Im not familiar on dependency injection Remove Car's explicit reference to Engine by using dependency injection. class Car attr_reader :engine def engine @engine ||= Engine.new(4) end def move engine.accelerate end end class Engine attr_reader :cylinders def initialize(cylinders) @cylinders = cylinders end def accelerate end end -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/3673d7f3-b4b2-4ffb-881c-d2b6c4169d64%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.