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_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_COMMON_TYPE_ARITY)
  23 #define BOOST_COMMON_TYPE_ARITY 3
  24 #endif
  25
  26 //----------------------------------------------------------------------------//
  27 #if defined(BOOST_NO_CXX11_DECLTYPE) && !defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
  28 #include <boost/typeof/typeof.hpp>   // boost wonders never cease!
  29 #endif
  30
  31 //----------------------------------------------------------------------------//
  32 #ifndef BOOST_NO_CXX11_STATIC_ASSERT
  33 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) static_assert(CND,MSG)
  34 #elif defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
  35 #include <boost/mpl/assert.hpp>
  36 #include <boost/mpl/bool.hpp>
  37 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES)                                 \
  38     BOOST_MPL_ASSERT_MSG(boost::mpl::bool_< (CND) >::type::value, MSG, TYPES)
  39 #else
  40 #include <boost/static_assert.hpp>
  41 #define BOOST_COMMON_TYPE_STATIC_ASSERT(CND, MSG, TYPES) BOOST_STATIC_ASSERT(CND)
  42 #endif
  43
  44 #if !defined(BOOST_NO_CXX11_STATIC_ASSERT) || !defined(BOOST_COMMON_TYPE_USES_MPL_ASSERT)
  45 #define BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE "must be complete type"
  46 #endif
  47
  48 #if defined(BOOST_NO_CXX11_DECLTYPE) && defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
  49 #include <boost/type_traits/detail/common_type_imp.hpp>
  50 #include <boost/type_traits/remove_cv.hpp>
  51 #endif
  52 #include <boost/mpl/if.hpp>
  53 #include <boost/utility/declval.hpp>
  54 #include <boost/type_traits/add_rvalue_reference.hpp>
  55
  56 //----------------------------------------------------------------------------//
  57 //                                                                            //
  58 //                           C++03 implementation of                          //
  59 //             20.9.7.6 Other transformations [meta.trans.other]              //
  60 //                          Written by Howard Hinnant                         //
  61 //      Adapted for Boost by Beman Dawes, Vicente Botet and  Jeffrey Hellrung //
  62 //                                                                            //
  63 //----------------------------------------------------------------------------//
  64
  65 namespace boost {
  66
  67 // prototype
  68 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
  69     template<typename... T>
  70     struct common_type;
  71 #else // or no specialization
  72     template <class T, class U = void, class V = void>
  73     struct common_type
  74     {
  75     public:
  76         typedef typename common_type<typename common_type<T, U>::type, V>::type type;
  77     };
  78 #endif
  79
  80
  81 // 1 arg
  82     template<typename T>
  83 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
  84     struct common_type<T>
  85 #else
  86     struct common_type<T, void, void>
  87
  88 #endif
  89     {
  90         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
  91     public:
  92         typedef T type;
  93     };
  94
  95 // 2 args
  96 namespace type_traits_detail {
  97
  98     template <class T, class U>
  99     struct common_type_2
 100     {
 101     private:
 102         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(T) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (T));
 103         BOOST_COMMON_TYPE_STATIC_ASSERT(sizeof(U) > 0, BOOST_COMMON_TYPE_MUST_BE_A_COMPLE_TYPE, (U));
 104         static bool declval_bool();  // workaround gcc bug; not required by std
 105         static typename add_rvalue_reference<T>::type declval_T();  // workaround gcc bug; not required by std
 106         static typename add_rvalue_reference<U>::type declval_U();  // workaround gcc bug; not required by std
 107         static typename add_rvalue_reference<bool>::type declval_b();
 108
 109 #if !defined(BOOST_NO_CXX11_DECLTYPE)
 110     public:
 111         typedef decltype(declval<bool>() ? declval<T>() : declval<U>()) type;
 112 #elif defined(BOOST_COMMON_TYPE_DONT_USE_TYPEOF)
 113     public:
 114     typedef typename detail_type_traits_common_type::common_type_impl<
 115           typename remove_cv<T>::type,
 116           typename remove_cv<U>::type
 117       >::type type;
 118 #else
 119     public:
 120         typedef BOOST_TYPEOF_TPL(declval_b() ? declval_T() : declval_U()) type;
 121 #endif
 122
 123 #if defined(__GNUC__) && __GNUC__ == 3 && (__GNUC_MINOR__ == 2 || __GNUC_MINOR__ == 3)
 124     public:
 125         void public_dummy_function_just_to_silence_warning();
 126 #endif
 127     };
 128
 129     template <class T>
 130     struct common_type_2<T, T>
 131     {
 132         typedef T type;
 133     };
 134     }
 135
 136 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
 137     template <class T, class U>
 138     struct common_type<T, U>
 139 #else
 140     template <class T, class U>
 141     struct common_type<T, U, void>
 142 #endif
 143     : public type_traits_detail::common_type_2<T,U>
 144     { };
 145
 146
 147 // 3 or more args
 148 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
 149     template<typename T, typename U, typename... V>
 150     struct common_type<T, U, V...> {
 151     public:
 152         typedef typename common_type<typename common_type<T, U>::type, V...>::type type;
 153     };
 154 #endif
 155 }  // namespace boost
 156
 157 #endif  // BOOST_TYPE_TRAITS_COMMON_TYPE_HPP