Add generics to ContainerInterface

Author: loic425

src/ContainerInterface.php

@@ -12,12 +12,14 @@ interface ContainerInterface
     /**
      * Finds an entry of the container by its identifier and returns it.
      *
-     * @param string $id Identifier of the entry to look for.
+     * @template T of mixed
+     *
+     * @param T|string $id Identifier of the entry to look for.
      *
      * @throws NotFoundExceptionInterface  No entry was found for **this** identifier.
      * @throws ContainerExceptionInterface Error while retrieving the entry.
      *
-     * @return mixed Entry.
+     * @return T|mixed Entry.
      */
     public function get(string $id);