1//
2// cpp03/require_free.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/require.hpp>
12#include <cassert>
13
14template <int>
15struct prop
16{
17 static const bool is_requirable = true;
18};
19
20template <int>
21struct object
22{
23 template <int N>
24 friend object<N> require(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 const bool value = true;
37};
38
39namespace traits {
40
41template<int N, int M>
42struct 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
53int main()
54{
55 object<1> o1 = {};
56 object<2> o2 = boost::asio::require(o1, prop<2>());
57 object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
58 object<4> o4 = boost::asio::require(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::require(o5, prop<2>());
65 object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
66 object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
67 (void)o6;
68 (void)o7;
69 (void)o8;
70}
71

source code of boost/libs/asio/test/properties/cpp03/require_free.cpp