[C++-sig] how to wrap getter returning shared_ptr<T>

[Langston, Matthew David]

I answered my own question through trial-and-error experimentation. If I want to have Boost.Python return a "shared_ptr < Bar >", then I must export Bar to python using the second template argument to class_ as follows:

class_< Bar, shared_ptr < Bar > > ( "Bar" ).add_property ("message",
&Bar::get_Message);

Matt

-----Original Message-----
From: Langston, Matthew David 
Sent: Monday, December 09, 2002 4:09 PM
To: 'c++-sig at python.org'
Subject: [C++-sig] how to wrap getter returning shared_ptr<T>

How do I wrap a C++ member function that returns a shared_ptr? Here is an example of what I want to do:

class Bar
{
private:
    std::string m_message;
public:
    Bar() { m_message = "Bar: Hello, world"; }
    std::string get_Message() { return m_message; }
};

class Foo
{
private:
    shared_ptr<Bar> m_bar;
public:
    Foo() : m_bar( new Bar() ) {}
    shared_ptr<Bar> get_Bar() const { return m_bar; }
};


BOOST_PYTHON_MODULE(PyTest)
{
    class_< Bar > ( "Bar" ).add_property ("message", &Bar::get_Message);
    class_< Foo > ( "Foo" ).add_property ("bar"    , &Foo::get_Bar );
}


This code compiles and links fine, but when I try to access Foo::get_Bar from python I get the python error message " TypeError: bad argument type for built-in operation". This is the python script I used:


foo = Foo()
print foo.bar.message


I naively expected Boost.Python to just "do the right thing" w.r.t. a member function returning a boost::shared_ptr. What am I doing wrong?

Warmest regards, Matt

--
Matthew D. Langston
SLD, Stanford Linear Accelerator Center
langston at SLAC.Stanford.EDU


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