use someClass\sub as Class;
use someAnotherClass\sub as AnotherClass;
$class = "Class\DummyClass";
$anotherClass = "AnotherClass\DummyClass";
call_user_func([new $class, "function"]);
call_user_func([new $anotherClass, "anotherFunction"]);
> Fatal error: Uncaught Error: Class 'Class\DummyClass' not found ...