Metaphor

From the Greek: μεταφορά - metaphora, meaning "transfer"

Rationale

As programmers an awful lot of what we do revolves around taking an input, doing something to it, and sending the result somewhere. Quite a bit of time is wasted writing the "glue" that transfers the results from one place to the next. Metaphor aims to provide a standardised and easy to use way of passing results, leaving you to concentrate on the bit that's important - the business logic.

Programming with Metaphor

metaphor = Metaphor.new
metaphor.processors << Foo.new
metaphor.processors << Bar.new
metaphor.processors << Baz.new
metaphor.processors << Metaphor::Processor::PrintMessage.new

# Process one message
metaphor.call(headers, body) # => [ new_headers, new_body ]
                             # => false (if halted by processor)

# Process messages from this class until the Ruby VM is killed or the
# input returns nil
metaphor.call(StdinInput.new)

Classes used for input must respond to #get and return an array of headers and the message body:

class StdinInput
  def get
    # return an array like this:
    [
      { "header" => "value", ... }, # Message headers
      "body"                        # Message body
    ]
  end
end

Classes used as processors must respond to #call(headers, body):

class PrintMessage
  def call(headers, body)
    puts "Headers: #{headers.inspect}"
    puts "Body   : #{body.inspect}"
  end
end

The return value of #call controls what happens to the message. If the processor returns:

• An array of headers and the message body
  • they are passed to the next processor
• Boolean false (or something that is === to it)
  • Metaphor stops processing this message and discards it
• Any other value that is not false
  • Metaphor passes the same headers and message that were passed into this processor to the next processor in the chain

Contributing

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with the Rakefile or Metaphor::VERSION. If you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull.
• Send me a pull request. Bonus points for topic branches.

Authors

• Sean O'Halpin
• Craig R Webster http://barkingiguana.com/

License

Released under the MIT licence. See the LICENSE file for details.