[C++-sig] Regression in Boost.Python v1.33

[Niall Douglas]

On 12 Oct 2005 at 11:41, David Abrahams wrote:

> > Any movement on the below? Do you want me to submit a patch to 
> > type_traits or just to BPL?
> 
> >> 1. The best solution is to patch type_traits::add_reference<> with a 
> >> specialisation for void whereby it won't ever add a reference to a 
> >> void. AFAIK it's an illegal type anyway. 
> 
> I am surprised that add_reference doesn't already act that way.  If
> that is enough to fix your problem, I think you should post, and we
> should accept, the patch.

You were right that add_reference /does/ already act that way. I 
tried a test example with the same form as the bug and no matter what 
I do, the compiler compiles it just fine.

Whatever is going on, it seems that you need to be deep down inside 
BPL to see it :(

The easiest solution is a specialisation for const volatile void, 
exampled by the attached registered.hpp.

Cheers,
Niall




-------------- next part --------------
// Copyright David Abrahams 2002.
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#ifndef REGISTERED_DWA2002710_HPP
# define REGISTERED_DWA2002710_HPP
# include <boost/python/type_id.hpp>
# include <boost/python/converter/registry.hpp>
# include <boost/python/converter/registrations.hpp>
# include <boost/type_traits/transform_traits.hpp>
# include <boost/type_traits/cv_traits.hpp>
# include <boost/detail/workaround.hpp>

namespace boost {

// You'll see shared_ptr mentioned in this header because we need to
// note which types are shared_ptrs in their registrations, to
// implement special shared_ptr handling for rvalue conversions.
template <class T> class shared_ptr;

namespace python { namespace converter { 

struct registration;

namespace detail
{
  template <class T>
  struct registered_base
  {
      static registration const& converters;
  };
}

template <class T>
struct registered
  : detail::registered_base<
        typename add_reference<
            typename add_cv<T>::type
        >::type
    >
{
};

# if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) \
    && !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310))
// collapses a few more types to the same static instance.  MSVC7.1
// fails to strip cv-qualification from array types in typeid.  For
// some reason we can't use this collapse there or array converters
// will not be found.
template <class T>
struct registered<T&>
  : registered<T> {};
# endif

//
// implementations
//
namespace detail
{
  inline void
  register_shared_ptr0(...)
  {
  }
  
  template <class T>
  inline void
  register_shared_ptr0(shared_ptr<T>*)
  {
      registry::lookup_shared_ptr(type_id<shared_ptr<T> >());
  }
  
  template <class T>
  inline void
  register_shared_ptr1(T const volatile*)
  {
      detail::register_shared_ptr0((T*)0);
  }
  
  template <class T>
  registration const& 
  registry_lookup()
  {
      detail::register_shared_ptr1((T*)0);
      return registry::lookup(type_id<T&>());
  }

  template <>
  registration const& 
  registry_lookup<const volatile void>()
  {
      detail::register_shared_ptr1((void*)0);
      return registry::lookup(type_id<void>());
  }

  template <class T>
	  registration const& registered_base<T>::converters = detail::registry_lookup<typename remove_reference<T>::type>();

}

}}} // namespace boost::python::converter

#endif // REGISTERED_DWA2002710_HPP