[C++-sig] Re: implicitly_convertible<> & auto_ptr

[Nicolas Lelong]

> Can't you do it with a wrapper?
> addBigDataDerived(BigDataStore &store, char const* name,
std::auto_ptr<BigDataDerived> data){store.addBigData(name,data);}
>   python::class_<BigDataStore, boost::noncopyable>("BigDataStore")
>     .def("addBigData", &BigDataStore::addBigData,
python::with_custodian_and_ward<1,2>() )
>     .def("addBigData", &addBigDataDerived,
python::with_custodian_and_ward<1,2>() );

Ooops, by the way, it should be "python::with_custodian_and_ward<1,3>()" but
I do wonder if it's really useful because of the auto_ptr stuff already
stating a transfer of ownership.

>
> I know it isn't very convenient, but it may work;

Yep, thanks, that's a valid workaround that will suit my needs for the
moment. I'm still curious about the implicitly_convertible<> stuff.
I have to train to get the 'wrapper reflex' !

> BTW how is this supposed to work:
>       big = BigDataDerived()
>       bigstore = BigDataStore()
>       bigstore.addBigData('dumb', big)
>       big.doSomething()  ///// <- is it going to crash???

I'm not yet very confident with Python & BPL ownership rules, but it seems
that in the above the transfer of ownership is done, and 'big' is no longer
a 'valid reference' to the object transfered. I added a small 'doSomething'
method, and your test case leads to a friendly 'bad argument type for
built-in operation' which, I suppose, indicates the 'big' object is no
longer accessible via the 'big' symbol.