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

20 Dec 2009


      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