boost/detail/is_incrementable.hpp

   1 // Copyright David Abrahams 2004. Use, modification and distribution is
   2 // subject to the Boost Software License, Version 1.0. (See accompanying
   3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   4 #ifndef IS_INCREMENTABLE_DWA200415_HPP
   5 # define IS_INCREMENTABLE_DWA200415_HPP
   6
   7 # include <boost/type_traits/detail/template_arity_spec.hpp>
   8 # include <boost/type_traits/remove_cv.hpp>
   9 # include <boost/mpl/aux_/lambda_support.hpp>
  10 # include <boost/mpl/bool.hpp>
  11 # include <boost/detail/workaround.hpp>
  12
  13 // Must be the last include
  14 # include <boost/type_traits/detail/bool_trait_def.hpp>
  15
  16 namespace boost { namespace detail {
  17
  18 // is_incrementable<T> metafunction
  19 //
  20 // Requires: Given x of type T&, if the expression ++x is well-formed
  21 // it must have complete type; otherwise, it must neither be ambiguous
  22 // nor violate access.
  23
  24 // This namespace ensures that ADL doesn't mess things up.
  25 namespace is_incrementable_
  26 {
  27   // a type returned from operator++ when no increment is found in the
  28   // type's own namespace
  29   struct tag {};
  30
  31   // any soaks up implicit conversions and makes the following
  32   // operator++ less-preferred than any other such operator that
  33   // might be found via ADL.
  34   struct any { template <class T> any(T const&); };
  35
  36   // This is a last-resort operator++ for when none other is found
  37 # if BOOST_WORKAROUND(__GNUC__, == 4) && __GNUC_MINOR__ == 0 && __GNUC_PATCHLEVEL__ == 2
  38
  39 }
  40
  41 namespace is_incrementable_2
  42 {
  43   is_incrementable_::tag operator++(is_incrementable_::any const&);
  44   is_incrementable_::tag operator++(is_incrementable_::any const&,int);
  45 }
  46 using namespace is_incrementable_2;
  47
  48 namespace is_incrementable_
  49 {
  50
  51 # else
  52
  53   tag operator++(any const&);
  54   tag operator++(any const&,int);
  55
  56 # endif
  57
  58 # if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202)) \
  59     || BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
  60 #  define BOOST_comma(a,b) (a)
  61 # else
  62   // In case an operator++ is found that returns void, we'll use ++x,0
  63   tag operator,(tag,int);
  64 #  define BOOST_comma(a,b) (a,b)
  65 # endif
  66
  67 # if defined(BOOST_MSVC)
  68 #  pragma warning(push)
  69 #  pragma warning(disable:4913) // Warning about operator,
  70 # endif
  71
  72   // two check overloads help us identify which operator++ was picked
  73   char (& check(tag) )[2];
  74
  75   template <class T>
  76   char check(T const&);
  77
  78
  79   template <class T>
  80   struct impl
  81   {
  82       static typename boost::remove_cv<T>::type& x;
  83
  84       BOOST_STATIC_CONSTANT(
  85           bool
  86         , value = sizeof(is_incrementable_::check(BOOST_comma(++x,0))) == 1
  87       );
  88   };
  89
  90   template <class T>
  91   struct postfix_impl
  92   {
  93       static typename boost::remove_cv<T>::type& x;
  94
  95       BOOST_STATIC_CONSTANT(
  96           bool
  97         , value = sizeof(is_incrementable_::check(BOOST_comma(x++,0))) == 1
  98       );
  99   };
 100
 101 # if defined(BOOST_MSVC)
 102 #  pragma warning(pop)
 103 # endif
 104
 105 }
 106
 107 # undef BOOST_comma
 108
 109 template<typename T>
 110 struct is_incrementable
 111 BOOST_TT_AUX_BOOL_C_BASE(::boost::detail::is_incrementable_::impl<T>::value)
 112 {
 113     BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(::boost::detail::is_incrementable_::impl<T>::value)
 114     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_incrementable,(T))
 115 };
 116
 117 template<typename T>
 118 struct is_postfix_incrementable
 119 BOOST_TT_AUX_BOOL_C_BASE(::boost::detail::is_incrementable_::impl<T>::value)
 120 {
 121     BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(::boost::detail::is_incrementable_::postfix_impl<T>::value)
 122     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_postfix_incrementable,(T))
 123 };
 124
 125 } // namespace detail
 126
 127 BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1, ::boost::detail::is_incrementable)
 128 BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1, ::boost::detail::is_postfix_incrementable)
 129
 130 } // namespace boost
 131
 132 # include <boost/type_traits/detail/bool_trait_undef.hpp>
 133
 134 #endif // IS_INCREMENTABLE_DWA200415_HPP