1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
/// Waits on multiple concurrent branches, returning when the **first** branch
/// completes, cancelling the remaining branches.
///
/// The `select!` macro must be used inside of async functions, closures, and
/// blocks.
///
/// The `select!` macro accepts one or more branches with the following pattern:
///
/// ```text
/// <pattern> = <async expression> (, if <precondition>)? => <handler>,
/// ```
///
/// Additionally, the `select!` macro may include a single, optional `else`
/// branch, which evaluates if none of the other branches match their patterns:
///
/// ```text
/// else => <expression>
/// ```
///
/// The macro aggregates all `<async expression>` expressions and runs them
/// concurrently on the **current** task. Once the **first** expression
/// completes with a value that matches its `<pattern>`, the `select!` macro
/// returns the result of evaluating the completed branch's `<handler>`
/// expression.
///
/// Additionally, each branch may include an optional `if` precondition. If the
/// precondition returns `false`, then the branch is disabled. The provided
/// `<async expression>` is still evaluated but the resulting future is never
/// polled. This capability is useful when using `select!` within a loop.
///
/// The complete lifecycle of a `select!` expression is as follows:
///
/// 1. Evaluate all provided `<precondition>` expressions. If the precondition
///    returns `false`, disable the branch for the remainder of the current call
///    to `select!`. Re-entering `select!` due to a loop clears the "disabled"
///    state.
/// 2. Aggregate the `<async expression>`s from each branch, including the
///    disabled ones. If the branch is disabled, `<async expression>` is still
///    evaluated, but the resulting future is not polled.
/// 3. Concurrently await on the results for all remaining `<async expression>`s.
/// 4. Once an `<async expression>` returns a value, attempt to apply the value
///    to the provided `<pattern>`, if the pattern matches, evaluate `<handler>`
///    and return. If the pattern **does not** match, disable the current branch
///    and for the remainder of the current call to `select!`. Continue from step 3.
/// 5. If **all** branches are disabled, evaluate the `else` expression. If no
///    else branch is provided, panic.
///
/// # Runtime characteristics
///
/// By running all async expressions on the current task, the expressions are
/// able to run **concurrently** but not in **parallel**. This means all
/// expressions are run on the same thread and if one branch blocks the thread,
/// all other expressions will be unable to continue. If parallelism is
/// required, spawn each async expression using [`tokio::spawn`] and pass the
/// join handle to `select!`.
///
/// [`tokio::spawn`]: crate::spawn
///
/// # Fairness
///
/// By default, `select!` randomly picks a branch to check first. This provides
/// some level of fairness when calling `select!` in a loop with branches that
/// are always ready.
///
/// This behavior can be overridden by adding `biased;` to the beginning of the
/// macro usage. See the examples for details. This will cause `select` to poll
/// the futures in the order they appear from top to bottom. There are a few
/// reasons you may want this:
///
/// - The random number generation of `tokio::select!` has a non-zero CPU cost
/// - Your futures may interact in a way where known polling order is significant
///
/// But there is an important caveat to this mode. It becomes your responsibility
/// to ensure that the polling order of your futures is fair. If for example you
/// are selecting between a stream and a shutdown future, and the stream has a
/// huge volume of messages and zero or nearly zero time between them, you should
/// place the shutdown future earlier in the `select!` list to ensure that it is
/// always polled, and will not be ignored due to the stream being constantly
/// ready.
///
/// # Panics
///
/// The `select!` macro panics if all branches are disabled **and** there is no
/// provided `else` branch. A branch is disabled when the provided `if`
/// precondition returns `false` **or** when the pattern does not match the
/// result of `<async expression>`.
///
/// # Cancellation safety
///
/// When using `select!` in a loop to receive messages from multiple sources,
/// you should make sure that the receive call is cancellation safe to avoid
/// losing messages. This section goes through various common methods and
/// describes whether they are cancel safe.  The lists in this section are not
/// exhaustive.
///
/// The following methods are cancellation safe:
///
///  * [`tokio::sync::mpsc::Receiver::recv`](crate::sync::mpsc::Receiver::recv)
///  * [`tokio::sync::mpsc::UnboundedReceiver::recv`](crate::sync::mpsc::UnboundedReceiver::recv)
///  * [`tokio::sync::broadcast::Receiver::recv`](crate::sync::broadcast::Receiver::recv)
///  * [`tokio::sync::watch::Receiver::changed`](crate::sync::watch::Receiver::changed)
