Finding `Mdm::Module::Class` by INTERSECTING `Mdm::Module::Ancestor#descendants`, which are `Mdm::Module::Classes`, to determine if a new `Mdm::Module::Class` should be created for the combination of one or two `Mdm::Module::Ancestor`. Uses WeakRef to allow garbage collection of `Mdm::Module::Class` after use.

metasploit_class.rb

  # `*::Module::Class` holding metadata for this class.
  #
  # @return [Mdm::Module::Class]
  def module_class
    begin
      strong_reference = nil
      
      if @module_class
        strong_reference = @module_class.__getobj__
      else
        ActiveRecord::Base.connection_pool.with_connection do
          ActiveRecord::Base.transaction do
            module_class_sets = module_ancestors.map(&:descendants)
            module_class_intersection = module_class_sets.inject { |intersection, module_class_set|
              intersection.intersect module_class_set
            }
            module_class_intersection_sql = module_class_intersection.to_sql
            strong_reference = Mdm::Module::Class.find_by_sql(module_class_intersection_sql).first

            unless strong_reference
              strong_reference = Mdm::Module::Class.new(ancestors: ancestors)
            end

          end
        end

        # memoize as a weak reference so that garbage collector can save memory and thousands of Mdm::Module::Classes
        # don't have to remain in memory.
        @module_class = WeakRef.new(strong_reference)
      end
    rescue WeakRef::RefError
      # try again by rebuilding weakref for @module_class
      @module_class = nil
      retry
    end

    # Return a strong reference so consuming code doesn't have to handle the weakref being garbage collected.
    strong_reference
  end