1 | // |
2 | // deferred.hpp |
3 | // ~~~~~~~~~~~~ |
4 | // |
5 | // Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
6 | // |
7 | // Distributed under the Boost Software License, Version 1.0. (See accompanying |
8 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
9 | // |
10 | |
11 | #ifndef BOOST_ASIO_DEFERRED_HPP |
12 | #define BOOST_ASIO_DEFERRED_HPP |
13 | |
14 | #if defined(_MSC_VER) && (_MSC_VER >= 1200) |
15 | # pragma once |
16 | #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) |
17 | |
18 | #include <boost/asio/detail/config.hpp> |
19 | #include <tuple> |
20 | #include <boost/asio/associator.hpp> |
21 | #include <boost/asio/async_result.hpp> |
22 | #include <boost/asio/detail/type_traits.hpp> |
23 | #include <boost/asio/detail/utility.hpp> |
24 | |
25 | #include <boost/asio/detail/push_options.hpp> |
26 | |
27 | namespace boost { |
28 | namespace asio { |
29 | |
30 | /// Trait for detecting objects that are usable as deferred operations. |
31 | template <typename T> |
32 | struct is_deferred : false_type |
33 | { |
34 | }; |
35 | |
36 | /// Helper type to wrap multiple completion signatures. |
37 | template <typename... Signatures> |
38 | struct deferred_signatures |
39 | { |
40 | }; |
41 | |
42 | namespace detail { |
43 | |
44 | // Helper trait for getting the completion signatures of the tail in a sequence |
45 | // when invoked with the specified arguments. |
46 | |
47 | template <typename Tail, typename... Signatures> |
48 | struct deferred_sequence_signatures; |
49 | |
50 | template <typename Tail, typename R, typename... Args, typename... Signatures> |
51 | struct deferred_sequence_signatures<Tail, R(Args...), Signatures...> |
52 | : completion_signature_of<decltype(declval<Tail>()(declval<Args>()...))> |
53 | { |
54 | static_assert( |
55 | !is_same<decltype(declval<Tail>()(declval<Args>()...)), void>::value, |
56 | "deferred functions must produce a deferred return type" ); |
57 | }; |
58 | |
59 | // Completion handler for the head component of a deferred sequence. |
60 | template <typename Handler, typename Tail> |
61 | class deferred_sequence_handler |
62 | { |
63 | public: |
64 | template <typename H, typename T> |
65 | explicit deferred_sequence_handler(H&& handler, T&& tail) |
66 | : handler_(static_cast<H&&>(handler)), |
67 | tail_(static_cast<T&&>(tail)) |
68 | { |
69 | } |
70 | |
71 | template <typename... Args> |
72 | void operator()(Args&&... args) |
73 | { |
74 | static_cast<Tail&&>(tail_)( |
75 | static_cast<Args&&>(args)...)( |
76 | static_cast<Handler&&>(handler_)); |
77 | } |
78 | |
79 | //private: |
80 | Handler handler_; |
81 | Tail tail_; |
82 | }; |
83 | |
84 | template <typename Head, typename Tail, typename... Signatures> |
85 | class deferred_sequence_base |
86 | { |
87 | private: |
88 | struct initiate |
89 | { |
90 | template <typename Handler> |
91 | void operator()(Handler&& handler, Head head, Tail&& tail) |
92 | { |
93 | static_cast<Head&&>(head)( |
94 | deferred_sequence_handler<decay_t<Handler>, decay_t<Tail>>( |
95 | static_cast<Handler&&>(handler), static_cast<Tail&&>(tail))); |
96 | } |
97 | }; |
98 | |
99 | Head head_; |
100 | Tail tail_; |
101 | |
102 | public: |
103 | template <typename H, typename T> |
104 | constexpr explicit deferred_sequence_base(H&& head, T&& tail) |
105 | : head_(static_cast<H&&>(head)), |
106 | tail_(static_cast<T&&>(tail)) |
107 | { |
108 | } |
109 | |
110 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signatures...) CompletionToken> |
111 | auto operator()(CompletionToken&& token) && |
112 | -> decltype( |
113 | async_initiate<CompletionToken, Signatures...>( |
