inheritance - PHP Abstract class return type of child class

Solution:

ThatreturnType should beMyAbstractClass, without any implementation (child implements).

This might not be possible, but the child can return an instance of it's own. For dynamic configuration the$model can have configurations specific to the parent - and the child.

Make everything abstract, withabstract class andabstract static function:

abstract class Model {
    abstract static function fromArray( array $model ): Model;
    abstract static function fromID( int $id ): Model;
}

class LightSettings extends Model {
    public function __construct( array|null $config ) {
        parent::__construct( $config );
    }
    static function fromArray( array $model ): LightSettings {
        return new LightSettings( $model );
    } 
    static function fromID( int $$preset_id ): LightSettings {
        return new LightSettings( null )->load( $preset_id );
    }
    ...
}
Copy code

The constructor obviously could as well takeint $$preset_id, but it's flexible.

Solution:

Intended this to be a comment but it is too long for a comment.

Building on Martin Zeitler's answer (sorry Martin, I'm copying your code here below) with an extra static method in the Model class:

abstract class Model {
    abstract static function fromArray( array $model ): Model;
    abstract static function fromID( int $id ): Model;

    // Common stuff for the fromArray factory
    protected static function populateFromArray(Model $model, array $modelArray): Model {
    // Do whatever is common here
    return $model;
}

class LightSettings extends Model {
    static function fromArray( array $model ): LightSettings {
        return parent::populateFromArray(new LightSettings(), $model);
    }
enter code here
    static function fromID( int $$preset_id ): LightSettings {
        // Similar implementation as in fromArray()
    }
    ...
}
Copy code

Solution:

Ok, your question was:

How can an abstract class in PHP return the type of the child extending it?

respectively

How can i define the return type of that function in the MyAbstractClass so that no mather what child calls that method it will return the child's class instead of the parent one.

Short answer is: you can't

Inheritance works top to bottom... under no circumstance can a parent class know it's children.

Imagine a framework. Classes from the framework are intended to be derived. But not the author of the framework writes the inherited class, but some developer who has downloaded that framework and uses it in his/her project. And there can thousands of developers who have done the same, but with different child classes. How would the author of the framework would know all the derived classes? He can't, right?