Monitoring variable changes

Monitoring variable changes

[spamfilteraccount]

I have a user option for my package which is a list of strings. I use
this list very frequently in my code and since speed is an issue I want
to do some preprocessing on it.

The problem is the user can change the option anytime (even via setq)
and I need to ensure the preprocessed value always reflects the actual
contents of the user option.

Is there a better way to do this than saving the previous value of the
user option and comparing it to the current value every time before I
try to use the preprocessed value?

Some hook maybe which can be set to be called when a variable is
changed regardless of how it is set?

Re: Monitoring variable changes

[spamfilteraccount]

spamfilteraccount@gmail.com wrote:
>
> Is there a better way to do this than saving the previous value of the
> user option and comparing it to the current value every time before I
> try to use the preprocessed value?

The best solution I could come up with was creating a wrapper function
which ensures the cached value is always up-to-date. It does the some
kind of preprocessing for different variables.  I copy it here for
reference:


(defun get-cached-value (sourcevar)
  "Return cached value for the given source variable SOURCEVAR."
  (let ((cachevar (intern (concat (symbol-name sourcevar) "-cache")))
        (prevvar (intern (concat (symbol-name sourcevar) "-prev"))))
    (unless (and (boundp cachevar)
                 (eq (eval prevvar) (eval sourcevar)))
      (set cachevar
           ;; do some caching/preprocessing here
           ...)
      (set prevvar (eval sourcevar)))
    (eval cachevar)))


Invocation: (get-cached-value 'varname)