1 /*! 2 @file 3 Adapts `std::pair` for use with Hana. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_EXT_STD_PAIR_HPP 11 #define BOOST_HANA_EXT_STD_PAIR_HPP 12 13 #include <boost/hana/config.hpp> 14 #include <boost/hana/fwd/core/make.hpp> 15 #include <boost/hana/fwd/core/tag_of.hpp> 16 #include <boost/hana/fwd/first.hpp> 17 #include <boost/hana/fwd/second.hpp> 18 19 #include <utility> 20 21 22 #ifdef BOOST_HANA_DOXYGEN_INVOKED 23 namespace std { 24 //! @ingroup group-ext-std 25 //! Adaptation of `std::pair` for Hana. 26 //! 27 //! 28 //! Modeled concepts 29 //! ---------------- 30 //! A `std::pair` models exactly the same concepts as a `hana::pair`. 31 //! Please refer to the documentation of `hana::pair` for details. 32 //! 33 //! @include example/ext/std/pair.cpp 34 template <typename First, typename Second> 35 struct pair { }; 36 } 37 #endif 38 39 40 BOOST_HANA_NAMESPACE_BEGIN 41 namespace ext { namespace std { struct pair_tag; }} 42 43 template <typename First, typename Second> 44 struct tag_of<std::pair<First, Second>> { 45 using type = ext::std::pair_tag; 46 }; 47 48 ////////////////////////////////////////////////////////////////////////// 49 // Product 50 ////////////////////////////////////////////////////////////////////////// 51 template <> 52 struct make_impl<ext::std::pair_tag> { 53 template <typename X, typename Y> applymake_impl54 static constexpr decltype(auto) apply(X&& x, Y&& y) { 55 return std::make_pair(static_cast<X&&>(x), 56 static_cast<Y&&>(y)); 57 } 58 }; 59 60 template <> 61 struct first_impl<ext::std::pair_tag> { 62 template <typename T, typename U> applyfirst_impl63 static constexpr T const& apply(std::pair<T, U> const& p) 64 { return p.first; } 65 66 template <typename T, typename U> applyfirst_impl67 static constexpr T& apply(std::pair<T, U>& p) 68 { return p.first; } 69 70 template <typename T, typename U> applyfirst_impl71 static constexpr T&& apply(std::pair<T, U>&& p) 72 { return static_cast<T&&>(p.first); } 73 }; 74 75 template <> 76 struct second_impl<ext::std::pair_tag> { 77 template <typename T, typename U> applysecond_impl78 static constexpr U const& apply(std::pair<T, U> const& p) 79 { return p.second; } 80 81 template <typename T, typename U> applysecond_impl82 static constexpr U& apply(std::pair<T, U>& p) 83 { return p.second; } 84 85 template <typename T, typename U> applysecond_impl86 static constexpr U&& apply(std::pair<T, U>&& p) 87 { return static_cast<U&&>(p.second); } 88 }; 89 BOOST_HANA_NAMESPACE_END 90 91 #endif // !BOOST_HANA_EXT_STD_PAIR_HPP 92