114 | initiate(), token, static_cast<Head&&>(this->head_), |
115 | static_cast<Tail&&>(this->tail_))) |
116 | { |
117 | return async_initiate<CompletionToken, Signatures...>(initiate(), |
118 | token, static_cast<Head&&>(head_), static_cast<Tail&&>(tail_)); |
119 | } |
120 | |
121 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signatures...) CompletionToken> |
122 | auto operator()(CompletionToken&& token) const & |
123 | -> decltype( |
124 | async_initiate<CompletionToken, Signatures...>( |
125 | initiate(), token, this->head_, this->tail_)) |
126 | { |
127 | return async_initiate<CompletionToken, Signatures...>( |
128 | initiate(), token, head_, tail_); |
129 | } |
130 | }; |
131 | |
132 | // Two-step application of variadic Signatures to determine correct base type. |
133 | |
134 | template <typename Head, typename Tail> |
135 | struct deferred_sequence_types |
136 | { |
137 | template <typename... Signatures> |
138 | struct op1 |
139 | { |
140 | typedef deferred_sequence_base<Head, Tail, Signatures...> type; |
141 | }; |
142 | |
143 | template <typename... Signatures> |
144 | struct op2 |
145 | { |
146 | typedef typename deferred_sequence_signatures<Tail, Signatures...>::template |
147 | apply<op1>::type::type type; |
148 | }; |
149 | |
150 | typedef typename completion_signature_of<Head>::template |
151 | apply<op2>::type::type base; |
152 | }; |
153 | |
154 | } // namespace detail |
155 | |
156 | /// Used to represent an empty deferred action. |
157 | struct deferred_noop |
158 | { |
159 | /// No effect. |
160 | template <typename... Args> |
161 | void operator()(Args&&...) && |
162 | { |
163 | } |
164 | |
165 | /// No effect. |
166 | template <typename... Args> |
167 | void operator()(Args&&...) const & |
168 | { |
169 | } |
170 | }; |
171 | |
172 | #if !defined(GENERATING_DOCUMENTATION) |
173 | template <> |
174 | struct is_deferred<deferred_noop> : true_type |
175 | { |
176 | }; |
177 | #endif // !defined(GENERATING_DOCUMENTATION) |
178 | |
179 | /// Tag type to disambiguate deferred constructors. |
180 | struct deferred_init_tag {}; |
181 | |
182 | /// Wraps a function object so that it may be used as an element in a deferred |
183 | /// composition. |
184 | template <typename Function> |
185 | class deferred_function |
186 | { |
187 | public: |
188 | /// Constructor. |
189 | template <typename F> |
190 | constexpr explicit deferred_function(deferred_init_tag, F&& function) |
191 | : function_(static_cast<F&&>(function)) |
192 | { |
193 | } |
194 | |
195 | //private: |
196 | Function function_; |
197 | |
198 | public: |
199 | template <typename... Args> |
200 | auto operator()(Args&&... args) && |
201 | -> decltype( |
202 | static_cast<Function&&>(this->function_)(static_cast<Args&&>(args)...)) |
203 | { |
204 | return static_cast<Function&&>(function_)(static_cast<Args&&>(args)...); |
205 | } |
206 | |
207 | template <typename... Args> |
208 | auto operator()(Args&&... args) const & |
209 | -> decltype(Function(function_)(static_cast<Args&&>(args)...)) |
210 | { |
211 | return Function(function_)(static_cast<Args&&>(args)...); |
212 | } |
213 | }; |
214 | |
215 | #if !defined(GENERATING_DOCUMENTATION) |
216 | template <typename Function> |
217 | struct is_deferred<deferred_function<Function>> : true_type |
218 | { |
219 | }; |
220 | #endif // !defined(GENERATING_DOCUMENTATION) |
221 | |
222 | /// Encapsulates deferred values. |
223 | template <typename... Values> |
224 | class BOOST_ASIO_NODISCARD deferred_values |
225 | { |
226 | private: |
227 | std::tuple<Values...> values_; |
228 | |
229 | struct initiate |
