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
//! Streams
//!
//! This module contains a number of functions for working with `Streams`s
//! that return `Result`s, allowing for short-circuiting computations.

#[cfg(feature = "compat")]
use crate::compat::Compat;
use core::pin::Pin;
use futures_core::{
    future::{Future, TryFuture},
    stream::TryStream,
    task::{Context, Poll},
};

mod and_then;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::and_then::AndThen;

mod err_into;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::err_into::ErrInto;

mod inspect_ok;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::inspect_ok::InspectOk;

mod inspect_err;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::inspect_err::InspectErr;

mod into_stream;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::into_stream::IntoStream;

mod map_ok;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::map_ok::MapOk;

mod map_err;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::map_err::MapErr;

mod or_else;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::or_else::OrElse;

mod try_next;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_next::TryNext;

mod try_for_each;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_for_each::TryForEach;

mod try_filter;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_filter::TryFilter;

mod try_filter_map;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_filter_map::TryFilterMap;

mod try_flatten;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_flatten::TryFlatten;

mod try_collect;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_collect::TryCollect;

mod try_concat;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_concat::TryConcat;

mod try_fold;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_fold::TryFold;

mod try_skip_while;
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::try_skip_while::TrySkipWhile;

cfg_target_has_atomic! {
    #[cfg(feature = "alloc")]
    mod try_buffer_unordered;
    #[cfg(feature = "alloc")]
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_buffer_unordered::TryBufferUnordered;

    #[cfg(feature = "alloc")]
    mod try_for_each_concurrent;
    #[cfg(feature = "alloc")]
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::try_for_each_concurrent::TryForEachConcurrent;
}

#[cfg(feature = "io")]
#[cfg(feature = "std")]
mod into_async_read;
#[cfg(feature = "io")]
#[cfg(feature = "std")]
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
pub use self::into_async_read::IntoAsyncRead;

impl<S: ?Sized + TryStream> TryStreamExt for S {}

/// Adapters specific to `Result`-returning streams
pub trait TryStreamExt: TryStream {
    /// Wraps the current stream in a new stream which converts the error type
    /// into the one provided.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let mut stream =
    ///     stream::iter(vec![Ok(()), Err(5i32)])
    ///         .err_into::<i64>();
    ///
    /// assert_eq!(stream.try_next().await, Ok(Some(())));
    /// assert_eq!(stream.try_next().await, Err(5i64));
    /// # })
    /// ```
    fn err_into<E>(self) -> ErrInto<Self, E>
    where
        Self: Sized,
        Self::Error: Into<E>,
    {
        ErrInto::new(self)
    }

    /// Wraps the current stream in a new stream which maps the success value
    /// using the provided closure.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let mut stream =
    ///     stream::iter(vec![Ok(5), Err(0)])
    ///         .map_ok(|x| x + 2);
    ///
    /// assert_eq!(stream.try_next().await, Ok(Some(7)));
    /// assert_eq!(stream.try_next().await, Err(0));
    /// # })
    /// ```
    fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
    where
        Self: Sized,
        F: FnMut(Self::Ok) -> T,
    {
        MapOk::new(self, f)
    }

    /// Wraps the current stream in a new stream which maps the error value
    /// using the provided closure.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let mut stream =
    ///     stream::iter(vec![Ok(5), Err(0)])
    ///         .map_err(|x| x + 2);
    ///
    /// assert_eq!(stream.try_next().await, Ok(Some(5)));
    /// assert_eq!(stream.try_next().await, Err(2));
    /// # })
    /// ```
    fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
    where
        Self: Sized,
        F: FnMut(Self::Error) -> E,
    {
        MapErr::new(self, f)
    }

