1//
2// cpp11/can_prefer_free_prefer.cpp
3// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4//
5// Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com)
6//
7// Distributed under the Boost Software License, Version 1.0. (See accompanying
8// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
9//
10
11#include <boost/asio/prefer.hpp>
12#include <cassert>
13
14template <int>
15struct prop
16{
17 static constexpr bool is_preferable = true;
18};
19
20template <int>
21struct object
22{
23 template <int N>
24 friend constexpr object<N> prefer(const object&, prop<N>)
25 {
26 return object<N>();
27 }
28};
29
30namespace boost {
31namespace asio {
32
33template<int N, int M>
34struct is_applicable_property<object<N>, prop<M> >
35{
36 static constexpr bool value = true;
37};
38
39} // namespace asio
40} // namespace boost
41
42int main()
43{
44 static_assert(boost::asio::can_prefer<object<1>, prop<2>>::value, "");
45 static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>>::value, "");
46 static_assert(boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4>>::value, "");
47 static_assert(boost::asio::can_prefer<const object<1>, prop<2>>::value, "");
48 static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>>::value, "");
49 static_assert(boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4>>::value, "");
50}
51

source code of boost/libs/asio/test/properties/cpp11/can_prefer_free_prefer.cpp