[857] | 1 | // (C) Copyright David Abrahams 2002.
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| 2 | // (C) Copyright Jeremy Siek 2002.
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| 3 | // (C) Copyright Thomas Witt 2002.
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| 4 | // Distributed under the Boost Software License, Version 1.0. (See
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| 5 | // accompanying file LICENSE_1_0.txt or copy at
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| 6 | // http://www.boost.org/LICENSE_1_0.txt)
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| 7 | #ifndef BOOST_ENABLE_IF_23022003THW_HPP
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| 8 | #define BOOST_ENABLE_IF_23022003THW_HPP
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| 9 |
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| 10 | #include <boost/detail/workaround.hpp>
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| 11 | #include <boost/mpl/identity.hpp>
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| 12 |
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| 13 | #include <boost/iterator/detail/config_def.hpp>
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| 14 |
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| 15 | //
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| 16 | // Boost iterators uses its own enable_if cause we need
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| 17 | // special semantics for deficient compilers.
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| 18 | // 23/02/03 thw
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| 19 | //
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| 20 |
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| 21 | namespace boost
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| 22 | {
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| 23 |
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| 24 | namespace iterators
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| 25 | {
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| 26 | //
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| 27 | // Base machinery for all kinds of enable if
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| 28 | //
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| 29 | template<bool>
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| 30 | struct enabled
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| 31 | {
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| 32 | template<typename T>
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| 33 | struct base
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| 34 | {
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| 35 | typedef T type;
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| 36 | };
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| 37 | };
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| 38 |
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| 39 | //
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| 40 | // For compilers that don't support "Substitution Failure Is Not An Error"
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| 41 | // enable_if falls back to always enabled. See comments
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| 42 | // on operator implementation for consequences.
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| 43 | //
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| 44 | template<>
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| 45 | struct enabled<false>
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| 46 | {
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| 47 | template<typename T>
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| 48 | struct base
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| 49 | {
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| 50 | #ifdef BOOST_NO_SFINAE
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| 51 |
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| 52 | typedef T type;
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| 53 |
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| 54 | // This way to do it would give a nice error message containing
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| 55 | // invalid overload, but has the big disadvantage that
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| 56 | // there is no reference to user code in the error message.
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| 57 | //
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| 58 | // struct invalid_overload;
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| 59 | // typedef invalid_overload type;
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| 60 | //
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| 61 | #endif
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| 62 | };
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| 63 | };
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| 64 |
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| 65 |
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| 66 | template <class Cond,
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| 67 | class Return>
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| 68 | struct enable_if
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| 69 | # if !defined(BOOST_NO_SFINAE) && !defined(BOOST_NO_IS_CONVERTIBLE)
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| 70 | : enabled<(Cond::value)>::template base<Return>
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| 71 | # else
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| 72 | : mpl::identity<Return>
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| 73 | # endif
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| 74 | {
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| 75 | # if BOOST_WORKAROUND(BOOST_MSVC, <= 1200)
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| 76 | typedef Return type;
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| 77 | # endif
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| 78 | };
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| 79 |
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| 80 | } // namespace iterators
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| 81 |
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| 82 | } // namespace boost
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| 83 |
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| 84 | #include <boost/iterator/detail/config_undef.hpp>
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| 85 |
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| 86 | #endif // BOOST_ENABLE_IF_23022003THW_HPP
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