Dependency injection (+ singletons)

gistfile1.md

# hardcoded behaviour
class Cow
  def speak
    'Mooooo!'
  end
end

# creature dependency example
# with and without singletons
class Animal
  def initialize(source)
    @source = source
  end

  def speak_class
    @source.speak
  end

  def speak_instance
    @source.new.speak
  end
end

class Cow
  def speak
    "Moooo!"
  end
end

class Bird
  def self.speak
    "Tweet!"
  end
end


#Animal.new(Cow).speak_class
#=> NoMethodError: undefined method 'speak' for Cow:Class
#
#Animal.new(Cow).speak_instance
#=> "Moooo!"
#
#Animal.new(Bird).speak_class
#=> "Tweet!"
#
#Animal.new(Bird).speak_instance
#=> NoMethodError: undefined method 'speak' for #<Bird:0x00000000ff96c8>