UnionTypes.php

<?php
class Foo {
    public function run(): string {
        return __CLASS__;
    }
}

class Bar {
    public function run(): string {
        return __CLASS__;
    }
}

class FooBar {
    public function execute(Foo|Bar $executable): string|int {
        return $executable->run();
    }
}

$fooBar = new FooBar;
echo $fooBar->execute(new Foo);
echo $fooBar->execute(new Bar);