PHPでDDD（ドメイン駆動設計）やるにはどうすればいいのか考え中。

AbstractEntity.php

<?php

class AbstractEntity implements EntityInterface
{
}

AbstractValue.php

<?php

abstract class ValueObject
{
  private $value;
  private static $instances = array();

  private function __construct($value)
  {
    if (!$this->assert($value)) throw new \Exception("invalid value: {$value}");
    $this->value = $value;
  }

  public static function getInstance($value)
  {
    if (!isset(self::$instances[$value])) {
      $class_name = get_called_class();
      self::$instances[$value] = new $class_name($value);
    }
    return self::$instances[$value];
  }

  abstract public function assert($value);
  abstract public function toString();
}

EntityInterface.php

<?php

interface EntityInterface
{
}

RepositoryInterface.php

<?php

interface RepositoryInterface
{
  
}

SpecificationInterface.php

<?php

interface SpecificationInterface
{
  public function isSatisfiedBy(EntityInterface $entity);
  public function satisfyingElementsFrom(RepositoryInterface repository);
}