Add detail::bind_continuation

include/boost/beast/core/bind_continuation.hpp

@@ -0,0 +1,55 @@
+//
+// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_BIND_CONTINUATION_HPP
+#define BOOST_BEAST_BIND_CONTINUATION_HPP
+
+#include <boost/beast/core/detail/config.hpp>
+#include <boost/beast/core/detail/remap_post_to_defer.hpp>
+#include <boost/asio/bind_executor.hpp>
+#include <boost/core/empty_value.hpp>
+#include <type_traits>
+#include <utility>
+
+namespace boost {
+namespace beast {
+
+/** Mark a completion handler as a continuation.
+
+    This function wraps a completion handler to associate it with an
+    executor whose `post` operation is remapped to the `defer` operation.
+    It is used by composed asynchronous operation implementations to
+    indicate that a completion handler submitted to an initiating
+    function represents a continuation of the current asynchronous
+    flow of control.
+
+    @see
+
+    @li <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4242.html">[N4242] Executors and Asynchronous Operations, Revision 1</a>
+*/
+template<class Executor, class CompletionHandler>
+#if BOOST_BEAST_DOXYGEN
+__implementation_defined__
+#else
+net::executor_binder<typename
+    std::decay<CompletionHandler>::type,
+    detail::remap_post_to_defer<Executor>>
+#endif
+bind_continuation(
+    Executor const& ex, CompletionHandler&& handler)
+{
+    return net::bind_executor(
+        detail::remap_post_to_defer<Executor>(ex),
+        std::forward<CompletionHandler>(handler));
+}
+
+} // beast
+} // boost
+
+#endif

include/boost/beast/core/detail/remap_post_to_defer.hpp

@@ -0,0 +1,109 @@
+//
+// Copyright (c) 2019 Vinnie Falco (vinnie dot falco at gmail 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_DETAIL_REMAP_POST_TO_DEFER_HPP
+#define BOOST_BEAST_DETAIL_REMAP_POST_TO_DEFER_HPP
+
+#include <boost/asio/bind_executor.hpp>
+#include <boost/asio/is_executor.hpp>
+#include <boost/core/empty_value.hpp>
+#include <type_traits>
+#include <utility>
+
+namespace boost {
+namespace beast {
+namespace detail {
+
+template<class Executor>
+class remap_post_to_defer
+    : private boost::empty_value<Executor>
+{
+    BOOST_STATIC_ASSERT(
+        net::is_executor<Executor>::value);
+
+    Executor const&
+    ex() const noexcept
+    {
+        return this->get();
+    }
+
+public:
+    remap_post_to_defer(
+        remap_post_to_defer&&) = default;
+
+    remap_post_to_defer(
+        remap_post_to_defer const&) = default;
+
+    explicit
+    remap_post_to_defer(
+        Executor const& ex)
+        : boost::empty_value<Executor>(
+            boost::empty_init_t{}, ex)
+    {
+    }
+
+    bool
+    operator==(
+        remap_post_to_defer const& other) const noexcept
+    {
+        return ex() == other.ex();
+    }
+
+    bool
+    operator!=(
+        remap_post_to_defer const& other) const noexcept
+    {
+        return ex() != other.ex();
+    }
+
+    decltype(std::declval<Executor const&>().context())
+    context() const noexcept
+    {
+        return ex().context();
+    }
+
+    void
+    on_work_started() const noexcept
+    {
+        ex().on_work_started();
+    }
+
+    void
+    on_work_finished() const noexcept
+    {
+        ex().on_work_finished();
+    }
+
+    template<class F, class A>
+    void
+    dispatch(F&& f, A const& a) const
+    {
+        ex().dispatch(std::forward<F>(f), a);
+    }
+
+    template<class F, class A>
+    void
+    post(F&& f, A const& a) const
+    {
+        ex().defer(std::forward<F>(f), a);
+    }
+
+    template<class F, class A>
+    void
+    defer(F&& f, A const& a) const
+    {
+        ex().defer(std::forward<F>(f), a);
+    }
+};
+
+} // detail
+} // beast
+} // boost
+
+#endif