[C++-sig] doing iterators another way...

[Leonard "paniq" Ritter]

the approach below has the flaw that recursive iterations will fail 
since the enumerator is not cloned. for that purpose i added a Clone() 
method to the enumerator interface which is called in 
MakePythonIteratorFromEnumerator, where a Ptr<T> (a custom smart pointer 
class) is returned, hence suspending the need for a return value call 
policy.

Leonard "paniq" Ritter wrote:

> the example that is given in the tutorial for iterators is giving a 
> standard way of solving the problem for c++ iterators, but i'm also 
> using enumerators which provide a set of current/next/reset commands. 
> for those interested, this is how i turned my class into an iterator:
>
>        template<typename T>
>        struct Enumerator : Mu::Interface::Unknown
>        {                      typedef typename Ptrfy<T>::Type 
> ElementReturnType;
>
>            virtual Mu::Result Mu_InterfaceCall MoveNext(Bool& 
> succeeded) = 0;
>            virtual Mu::Result Mu_InterfaceCall Current(T& current) = 0;
>            virtual Mu::Result Mu_InterfaceCall Reset() = 0;
>
>            Mu_WrapGetMethod(MoveNext,Bool);
>            Mu_WrapGetMethod(Current,ElementReturnType);
>        };
>
>        template<typename T>
>        typename T::ElementReturnType iterator_next(T* enumerator)
>        {
>            if (!enumerator->MoveNext())
>            {
>                PyErr_SetString(PyExc_StopIteration,"");
>                boost::python::throw_error_already_set();
>            }
>            return enumerator->Current();
>        }
>
>        template<typename T>
>        T* MakePythonIteratorFromEnumerator(T* enumerator)
>        {                      enumerator->Reset();
>            return enumerator;
>        }
>
>    and here's some pseudo-boost.python code:
>
>    class_<EnumeratorClass, bases<Mu::Interface::Unknown> 
> >("EnumeratorClass")
>        .def("__iter__", 
> &MakePythonIteratorFromEnumerator<EnumeratorClass>, 
> return_internal_reference<>())
>        .def("next", &iterator_next<EnumeratorClass>)
>   ;
>
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