Feature #1200

Possibility for using named and normal groups together in regular expressions

Added by Wolfgang Nádasi-Donner almost 7 years ago. Updated almost 4 years ago.



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 "(" +
"[]?" +
"(?:\(\g<-1>\)" +
?" +
")*?" +
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}'"
puts "Nicht O.K.: '#{s}'"

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}(?[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.

Related issues

Related to Ruby trunk - Feature #1201: Add relative group reference in back reference with nest level in regular expressions (e.g. \k<-5+1>) Closed 02/25/2009


#1 Updated by Wolfgang Nádasi-Donner almost 7 years ago

Typo: I've written "[0-9}+" instead of "[0-9]+" several times, sorry.

#2 Updated by Akira Tanaka over 6 years ago

I'd like to use simple paren as a shy group.

If we allow both named and unnamed capturing group in a regexp, I recommend unnamed capturing have a new syntax, such as (?<>...).


#3 Updated by Marc-Andre Lafortune about 6 years ago

  • Assignee set to Yukihiro Matsumoto
  • Target version changed from 1.9.1 to 2.0.0



#4 Updated by Shyouhei Urabe about 5 years ago

  • Status changed from Open to Assigned



#5 Updated by Yui NARUSE almost 4 years ago

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

Mixed regexp both named and unnamed capturing group is disallowed by design of Ruby.

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