Ruby Private Constant

How can we define a private constant in Ruby❓

Let’s define PRIVATE_CONSTANT in the private section.

# private_constant.rb
module MyModule
  private

  PRIVATE_CONSTANT = 'Is this private?'
end

The result:

require './private_constant'

puts MyModule::PRIVATE_CONSTANT #=> Is this private?

It’s not private! 👎

private_constant

To make it private, use private_constant keyword.

# private_constant.rb
module MyModule
  PRIVATE_CONSTANT = 'Is this private?'
  private_constant :PRIVATE_CONSTANT
end

The result:

require './private_constant'

puts MyModule::PRIVATE_CONSTANT #=> private constant MyModule::PRIVATE_CONSTANT referenced (NameError)

The error:

private constant MyModule::PRIVATE_CONSTANT referenced (NameError)

It raises NameError because the code tries to reference private constant.

Use private_constant to make a private constant in Ruby.

module YourModule
  YOUR_CONSTANT = ...
  private_constant :YOUR_CONSTANT
end