How to understand nil vs. empty vs. blank in Ruby

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

Answer 1

nil? is a standard Ruby method that can be called on all objects and returns true if the object is nil:

b = nil
b.nil? # => true

empty? is a standard Ruby method that can be called on some objects such as Strings, Arrays and Hashes and returns true if these objects contain no element:

a = []
a.empty? # => true

b = ["2","4"]
b.empty? # => false

empty? cannot be called on nil objects.

blank? is a Rails method that can be called on nil objects as well as empty objects.

Answer 2

• Everything that is nil? is blank?
• Everything that is empty? is blank?
• Nothing that is empty? is nil?
• Nothing that is nil? is empty?

tl;dr -- only use blank? & present? unless you want to distinguish between "" and " "

Answer 3

I made this useful table with all the cases:

blank?, present? are provided by Rails.

Answer 4

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 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

Everybody else has explained well what is the difference.

I would like to add in Ruby On Rails, it is better to use obj.blank? or obj.present? instead of obj.nil? or obj.empty?.

obj.blank? handles all types nil, '', [], {}, and returns true if values are not available and returns false if values are available on any type of object.