[C++-sig] Boost Python: Howto wrap "out" arguments of a methode

[Alexander Eisenhuth]

David Abrahams schrieb:
> on Mon Jun 04 2007, Alexander Eisenhuth <newsuser-AT-stacom-software.de> wrote:
> 
>> How to wrap methode Get with Boost.Python?
> 
> First, I suggest you take your question to the C++-sig
> (http://www.boost.org/more/mailing_lists.htm#cplussig).
> 
> 
>>       class MyClass {
>>       public:
>>           MyClass();
>>
>>           void GetX(double &pos_x);
>> [...]
>>
>>
>> I'v tried it with:
>>
>>           .def(
>>               "GetX"
>>               , &::MyClass::GetX
>>               , bp::arg("")
>>               , bp::return_value_policy<bp::return_arg<1>() >()
>>
>> But when I try it in python:
>>
>> Boost.Python.ArgumentError: Python argument types in
>>       MyClass.GetX(MyClass, int)
>> did not match C++ signature:
>>       GetX(class MyClass::LedPosition_C {lvalue}, int {lvalue} )
>>
>> Any ideas?
> 
> return_value_policy is only good for telling Boost.Python how to
> handle the actual (non-void) return value of your C++ function.  In
> your case, create a thin wrapper function:

Ok, thanks for that hint.

> 
>      double GetX2(MyClass& self, double pos_x) 
>      { self.GetX(pos_x); return pos_x; }
> 
> and wrap that instead of GetX:
> 
>            .def("GetX", GetX2)
> 

So boost.python doesn't have a mechanism to transform in the wrapper code a call 
by reference into return value?