    /// Chain on a computation for when a value is ready, passing the successful
    /// results to the provided closure `f`.
    ///
    /// This function can be used to run a unit of work when the next successful
    /// value on a stream is ready. The closure provided will be yielded a value
    /// when ready, and the returned future will then be run to completion to
    /// produce the next value on this stream.
    ///
    /// Any errors produced by this stream will not be passed to the closure,
    /// and will be passed through.
    ///
    /// The returned value of the closure must implement the `TryFuture` trait
    /// and can represent some more work to be done before the composed stream
    /// is finished.
    ///
    /// Note that this function consumes the receiving stream and returns a
    /// wrapped version of it.
    ///
    /// To process the entire stream and return a single future representing
    /// success or error, use `try_for_each` instead.
    ///
    /// # Examples
    ///
    /// ```
    /// use futures::channel::mpsc;
    /// use futures::future;
    /// use futures::stream::TryStreamExt;
    ///
    /// let (_tx, rx) = mpsc::channel::<Result<i32, ()>>(1);
    ///
    /// let rx = rx.and_then(|result| {
    ///     future::ok(if result % 2 == 0 {
    ///         Some(result)
    ///     } else {
    ///         None
    ///     })
    /// });
    /// ```
    fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
    where
        F: FnMut(Self::Ok) -> Fut,
        Fut: TryFuture<Error = Self::Error>,
        Self: Sized,
    {
        AndThen::new(self, f)
    }

    /// Chain on a computation for when an error happens, passing the
    /// erroneous result to the provided closure `f`.
    ///
    /// This function can be used to run a unit of work and attempt to recover from
    /// an error if one happens. The closure provided will be yielded an error
    /// when one appears, and the returned future will then be run to completion
    /// to produce the next value on this stream.
    ///
    /// Any successful values produced by this stream will not be passed to the
    /// closure, and will be passed through.
    ///
    /// The returned value of the closure must implement the [`TryFuture`](futures_core::future::TryFuture) trait
    /// and can represent some more work to be done before the composed stream
    /// is finished.
    ///
    /// Note that this function consumes the receiving stream and returns a
    /// wrapped version of it.
    fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
    where
        F: FnMut(Self::Error) -> Fut,
        Fut: TryFuture<Ok = Self::Ok>,
        Self: Sized,
    {
        OrElse::new(self, f)
    }

    /// Do something with the success value of this stream, afterwards passing
    /// it on.
    ///
    /// This is similar to the `StreamExt::inspect` method where it allows
    /// easily inspecting the success value as it passes through the stream, for
    /// example to debug what's going on.
    fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
    where
        F: FnMut(&Self::Ok),
        Self: Sized,
    {
        InspectOk::new(self, f)
    }

    /// Do something with the error value of this stream, afterwards passing it on.
    ///
    /// This is similar to the `StreamExt::inspect` method where it allows
    /// easily inspecting the error value as it passes through the stream, for
    /// example to debug what's going on.
    fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
    where
        F: FnMut(&Self::Error),
        Self: Sized,
    {
        InspectErr::new(self, f)
    }

    /// Wraps a [`TryStream`] into a type that implements
    /// [`Stream`](futures_core::stream::Stream)
    ///
    /// [`TryStream`]s currently do not implement the
    /// [`Stream`](futures_core::stream::Stream) trait because of limitations
    /// of the compiler.
    ///
    /// # Examples
    ///
    /// ```
    /// use futures::stream::{Stream, TryStream, TryStreamExt};
    ///
    /// # type T = i32;
    /// # type E = ();
    /// fn make_try_stream() -> impl TryStream<Ok = T, Error = E> { // ... }
    /// # futures::stream::empty()
    /// # }
    /// fn take_stream(stream: impl Stream<Item = Result<T, E>>) { /* ... */ }
    ///
    /// take_stream(make_try_stream().into_stream());
    /// ```
    fn into_stream(self) -> IntoStream<Self>
    where
        Self: Sized,
    {
        IntoStream::new(self)
    }

    /// Creates a future that attempts to resolve the next item in the stream.
    /// If an error is encountered before the next item, the error is returned
    /// instead.
    ///
    /// This is similar to the `Stream::next` combinator, but returns a
    /// `Result<Option<T>, E>` rather than an `Option<Result<T, E>>`, making
    /// for easy use with the `?` operator.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let mut stream = stream::iter(vec![Ok(()), Err(())]);
    ///
    /// assert_eq!(stream.try_next().await, Ok(Some(())));
    /// assert_eq!(stream.try_next().await, Err(()));
    /// # })
    /// ```
    fn try_next(&mut self) -> TryNext<'_, Self>
    where
        Self: Unpin,
    {
        TryNext::new(self)
    }

