class String
  def tsub subs
    [].tap do |item|
      self.split("%_").each do|elem|
        match = elem.match(/^\d/)
        unless match.nil?
          (0..match.length-1).each do |i|
            index = (match[i]).to_i
            #puts "index: #{index}  match #{match[i]} subs: #{subs[index]}"
            unless index < 0 or subs[index].nil?
              elem.gsub! match[i], subs[index]
            else
              elem = "%_#{elem}"
            end
          end
        end
        item << elem
      end
    end.join ""
  end
end

puts "original"
o = "Hello, %_0. Sup? %_1"
puts o
puts "interpolated"
puts o.tsub ["Andrew", "Bye"]
puts "original"
y = "%_0 Hello, %_0. Sup? %_1"
puts y
puts "interpolated"
puts y.tsub ["Andrew", "Bye"]



puts "I work  %_0 way %_1".tsub ["this", "as well"]
puts "This %_-1 will %_0 fail %_6 as long as negative numbers will not be used".tsub ["not"]