--- /dev/null
+//
+// experimental/deferred.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2022 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_EXPERIMENTAL_DEFERRED_HPP
+#define BOOST_ASIO_EXPERIMENTAL_DEFERRED_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <tuple>
+#include <boost/asio/associator.hpp>
+#include <boost/asio/async_result.hpp>
+#include <boost/asio/detail/type_traits.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace experimental {
+
+/// Trait for detecting objects that are usable as deferred operations.
+template <typename T>
+struct is_deferred : false_type
+{
+};
+
+namespace detail {
+
+// Helper trait for getting the completion signature from an async operation.
+
+struct deferred_signature_probe {};
+
+template <typename T>
+struct deferred_signature_probe_result
+{
+ typedef T type;
+};
+
+template <typename T>
+struct deferred_signature
+{
+ typedef typename decltype(
+ declval<T>()(declval<deferred_signature_probe>()))::type type;
+};
+
+// Helper trait for getting the completion signature of the tail in a sequence
+// when invoked with the specified arguments.
+
+template <typename HeadSignature, typename Tail>
+struct deferred_sequence_signature;
+
+template <typename R, typename... Args, typename Tail>
+struct deferred_sequence_signature<R(Args...), Tail>
+{
+ static_assert(
+ !is_same<decltype(declval<Tail>()(declval<Args>()...)), void>::value,
+ "deferred functions must produce a deferred return type");
+
+ typedef typename decltype(
+ declval<Tail>()(declval<Args>()...)(
+ declval<deferred_signature_probe>()))::type type;
+};
+
+// Completion handler for the head component of a deferred sequence.
+template <typename Handler, typename Tail>
+class deferred_sequence_handler
+{
+public:
+ template <typename H, typename T>
+ explicit deferred_sequence_handler(
+ BOOST_ASIO_MOVE_ARG(H) handler, BOOST_ASIO_MOVE_ARG(T) tail)
+ : handler_(BOOST_ASIO_MOVE_CAST(H)(handler)),
+ tail_(BOOST_ASIO_MOVE_CAST(T)(tail))
+ {
+ }
+
+ template <typename... Args>
+ void operator()(BOOST_ASIO_MOVE_ARG(Args)... args)
+ {
+ BOOST_ASIO_MOVE_OR_LVALUE(Tail)(tail_)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...)(
+ BOOST_ASIO_MOVE_OR_LVALUE(Handler)(handler_));
+ }
+
+//private:
+ Handler handler_;
+ Tail tail_;
+};
+
+} // namespace detail
+
+/// Used to represent an empty deferred action.
+struct deferred_noop
+{
+ /// No effect.
+ template <typename... Args>
+ void operator()(BOOST_ASIO_MOVE_ARG(Args)...) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ /// No effect.
+ template <typename... Args>
+ decltype(auto) operator()(BOOST_ASIO_MOVE_ARG(Args)...) const &
+ {
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <>
+struct is_deferred<deferred_noop> : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Tag type to disambiguate deferred constructors.
+struct deferred_init_tag {};
+
+/// Wraps a function object so that it may be used as an element in a deferred
+/// composition.
+template <typename Function>
+class deferred_function
+{
+public:
+ /// Constructor.
+ template <typename F>
+ BOOST_ASIO_CONSTEXPR explicit deferred_function(
+ deferred_init_tag, BOOST_ASIO_MOVE_ARG(F) function)
+ : function_(BOOST_ASIO_MOVE_CAST(F)(function))
+ {
+ }
+
+ template <typename... Args>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(Args)... args) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return BOOST_ASIO_MOVE_CAST(Function)(function_)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ template <typename... Args>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(Args)... args) const &
+ {
+ return deferred_function(*this)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+
+//private:
+ Function function_;
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <typename Function>
+struct is_deferred<deferred_function<Function> > : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Encapsulates deferred values.
+template <typename... Values>
+class BOOST_ASIO_NODISCARD deferred_values
+{
+private:
+ std::tuple<Values...> values_;
+
+ struct initiate
+ {
+ template <typename Handler, typename... V>
+ void operator()(Handler handler, BOOST_ASIO_MOVE_ARG(V)... values)
+ {
+ BOOST_ASIO_MOVE_OR_LVALUE(Handler)(handler)(
+ BOOST_ASIO_MOVE_CAST(V)(values)...);
+ }
+ };
+
+ template <typename CompletionToken, std::size_t... I>
+ decltype(auto) invoke_helper(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token,
+ std::index_sequence<I...>)
+ {
+ return boost::asio::async_initiate<CompletionToken, void(Values...)>(
+ initiate(), token,
+ std::get<I>(BOOST_ASIO_MOVE_CAST(std::tuple<Values...>)(values_))...);
+ }
+
+public:
+ /// Construct a deferred asynchronous operation from the arguments to an
+ /// initiation function object.
