Truthy, Falsey, nil?, any?, empty?, blank? and present? in Ruby and Ruby on Rails

Published: by Creative Commons Licence

Here's a quick comparison of Ruby's truthy, falsey, nil?, any?, empty? against Ruby on Rails' blank? and present?.

TL;DR

Ruby

Truthy Used to evaluate if/unless conditions. Everything is truthy except for nil and false.
Falsey The negation of truthy. Only nil and false are falsey in Ruby.
nil? Defined on Ruby's Object class.
empty? Defined only for certain objects of Array, Hash, String etc. It throws NoMethodError for nil, TrueClass, FalseClass, Integer etc.
any? Defined in the mixin module Enumerable, which is included in classes like Array and Hash.

Rails

blank?, present? Defined in Ruby on Rails' ActiveSupport, which can also be installed independently without Rails.
blank? nil, false, empty/whitespace strings, empty arrays, hashes and any other objects with object.empty? is true.
present? The negation of blank?, i.e. !blank?.
0 is not blank (i.e. 0.present? # => true).

Summary

Methods Values
Truthy true, "", "\n", "Hello", 0, 1.25, [], [nil, false], [1, 2], {}, {:colour=>nil}
Falsey nil, false
nil? nil
any? [1, 2], {:colour=>nil}
empty? "", [], {}
blank? nil, false, "", "\n", [], {}
present? true, "Hello", 0, 1.25, [nil, false], [1, 2], {:colour=>nil}
  truthy falsey nil? any? empty? blank? present?
nil   ✓ ✓ NoMethodError NoMethodError ✓  
               
false   ✓   NoMethodError NoMethodError ✓  
true ✓     NoMethodError NoMethodError   ✓
               
"" ✓     NoMethodError ✓ ✓  
"\n" ✓     NoMethodError   ✓  
"Hello" ✓     NoMethodError     ✓
               
0 ✓     NoMethodError NoMethodError   ✓
1.25 ✓     NoMethodError NoMethodError   ✓
               
[] ✓       ✓ ✓  
[nil, false] ✓           ✓
[1, 2] ✓     ✓     ✓
               
{} ✓       ✓ ✓  
{ colour: nil } ✓     ✓     ✓
               
Object responds to empty? and evaluate to true ✓       ✓ ✓  

Difference between any? and empty?

any? is defined in the mixin module Enumerable to check if the enumberable contains the values evaluated from a given block. When no block is given, it returns true if the object contains a value other than false or nil.

Since Array, Hash both include the Enumerable module, both any? and empty? methods become available.

  • For Hashes, any? is an antonym of empty?, i.e. {}.any? is false and {}.empty? is true.
  • For Arrays, any? is almost the antonym of empty?, except for nil and false, that [nil, false].any? is false, while [nil, false].empty? is also false.

Difference between empty? and blank?

empty? is simply a Ruby method defined on certain classes, e.g. Array, Hash, String, while blank?/present? are Ruby on Rails methods defined in ActiveSupport, which can also be installed independently with Rails.

By definition, blank? includes:

  • nil
  • false
  • empty/whitespace strings
  • empty arrays, hashes
  • any other objects with object.empty? is true

Difference between blank? and present?

present? is just a negation of blank?.

# File activesupport/lib/active_support/core_ext/object/blank.rb, line 25
def present?
  !blank?
end

The presence method

Defined together with present?, presence method returns the receiver if it's present otherwise returns nil.

object.presence is equivalent to object.present? ? object : nil.

For example, something like

def display_name
  return user.name if user.name.present?

  "Demo User"
end

becomes

def display_name
  user.name.presence || "Demo User"
end

[Bonus] Logical Operators

Operator Name Description Example
! Logical Not Negates the truthy or falsey value of an object !user.active?
!! Logical Truthy Returns the truthy or falsey of an object !![]
&& Logical And Returns true if both statements are truthy user.name.present? && user.active?
|| Logicall Or Returns true if one of the statements is truthy user.name.blank? || user.discarded? 
nil && true # => nil
true && nil # => nil
nil || "" # => ""
nil || true # => true
0 && 1.25 # => 1.25
0 || 1.25 # => 0

Sample Code

Example

require "active_support"
require "active_support/core_ext/object/blank"

VALUES = [
  nil, false, true, "", "\n", "Hello", 0, 1.25, [], [nil, false], [1, 2], {}, { colour: nil }
]

puts `ruby -v`
puts `rails -v`
puts

puts "All Values: #{VALUES}"
puts

puts "Truthy: #{VALUES.select { |v| !!v == true } }"
puts "Falsey: #{VALUES.select { |v| !!v == false } }"
puts "nil?: #{VALUES.select { |v| v.nil? == true } }"
puts "any?: #{VALUES.select { |v| v.respond_to?(:any?) && v.any? == true } }"
puts "empty?: #{VALUES.select { |v| v.respond_to?(:empty?) && v.empty? == true } }"

puts

puts "blank?: #{VALUES.select { |v| v.blank? == true } }"
puts "present?: #{VALUES.select { |v| v.present? == true } }"

Results

ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin18]
Rails 6.0.3.5

All Values: nil, false, true, "", "\n", "Hello", 0, 1.25, [], [nil, false], [1, 2], {}, {:colour=>nil}

Truthy: true, "", "\n", "Hello", 0, 1.25, [], [nil, false], [1, 2], {}, {:colour=>nil}
Falsey: nil, false
nil?: nil
any?: [1, 2], {:colour=>nil}
empty?: "", [], {}

blank?: nil, false, "", "\n", [], {}
present?: true, "Hello", 0, 1.25, [nil, false], [1, 2], {:colour=>nil}