PHPStan / @return all possible children that extend specific class

Question

I have a problem with @return types. It seems that either it's a bug in PHPStan or I'm doing something wrong.

abstract class Aclass {}
final class Bclass extends Aclass {}
final class Cclass extends Aclass {}

final class Factory {
    /**
     * @template T of Aclass
     * @param class-string<T> $param
     * @return T
     */
    public function create($param) {
        // some kind of factory logic
        return new Bclass();
    }
}

No error:

abstract class Aclass {}
final class Bclass extends Aclass {}
final class Cclass extends Aclass {}

final class Factory {
    /**
     * @template T of Aclass
     * @param class-string<T> $param
     * @return Aclass
     */
    public function create($param) {
        // some kind of factory logic
        return new Bclass();
    }
}

Why does PHPStan give me an error? Isn't @template T of Aclass + @return T the same as @return Aclass?

I'm expecting no errors.

Olivier · Accepted Answer · 2024-09-01 07:55:09Z

0

T of Aclass means that T is either Aclass or an inherited class.

So, in this case:

final class Factory {
    /**
     * @template T of Aclass
     * @param class-string<T> $param
     * @return T
     */
    public function create($param) {
        // some kind of factory logic
        return new Bclass();
    }
}

T may be Cclass. But the method returns an instance of Bclass, which does not extend Cclass, hence the error.

This code gives no error:

final class Factory {
    /**
     * @template T of Aclass
     * @param class-string<T> $param
     * @return T
     */
    public function create($param) {
        // some kind of factory logic
        return new $param();
    }
}

answered Sep 1, 2024 at 7:55

Olivier

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1 Comment

Slava Basko Over a year ago

Unfortunately return new $param(); is not working for me because of different naming constructors. public function create($param) { // some kind of factory logic if ($condition1) { return Bclass::createOne(); } elseif ($condition2) { return Bclass::createTwo(); } elseif ($condition3) { return Cclass::createThree(); } // etc. throw new \InvalidArgumentException('Invalid class name'); }

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