ceph/src/boost/boost/type_traits/detail/has_postfix_operator.hpp

   1 //  (C) Copyright 2009-2011 Frederic Bron, Robert Stewart, Steven Watanabe & Roman Perepelitsa.
   2 //
   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 #include <boost/config.hpp>
  10 #include <boost/type_traits/detail/yes_no_type.hpp>
  11 #include <boost/type_traits/integral_constant.hpp>
  12 #include <boost/type_traits/is_const.hpp>
  13 #include <boost/type_traits/is_fundamental.hpp>
  14 #include <boost/type_traits/is_pointer.hpp>
  15 #include <boost/type_traits/is_same.hpp>
  16 #include <boost/type_traits/is_void.hpp>
  17 #include <boost/type_traits/remove_cv.hpp>
  18 #include <boost/type_traits/remove_pointer.hpp>
  19 #include <boost/type_traits/remove_reference.hpp>
  20
  21 // avoid warnings
  22 #if defined(__GNUC__)
  23 #   pragma GCC system_header
  24 #elif defined(BOOST_MSVC)
  25 #   pragma warning ( push )
  26 #   pragma warning ( disable : 4244 4913)
  27 #   if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000)
  28 #       pragma warning ( disable : 6334)
  29 #   endif
  30 #endif
  31
  32 namespace boost {
  33 namespace detail {
  34
  35 // This namespace ensures that argument-dependent name lookup does not mess things up.
  36 namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) {
  37
  38 // 1. a function to have an instance of type T without requiring T to be default
  39 // constructible
  40 template <typename T> T &make();
  41
  42
  43 // 2. we provide our operator definition for types that do not have one already
  44
  45 // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is
  46 // found in the type's own namespace (our own operator is used) so that we have
  47 // a means to know that our operator was used
  48 struct no_operator { };
  49
  50 // this class allows implicit conversions and makes the following operator
  51 // definition less-preferred than any other such operators that might be found
  52 // via argument-dependent name lookup
  53 struct any { template <class T> any(T const&); };
  54
  55 // when operator BOOST_TT_TRAIT_OP is not available, this one is used
  56 no_operator operator BOOST_TT_TRAIT_OP (const any&, int);
  57
  58
  59 // 3. checks if the operator returns void or not
  60 // conditions: Lhs!=void
  61
  62 // we first redefine "operator," so that we have no compilation error if
  63 // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of
  64 // (lhs BOOST_TT_TRAIT_OP, returns_void_t()) to deduce if
  65 // operator BOOST_TT_TRAIT_OP returns void or not:
  66 // - operator BOOST_TT_TRAIT_OP returns void   -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns returns_void_t
  67 // - operator BOOST_TT_TRAIT_OP returns !=void -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns int
  68 struct returns_void_t { };
  69 template <typename T> int operator,(const T&, returns_void_t);
  70 template <typename T> int operator,(const volatile T&, returns_void_t);
  71
  72 // this intermediate trait has member value of type bool:
  73 // - value==true -> operator BOOST_TT_TRAIT_OP returns void
  74 // - value==false -> operator BOOST_TT_TRAIT_OP does not return void
  75 template < typename Lhs >
  76 struct operator_returns_void {
  77    // overloads of function returns_void make the difference
  78    // yes_type and no_type have different size by construction
  79    static ::boost::type_traits::yes_type returns_void(returns_void_t);
  80    static ::boost::type_traits::no_type returns_void(int);
  81    BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((make<Lhs>() BOOST_TT_TRAIT_OP,returns_void_t())))));
  82 };
  83
  84
  85 // 4. checks if the return type is Ret or Ret==dont_care
  86 // conditions: Lhs!=void
  87
  88 struct dont_care { };
  89
  90 template < typename Lhs, typename Ret, bool Returns_void >
  91 struct operator_returns_Ret;
  92
  93 template < typename Lhs >
  94 struct operator_returns_Ret < Lhs, dont_care, true > {
  95    BOOST_STATIC_CONSTANT(bool, value = true);
