require_concept_free.cpp
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//
// cpp14/require_concept_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_concept.hpp"
#include <cassert>
template <int>
struct prop
{
template <typename> static constexpr bool is_applicable_property_v = true;
static constexpr bool is_requirable_concept = true;
};
template <int>
struct object
{
template <int N>
friend constexpr object<N> require_concept(const object&, prop<N>)
{
return object<N>();
}
};
int main()
{
object<1> o1 = {};
object<2> o2 = asio::require_concept(o1, prop<2>());
(void)o2;
const object<1> o3 = {};
object<2> o4 = asio::require_concept(o3, prop<2>());
(void)o4;
constexpr object<2> o5 = asio::require_concept(object<1>(), prop<2>());
(void)o5;
}