libs/sigc++2/sigc++/type_traits.h

   1 /*
   2  * Copyright 2002, The libsigc++ Development Team
   3  *
   4  *  This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Lesser General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2.1 of the License, or (at your option) any later version.
   8  *
   9  *  This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  12  *  Lesser General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU Lesser General Public
  15  *  License along with this library; if not, write to the Free Software
  16  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  17  *
  18  */
  19 #ifndef _SIGC_TYPE_TRAIT_H_
  20 #define _SIGC_TYPE_TRAIT_H_
  21
  22 #include <sigc++config.h> //To get SIGC_SELF_REFERENCE_IN_MEMBER_INITIALIZATION
  23
  24
  25 namespace sigc {
  26
  27 template <class T_type>
  28 struct type_trait
  29 {
  30   typedef T_type  type;
  31   typedef T_type& pass;
  32   typedef const T_type& take;
  33   typedef T_type* pointer;
  34 };
  35
  36 template <class T_type, int N>
  37 struct type_trait<T_type[N]>
  38 {
  39   typedef T_type*  type;
  40   typedef T_type*& pass;
  41   typedef const T_type*& take;
  42   typedef T_type** pointer;
  43 };
  44
  45 template <class T_type>
  46 struct type_trait<T_type&>
  47 {
  48   typedef T_type  type;
  49   typedef T_type& pass;
  50   typedef T_type& take;
  51   typedef T_type* pointer;
  52 };
  53
  54 template <class T_type>
  55 struct type_trait<const T_type&>
  56 {
  57   typedef const T_type  type;
  58   typedef const T_type& pass;
  59   typedef const T_type& take;
  60   typedef const T_type* pointer;
  61 };
  62
  63 template<>
  64 struct type_trait<void>
  65 {
  66   typedef void  type;
  67   typedef void  pass;
  68   typedef void  take;
  69   typedef void* pointer;
  70 };
  71
  72
  73 // From Esa Pulkkin:
  74 /**
  75  * Compile-time determination of base-class relationship in C++
  76  * (adapted to match the syntax of boost's type_traits library).
  77  *
  78  * Use this to provide a template specialization for a set of types.
  79  * For instance,
  80  *
  81  * template < class T_thing, bool Tval_derives_from_something = sigc::is_base_and_derived<Something, T_thing>::value >
  82  * class TheTemplate
  83  * {
  84  *   //Standard implementation.
  85  * }
  86  *
  87  * //Specialization for T_things that derive from Something (Tval_derives_from_something is true)
  88  * template <class T_thing>
  89  * class TheTemplate<T_thing, true>
  90  * {
  91  *   T_thing thing;
  92      thing.method_that_is_in_something();
  93  * }
  94  */
  95 template <class T_base, class T_derived>
  96 struct is_base_and_derived
  97 {
  98 private:
  99   struct big {
 100     char memory[64];
 101   };
 102
 103 #ifndef SIGC_SELF_REFERENCE_IN_MEMBER_INITIALIZATION
 104
 105   //Allow the internal inner class to access the other (big) inner
 106   //class.  The Tru64 compiler needs this. murrayc.
 107   friend struct internal_class;
 108
 109   //Certain compilers, notably GCC 3.2, require these functions to be inside an inner class.
 110   struct internal_class
 111   {
 112     static big  is_base_class_(...);
 113     static char is_base_class_(typename type_trait<T_base>::pointer);
 114   };
 115
 116 public:
 117   static const bool value =
 118     sizeof(internal_class::is_base_class_(reinterpret_cast<typename type_trait<T_derived>::pointer>(0))) ==
 119     sizeof(char);
 120
 121 #else //SIGC_SELF_REFERENCE_IN_MEMBER_INITIALIZATION
 122
 123   //The AIX xlC compiler does not like these 2 functions being in the inner class.
 124   //It says "The incomplete type "test" must not be used as a qualifier.
 125   //It does not seem necessary anyway. murrayc.
 126   static big  is_base_class_(...);
 127   static char is_base_class_(typename type_trait<T_base>::pointer);
 128
 129 public:
 130   static const bool value =
 131     sizeof(is_base_class_(reinterpret_cast<typename type_trait<T_derived>::pointer>(0))) ==
 132     sizeof(char);
 133
 134 #endif //SIGC_SELF_REFERENCE_IN_MEMBER_INITIALIZATION
 135
 136   void avoid_gcc3_warning_(); //Not implemented. g++ 3.3.5 (but not 3.3.4, and not 3.4) warn that there are no public methods, even though there is a public variable.
 137 };
 138
 139 template <class T_base>
 140 struct is_base_and_derived<T_base, T_base>
 141 {
 142   static const bool value = true;
 143 };
 144
 145 } /* namespace sigc */
 146
 147 #endif /* _SIGC_TYPE_TRAIT_H_ */