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 #include "boost/type_traits/intrinsics.hpp"
  17
  18 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
  19 #   include "boost/type_traits/remove_cv.hpp"
  20 #   include "boost/type_traits/is_class.hpp"
  21 #   include "boost/type_traits/add_reference.hpp"
  22 #else
  23 #   include "boost/type_traits/is_reference.hpp"
  24 #   include "boost/type_traits/is_pointer.hpp"
  25 #   include "boost/type_traits/is_member_pointer.hpp"
  26 #   include "boost/type_traits/is_array.hpp"
  27 #   include "boost/type_traits/is_void.hpp"
  28 #   include "boost/type_traits/detail/ice_and.hpp"
  29 #   include "boost/type_traits/detail/ice_not.hpp"
  30 #endif
  31
  32 // should be always the last #include directive
  33 #include "boost/type_traits/detail/bool_trait_def.hpp"
  34
  35 namespace boost {
  36
  37 namespace detail {
  38
  39 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
  40 template <typename T>
  41 struct empty_helper_t1 : public T
  42 {
  43     empty_helper_t1();  // hh compiler bug workaround
  44     int i[256];
  45 };
  46
  47 struct empty_helper_t2 { int i[256]; };
  48
  49 #ifndef __BORLANDC__
  50
  51 template <typename T, bool is_a_class = false>
  52 struct empty_helper
  53 {
  54     BOOST_STATIC_CONSTANT(bool, value = false);
  55 };
  56
  57 template <typename T>
  58 struct empty_helper<T, true>
  59 {
  60     BOOST_STATIC_CONSTANT(
  61         bool, value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2))
  62         );
  63 };
  64
  65 template <typename T>
  66 struct is_empty_impl
  67 {
  68     typedef typename remove_cv<T>::type cvt;
  69     BOOST_STATIC_CONSTANT(
  70         bool, value = (
  71             ::boost::type_traits::ice_or<
  72               ::boost::detail::empty_helper<cvt,::boost::is_class<T>::value>::value
  73               , BOOST_IS_EMPTY(cvt)
  74             >::value
  75             ));
  76 };
  77
  78 #else // __BORLANDC__
  79
  80 template <typename T, bool is_a_class, bool convertible_to_int>
  81 struct empty_helper
  82 {
  83     BOOST_STATIC_CONSTANT(bool, value = false);
  84 };
  85
  86 template <typename T>
  87 struct empty_helper<T, true, false>
  88 {
  89     BOOST_STATIC_CONSTANT(bool, value = (
  90         sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)
  91         ));
  92 };
  93
  94 template <typename T>
  95 struct is_empty_impl
  96 {
  97    typedef typename remove_cv<T>::type cvt;
  98    typedef typename add_reference<T>::type r_type;
  99
 100    BOOST_STATIC_CONSTANT(
 101        bool, value = (
 102            ::boost::type_traits::ice_or<
 103               ::boost::detail::empty_helper<
 104                   cvt
 105                 , ::boost::is_class<T>::value
 106                 , ::boost::is_convertible< r_type,int>::value
 107               >::value
 108               , BOOST_IS_EMPTY(cvt)
 109            >::value));
 110 };
 111
 112 #endif // __BORLANDC__
 113
 114 #else // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 115
 116 #ifdef BOOST_MSVC6_MEMBER_TEMPLATES
 117
 118 template <typename T>
 119 struct empty_helper_t1 : public T
 120 {
 121    empty_helper_t1();
 122    int i[256];
 123 };
 124
 125 struct empty_helper_t2 { int i[256]; };
 126
 127 template <typename T>
 128 struct empty_helper_base
 129 {
 130    enum { value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)) };
 131 };
 132
 133 template <typename T>
 134 struct empty_helper_nonbase
 135 {
 136    enum { value = false };
 137 };
 138
 139 template <bool base>
 140 struct empty_helper_chooser
 141 {
 142    template <typename T> struct result_
 143    {
 144       typedef empty_helper_nonbase<T> type;
 145    };
 146 };
 147
 148 template <>
 149 struct empty_helper_chooser<true>
 150 {
 151    template <typename T> struct result_
 152    {
 153       typedef empty_helper_base<T> type;
 154    };
 155 };
 156
 157 template <typename T>
 158 struct is_empty_impl
 159 {
 160    typedef ::boost::detail::empty_helper_chooser<
 161       ::boost::type_traits::ice_and<
 162          ::boost::type_traits::ice_not< ::boost::is_reference<T>::value >::value,
 163          ::boost::type_traits::ice_not< ::boost::is_convertible<T,double>::value >::value,
 164          ::boost::type_traits::ice_not< ::boost::is_pointer<T>::value >::value,
 165          ::boost::type_traits::ice_not< ::boost::is_member_pointer<T>::value >::value,
 166          ::boost::type_traits::ice_not< ::boost::is_array<T>::value >::value,
 167          ::boost::type_traits::ice_not< ::boost::is_void<T>::value >::value,
 168          ::boost::type_traits::ice_not<
 169             ::boost::is_convertible<T,void const volatile*>::value
 170             >::value
 171       >::value > chooser;
 172
 173    typedef typename chooser::template result_<T> result;
 174    typedef typename result::type eh_type;
 175
 176    BOOST_STATIC_CONSTANT(bool, value =
 177       (::boost::type_traits::ice_or<eh_type::value, BOOST_IS_EMPTY(T)>::value));
 178 };
 179
 180 #else
 181
 182 template <typename T> struct is_empty_impl
 183 {
 184     BOOST_STATIC_CONSTANT(bool, value = BOOST_IS_EMPTY(T));
 185 };
 186
 187 #endif  // BOOST_MSVC6_MEMBER_TEMPLATES
 188
 189 #endif  // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 190
 191 // these help when the compiler has no partial specialization support:
 192 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void,false)
 193 #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
 194 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void const,false)
 195 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void volatile,false)
 196 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void const volatile,false)
 197 #endif
 198
 199 } // namespace detail
 200
 201 BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_empty,T,::boost::detail::is_empty_impl<T>::value)
 202
 203 } // namespace boost
 204
 205 #include "boost/type_traits/detail/bool_trait_undef.hpp"
 206
 207 #endif // BOOST_TT_IS_EMPTY_HPP_INCLUDED
 208