finally got all those copy / assgnment flavours straight.
Still unsolved: unable to instantiate the Variant template
for a type with private assignment operator (like e.g. Time )
The problem is our virtual assignement operator, which forces
instantiation of the implementation (for the VTable), even if
the actual assignment is never invoked.
- we do not want type mutations
- we do not want "empty" records ever
- we do not support "probing" for contents
- visitor style access for generic value handling
