php - 何时在继承中重新声明类属性以进行更严格更明确的类型定义

Question

开门见山。

abstract class AbstractRepository {

    private $mapper;

    public function __construct(AbstractMapper $mapper) {
        $this->mapper = $mapper;
    }

    public function save(AbstractEntity $entity) {
        return $this->mapper->save($entity);
    }

    public function delete(AbstractEntity $entity) {
        return $this->mapper->delete($entity);
    }

}

class UserRepository extends AbstractRepository {

    private $userMapper;

    public function __construct(UserMapper $userMapper) {
        parent::__construct($userMapper);
        $this->userMapper = $userMapper;
    }

    public function fetchByUsername($username) {
        return $this->userMapper->fetch( array('username' => $username) );

}

---

VS

abstract class AbstractRepository {

    // Different visibility
    protected $mapper;

    public function __construct(AbstractMapper $mapper) {
        $this->mapper = $mapper;
    }

    public function save(AbstractEntity $entity) {
        return $this->mapper->save($entity);
    }

    public function delete(AbstractEntity $entity) {
        return $this->mapper->delete($entity);
    }

}

class UserRepository extends AbstractRepository {

    // $userMapper property gone

    public function __construct(UserMapper $userMapper) {
        parent::__construct($userMapper);
    }

    public function fetchByUsername($username) {
        return $this->mapper->fetch( array('username' => $username) );

}

我喜欢第一种方式，因为它UserRepository拥有UserMapper.

第二种方式更好，因为代码少但走线

return $this->mapper->fetch( array('username' => $username) );

它并不像

return $this->userMapper->fetch( array('username' => $username) );

当我在用户存储库中时，我知道这$this->mapper是 a 的一个实例，UserMapper但我更喜欢像$this->userMapper.

有没有关于在这种情况下最好做什么的规则？

谢谢。

Answer 1

您的第一种方法没有意义......您正在复制代码。

您必须了解的是，它UserRepository仍然具有$mapper属性。它只是不能直接访问，因为它是private. 您需要访问器方法来执行此操作：

abstract class AbstractRepository {

    // Different visibility
    private $mapper;

    public function __construct(AbstractMapper $mapper) {
        $this->mapper = $mapper;
    }

    protected function getMapper() {
        return $this->mapper;
    }

    public function save(AbstractEntity $entity) {
        return $this->mapper->save($entity);
    }

    public function delete(AbstractEntity $entity) {
        return $this->mapper->delete($entity);
    }

}

class UserRepository extends AbstractRepository {

    // $userMapper property gone

    public function __construct(UserMapper $userMapper) {
        parent::__construct($userMapper);
    }

    public function fetchByUsername($username) {
        return $this->getMapper()->fetch( array('username' => $username) );

}

通过这种方式，您可以确保任何子*Repository类都会对 进行任何奇怪的操作$mapper，但您仍然可以使用getMapper.

您的第二种方法也是正确的，但限制较少。