抽象方法中的PHP类型提示接口和方法实现中的类型提示接口的子类 [英] PHP type hint interface in abstract methods and type hint interface's child class in method implementation

问题描述

想象一下我有一个简单的界面:

Imagine I have a simple interface:

interface A {}

然后，我有一些实现该接口的类:

Then, I have some classes implementing that interface:

class B implements A {}
class C implements A {}

然后，我有一个类，该类的方法将类B的对象作为参数(我不能在这里使用接口类型提示，因为只有类B具有类D所需的某些独特功能):

Then, I have a class which have a method which expects object of class B as an argument (I can not use interface type hint here because only class B have some unique features class D requires):

class D
{
    public function foo(B $bar) { /*...*/ }
}

但是，我还有另一个具有相同方法的类，现在希望将C类的对象作为参数(我不能在这里使用接口类型提示，因为只有C类具有E类所需的某些独特功能):

But, I also have another class with the same method which now expectes object of class C as an argument (I can not use interface type hint here because only class C have some unique features class E requires):

class E
{
    public function foo(C $bar); { /*...*/ }
}

并且必须在其他地方使用类D和E的对象，并且我必须确保这些对象将具有方法foo，所以我得到了以下(抽象类在这里不是一个错误) ，而不应该使用接口，因为在现实生活中此类也应该包含一些非抽象方法):

And objects of class D and E have to be used somewhere else and I have to make sure that these objects will have method foo, so I ended up with the following (abstract class is not a mistake here, should not use interface instead, because in real life this class should contain some non-abstract methods too):

abstract class DE
{
    abstract public function foo(A $bar); // type-hint interface
}

然后我编辑了我的班级，以便他们扩展班级DE:

Then I edited my classes so they extend class DE:

class D extends DE 
{
    public function foo(B $bar); // class B implements A
}

class E extends DE 
{
    public function foo(C $bar); // class C implements A
}

在我看来，这段代码在逻辑上是有效的，因为我们可能会在本文中尝试描述这种情况，但是我很惊讶地看到致命错误并显示以下消息: Declaration of of. .必须与..

To my mind this code is logically valid, because we may have situations I tried to describe in this post, but I was surprised to see Fatal error with the message : Declaration of .. must be compatible with ..

所以我的问题如下:如何确保几个对象将具有特定的方法，并且每个对象中的该方法将仅接受特定的对象作为参数?

到目前为止，我看到的唯一解决方法是以下内容(，但我相信对此有更好的解决方案):

As of now, the only workaround I see is something like the following (but I believe there is a better solution for this):

interface A {}
class B implements A {}
class C implements A {}

interface DE 
{
    public function foo(A $bar);
}

class D implements DE 
{
    public function foo(A $bar) 
    {
        assert($bar instanceof B);
        /*...*/
    }
}

class E implements DE 
{
    public function foo(A $bar)
    {
        assert($bar instanceof C);
        /*...*/
    }
}

推荐答案

一个问题是类D和E分别需要具体的类B和C.现在，由于您不应该鼓励类继承，因此我将尽量避免在方法签名中放置具体的类.如果您的班级需要使用具体的班级，请不要泄漏该信息，请将其保密.

One problem is classes D and E requiring concrete classes, B and C respectively. Now since you should be discouraging class inheritance I would avoid putting concrete classes in method signatures as much as I can. If your class needs to use a concrete class don’t leak that information, keep it private.

所以最好有:

public function foo(SomethingAbstract $noIdeaWhatIAmButIDoStuff) {
    $concrete = SomethingConcreteThatMakesUseOfAbstract($noIdeaWhatIAmButIDoStuff);
}

than:

public function foo(SomethingConcrete $tmi) {

}

我建议遵循以下思路:

abstract class DE {

    public abstract function foo(A $a);

}

class D extends DE {

    public function foo(A $a) {
        $b = new B($a);
        //do with $b what you please
    }

}

class E extends DE {

    public function foo(A $a) {
        $c = new C($a);
        //now you can use $c which will leverage $a
    }

}

如果B和C对象也需要实现A(例如您的示例)，那么您就有一个装饰器模式.

If B and C objects need also to implement A (like in your example) then you have a decorator pattern.

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