///  * [`tokio::net::TcpListener::accept`](crate::net::TcpListener::accept)
///  * [`tokio::net::UnixListener::accept`](crate::net::UnixListener::accept)
///  * [`tokio::io::AsyncReadExt::read`](crate::io::AsyncReadExt::read) on any `AsyncRead`
///  * [`tokio::io::AsyncReadExt::read_buf`](crate::io::AsyncReadExt::read_buf) on any `AsyncRead`
///  * [`tokio::io::AsyncWriteExt::write`](crate::io::AsyncWriteExt::write) on any `AsyncWrite`
///  * [`tokio::io::AsyncWriteExt::write_buf`](crate::io::AsyncWriteExt::write_buf) on any `AsyncWrite`
///  * [`tokio_stream::StreamExt::next`](https://docs.rs/tokio-stream/0.1/tokio_stream/trait.StreamExt.html#method.next) on any `Stream`
///  * [`futures::stream::StreamExt::next`](https://docs.rs/futures/0.3/futures/stream/trait.StreamExt.html#method.next) on any `Stream`
///
/// The following methods are not cancellation safe and can lead to loss of data:
///
///  * [`tokio::io::AsyncReadExt::read_exact`](crate::io::AsyncReadExt::read_exact)
///  * [`tokio::io::AsyncReadExt::read_to_end`](crate::io::AsyncReadExt::read_to_end)
///  * [`tokio::io::AsyncReadExt::read_to_string`](crate::io::AsyncReadExt::read_to_string)
///  * [`tokio::io::AsyncWriteExt::write_all`](crate::io::AsyncWriteExt::write_all)
///
/// The following methods are not cancellation safe because they use a queue for
/// fairness and cancellation makes you lose your place in the queue:
///
///  * [`tokio::sync::Mutex::lock`](crate::sync::Mutex::lock)
///  * [`tokio::sync::RwLock::read`](crate::sync::RwLock::read)
///  * [`tokio::sync::RwLock::write`](crate::sync::RwLock::write)
///  * [`tokio::sync::Semaphore::acquire`](crate::sync::Semaphore::acquire)
///  * [`tokio::sync::Notify::notified`](crate::sync::Notify::notified)
///
/// To determine whether your own methods are cancellation safe, look for the
/// location of uses of `.await`. This is because when an asynchronous method is
/// cancelled, that always happens at an `.await`. If your function behaves
/// correctly even if it is restarted while waiting at an `.await`, then it is
/// cancellation safe.
///
/// Be aware that cancelling something that is not cancellation safe is not
/// necessarily wrong. For example, if you are cancelling a task because the
/// application is shutting down, then you probably don't care that partially
/// read data is lost.
///
/// # Examples
///
/// Basic select with two branches.
///
/// ```
/// async fn do_stuff_async() {
///     // async work
/// }
///
/// async fn more_async_work() {
///     // more here
/// }
///
/// #[tokio::main]
/// async fn main() {
///     tokio::select! {
///         _ = do_stuff_async() => {
///             println!("do_stuff_async() completed first")
///         }
///         _ = more_async_work() => {
///             println!("more_async_work() completed first")
///         }
///     };
/// }
/// ```
///
/// Basic stream selecting.
///
/// ```
/// use tokio_stream::{self as stream, StreamExt};
///
/// #[tokio::main]
/// async fn main() {
///     let mut stream1 = stream::iter(vec![1, 2, 3]);
///     let mut stream2 = stream::iter(vec![4, 5, 6]);
///
///     let next = tokio::select! {
///         v = stream1.next() => v.unwrap(),
///         v = stream2.next() => v.unwrap(),
///     };
///
///     assert!(next == 1 || next == 4);
/// }
/// ```
///
/// Collect the contents of two streams. In this example, we rely on pattern
/// matching and the fact that `stream::iter` is "fused", i.e. once the stream
/// is complete, all calls to `next()` return `None`.
///
/// ```
/// use tokio_stream::{self as stream, StreamExt};
///
/// #[tokio::main]
/// async fn main() {
///     let mut stream1 = stream::iter(vec![1, 2, 3]);
///     let mut stream2 = stream::iter(vec![4, 5, 6]);
///
///     let mut values = vec![];
///
///     loop {
///         tokio::select! {
///             Some(v) = stream1.next() => values.push(v),
///             Some(v) = stream2.next() => values.push(v),
///             else => break,
///         }
///     }
///
///     values.sort();
///     assert_eq!(&[1, 2, 3, 4, 5, 6], &values[..]);
/// }
/// ```
///
/// Using the same future in multiple `select!` expressions can be done by passing
/// a reference to the future. Doing so requires the future to be [`Unpin`]. A
/// future can be made [`Unpin`] by either using [`Box::pin`] or stack pinning.
///
/// [`Unpin`]: std::marker::Unpin
/// [`Box::pin`]: std::boxed::Box::pin
///
/// Here, a stream is consumed for at most 1 second.
///
/// ```
/// use tokio_stream::{self as stream, StreamExt};
/// use tokio::time::{self, Duration};
///
/// #[tokio::main]
/// async fn main() {
///     let mut stream = stream::iter(vec![1, 2, 3]);
///     let sleep = time::sleep(Duration::from_secs(1));
///     tokio::pin!(sleep);
///
///     loop {
///         tokio::select! {
///             maybe_v = stream.next() => {
///                 if let Some(v) = maybe_v {
///                     println!("got = {}", v);
///                 } else {
