Missing attribute `class` of service-factory

[lex111]

As of Symfony 3.3 when using factory-service without specifying a class attribute, this warning will be displayed:

PHP Deprecated: Relying on its factory's return-type to define the class of service "app.factory.translator" is deprecated since Symfony 3.3 and won't work in 4.0. Set the "class" attribute to ... on the service definition instead

It is necessary to supplement the information on this page, that it is necessary to specify the class attribute with the name of the class that the factory creates.