Re: [Boost-users] [boost::variant] problem with swap

Subject: Re: [Boost-users] [boost::variant] problem with swap
From: Ondrej Kuncar (kxenator_at_[hidden])
Date: 2009-12-20 11:44:47

On 20.12.2009 16:53, Steven Watanabe wrote:
> AMDG
> 
> Ondrej Kuncar wrote:
>> I have problems to compile this code with Visual Studio 9.0 SP1 and
>> Boost 1.41:
>>
>> -------------------------------------------------------------------
>>
>> #include <boost/variant.hpp>
>> #include <deque>
>>
>> typedef boost::variant<std::deque<int>::iterator> SemanticValue;
>>
>> int main() {
>>     SemanticValue v1;
>>     SemanticValue v2;
>>     v1.swap(v2);
>> }
>>
>> -------------------------------------------------------------------
>>
>> I got this error:
>>
>> c:\program files\boost\boost_1_41_0\boost\variant\detail\move.hpp(155) :
>> error C2668: 'std::swap' : ambiguous call to overloaded function
>>         c:\program
>> files\boost\boost_1_41_0\boost\variant\detail\move.hpp(141): could be
>> 'void boost::detail::variant::detail::move_swap::swap<T>(T &,T &)'
>>         with
>>         [
>>             T=T0
>>         ]
>>         c:\program files\microsoft visual studio
>> 9.0\vc\include\utility(16): or       'void std::swap<T>(_Ty &,_Ty &)'
>> [found using argument-dependent lookup]
>>         with
>>         [
>>             T=T0,
>>             _Ty=T0
>>         ]
>>         while trying to match the argument list '(T0, T0)'
>> <snip>
>>
>>
>> Do you have any ideas?
>>   
> 
> This is a known bug.  I believe that there's an open trac ticket
> for it.  I don't think anyone has found a good solution yet.
> 
> In Christ,
> Steven Watanabe

You are right, it's https://svn.boost.org/trac/boost/ticket/2839
It seems for me that only reasonable workaround is the following hack:

------------------------------------------------------------------

#include <boost/variant.hpp>
#include <deque>

typedef boost::variant<std::deque<int>::iterator> SemanticValue;

namespace std {
        inline void swap(std::deque<int>::iterator &s1,
std::deque<int>::iterator &s2) {
                std::swap<std::deque<int>::iterator>(s1,s2);
        }
}

int main() {
        SemanticValue v1;
        SemanticValue v2;
        v1.swap(v2);
}

------------------------------------------------------------------

OK