A concise explanation of nil v. empty v. blank in

Question

I find myself repeatedly looking for a clear definition of the differences of nil?, blank?, and empty? in Ruby on Rails. Here's the closest I've come:

• blank? objects are false, empty, or a whitespace string. For example, "", " ", nil, [], and {} are blank.

• nil? objects are instances of NilClass.

• empty? objects are class-specific, and the definition varies from class to class. A string is empty if it has no characters, and an array is empty if it contains no items.

Is there anything missing, or a tighter comparison that can be made?

Answer 1

exists? method can be used to check whether the data exists in the database or not. It returns boolean values either true or false.

Answer 2

A special case is when trying to assess if a boolean value is nil:

false.present? == false
false.blank? == true
false.nil? == false

In this case the recommendation would be to use .nil?

Answer 3

Rails 4

an alternative to @corban-brook 's 'Array gotcha: blank?' for checking if an arrays only holds empty values and can be regarded as blank? true:

[ nil, '' ].all? &:blank? == true

one could also do:

[nil, '', "", " ",'  '].reject(&:blank?).blank? == true

Answer 4

I made this useful table with all the cases:

blank?, present? are provided by Rails.

Answer 5

One difference is that .nil? and .empty? are methods that are provided by the programming language Ruby, whereas .blank? is something added by the web development framework Rails.

Answer 6

Just a little note about the any? recommendation: He's right that it's generally equivalent to !empty?. However, any? will return true to a string of just whitespace (ala " ").

And of course, see the 1.9 comment above, too.