boost_asio 0.1.0

Boost C++ library boost_asio packaged using Zanbil
Documentation 
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//
// cpp03/can_prefer_not_applicable_free_prefer.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2025 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 <boost/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 boost {
namespace asio {
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
} // namespace boost

int main()
{
  assert((!boost::asio::can_prefer<object<1>, prop<2> >::value));
  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3> >::value));
  assert((!boost::asio::can_prefer<object<1>, prop<2>, prop<3>, prop<4> >::value));
  assert((!boost::asio::can_prefer<const object<1>, prop<2> >::value));
  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3> >::value));
  assert((!boost::asio::can_prefer<const object<1>, prop<2>, prop<3>, prop<4> >::value));
}