Define memoized methods with style

memoizable.rb

#!/usr/bin/env ruby

module Memoizable
  # This would be `extend ActiveSupport::Concern` in Rails
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def define_memoized(method)
      define_method method do |*args|
        # Prevent being called with arguments
        raise ArgumentError, "`#{self.class.name}##{method}` is a memoized method and therefore cannot be called with arguments (arguments were #{args})" if args.any?

        # Memoize
        instance_variable_name = :"@#{method}"
        return instance_variable_get(instance_variable_name) if instance_variable_defined?(instance_variable_name)
        instance_variable_set(instance_variable_name, yield)
      end
    end
  end
end

class Bar
  include Memoizable

  define_memoized :foo do
    puts 'Calling “Bar#foo” logic!'
    'yes'
  end
end

bar = Bar.new
5.times { puts bar.foo }
# => Calling “Bar#foo” logic!
# => yes
# => yes
# => yes
# => yes
# => yes