///                     break;
///                 }
///             }
///             _ = &mut sleep => {
///                 println!("timeout");
///                 break;
///             }
///         }
///     }
/// }
/// ```
///
/// Joining two values using `select!`.
///
/// ```
/// use tokio::sync::oneshot;
///
/// #[tokio::main]
/// async fn main() {
///     let (tx1, mut rx1) = oneshot::channel();
///     let (tx2, mut rx2) = oneshot::channel();
///
///     tokio::spawn(async move {
///         tx1.send("first").unwrap();
///     });
///
///     tokio::spawn(async move {
///         tx2.send("second").unwrap();
///     });
///
///     let mut a = None;
///     let mut b = None;
///
///     while a.is_none() || b.is_none() {
///         tokio::select! {
///             v1 = (&mut rx1), if a.is_none() => a = Some(v1.unwrap()),
///             v2 = (&mut rx2), if b.is_none() => b = Some(v2.unwrap()),
///         }
///     }
///
///     let res = (a.unwrap(), b.unwrap());
///
///     assert_eq!(res.0, "first");
///     assert_eq!(res.1, "second");
/// }
/// ```
///
/// Using the `biased;` mode to control polling order.
///
/// ```
/// #[tokio::main]
/// async fn main() {
///     let mut count = 0u8;
///
///     loop {
///         tokio::select! {
///             // If you run this example without `biased;`, the polling order is
///             // pseudo-random, and the assertions on the value of count will
///             // (probably) fail.
///             biased;
///
///             _ = async {}, if count < 1 => {
///                 count += 1;
///                 assert_eq!(count, 1);
///             }
///             _ = async {}, if count < 2 => {
///                 count += 1;
///                 assert_eq!(count, 2);
///             }
///             _ = async {}, if count < 3 => {
///                 count += 1;
///                 assert_eq!(count, 3);
///             }
///             _ = async {}, if count < 4 => {
///                 count += 1;
///                 assert_eq!(count, 4);
///             }
///
///             else => {
///                 break;
///             }
///         };
///     }
/// }
/// ```
///
/// ## Avoid racy `if` preconditions
///
/// Given that `if` preconditions are used to disable `select!` branches, some
/// caution must be used to avoid missing values.
///
/// For example, here is **incorrect** usage of `sleep` with `if`. The objective
/// is to repeatedly run an asynchronous task for up to 50 milliseconds.
/// However, there is a potential for the `sleep` completion to be missed.
///
/// ```no_run,should_panic
/// use tokio::time::{self, Duration};
///
/// async fn some_async_work() {
///     // do work
/// }
///
/// #[tokio::main]
/// async fn main() {
///     let sleep = time::sleep(Duration::from_millis(50));
///     tokio::pin!(sleep);
///
///     while !sleep.is_elapsed() {
///         tokio::select! {
///             _ = &mut sleep, if !sleep.is_elapsed() => {
///                 println!("operation timed out");
///             }
///             _ = some_async_work() => {
///                 println!("operation completed");
///             }
///         }
///     }
///
///     panic!("This example shows how not to do it!");
/// }
/// ```
///
/// In the above example, `sleep.is_elapsed()` may return `true` even if
/// `sleep.poll()` never returned `Ready`. This opens up a potential race
/// condition where `sleep` expires between the `while !sleep.is_elapsed()`
/// check and the call to `select!` resulting in the `some_async_work()` call to
/// run uninterrupted despite the sleep having elapsed.
///
/// One way to write the above example without the race would be:
///
/// ```
/// use tokio::time::{self, Duration};
///
/// async fn some_async_work() {
/// # time::sleep(Duration::from_millis(10)).await;
///     // do work
/// }
///
/// #[tokio::main]
/// async fn main() {
///     let sleep = time::sleep(Duration::from_millis(50));
///     tokio::pin!(sleep);
///
///     loop {
///         tokio::select! {
///             _ = &mut sleep => {
///                 println!("operation timed out");
///                 break;
///             }
///             _ = some_async_work() => {
///                 println!("operation completed");
///             }
///         }
///     }
/// }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
macro_rules! select {
    // Uses a declarative macro to do **most** of the work. While it is possible
    // to implement fully with a declarative macro, a procedural macro is used
    // to enable improved error messages.
    //
    // The macro is structured as a tt-muncher. All branches are processed and
    // normalized. Once the input is normalized, it is passed to the top-most
    // rule. When entering the macro, `@{ }` is inserted at the front. This is
    // used to collect the normalized input.
    //
    // The macro only recurses once per branch. This allows using `select!`
    // without requiring the user to increase the recursion limit.

