boost/boost/type_traits/is_empty.hpp

   1
   2 // (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
   3 // Permission to copy, use, modify, sell and distribute this software is
   4 // granted provided this copyright notice appears in all copies. This software
   5 // is provided "as is" without express or implied warranty, and with no claim
   6 // as to its suitability for any purpose.
   7 //
   8 // See http://www.boost.org for most recent version including documentation.
   9
  10 #ifndef BOOST_TT_IS_EMPTY_HPP_INCLUDED
  11 #define BOOST_TT_IS_EMPTY_HPP_INCLUDED
  12
  13 #include "boost/type_traits/is_convertible.hpp"
  14 #include "boost/type_traits/detail/ice_or.hpp"
  15 #include "boost/type_traits/config.hpp"
  16
  17 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
  18 #   include "boost/type_traits/remove_cv.hpp"
  19 #   include "boost/type_traits/is_class.hpp"
  20 #   include "boost/type_traits/add_reference.hpp"
  21 #else
  22 #   include "boost/type_traits/is_reference.hpp"
  23 #   include "boost/type_traits/is_pointer.hpp"
  24 #   include "boost/type_traits/is_member_pointer.hpp"
  25 #   include "boost/type_traits/is_array.hpp"
  26 #   include "boost/type_traits/is_void.hpp"
  27 #   include "boost/type_traits/detail/ice_and.hpp"
  28 #   include "boost/type_traits/detail/ice_not.hpp"
  29 #endif
  30
  31 // should be always the last #include directive
  32 #include "boost/type_traits/detail/bool_trait_def.hpp"
  33
  34 namespace boost {
  35
  36 namespace detail {
  37
  38 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
  39 template <typename T>
  40 struct empty_helper_t1 : public T
  41 {
  42     empty_helper_t1();  // hh compiler bug workaround
  43     int i[256];
  44 };
  45
  46 struct empty_helper_t2 { int i[256]; };
  47
  48 #ifndef __BORLANDC__
  49
  50 template <typename T, bool is_a_class = false>
  51 struct empty_helper
  52 {
  53     BOOST_STATIC_CONSTANT(bool, value = false);
  54 };
  55
  56 template <typename T>
  57 struct empty_helper<T, true>
  58 {
  59     BOOST_STATIC_CONSTANT(
  60         bool, value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2))
  61         );
  62 };
  63
  64 template <typename T>
  65 struct is_empty_impl
  66 {
  67     typedef typename remove_cv<T>::type cvt;
  68     BOOST_STATIC_CONSTANT(
  69         bool, value = (
  70             ::boost::type_traits::ice_or<
  71               ::boost::detail::empty_helper<cvt,::boost::is_class<T>::value>::value
  72               , BOOST_IS_EMPTY(cvt)
  73             >::value
  74             ));
  75 };
  76
  77 #else // __BORLANDC__
  78
  79 template <typename T, bool is_a_class, bool convertible_to_int>
  80 struct empty_helper
  81 {
  82     BOOST_STATIC_CONSTANT(bool, value = false);
  83 };
  84
  85 template <typename T>
  86 struct empty_helper<T, true, false>
  87 {
  88     BOOST_STATIC_CONSTANT(bool, value = (
  89         sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)
  90         ));
  91 };
  92
  93 template <typename T>
  94 struct is_empty_impl
  95 {
  96    typedef typename remove_cv<T>::type cvt;
  97    typedef typename add_reference<T>::type r_type;
  98
  99    BOOST_STATIC_CONSTANT(
 100        bool, value = (
 101            ::boost::type_traits::ice_or<
 102               ::boost::detail::empty_helper<
 103                   cvt
 104                 , ::boost::is_class<T>::value
 105                 , ::boost::is_convertible< r_type,int>::value
 106               >::value
 107               , BOOST_IS_EMPTY(cvt)
 108            >::value));
 109 };
 110
 111 #endif // __BORLANDC__
 112
 113 #else // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 114
 115 #ifdef BOOST_MSVC6_MEMBER_TEMPLATES
 116
 117 template <typename T>
 118 struct empty_helper_t1 : public T
 119 {
 120    empty_helper_t1();
 121    int i[256];
 122 };
 123
 124 struct empty_helper_t2 { int i[256]; };
 125
 126 template <typename T>
 127 struct empty_helper_base
 128 {
 129    enum { value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)) };
 130 };
 131
 132 template <typename T>
 133 struct empty_helper_nonbase
 134 {
 135    enum { value = false };
 136 };
 137
 138 template <bool base>
 139 struct empty_helper_chooser
 140 {
 141    template <typename T> struct result_
 142    {
 143       typedef empty_helper_nonbase<T> type;
 144    };
 145 };
 146
 147 template <>
 148 struct empty_helper_chooser<true>
 149 {
 150    template <typename T> struct result_
 151    {
 152       typedef empty_helper_base<T> type;
 153    };
 154 };
 155
 156 template <typename T>
 157 struct is_empty_impl
 158 {
 159    typedef ::boost::detail::empty_helper_chooser<
 160       ::boost::type_traits::ice_and<
 161          ::boost::type_traits::ice_not< ::boost::is_reference<T>::value >::value,
 162          ::boost::type_traits::ice_not< ::boost::is_convertible<T,double>::value >::value,
 163          ::boost::type_traits::ice_not< ::boost::is_pointer<T>::value >::value,
 164          ::boost::type_traits::ice_not< ::boost::is_member_pointer<T>::value >::value,
 165          ::boost::type_traits::ice_not< ::boost::is_array<T>::value >::value,
 166          ::boost::type_traits::ice_not< ::boost::is_void<T>::value >::value,
 167          ::boost::type_traits::ice_not<
 168             ::boost::is_convertible<T,void const volatile*>::value
 169             >::value
 170       >::value > chooser;
 171
 172    typedef typename chooser::template result_<T> result;
 173    typedef typename result::type eh_type;
 174
 175    BOOST_STATIC_CONSTANT(bool, value =
 176       (::boost::type_traits::ice_or<eh_type::value, BOOST_IS_EMPTY(T)>::value));
 177 };
 178
 179 #else
 180
 181 template <typename T> struct is_empty_impl
 182 {
 183     BOOST_STATIC_CONSTANT(bool, value = BOOST_IS_EMPTY(T));
 184 };
 185
 186 #endif  // BOOST_MSVC6_MEMBER_TEMPLATES
 187
 188 #endif  // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 189
 190 } // namespace detail
 191
 192 BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_empty,T,::boost::detail::is_empty_impl<T>::value)
 193
 194 } // namespace boost
 195
 196 #include "boost/type_traits/detail/bool_trait_undef.hpp"
 197
 198 #endif // BOOST_TT_IS_EMPTY_HPP_INCLUDED