A lot of the times, your software will be split into separate layers, where each layer has its own responsibility (think about MVC, for example). The chances are that the layer that does the validation of incoming data is not the same that determines what to do next, or the layer that displays messages to a user.

This is why Particle\Validator results a ValidationResult class: so that you can pass that to other layers which will then determine what to do with the result. Usage of this class can not be any simpler:

use Particle\Validator\ValidationResult;
use Particle\Validator\Validator;

class MyEntity 
    protected $id;

    public function setId($id)
        $this->id = $id;
        return $this;

    public function validate() {
        $v = new Validator;

        return new $v->validate($this->values());

    protected function values()
        return [
            'id' => $this->id,

// in a controller:
$entity = new Entity();

$result = $entity->validate();

if (!$result->isValid()) {
    return $this->renderTemplate([
        'messages' => $result->getMessages() // or maybe even just pass in $result.