Using variables in a Ruby Gem

Question

What is the correct way to use configurable variables in a Ruby gem to be used in a Rails app? We use timezone in this example which is likely a constant but would also be using installation-specific variables such as home_city, etc.

1. Constants
   Can set constants in an initializer:

   config/initializer/mygem.rb
   TIMEZONE = "Eastern Standard"
   

   However, if used in an class variable declaration, the variable is not defined.

   module Foo
     module Bar
       class TickTock  
         class_attribute :tz  
         self.tz = "#{TIMEZONE} Time zone"  # uninitialized constant Foo::Bar::TickTock::TIMEZONE  
   

2. Config variables

   config/initializer/mygem.rb  
   config.x.timezone = "Eastern Standard"  
   

   module Foo
     module Bar
       class TickTock  
         self.tz = "#{Rails.configuration.x.timezone} Time zone" # undefined method `configuration` for Foo::Bar::TickTock:Module
   

3. Environment variables: We would prefer not use environment variables in the gem itself. We would like to avoid

   self.tz = "#{ENV['TIMEZONE']} Time zone"
   

4. Other

Answer 1

The best way to do this is use ActiveSupport::Configurable module.

With this module, you can create a configuration file like this:

/config/initializers/my_gem.rb

MyGem.config do |config|
  config.timezone = 'BRT'
end

This answer can be usefull too.