class Hashie::Dash

def self.inherited(klass)
  super
  (@subclasses ||= Set.new) << klass
  klass.instance_variable_set('@properties', self.properties.dup)
  klass.instance_variable_set('@defaults', self.defaults.dup)
  klass.instance_variable_set('@required_properties', self.required_properties.dup)
end