boost/detail/select_type.hpp

   1 // (C) Copyright David Abrahams 2001.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5 //
   6 // See http://www.boost.org for most recent version including documentation.
   7
   8 // Revision History
   9 // 09 Feb 01  Applied John Maddock's Borland patch Moving <true>
  10 //            specialization to unspecialized template (David Abrahams)
  11 // 06 Feb 01  Created (David Abrahams)
  12
  13 #ifndef SELECT_TYPE_DWA20010206_HPP
  14 # define SELECT_TYPE_DWA20010206_HPP
  15
  16 namespace boost { namespace detail {
  17
  18   // Template class if_true -- select among 2 types based on a bool constant expression
  19   // Usage:
  20   //   typename if_true<(bool_const_expression)>::template then<true_type, false_type>::type
  21
  22   // HP aCC cannot deal with missing names for template value parameters
  23   template <bool b> struct if_true
  24   {
  25       template <class T, class F>
  26       struct then { typedef T type; };
  27   };
  28
  29   template <>
  30   struct if_true<false>
  31   {
  32       template <class T, class F>
  33       struct then { typedef F type; };
  34   };
  35 }}
  36 #endif // SELECT_TYPE_DWA20010206_HPP