[C++-sig] How To Determine Return Policy???

[chuzo okuda]

I would like to know how to set correct return policy? It took me quite
a while to narrow down to where the problem was. So, my question is:

How do I determine which return policy should I be using???

In the example of test/test_pointer_adoption.cpp, it uses
return_internal_reference as in:

.def("get_inner", &A::get_inner, return_internal_reference<>())

and

struct A {
<snip>
    inner& get_inner() {return x;}
    inner x;
};

Initially I used return_internal_reference because of the above example
and if you replace inner with string in struct A, it made sense to me to
use return_internal_reference...
Here are codes that must use a specific return policy with my
comments...

------------ source code ------------------
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_internal_reference.hpp>
#include <boost/python/copy_non_const_reference.hpp>
#include <boost/python/return_value_policy.hpp>

class Tag {
public:
   Tag():mName("") {}
   Tag(const std::string& name):mName(name) {}
   ~Tag() {}
   const std::string& name() const {return mName;}
private:
   std::string mName;
};

BOOST_PYTHON_MODULE_INIT(Test2)
{
   using namespace boost::python;
   module TagMod("Test2");
   TagMod
      .add(
           class_<Tag> ("Tag")
           .def_init()
           .def_init(args<const std::string&>())
           // this line causes compiling errors
           //.def("show", &Tag::name)
           // return_internal_reference compiles, t=Tag("hello") creates
           // instances, but t.show() cause TypeError.
           //.def("show", &Tag::name, return_internal_reference<>())
           // this one works alright...
           .def("show", &Tag::name,
return_value_policy<copy_non_const_reference>())
           )
      ;
}