The Difference Between nil?, empty?, and blank? in Ruby

nil?

As expected, you can use nil? to check if an object is nil. It returns true only when the object is nil. For all other values, it returns false.

nil_object = nil
nil_object.nil?   # true

data = Hash.new
data.nil?         # false

empty?

You can use this method on strings, arrays, and hashes. It returns true in the following cases:

1. String doesn’t have any characters, i.e. str.length == 0
2. Array doesn’t contain any elements, i.e. arr.length == 0
3. Hash doesn’t have any key-value pairs, i.e. hash.length == 0

[].empty?         # true
''.empty?         # true
{}.empty?         # true
nil.empty?        # NoMethodError
false.empty?      # NoMethodError

It’s important to note that an object can be empty and not nil. For example:

names = []
names.empty?  # true
names.nil?    # false

If you try to call .empty? on a nil or any other object, Ruby throws NoMethodError.

nil.empty?

# undefined method `empty?' for nil:NilClass (NoMethodError)

blank?

This is a nice syntactic sugar implemented in Rails. An object is blank if it’s nil, false, or empty. For example, nil,false, '', [], {}are all blank.

You can think of blank? as a shorthand for the following code.

!val || val.empty?

Here's how it works for various values.

nil.blank?    # true
false.blank?  # true
''.blank?     # true
[].blank?     # true
{}.blank?     # true

In addition, .blank? returns true if a string contains only whitespace characters.

"  ".blank? # true

Rails also provides present?, which is the opposite of blank?. It checks if the value is not blank.