class CallbackValidator

CallbackValidatorTest.php in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Tests/Constraints/CallbackValidatorTest.php

class CallbackValidator extends ConstraintValidator {

  /**
   * {@inheritDoc}
   */
  public function validate($object, Constraint $constraint) {
    if (null === $object) {
      return;
    }

    // has to be an array so that we can differentiate between callables
    // and method names
    if (!is_array($constraint->methods)) {
      throw new UnexpectedTypeException($constraint->methods, 'array');
    }
    $methods = $constraint->methods;
    foreach ($methods as $method) {
      if (is_array($method) || $method instanceof \Closure) {
        if (!is_callable($method)) {
          throw new ConstraintDefinitionException(sprintf('"%s::%s" targeted by Callback constraint is not a valid callable', $method[0], $method[1]));
        }
        call_user_func($method, $object, $this->context);
      }
      else {
        if (!method_exists($object, $method)) {
          throw new ConstraintDefinitionException(sprintf('Method "%s" targeted by Callback constraint does not exist', $method));
        }
        $object
          ->{$method}($this->context);
      }
    }
  }

}