Step-by-step refactoring

gistfile1.rb

# First iteration
class Post
  def publish
    self.published_at = Time.now
    save
  end
end

# Second iteration
# published_at logic gets more complex
class PublishTime
  def initialize(special_timing)
    @special_timing = special_timing
  end
  
  def stamp
    if @special_timing
      Time.now * 100 - 365
    else
      Time.now
    end
  end
end

class Post
  def publish
    publish_time = PublishTime.new(self.special_timing?)
    self.published_at = publish_time.stamp
    save
  end
end

# Iteration 3 - lots of different timings
# We figure out the strategy at runtime
# DI!
class Post
  def publish(time = PublishTime.new)
    time.special_timing = self.special_timing?
    self.published_at = time
    save
  end
end

# PublishTimeFactory: wysiwyg ok?
class PostController
  def create
    post = Post.new(params[:post])
    PublishTimeFactory.for(post, rand(9))
    post.publish(time)
  end
end

I don't think anything is tied to the database, I don't show #save's implementation and I'm never specifying ActiveRecord.

Sure, I guess that's just what I assumed based on the fact that there was no implementation shown for Post#special_timing?. But I think the point still stands, if that was coming from the database, then this would be an example where I would not use DI. I'm not sure if that's helpful.

Still, we can change this example to pass something other than a boolean tied to post. I think the central point still I was making works in any case, or no?

I guess the central point I'm trying to make is that DI is just a tool. The important thing is that we encourage code that is easily extensible by adding additional objects/classes not by modifying ones that already exist. Especially as we endeavor to make code reuse more of a goal. If we don't we're going to be walking into a whole boatful of prod errors.