Using regexp groups in the action

[jkitchin]

I find myself doing something like this a lot lately. I have a regexp with some groups in it that match text I want to make a button of, but in the action I only need to use part of the text. For example below will make a #hashtag into a button, but in the action I only need the "hashtag", e.g. to open the hashtag on Twitter or something.

;; The hashtag is in group 1.
(setq hashtag-regexp "\\(^\\|[[:space:]]\\|\\s(\\)\\(?2:#\\(?1:[[:alnum:]]*\\)\\)")

(button-lock-set-button
 hashtag-regexp
 (lambda ()
   (interactive)
   (goto-char (1- (previous-single-property-change (point) 'button-lock)))
   (save-match-data
     (looking-at hashtag-regexp)
     (message (match-string-no-properties 1))))
 :grouping 2
 :additional-property 'button-lock
 :face (list 'link)
 :help-echo "Click me to open the hashtag.")

The most robust way I have found so far is via property searching to get to the beginning of the match, and then "look at it" again. Is this the right approach to doing this?