ceph/src/boost/libs/type_traits/include/boost/type_traits/detail/has_binary_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_base_of.hpp>
  13 #include <boost/type_traits/is_const.hpp>
  14 #include <boost/type_traits/is_convertible.hpp>
  15 #include <boost/type_traits/is_fundamental.hpp>
  16 #include <boost/type_traits/is_integral.hpp>
  17 #include <boost/type_traits/is_pointer.hpp>
  18 #include <boost/type_traits/is_same.hpp>
  19 #include <boost/type_traits/is_void.hpp>
  20 #include <boost/type_traits/remove_cv.hpp>
  21 #include <boost/type_traits/remove_pointer.hpp>
  22 #include <boost/type_traits/remove_reference.hpp>
  23
  24 // cannot include this header without getting warnings of the kind:
  25 // gcc:
  26 //    warning: value computed is not used
  27 //    warning: comparison between signed and unsigned integer expressions
  28 // msvc:
  29 //    warning C4018: '<' : signed/unsigned mismatch
  30 //    warning C4244: '+=' : conversion from 'double' to 'char', possible loss of data
  31 //    warning C4547: '*' : operator before comma has no effect; expected operator with side-effect
  32 //    warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning)
  33 //    warning C4804: '<' : unsafe use of type 'bool' in operation
  34 //    warning C4805: '==' : unsafe mix of type 'bool' and type 'char' in operation
  35 // cannot find another implementation -> declared as system header to suppress these warnings.
  36 #if defined(__GNUC__)
  37 #   pragma GCC system_header
  38 #elif defined(BOOST_MSVC)
  39 #   pragma warning ( push )
  40 #   pragma warning ( disable : 4018 4244 4547 4800 4804 4805 4913)
  41 #   if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000)
  42 #       pragma warning ( disable : 6334)
  43 #   endif
  44 #endif
  45
  46 namespace boost {
  47 namespace detail {
  48
  49 // This namespace ensures that argument-dependent name lookup does not mess things up.
  50 namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) {
  51
  52 // 1. a function to have an instance of type T without requiring T to be default
  53 // constructible
  54 template <typename T> T &make();
  55
  56
  57 // 2. we provide our operator definition for types that do not have one already
  58
  59 // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is
  60 // found in the type's own namespace (our own operator is used) so that we have
  61 // a means to know that our operator was used
  62 struct no_operator { };
  63
  64 // this class allows implicit conversions and makes the following operator
  65 // definition less-preferred than any other such operators that might be found
  66 // via argument-dependent name lookup
  67 struct any { template <class T> any(T const&); };
  68
  69 // when operator BOOST_TT_TRAIT_OP is not available, this one is used
  70 no_operator operator BOOST_TT_TRAIT_OP (const any&, const any&);
  71
  72
  73 // 3. checks if the operator returns void or not
  74 // conditions: Lhs!=void and Rhs!=void
  75
  76 // we first redefine "operator," so that we have no compilation error if
  77 // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of
  78 // (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) to deduce if
  79 // operator BOOST_TT_TRAIT_OP returns void or not:
  80 // - operator BOOST_TT_TRAIT_OP returns void   -> (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns returns_void_t
  81 // - operator BOOST_TT_TRAIT_OP returns !=void -> (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns int
  82 struct returns_void_t { };
  83 template <typename T> int operator,(const T&, returns_void_t);
  84 template <typename T> int operator,(const volatile T&, returns_void_t);
  85
  86 // this intermediate trait has member value of type bool:
  87 // - value==true -> operator BOOST_TT_TRAIT_OP returns void
  88 // - value==false -> operator BOOST_TT_TRAIT_OP does not return void
  89 template < typename Lhs, typename Rhs >
  90 struct operator_returns_void {
  91    // overloads of function returns_void make the difference
  92    // yes_type and no_type have different size by construction
  93    static ::boost::type_traits::yes_type returns_void(returns_void_t);
  94    static ::boost::type_traits::no_type returns_void(int);
  95    BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>(),returns_void_t())))));
  96 };
  97
  98
  99 // 4. checks if the return type is Ret or Ret==dont_care
 100 // conditions: Lhs!=void and Rhs!=void
 101
 102 struct dont_care { };
 103
 104 template < typename Lhs, typename Rhs, typename Ret, bool Returns_void >
 105 struct operator_returns_Ret;
 106
 107 template < typename Lhs, typename Rhs >
 108 struct operator_returns_Ret < Lhs, Rhs, dont_care, true > {
 109    BOOST_STATIC_CONSTANT(bool, value = true);
