ioc_container_sample.rb

class Container
  module Dependent
    def dependencies(*deps)
      @dependencies ||= []
      deps.each { |d| @dependencies << d }
      @dependencies.uniq!
    end
  end

  attr_reader :instances

  def initialize
    @instances = {}
  end

  def register(name, instance)
    @instances[name] = instance
  end

  def get(name)
    instances[name]
  end

  def inject(klass)
    klass.instance_variable_get(:@dependencies).each do |d|
      klass.instance_variable_set(:"@#{d}", get(d))
      klass.send(:define_method, d) { self.class.instance_variable_get(:"@#{d}") }
    end
  end
end

class Worker
  extend Container::Dependent
  dependencies 'logger'

  def perform
    5.times { logger.info('Hello World!') }
  end
end

class Logger
  def info(str)
    puts str
  end
end

class SilentLogger
  def info(str)
    str
  end
end

container = Container.new

container.register('logger', Logger.new)
container.inject(Worker)
Worker.new.perform

container.register('logger', SilentLogger.new)
container.inject(Worker)
Worker.new.perform