Difference Between .Nil, .Blank? and .Empty

Difference between .nil?, .blank? and .empty?

In Ruby, nil in an object (a single instance of the class NilClass). This means that methods can be called on it. nil? is a standard method in Ruby that can be called on all objects and returns true for the nil object and false for anything else.

empty? is a standard Ruby method on some objects like Arrays, Hashes and Strings. Its exact behaviour will depend on the specific object, but typically it returns true if the object contains no elements.

blank? is not a standard Ruby method but is added to all objects by Rails and returns true for nil, false, empty, or a whitespace string.

Because empty? is not defined for all objects you would get a NoMethodError if you called empty? on nil so to avoid having to write things like if x.nil? || x.empty? Rails adds the blank? method.

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After answering, I found an earlier question, "How to understand nil vs. empty vs. blank in Rails (and Ruby)", so you should check the answers to that too.

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

.nil? can be used on any object and is true if the object is nil.

.empty? can be used on strings, arrays and hashes and returns true if:

• String length == 0
• Array length == 0
• Hash length == 0

Running .empty? on something that is nil will throw a NoMethodError.

That is where .blank? comes in. It is implemented by Rails and will operate on any object as well as work like .empty? on strings, arrays and hashes.

nil.blank? == true
false.blank? == true
[].blank? == true
{}.blank? == true
"".blank? == true
5.blank? == false
0.blank? == false

.blank? also evaluates true on strings which are non-empty but contain only whitespace:

"  ".blank? == true
"  ".empty? == false

Rails also provides .present?, which returns the negation of .blank?.

Array gotcha: blank? will return false even if all elements of an array are blank. To determine blankness in this case, use all? with blank?, for example:

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

Testing for empty or nil-value string

The second clause does not need a !variable.nil? check—if evaluation reaches that point, variable.nil is guaranteed to be false (because of short-circuiting).

This should be sufficient:

variable = id if variable.nil? || variable.empty?

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If you're working with Ruby on Rails, Object.blank? solves this exact problem:

An object is blank if it’s false, empty, or a whitespace string. For example, "", " ", nil, [], and {} are all blank.

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

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

Nil and boolean in Ruby

The statement goes through the conditions in order, will stop when a falsy result is obtained and return the value of the last evaluation performed.

In contrary to && which stops at a falsy value, || will stop at a truthy value instead.

Check if Variable is Empty - Angular 2

Lets say we have a variable called x, as below:

var x;

following statement is valid,

x = 10;
x = "a";
x = 0;
x = undefined;
x = null;

1. Number:

x = 10;
if(x){
//True
}

and for x = undefined or x = 0 (be careful here)

if(x){
 //False
}

2. String x = null , x = undefined or x = ""

if(x){
  //False
}

3 Boolean x = false and x = undefined,

if(x){
  //False
}

By keeping above in mind we can easily check, whether variable is empty, null, 0 or undefined in Angular js. Angular js doest provide separate API to check variable values emptiness.

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