I’ve been on the interview circuit of late – as stressful as that can be, I feel like I’ve learned a lot through the wide array of interesting challenges that have been dropped on me. One of the cooler ones involved using a regular expression to take a MadLib, number the fields (and subsequently to fill in the verbs, adjectives and nouns of said MadLib). Initially the text just had parts of speech denoted inside of brackets like so: {verb}.
So this was an interesting new issue – I’ve never had to match and replace that quantity of items in one passage. I also haven’t needed as much information from a pattern match… ever.
The first step wasn’t so tough after a bit of creative google-ing – I built an enumerator to catch all the matchdata in an array. Like so:
original_text.to_enum(:scan, /{(.*?)}/).map { Regexp.last_match }
This gave me a new array of each last_match via RegExp’s last_match class method (obvi) viag my old friend #scan. Once you have that data there are a ton of built in match variables and methods to make your life easier which we’re going to go over now:
Instance methods:
hypothetical_match_data_object.captures
=> Gives you the actual matched string – so in this case “verb” or “noun” – if you have one match it’s also stored in the global variable $+
hypothetical_match_data_object.begin(0)
=> Gives you the starting position of the first character in the matched string. The argument allows you to offset that by a character. No idea why, but if you want to you can. When used with insert (which can take character position as an initial argument) you can do some nifty stuff here.
hypothetical_match_data_object.to_s
=> Gives you the full match so in this case “{verb}” or “{noun}” – if you have one match it’s also stored in the global variable $&
hypothetical_match_data_object.end(0)
=> Gives the position of the last character in the matched string. Once again, the argument allows you to offset that by a character. No idea why, but if you want to knock yourself out.
Other potentially useful Matchdata global variables / instance methods:
$` => Gives you the full string prior to match. #pre_match does the same thing as an instance method.
$’ => Gives you the full string after the match. #post_match does the same thing as an instance method.
$1 - $9 => Gives you the content of numerous successful pattern matches.
Preeeeety kewl, eh?