+ template <typename... V>
+ BOOST_ASIO_CONSTEXPR explicit deferred_values(
+ deferred_init_tag, BOOST_ASIO_MOVE_ARG(V)... values)
+ : values_(BOOST_ASIO_MOVE_CAST(V)(values)...)
+ {
+ }
+
+ /// Initiate the deferred operation using the supplied completion token.
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(void(Values...)) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return this->invoke_helper(
+ BOOST_ASIO_MOVE_CAST(CompletionToken)(token),
+ std::index_sequence_for<Values...>());
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(void(Values...)) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) const &
+ {
+ return deferred_values(*this)(
+ BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <typename... Values>
+struct is_deferred<deferred_values<Values...> > : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Encapsulates a deferred asynchronous operation.
+template <typename Signature, typename Initiation, typename... InitArgs>
+class BOOST_ASIO_NODISCARD deferred_async_operation
+{
+private:
+ typename decay<Initiation>::type initiation_;
+ typedef std::tuple<typename decay<InitArgs>::type...> init_args_t;
+ init_args_t init_args_;
+
+ template <typename CompletionToken, std::size_t... I>
+ decltype(auto) invoke_helper(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token,
+ std::index_sequence<I...>)
+ {
+ return boost::asio::async_initiate<CompletionToken, Signature>(
+ BOOST_ASIO_MOVE_CAST(typename decay<Initiation>::type)(initiation_),
+ token, std::get<I>(BOOST_ASIO_MOVE_CAST(init_args_t)(init_args_))...);
+ }
+
+public:
+ /// Construct a deferred asynchronous operation from the arguments to an
+ /// initiation function object.
+ template <typename I, typename... A>
+ BOOST_ASIO_CONSTEXPR explicit deferred_async_operation(
+ deferred_init_tag, BOOST_ASIO_MOVE_ARG(I) initiation,
+ BOOST_ASIO_MOVE_ARG(A)... init_args)
+ : initiation_(BOOST_ASIO_MOVE_CAST(I)(initiation)),
+ init_args_(BOOST_ASIO_MOVE_CAST(A)(init_args)...)
+ {
+ }
+
+ /// Initiate the asynchronous operation using the supplied completion token.
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signature) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return this->invoke_helper(
+ BOOST_ASIO_MOVE_CAST(CompletionToken)(token),
+ std::index_sequence_for<InitArgs...>());
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signature) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) const &
+ {
+ return deferred_async_operation(*this)(
+ BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <typename Signature, typename Initiation, typename... InitArgs>
+struct is_deferred<
+ deferred_async_operation<Signature, Initiation, InitArgs...> > : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Defines a link between two consecutive operations in a sequence.
+template <typename Head, typename Tail>
+class BOOST_ASIO_NODISCARD deferred_sequence
+{
+private:
+ typedef typename detail::deferred_sequence_signature<
+ typename detail::deferred_signature<Head>::type, Tail>::type
+ signature;
+
+public:
+ template <typename H, typename T>
+ BOOST_ASIO_CONSTEXPR explicit deferred_sequence(deferred_init_tag,
+ BOOST_ASIO_MOVE_ARG(H) head, BOOST_ASIO_MOVE_ARG(T) tail)
+ : head_(BOOST_ASIO_MOVE_CAST(H)(head)),
+ tail_(BOOST_ASIO_MOVE_CAST(T)(tail))
+ {
+ }
+
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(signature) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return boost::asio::async_initiate<CompletionToken, signature>(
+ initiate(), token, BOOST_ASIO_MOVE_OR_LVALUE(Head)(head_),
+ BOOST_ASIO_MOVE_OR_LVALUE(Tail)(tail_));
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ template <BOOST_ASIO_COMPLETION_TOKEN_FOR(signature) CompletionToken>
+ decltype(auto) operator()(
+ BOOST_ASIO_MOVE_ARG(CompletionToken) token) const &
+ {
+ return deferred_sequence(*this)(
+ BOOST_ASIO_MOVE_CAST(CompletionToken)(token));
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+
+private:
+ struct initiate
+ {
+ template <typename Handler>
+ void operator()(BOOST_ASIO_MOVE_ARG(Handler) handler,
+ Head head, BOOST_ASIO_MOVE_ARG(Tail) tail)
+ {
+ BOOST_ASIO_MOVE_OR_LVALUE(Head)(head)(
+ detail::deferred_sequence_handler<
+ typename decay<Handler>::type,
+ typename decay<Tail>::type>(
+ BOOST_ASIO_MOVE_CAST(Handler)(handler),
+ BOOST_ASIO_MOVE_CAST(Tail)(tail)));
+ }
+ };
+
+ Head head_;
+ Tail tail_;
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <typename Head, typename Tail>
+struct is_deferred<deferred_sequence<Head, Tail> > : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Used to represent a deferred conditional branch.
