ceph/src/boost/boost/iostreams/detail/is_dereferenceable.hpp

   1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
   2 // (C) Copyright 2005-2007 Jonathan Turkanis
   3 // (C) Copyright David Abrahams 2004.
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
   6
   7 // See http://www.boost.org/libs/iostreams for documentation.
   8
   9 #ifndef BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
  10 #define BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
  11
  12 # include <boost/type_traits/remove_cv.hpp>
  13 # include <boost/mpl/aux_/lambda_support.hpp>
  14 # include <boost/mpl/bool.hpp>
  15 # include <boost/detail/workaround.hpp>
  16
  17 namespace boost { namespace iostreams { namespace detail {
  18
  19 // is_dereferenceable<T> metafunction
  20 //
  21 // Requires: Given x of type T&, if the expression *x is well-formed
  22 // it must have complete type; otherwise, it must neither be ambiguous
  23 // nor violate access.
  24
  25 // This namespace ensures that ADL doesn't mess things up.
  26 namespace is_dereferenceable_
  27 {
  28   // a type returned from operator* when no increment is found in the
  29   // type's own namespace
  30   struct tag {};
  31
  32   // any soaks up implicit conversions and makes the following
  33   // operator* less-preferred than any other such operator that
  34   // might be found via ADL.
  35   struct any { template <class T> any(T const&); };
  36
  37   // This is a last-resort operator* for when none other is found
  38   tag operator*(any const&);
  39
  40 # if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202))
  41 #  define BOOST_comma(a,b) (a)
  42 # else
  43   // In case an operator++ is found that returns void, we'll use ++x,0
  44   tag operator,(tag,int);
  45 #  define BOOST_comma(a,b) (a,b)
  46 # endif
  47
  48   // two check overloads help us identify which operator++ was picked
  49   char (& check_increment(tag) )[2];
  50
  51   template <class T>
  52   char check_increment(T const&);
  53
  54   template <class T>
  55   struct impl
  56   {
  57       static typename boost::remove_cv<T>::type& x;
  58
  59       BOOST_STATIC_CONSTANT(
  60           bool
  61         , value = sizeof(is_dereferenceable_::check_increment(BOOST_comma(*x,0))) == 1
  62       );
  63   };
  64 }
  65
  66 # undef BOOST_comma
  67
  68 template<typename T>
  69 struct is_dereferenceable
  70     : public ::boost::integral_constant<bool, is_dereferenceable_::impl<T>::value >
  71 {
  72     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_dereferenceable,(T))
  73 };
  74
  75 } }
  76
  77
  78 } // End namespaces detail, iostreams, boost.
  79
  80 #endif // BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED