prefer_free_prefer.cpp
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//
// cpp03/prefer_free_prefer.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/prefer.hpp"
#include <cassert>
template <int>
struct prop
{
static const bool is_preferable = true;
};
template <int>
struct object
{
template <int N>
friend object<N> prefer(const object&, prop<N>)
{
return object<N>();
}
};
namespace asio {
template<int N, int M>
struct is_applicable_property<object<N>, prop<M> >
{
static const bool value = true;
};
namespace traits {
template<int N, int M>
struct prefer_free<object<N>, prop<M> >
{
static const bool is_valid = true;
static const bool is_noexcept = true;
typedef object<M> result_type;
};
} // namespace traits
} // namespace asio
int main()
{
object<1> o1 = {};
object<2> o2 = asio::prefer(o1, prop<2>());
object<3> o3 = asio::prefer(o1, prop<2>(), prop<3>());
object<4> o4 = asio::prefer(o1, prop<2>(), prop<3>(), prop<4>());
(void)o2;
(void)o3;
(void)o4;
const object<1> o5 = {};
object<2> o6 = asio::prefer(o5, prop<2>());
object<3> o7 = asio::prefer(o5, prop<2>(), prop<3>());
object<4> o8 = asio::prefer(o5, prop<2>(), prop<3>(), prop<4>());
(void)o6;
(void)o7;
(void)o8;
}