[Boost-users] [variant] trouble using recursive_variant with MSVC ...

From: Andy Wu (zilong.wu_at_[hidden])
Date: 2006-11-06 00:48:21

Hi all,

I'm trying to use the recursive variant as following:

    typedef boost::make_recursive_variant<
        int,
        std::vector<boost::recursive_variant_>,
        std::map<std::string, boost::recursive_variant_>
            >::type var_t;

...

var_t var(34);
...

VC 8.0 can not compile with error C2079: 'std::pair<_Ty1,_Ty2>::second' uses
undefined struct 'boost::recursive_variant_'
Struct recursive_variant_ is declared but not implement at all. But GCC
works well. I'm confused how to solve the problem.

Here is the whole program:

#include "boost/variant.hpp"

#include <iostream>
#include <sstream>
#include <vector>
#include <map>

struct vector_printer
: boost::static_visitor<std::string>
{
    template <typename T>
        std::string *operator*()(const std::vector<T>& vec) const
        {
            std::ostringstream ost;

            ost << "( ";

            typename std::vector<T>::const_iterator it = vec.begin();
            *for* (; it != vec.end(); ++it)
                ost << boost::apply_visitor( vector_printer(), *it );

            ost << ") ";

            *return* ost.str();
        }

    template <typename T>
        std::string *operator*()(const std::map<std::string, T>& m) const
        {
            std::ostringstream ost;

            ost << "( ";

            typename std::map<std::string, T>::const_iterator it = m.begin();
            *for* (; it != m.end(); ++it)
                ost << it->first << '\t' << boost::apply_visitor(
vector_printer(), it->second );

            ost << ") ";

            *return* ost.str();
        }

    template <typename T>
        std::string *operator*()(const T& operand) const
        {
            std::ostringstream ost;
            ost << operand << ' ';
            *return* ost.str();
        }

};

int main(int , char* [])
{
    typedef boost::make_recursive_variant<
        int,
        std::vector<boost::recursive_variant_>,
        std::map<std::string, boost::recursive_variant_>
            >::type var_t;

    std::vector<var_t> vec;
    vec.push_back(3);
    vec.push_back(5);
    vec.push_back(vec);
    vec.push_back(7);

    var_t var(vec);
    std::string result( boost::apply_visitor( vector_printer(), var ) );

    std::cout << "result: " << result << '\n';

    *return* 0;
}

And the compile error from VC8 is :

test_map_variant.cpp
D:\Program\boost\boost_1_33_1\boost/type_traits/is_base_and_derived.hpp :
warning C4819: The file contains a character that cannot be represented in
the current code page (936). Save the file in Unicode format to prevent data
loss
D:\Program\boost\boost_1_33_1\boost/utility/enable_if.hpp : warning C4819:
The file contains a character that cannot be represented in the current code
page (936). Save the file in Unicode format to prevent data loss
D:\Program\boost\boost_1_33_1\boost/type_traits/is_base_and_derived.hpp :
warning C4819: The file contains a character that cannot be represented in
the current code page (936). Save the file in Unicode format to prevent data
loss
D:\Program\boost\boost_1_33_1\boost/utility/enable_if.hpp : warning C4819:
The file contains a character that cannot be represented in the current code
page (936). Save the file in Unicode format to prevent data loss
D:\Program\boost\boost_1_33_1\boost/utility/enable_if.hpp : warning C4819:
The file contains a character that cannot be represented in the current code
page (936). Save the file in Unicode format to prevent data loss
D:\Program\vs8\VC\INCLUDE\utility(54) : error C2079:
'std::pair<_Ty1,_Ty2>::second' uses undefined struct
'boost::recursive_variant_'
        with
        [
            _Ty1=const std::string,
            _Ty2=boost::recursive_variant_
        ]
        D:\Program\vs8\VC\INCLUDE\vector(1083) : see reference to class
template instantiation 'std::pair<_Ty1,_Ty2>' being compiled
        with
        [
            _Ty1=const std::string,
            _Ty2=boost::recursive_variant_
        ]
        D:\Program\vs8\VC\INCLUDE\vector(1082) : while compiling class
template member function 'void
std::vector<_Ty>::_Destroy(boost::variant<T0_,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,T16,T17,T18,T19>
*,boost::variant<T0_,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,T16,T17,T18,T19>
*)'
        with
        [
            _Ty=var_t,
            T0_=boost::detail::variant::recursive_flag<int>,
            T1=std::vector<boost::recursive_variant_>,
            T2=std::map<std::string,boost::recursive_variant_>,
            T3=boost::detail::variant::void_,
            T4=boost::detail::variant::void_,
            T5=boost::detail::variant::void_,
            T6=boost::detail::variant::void_,
            T7=boost::detail::variant::void_,
            T8=boost::detail::variant::void_,
            T9=boost::detail::variant::void_,
            T10=boost::detail::variant::void_,
            T11=boost::detail::variant::void_,
            T12=boost::detail::variant::void_,
            T13=boost::detail::variant::void_,
            T14=boost::detail::variant::void_,
            T15=boost::detail::variant::void_,
            T16=boost::detail::variant::void_,
            T17=boost::detail::variant::void_,
            T18=boost::detail::variant::void_,
            T19=boost::detail::variant::void_
        ]
        test_map_variant.cpp(63) : see reference to class template
instantiation 'std::vector<_Ty>' being compiled
        with
        [
            _Ty=var_t
        ]

-- 
B. R.
Andy