How to return an interface of a generic type instead of a generic itself?

[dr0bz]

class Car
{
}

/**
 * @template S of object
 */
interface BuilderInterface
{
    /**
     * @return S
     */
    public function build(): object;
}

/**
 * @implements BuilderInterface<Car>
 */
class CarBuilder implements BuilderInterface
{
    public function build(): object
    {
        return new Car();
    }
    
    public function notAnInterfaceFunc(): void
    {
    }
}

/**
 * @template T of BuilderInterface
 * @param class-string<T> $builderClass
 * @return T
 */
function createBuilder(string $builderClass): BuilderInterface
{   
    return new $builderClass();
}

/**
 * @template T of BuilderInterface
 * @param class-string<T> $builderClass
 * @return BuilderInterface
 */
function createBuilder1(string $builderClass): BuilderInterface
{   
    return new $builderClass();
}

$builder = createBuilder(CarBuilder::class);
\PHPStan\dumpType($builder->build()); // proper return object is of type Car
$builder->notAnInterfaceFunc(); // the function is callable


$builder1 = createBuilder1(CarBuilder::class);
\PHPStan\dumpType($builder1->build()); // return object is 'object'
$builder1->notAnInterfaceFunc(); // is not callable

https://phpstan.org/r/3fa3c78c-fff1-4590-8778-51e7475c470a

Hi,

take a look at both createBuilder() functions. The second one acts like i want and returns an interface of CarBuilder::class, but it doesn't properly sets the generic type for the CarBuilder class.

What i want:

• $builder->build() returns an object of type Car
• createBuilder() returns only the BuilderInterface. notAnInterfaceFunc() should not be callable.

Best regards and thanks,
dr0bz

[mad-briller]

Is this what you are after?

https://phpstan.org/r/f7afea05-b6b5-4941-9d49-30118ff45252

[dr0bz]

Thanks for fast reply!

No i want, that BuilderInterface::build() returns the Car instance, like the line:19 declares. Any thoughts?

[mad-briller]

how about this?
https://phpstan.org/r/3fcea396-18ae-4d4e-8b0f-cdd808fa5dd7

[dr0bz]

YES! That's how it should work. Nice!

As a downside phpactor is not understanding in that case, that $builder->build() returns a Car - no autocompletion :(

class Car
{
    public function getName(): string
    {
        return 'Trabant';
    }
}

getName() is not suggested in that case. PHPStorm on his side is managing this. But only on that example. I have a more advanced implementation in my project (with your suggestion now), where PHPStorm sucks as well - dumpType() show the right type.

However, thanks!

[dr0bz]

Let's see whether Phpactor can fix it or suggest something.

phpactor/phpactor#2641

P.S.: @mad-briller 'downside' above is the wrong word:) Your solution is top. It's more my disappointment that there is no autocompletion support.