This is Anti-pattern—thoughts on programming and whatnot by Brandon Weiss.

Explicit Privates

May 16th, 2016

Years ago I wrote about the different styles of private declarations in Ruby and my personal preference. It was the best I could see at the time, but it was only marginally better than the rest and totally non-standard. Now I think I’ve finally arrived at a style that is superior to all of them.

To recap, the common style is this.

class Stuff

  def something_public
    # …
  end

  private

  def something_private
    # …
  end

end

Despite being ubiquitous, it’s actually awful. If your file is large, the only way to know if a method you’re looking at is private or not is to keep scrolling upwards until you either see a private or class declaration. All Rubyists have done this so many times now it’s become habitual. We’ve all internalized this as normal and we don’t ever think about how absurd it is. There’s a better way, though. If you’re a savvy Rubyist, you might be aware that the private declaration doesn’t affect class methods.

class Stuff

  private

  def self.something_private
    # Not actually private
  end

end

Never having tried to directly call a class method I’d declared as private, I didn’t discover this for years. To actually make a class method private you have to use private_class_method.

class Stuff

  def self.something_private
    # Now this is private
  end
  private_class_method :something_private

end

Which led me to realize you can do the same thing with instance methods and private.

class Stuff

  def something_private
    # This is private
  end
  private :something_private

end

And even better, the private declarations can be inlined.

class Stuff

  def something_public
    # …
  end

  private def something_private
    # …
  end

  private_class_method def self.classy_private
    # …
  end

end

This works because the return value of a method declaration is the method name as a symbol, which gets passed as an argument to private and private_class_method.

Whatever your initial gut reaction is to the repetition, it will quickly be replaced by the surprising relief of knowing immediately whether the method you’re working on is public or private and not having to jump around to find out. I’ve been using this for the last several months and it’s great. Try it—you’ll come to love it too.