return nil vs return false in Ruby

Question

So, I have this code from a colleague with lots of return false and return true.

For example this method:

def has_only_one_uploaded_image?
  return false if images.size > 1
  method_here
end

If I remove the false as the return value, will it still work if I use it from other conditions?

like in this method...

def commission_plan_product_available?
  (has_only_one_uploaded_image? ||
    (has_many_images? && images_are_saved?))
end

I'm confused as to when to use the proper boolean return and when I should not.

I'm new to Ruby (not sure if nil can be also false in conditionals, please bear with me. Thank you.

Can someone shed some light please?

Answer 1

nil is "falsey", and if used directly in a conditional - or combined using logical operators &&, || etc, will behave the same as false, and your uses of it should work as you intend.

However, it is usually better practice to return true or false values from methods that behave like booleans. There is little or no extra cost, true and false are the same sort of thing internally to Ruby as nil (a simple VALUE with fixed content, it is not resolved as a pointer).

Returning nil conditionally makes more sense when you have a method which either returns an object you have asked for, or "nothing" for some good reason (e.g. you ask for a User with a specific id, but there is no such User).

If in doubt, think of how you would document the method. If you would need to explain to a user why it returns true or nil, and the explanation for this choice seems convoluted, then it would be much simpler to do what is expected and return true or false

For a very few methods, it may even make sense to return true, false or nil - the last one being essentially "I don't know". A method that caches the output from another method that returns true or false might do this.