foo.rb

module Matchers
  def add_matcher
    [BaseUrlMatcher, YoutubeMatcher].each do |m|
      extend m if m.const_get(:Pattern).match @url
    end
  end

  module BaseUrlMatcher
    Pattern = //

    def summary
      "Base #{@url}"
    end
  end

  module YoutubeMatcher
    Pattern = /youtube\.com/

    def summary
      "Youtube #{@url}"
    end
  end

end


class Visit
  include Matchers

  def initialize(url)
    @url = url
    add_matcher
  end
end

foo = Visit.new('http://youtube.com')
puts foo.summary #= Youtube matcher


bar = Visit.new('http://cbc.ca')
puts bar.summary #= Base matcher