[C++-sig] Non-const reference arguments and from_python conversions

[Bilokon, Paul]

P.S. I'm looking at

http://www.boost.org/doc/libs/1_35_0/libs/python/doc/v2/faq.html#questio
n2

And it says

Using custom rvalue converters. Boost.Python "rvalue converters" match
function signatures such as: 
void foo(std::vector<double> const& array); // pass by const-reference
void foo(std::vector<double> array); // pass by value

Does this mean the argument MUST be passed by const-reference or by
value (i.e. it can't be a non-const reference or a pointer)?

Many thanks,
Paul

> _____________________________________________ 
> From: 	Bilokon, Paul  
> Sent:	Tuesday, May 20, 2008 1:56 PM
> To:	Development of Python/C++ integration
> Subject:	Non-const reference arguments and from_python
> conversions
> 
> Hi all,
> 
> I have written a from_python_stream converter for Python streams (like
> sys.stdout).
> 
> The converter registers itself as follows:
> 
>         	boost::python::converter::registry::push_back(
>                 &convertible,
>                 &construct,
>                 boost::python::type_id<_Stream>());
> 
> So nothing unusual here. _Stream is the template argument.
> 
> Then I do the following:
> 
>     StreamConversions::from_python_stream<reference_wrapper<ostream>
> >();
> 
> Again, nothing unusual here.
> 
> I'm testing it on two functions:
> 
> void outTest(const ostream & out)
> {
> 	// cout << "Test-----outTest successful" << endl;
> }
> 
> void outTestRef(ostream & out)
> {
> 	cout << "Test-----outTest successful" << endl;
> }
> 
> Which are registered like this:
> 
>     def("outTest", outTest);
>     def("outTestRef", outTestRef);
> 
> Obviously I need outTestRef to work. Otherwise I can't use operator<<,
> so what's the point.
> 
> Unfortunately, outTest works, outTestRef does not work:
> 
> outTest(sys.stderr) # works
> outTestRef(sys.stderr) # fails
> 
> The error is:
> 
>   File "proto_test.py", line 23, in <module>
>     outTestRef(sys.stderr)
> Boost.Python.ArgumentError: Python argument types in
>     pyamp.proto.outTestRef(file)
> did not match C++ signature:
>     outTestRef(class std::basic_ostream<char,struct
> std::char_traits<char> > {lvalue})
> 
> Hence the question: is there absolutely no support for non-const
> reference arguments?
> 
> Many thanks for your help!
> 
> Regards,
> Paul
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