def direct_descendants(include_singletons = false)
      return _inherited_by if BBLib.in_opal?
      ObjectSpace.each_object(Class).select do |c|
        (include_singletons || !c.singleton_class?) && c.ancestors[1..-1].find { |k| k.is_a?(Class) } == self
      end
    end
def direct_descendants(include_singletons = false)
      return _inherited_by if BBLib.in_opal?
      ObjectSpace.each_object(Class).select do |c|
        (include_singletons || !c.singleton_class?) && c.ancestors[1..-1].find { |k| k.is_a?(Class) } == self
      end
    end
Return all classes that directly inherit from this class