ACE/ace/If_Then_Else.h

   1 // -*- C++ -*-
   2
   3 //=============================================================================
   4 /**
   5  *  @file    If_Then_Else.h
   6  *
   7  *  @c ACE::If_Then_Else traits template based on the @c IfThenElse
   8  *  template described in the book "C++ Templates" by Vandevoorde and
   9  *  Josuttis.
  10  *
  11  *  @author Ossama Othman <ossama@dre.vanderbilt.edu>
  12  */
  13 //=============================================================================
  14
  15 #ifndef ACE_IF_THEN_ELSE_H
  16 #define ACE_IF_THEN_ELSE_H
  17
  18 #include /**/ "ace/config-lite.h"
  19
  20 ACE_BEGIN_VERSIONED_NAMESPACE_DECL
  21
  22 namespace ACE
  23 {
  24   /**
  25    * @struct If_Then_Else
  26    *
  27    * @brief Compile-time selection of type based on a boolean value.
  28    *
  29    * This primary template selects the second or third argument based
  30    * on the value of the boolean first argument.
  31    *
  32    * Usage example:
  33    *
  34    * \code
  35    *
  36    *   template <typename T>
  37    *   class Foo
  38    *   {
  39    *   public:
  40    *     // Set "TheType" to be the larger of "T" and  "int".
  41    *     typedef typename If_Then_Else<(sizeof (T) > sizeof (int)),
  42    *                                   T,
  43    *                                   int>::result_type TheType;
  44    *   };
  45    *
  46    * \endcode
  47    *
  48    * @note This merely a forward declaration since we really only care
  49    *       about the partial specializations below.
  50    */
  51   template <bool C, typename Ta, typename Tb>
  52   struct If_Then_Else;
  53
  54   /**
  55    * @struct If_Then_Else
  56    *
  57    * @brief Select of type @a Ta if boolean value is @c true.
  58    *
  59    * This partial specialization selects the type @a Ta if the boolean
  60    * first argument is @c true.
  61    */
  62   template <typename Ta, typename Tb>
  63   struct If_Then_Else<true, Ta, Tb>
  64   {
  65     typedef Ta result_type;
  66   };
  67
  68   /**
  69    * @struct If_Then_Else
  70    *
  71    * @brief Select of type @a Tb if boolean value is @c false.
  72    *
  73    * This partial specialization selects the type @a Tb if the boolean
  74    * first argument is @c false.
  75    */
  76   template <typename Ta, typename Tb>
  77   struct If_Then_Else<false, Ta, Tb>
  78   {
  79     typedef Tb result_type;
  80   };
  81 }
  82
  83 ACE_END_VERSIONED_NAMESPACE_DECL
  84
  85 #endif  /* ACE_IF_THEN_ELSE_H */