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Re: Getting more info on a variable in Customize buffers

From: drkm
Subject: Re: Getting more info on a variable in Customize buffers
Date: Mon, 03 Jan 2005 18:28:42 +0100
User-agent: Gnus/5.110003 (No Gnus v0.3) Emacs/21.3.50 (windows-nt)

Stefan <address@hidden> writes:

> The problem is that custom's "variables" aren't the same as
> Elisp variables.  They look very much alike, and they usually are exactly
> the same, but that's not always the case.
> The :get, :set, and :init thingies allow you to define a custom setting
> "foo-bar" which controls "toto" rather than the variable "foo-bar".

  So a big difference between variables and customs is:

    - with a variable, you can `setq' it before evaluate its
      definition, to overload its default value.  It's very convenient
      in .emacs.  For example, you don't have to load any library to
      change the variable value;

    - with a custom, you have to wait its definition to be evaluated
      before setting it in any way, to have its :get and al. to be
      known.  So you have to deal with `require' or `eval-after-load'
      in .emacs, or correctly load autoloads file if provided (and if
      it contains the desired defcustom form).

  Right ?

  If it is, I don't know any standard way to do that directly in
ELisp, if I don't want to use Customize.  I think about something
like :

    (defmacro set-custom (custom value lib)
      (if (boundp custom)
          `(set-variable ',custom ,value)
        `(eval-after-load ,lib
           '(set-variable ',custom ,value))))

  But for using it, I have to know CUSTOM to be defined as a custom,
where it is defined, etc.  And this doesn't deal with non-evaluating
the "default value form" (in defcustom) if `set-custom' is evaluated
before loading the LIB.

  This point can be important if the custom' value is used when
loading the file, for example to compute the default value of another

    (defcustom a-custom 'default
      :set ...)

    (defvar a-internal-var (compute a-custom))

  How can I do in this case to change the value of `a-custom' (and
have `a-internal-var' correctly set)?  Hum, I suppose it's the
responsability of the :set'er of `a-custom'...

  So what's the clean way to set custom' value in ELisp, in a user
point of view?


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