230 | { |
231 | template <typename Handler, typename... V> |
232 | void operator()(Handler handler, V&&... values) |
233 | { |
234 | static_cast<Handler&&>(handler)(static_cast<V&&>(values)...); |
235 | } |
236 | }; |
237 | |
238 | template <typename CompletionToken, std::size_t... I> |
239 | auto invoke_helper(CompletionToken&& token, detail::index_sequence<I...>) |
240 | -> decltype( |
241 | async_initiate<CompletionToken, void(Values...)>(initiate(), token, |
242 | std::get<I>(static_cast<std::tuple<Values...>&&>(this->values_))...)) |
243 | { |
244 | return async_initiate<CompletionToken, void(Values...)>(initiate(), token, |
245 | std::get<I>(static_cast<std::tuple<Values...>&&>(values_))...); |
246 | } |
247 | |
248 | template <typename CompletionToken, std::size_t... I> |
249 | auto const_invoke_helper(CompletionToken&& token, |
250 | detail::index_sequence<I...>) |
251 | -> decltype( |
252 | async_initiate<CompletionToken, void(Values...)>( |
253 | initiate(), token, std::get<I>(values_)...)) |
254 | { |
255 | return async_initiate<CompletionToken, void(Values...)>( |
256 | initiate(), token, std::get<I>(values_)...); |
257 | } |
258 | |
259 | public: |
260 | /// Construct a deferred asynchronous operation from the arguments to an |
261 | /// initiation function object. |
262 | template <typename... V> |
263 | constexpr explicit deferred_values( |
264 | deferred_init_tag, V&&... values) |
265 | : values_(static_cast<V&&>(values)...) |
266 | { |
267 | } |
268 | |
269 | /// Initiate the deferred operation using the supplied completion token. |
270 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(void(Values...)) CompletionToken> |
271 | auto operator()(CompletionToken&& token) && |
272 | -> decltype( |
273 | this->invoke_helper( |
274 | static_cast<CompletionToken&&>(token), |
275 | detail::index_sequence_for<Values...>())) |
276 | { |
277 | return this->invoke_helper( |
278 | static_cast<CompletionToken&&>(token), |
279 | detail::index_sequence_for<Values...>()); |
280 | } |
281 | |
282 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(void(Values...)) CompletionToken> |
283 | auto operator()(CompletionToken&& token) const & |
284 | -> decltype( |
285 | this->const_invoke_helper( |
286 | static_cast<CompletionToken&&>(token), |
287 | detail::index_sequence_for<Values...>())) |
288 | { |
289 | return this->const_invoke_helper( |
290 | static_cast<CompletionToken&&>(token), |
291 | detail::index_sequence_for<Values...>()); |
292 | } |
293 | }; |
294 | |
295 | #if !defined(GENERATING_DOCUMENTATION) |
296 | template <typename... Values> |
297 | struct is_deferred<deferred_values<Values...>> : true_type |
298 | { |
299 | }; |
300 | #endif // !defined(GENERATING_DOCUMENTATION) |
301 | |
302 | /// Encapsulates a deferred asynchronous operation. |
303 | template <typename Signature, typename Initiation, typename... InitArgs> |
304 | class BOOST_ASIO_NODISCARD deferred_async_operation |
305 | { |
306 | private: |
307 | typedef decay_t<Initiation> initiation_t; |
308 | initiation_t initiation_; |
309 | typedef std::tuple<decay_t<InitArgs>...> init_args_t; |
310 | init_args_t init_args_; |
311 | |
312 | template <typename CompletionToken, std::size_t... I> |
313 | auto invoke_helper(CompletionToken&& token, detail::index_sequence<I...>) |
314 | -> decltype( |
315 | async_initiate<CompletionToken, Signature>( |
316 | static_cast<initiation_t&&>(initiation_), token, |
317 | std::get<I>(static_cast<init_args_t&&>(init_args_))...)) |
318 | { |
319 | return async_initiate<CompletionToken, Signature>( |
320 | static_cast<initiation_t&&>(initiation_), token, |
