-buffer buf

or maybe

   (dolist (buf (buffer-list))
     (when (eq 'foo-mode (buffer-mode buf))
       (with-current-buffer buf

neither of which seems any better than:

   (dolist (buf (buffer-list))
     (with-current-buffer buf
       (when (derived-mode-p 'foo-mode)

> I don't see how having something like `buffer-mode' would be a bad
> thing for Emacs hackers.

I'm not saying it's bad, but I'd like to see compelling use cases first.

BTW, when I said:
> I don't think we just want to provide `buffer-mode'.

I really meant "just buffer-mode", as opposed to "something like


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