  96 };
  97
  98 template < typename Lhs >
  99 struct operator_returns_Ret < Lhs, dont_care, false > {
 100    BOOST_STATIC_CONSTANT(bool, value = true);
 101 };
 102
 103 template < typename Lhs >
 104 struct operator_returns_Ret < Lhs, void, true > {
 105    BOOST_STATIC_CONSTANT(bool, value = true);
 106 };
 107
 108 template < typename Lhs >
 109 struct operator_returns_Ret < Lhs, void, false > {
 110    BOOST_STATIC_CONSTANT(bool, value = false);
 111 };
 112
 113 template < typename Lhs, typename Ret >
 114 struct operator_returns_Ret < Lhs, Ret, true > {
 115    BOOST_STATIC_CONSTANT(bool, value = false);
 116 };
 117
 118 // otherwise checks if it is convertible to Ret using the sizeof trick
 119 // based on overload resolution
 120 // condition: Ret!=void and Ret!=dont_care and the operator does not return void
 121 template < typename Lhs, typename Ret >
 122 struct operator_returns_Ret < Lhs, Ret, false > {
 123    static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret
 124    static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise
 125
 126    BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(make<Lhs>() BOOST_TT_TRAIT_OP))==sizeof(::boost::type_traits::yes_type)));
 127 };
 128
 129
 130 // 5. checks for operator existence
 131 // condition: Lhs!=void
 132
 133 // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other
 134 // existing one;
 135 // this is done with redefinition of "operator," that returns no_operator or has_operator
 136 struct has_operator { };
 137 no_operator operator,(no_operator, has_operator);
 138
 139 template < typename Lhs >
 140 struct operator_exists {
 141    static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists
 142    static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise
 143
 144    BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((make<Lhs>() BOOST_TT_TRAIT_OP),make<has_operator>())))==sizeof(::boost::type_traits::yes_type)));
 145 };
 146
 147
 148 // 6. main trait: to avoid any compilation error, this class behaves
 149 // differently when operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the
 150 // standard.
 151 // Forbidden_if is a bool that is:
 152 // - true when the operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the standard
 153 //   (would yield compilation error if used)
 154 // - false otherwise
 155 template < typename Lhs, typename Ret, bool Forbidden_if >
 156 struct trait_impl1;
 157
 158 template < typename Lhs, typename Ret >
 159 struct trait_impl1 < Lhs, Ret, true > {
 160    BOOST_STATIC_CONSTANT(bool, value = false);
 161 };
 162
 163 template < typename Lhs, typename Ret >
 164 struct trait_impl1 < Lhs, Ret, false > {
 165    BOOST_STATIC_CONSTANT(bool,
 166       value = (operator_exists < Lhs >::value && operator_returns_Ret < Lhs, Ret, operator_returns_void < Lhs >::value >::value));
 167 };
 168
 169 // specialization needs to be declared for the special void case
 170 template < typename Ret >
 171 struct trait_impl1 < void, Ret, false > {
 172    BOOST_STATIC_CONSTANT(bool, value = false);
 173 };
 174
 175 // defines some typedef for convenience
 176 template < typename Lhs, typename Ret >
 177 struct trait_impl {
 178    typedef typename ::boost::remove_reference<Lhs>::type Lhs_noref;
 179    typedef typename ::boost::remove_cv<Lhs_noref>::type Lhs_nocv;
 180    typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Lhs_noref>::type >::type >::type Lhs_noptr;
 181    BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Lhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value));
 182 };
 183
 184 } // namespace impl
 185 } // namespace detail
 186
 187 // this is the accessible definition of the trait to end user
 188 template <class Lhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care>
 189 struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl< Lhs, Ret >::value)>{};
 190
 191 } // namespace boost
 192
 193 #if defined(BOOST_MSVC)
 194 #   pragma warning ( pop )
 195 #endif