Active Support Presence and the Single Line Method

Ruby and Rails are both built to help us write concise, meaningful code. One pattern I constantly find myself writing is a method that returns one thing, if it exists, or a default value. This can work well upfront, but it takes a little more care if the case gets any more complex. Fortunately, Rails has just the trick to keep the more complex case nice and lean in its ActiveSupport gem.

Let’s look at an example that works without Rails.

def title
  label || 'New Page'
end

The above looks great. It will return label, if it exists, or it falls back to returning ‘New Page’. I’m pretty thrilled with it. But what if we need to titleize the label?

def title
  label.titleize || 'New Page'
end

Unfortunately, the above will throw an error if label is nil. That kind of defeats the purpose of the conditional in the first place. At this point, it’d be easy to toss away our desire for concisement and write the following:

def title
  if label.present?
    label.titleize
  else
    'New Page'
  end
end

Our new method will work. But how can we leverage Rails to make our method a little sharper? ActiveSupport comes with a #presence method that returns the original object, if it exists, or nil otherwise. Let’s see it in action.

def title
  label.titleize.presence || 'New Page'
end

Boom! Our method is nice, lean, and readable. #presence is the secret to manipulating and returning a variable before it exists or falling back to a default.