[boost] [1.43.0] [variant] Compilation errors when swapping variant type objects

Subject: [boost] [1.43.0] [variant] Compilation errors when swapping variant type objects
From: Adam Badura (a.badura_at_[hidden])
Date: 2010-09-29 01:50:09

    We are using Boost 1.43.0 (we tried to move to 1.44.0 but there were 
some problems which I reported some time ago) in Visual Studio 2010.
    And there are some compilation problems when variant type objects are 
swapped. This does not affect all variant types but I didn't figured out 
what are the exact conditions (however I guess it is likely something with 
namespaces and templates).

    Following code demonstrates the issue:
----------------------------------------
#include <cstdlib>
#include <list>
#include <boost/variant.hpp>

int main()
{
        typedef boost::variant< std::list< int >::iterator > variant_type;

        variant_type v;
        variant_type().swap( v );

        return EXIT_SUCCESS;
}
----------------------------------------

compilation fails with following message:
----------------------------------------
1>d:\libraries\boost_1_43_0\boost\variant\detail\move.hpp(155): error C2668: 
'boost::detail::variant::detail::move_swap::swap' : ambiguous call to 
overloaded function
1>          d:\libraries\boost_1_43_0\boost\variant\detail\move.hpp(141): 
could be 'void boost::detail::variant::detail::move_swap::swap<T>(T &,T &)'
1>          with
1>          [
1>              T=T0
1>          ]
1>          c:\program files\microsoft visual studio 
10.0\vc\include\utility(100): or       'void std::swap<T>(_Ty &,_Ty &)' 
[found using argument-dependent lookup]
1>          with
1>          [
1>              T=T0,
1>              _Ty=T0
1>          ]
1>          while trying to match the argument list '(T0, T0)'
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(698) : see 
reference to function template instantiation 'void 
boost::detail::variant::move_swap<T>(T &,T &)' being compiled
1>          with
1>          [
1>              T=T0
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(825) : see 
reference to function template instantiation 'void 
boost::detail::variant::swap_with<Variant>::operator ()<T>(T &) const' being 
compiled
1>          with
1>          [
1> 
Variant=boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>,
1>              T=T0
1>          ]
1> 
d:\libraries\boost_1_43_0\boost\variant\detail\visitation_impl.hpp(141) : 
see reference to function template instantiation 'void 
boost::detail::variant::invoke_visitor<Visitor>::internal_visit<T>(T &,int)' 
being compiled
1>          with
1>          [
1> 
Visitor=boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>,
1>              T=T0
1>          ]
1> 
d:\libraries\boost_1_43_0\boost\variant\detail\visitation_impl.hpp(169) : 
see reference to function template instantiation 'void 
boost::detail::variant::visitation_impl_invoke_impl<Visitor,VoidPtrCV,T>(int,Visitor 
&,VoidPtrCV,T *,boost::mpl::false_)' being compiled
1>          with
1>          [
1> 
Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>>,
1>              VoidPtrCV=void *,
1>              T=T0
1>          ]
1> 
d:\libraries\boost_1_43_0\boost\variant\detail\visitation_impl.hpp(252) : 
see reference to function template instantiation 'void 
boost::detail::variant::visitation_impl_invoke<Visitor,VoidPtrCV,T0,NoBackupFlag>(int,Visitor 
&,VoidPtrCV,T *,NoBackupFlag,int)' being compiled
1>          with
1>          [
1> 
Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>>,
1>              VoidPtrCV=void *,
1> 
NoBackupFlag=boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>::has_fallback_type_,
1>              T=T0
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(1769) : see 
reference to function template instantiation 'void 
boost::detail::variant::visitation_impl<first_which,first_step,Visitor,VoidPtrCV,boost::variant<T0_>::has_fallback_type_>(const 
int,const int,Visitor &,VoidPtrCV,boost::mpl::false_,NoBackupFlag,Which 
*,step0 *)' being compiled
1>          with
1>          [
1> 
Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>>,
1>              VoidPtrCV=void *,
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>,
1> 
NoBackupFlag=boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>::has_fallback_type_,
1>              Which=first_which,
1>              step0=first_step
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(1780) : see 
reference to function template instantiation 'void 
boost::variant<T0_>::internal_apply_visitor_impl<Visitor,void*>(int,int,Visitor 
&,VoidPtrCV)' being compiled
1>          with
1>          [
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>,
1> 
Visitor=boost::detail::variant::invoke_visitor<boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>>,
1>              VoidPtrCV=void *
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(1803) : see 
reference to function template instantiation 'void 
boost::variant<T0_>::internal_apply_visitor<boost::detail::variant::invoke_visitor<Visitor>>(boost::detail::variant::invoke_visitor<Visitor> 
&)' being compiled
1>          with
1>          [
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>,
1> 
Visitor=boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(1637) : see 
reference to function template instantiation 'void 
boost::variant<T0_>::apply_visitor<boost::detail::variant::swap_with<Variant>>(Visitor 
&)' being compiled
1>          with
1>          [
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>,
1> 
Variant=boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>,
1> 
Visitor=boost::detail::variant::swap_with<boost::variant<std::_List_iterator<std::_List_val<int,std::allocator<int>>>>>
1>          ]
1>          d:\libraries\boost_1_43_0\boost\variant\variant.hpp(1631) : 
while compiling class template member function 'void 
boost::variant<T0_>::swap(boost::variant<T0_> &)'
1>          with
1>          [
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>
1>          ]
1>          d:\test\simple\simple.cpp(10) : see reference to class template 
instantiation 'boost::variant<T0_>' being compiled
1>          with
1>          [
1> 
T0_=std::_List_iterator<std::_List_val<int,std::allocator<int>>>
1>          ]
----------------------------------------

    Adam Badura