    /// Attempts to run this stream to completion, executing the provided
    /// asynchronous closure for each element on the stream.
    ///
    /// The provided closure will be called for each item this stream produces,
    /// yielding a future. That future will then be executed to completion
    /// before moving on to the next item.
    ///
    /// The returned value is a [`Future`](futures_core::future::Future) where the
    /// [`Output`](futures_core::future::Future::Output) type is
    /// `Result<(), Self::Error>`. If any of the intermediate
    /// futures or the stream returns an error, this future will return
    /// immediately with an error.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::future;
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let mut x = 0i32;
    ///
    /// {
    ///     let fut = stream::repeat(Ok(1)).try_for_each(|item| {
    ///         x += item;
    ///         future::ready(if x == 3 { Err(()) } else { Ok(()) })
    ///     });
    ///     assert_eq!(fut.await, Err(()));
    /// }
    ///
    /// assert_eq!(x, 3);
    /// # })
    /// ```
    fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>
    where
        F: FnMut(Self::Ok) -> Fut,
        Fut: TryFuture<Ok = (), Error = Self::Error>,
        Self: Sized,
    {
        TryForEach::new(self, f)
    }

    /// Skip elements on this stream while the provided asynchronous predicate
    /// resolves to `true`.
    ///
    /// This function is similar to [`StreamExt::skip_while`](crate::stream::StreamExt::skip_while)
    /// but exits early if an error occurs.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::future;
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(3), Ok(2)]);
    /// let stream = stream.try_skip_while(|x| future::ready(Ok(*x < 3)));
    ///
    /// let output: Result<Vec<i32>, i32> = stream.try_collect().await;
    /// assert_eq!(output, Ok(vec![3, 2]));
    /// # })
    /// ```
    fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
    where
        F: FnMut(&Self::Ok) -> Fut,
        Fut: TryFuture<Ok = bool, Error = Self::Error>,
        Self: Sized,
    {
        TrySkipWhile::new(self, f)
    }

    /// Attempts to run this stream to completion, executing the provided asynchronous
    /// closure for each element on the stream concurrently as elements become
    /// available, exiting as soon as an error occurs.
    ///
    /// This is similar to
    /// [`StreamExt::for_each_concurrent`](crate::stream::StreamExt::for_each_concurrent),
    /// but will resolve to an error immediately if the underlying stream or the provided
    /// closure return an error.
    ///
    /// This method is only available when the `std` or `alloc` feature of this
    /// library is activated, and it is activated by default.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::oneshot;
    /// use futures::stream::{self, StreamExt, TryStreamExt};
    ///
    /// let (tx1, rx1) = oneshot::channel();
    /// let (tx2, rx2) = oneshot::channel();
    /// let (_tx3, rx3) = oneshot::channel();
    ///
    /// let stream = stream::iter(vec![rx1, rx2, rx3]);
    /// let fut = stream.map(Ok).try_for_each_concurrent(
    ///     /* limit */ 2,
    ///     |rx| async move {
    ///         let res: Result<(), oneshot::Canceled> = rx.await;
    ///         res
    ///     }
    /// );
    ///
    /// tx1.send(()).unwrap();
    /// // Drop the second sender so that `rx2` resolves to `Canceled`.
    /// drop(tx2);
    ///
    /// // The final result is an error because the second future
    /// // resulted in an error.
    /// assert_eq!(Err(oneshot::Canceled), fut.await);
    /// # })
    /// ```
    #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
    #[cfg(feature = "alloc")]
    fn try_for_each_concurrent<Fut, F>(
        self,
        limit: impl Into<Option<usize>>,
        f: F,
    ) -> TryForEachConcurrent<Self, Fut, F>
    where
        F: FnMut(Self::Ok) -> Fut,
        Fut: Future<Output = Result<(), Self::Error>>,
        Self: Sized,
    {
        TryForEachConcurrent::new(self, limit.into(), f)
    }

