Boost C++ Libraries

boost/asio/query.hpp

//
// query.hpp
// ~~~~~~~~~
//
// Copyright (c) 2003-2024 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)
//

#ifndef BOOST_ASIO_QUERY_HPP
#define BOOST_ASIO_QUERY_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/config.hpp>
#include <boost/asio/detail/type_traits.hpp>
#include <boost/asio/is_applicable_property.hpp>
#include <boost/asio/traits/query_member.hpp>
#include <boost/asio/traits/query_free.hpp>
#include <boost/asio/traits/static_query.hpp>

#include <boost/asio/detail/push_options.hpp>

#if defined(GENERATING_DOCUMENTATION)

namespace boost {
namespace asio {

/// A customisation point that queries the value of a property.
/**
 * The name <tt>query</tt> denotes a customization point object. The
 * expression <tt>boost::asio::query(E, P)</tt> for some
 * subexpressions <tt>E</tt> and <tt>P</tt> (with types <tt>T =
 * decay_t<decltype(E)></tt> and <tt>Prop = decay_t<decltype(P)></tt>) is
 * expression-equivalent to:
 *
 * @li If <tt>is_applicable_property_v<T, Prop></tt> is not a well-formed
 *   constant expression with value <tt>true</tt>, <tt>boost::asio::query(E,
 *   P)</tt> is ill-formed.
 *
 * @li Otherwise, <tt>Prop::template static_query_v<T></tt> if the expression
 *   <tt>Prop::template static_query_v<T></tt> is a well-formed constant
 *   expression.
 *
 * @li Otherwise, <tt>(E).query(P)</tt> if the expression
 *   <tt>(E).query(P)</tt> is well-formed.
 *
 * @li Otherwise, <tt>query(E, P)</tt> if the expression
 *   <tt>query(E, P)</tt> is a valid expression with overload
 *   resolution performed in a context that does not include the declaration
 *   of the <tt>query</tt> customization point object.
 *
 * @li Otherwise, <tt>boost::asio::query(E, P)</tt> is ill-formed.
 */
inline constexpr unspecified query = unspecified;

/// A type trait that determines whether a @c query expression is well-formed.
/**
 * Class template @c can_query is a trait that is derived from
 * @c true_type if the expression <tt>boost::asio::query(std::declval<T>(),
 * std::declval<Property>())</tt> is well formed; otherwise @c false_type.
 */
template <typename T, typename Property>
struct can_query :
  integral_constant<bool, automatically_determined>
{
};

/// A type trait that determines whether a @c query expression will
/// not throw.
/**
 * Class template @c is_nothrow_query is a trait that is derived from
 * @c true_type if the expression <tt>boost::asio::query(std::declval<T>(),
 * std::declval<Property>())</tt> is @c noexcept; otherwise @c false_type.
 */
template <typename T, typename Property>
struct is_nothrow_query :
  integral_constant<bool, automatically_determined>
{
};

/// A type trait that determines the result type of a @c query expression.
/**
 * Class template @c query_result is a trait that determines the result
 * type of the expression <tt>boost::asio::query(std::declval<T>(),
 * std::declval<Property>())</tt>.
 */
template <typename T, typename Property>
struct query_result
{
  /// The result of the @c query expression.
  typedef automatically_determined type;
};

} // namespace asio
} // namespace boost

#else // defined(GENERATING_DOCUMENTATION)

namespace boost_asio_query_fn {

using boost::asio::conditional_t;
using boost::asio::decay_t;
using boost::asio::declval;
using boost::asio::enable_if_t;
using boost::asio::is_applicable_property;
using boost::asio::traits::query_free;
using boost::asio::traits::query_member;
using boost::asio::traits::static_query;

void query();

enum overload_type
{
  static_value,
  call_member,
  call_free,
  ill_formed
};

template <typename Impl, typename T, typename Properties,
    typename = void, typename = void, typename = void, typename = void>
struct call_traits
{
  static constexpr overload_type overload = ill_formed;
  static constexpr bool is_noexcept = false;
  typedef void result_type;
};

template <typename Impl, typename T, typename Property>
struct call_traits<Impl, T, void(Property),
  enable_if_t<
    is_applicable_property<
      decay_t<T>,
      decay_t<Property>
    >::value
  >,
  enable_if_t<
    static_query<T, Property>::is_valid
  >> :
  static_query<T, Property>
{
  static constexpr overload_type overload = static_value;
};

