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Ruby

Posted by Hamilton Steele
Hamilton Steele
8,717 Points

Using nil vs false (specifically in find_index method)

So I just had a quick question about this part of Jason's code:

def find_index(name)
    index = 0
    found = false
    todo_items.each do |todo_item|
      if todo_item.name == name
        found = true
      end
      if found
        break
      else
        index += 1
      end
    end
    if found
      return index
    else
      return nil
    end
  end

specifically this part of the code...

    if found
      return index
    else
      return nil
    end

why in this find_index method in the todo_list.rb do we return "nil" instead of just "false"?

what's the advantage of using nil if nil also evaluates to false anyways?

2 Answers

Damian Kosowski
Damian Kosowski
19,746 Points
Damian Kosowski
Damian Kosowski
19,746 Points

One situation that pops into my mind is the difference between nil.nil? and false.nil? - the former evaluates to true the latter to false. So basically if we would use a control expression like - if variable.nil? do something and if not do something else - and we would get the variable from some earlier method, it would be important if that earlier method returns false or nil. I hope that makes sense. I would also love to hear if anyone has some other examples :)

Hamilton Steele
Hamilton Steele
8,717 Points

Yes! That actually totally makes sense. Thanks!

Damian Kosowski
Damian Kosowski
19,746 Points
Damian Kosowski
Damian Kosowski
19,746 Points

I would say that in this particular case we don't expect this method to return a true or false value. In Ruby methods that end with a question mark "?" by convention return a boolean. This method should just return the index and if it isn't found should return nothing.

Hamilton Steele
Hamilton Steele
8,717 Points

Yes, I understand that. But really, I'm just wondering, I guess functionally, what is the difference between nil and false? If nil evaluates as false anyways, why not use false? Is it simply just being more explicit for code readability or is there some other reason nil is best to use.

I guess what I'm asking is: I know that there is a difference between nil (or nothing) versus false, but is there a situation in ruby where using false instead of nil would produce something totally unexpected or is using nil just more explicit. I guess nil is the only instance of it's own class so it has its own methods that can work on it?

Thanks for the reply