From: Austin Ziegler <halostatue@...>
Date: 2004-08-23T09:09:41+09:00
Subject: Re: Regexp scanning with MatchData (Re: multiple regexp matches)

On Mon, 23 Aug 2004 07:33:18 +0900, nobu.nokada@softhome.net
<nobu.nokada@softhome.net> wrote:
> At Sun, 22 Aug 2004 14:00:45 +0900,
> Austin Ziegler wrote in [ruby-talk:110110]:
> > Proposal:
> > <code>String#scan</code>, <code>#sub</code>, and <code>#gsub</code>
> > yield MatchData objects instead of Strings. I think that this could be
> > achieved while breaking the least amount of code by adding a #to_str
> > implementation to MatchData.
> #to_str doesn't solve everything.  MatchData#[] returns a matched
> portion for sub-patterns, whereas String#[] returns a byte at
> the position.

Agreed. It also is 100% incompatible on #scan with groups in the
regexp (e.g., "foobar".scan(/(..)(.)/) will yield [["fo", "o"], ["ba",
"b"]]. This is the argument for Regexp#scan instead of modifying
String#scan. However, this is something that I believe should be
changed. An alternative is to yield both the normal values and the
match -- but that itself will be incompatible with #scan and most
current uses of #gsub and #sub that use the match value.

Yet another alternative is to add an optional parameter in all cases.
String#gsub currently expects a regexp and a replace pattern OR a
regexp and a block. #gsub could be modified such that when it gets a
regexp, a "boolean", and a block, it yields something different. This
could be, for example:

  String#gsub(pattern, true) { |match_data| ... }
  String#gsub(pattern) { |string| ... }

I would actually rather see the opposite form, if we do this:

  String#gsub(pattern, true) { |string| ... }
  String#gsub(pattern) { |match_data| ... }

This would encourage the use of the new form. By doing it this way, a
transition period can be introduced for this (e.g., it in 1.8.3 it may
warn that the current replace will be changed to yield a match_data
instead of a string; in 1.9 it yields a match_data instead of a
string).

I have *not* analysed code out there that uses #gsub/#scan/#sub, but I
think that this is an ideal change.

-austin (I'm also adding this to the discussion on RCR276)
-- 
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca