Falsy Values in Ruby

Published: Tuesday, May 17, 2022

Updated: Wednesday, May 18, 2022

Greetings, friends! When working with Boolean contexts such as in if statements and for loops, you'll need to know what values make the condition fail due to a falsy value. The falsy values in Ruby are the following:

The false boolean value
The nil object

Both of these values will cause a boolean condition to fail:

ruby

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if false
  puts '1. You will see me if the condition is truthy.'
else
  puts '1. You will see me if the condition is falsy.'
end

if nil
  puts '2. You will see me if the condition is truthy.'
else
  puts '2. You will see me if the condition is falsy.'
end

=begin OUTPUT:
1. You will see me if the condition is falsy.
2. You will see me if the condition is falsy.
=end

tip

You can try out this code by copying and pasting it to run.rb.

The conditional statement in every if statement will fail due to the falsy values, causing the else block to run.

If you are familiar with JavaScript or read my post on falsy values in JavaScript, then you'll quickly realize that JavaScript treats more values as falsy than Ruby. In fact, the value of zero 0 is actually considered truthy in Ruby!

ruby

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if 0
  puts 'You will see me if the condition is truthy.'
else
  puts 'You will see me if the condition is falsy.'
end

=begin OUTPUT:
You will see me if the condition is truthy.
=end

Empty strings, empty arrays, and empty hashes are all considered truthy in Ruby:

ruby

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if ""
  puts '1. You will see me if the condition is truthy.'
else
  puts '1. You will see me if the condition is falsy.'
end

if []
  puts '2. You will see me if the condition is truthy.'
else
  puts '2. You will see me if the condition is falsy.'
end

if {}
  puts '3. You will see me if the condition is truthy.'
else
  puts '3. You will see me if the condition is falsy.'
end

=begin OUTPUT:
1. You will see me if the condition is truthy.
2. You will see me if the condition is truthy.
3. You will see me if the condition is truthy.
=end

Keep all this information in mind when you are developing web applications using Ruby on Rails when switching between Ruby and JavaScript! It's important to know what is considered falsy in Ruby versus what is considered falsy in JavaScript.