[boost] is_polymorphic bug

From: Alexander Nasonov (alnsn-mycop_at_[hidden])
Date: 2003-05-21 03:21:12

This little program doesn't work:

#include <boost/type_traits.hpp>

struct Poly { virtual int foo() = 0; };

int main()
{
    boost::is_polymorphic<Poly>::value;
}
   
[alnsn_at_sat-pc test]$ icc -I $BOOST_ROOT is_polymorphic.cpp 
is_polymorphic.cpp
/usr/local/src/boost/boost/type_traits/is_polymorphic.hpp(39): error: return 
type is not identical to nor covariant with return type "int" of overridden 
virtual function function "Poly::foo"
        virtual void foo();
                     ^
          detected during:
            instantiation of class 
"boost::detail::is_polymorphic_imp1<T>::d2 [with T=Poly]" at line 44
            instantiation of class "boost::detail::is_polymorphic_imp1<T> 
[with T=Poly]" at line 79
            instantiation of class "boost::detail::is_polymorphic_imp<T> 
[with T=Poly]" at line 84
            instantiation of class "boost::is_polymorphic<T> [with T=Poly]" 
at line 7 of "is_polymorphic.cpp"

compilation aborted for is_polymorphic.cpp (code 2)

It has a simple workaround though. Virtual function foo should have unique 
signature. One argument of unique type is enough:

// File boost/type_traits/is_polymorphic.hpp
// ...

template <class T>
struct is_polymorphic_imp1
{

  // ...

   struct d2 : public ncvT
   {
      d2();
      virtual ~d2()throw();
#  ifndef BOOST_MSVC
      // for some reason this messes up VC++ when T has virtual bases:
      struct unique {};
      virtual void foo(unique);
#  endif
      char padding[256];
   };

  // ...

};

-- 
Alexander Nasonov
Remove minus and all between minus and at from my e-mail for timely response