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include/asio/associated_cancellation_slot.hpp
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include/asio/associated_cancellation_slot.hpp
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//
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// associated_cancellation_slot.hpp
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef ASIO_ASSOCIATED_CANCELLATION_SLOT_HPP
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#define ASIO_ASSOCIATED_CANCELLATION_SLOT_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include "asio/detail/config.hpp"
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#include "asio/associator.hpp"
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#include "asio/cancellation_signal.hpp"
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#include "asio/detail/functional.hpp"
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#include "asio/detail/type_traits.hpp"
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#include "asio/detail/push_options.hpp"
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namespace asio {
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template <typename T, typename CancellationSlot>
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struct associated_cancellation_slot;
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namespace detail {
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template <typename T, typename = void>
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struct has_cancellation_slot_type : false_type
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{
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};
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template <typename T>
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struct has_cancellation_slot_type<T, void_t<typename T::cancellation_slot_type>>
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: true_type
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{
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};
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template <typename T, typename S, typename = void, typename = void>
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struct associated_cancellation_slot_impl
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{
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typedef void asio_associated_cancellation_slot_is_unspecialised;
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typedef S type;
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static type get(const T&) noexcept
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{
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return type();
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}
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static const type& get(const T&, const S& s) noexcept
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{
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return s;
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}
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};
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template <typename T, typename S>
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struct associated_cancellation_slot_impl<T, S,
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void_t<typename T::cancellation_slot_type>>
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{
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typedef typename T::cancellation_slot_type type;
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static auto get(const T& t) noexcept
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-> decltype(t.get_cancellation_slot())
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{
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return t.get_cancellation_slot();
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}
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static auto get(const T& t, const S&) noexcept
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-> decltype(t.get_cancellation_slot())
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{
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return t.get_cancellation_slot();
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}
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};
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template <typename T, typename S>
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struct associated_cancellation_slot_impl<T, S,
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enable_if_t<
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!has_cancellation_slot_type<T>::value
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>,
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void_t<
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typename associator<associated_cancellation_slot, T, S>::type
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>> : associator<associated_cancellation_slot, T, S>
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{
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};
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} // namespace detail
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/// Traits type used to obtain the cancellation_slot associated with an object.
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/**
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* A program may specialise this traits type if the @c T template parameter in
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* the specialisation is a user-defined type. The template parameter @c
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* CancellationSlot shall be a type meeting the CancellationSlot requirements.
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*
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* Specialisations shall meet the following requirements, where @c t is a const
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* reference to an object of type @c T, and @c s is an object of type @c
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* CancellationSlot.
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*
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* @li Provide a nested typedef @c type that identifies a type meeting the
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* CancellationSlot requirements.
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*
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* @li Provide a noexcept static member function named @c get, callable as @c
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* get(t) and with return type @c type or a (possibly const) reference to @c
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* type.
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*
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* @li Provide a noexcept static member function named @c get, callable as @c
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* get(t,s) and with return type @c type or a (possibly const) reference to @c
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* type.
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*/
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template <typename T, typename CancellationSlot = cancellation_slot>
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struct associated_cancellation_slot
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#if !defined(GENERATING_DOCUMENTATION)
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: detail::associated_cancellation_slot_impl<T, CancellationSlot>
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#endif // !defined(GENERATING_DOCUMENTATION)
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{
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#if defined(GENERATING_DOCUMENTATION)
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/// If @c T has a nested type @c cancellation_slot_type,
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/// <tt>T::cancellation_slot_type</tt>. Otherwise
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/// @c CancellationSlot.
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typedef see_below type;
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/// If @c T has a nested type @c cancellation_slot_type, returns
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/// <tt>t.get_cancellation_slot()</tt>. Otherwise returns @c type().
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static decltype(auto) get(const T& t) noexcept;
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/// If @c T has a nested type @c cancellation_slot_type, returns
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/// <tt>t.get_cancellation_slot()</tt>. Otherwise returns @c s.
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static decltype(auto) get(const T& t,
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const CancellationSlot& s) noexcept;
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#endif // defined(GENERATING_DOCUMENTATION)
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};
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/// Helper function to obtain an object's associated cancellation_slot.
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/**
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* @returns <tt>associated_cancellation_slot<T>::get(t)</tt>
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*/
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template <typename T>
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ASIO_NODISCARD inline typename associated_cancellation_slot<T>::type
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get_associated_cancellation_slot(const T& t) noexcept
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{
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return associated_cancellation_slot<T>::get(t);
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}
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/// Helper function to obtain an object's associated cancellation_slot.
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/**
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* @returns <tt>associated_cancellation_slot<T,
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* CancellationSlot>::get(t, st)</tt>
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*/
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template <typename T, typename CancellationSlot>
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ASIO_NODISCARD inline auto get_associated_cancellation_slot(
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const T& t, const CancellationSlot& st) noexcept
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-> decltype(associated_cancellation_slot<T, CancellationSlot>::get(t, st))
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{
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return associated_cancellation_slot<T, CancellationSlot>::get(t, st);
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}
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template <typename T, typename CancellationSlot = cancellation_slot>
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using associated_cancellation_slot_t =
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typename associated_cancellation_slot<T, CancellationSlot>::type;
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namespace detail {
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template <typename T, typename S, typename = void>
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struct associated_cancellation_slot_forwarding_base
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{
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};
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template <typename T, typename S>
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struct associated_cancellation_slot_forwarding_base<T, S,
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enable_if_t<
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is_same<
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typename associated_cancellation_slot<T,
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S>::asio_associated_cancellation_slot_is_unspecialised,
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void
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>::value
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>>
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{
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typedef void asio_associated_cancellation_slot_is_unspecialised;
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};
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} // namespace detail
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/// Specialisation of associated_cancellation_slot for @c
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/// std::reference_wrapper.
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template <typename T, typename CancellationSlot>
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struct associated_cancellation_slot<reference_wrapper<T>, CancellationSlot>
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#if !defined(GENERATING_DOCUMENTATION)
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: detail::associated_cancellation_slot_forwarding_base<T, CancellationSlot>
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#endif // !defined(GENERATING_DOCUMENTATION)
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{
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/// Forwards @c type to the associator specialisation for the unwrapped type
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/// @c T.
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typedef typename associated_cancellation_slot<T, CancellationSlot>::type type;
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/// Forwards the request to get the cancellation slot to the associator
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/// specialisation for the unwrapped type @c T.
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static type get(reference_wrapper<T> t) noexcept
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{
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return associated_cancellation_slot<T, CancellationSlot>::get(t.get());
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}
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/// Forwards the request to get the cancellation slot to the associator
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/// specialisation for the unwrapped type @c T.
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static auto get(reference_wrapper<T> t, const CancellationSlot& s) noexcept
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-> decltype(
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associated_cancellation_slot<T, CancellationSlot>::get(t.get(), s))
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{
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return associated_cancellation_slot<T, CancellationSlot>::get(t.get(), s);
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}
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};
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_ASSOCIATED_CANCELLATION_SLOT_HPP
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