Use
The practical use of advice functions is generally to modify or otherwise extend the behavior of functions which cannot be easily modified or extended. The Emacspeak Emacs-addon makes extensive use of advice: it must modify thousands of existing Emacs modules and functions such that it can produce audio output for the blind corresponding to the visual presentation, but it would obviously be infeasible to copy all of them and redefine them to produce audio output in addition to their normal outputs; so, the Emacspeak programmers define advice functions which run before and after.
Another Emacs example; suppose after one corrected a misspelled word through ispell, one wanted to re-spellcheck the entire buffer. ispell-word offers no such functionality, even if the spellchecked word is used a thousand times. One could track down the definition of ispell-word, copy it into one's .emacs, and write the additional functionality, but this is tedious, prone to broken-ness (the .emacs version will get out of sync with the actual Ispell Elisp module, if it even works out of its home). What one wants is fairly simple: just to run another command after ispell-word runs. Using advice functions, it can be done as simply as this:
(defadvice ispell (after advice) (flyspell-buffer))
(ad-activate 'ispell t) Read more about this topic: Advice (programming)
Famous quotes containing the word use:
“... it is use, and use alone, which leads one of us, tolerably trained to recognize any criterion of grace or any sense of the fitness of things, to tolerate ... the styles of dress to which we are more or less conforming every day of our lives. Fifty years hence they will seem to us as uncultivated as the nose-rings of the Hottentot seem today.”
—Elizabeth Stuart Phelps (1844–1911)