src/boost/boost/type_traits/common_type.hpp

   1 //  common_type.hpp  ---------------------------------------------------------//
   2
   3 //  Copyright 2008 Howard Hinnant
   4 //  Copyright 2008 Beman Dawes
   5
   6 //  Distributed under the Boost Software License, Version 1.0.
   7 //  See http://www.boost.org/LICENSE_1_0.txt
   8
   9 #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP
  10 #define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP
  11
  12 #include <boost/config.hpp>
  13
  14 #if defined(__SUNPRO_CC) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
  15 #  define BOOST_COMMON_TYPE_DONT_USE_TYPEOF
  16 #endif
  17 #if defined(__IBMCPP__) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
  18 #  define BOOST_COMMON_TYPE_DONT_USE_TYPEOF
  19 #endif
  20
  21 //----------------------------------------------------------------------------//
  22 #if defined(BOOST_NO_VARIADIC_TEMPLATES) && !defined(BOOST_COMMON_TYPE_ARITY)
  23 #define BOOST_COMMON_TYPE_ARITY 3
  24 #endif
  25
  26 //----------------------------------------------------------------------------//
  27 #if defined(BOOST_NO_DECLTYPE) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF) && !defined(BOOST_TYPEOF_SILENT)
  28 #define BOOST_TYPEOF_SILENT
  29 #include <boost/typeof/typeof.hpp>   // boost wonders never cease!
  30 #endif
  31
  32 //----------------------------------------------------------------------------//
  33 #ifndef BOOST_NO_STATIC_ASSERT
  34 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) static_assert(CND,MSG)
  35 #elif defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
  36 #include <boost/mpl/assert.hpp>
  37 #include <boost/mpl/bool.hpp>
  38 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES)                                 \
  39     BOOST_MPL_ASSERT_MSG(boost::mpl::bool_< (CND) >::type::value, MSG, TYPES)
  40 #else
  41 #include <boost/static_assert.hpp>
  42 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) BOOST_STATIC_ASSERT(CND)
  43 #endif
  44
  45 #if !defined(BOOST_NO_STATIC_ASSERT) || !defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
  46 #define BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE "must be complete type"
  47 #endif
  48
  49 #if defined(BOOST_NO_DECLTYPE) && defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
  50 #include <boost/type_traits/detail/common_type_imp.hpp>
  51 #include <boost/type_traits/remove_cv.hpp>
  52 #endif
  53 #include <boost/mpl/if.hpp>
  54 #include <boost/utility/declval.hpp>
  55 #include <boost/type_traits/add_rvalue_reference.hpp>
  56
  57 //----------------------------------------------------------------------------//
  58 //                                                                            //
  59 //                           C++03 implementation of                          //
  60 //             20.6.7 Other transformations [meta.trans.other]                //
  61 //                          Written by Howard Hinnant                         //
  62 //      Adapted for Boost by Beman Dawes, Vicente Botet and  Jeffrey Hellrung //
  63 //                                                                            //
  64 //----------------------------------------------------------------------------//
  65
  66 namespace boost {
  67
  68 // prototype
  69 #if !defined(BOOST_NO_VARIADIC_TEMPLATES)
  70     template<typename... T>
  71     struct common_type;
  72 #else // or no specialization
  73     template <class T, class U = void, class V = void>
  74     struct common_type
  75     {
  76     public:
  77         typedef typename common_type<typename common_type<T, U>::type, V>::type type;
  78     };
  79 #endif
  80
  81
  82 // 1 arg
  83     template<typename T>
  84 #if !defined(BOOST_NO_VARIADIC_TEMPLATES)
  85     struct common_type<T>
  86 #else
  87     struct common_type<T, void, void>
  88
  89 #endif
  90     {
  91         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
  92     public:
  93         typedef T type;
  94     };
  95
  96 // 2 args
  97 namespace type_traits_detail {
  98
  99     template <class T, class U>
 100     struct common_type_2
 101     {
 102     private:
 103         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
 104         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(U) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (U));
 105         static bool declval_bool();  // workaround gcc bug; not required by std
 106         static typename add_rvalue_reference<T>::type declval_T();  // workaround gcc bug; not required by std
 107         static typename add_rvalue_reference<U>::type declval_U();  // workaround gcc bug; not required by std
 108         static typename add_rvalue_reference<bool>::type declval_b();
 109
 110 #if !defined(BOOST_NO_DECLTYPE)
 111     public:
 112         typedef decltype(declval<bool>() ? declval<T>() : declval<U>()) type;
 113 #elif defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
 114     public:
 115     typedef typename detail_type_traits_common_type::common_type_impl<
 116           typename remove_cv<T>::type,
 117           typename remove_cv<U>::type
 118       >::type type;
 119 #else
 120     public:
 121         typedef BOOST_TYPEOF_TPL(declval_b() ? declval_T() : declval_U()) type;
 122 #endif
 123
 124 #if defined(__GNUC__) && __GNUC__ == 3 && (__GNUC_MINOR__ == 2 || __GNUC_MINOR__ == 3)
 125     public:
 126         void public_dummy_function_just_to_silence_warning();
 127 #endif
 128     };
 129
 130     template <class T>
 131     struct common_type_2<T, T>
 132     {
 133         typedef T type;
 134     };
 135     }
 136
 137 #if !defined(BOOST_NO_VARIADIC_TEMPLATES)
 138     template <class T, class U>
 139     struct common_type<T, U>
 140 #else
 141     template <class T, class U>
 142     struct common_type<T, U, void>
 143 #endif
 144     : public type_traits_detail::common_type_2<T,U>
 145     { };
 146
 147
 148 // 3 or more args
 149 #if !defined(BOOST_NO_VARIADIC_TEMPLATES)
 150     template<typename T, typename U, typename... V>
 151     struct common_type<T, U, V...> {
 152     public:
 153         typedef typename common_type<typename common_type<T, U>::type, V...>::type type;
 154     };
 155 #endif
 156 }  // namespace boost
 157
 158 #endif  // BOOST_TYPE_TRAITS_COMMON_TYPE_HPP