[857] | 1 | // Copyright David Abrahams 2003. Use, modification and distribution is
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| 2 | // subject to the Boost Software License, Version 1.0. (See accompanying
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| 3 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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| 4 | #ifndef MINIMUM_CATEGORY_DWA20031119_HPP
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| 5 | # define MINIMUM_CATEGORY_DWA20031119_HPP
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| 6 |
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| 7 | # include <boost/type_traits/is_convertible.hpp>
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| 8 | # include <boost/type_traits/is_same.hpp>
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| 9 |
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| 10 | # include <boost/mpl/aux_/lambda_support.hpp>
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| 11 |
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| 12 | namespace boost { namespace detail {
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| 13 | //
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| 14 | // Returns the minimum category type or error_type
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| 15 | // if T1 and T2 are unrelated.
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| 16 | //
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| 17 | // For compilers not supporting is_convertible this only
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| 18 | // works with the new boost return and traversal category
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| 19 | // types. The exact boost _types_ are required. No derived types
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| 20 | // will work.
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| 21 | //
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| 22 | //
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| 23 | template <bool GreaterEqual, bool LessEqual>
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| 24 | struct minimum_category_impl
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| 25 | # if BOOST_WORKAROUND(BOOST_MSVC, == 1200)
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| 26 | {
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| 27 | template <class T1, class T2> struct apply
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| 28 | {
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| 29 | typedef T2 type;
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| 30 | };
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| 31 | typedef void type;
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| 32 | }
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| 33 | # endif
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| 34 | ;
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| 35 |
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| 36 | template <class T1, class T2>
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| 37 | struct error_not_related_by_convertibility;
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| 38 |
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| 39 | template <>
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| 40 | struct minimum_category_impl<true,false>
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| 41 | {
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| 42 | template <class T1, class T2> struct apply
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| 43 | {
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| 44 | typedef T2 type;
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| 45 | };
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| 46 | };
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| 47 |
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| 48 | template <>
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| 49 | struct minimum_category_impl<false,true>
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| 50 | {
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| 51 | template <class T1, class T2> struct apply
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| 52 | {
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| 53 | typedef T1 type;
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| 54 | };
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| 55 | };
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| 56 |
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| 57 | template <>
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| 58 | struct minimum_category_impl<true,true>
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| 59 | {
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| 60 | template <class T1, class T2> struct apply
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| 61 | {
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| 62 | BOOST_STATIC_ASSERT((is_same<T1,T2>::value));
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| 63 | typedef T1 type;
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| 64 | };
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| 65 | };
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| 66 |
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| 67 | template <>
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| 68 | struct minimum_category_impl<false,false>
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| 69 | {
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| 70 | template <class T1, class T2> struct apply
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| 71 | : error_not_related_by_convertibility<T1,T2>
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| 72 | {
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| 73 | };
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| 74 | };
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| 75 |
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| 76 | template <class T1 = mpl::_1, class T2 = mpl::_2>
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| 77 | struct minimum_category
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| 78 | {
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| 79 | typedef minimum_category_impl<
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| 80 | # if BOOST_WORKAROUND(BOOST_MSVC, == 1200) // ETI workaround
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| 81 | is_same<T2,int>::value ||
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| 82 | # endif
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| 83 | ::boost::is_convertible<T1,T2>::value
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| 84 | , ::boost::is_convertible<T2,T1>::value
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| 85 | # if BOOST_WORKAROUND(BOOST_MSVC, == 1200) // ETI workaround
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| 86 | || is_same<T1,int>::value
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| 87 | # endif
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| 88 | > outer;
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| 89 |
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| 90 | typedef typename outer::template apply<T1,T2> inner;
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| 91 | typedef typename inner::type type;
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| 92 |
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| 93 | BOOST_MPL_AUX_LAMBDA_SUPPORT(2,minimum_category,(T1,T2))
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| 94 | };
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| 95 |
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| 96 | template <>
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| 97 | struct minimum_category<mpl::_1,mpl::_2>
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| 98 | {
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| 99 | template <class T1, class T2>
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| 100 | struct apply : minimum_category<T1,T2>
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| 101 | {};
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| 102 |
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| 103 | BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(2,minimum_category,(mpl::_1,mpl::_2))
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| 104 | };
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| 105 |
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| 106 | # if BOOST_WORKAROUND(BOOST_MSVC, == 1200) // ETI workaround
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| 107 | template <>
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| 108 | struct minimum_category<int,int>
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| 109 | {
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| 110 | typedef int type;
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| 111 | };
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| 112 | # endif
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| 113 |
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| 114 | }} // namespace boost::detail
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| 115 |
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| 116 | #endif // MINIMUM_CATEGORY_DWA20031119_HPP
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