nyan.rb

module Nyan
  class ConfigStore
    class << self
      attr_writer :setting_a, :setting_b, :setting_c

      def setting_a
        @setting_a || "default a"
      end

      def setting_b
        @setting_b || "default b"
      end

      def setting_c
        @setting_c || "default c"
      end
    end
  end

  class Processor
    def run
      a =  ConfigStore.setting_a
      b =  ConfigStore.setting_b
      c =  ConfigStore.setting_c

      p "a: #{a}, b: #{b}, c: #{c}"
    end
  end

  def self.configure
    yield ConfigStore
  end
end

# configure process global options
Nyan.configure do |c|
  c.setting_a = "aa"
  c.setting_c = "cc"
end

a = Nyan::Processor.new
a.run # => "a: aa, b: default b, c: cc"