[C++-sig] Boost Python loss of values

[Jim Bosch]

On 08/26/2011 08:27 AM, Jay Riley wrote:
> Hi Jim,
>
> Thanks for the suggestion, unfortunately it didn't work. It really feels
> like it's making a copy for some reason as once I return to the
>
> int AttackWrapper::CalculateDamage(const
> std::vector<Game::Battles::BattleCharacter*>& users,
> Game::Battles::BattleCharacter* target, const
> std::vector<Actions::ActionTarget>& targets, Game::Battles::BattleField
> *field)
> {
> return call_method<int>(self, "CalculateDamage", users, ptr(target),
> targets, ptr(field));
> }
>
> function, the value are back to their expected value. Slicing wouldn't
> be a problem here would it, since Hit is a member of the base class anyways?
>

Yes, that's right.  What exactly is "self", above?  I assume it's a data 
member of AttackWrapper of type PyObject *, which shouldn't produce a 
copy, but if it's something else, well, that could be a factor.

Jim



>  > Date: Thu, 25 Aug 2011 13:18:04 -0700
>  > From: talljimbo at gmail.com
>  > To: cplusplus-sig at python.org
>  > CC: super24bitsound at hotmail.com
>  > Subject: Re: [C++-sig] Boost Python loss of values
>  >
>  > On 08/25/2011 04:17 AM, Jay Riley wrote:
>  >
>  > >
>  > > And the python exposing is done as follows:
>  > >
>  > > class_<Attack, AttackWrapper, boost::shared_ptr<Attack>, bases<Action>
>  > > >("Attack")
>  > > .def("CalculateDamage", &AttackWrapper::CalculateDamageDefault);
>  > >
>  >
>  > This bit looks a little suspect, and I'm surprised that it compiles -
>  > class_ should only take 4 arguments if one of them is boost::noncopyable.
>  >
>  > I think you mean:
>  >
>  > class_< Attack, boost::shared_ptr<AttackWrapper>, bases<Action> >
>  > (...)
>  >
>  > See
>  >
>  > http://www.boost.org/doc/libs/1_47_0/libs/python/doc/v2/class.html
>  >
>  > for details of the arguments to class_.
>  >
>  > I don't have a good idea as to why this would cause the problem you're
>  > seeing (maybe you're slicing your AttackWrapper instances into Attack
>  > instances?) but I'd recommend fixing it first.
>  >
>  > Good Luck!
>  >
>  > Jim Bosch
>
>
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