From: Robert Klemme <shortcutter@...>
Date: 2010-11-08T19:38:28+09:00
Subject: [ruby-core:33104] Re: Suggestion for MatchData#first and #last

On Mon, Nov 8, 2010 at 10:04 AM, NARUSE, Yui <naruse@airemix.jp> wrote:
> 2010/11/8 Robert Klemme <shortcutter@googlemail.com>:
>> On Mon, Nov 8, 2010 at 9:34 AM, NARUSE, Yui <naruse@airemix.jp> wrote:
>>> 2010/11/8 Robert Klemme <shortcutter@googlemail.com>:
>>>> Btw, I just notice this
>>>>
>>>> irb(main):016:0> /(?<f>fo+).*(\g<f>)/ =~ "foooobarfoo"
>>>> => 0
>>>> irb(main):017:0> $1
>>>> => "foo"
>>>> irb(main):018:0> $2
>>>> => nil
>>>> irb(main):019:0> f
>>>> => "foo"
>>>> irb(main):020:0> RUBY_VERSION
>>>> => "1.9.1"
>>>> irb(main):021:0> RUBY_PATCHLEVEL
>>>> => 429
>>>>
>>>> I thought named group would have the same capturing semantics as
>>>> unnamed groups but apparently the leading named group is not
>>>> considered as capturing. �Is the behavior shown above intended?
>>>
>>> When you use named capture, you can't use normal parentheses.
>>> It becomes (? .. ).
>>
>> I think this is not true, because as long as I do not use \g I can
>> access the group via name *and* via index:
>>
>> irb(main):004:0> /(?<a>fo+)/ =~ "foobar"
>> => 0
>> irb(main):005:0> $1
>> => "foo"
>> irb(main):006:0> a
>> => "foo"
>>
>> That's also in line with what the doc says
>> http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt
>>
>> Or did you mean "when using *calls* to named captures"? �Because
>> that's where the difference comes in.
>
> I mean, in RE.txt's words, named group.
> When you use named group, (?<f>...), in a regexp,
> (...) in the regexp is treated as (?...).

Ah, you mean that a single named group makes all "regular" groups
loose their capturing feature and behave like non capturing groups.
Thanks!

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/