321 | std::get<I>(static_cast<init_args_t&&>(init_args_))...); |
322 | } |
323 | |
324 | template <typename CompletionToken, std::size_t... I> |
325 | auto const_invoke_helper(CompletionToken&& token, |
326 | detail::index_sequence<I...>) const & |
327 | -> decltype( |
328 | async_initiate<CompletionToken, Signature>( |
329 | initiation_t(initiation_), token, std::get<I>(init_args_)...)) |
330 | { |
331 | return async_initiate<CompletionToken, Signature>( |
332 | initiation_t(initiation_), token, std::get<I>(init_args_)...); |
333 | } |
334 | |
335 | public: |
336 | /// Construct a deferred asynchronous operation from the arguments to an |
337 | /// initiation function object. |
338 | template <typename I, typename... A> |
339 | constexpr explicit deferred_async_operation( |
340 | deferred_init_tag, I&& initiation, A&&... init_args) |
341 | : initiation_(static_cast<I&&>(initiation)), |
342 | init_args_(static_cast<A&&>(init_args)...) |
343 | { |
344 | } |
345 | |
346 | /// Initiate the asynchronous operation using the supplied completion token. |
347 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signature) CompletionToken> |
348 | auto operator()(CompletionToken&& token) && |
349 | -> decltype( |
350 | this->invoke_helper( |
351 | static_cast<CompletionToken&&>(token), |
352 | detail::index_sequence_for<InitArgs...>())) |
353 | { |
354 | return this->invoke_helper( |
355 | static_cast<CompletionToken&&>(token), |
356 | detail::index_sequence_for<InitArgs...>()); |
357 | } |
358 | |
359 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signature) CompletionToken> |
360 | auto operator()(CompletionToken&& token) const & |
361 | -> decltype( |
362 | this->const_invoke_helper( |
363 | static_cast<CompletionToken&&>(token), |
364 | detail::index_sequence_for<InitArgs...>())) |
365 | { |
366 | return this->const_invoke_helper( |
367 | static_cast<CompletionToken&&>(token), |
368 | detail::index_sequence_for<InitArgs...>()); |
369 | } |
370 | }; |
371 | |
372 | /// Encapsulates a deferred asynchronous operation thas has multiple completion |
373 | /// signatures. |
374 | template <typename... Signatures, typename Initiation, typename... InitArgs> |
375 | class BOOST_ASIO_NODISCARD deferred_async_operation< |
376 | deferred_signatures<Signatures...>, Initiation, InitArgs...> |
377 | { |
378 | private: |
379 | typedef decay_t<Initiation> initiation_t; |
380 | initiation_t initiation_; |
381 | typedef std::tuple<decay_t<InitArgs>...> init_args_t; |
382 | init_args_t init_args_; |
383 | |
384 | template <typename CompletionToken, std::size_t... I> |
385 | auto invoke_helper(CompletionToken&& token, detail::index_sequence<I...>) |
386 | -> decltype( |
387 | async_initiate<CompletionToken, Signatures...>( |
388 | static_cast<initiation_t&&>(initiation_), token, |
389 | std::get<I>(static_cast<init_args_t&&>(init_args_))...)) |
390 | { |
391 | return async_initiate<CompletionToken, Signatures...>( |
392 | static_cast<initiation_t&&>(initiation_), token, |
393 | std::get<I>(static_cast<init_args_t&&>(init_args_))...); |
394 | } |
395 | |
396 | template <typename CompletionToken, std::size_t... I> |
397 | auto const_invoke_helper(CompletionToken&& token, |
398 | detail::index_sequence<I...>) const & |
399 | -> decltype( |
400 | async_initiate<CompletionToken, Signatures...>( |
401 | initiation_t(initiation_), token, std::get<I>(init_args_)...)) |
402 | { |
403 | return async_initiate<CompletionToken, Signatures...>( |
404 | initiation_t(initiation_), token, std::get<I>(init_args_)...); |
405 | } |
406 | |
407 | public: |