 110 };
 111
 112 template < typename Lhs, typename Rhs >
 113 struct operator_returns_Ret < Lhs, Rhs, dont_care, false > {
 114    BOOST_STATIC_CONSTANT(bool, value = true);
 115 };
 116
 117 template < typename Lhs, typename Rhs >
 118 struct operator_returns_Ret < Lhs, Rhs, void, true > {
 119    BOOST_STATIC_CONSTANT(bool, value = true);
 120 };
 121
 122 template < typename Lhs, typename Rhs >
 123 struct operator_returns_Ret < Lhs, Rhs, void, false > {
 124    BOOST_STATIC_CONSTANT(bool, value = false);
 125 };
 126
 127 template < typename Lhs, typename Rhs, typename Ret >
 128 struct operator_returns_Ret < Lhs, Rhs, Ret, true > {
 129    BOOST_STATIC_CONSTANT(bool, value = false);
 130 };
 131
 132 // otherwise checks if it is convertible to Ret using the sizeof trick
 133 // based on overload resolution
 134 // condition: Ret!=void and Ret!=dont_care and the operator does not return void
 135 template < typename Lhs, typename Rhs, typename Ret >
 136 struct operator_returns_Ret < Lhs, Rhs, Ret, false > {
 137    static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret
 138    static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise
 139
 140    BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>()))==sizeof(::boost::type_traits::yes_type)));
 141 };
 142
 143
 144 // 5. checks for operator existence
 145 // condition: Lhs!=void and Rhs!=void
 146
 147 // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other
 148 // existing one;
 149 // this is done with redefinition of "operator," that returns no_operator or has_operator
 150 struct has_operator { };
 151 no_operator operator,(no_operator, has_operator);
 152
 153 template < typename Lhs, typename Rhs >
 154 struct operator_exists {
 155    static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists
 156    static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise
 157
 158    BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>()),make<has_operator>())))==sizeof(::boost::type_traits::yes_type)));
 159 };
 160
 161
 162 // 6. main trait: to avoid any compilation error, this class behaves
 163 // differently when operator BOOST_TT_TRAIT_OP(Lhs, Rhs) is forbidden by the
 164 // standard.
 165 // Forbidden_if is a bool that is:
 166 // - true when the operator BOOST_TT_TRAIT_OP(Lhs, Rhs) is forbidden by the standard
 167 //   (would yield compilation error if used)
 168 // - false otherwise
 169 template < typename Lhs, typename Rhs, typename Ret, bool Forbidden_if >
 170 struct trait_impl1;
 171
 172 template < typename Lhs, typename Rhs, typename Ret >
 173 struct trait_impl1 < Lhs, Rhs, Ret, true > {
 174    BOOST_STATIC_CONSTANT(bool, value = false);
 175 };
 176
 177 template < typename Lhs, typename Rhs, typename Ret >
 178 struct trait_impl1 < Lhs, Rhs, Ret, false > {
 179    BOOST_STATIC_CONSTANT(bool,
 180       value = (operator_exists < Lhs, Rhs >::value && operator_returns_Ret < Lhs, Rhs, Ret, operator_returns_void < Lhs, Rhs >::value >::value));
 181 };
 182
 183 // some specializations needs to be declared for the special void case
 184 template < typename Rhs, typename Ret >
 185 struct trait_impl1 < void, Rhs, Ret, false > {
 186    BOOST_STATIC_CONSTANT(bool, value = false);
 187 };
 188
 189 template < typename Lhs, typename Ret >
 190 struct trait_impl1 < Lhs, void, Ret, false > {
 191    BOOST_STATIC_CONSTANT(bool, value = false);
 192 };
 193
 194 template < typename Ret >
 195 struct trait_impl1 < void, void, Ret, false > {
 196    BOOST_STATIC_CONSTANT(bool, value = false);
 197 };
 198
 199 // defines some typedef for convenience
 200 template < typename Lhs, typename Rhs, typename Ret >
 201 struct trait_impl {
 202    typedef typename ::boost::remove_reference<Lhs>::type Lhs_noref;
 203    typedef typename ::boost::remove_reference<Rhs>::type Rhs_noref;
 204    typedef typename ::boost::remove_cv<Lhs_noref>::type Lhs_nocv;
 205    typedef typename ::boost::remove_cv<Rhs_noref>::type Rhs_nocv;
 206    typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Lhs_noref>::type >::type >::type Lhs_noptr;
 207    typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Rhs_noref>::type >::type >::type Rhs_noptr;
 208    BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Lhs_noref, Rhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value));
 209 };
 210
 211 } // namespace impl
 212 } // namespace detail
 213
 214 // this is the accessible definition of the trait to end user
 215 template <class Lhs, class Rhs=Lhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care>
 216 struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl < Lhs, Rhs, Ret >::value)>{};
 217
 218 } // namespace boost
 219
 220 #if defined(BOOST_MSVC)
 221 #   pragma warning ( pop )
 222 #endif