| // |
| // cpp03/prefer_free_require.cpp |
| // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| // |
| // Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See accompanying |
| // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| // |
| |
| #include <boost/asio/prefer.hpp> |
| #include <cassert> |
| |
| template <int> |
| struct prop |
| { |
| static const bool is_preferable = true; |
| }; |
| |
| template <int> |
| struct object |
| { |
| template <int N> |
| friend object<N> require(const object&, prop<N>) |
| { |
| return object<N>(); |
| } |
| }; |
| |
| namespace boost { |
| namespace asio { |
| |
| template<int N, int M> |
| struct is_applicable_property<object<N>, prop<M> > |
| { |
| static const bool value = true; |
| }; |
| |
| namespace traits { |
| |
| template<int N, int M> |
| struct require_free<object<N>, prop<M> > |
| { |
| static const bool is_valid = true; |
| static const bool is_noexcept = true; |
| typedef object<M> result_type; |
| }; |
| |
| } // namespace traits |
| } // namespace asio |
| } // namespace boost |
| |
| int main() |
| { |
| object<1> o1 = {}; |
| object<2> o2 = boost::asio::prefer(o1, prop<2>()); |
| object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>()); |
| object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>()); |
| (void)o2; |
| (void)o3; |
| (void)o4; |
| |
| const object<1> o5 = {}; |
| object<2> o6 = boost::asio::prefer(o5, prop<2>()); |
| object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>()); |
| object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>()); |
| (void)o6; |
| (void)o7; |
| (void)o8; |
| } |