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