#ruby-202001101130.rb

module Foo
  @some_variable = 'default value'
  
  # https://stackoverflow.com/questions/2505067/class-self-idiom-in-ruby
  class << self
    # Allow setting through:
    #
    #     Foo.some_variable = 'some value'
    #
    # and getting through:
    #
    #     Foo.some_variable
    #
    # You can also use #attr_reader or #attr_writer if you only
    # want a getter or setter.
    #
    # https://ruby-doc.org/core-2.7.0/Module.html#method-i-attr_accessor
    attr_accessor :some_variable
    
    def some_method
      # use the getter to retrieve the value of @some_variable
      puts "do something with #{some_variable}"
    end
  end
end

Foo.some_method
# prints: do something with default value

Foo.some_variable = 'configured value'

Foo.some_method
# prints: do something with configered value