ceph/src/boost/libs/iterator/include/boost/iterator/minimum_category.hpp

   1 // Copyright David Abrahams 2003. 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 BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_
   5 # define BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_
   6
   7 # include <boost/static_assert.hpp>
   8 # include <boost/type_traits/is_convertible.hpp>
   9 # include <boost/type_traits/is_same.hpp>
  10
  11 # include <boost/mpl/placeholders.hpp>
  12 # include <boost/mpl/aux_/lambda_support.hpp>
  13
  14 namespace boost {
  15 namespace iterators {
  16 namespace detail {
  17
  18 template <bool GreaterEqual, bool LessEqual>
  19 struct minimum_category_impl;
  20
  21 template <class T1, class T2>
  22 struct error_not_related_by_convertibility;
  23
  24 template <>
  25 struct minimum_category_impl<true,false>
  26 {
  27     template <class T1, class T2> struct apply
  28     {
  29         typedef T2 type;
  30     };
  31 };
  32
  33 template <>
  34 struct minimum_category_impl<false,true>
  35 {
  36     template <class T1, class T2> struct apply
  37     {
  38         typedef T1 type;
  39     };
  40 };
  41
  42 template <>
  43 struct minimum_category_impl<true,true>
  44 {
  45     template <class T1, class T2> struct apply
  46     {
  47         BOOST_STATIC_ASSERT((is_same<T1,T2>::value));
  48         typedef T1 type;
  49     };
  50 };
  51
  52 template <>
  53 struct minimum_category_impl<false,false>
  54 {
  55     template <class T1, class T2> struct apply
  56       : error_not_related_by_convertibility<T1,T2>
  57     {
  58     };
  59 };
  60
  61 } // namespace detail
  62
  63 //
  64 // Returns the minimum category type or fails to compile
  65 // if T1 and T2 are unrelated.
  66 //
  67 template <class T1 = mpl::_1, class T2 = mpl::_2>
  68 struct minimum_category
  69 {
  70     typedef boost::iterators::detail::minimum_category_impl<
  71         ::boost::is_convertible<T1,T2>::value
  72       , ::boost::is_convertible<T2,T1>::value
  73     > outer;
  74
  75     typedef typename outer::template apply<T1,T2> inner;
  76     typedef typename inner::type type;
  77
  78     BOOST_MPL_AUX_LAMBDA_SUPPORT(2,minimum_category,(T1,T2))
  79 };
  80
  81 template <>
  82 struct minimum_category<mpl::_1,mpl::_2>
  83 {
  84     template <class T1, class T2>
  85     struct apply : minimum_category<T1,T2>
  86     {};
  87
  88     BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(2,minimum_category,(mpl::_1,mpl::_2))
  89 };
  90
  91 } // namespace iterators
  92
  93 } // namespace boost
  94
  95 #endif // BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_