Class unions in package distr defined for internal
purposes; these are OptionalNumeric,
Arguments
Objects from the Class
All of these classes are virtual:
No objects may be created from them.
Details
These classes are used internally to make available methods or to allow
slots of classes to be filled with varying types. In particular
"OptionalNumeric": may contain objects of class "numeric"
or "NULL"; it is used e.g. for slot nuisance of class
"ParamFamParameter", as it may or may not be present but if so
it has to be numeric.