+template <typename OnTrue = deferred_noop,
+ typename OnFalse = deferred_noop>
+class BOOST_ASIO_NODISCARD deferred_conditional
+{
+public:
+ /// Construct a deferred conditional with the value to determine which branch
+ /// will be executed.
+ BOOST_ASIO_CONSTEXPR explicit deferred_conditional(bool b)
+ : on_true_(),
+ on_false_(),
+ bool_(b)
+ {
+ }
+
+ /// Invoke the conditional branch bsaed on the stored alue.
+ template <typename... Args>
+ auto operator()(BOOST_ASIO_MOVE_ARG(Args)... args) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ if (bool_)
+ {
+ return BOOST_ASIO_MOVE_OR_LVALUE(OnTrue)(on_true_)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+ else
+ {
+ return BOOST_ASIO_MOVE_OR_LVALUE(OnFalse)(on_false_)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+ }
+
+#if defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+ template <typename... Args>
+ auto operator()(BOOST_ASIO_MOVE_ARG(Args)... args) const &
+ {
+ return deferred_conditional(*this)(
+ BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+#endif // defined(BOOST_ASIO_HAS_REF_QUALIFIED_FUNCTIONS)
+
+ /// Set the true branch of the conditional.
+ template <typename T>
+ deferred_conditional<T, OnFalse> then(T on_true,
+ typename constraint<
+ is_deferred<T>::value
+ >::type* = 0,
+ typename constraint<
+ is_same<
+ typename conditional<true, OnTrue, T>::type,
+ deferred_noop
+ >::value
+ >::type* = 0) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return deferred_conditional<T, OnFalse>(
+ bool_, BOOST_ASIO_MOVE_CAST(T)(on_true),
+ BOOST_ASIO_MOVE_CAST(OnFalse)(on_false_));
+ }
+
+ /// Set the false branch of the conditional.
+ template <typename T>
+ deferred_conditional<OnTrue, T> otherwise(T on_false,
+ typename constraint<
+ is_deferred<T>::value
+ >::type* = 0,
+ typename constraint<
+ !is_same<
+ typename conditional<true, OnTrue, T>::type,
+ deferred_noop
+ >::value
+ >::type* = 0,
+ typename constraint<
+ is_same<
+ typename conditional<true, OnFalse, T>::type,
+ deferred_noop
+ >::value
+ >::type* = 0) BOOST_ASIO_RVALUE_REF_QUAL
+ {
+ return deferred_conditional<OnTrue, T>(
+ bool_, BOOST_ASIO_MOVE_CAST(OnTrue)(on_true_),
+ BOOST_ASIO_MOVE_CAST(T)(on_false));
+ }
+
+private:
+ template <typename T, typename F> friend class deferred_conditional;
+
+ // Helper constructor.
+ template <typename T, typename F>
+ explicit deferred_conditional(bool b, BOOST_ASIO_MOVE_ARG(T) on_true,
+ BOOST_ASIO_MOVE_ARG(F) on_false)
+ : on_true_(BOOST_ASIO_MOVE_CAST(T)(on_true)),
+ on_false_(BOOST_ASIO_MOVE_CAST(F)(on_false)),
+ bool_(b)
+ {
+ }
+
+ OnTrue on_true_;
+ OnFalse on_false_;
+ bool bool_;
+};
+
+#if !defined(GENERATING_DOCUMENTATION)
+template <typename OnTrue, typename OnFalse>
+struct is_deferred<deferred_conditional<OnTrue, OnFalse> > : true_type
+{
+};
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+/// Class used to specify that an asynchronous operation should return a
+/// function object to lazily launch the operation.
+/**
+ * The deferred_t class is used to indicate that an asynchronous operation
+ * should return a function object which is itself an initiation function. A
+ * deferred_t object may be passed as a completion token to an asynchronous
+ * operation, typically using the special value @c boost::asio::deferred. For
+ * example:
+ *
+ * @code auto my_deferred_op
+ * = my_socket.async_read_some(my_buffer,
+ * boost::asio::experimental::deferred); @endcode
+ *
+ * The initiating function (async_read_some in the above example) returns a
+ * function object that will lazily initiate the operation.
