Service.php

class MyService {
    private $finderFactory;
    
    public function __construct(callable $finderFactory) 
    {
        $this->finderFactory = $finderFactory;
    }
    
    public function findStuff()
    {
        $finder = $this->finderFactory();
        
        $finder->doStuff();
        ...
    }
}

    $finder = $this->finderFactory();

won't work. I know it's just an example :)