Strong Concern (explicit manage concern dependencies both ways)

strong_concern.rb

# naive implementation
class TwoWayDelegate
  attr :_subject
  def initialize(subject)
    @_subject = subject
  end

  def inspect
    "TwoWayDelegate <#{methods.sort}>"
  end
end

module Concern
  def concern(mod, options)
    delegator_class = Class.new(TwoWayDelegate)
    delegator_class.send(:include, mod)
    options[:uses].each do |meth|
      delegator_class.send :define_method, meth do |*args, &block|
        @_subject.send(meth, *args, &block)
      end
    end

    options[:exports].each do |meth|
      define_method meth do |*args, &block|
        @_concerns ||= {}
        @_concerns[mod.to_s] ||= delegator_class.new(self)
        @_concerns[mod.to_s].send(meth,*args, &block)
      end
    end
  end
end

#USAGE

module FullNamed
  def full_name
    "#{first_name} #{last_name}"
  end
end

module AgeAssertions
  def young?
    if age < 16
      true
    else
      false
    end
  end

  def reproductive?
    if age > 16 && age < 70
      true
    else
      false
    end
  end
end

class Person
  extend Concern

  attr :first_name
  attr :last_name
  attr :age

  def initialize(first_name, last_name, age)
    @first_name, @last_name = first_name, last_name
    @age = age
  end


  concern AgeAssertions,
    uses: %w[age],
    exports: %w[young? reproductive?]

  concern FullNamed,
    uses: %w[first_name last_name],
    exports: %w[full_name]

end

nicola = Person.new('nicola', 'rhyzhikov', 33)

p nicola.full_name
p nicola.young?
p nicola.reproductive?