From joker.eph at gmail.com  Sat Apr 19 09:27:18 2014
From: joker.eph at gmail.com (Mehdi AMINI)
Date: Sat, 19 Apr 2014 00:27:18 -0700
Subject: [C++-sig] Fail to initialize boost::python::object with a class
 with an overloaded operator&
Message-ID: <53522556.9020209@gmail.com>

Hi,

Possibly related but old: 
https://mail.python.org/pipermail/cplusplus-sig/2005-October/009304.html

Trying to create a boost::python::object with an instance of a class 
that has a "crazy" operator& fails here:

boost/python/converter/arg_to_python.hpp:209:9: error: no matching 
constructor for initialization of 
'boost::python::converter::detail::arg_to_python_base'
       : arg_to_python_base(&x, registered<T>::converters)

Replacing "&x" with "addressof(x)" solve the issue, if you don't see any 
drawback I suggest it could be changed in the next release :)


Note:

I know that overloading wildy the operator& is considered as bad, but my 
sample code seems quite "standard":

   std::vector<bool> v { true };
   boost::python::object b_(v[0]);

It fails when compiling with libc++ as they handle (the infamous) 
std::vector<bool> in a (non standard) way similar as std::bitset and 
provided a class to wrap reference to element of the vector.
This __bit_reference overloads the operator& to return a __bit_iterator, 
which breaks boost::python::object initialization.


The trace is:

include/boost/python/converter/arg_to_python.hpp:256:7: note: in 
instantiation of member function 
'boost::python::converter::detail::value_arg_to_python<std::__1::__bit_reference<std::__1::vector<bool, 
std::__1::allocator<bool> >, true> >::value_arg_to_python'
       requested here
     : base(x)
       ^
include/boost/python/object_core.hpp:393:33: note: in instantiation of 
member function 
'boost::python::converter::arg_to_python<std::__1::__bit_reference<std::__1::vector<bool, 
std::__1::allocator<bool> >, true> >::arg_to_python' requested here
           return python::incref(converter::arg_to_python<T>(x).get());
                                            ^
include/boost/python/object_core.hpp:312:10: note: in instantiation of 
function template specialization 
'boost::python::api::object_initializer_impl<false, 
false>::get<std::__1::__bit_reference<std::__1::vector<bool, 
std::__1::allocator<bool> >, true> >'
       requested here
       >::get(
          ^
include/boost/python/object_core.hpp:334:23: note: in instantiation of 
function template specialization 
'boost::python::api::object_base_initializer<std::__1::__bit_reference<std::__1::vector<bool, 
std::__1::allocator<bool> >, true> >' requested here
         : object_base(object_base_initializer(x))
                              ^
helloworld.cpp:28:25: note: in instantiation of function template 
specialization 
'boost::python::api::object::object<std::__1::__bit_reference<std::__1::vector<bool, 
std::__1::allocator<bool> >, true> >' requested here
   boost::python::object b_(v[0]);
                                         ^
include/boost/python/converter/arg_to_python_base.hpp:20:7: note: 
candidate constructor not viable: no known conversion from 
'__bit_iterator<std::__1::vector<bool, std::__1::allocator<bool> >, 
false>' to 'const volatile void *' for 1st argument
       arg_to_python_base(void const volatile* source, registration const&);
       ^

Best,

Mehdi