When to use nil, blank, empty?

Ruby on-RailsRuby

Ruby on-Rails Problem Overview

Is there any guidelines on how to differentiate between .nil?, .blank? and .empty??

I'm generally always confused as to when to use them in my application as they all seem to mean the same thing but have different meanings.

Does anyone have any cheat sheet on the gory details?

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Here I made this useful table with all the casesenter image description here

Solution 2 - Ruby on-Rails

  • nil? - checks to see if variable is referencing an object or not

  • empty? - may be used to check on various object types like empty string "" or empty array []

  • blank? - checks for nil? or empty?.

Solution 3 - Ruby on-Rails

  • nil? is defined on all Objects, it only returns true on the nil singleton.

  • blank? is defined on all objects too, it returns true if the object also responds to empty? and is empty, or is a false type value (!object is always true).

  • empty? is defined on several collection objects, and is true if it has no elements. It is also defined on String.

note that blank? is ActiveSupport and not in Rails 1.8.

Solution 4 - Ruby on-Rails

I found a good explanation here:

> nil? tests whether the object is > exactly nil, that is whether it is the > one and only want instance of > NilClass. > > empty? is a method some objects > respond to. You need to check the > documentation for each case. For > example, and empty array is one that > is not nil (it is an array right?) and > has no elements. An empty string is > one that is not nil (it is a string > right?) and has no bytes, nothing. > > The blank? method you ask for does not > belong to Ruby, it is a Rails > extension: > http://api.rubyonrails.com/classes/Object.html#M000011.

If you click through to the link at the end of that post you will find that the blank? method simply combines the nil? and empty? method calls.

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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionDavid CView Question on Stackoverflow
Solution 1 - Ruby on-RailsJulian PopovView Answer on Stackoverflow
Solution 2 - Ruby on-RailsKarmen BlakeView Answer on Stackoverflow
Solution 3 - Ruby on-RailscwninjaView Answer on Stackoverflow
Solution 4 - Ruby on-RailsAndrew HareView Answer on Stackoverflow