class ActiveModel::Validations::AcceptanceValidator::AttributeDefinition

def define_on(klass)
  attr_readers = attributes.reject { |name| klass.attribute_method?(name) }
  attr_writers = attributes.reject { |name| klass.attribute_method?("#{name}=") }
  klass.send(:attr_reader, *attr_readers)
  klass.send(:attr_writer, *attr_writers)
end