class ActiveModel::Validations::AcceptanceValidator::LazilyDefineAttributes

def initialize(attribute_definition)
  define_method(:respond_to_missing?) do |method_name, include_private = false|
    super(method_name, include_private) || attribute_definition.matches?(method_name)
  end
  define_method(:method_missing) do |method_name, *args, &block|
    if attribute_definition.matches?(method_name)
      attribute_definition.define_on(self.class)
      send(method_name, *args, &block)
    else
      super(method_name, *args, &block)
    end
  end
end