408 | /// Construct a deferred asynchronous operation from the arguments to an |
409 | /// initiation function object. |
410 | template <typename I, typename... A> |
411 | constexpr explicit deferred_async_operation( |
412 | deferred_init_tag, I&& initiation, A&&... init_args) |
413 | : initiation_(static_cast<I&&>(initiation)), |
414 | init_args_(static_cast<A&&>(init_args)...) |
415 | { |
416 | } |
417 | |
418 | /// Initiate the asynchronous operation using the supplied completion token. |
419 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signatures...) CompletionToken> |
420 | auto operator()(CompletionToken&& token) && |
421 | -> decltype( |
422 | this->invoke_helper( |
423 | static_cast<CompletionToken&&>(token), |
424 | detail::index_sequence_for<InitArgs...>())) |
425 | { |
426 | return this->invoke_helper( |
427 | static_cast<CompletionToken&&>(token), |
428 | detail::index_sequence_for<InitArgs...>()); |
429 | } |
430 | |
431 | template <BOOST_ASIO_COMPLETION_TOKEN_FOR(Signatures...) CompletionToken> |
432 | auto operator()(CompletionToken&& token) const & |
433 | -> decltype( |
434 | this->const_invoke_helper( |
435 | static_cast<CompletionToken&&>(token), |
436 | detail::index_sequence_for<InitArgs...>())) |
437 | { |
438 | return this->const_invoke_helper( |
439 | static_cast<CompletionToken&&>(token), |
440 | detail::index_sequence_for<InitArgs...>()); |
441 | } |
442 | }; |
443 | |
444 | #if !defined(GENERATING_DOCUMENTATION) |
445 | template <typename Signature, typename Initiation, typename... InitArgs> |
446 | struct is_deferred< |
447 | deferred_async_operation<Signature, Initiation, InitArgs...>> : true_type |
448 | { |
449 | }; |
450 | #endif // !defined(GENERATING_DOCUMENTATION) |
451 | |
452 | /// Defines a link between two consecutive operations in a sequence. |
453 | template <typename Head, typename Tail> |
454 | class BOOST_ASIO_NODISCARD deferred_sequence : |
455 | public detail::deferred_sequence_types<Head, Tail>::base |
456 | { |
457 | public: |
458 | template <typename H, typename T> |
459 | constexpr explicit deferred_sequence(deferred_init_tag, H&& head, T&& tail) |
460 | : detail::deferred_sequence_types<Head, Tail>::base( |
461 | static_cast<H&&>(head), static_cast<T&&>(tail)) |
462 | { |
463 | } |
464 | |
465 | #if defined(GENERATING_DOCUMENTATION) |
466 | template <typename CompletionToken> |
467 | auto operator()(CompletionToken&& token) &&; |
468 | |
469 | template <typename CompletionToken> |
470 | auto operator()(CompletionToken&& token) const &; |
471 | #endif // defined(GENERATING_DOCUMENTATION) |
472 | }; |
473 | |
474 | #if !defined(GENERATING_DOCUMENTATION) |
475 | template <typename Head, typename Tail> |
476 | struct is_deferred<deferred_sequence<Head, Tail>> : true_type |
477 | { |
478 | }; |
479 | #endif // !defined(GENERATING_DOCUMENTATION) |
480 | |
481 | /// Used to represent a deferred conditional branch. |
482 | template <typename OnTrue = deferred_noop, typename OnFalse = deferred_noop> |
483 | class BOOST_ASIO_NODISCARD deferred_conditional |
484 | { |
485 | private: |
486 | template <typename T, typename F> friend class deferred_conditional; |
487 | |
488 | // Helper constructor. |
489 | template <typename T, typename F> |
490 | explicit deferred_conditional(bool b, T&& on_true, F&& on_false) |
491 | : on_true_(static_cast<T&&>(on_true)), |
492 | on_false_(static_cast<F&&>(on_false)), |
493 | bool_(b) |
494 | { |
495 | } |
496 | |
497 | OnTrue on_true_; |
498 | OnFalse on_false_; |
499 | bool bool_; |
500 | |
501 | public: |
502 | /// Construct a deferred conditional with the value to determine which branch |
