From: Jacob Fugal <lukfugl@...>
Date: 2006-02-07T02:09:02+09:00
Subject: Re: Merging regular expressions

On 2/6/06, Anthony Durity <anthony.durity@gmail.com> wrote:
> r[0] = /a/
> r[1] = /b/
> m = Regexp.union(r0.source, r1.source)
> # _but_ when I go to check s with
> m =~ s
> # if it matches, i want it to tell me which of the original r[i] would have matched!

How about:

  class Regexp
    class Union
      def initialize( *regexen )
        @regexen = regexen
      end

      def <<( regex )
        @regexen << regex
      end

      def =~( other )
        regexen = @regexen.select{ |regex| regex =~ other }
        raise "ambiguous input" if regexen.size > 1
        return nil if @regexen.empty?
        return @regexen.index(regexen[0])
      end

      def []( index )
        @regexen[index]
      end
    end

    def self.union( *regexen )
      Regexp::Union.new( *regexen )
    end
  end

Usage:

  r = []
  r << /a/
  r << /b/
  m = Regexp.union( *r )
  m =~ "a test" # => 0
  m =~ "test b" # => 1
  m =~ "none" # => nil
  m =~ "ambiguous" # raises "ambiguous input"

Jacob Fugal