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(elisp)Around-Advice

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Around-Advice
=============

   Around-advice lets you "wrap" a Lisp expression "around" the
original function definition.  You specify where the original function
definition should go by means of the special symbol `ad-do-it'.  Where
this symbol occurs inside the around-advice body, it is replaced with a
`progn' containing the forms of the surrounded code.  Here is an
example:

     (defadvice foo (around foo-around)
       "Ignore case in `foo'."
       (let ((case-fold-search t))
         ad-do-it))

Its effect is to make sure that case is ignored in searches when the
original definition of `foo' is run.

 - Variable: ad-do-it
     This is not really a variable, but it is somewhat used like one in
     around-advice.  It specifies the place to run the function's
     original definition and other "earlier" around-advice.

   If the around-advice does not use `ad-do-it', then it does not run
the original function definition.  This provides a way to override the
original definition completely.  (It also overrides lower-positioned
pieces of around-advice).

   If the around-advice uses `ad-do-it' more than once, the original
definition is run at each place.  In this way, around-advice can execute
the original definition (and lower-positioned pieces of around-advice)
several times.  Another way to do that is by using `ad-do-it' inside of
a loop.