    /// Attempt to transform a stream into a collection,
    /// returning a future representing the result of that computation.
    ///
    /// This combinator will collect all successful results of this stream and
    /// collect them into the specified collection type. If an error happens then all
    /// collected elements will be dropped and the error will be returned.
    ///
    /// The returned future will be resolved when the stream terminates.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::mpsc;
    /// use futures::stream::TryStreamExt;
    /// use std::thread;
    ///
    /// let (tx, rx) = mpsc::unbounded();
    ///
    /// thread::spawn(move || {
    ///     for i in 1..=5 {
    ///         tx.unbounded_send(Ok(i)).unwrap();
    ///     }
    ///     tx.unbounded_send(Err(6)).unwrap();
    /// });
    ///
    /// let output: Result<Vec<i32>, i32> = rx.try_collect().await;
    /// assert_eq!(output, Err(6));
    /// # })
    /// ```
    fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C>
    where
        Self: Sized,
    {
        TryCollect::new(self)
    }

    /// Attempt to filter the values produced by this stream according to the
    /// provided asynchronous closure.
    ///
    /// As values of this stream are made available, the provided predicate `f`
    /// will be run on them. If the predicate returns a `Future` which resolves
    /// to `true`, then the stream will yield the value, but if the predicate
    /// return a `Future` which resolves to `false`, then the value will be
    /// discarded and the next value will be produced.
    ///
    /// All errors are passed through without filtering in this combinator.
    ///
    /// Note that this function consumes the stream passed into it and returns a
    /// wrapped version of it, similar to the existing `filter` methods in
    /// the standard library.
    ///
    /// # Examples
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::future;
    /// use futures::stream::{self, StreamExt, TryStreamExt};
    ///
    /// let stream = stream::iter(vec![Ok(1i32), Ok(2i32), Ok(3i32), Err("error")]);
    /// let mut evens = stream.try_filter(|x| {
    ///     future::ready(x % 2 == 0)
    /// });
    ///
    /// assert_eq!(evens.next().await, Some(Ok(2)));
    /// assert_eq!(evens.next().await, Some(Err("error")));
    /// # })
    /// ```
    fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
    where
        Fut: Future<Output = bool>,
        F: FnMut(&Self::Ok) -> Fut,
        Self: Sized,
    {
        TryFilter::new(self, f)
    }

    /// Attempt to filter the values produced by this stream while
    /// simultaneously mapping them to a different type according to the
    /// provided asynchronous closure.
    ///
    /// As values of this stream are made available, the provided function will
    /// be run on them. If the future returned by the predicate `f` resolves to
    /// [`Some(item)`](Some) then the stream will yield the value `item`, but if
    /// it resolves to [`None`] then the next value will be produced.
    ///
    /// All errors are passed through without filtering in this combinator.
    ///
    /// Note that this function consumes the stream passed into it and returns a
    /// wrapped version of it, similar to the existing `filter_map` methods in
    /// the standard library.
    ///
    /// # Examples
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, StreamExt, TryStreamExt};
    /// use futures::pin_mut;
    ///
    /// let stream = stream::iter(vec![Ok(1i32), Ok(6i32), Err("error")]);
    /// let halves = stream.try_filter_map(|x| async move {
    ///     let ret = if x % 2 == 0 { Some(x / 2) } else { None };
    ///     Ok(ret)
    /// });
    ///
    /// pin_mut!(halves);
    /// assert_eq!(halves.next().await, Some(Ok(3)));
    /// assert_eq!(halves.next().await, Some(Err("error")));
    /// # })
    /// ```
    fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
    where
        Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
        F: FnMut(Self::Ok) -> Fut,
        Self: Sized,
    {
        TryFilterMap::new(self, f)
    }

