There's no such thing as "throwing by reference". It is simply impossible. There's no syntax for that. Every time you try to "throw a reference", a copy of the referenced object is actually thrown. Needless to say, there are no attempts to throw by reference in your code.

It is possible to catch a previously thrown exception by reference (even by a ...

instead of

in your catch clauses and still get the correctly behaving code, i.e. the original object (with modifications) will continue its flight throgh the handler hierarchy.