    // All input is normalized, now transform.
    (@ {
        // The index of the future to poll first (in bias mode), or the RNG
        // expression to use to pick a future to poll first.
        start=$start:expr;

        // One `_` for each branch in the `select!` macro. Passing this to
        // `count!` converts $skip to an integer.
        ( $($count:tt)* )

        // Normalized select branches. `( $skip )` is a set of `_` characters.
        // There is one `_` for each select branch **before** this one. Given
        // that all input futures are stored in a tuple, $skip is useful for
        // generating a pattern to reference the future for the current branch.
        // $skip is also used as an argument to `count!`, returning the index of
        // the current select branch.
        $( ( $($skip:tt)* ) $bind:pat = $fut:expr, if $c:expr => $handle:expr, )+

        // Fallback expression used when all select branches have been disabled.
        ; $else:expr

    }) => {{
        // Enter a context where stable "function-like" proc macros can be used.
        //
        // This module is defined within a scope and should not leak out of this
        // macro.
        mod util {
            // Generate an enum with one variant per select branch
            $crate::select_priv_declare_output_enum!( ( $($count)* ) );
        }

        // `tokio::macros::support` is a public, but doc(hidden) module
        // including a re-export of all types needed by this macro.
        use $crate::macros::support::Future;
        use $crate::macros::support::Pin;
        use $crate::macros::support::Poll::{Ready, Pending};

        const BRANCHES: u32 = $crate::count!( $($count)* );

        let mut disabled: util::Mask = Default::default();

        // First, invoke all the pre-conditions. For any that return true,
        // set the appropriate bit in `disabled`.
        $(
            if !$c {
                let mask: util::Mask = 1 << $crate::count!( $($skip)* );
                disabled |= mask;
            }
        )*

        // Create a scope to separate polling from handling the output. This
        // adds borrow checker flexibility when using the macro.
        let mut output = {
            // Safety: Nothing must be moved out of `futures`. This is to
            // satisfy the requirement of `Pin::new_unchecked` called below.
            let mut futures = ( $( $fut , )+ );

            $crate::macros::support::poll_fn(|cx| {
                // Track if any branch returns pending. If no branch completes
                // **or** returns pending, this implies that all branches are
                // disabled.
                let mut is_pending = false;

                // Choose a starting index to begin polling the futures at. In
                // practice, this will either be a pseudo-randomly generated
                // number by default, or the constant 0 if `biased;` is
                // supplied.
                let start = $start;

                for i in 0..BRANCHES {
                    let branch;
                    #[allow(clippy::modulo_one)]
                    {
                        branch = (start + i) % BRANCHES;
                    }
                    match branch {
                        $(
                            #[allow(unreachable_code)]
                            $crate::count!( $($skip)* ) => {
                                // First, if the future has previously been
                                // disabled, do not poll it again. This is done
                                // by checking the associated bit in the
                                // `disabled` bit field.
                                let mask = 1 << branch;

                                if disabled & mask == mask {
                                    // The future has been disabled.
                                    continue;
                                }

                                // Extract the future for this branch from the
                                // tuple
                                let ( $($skip,)* fut, .. ) = &mut futures;

                                // Safety: future is stored on the stack above
                                // and never moved.
                                let mut fut = unsafe { Pin::new_unchecked(fut) };

                                // Try polling it
                                let out = match Future::poll(fut, cx) {
                                    Ready(out) => out,
                                    Pending => {
                                        // Track that at least one future is
                                        // still pending and continue polling.
                                        is_pending = true;
                                        continue;
                                    }
                                };

                                // Disable the future from future polling.
                                disabled |= mask;

                                // The future returned a value, check if matches
                                // the specified pattern.
                                #[allow(unused_variables)]
                                #[allow(unused_mut)]
                                match &out {
                                    $crate::select_priv_clean_pattern!($bind) => {}
                                    _ => continue,
                                }

