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   1 //-----------------------------------------------------------------------------
   2 // boost variant/detail/over_sequence.hpp header file
   3 // See http://www.boost.org for updates, documentation, and revision history.
   4 //-----------------------------------------------------------------------------
   5 //
   6 // Copyright (c) 2003
   7 // Eric Friedman
   8 //
   9 // Portions Copyright (C) 2002 David Abrahams
  10 //
  11 // Distributed under the Boost Software License, Version 1.0. (See
  12 // accompanying file LICENSE_1_0.txt or copy at
  13 // http://www.boost.org/LICENSE_1_0.txt)
  14
  15 #ifndef BOOST_VARIANT_DETAIL_OVER_SEQUENCE_HPP
  16 #define BOOST_VARIANT_DETAIL_OVER_SEQUENCE_HPP
  17
  18 #include "boost/mpl/aux_/config/ctps.hpp"
  19 #if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  20 #   include "boost/mpl/eval_if.hpp"
  21 #   include "boost/mpl/bool.hpp"
  22 #   include "boost/mpl/identity.hpp"
  23 #   include "boost/type.hpp"
  24 #endif
  25
  26
  27 namespace boost {
  28 namespace detail { namespace variant {
  29
  30 ///////////////////////////////////////////////////////////////////////////////
  31 // (detail) class over_sequence
  32 //
  33 // Wrapper used to indicate bounded types for variant are from type sequence.
  34 //
  35 template <typename Types>
  36 struct over_sequence
  37 {
  38     typedef Types type;
  39 };
  40
  41 ///////////////////////////////////////////////////////////////////////////////
  42 // (detail) metafunction is_over_sequence (modeled on code by David Abrahams)
  43 //
  44 // Indicates whether the specified type is of form over_sequence<...> or not.
  45 //
  46
  47 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  48
  49 template <typename T>
  50 struct is_over_sequence
  51     : mpl::false_
  52 {
  53 };
  54
  55 template <typename Types>
  56 struct is_over_sequence< over_sequence<Types> >
  57     : mpl::true_
  58 {
  59 };
  60
  61 #else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  62
  63 typedef char (&yes_over_sequence_t)[1];
  64 typedef char (&no_over_sequence_t)[2];
  65
  66 no_over_sequence_t is_over_sequence_test(...);
  67
  68 template<typename T>
  69 yes_over_sequence_t is_over_sequence_test(
  70       type< ::boost::detail::variant::over_sequence<T> >
  71     );
  72
  73 template<typename T>
  74 struct is_over_sequence_impl
  75 {
  76     BOOST_STATIC_CONSTANT(bool, value = (
  77           sizeof(is_over_sequence_test(type<T>()))
  78           == sizeof(yes_over_sequence_t)
  79         ));
  80 };
  81
  82 template <typename T>
  83 struct is_over_sequence
  84     : mpl::bool_<
  85           ::boost::detail::variant::is_over_sequence_impl<T>::value
  86         >
  87 {
  88 };
  89
  90 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
  91
  92 }} // namespace detail::variant
  93 } // namespace boost
  94
  95 #endif // BOOST_VARIANT_DETAIL_OVER_SEQUENCE_HPP