[Rivet] Dangerous casting to FinalState

[Frank Siegert]

Hi Andy,

> Does that problem disappear if you define remainder as a reference,
> either as VetoedFinalState& or FinalState&?

Yes, even for FinalState& the problem disappears. That's case 2a in my
original examples.

> It would also be useful if you could use the -l TRACE flag (if I
> remember the syntax correctly) when running, and send the resulting log
> so we can see if that parent address corresponds to something. Offhand
> it looks like a bit of an odd address value: is this the sort of pointer
> value that corresponds to a non-heap-allocated local?

I have no idea on the pointer value here, but I have put the full log into
http://cern.ch/fsiegert/tmp/trace.log

> When assigning a Projection like this, a copy will be made. Does
> VetoedFinalState have a copy assignment operator, copy constructor, etc.
> defined as per the Rule of Three
> (http://en.wikipedia.org/wiki/Rule_of_three_%28C%2B%2B_programming%29)
> to make this safe? I genuinely can't remember if we do that, since
> copying of projections isn't really the idea. If we don't perhaps we
> could make it a rule in Projection implementation to always hide (i.e.
> make private) the copy constructor and copy assignment operators to
> simply ban copy by value and hence force use of references. I forget if
> this can be done on the Projection base class or if each new derived
> class would need to explicitly re-hide them. Anyway, food for thought
> albeit not quite at black belt level ;-)

We don't seem to explicitly define any of the three (copy assignment
operator, copy constructor, destructor). I guess the copying that you
mean stems from the clone() function, which probably is using the
constructor from a FinalState instead of a copy constructor? If our
projection registration/cloning can't cope with normal C++ copying
then we should indeed either fix it or hide the copy
constructors/operators. I have to admit that I didn't even realise
that we are internally cloning projections upon registration, and
whatever magic is connected to that. It's probably nothing
super-urgent to fix, since at least it won't give wrong results. But
I'd expect the black-belts to understand this much better than I
(challenge!).

Cheers,
Frank