I just ran into a problem caused by the TR1-ization of the type traits library. I had a function defined this way:
template <class T> typename is_fundamental<T>::type f(T) { return mpl::bool_< is_fundamental<T>::value >(); }
that wouldn't compile. Eventually I discovered that it was because type traits now yield instances of integral_constant<T,N> (is that documented somewhere now?)
Yep.
integral_constant<T,N> is derived from mpl::integral_c<T,N>, but mpl::bool_<N> is not derived from integral_constant<T,N>. I can understand not wanting to introduce that sort of two-way coupling between the libraries, but it also seems like the only way to make everything work smoothly.
integral_constant<bool,b> derives from mpl::bool_<b> for backwards compatibility. Stupid question but why doesn't your function do: template <class T> typename is_fundamental<T>::type f(T) { return is_fundamental<T>::type(); } John.