# File lib/travis/cli/parser.rb, line 17
      def on(*args, &block)
        block ||= begin
          full_arg = args.detect { |a| a.start_with? '--' }
          name = full_arg.gsub(/^--(\[no-\])?(\S+).*$/, '\2').gsub('-', '_')
          attr_reader(name)               unless method_defined? name
          attr_writer(name)               unless method_defined? "#{name}="
          alias_method("#{name}?", name)  unless method_defined? "#{name}?"
          proc { |instance, value| instance.public_send("#{name}=", value) }
        end

        on_initialize do |instance|
          instance.parser.on(*args) do |value|
            block.call(instance, value)
          end
        end
      end