boost/type_traits/is_empty.hpp

   1
   2 // (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
   3 //  Use, modification and distribution are subject to the Boost Software License,
   4 //  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   5 //  http://www.boost.org/LICENSE_1_0.txt).
   6 //
   7 //  See http://www.boost.org/libs/type_traits for most recent version including documentation.
   8
   9 #ifndef BOOST_TT_IS_EMPTY_HPP_INCLUDED
  10 #define BOOST_TT_IS_EMPTY_HPP_INCLUDED
  11
  12 #include <boost/type_traits/is_convertible.hpp>
  13 #include <boost/type_traits/detail/ice_or.hpp>
  14 #include <boost/type_traits/config.hpp>
  15 #include <boost/type_traits/intrinsics.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 #ifndef BOOST_INTERNAL_IS_EMPTY
  35 #define BOOST_INTERNAL_IS_EMPTY(T) false
  36 #else
  37 #define BOOST_INTERNAL_IS_EMPTY(T) BOOST_IS_EMPTY(T)
  38 #endif
  39
  40 namespace boost {
  41
  42 namespace detail {
  43
  44 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
  45
  46 #ifdef BOOST_MSVC
  47 #pragma warning(push)
  48 #pragma warning(disable:4624) // destructor could not be generated
  49 #endif
  50
  51 template <typename T>
  52 struct empty_helper_t1 : public T
  53 {
  54     empty_helper_t1();  // hh compiler bug workaround
  55     int i[256];
  56 private:
  57    // suppress compiler warnings:
  58    empty_helper_t1(const empty_helper_t1&);
  59    empty_helper_t1& operator=(const empty_helper_t1&);
  60 };
  61
  62 #ifdef BOOST_MSVC
  63 #pragma warning(pop)
  64 #endif
  65
  66 struct empty_helper_t2 { int i[256]; };
  67
  68 #if !BOOST_WORKAROUND(__BORLANDC__, < 0x600)
  69
  70 template <typename T, bool is_a_class = false>
  71 struct empty_helper
  72 {
  73     BOOST_STATIC_CONSTANT(bool, value = false);
  74 };
  75
  76 template <typename T>
  77 struct empty_helper<T, true>
  78 {
  79     BOOST_STATIC_CONSTANT(
  80         bool, value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2))
  81         );
  82 };
  83
  84 template <typename T>
  85 struct is_empty_impl
  86 {
  87     typedef typename remove_cv<T>::type cvt;
  88     BOOST_STATIC_CONSTANT(
  89         bool, value = (
  90             ::boost::type_traits::ice_or<
  91               ::boost::detail::empty_helper<cvt,::boost::is_class<T>::value>::value
  92               , BOOST_INTERNAL_IS_EMPTY(cvt)
  93             >::value
  94             ));
  95 };
  96
  97 #else // __BORLANDC__
  98
  99 template <typename T, bool is_a_class, bool convertible_to_int>
 100 struct empty_helper
 101 {
 102     BOOST_STATIC_CONSTANT(bool, value = false);
 103 };
 104
 105 template <typename T>
 106 struct empty_helper<T, true, false>
 107 {
 108     BOOST_STATIC_CONSTANT(bool, value = (
 109         sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)
 110         ));
 111 };
 112
 113 template <typename T>
 114 struct is_empty_impl
 115 {
 116    typedef typename remove_cv<T>::type cvt;
 117    typedef typename add_reference<T>::type r_type;
 118
 119    BOOST_STATIC_CONSTANT(
 120        bool, value = (
 121            ::boost::type_traits::ice_or<
 122               ::boost::detail::empty_helper<
 123                   cvt
 124                 , ::boost::is_class<T>::value
 125                 , ::boost::is_convertible< r_type,int>::value
 126               >::value
 127               , BOOST_INTERNAL_IS_EMPTY(cvt)
 128            >::value));
 129 };
 130
 131 #endif // __BORLANDC__
 132
 133 #else // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 134
 135 #ifdef BOOST_MSVC6_MEMBER_TEMPLATES
 136
 137 template <typename T>
 138 struct empty_helper_t1 : public T
 139 {
 140    empty_helper_t1();
 141    int i[256];
 142 };
 143
 144 struct empty_helper_t2 { int i[256]; };
 145
 146 template <typename T>
 147 struct empty_helper_base
 148 {
 149    enum { value = (sizeof(empty_helper_t1<T>) == sizeof(empty_helper_t2)) };
 150 };
 151
 152 template <typename T>
 153 struct empty_helper_nonbase
 154 {
 155    enum { value = false };
 156 };
 157
 158 template <bool base>
 159 struct empty_helper_chooser
 160 {
 161    template <typename T> struct result_
 162    {
 163       typedef empty_helper_nonbase<T> type;
 164    };
 165 };
 166
 167 template <>
 168 struct empty_helper_chooser<true>
 169 {
 170    template <typename T> struct result_
 171    {
 172       typedef empty_helper_base<T> type;
 173    };
 174 };
 175
 176 template <typename T>
 177 struct is_empty_impl
 178 {
 179    typedef ::boost::detail::empty_helper_chooser<
 180       ::boost::type_traits::ice_and<
 181          ::boost::type_traits::ice_not< ::boost::is_reference<T>::value >::value,
 182          ::boost::type_traits::ice_not< ::boost::is_convertible<T,double>::value >::value,
 183          ::boost::type_traits::ice_not< ::boost::is_pointer<T>::value >::value,
 184          ::boost::type_traits::ice_not< ::boost::is_member_pointer<T>::value >::value,
 185          ::boost::type_traits::ice_not< ::boost::is_array<T>::value >::value,
 186          ::boost::type_traits::ice_not< ::boost::is_void<T>::value >::value,
 187          ::boost::type_traits::ice_not<
 188             ::boost::is_convertible<T,void const volatile*>::value
 189             >::value
 190       >::value > chooser;
 191
 192    typedef typename chooser::template result_<T> result;
 193    typedef typename result::type eh_type;
 194
 195    BOOST_STATIC_CONSTANT(bool, value =
 196       (::boost::type_traits::ice_or<eh_type::value, BOOST_INTERNAL_IS_EMPTY(T)>::value));
 197 };
 198
 199 #else
 200
 201 template <typename T> struct is_empty_impl
 202 {
 203     BOOST_STATIC_CONSTANT(bool, value = BOOST_INTERNAL_IS_EMPTY(T));
 204 };
 205
 206 #endif  // BOOST_MSVC6_MEMBER_TEMPLATES
 207
 208 #endif  // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 209
 210 // these help when the compiler has no partial specialization support:
 211 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void,false)
 212 #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
 213 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void const,false)
 214 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void volatile,false)
 215 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_empty,void const volatile,false)
 216 #endif
 217
 218 } // namespace detail
 219
 220 BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_empty,T,::boost::detail::is_empty_impl<T>::value)
 221
 222 } // namespace boost
 223
 224 #include <boost/type_traits/detail/bool_trait_undef.hpp>
 225
 226 #undef BOOST_INTERNAL_IS_EMPTY
 227
 228 #endif // BOOST_TT_IS_EMPTY_HPP_INCLUDED
 229