In case you have a public readonly property in a class you need to extend, adding other properties, this can be a way to do it:

<?php

class A {
    public function __construct(
        public readonly int $prop
    ) {}
}

class B extends A {
    public function __construct(
        int $prop,
        public readonly int $prop2
    ) {
        parent::__construct($prop);
    }
}
?>