503 | /// will be executed. |
504 | constexpr explicit deferred_conditional(bool b) |
505 | : on_true_(), |
506 | on_false_(), |
507 | bool_(b) |
508 | { |
509 | } |
510 | |
511 | /// Invoke the conditional branch bsaed on the stored value. |
512 | template <typename... Args> |
513 | auto operator()(Args&&... args) && |
514 | -> decltype(static_cast<OnTrue&&>(on_true_)(static_cast<Args&&>(args)...)) |
515 | { |
516 | if (bool_) |
517 | { |
518 | return static_cast<OnTrue&&>(on_true_)(static_cast<Args&&>(args)...); |
519 | } |
520 | else |
521 | { |
522 | return static_cast<OnFalse&&>(on_false_)(static_cast<Args&&>(args)...); |
523 | } |
524 | } |
525 | |
526 | template <typename... Args> |
527 | auto operator()(Args&&... args) const & |
528 | -> decltype(on_true_(static_cast<Args&&>(args)...)) |
529 | { |
530 | if (bool_) |
531 | { |
532 | return on_true_(static_cast<Args&&>(args)...); |
533 | } |
534 | else |
535 | { |
536 | return on_false_(static_cast<Args&&>(args)...); |
537 | } |
538 | } |
539 | |
540 | /// Set the true branch of the conditional. |
541 | template <typename T> |
542 | deferred_conditional<T, OnFalse> then(T on_true, |
543 | constraint_t< |
544 | is_deferred<T>::value |
545 | >* = 0, |
546 | constraint_t< |
547 | is_same< |
548 | conditional_t<true, OnTrue, T>, |
549 | deferred_noop |
550 | >::value |
551 | >* = 0) && |
552 | { |
553 | return deferred_conditional<T, OnFalse>( |
554 | bool_, static_cast<T&&>(on_true), |
555 | static_cast<OnFalse&&>(on_false_)); |
556 | } |
557 | |
558 | /// Set the false branch of the conditional. |
559 | template <typename T> |
560 | deferred_conditional<OnTrue, T> otherwise(T on_false, |
561 | constraint_t< |
562 | is_deferred<T>::value |
563 | >* = 0, |
564 | constraint_t< |
565 | !is_same< |
566 | conditional_t<true, OnTrue, T>, |
567 | deferred_noop |
568 | >::value |
569 | >* = 0, |
570 | constraint_t< |
571 | is_same< |
572 | conditional_t<true, OnFalse, T>, |
573 | deferred_noop |
574 | >::value |
575 | >* = 0) && |
576 | { |
577 | return deferred_conditional<OnTrue, T>( |
578 | bool_, static_cast<OnTrue&&>(on_true_), |
579 | static_cast<T&&>(on_false)); |
580 | } |
581 | }; |
582 | |
583 | #if !defined(GENERATING_DOCUMENTATION) |
584 | template <typename OnTrue, typename OnFalse> |
585 | struct is_deferred<deferred_conditional<OnTrue, OnFalse>> : true_type |
586 | { |
587 | }; |
588 | #endif // !defined(GENERATING_DOCUMENTATION) |
589 | |
590 | /// Class used to specify that an asynchronous operation should return a |
591 | /// function object to lazily launch the operation. |
592 | /** |
593 | * The deferred_t class is used to indicate that an asynchronous operation |
594 | * should return a function object which is itself an initiation function. A |
595 | * deferred_t object may be passed as a completion token to an asynchronous |
596 | * operation, typically using the special value @c boost::asio::deferred. For |
597 | * example: |
598 | * |
599 | * @code auto my_deferred_op |
600 | * = my_socket.async_read_some(my_buffer, |
601 | * boost::asio::deferred); @endcode |
602 | * |
603 | * The initiating function (async_read_some in the above example) returns a |
604 | * function object that will lazily initiate the operation. |
605 | */ |
606 | class deferred_t |
607 | { |
608 | public: |
609 | /// Default constructor. |
610 | constexpr deferred_t() |
611 | { |
612 | } |
613 | |
614 | /// Adapts an executor to add the @c deferred_t completion token as the |
615 | /// default. |
616 | template <typename InnerExecutor> |
617 | struct executor_with_default : InnerExecutor |
