template<class InterfaceType>
class Convert
{
public:
   static DerivedType1<IDerivedType1> Cast(const BaseType<IBaseType>& base_type, void* fake_type = 0);
   static DerivedType2<IDerivedType2> Cast(const BaseType<IBaseType>& base_type, int* fake_type = 0);

private:
   Convert();
   ~Convert();
}

DerivedType1<IDerivedType1> result = Convert<IDerivedType1>::Cast(test, (void*)0);

DerivedType1<IDerivedType1> result = Convert<IDerivedType1>::Cast(test);

T>template<class InterfaceType>
T>class Convert
T>{
T>public:
T>   static DerivedType1<IDerivedType1> Cast(const BaseType<IBaseType>& base_type, void* fake_type = 0);
T>   static DerivedType2<IDerivedType2> Cast(const BaseType<IBaseType>& base_type, int* fake_type = 0);

T>private:
T>   Convert();
T>   ~Convert();
T>}

T>DerivedType1<IDerivedType1> result = Convert<IDerivedType1>::Cast(test, (void*)0);
T>

T>DerivedType1<IDerivedType1> result = Convert<IDerivedType1>::Cast(test);
T>

template< typename tp_Required, typename tp_Original, typename tp_Enable = void > class
t_ExplicitCastImpl; // специализации содержат статический метод Cast(tp_Original & original) -> tp_Required &

template< typename tp_Required, typename tp_Original > decltype(auto)
explicit_cast(tp_Original & original) throw()
{
    return(t_ExplicitCastImpl< tp_Required, tp_Original >::Cast(original));
}
...
IBaseType test;
auto & result(explicit_cast< IDerivedType1 & >(test));