class Regexp
  # Returns the number of backreferencing subexpressions.
  #
  #   /(a)(b)(c)/.arity  #=> 3
  #   /(a(b(c)))/.arity  #=> 3
  #
  # Note: This is not perfect, especially with regards to \x
  # and embedded comments.
  def arity
    self.source.scan( /(?!\\)[(](?!\?[#=:!>-imx])/ ).length
  end
end



#  _____         _
# |_   _|__  ___| |_
#   | |/ _ \/ __| __|
#   | |  __/\__ \ |_
#   |_|\___||___/\__|
#
=begin test

  require 'test/unit'

  class TCRegexp < Test::Unit::TestCase

    def test_arity
      r = /(1)(2)(3)/
      assert_equal( 3, r.arity )
      r = /(1)(2)(3)(4)/
      assert_equal( 4, r.arity )
      r = /(1)(2)((a)3)/
      assert_equal( 4, r.arity )
      r = /(?#nothing)(1)(2)(3)(?=3)/
      assert_equal( 3, r.arity )
    end

  end

=end