                                // The select is complete, return the value
                                return Ready($crate::select_variant!(util::Out, ($($skip)*))(out));
                            }
                        )*
                        _ => unreachable!("reaching this means there probably is an off by one bug"),
                    }
                }

                if is_pending {
                    Pending
                } else {
                    // All branches have been disabled.
                    Ready(util::Out::Disabled)
                }
            }).await
        };

        match output {
            $(
                $crate::select_variant!(util::Out, ($($skip)*) ($bind)) => $handle,
            )*
            util::Out::Disabled => $else,
            _ => unreachable!("failed to match bind"),
        }
    }};

    // ==== Normalize =====

    // These rules match a single `select!` branch and normalize it for
    // processing by the first rule.

    (@ { start=$start:expr; $($t:tt)* } ) => {
        // No `else` branch
        $crate::select!(@{ start=$start; $($t)*; panic!("all branches are disabled and there is no else branch") })
    };
    (@ { start=$start:expr; $($t:tt)* } else => $else:expr $(,)?) => {
        $crate::select!(@{ start=$start; $($t)*; $else })
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block, $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block, $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, })
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, })
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr, $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
    };
    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr, $($r:tt)* ) => {
        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
    };

    // ===== Entry point =====

    (biased; $p:pat = $($t:tt)* ) => {
        $crate::select!(@{ start=0; () } $p = $($t)*)
    };

    ( $p:pat = $($t:tt)* ) => {
        // Randomly generate a starting point. This makes `select!` a bit more
        // fair and avoids always polling the first future.
        $crate::select!(@{ start={ $crate::macros::support::thread_rng_n(BRANCHES) }; () } $p = $($t)*)
    };
    () => {
        compile_error!("select! requires at least one branch.")
    };
}

// And here... we manually list out matches for up to 64 branches... I'm not
// happy about it either, but this is how we manage to use a declarative macro!

#[macro_export]
#[doc(hidden)]
macro_rules! count {
    () => {
        0
    };
    (_) => {
        1
    };
    (_ _) => {
        2
    };
    (_ _ _) => {
        3
    };
    (_ _ _ _) => {
        4
    };
    (_ _ _ _ _) => {
        5
    };
    (_ _ _ _ _ _) => {
        6
    };
    (_ _ _ _ _ _ _) => {
        7
    };
    (_ _ _ _ _ _ _ _) => {
        8
    };
    (_ _ _ _ _ _ _ _ _) => {
        9
    };
    (_ _ _ _ _ _ _ _ _ _) => {
        10
    };
    (_ _ _ _ _ _ _ _ _ _ _) => {
        11
    };
    (_ _ _ _ _ _ _ _ _ _ _ _) => {
        12
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _) => {
        13
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        14
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        15
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        16
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        17
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        18
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        19
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        20
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        21
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        22
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        23
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        24
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        25
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        26
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        27
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        28
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        29
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        30
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        31
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        32
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        33
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        34
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        35
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        36
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        37
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        38
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        39
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        40
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        41
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        42
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        43
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        44
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        45
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        46
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        47
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        48
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        49
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        50
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        51
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        52
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        53
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        54
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        55
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        56
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        57
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        58
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        59
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        60
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        61
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        62
    };
    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
        63
    };
}

#[macro_export]
#[doc(hidden)]
macro_rules! select_variant {
    ($($p:ident)::*, () $($t:tt)*) => {
        $($p)::*::_0 $($t)*
    };
    ($($p:ident)::*, (_) $($t:tt)*) => {
        $($p)::*::_1 $($t)*
    };
    ($($p:ident)::*, (_ _) $($t:tt)*) => {
        $($p)::*::_2 $($t)*
    };
    ($($p:ident)::*, (_ _ _) $($t:tt)*) => {
        $($p)::*::_3 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _) $($t:tt)*) => {
        $($p)::*::_4 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_5 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_6 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_7 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_8 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_9 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_10 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_11 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_12 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_13 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_14 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_15 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_16 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_17 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_18 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_19 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_20 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_21 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_22 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_23 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_24 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_25 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_26 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_27 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_28 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_29 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_30 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_31 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_32 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_33 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_34 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_35 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_36 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_37 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_38 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_39 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_40 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_41 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_42 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_43 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_44 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_45 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_46 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_47 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_48 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_49 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_50 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_51 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_52 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_53 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_54 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_55 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_56 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_57 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_58 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_59 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_60 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_61 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_62 $($t)*
    };
    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
        $($p)::*::_63 $($t)*
    };
}