1//
2// cpp14/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 template <typename> static constexpr bool is_applicable_property_v = true;
18 static constexpr bool is_requirable = true;
19};
20
21template <int>
22struct object
23{
24 template <int N>
25 friend constexpr object<N> require(const object&, prop<N>)
26 {
27 return object<N>();
28 }
29};
30
31int main()
32{
33 object<1> o1 = {};
34 object<2> o2 = boost::asio::require(o1, prop<2>());
35 object<3> o3 = boost::asio::require(o1, prop<2>(), prop<3>());
36 object<4> o4 = boost::asio::require(o1, prop<2>(), prop<3>(), prop<4>());
37 (void)o2;
38 (void)o3;
39 (void)o4;
40
41 const object<1> o5 = {};
42 object<2> o6 = boost::asio::require(o5, prop<2>());
43 object<3> o7 = boost::asio::require(o5, prop<2>(), prop<3>());
44 object<4> o8 = boost::asio::require(o5, prop<2>(), prop<3>(), prop<4>());
45 (void)o6;
46 (void)o7;
47 (void)o8;
48
49 constexpr object<2> o9 = boost::asio::require(object<1>(), prop<2>());
50 constexpr object<3> o10 = boost::asio::require(object<1>(), prop<2>(), prop<3>());
51 constexpr object<4> o11 = boost::asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
52 (void)o9;
53 (void)o10;
54 (void)o11;
55}
56

source code of boost/libs/asio/test/properties/cpp14/require_free.cpp