Re: [Boost-bugs] [Boost C++ Libraries] #1179: [boost.python] can not export a union in VC2005sp1

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #1179: [boost.python] can not export a union in VC2005sp1
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-06-26 20:55:11

#1179: [boost.python] can not export a union in VC2005sp1
-------------------------------------------+--------------------------------
  Reporter:  qiaozhiqiang_at_[hidden]  |       Owner:  dave               
      Type:  Bugs                          |      Status:  new                
 Milestone:  To Be Determined              |   Component:  Python             
   Version:  Boost 1.34.0                  |    Severity:  Problem            
Resolution:                                |    Keywords:  python export union
-------------------------------------------+--------------------------------
Old description:

> // Visual V++ 2005(8.0) sp1, union not is_class.
> // because there is BOOST_STATIC_ASSERT(is_class<T>::value) in
> make_instance_impl
> // can not export union. eg, class_<union my_u>
> // can not return_internal_reference<> when not is_class, eg, return
> char*, char&, union u&
> // delete BOOST_STATIC_ASSERT(is_class<T>::value); of make_instance_impl,
> then compile OK, and work not all OK
> boost/python/object/make_instance.hpp
> template <class T, class Holder, class Derived>
> struct make_instance_impl
> {
>     typedef objects::instance<Holder> instance_t;
>
>     template <class Arg>
>     static inline PyObject* execute(Arg& x)
>     {
>                 // must is_class ??
> BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value);
>         BOOST_STATIC_ASSERT(is_class<T>::value);
>
> ///////////////////////////////
> #include <boost/python.hpp>
> using namespace boost::python;
>
> union my_u
> {
>         int a;
>         char b;
>         char& get_ref()
>         {
>                 return b;
>         }
>         char* get_ptr()
>         {
>                 return *b;
>         }
> }
>
> struct my_s
> {
>         my_u u;
>         my_u& get_ref()
>         {
>                 return u;
>         }
>         my_u* get_ptr()
>         {
>                 return &u;
>         }
> };
>
> void my_module()
> {
>
>         //1. compile ERROR: my_u not is_class, my_u is_union, I modify
> one line in make_instance.hpp
>         // BOOST_STATIC_ASSERT(is_class<T>::value)      to
> BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value)
>         // and work OK, why not export an union?
>         class_<my_u > u_class("my_u", init< >());
>         u_class.def_readwrite("a", &my_u::a);
>         u_class.def_readwrite("b", &my_u::b);
>

>         //2. compile ERROR:  char not is_class, delete
> BOOST_STATIC_ASSERT(is_class<T>::value), but run error
>         u_class.def("get_ref", &my_u::get_ref, return_internal_reference<
> >());
>
>         //3. compile ERROR:  char not is_class, delete
> BOOST_STATIC_ASSERT(is_class<T>::value), but run error
>         u_class.def("get_ptr", &my_u::get_ptr, return_internal_reference<
> >());
>
>         //4. compile OK, but run ERROR, I need it return a char
>         .def("get_value", &my_u::get_ptr,
>                  return_value_policy<return_by_value>());
>
>         //5. compile ERROR, char* is not a reference, I need but have no
> copy_non_const_pointer
>         u_class.def("get_copy", &my_u::get_ptr,
>                  return_value_policy<copy_non_const_reference>());
>

>         class_<my_s >  s_class("my_s", init<  >());
>
>         //6. compile OK, buy run ERROR:
>         // s = my_s()
>         // s.u.a = 100
>         // print s.u.a
>         // but output s.u.a != 100  !!!
>         // s.u.a = 100  is  s.get_u().set_a(100) and get_u() not return
> u(is_union) by ref ?
>         s_class.def_readwrite("u", &my_s::u);
>
>         // 7. compile ERROR: my_u not is_class, is_union, modify
> BOOST_STATIC_ASSERT(is_class<T>::value)        to
>         // BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value)
>         s_class.def("get_ptr", &my_s::get_ptr,
> return_internal_reference<>());
>         s_class.def("get_ref", &my_s::get_ref,
> return_value_policy<return_by_value>());//compile ok
> }

New description:

 {{{
 // Visual V++ 2005(8.0) sp1, union not is_class.
 // because there is BOOST_STATIC_ASSERT(is_class<T>::value) in
 make_instance_impl
 // can not export union. eg, class_<union my_u>
 // can not return_internal_reference<> when not is_class, eg, return
 char*, char&, union u&
 // delete BOOST_STATIC_ASSERT(is_class<T>::value); of make_instance_impl,
 then compile OK, and work not all OK
 boost/python/object/make_instance.hpp
 template <class T, class Holder, class Derived>
 struct make_instance_impl
 {
     typedef objects::instance<Holder> instance_t;

     template <class Arg>
     static inline PyObject* execute(Arg& x)
     {
                 // must is_class ?? BOOST_STATIC_ASSERT(is_class<T>::value
 || is_union<T>::value);
         BOOST_STATIC_ASSERT(is_class<T>::value);

 ///////////////////////////////
 #include <boost/python.hpp>
 using namespace boost::python;

 union my_u
 {
         int a;
         char b;
         char& get_ref()
         {
                 return b;
         }
         char* get_ptr()
         {
                 return *b;
         }
 }

 struct my_s
 {
         my_u u;
         my_u& get_ref()
         {
                 return u;
         }
         my_u* get_ptr()
         {
                 return &u;
         }
 };

 void my_module()
 {

         //1. compile ERROR: my_u not is_class, my_u is_union, I modify one
 line in make_instance.hpp
         // BOOST_STATIC_ASSERT(is_class<T>::value)      to
 BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value)
         // and work OK, why not export an union?
         class_<my_u > u_class("my_u", init< >());
         u_class.def_readwrite("a", &my_u::a);
         u_class.def_readwrite("b", &my_u::b);


         //2. compile ERROR:  char not is_class, delete
 BOOST_STATIC_ASSERT(is_class<T>::value), but run error
         u_class.def("get_ref", &my_u::get_ref, return_internal_reference<
 >());

         //3. compile ERROR:  char not is_class, delete
 BOOST_STATIC_ASSERT(is_class<T>::value), but run error
         u_class.def("get_ptr", &my_u::get_ptr, return_internal_reference<
 >());

         //4. compile OK, but run ERROR, I need it return a char
         .def("get_value", &my_u::get_ptr,
                  return_value_policy<return_by_value>());

         //5. compile ERROR, char* is not a reference, I need but have no
 copy_non_const_pointer
         u_class.def("get_copy", &my_u::get_ptr,
                  return_value_policy<copy_non_const_reference>());


         class_<my_s >  s_class("my_s", init<  >());

         //6. compile OK, buy run ERROR:
         // s = my_s()
         // s.u.a = 100
         // print s.u.a
         // but output s.u.a != 100  !!!
         // s.u.a = 100  is  s.get_u().set_a(100) and get_u() not return
 u(is_union) by ref ?
         s_class.def_readwrite("u", &my_s::u);

         // 7. compile ERROR: my_u not is_class, is_union, modify
 BOOST_STATIC_ASSERT(is_class<T>::value)        to
         // BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value)
         s_class.def("get_ptr", &my_s::get_ptr,
 return_internal_reference<>());
         s_class.def("get_ref", &my_s::get_ref,
 return_value_policy<return_by_value>());//compile ok
 }
 }}}

Comment (by dave):

 Fix formatting mess

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/1179#comment:1>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.