Is there a Ruby, or Ruby-ism for not_nil? opposite of nil? method?

Question

I am not experienced in Ruby, so my code feels "ugly" and not idiomatic:

def logged_in?
  !user.nil?
end

I'd rather have something like

def logged_in?
  user.not_nil?
end

But cannot find such a method that opposites nil?

Solution 1

when you're using ActiveSupport, there's user.present? http://api.rubyonrails.org/classes/Object.html#method-i-present%3F, to check just for non-nil, why not use

def logged_in?
  user # or !!user if you really want boolean's
end

Solution 2

You seem overly concerned with booleans.

def logged_in?
  user
end

If the user is nil, then logged_in? will return a "falsey" value. Otherwise, it will return an object. In Ruby we don't need to return true or false, since we have "truthy" and "falsey" values like in JavaScript.

Update

If you're using Rails, you can make this read more nicely by using the present? method:

def logged_in?
  user.present?
end

Solution 3

Beware other answers presenting present? as an answer to your question.

present? is the opposite of blank? in rails.

present? checks if there is a meaningful value. These things can fail a present? check:

"".present? # false
"    ".present? # false
[].present? # false
false.present? # false
YourActiveRecordModel.where("false = true").present? # false

Whereas a !nil? check gives:

!"".nil? # true
!"    ".nil? # true
![].nil? # true
!false.nil? # true
!YourActiveRecordModel.where("false = true").nil? # true

nil? checks if an object is actually nil. Anything else: an empty string, 0, false, whatever, is not nil.

present? is very useful, but definitely not the opposite of nil?. Confusing the two can lead to unexpected errors.

For your use case present? will work, but it's always wise to be aware of the difference.

Solution 4

Maybe this could be an approach:

class Object
  def not_nil?
    !nil?
  end
end

Solution 5

May I offer the Ruby-esque ! method on the result from the nil? method.

def logged_in?
  user.nil?.!
end

So esoteric that RubyMine IDE will flag it as an error. ;-)

View more solutions

Comments

[berkes]

I added a tag to my original post, indicating that -indeed- I am using Rails, hence the user.present? is present. AFAIK that indeed is the exact opposite of nil? Hence exactly what I need (in this context, a rails project)

[berkes]

Good idea. I make from this that there is no not_nil? in Ruby. But should this not be !self.nil? rather then !nil?, or is selfimplicit?

[MarkD]

You don't need self. It will be implied.

[lambshaanxy]

Beware: present? requires a non-blank string. ! "".nil? returns true, but "".present? returns false.

[likethesky]

Beware 2: I'll also note that !!user does NOT distinguish between user being nil and user being false; the double-bang usage conflates those two. So if you're truly wanting to determine if an object is not nil (meaning, it's: true, false, 0, "", anything other than nil), you need to use the 'ugly' approach that berkes doesn't like or the monkeypatch that @Tempus proposes below. Of course in this case where not nil is not needed (a user in Rails), the approach taken by Samo is the least ugly, imo.

[Dudo]

false.present? == false !false.nil? == true

[tokland]

The expectation with a method ending with a ? is that it returns a boolean. !!value is the classic way to convert anything to a boolean. Not exactly the same, but in this case Object#present? in RoR is also good.

[Ekkstein]

This answer doesn't at all answer the question asked. It's an answer to this particular implementation problem.

[justingordon]

this actually breaks in Ruby 2.4 with Path! [43] (pry) #<ReactOnRails::AssetsPrecompile>: 0> assets_path.blank? true [44] (pry) #<ReactOnRails::AssetsPrecompile>: 0> assets_path.to_s "/var/folders/rp/_k99k0pn0rsb4d3lm9l3dnjh0000gn/T/d20170603-‌​96466-zk7di7" [45] (pry) #<ReactOnRails::AssetsPrecompile>: 0> assets_path.present? false [46] (pry) #<ReactOnRails::AssetsPrecompile>: 0> assets_path.nil? false

[A Fader Darkly]

Self is implied when reading from instance methods (or accessors, which are really just methods). When setting values, a variable local to the method will be created before Ruby checks the class instance for a setter method of the same name. General rule: if you have an attr_accessor called xxx, use "self.xxx = 3" (setting a value) or "temp = xxx" (reading the value). Using "xxx = 3" will not update the accessor, just create a new variable in the method scope.

[Mike]

This answer is not correct. false.nil? is false, while false.present? is ALSO false!

[berkes]

How is that different from my_hash.values_at("Name", "name").find?

[Ian]

It's exactly the same. I had some other logic in my original map that I removed for simplicity in this example, so as-written here it's interchangeable with values_at. The important part is what gets passed to find.

[Yason]

Should be included in the accepted answer. false.blank? is not same as as false.nil?

[Abhinav Kaushal Keshari]

present? will query your database, nil? will not, be careful with that