Return all of the registered classes.

        :return:  an ``dict`` of task_family -> class

def _get_reg(cls):
        """Return all of the registered classes.

        :return:  an ``dict`` of task_family -> class
        """
        # We have to do this on-demand in case task names have changed later
        reg = dict()
        for task_cls in cls._reg:
            if not task_cls._visible_in_registry:
                continue

            name = task_cls.get_task_family()
            if name in reg and \
                    (reg[name] == Register.AMBIGUOUS_CLASS or  # Check so issubclass doesn't crash
                     not issubclass(task_cls, reg[name])):
                # Registering two different classes - this means we can't instantiate them by name
                # The only exception is if one class is a subclass of the other. In that case, we
                # instantiate the most-derived class (this fixes some issues with decorator wrappers).
                reg[name] = Register.AMBIGUOUS_CLASS
            else:
                reg[name] = task_cls

        return reg