[3408] | 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, < 1300) |
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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, < 1300) // 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, < 1300) // 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, < 1300) // 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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