From: Yui NARUSE <naruse@...>
Date: 2012-02-14T08:12:29+09:00
Subject: [ruby-core:42576] [ruby-trunk - Feature #1200][Rejected] Possibility for using named and normal groups together in regular expressions


Issue #1200 has been updated by Yui NARUSE.

Status changed from Assigned to Rejected
Assignee deleted (Yukihiro Matsumoto)

Mixed regexp both named and unnamed capturing group is disallowed by design of Ruby.
----------------------------------------
Feature #1200: Possibility for using named and normal groups together in regular expressions
https://bugs.ruby-lang.org/issues/1200

Author: Wolfgang N��dasi-Donner
Status: Rejected
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


=begin
 It should be possible to use named and normal groups together in ane regular expression.
 
 Reason: The new relative adressing possibilities for groups, \k<-n>, \k'-n', \g<-n>, and \g'-n' are very helpful for writing regular subexpresions to be used via #{...} more than once in a regular expresion. Example (longer explanations are only available in German on http://www.ruby-mine.de/2009/2/7/regul%C3%A4re-ausdr%C3%BCcke-teil-7-oniguruma-und-statische-relativbez%C3%BCge):
 
 # encoding: Windows-1252
 module Matchelements
   def bal()
     return "(" +
               "[^()]*?" +
               "(?:\\(\\g<-1>\\)" +
                 "[^()]*?" +
               ")*?" +
               ")"
   end
 end
 include Matchelements
 
 orgstrings= [
               'firstproc(x1(33, r(3, 4)), k(3, kk(3, 4)), l(3), x2(99))', # (x1, ., ., x2)
               'secondproc(x1(99,5), l(77, m( n(44), 29)), x2(15))',    # (x1, ., x2)
               'thirdproc(x1(66), x2(88))',    # (x1, x2)
               'fourthproc(x1(44), 1, 2, 3, x2(234))'    # (x1, ., ., ., x2)
             ]
 
 pattern = /\w+\(x1\(#{bal}*\),(?>#{bal},){1,2} x2\(#{bal}*\)/
 orgstrings.each do |s|
   if s.match(pattern)
     puts "      O.K.: '#{s}'"
   else
     puts "Nicht O.K.: '#{s}'"
   end
 end
 
 This works fine:
 
 >ruby191-p0 balmusterWorks.rb
       O.K.: 'firstproc(x1(33, r(3, 4)), k(3, kk(3, 4)), l(3), x2(99))'
       O.K.: 'secondproc(x1(99,5), l(77, m( n(44), 29)), x2(15))'
 Nicht O.K.: 'thirdproc(x1(66), x2(88))'
 Nicht O.K.: 'fourthproc(x1(44), 1, 2, 3, x2(234))'
 
 One Problem is still open, because in the regular expression, that uses the subexpresions, their groups still count. If one wants to extract parts of a match normal groups are necessary, which numbers must be known - e.g. /#{group}([0-9}+)#{group}/.
 
 In this case the usage of the result of ([0-9}+) is only possible, if one knows the number of the group. This is not visible from /#{group}([0-9}+)#{group}/, because the number of groups used in #{group} can only be seen by looking at the definition, which can be somewhere.
 
 A good solution is the usage of a named group /#{group}(?<number>[0-9}+)#{group}/, but then it is no longer possible to use normal groups together with relative access in the definition of regular subexpresions.
 
 It would be very helpul to allow both in one regular expression.
=end



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