Where is the information passed to `custom-set-variables` and `custom-set-faces` stored?

Question

The post's title pretty much says it all.

In particular, I want to find out what happens if I invoke custom-set-variables twice, with completely different arguments each time. E.g.

(custom-set-variables '(this "foo"))
(custom-set-variables '(that "bar"))

Does this have the same effect as

(custom-set-variables '(this "foo")
                      '(that "bar"))

?

And ditto for custom-set-faces.

Answer 1

They both just set the named variables. custom-set-variables sets the value of the variable as well as several other properties, while custom-set-faces only sets some properties. You can get these using the symbol-value and symbol-plist functions.

For example:

(custom-set-variables '(db48x/test 24 t) '(db48x/test 42 t))
(symbol-value 'db48x/test)
42
(symbol-plist 'db48x/test)
(theme-value ((user 42)) saved-value (42) saved-variable-comment nil force-value t variable-comment nil custom-requests 42)

For a face you have this:

(symbol-plist 'default)
(face-defface-spec ((t nil)) face-modified nil face 0 face-documentation "Basic default face." event-symbol-element-mask (default 0) event-symbol-elements (default) ...)

For more information about how variables get their values, I recommend section 8.1 Symbol Components of the ELisp manual. (Use M-: (info "(elisp) Symbol Components") to jump right to it.