gistfile1.php

<?php
class MyService
{
    private $repo;

    public function __construct(ObjectRepository $repo)
    {
        $this->repo = $repo;
    }
    
    public function doSomethingConsumingMyRepo()
    {
       $objects = $repo->findAll();
    }
}

//My custom implementation of an ObjectRepository
class SomeRepository implements ObjectRepository
{
    public function findAll()
    {
        //My implementation
    }
}

$repo = new SomeRepository();
new MyService($repo);

//EnityRepository also implements ObjectRepository
$repo = $entityManager->getRepository('MyEntity');
new MyService($repo);

//Both will work because my service depends on the ObjectRepository