[Boost-users] boost::type_traits::is_convertible.hpp ....how to assert a type is _not_ convertible?

17 Nov 2007

      hi all,

i've got 2 classes like this....

//=================================

struct Symbol : private std::string
{
public:
    Symbol(const char *cp):std::string(cp){}
    ~Symbol(){}
};

struct String : private std::string
{
public:
    String(const String &s):std::string(s.c_str()){}
    String(const char *cp):std::string(cp){}
    ~String(){}
};

//=================================
//
// and i'm trying to compile this....
//
//=================================

template<BinaryOp op, typename ObjectT>
Object binary_op(const ObjectT &arg1, const ObjectT &arg2)
{
    return undefined;
}

template<BinaryOp op>
class BinaryOpVisitor : public boost::static_visitor<Object>
{
public:

    template<typename ObjectT, typename ObjectU>
    Object operator()( const ObjectT &arg0, const ObjectU &arg1) const
    {
        bool const y = boost::is_convertible<ObjectT, ObjectU>::value;

        return undefined;
    }

    template<typename ObjectT>
    Object operator ()(const ObjectT &arg0, const ObjectT &arg1) const
    {
        return binary_op<op, ObjectT>(arg0, arg1);
    }
};

//=================================
//
// but using msvc 7.1 i'm getting the following error...
//
//      s:\lib\boost_1_33_1\boost\type_traits\is_convertible.hpp(202) :
//      error C2243: 'type cast' : conversion from 'Symbol *__w64 ' to 
'const std::basic_string<_Elem,_Traits,_Ax> &' exists, but is inaccessible
//
//
//=================================

    //  is_convertible.hpp(202) is as follows ...

    BOOST_STATIC_CONSTANT(bool, value =
        sizeof( _m_check(_m_from) ) == 
sizeof(::boost::type_traits::yes_type)
        );

//=================================
//
//
//   how do i tell (deceive?) the compiler that the conversion does not 
exist?

cheers,

jono poff
day-one digital
auckland, nz