require_free.cpp
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//
// cpp14/require_free.cpp
// ~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 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 "asio/require.hpp"
#include <cassert>
template <int>
struct prop
{
template <typename> static constexpr bool is_applicable_property_v = true;
static constexpr bool is_requirable = true;
};
template <int>
struct object
{
template <int N>
friend constexpr object<N> require(const object&, prop<N>)
{
return object<N>();
}
};
int main()
{
object<1> o1 = {};
object<2> o2 = asio::require(o1, prop<2>());
object<3> o3 = asio::require(o1, prop<2>(), prop<3>());
object<4> o4 = asio::require(o1, prop<2>(), prop<3>(), prop<4>());
(void)o2;
(void)o3;
(void)o4;
const object<1> o5 = {};
object<2> o6 = asio::require(o5, prop<2>());
object<3> o7 = asio::require(o5, prop<2>(), prop<3>());
object<4> o8 = asio::require(o5, prop<2>(), prop<3>(), prop<4>());
(void)o6;
(void)o7;
(void)o8;
constexpr object<2> o9 = asio::require(object<1>(), prop<2>());
constexpr object<3> o10 = asio::require(object<1>(), prop<2>(), prop<3>());
constexpr object<4> o11 = asio::require(object<1>(), prop<2>(), prop<3>(), prop<4>());
(void)o9;
(void)o10;
(void)o11;
}