return early vs if in ruby code

Question

I see two styles of writing the same thing:

def find_nest(animal)
  return unless animal.bird?
  GPS.find_nest(animal.do_crazy_stuff)
end

vs

def find_nest(animal)
  if animal.bird?
     GPS.find_nest(animal.do_crazy_stuff)
  end
end

Which one is more correct/preferable/following-best-practises? Or it does not matter?

Answer 1

As per Ruby style guide,

Prefer a guard clause when you can assert invalid data. A guard clause is a conditional statement at the top of a function that bails out as soon as it can.

# bad
def compute_thing(thing)
  if thing[:foo]
    update_with_bar(thing)
    if thing[:foo][:bar]
      partial_compute(thing)
    else
      re_compute(thing)
    end
  end
end

# good
def compute_thing(thing)
  return unless thing[:foo]
  update_with_bar(thing[:foo])
  return re_compute(thing) unless thing[:foo][:bar]
  partial_compute(thing)
end

Answer 2

It is obviously a matter of personal preference. But I prefer the early return. Not only does it make code "flatter" and easier to read, it also scales well with the number of checks. For example:

  def create_terms_of_service_notification
    return if Rails.env.test?
    return if current_user.accepted_tos?
    # imagine 5 more checks here. 
    # Now imagine them as a mess of nested ifs.

    # create the notification
  end