[boost] mpl::bool_ question

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2003-12-14 17:41:59

I have occassionally used mpl::bool_ as a tool for compile-time dispatch
based on a boolean condition. E.g.:

  template<typename T>
  void f(const T&, mpl::true_) { /* T is integral */ }

  template<typename T>
  void f(const T&, boost::mpl::false_) { /* T is non-integral */ }

  template<typename T>
  void f(const T& t) { f(t, mpl::bool_<is_integral<T>::value>()); }

Aside from the question of whether this is good programming style (e.g., it
is not self-documenting), I wonder if it is correct. Are the typedefs

  typedef bool_<true> true_;
  typedef bool_<false> false_;

part of the public interface of MPL, or are true_ and false_ only guaranteed
to be integral constant types with values true and false?

Jonathan