[boost] type_traits / MPL interoperability

From: David Abrahams (dave_at_[hidden])
Date: 2005-11-21 12:29:29

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?)

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.

Thoughts?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com