template <typename Impl, typename T, typename Property>
struct call_traits<Impl, T, void(Property),
  enable_if_t<
    is_applicable_property<
      decay_t<T>,
      decay_t<Property>
    >::value
  >,
  enable_if_t<
    !static_query<T, Property>::is_valid
  >,
  enable_if_t<
    query_member<typename Impl::template proxy<T>::type, Property>::is_valid
  >> :
  query_member<typename Impl::template proxy<T>::type, Property>
{
  static constexpr overload_type overload = call_member;
};

template <typename Impl, typename T, typename Property>
struct call_traits<Impl, T, void(Property),
  enable_if_t<
    is_applicable_property<
      decay_t<T>,
      decay_t<Property>
    >::value
  >,
  enable_if_t<
    !static_query<T, Property>::is_valid
  >,
  enable_if_t<
    !query_member<typename Impl::template proxy<T>::type, Property>::is_valid
  >,
  enable_if_t<
    query_free<T, Property>::is_valid
  >> :
  query_free<T, Property>
{
  static constexpr overload_type overload = call_free;
};

struct impl
{
  template <typename T>
  struct proxy
  {
#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
    struct type
    {
      template <typename P>
      auto query(P&& p)
        noexcept(
          noexcept(
            declval<conditional_t<true, T, P>>().query(static_cast<P&&>(p))
          )
        )
        -> decltype(
          declval<conditional_t<true, T, P>>().query(static_cast<P&&>(p))
        );
    };
#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
    typedef T type;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
  };

  template <typename T, typename Property>
  BOOST_ASIO_NODISCARD constexpr enable_if_t<
    call_traits<impl, T, void(Property)>::overload == static_value,
    typename call_traits<impl, T, void(Property)>::result_type
  >
  operator()(T&&, Property&&) const
    noexcept(call_traits<impl, T, void(Property)>::is_noexcept)
  {
    return static_query<decay_t<T>, decay_t<Property>>::value();
  }

  template <typename T, typename Property>
  BOOST_ASIO_NODISCARD constexpr enable_if_t<
    call_traits<impl, T, void(Property)>::overload == call_member,
    typename call_traits<impl, T, void(Property)>::result_type
  >
  operator()(T&& t, Property&& p) const
    noexcept(call_traits<impl, T, void(Property)>::is_noexcept)
  {
    return static_cast<T&&>(t).query(static_cast<Property&&>(p));
  }

  template <typename T, typename Property>
  BOOST_ASIO_NODISCARD constexpr enable_if_t<
    call_traits<impl, T, void(Property)>::overload == call_free,
    typename call_traits<impl, T, void(Property)>::result_type
  >
  operator()(T&& t, Property&& p) const
    noexcept(call_traits<impl, T, void(Property)>::is_noexcept)
  {
    return query(static_cast<T&&>(t), static_cast<Property&&>(p));
  }
};

template <typename T = impl>
struct static_instance
{
  static const T instance;
};

template <typename T>
const T static_instance<T>::instance = {};

} // namespace boost_asio_query_fn
namespace boost {
namespace asio {
namespace {

static constexpr const boost_asio_query_fn::impl&
  query = boost_asio_query_fn::static_instance<>::instance;

} // namespace

typedef boost_asio_query_fn::impl query_t;

template <typename T, typename Property>
struct can_query :
  integral_constant<bool,
    boost_asio_query_fn::call_traits<query_t, T, void(Property)>::overload !=
      boost_asio_query_fn::ill_formed>
{
};

#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

template <typename T, typename Property>
constexpr bool can_query_v = can_query<T, Property>::value;

#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

template <typename T, typename Property>
struct is_nothrow_query :
  integral_constant<bool,
    boost_asio_query_fn::call_traits<query_t, T, void(Property)>::is_noexcept>
{
};

#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

template <typename T, typename Property>
constexpr bool is_nothrow_query_v = is_nothrow_query<T, Property>::value;

#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

template <typename T, typename Property>
struct query_result
{
  typedef typename boost_asio_query_fn::call_traits<
      query_t, T, void(Property)>::result_type type;
};

template <typename T, typename Property>
using query_result_t = typename query_result<T, Property>::type;

} // namespace asio
} // namespace boost

#endif // defined(GENERATING_DOCUMENTATION)

#include <boost/asio/detail/pop_options.hpp>

#endif // BOOST_ASIO_QUERY_HPP