618 | { |
619 | /// Specify @c deferred_t as the default completion token type. |
620 | typedef deferred_t default_completion_token_type; |
621 | |
622 | /// Construct the adapted executor from the inner executor type. |
623 | template <typename InnerExecutor1> |
624 | executor_with_default(const InnerExecutor1& ex, |
625 | constraint_t< |
626 | conditional_t< |
627 | !is_same<InnerExecutor1, executor_with_default>::value, |
628 | is_convertible<InnerExecutor1, InnerExecutor>, |
629 | false_type |
630 | >::value |
631 | > = 0) noexcept |
632 | : InnerExecutor(ex) |
633 | { |
634 | } |
635 | }; |
636 | |
637 | /// Type alias to adapt an I/O object to use @c deferred_t as its |
638 | /// default completion token type. |
639 | template <typename T> |
640 | using as_default_on_t = typename T::template rebind_executor< |
641 | executor_with_default<typename T::executor_type>>::other; |
642 | |
643 | /// Function helper to adapt an I/O object to use @c deferred_t as its |
644 | /// default completion token type. |
645 | template <typename T> |
646 | static typename decay_t<T>::template rebind_executor< |
647 | executor_with_default<typename decay_t<T>::executor_type> |
648 | >::other |
649 | as_default_on(T&& object) |
650 | { |
651 | return typename decay_t<T>::template rebind_executor< |
652 | executor_with_default<typename decay_t<T>::executor_type> |
653 | >::other(static_cast<T&&>(object)); |
654 | } |
655 | |
656 | /// Creates a new deferred from a function. |
657 | template <typename Function> |
658 | constraint_t< |
659 | !is_deferred<decay_t<Function>>::value, |
660 | deferred_function<decay_t<Function>> |
661 | > operator()(Function&& function) const |
662 | { |
663 | return deferred_function<decay_t<Function>>( |
664 | deferred_init_tag{}, static_cast<Function&&>(function)); |
665 | } |
666 | |
667 | /// Passes through anything that is already deferred. |
668 | template <typename T> |
669 | constraint_t< |
670 | is_deferred<decay_t<T>>::value, |
671 | decay_t<T> |
672 | > operator()(T&& t) const |
673 | { |
674 | return static_cast<T&&>(t); |
675 | } |
676 | |
677 | /// Returns a deferred operation that returns the provided values. |
678 | template <typename... Args> |
679 | static constexpr deferred_values<decay_t<Args>...> values(Args&&... args) |
680 | { |
681 | return deferred_values<decay_t<Args>...>( |
682 | deferred_init_tag{}, static_cast<Args&&>(args)...); |
683 | } |
684 | |
685 | /// Creates a conditional object for branching deferred operations. |
686 | static constexpr deferred_conditional<> when(bool b) |
687 | { |
688 | return deferred_conditional<>(b); |
689 | } |
690 | }; |
691 | |
692 | /// Pipe operator used to chain deferred operations. |
693 | template <typename Head, typename Tail> |
694 | inline auto operator|(Head head, Tail&& tail) |
695 | -> constraint_t< |
696 | is_deferred<Head>::value, |
697 | decltype(static_cast<Head&&>(head)(static_cast<Tail&&>(tail))) |
698 | > |
699 | { |
700 | return static_cast<Head&&>(head)(static_cast<Tail&&>(tail)); |
701 | } |
702 | |
703 | /// A @ref completion_token object used to specify that an asynchronous |
704 | /// operation should return a function object to lazily launch the operation. |
705 | /** |
706 | * See the documentation for boost::asio::deferred_t for a usage example. |
707 | */ |
708 | constexpr deferred_t deferred; |
709 | |
710 | } // namespace asio |
711 | } // namespace boost |
712 | |
713 | #include <boost/asio/detail/pop_options.hpp> |
714 | |
715 | #include <boost/asio/impl/deferred.hpp> |
716 | |
717 | #endif // BOOST_ASIO_DEFERRED_HPP |
718 | |