boost::python string-convertible properties

I have a C++ class, which has the following methods: ``` class Bar { ... const Foo& getFoo() const; void setFoo(const Foo&); }; ``` where class `Foo` is convertible to `std::string` (it has an implicit constructor from `std::string` and an `std::string` cast operator). I define a Boost.Python wrapper class, which, among other things, defines a property based on previous two functions: ``` class_<Bar>("Bar") ... .add_property( "foo", make_function( &Bar::getFoo, return_value_policy<return_by_value>()), &Bar::setFoo) ... ``` I also mark the class as convertible to/from `std::string`. ``` implicitly_convertible<std::string, Foo>(); implicitly_convertible<Foo, std::string>(); ``` But at runtime I still get a conversion error trying to access this property: ``` TypeError: No to_python (by-value) converter found for C++ type: Foo ``` How to achieve the conversion without too much boilerplate of wrapper functions? (I already have all the conversion functions in class `Foo`, so duplication is undesirable.