boost/variant/detail/enable_recursive_fwd.hpp

   1 //-----------------------------------------------------------------------------
   2 // boost variant/detail/enable_recursive_fwd.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 // Distributed under the Boost Software License, Version 1.0. (See
  10 // accompanying file LICENSE_1_0.txt or copy at
  11 // http://www.boost.org/LICENSE_1_0.txt)
  12
  13 #ifndef BOOST_VARIANT_DETAIL_ENABLE_RECURSIVE_FWD_HPP
  14 #define BOOST_VARIANT_DETAIL_ENABLE_RECURSIVE_FWD_HPP
  15
  16 #include "boost/mpl/aux_/config/ctps.hpp"
  17
  18 #include "boost/mpl/bool_fwd.hpp"
  19
  20 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  21 #   include "boost/mpl/bool.hpp"
  22 #else
  23 #   include "boost/type_traits/is_base_and_derived.hpp"
  24 #endif
  25
  26 namespace boost {
  27 namespace detail { namespace variant {
  28
  29 ///////////////////////////////////////////////////////////////////////////////
  30 // (detail) tag recursive_flag
  31 //
  32 // Signifies that the variant should perform recursive substituion.
  33 //
  34
  35 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  36
  37 template <typename T>
  38 struct recursive_flag
  39 {
  40     typedef T type;
  41 };
  42
  43 #else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  44
  45 struct recursive_flag_tag
  46 {
  47 };
  48
  49 template <typename T>
  50 struct recursive_flag
  51     : recursive_flag_tag
  52 {
  53     typedef T type;
  54 };
  55
  56 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
  57
  58 ///////////////////////////////////////////////////////////////////////////////
  59 // (detail) metafunction is_recursive_flag
  60 //
  61 // Signifies that the variant should perform recursive substituion.
  62 //
  63
  64 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  65
  66 template <typename T>
  67 struct is_recursive_flag
  68     : mpl::false_
  69 {
  70 };
  71
  72 template <typename T>
  73 struct is_recursive_flag< recursive_flag<T> >
  74     : mpl::true_
  75 {
  76 };
  77
  78 #else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
  79
  80 template <typename T>
  81 struct is_recursive_flag
  82     : is_base_and_derived< recursive_flag_tag,T >
  83 {
  84 };
  85
  86 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
  87
  88 ///////////////////////////////////////////////////////////////////////////////
  89 // (detail) metafunction enable_recursive
  90 //
  91 // Attempts recursive_variant_ tag substitution, wrapping with
  92 // boost::recursive_wrapper if substituion occurs w/ non-indirect result
  93 // (i.e., not a reference or pointer) *and* NoWrapper is false_.
  94 //
  95 template <
  96       typename T
  97     , typename RecursiveVariant
  98     , typename NoWrapper = mpl::false_
  99     >
 100 struct enable_recursive;
 101
 102 ///////////////////////////////////////////////////////////////////////////////
 103 // (detail) metafunction class quoted_enable_recursive
 104 //
 105 // Same behavior as enable_recursive metafunction (see above).
 106 //
 107 template <
 108       typename RecursiveVariant
 109     , typename NoWrapper = mpl::false_
 110     >
 111 struct quoted_enable_recursive;
 112
 113 }} // namespace detail::variant
 114 } // namespace boost
 115
 116 #endif // BOOST_VARIANT_DETAIL_ENABLE_RECURSIVE_FWD_HPP