[C++-sig] extract<> with custom shared pointers

[Holger Brandsmeier]

Dear Boost::python experts,

I am trying to use a custom shared pointer type instead of
boost::shared_pointer, in my case Teuchos::RCP from the Trilinos
project. The details of Teuchos::RCP should not matter much here. In
any case there is a Doxygen documentation on the Trilinos webpage.

For completeness I attached a simple example code, but let me explain
here the problem. I have two simple classes A and B, where B is
derived from A.

The C++-functions:

void computeOnA(Teuchos::RCP<A> a)
{
    a->a *= 2;
}
and

void computeOnAs(boost::shared_ptr<A> a)
{
    a->a *= 2;
}
both work nicely from python.

The function

void computeOnTupleOfAs(const tuple& as)
{
  for(int i = 0; i < len(as); ++i) {
    boost::shared_ptr<A> a = extract<boost::shared_ptr<A> >(as[i]);
    computeOnAs(a);
  }
}
also works nicely, given both tuples containing instances of A or the
derived class B as expected.

However the function:
void computeOnTupleOfA(const tuple& as)
{
  for(int i = 0; i < len(as); ++i) {
    Teuchos::RCP<A> a = extract<Teuchos::RCP<A> >(as[i]);
    computeOnA(a);
  }
}
only works given tuples of A and not the derived class B, the
following error is shown:

TypeError: No registered converter was able to produce a C++ rvalue of
type Teuchos::RCP<A> from this Python object of type B.

So my question is, which magic do I need to do (I am willing to use
certain internals of boost::python) so that B elements can be
extracted from tuples of Bs.

I currently only provide the functions:
  T* get_pointer(Teuchos::RCP<T> const& p)
  T* get_pointer(Teuchos::RCP<T>& p)

Thanks for any help,
Holger
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