service.rb

class Service
  class << self
    def meta_def(name, &block)
      define_singleton_method(name, &block)
    end 
    
    def responses(hash)
      hash.each do |method_name, result|
        meta_def(method_name) do
          result
        end
      end
    end
  end
  responses :success => 20, :unreachable => 23
end

Service.success # => 20
Service.unreachable # => 23