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Re: Change in files.el

From: Stefan Monnier
Subject: Re: Change in files.el
Date: Sat, 28 Jan 2017 09:40:11 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

>> > +(defcustom save-some-buffers-default-predicate nil
>> > +  "Default predicate for `save-some-buffers'.
>> > +This allows you to stop `save-some-buffers' from asking
>> > +about certain files that you'd usually rather not save."
>> Please make it so that the var *always* has a function value.
> Why is that important?

- So that you don't have to wrap each and every use inside an `if'.
- Or so you don't have to fix the docstring to say what happens when the
  value is nil.
- Or so you can use `add-function' on it.
- More generally, so that you can slightly change its behavior without
  having to re-implement the default behavior by hand.
- Also, so as to make sure that it is *possible* to reimplement the
  default behavior by hand (i.e. to make sure the predicate has access to all
  the info it needs to reproduce the default behavior).

This is a rule we should try to follow for all *-function and
*-predicate variables (as well as similar cases, such as
process-filters and sentinels).


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