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Dependency Injection in Ruby 07 Oct 04

Introduction

At the 2004 Ruby Conference, Jamis Buck had the unenviable task to explain Dependency Injection to a bunch of Ruby developers. First of all, Dependency Injection (DI) and Inversion of Control (IoC) is hard to explain, the benefits are subtle and the dynamic nature of Ruby make those benefits even more marginal. Furthermore examples using DI/IoC are either too simple (and don’t convey the usefulness) or too complex (and difficult to explain in the space of an article or presentation). I once attempted to explain DI/IoC to a room of Java programmers (see onestepback.org/articles/dependencyinjection/), so I can’t pass up trying to explain it to Ruby developers.

Thanks goes to Jamis Buck (the author of the Copland DI/IoC framework) who took the time to review this article and provide feedback.

What is Dependency Injection?

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### Nginx ###
check process nginx with pidfile /run/nginx.pid
  start program = "/usr/sbin/service nginx start"
  stop program = "/usr/sbin/service nginx stop"
  if cpu > 60% for 2 cycles then alert
  if cpu > 80% for 5 cycles then restart
  if memory usage > 80% for 5 cycles then restart
  if failed host ovz1.j47454681.pq4yn.vps.myjino.ru port 80 protocol http
    then restart
  if 3 restarts within 5 cycles then timeout

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Test gist

dniman

require "money"

class Decorator < BasicObject
  undef_method :==

  def initialize(component)
    @component = component
  end

  def method_missing(name, *args, &block)