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1 | // |
2 | // cpp03/prefer_free_require.cpp | |
3 | // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
4 | // | |
5 | // Copyright (c) 2003-2020 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 | ||
14 | template <int> | |
15 | struct prop | |
16 | { | |
17 | static const bool is_preferable = true; | |
18 | }; | |
19 | ||
20 | template <int> | |
21 | struct object | |
22 | { | |
23 | template <int N> | |
24 | friend object<N> require(const object&, prop<N>) | |
25 | { | |
26 | return object<N>(); | |
27 | } | |
28 | }; | |
29 | ||
30 | namespace boost { | |
31 | namespace asio { | |
32 | ||
33 | template<int N, int M> | |
34 | struct is_applicable_property<object<N>, prop<M> > | |
35 | { | |
36 | static const bool value = true; | |
37 | }; | |
38 | ||
39 | namespace traits { | |
40 | ||
41 | template<int N, int M> | |
42 | struct require_free<object<N>, prop<M> > | |
43 | { | |
44 | static const bool is_valid = true; | |
45 | static const bool is_noexcept = true; | |
46 | typedef object<M> result_type; | |
47 | }; | |
48 | ||
49 | } // namespace traits | |
50 | } // namespace asio | |
51 | } // namespace boost | |
52 | ||
53 | int main() | |
54 | { | |
55 | object<1> o1 = {}; | |
56 | object<2> o2 = boost::asio::prefer(o1, prop<2>()); | |
57 | object<3> o3 = boost::asio::prefer(o1, prop<2>(), prop<3>()); | |
58 | object<4> o4 = boost::asio::prefer(o1, prop<2>(), prop<3>(), prop<4>()); | |
59 | (void)o2; | |
60 | (void)o3; | |
61 | (void)o4; | |
62 | ||
63 | const object<1> o5 = {}; | |
64 | object<2> o6 = boost::asio::prefer(o5, prop<2>()); | |
65 | object<3> o7 = boost::asio::prefer(o5, prop<2>(), prop<3>()); | |
66 | object<4> o8 = boost::asio::prefer(o5, prop<2>(), prop<3>(), prop<4>()); | |
67 | (void)o6; | |
68 | (void)o7; | |
69 | (void)o8; | |
70 | } |