🪧 Generics, covariance, and @method

[arnapou]

Hello,

I am afraid to open here a discussion which is already answered somewhere.

Introduction

PHPStan may not support what I am looking to do, and that's OK.
I couldn't find by myself the answer to that, if I missed something, don't hesitate to kick my ass 😅 .

What I want to do

I have a bunch of classes with a signature like that where ZZZ may vary.

class MyClass {
    public function foo(ZZZRequest $request): void {
        // ...
    }
}

All these ZZZRequest objects implements a same interface.

Because of contravariance, I don't want to declare the foo method into the interface.
👇 Doing this is not what I want because I cannot restrict the type in the implementations.

interface MyClassInterface {
    public function foo(RequestInterface $request): void;
}

I was then trying to play around with the @method phpdoc to achieve this goal

• let the implementation use the precise types of requests
• use PHPStan to enforce the types used in implementation in a covariant way.

What I tried so far

https://phpstan.org/r/523f2735-d2ca-420a-9c46-8089ff42aa03

// ━━━━━━━━━ Interface declaration ━━━━━━━━━

/**
 * @template-covariant T of object
 *
 * @method void test(T $k)
 */
interface IFace { }

// ━━━━━━━━━ Expected SUCCESS ━━━━━━━━━

/**
 * @implements IFace<stdClass>
 */
class Working implements IFace {
    public function test(stdClass $k): void { }
}

// ━━━━━━━━━ Expected FAILURE ━━━━━━━━━

/**
 * @implements IFace<int>
 */
class PhpdocNotCovariant implements IFace {
    public function test(int $k): void { }
}

/**
 * @implements IFace<stdClass>
 */
class PhpdocCovariantButNotReal implements IFace {
    public function test(int $k): void { }
}

Warning

You can see that when you respect the phpdoc generic covariant type, the method type is not checked by PHPStan.

That's may be normal, but it is a bit confusing.

[ondrejmirtes]

Generics provide a way how to solve this parameter contravariance problem. It's described here: https://phpstan.org/blog/generics-in-php-using-phpdocs#these-rules-are-useful%2C-but-sometimes-limiting

In your case it'd look like this: https://phpstan.org/r/ae194a3c-529c-44f5-a0bc-566af710a14d

[arnapou]

Thank you.
I missed that page even if I know all that (already used hundred of time in other projects).

What I missed to mention is that I wanted a hard-php-typed-argument 100% safe at runtime.

Thank you for your time 🤗.
I now know that there is no way to achieve my goal.

synthesis

	hard typing	phpstan help for covariance	runtime type-check
1️⃣ method(TYPE $arg)	✅	❌	✅ no need
2️⃣ method(IFACE $arg)	❌	✅	❌ need is debatable

conclusion

If I want the help of PHPStan + runtime type check 👉️ I then need to ensure the type at runtime in my method (instanceof, assert, whatever which does the job).