特征访问 class 依赖是个坏主意吗？

Question

我在 Stackexchange 上看到了一个示例（请注意访问 class 属性的特征）：

trait CheckPermissionTrait
{
    protected function checkPermission($object_id)
    {
        $judge = $this->container->get('acme_judge');

        $user  = $this->container->get('security.context')->getToken()->getUser();

        if( !$judge->isPermitted($user, $object_id) ) {
            throw $this->createAccessDeniedException("Brabbel");
        }
    }
}

并阅读其中一位回复者的评论：

Your trait, then is not a valid use-case: all of its users are required, by definition, to add a $this->container property to its dependencies, which will of course have an impact on that class' contract and the contract of its children.

为什么作者声称这是一个糟糕的用例，如果这可能是某人需要的？就像如果某人几乎没有 class 都具有所需的依赖关系并且所有这些都重复出现相同的逻辑，他们是否应该只复制代码？

Answer 1

确实以这种方式使用了 trait - 一个坏主意。如果有人决定在你的代码中使用这个特性——他必须确保 "container" 属性的存在。 "container" 应该是正确的类型（包括使用的方法）——否则会出错。实际上这段代码是不能重用的，而且这有潜在的bug。另外，它违反了SOLID规则的一个规则DIP（依赖倒置原则）。

可以解决这个问题：

interface ExampleContainerInterface{

}
trait CheckPermissionTrait
{
    protected $container;
    public function __construct(ExampleContainerInterface $container)
    {
        $this->container = $container;
    }

    protected function checkPermission($object_id)
    {
        $judge = $this->container->get('acme_judge');
        $user  = $this->container->get('security.context')->getToken()->getUser();
        if( !$judge->isPermitted($user, $object_id) ) {
            throw $this->createAccessDeniedException("Brabbel");
        }
    }
}

class ExampleClassA
{
    use CheckPermissionTrait;
}
class ExampleClassB
{
    use CheckPermissionTrait;
}

或者像这样 (php7):

interface ExampleContainerInterface{

}
trait CheckPermissionTrait
{
    abstract public function getContainer():ExampleContainerInterface;
    protected function checkPermission($object_id)
    {
        $container = $this->getContainer();
        $judge = $container->get('acme_judge');
        $user  = $container->get('security.context')->getToken()->getUser();
        if( !$judge->isPermitted($user, $object_id) ) {
            throw $this->createAccessDeniedException("Brabbel");
        }
    }
}

class ExampleClassA
{
    use CheckPermissionTrait;
    protected $container;
    public function getContainer():ExampleContainerInterface
    {
        return $this->container;
    }
}
class ExampleClassB
{
    use CheckPermissionTrait;

    protected $container;
    public function getContainer():ExampleContainerInterface
    {
        return $this->container;
    }
}

Answer 2

我同意这一点，我认为 traits 不应该使用 class 的任何方法或属性，但是当我阅读 laravel 框架源代码时，我看到很多滥用这个一些trait，比如InteractWithInput trait跟request是深度耦合的class，很迷惑

trait InteractsWithInput
{
    //the getInputSource method is defined in Request class
    public function input($key = null, $default = null)
    {
        return data_get(
            $this->getInputSource()->all() + $this->query->all(), $key, $default
        );
    }
}

class Request
{
    use InteractsWithInput
    protected function getInputSource()
    {
        if ($this->isJson()) {
            return $this->json();
        }

        return in_array($this->getRealMethod(), ['GET', 'HEAD']) ? $this->query : $this->request;
    }
}

特征访问 class 依赖是个坏主意吗？

Is trait accessing class dependency a bad idea?

php

oop

traits