304a305,329
> 
> //  bool_testable contributed by Sam Partington -----------------------------//
> 
> template <class T, class B = ::boost::detail::empty_base>
> struct bool_testable : B
> {
> private:
>   struct safe_bool
>   {
> #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
>   private:
>     template <class T, class B> friend class bool_testable;
> #endif
>     int x;
>     typedef int safe_bool::*type;
>   };
> public:
>   typedef safe_bool::type unspecified_bool_type;
>   operator unspecified_bool_type() const
>   {
>     return !static_cast<const T&>(*this) ? 0 : &safe_bool::x;
>   }
> };
> 
>