From: Robert Klemme <shortcutter@...>
Date: 2008-05-04T19:15:03+09:00
Subject: Re: Backreferences in case statements

On 03.05.2008 18:00, loveajax@gmail.com wrote:

> I am not sure if this is possible. I have a case statement which
> checks for a regular expression. For example:
> 
> case text
> when /(abc)(.)*/
> when /(xyz)(.)*/
> end
> 
> In the above snippet how can I use the instance variables pre_match
> and post_match? I tried calling these methods without any qualifiers
> but I got a NoMethodError. Where does Ruby store the MatchData if the
> matching is done in a case statement?

$ irb
irb(main):001:0> /b/ =~ "abc"
=> 1
irb(main):002:0> $`
=> "a"
irb(main):003:0> $'
=> "c"
irb(main):004:0> $~
=> #<MatchData:0x7ff9eb54>
irb(main):005:0> $~.to_a
=> ["b"]
irb(main):006:0> $~.pre_match
=> "a"
irb(main):007:0> $~.post_match
=> "c"
irb(main):008:0>

But why do you have groups in your regular expressions if you are not 
interested in the content?  Also "(.)*" seems a bit odd because it might 
not yield what you expect:

irb(main):008:0> /a(.)*/ =~ "abcdef"
=> 0
irb(main):009:0> $1
=> "f"

IMHO it is generally a bad idea to use grouping in the way you do it 
because it will capture a lot that you are not interested in.  It seems 
you might rather want "(.*)".

Kind regards

	robert