assert_is_S4(x, severity = getOption("assertive.severity", "stop"))
assert_is_s4(x, severity = getOption("assertive.severity", "stop"))
assert_is_ref_class_generator(x, severity = getOption("assertive.severity", "stop"))
assert_is_ref_class_object(x, severity = getOption("assertive.severity", "stop"))
is_s4(x, .xname = get_name_in_parent(x))
is_S4(x, .xname = get_name_in_parent(x))
is_ref_class_generator(x, .xname = get_name_in_parent(x))
is_ref_class_object(x, .xname = get_name_in_parent(x))