+ */
+class deferred_t
+{
+public:
+ /// Default constructor.
+ BOOST_ASIO_CONSTEXPR deferred_t()
+ {
+ }
+
+ /// Adapts an executor to add the @c deferred_t completion token as the
+ /// default.
+ template <typename InnerExecutor>
+ struct executor_with_default : InnerExecutor
+ {
+ /// Specify @c deferred_t as the default completion token type.
+ typedef deferred_t default_completion_token_type;
+
+ /// Construct the adapted executor from the inner executor type.
+ template <typename InnerExecutor1>
+ executor_with_default(const InnerExecutor1& ex,
+ typename constraint<
+ conditional<
+ !is_same<InnerExecutor1, executor_with_default>::value,
+ is_convertible<InnerExecutor1, InnerExecutor>,
+ false_type
+ >::type::value
+ >::type = 0) BOOST_ASIO_NOEXCEPT
+ : InnerExecutor(ex)
+ {
+ }
+ };
+
+ /// Type alias to adapt an I/O object to use @c deferred_t as its
+ /// default completion token type.
+#if defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES) \
+ || defined(GENERATING_DOCUMENTATION)
+ template <typename T>
+ using as_default_on_t = typename T::template rebind_executor<
+ executor_with_default<typename T::executor_type> >::other;
+#endif // defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES)
+ // || defined(GENERATING_DOCUMENTATION)
+
+ /// Function helper to adapt an I/O object to use @c deferred_t as its
+ /// default completion token type.
+ template <typename T>
+ static typename decay<T>::type::template rebind_executor<
+ executor_with_default<typename decay<T>::type::executor_type>
+ >::other
+ as_default_on(BOOST_ASIO_MOVE_ARG(T) object)
+ {
+ return typename decay<T>::type::template rebind_executor<
+ executor_with_default<typename decay<T>::type::executor_type>
+ >::other(BOOST_ASIO_MOVE_CAST(T)(object));
+ }
+
+ /// Creates a new deferred from a function.
+ template <typename Function>
+ typename constraint<
+ !is_deferred<typename decay<Function>::type>::value,
+ deferred_function<typename decay<Function>::type>
+ >::type operator()(BOOST_ASIO_MOVE_ARG(Function) function) const
+ {
+ return deferred_function<typename decay<Function>::type>(
+ deferred_init_tag{}, BOOST_ASIO_MOVE_CAST(Function)(function));
+ }
+
+ /// Passes through anything that is already deferred.
+ template <typename T>
+ typename constraint<
+ is_deferred<typename decay<T>::type>::value,
+ typename decay<T>::type
+ >::type operator()(BOOST_ASIO_MOVE_ARG(T) t) const
+ {
+ return BOOST_ASIO_MOVE_CAST(T)(t);
+ }
+
+ /// Returns a deferred operation that returns the provided values.
+ template <typename... Args>
+ static BOOST_ASIO_CONSTEXPR deferred_values<typename decay<Args>::type...>
+ values(BOOST_ASIO_MOVE_ARG(Args)... args)
+ {
+ return deferred_values<typename decay<Args>::type...>(
+ deferred_init_tag{}, BOOST_ASIO_MOVE_CAST(Args)(args)...);
+ }
+
+ /// Creates a conditional object for branching deferred operations.
+ static BOOST_ASIO_CONSTEXPR deferred_conditional<> when(bool b)
+ {
+ return deferred_conditional<>(b);
+ }
+};
+
+/// Pipe operator used to chain deferred operations.
+template <typename Head, typename Tail>
+inline auto operator|(Head head, BOOST_ASIO_MOVE_ARG(Tail) tail)
+ -> typename constraint<
+ is_deferred<Head>::value,
+ decltype(BOOST_ASIO_MOVE_OR_LVALUE(Head)(head)(
+ BOOST_ASIO_MOVE_CAST(Tail)(tail)))
+ >::type
+{
+ return BOOST_ASIO_MOVE_OR_LVALUE(Head)(head)(
+ BOOST_ASIO_MOVE_CAST(Tail)(tail));
+}
+
+/// A @ref completion_token object used to specify that an asynchronous
+/// operation should return a function object to lazily launch the operation.
+/**
+ * See the documentation for boost::asio::experimental::deferred_t for a usage
+ * example.
+ */
+#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr deferred_t deferred;
+#elif defined(BOOST_ASIO_MSVC)
+__declspec(selectany) deferred_t deferred;
+#endif
+
+} // namespace experimental
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#include <boost/asio/experimental/impl/deferred.hpp>
+
+#endif // BOOST_ASIO_EXPERIMENTAL_DEFERRED_HPP
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