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74 lines
1.8 KiB
C++
74 lines
1.8 KiB
C++
// Copyright (C) 2019 Andrzej Krzemienski.
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//
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// Use, modification, and distribution is subject to the Boost Software
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// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/lib/optional for documentation.
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//
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// You are welcome to contact the author at:
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// akrzemi1@gmail.com
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#include "boost/optional/optional.hpp"
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#ifdef BOOST_BORLANDC
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#pragma hdrstop
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#endif
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#ifndef BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
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#ifndef BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
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template <typename, typename>
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struct void_t
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{
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typedef void type;
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};
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template <typename T, typename = void>
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struct trait
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{
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};
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// the following trait emulates properties std::iterator_traits
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template <typename T>
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struct trait<T, BOOST_DEDUCED_TYPENAME void_t<BOOST_DEDUCED_TYPENAME T::value_type,
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BOOST_DEDUCED_TYPENAME boost::enable_if<boost::is_constructible<T, T&> >::type
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>::type>
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{
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typedef BOOST_DEDUCED_TYPENAME T::value_type value_type;
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};
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// This class emulates the properties of std::filesystem::path
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struct Path
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{
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#if __cplusplus >= 201103
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template <typename T, typename = BOOST_DEDUCED_TYPENAME trait<T>::value_type>
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Path(T const&);
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#else
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template <typename T>
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Path(T const&, BOOST_DEDUCED_TYPENAME trait<T>::value_type* = 0);
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#endif
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};
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#endif
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#endif
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int main()
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{
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#ifndef BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
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#ifndef BOOST_OPTIONAL_DETAIL_NO_SFINAE_FRIENDLY_CONSTRUCTORS
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boost::optional<Path> optFs1;
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boost::optional<Path> optFs2;
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optFs1 = optFs2;
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// the following still fails although it shouldn't
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//static_assert((std::is_copy_constructible<boost::optional<Path>>::value), "ERROR");
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#endif
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#endif
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}
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