参数类型可以在PHP中专用吗 [英] Can parameter types be specialized in PHP

问题描述

说我们有以下两个类:

abstract class Foo {
    public abstract function run(TypeA $object);
}

class Bar extends Foo {
    public function run(TypeB $object) {
        // Some code here
    }
}

TypeB类扩展了TypeA类.

The class TypeB extends the class TypeA.

尝试使用此方法会产生以下错误消息:

Trying to use this yields the following error message:

Bar :: run()的声明必须与Foo :: run()的声明兼容

在涉及参数类型时，PHP真的被打破了吗?还是我只是在这里遗漏了一点?

Is PHP really this broken when it comes to parameter types, or am I just missing the point here?

推荐答案

---

自 PHP 7.4(部分自7.2).

---

This answer is outdated since PHP 7.4 (partially since 7.2).

您描述的行为称为 协方差 并且在PHP中根本不支持.我不了解内部结构，但我可能会怀疑，在应用所谓的类型提示"检查时，PHP的核心根本不会评估继承树.

The behavior you describe is called covariance and is simply not supported in PHP. I don't know the internals but I might suspect that PHP's core does not evaluate the inheritance tree at all when applying the so called "type hint" checks.

顺便说一句，PHP也不支持 contravariance 上的这些类型提示(其他OOP语言通常支持的功能)-最有可能是上面提到的原因.因此，这也不起作用:

By the way, PHP also doesn't support contravariance on those type-hints (a feature commonly support in other OOP languages) - most likely to the reason is suspected above. So this doesn't work either:

abstract class Foo {
    public abstract function run(TypeB $object);
}

class Bar extends Foo {
    public function run(TypeA $object) {
        // Some code here
    }
}

最后是更多信息: 查看全文