From: 7stud 7stud <dolgun@...>
Date: 2007-03-14T16:54:23+09:00
Subject: ruby regex lookarounds?

In Programming Ruby(1st Ed), it says:
--------
The match operators return the character position at which the match
occurred. They also have the side effect of setting a whole load of Ruby
variables. $& receives the part of the string that was matched by the
pattern, $` receives the part of the string that preceded the match, and
$' receives the string after the match...

The match also sets the thread-global variables $~ and $1 through $9.
The variable $~ is a MatchData object (described beginning on page 336)
that holds everything you might want to know about the match. $1 and so
on hold the values of parts of the match.
-------
Here is an example:

irb(main):009:0> "abc" =~ /(a)(b)/
=> 0
irb(main):010:0> $&
=> "ab"
irb(main):011:0> $1
=> "a"
irb(main):012:0> $2
=> "b"

Now and example with a lookbehind:

irb(main):013:0> "abc" =~ /(?:ab)(c)/
=> 0
irb(main):014:0> $&
=> "abc"
irb(main):015:0> $1
=> "c"

Isn't that output inconsistent?  If Ruby wants to say that the regex
matches the whole string, then shouldn't $1 be 'ab'.  I know that
lookarounds shouldn't be considered part of the match--they are just
assertions, but Ruby's $& variable doesn't seem to respect that.

-- 
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