metaprogramming magic

meta.rb

module SafeConstDefinition

  extend ActiveSupport::Concern

  module ClassMethods

    def const_missing(name)
      puts "Warning: #{name} was not defined, assuming further definition. Keep calm tho."
      # Since Parent is defined after Child both in root and in SomeModule,
      # i need to have a mechanism to define a future const, but simple:
      #   const_set(name, Class.new)
      # doesn't do the thing, since it defines the constant within the class
      # rather than enclosing module
    end

  end

  included do
    extend SafeConstDefinition::ClassMethods
  end
end


module SomeModule
  class Child
    include SafeConstDefinition

    attribute :parent, Parent
  end

  class Parent
    include SafeConstDefinition

    attribute :child, Child
  end
end

class Child
  include SafeConstDefinition

  attribute :parent, Parent
end

class Parent
  include SafeConstDefinition

  attribute :child, Child
end

Seems that

      def parent_name
        name =~ /::[^:]+\Z/ ? $`.freeze : nil
      end

      def const_missing(name)
        puts "Warning: #{name} was not defined, assuming further definition. Keep calm tho."
        if parent_name.nil?
          Object.const_set(name, Class.new)
        else
          puts parent_name
          const_get(parent_name).const_set(name, Class.new)
        end
      end

did the trick!