A nice example of Meta programing from the earworm project

gistfile1.rb

    {
      'ogg' => Audio::OGG::Decoder,
      'mp3' => Audio::MPEG::Decoder,
    }.each do |type,klass|
      define_method(:"decode_#{type}") do |filename|
        reader = klass.new
        name = File.join(Dir::tmpdir,
          "#{File.basename(filename, ".#{type}")}.wav")
        File.open(filename, 'rb') { |input|
          File.open(name, 'wb') { |tmpfile|
            reader.decode(input, tmpfile)
          }
        }
        name
      end
    end