    /// Flattens a stream of streams into just one continuous stream.
    ///
    /// If this stream's elements are themselves streams then this combinator
    /// will flatten out the entire stream to one long chain of elements. Any
    /// errors are passed through without looking at them, but otherwise each
    /// individual stream will get exhausted before moving on to the next.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::mpsc;
    /// use futures::stream::{StreamExt, TryStreamExt};
    /// use std::thread;
    ///
    /// let (tx1, rx1) = mpsc::unbounded();
    /// let (tx2, rx2) = mpsc::unbounded();
    /// let (tx3, rx3) = mpsc::unbounded();
    ///
    /// thread::spawn(move || {
    ///     tx1.unbounded_send(Ok(1)).unwrap();
    /// });
    /// thread::spawn(move || {
    ///     tx2.unbounded_send(Ok(2)).unwrap();
    ///     tx2.unbounded_send(Err(3)).unwrap();
    /// });
    /// thread::spawn(move || {
    ///     tx3.unbounded_send(Ok(rx1)).unwrap();
    ///     tx3.unbounded_send(Ok(rx2)).unwrap();
    ///     tx3.unbounded_send(Err(4)).unwrap();
    /// });
    ///
    /// let mut stream = rx3.try_flatten();
    /// assert_eq!(stream.next().await, Some(Ok(1)));
    /// assert_eq!(stream.next().await, Some(Ok(2)));
    /// assert_eq!(stream.next().await, Some(Err(3)));
    /// # });
    /// ```
    fn try_flatten(self) -> TryFlatten<Self>
    where
        Self::Ok: TryStream,
        <Self::Ok as TryStream>::Error: From<Self::Error>,
        Self: Sized,
    {
        TryFlatten::new(self)
    }

    /// Attempt to execute an accumulating asynchronous computation over a
    /// stream, collecting all the values into one final result.
    ///
    /// This combinator will accumulate all values returned by this stream
    /// according to the closure provided. The initial state is also provided to
    /// this method and then is returned again by each execution of the closure.
    /// Once the entire stream has been exhausted the returned future will
    /// resolve to this value.
    ///
    /// This method is similar to [`fold`](crate::stream::StreamExt::fold), but will
    /// exit early if an error is encountered in either the stream or the
    /// provided closure.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    ///
    /// let number_stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2)]);
    /// let sum = number_stream.try_fold(0, |acc, x| async move { Ok(acc + x) });
    /// assert_eq!(sum.await, Ok(3));
    ///
    /// let number_stream_with_err = stream::iter(vec![Ok::<i32, i32>(1), Err(2), Ok(1)]);
    /// let sum = number_stream_with_err.try_fold(0, |acc, x| async move { Ok(acc + x) });
    /// assert_eq!(sum.await, Err(2));
    /// # })
    /// ```
    fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F>
    where
        F: FnMut(T, Self::Ok) -> Fut,
        Fut: TryFuture<Ok = T, Error = Self::Error>,
        Self: Sized,
    {
        TryFold::new(self, f, init)
    }

    /// Attempt to concatenate all items of a stream into a single
    /// extendable destination, returning a future representing the end result.
    ///
    /// This combinator will extend the first item with the contents of all
    /// the subsequent successful results of the stream. If the stream is empty,
    /// the default value will be returned.
    ///
    /// Works with all collections that implement the [`Extend`](std::iter::Extend) trait.
    ///
    /// This method is similar to [`concat`](crate::stream::StreamExt::concat), but will
    /// exit early if an error is encountered in the stream.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::mpsc;
    /// use futures::stream::TryStreamExt;
    /// use std::thread;
    ///
    /// let (tx, rx) = mpsc::unbounded::<Result<Vec<i32>, ()>>();
    ///
    /// thread::spawn(move || {
    ///     for i in (0..3).rev() {
    ///         let n = i * 3;
    ///         tx.unbounded_send(Ok(vec![n + 1, n + 2, n + 3])).unwrap();
    ///     }
    /// });
    ///
    /// let result = rx.try_concat().await;
    ///
    /// assert_eq!(result, Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
    /// # });
    /// ```
    fn try_concat(self) -> TryConcat<Self>
    where
        Self: Sized,
        Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,
    {
        TryConcat::new(self)
    }

    /// Attempt to execute several futures from a stream concurrently.
    ///
    /// This stream's `Ok` type must be a [`TryFuture`](futures_core::future::TryFuture) with an `Error` type
    /// that matches the stream's `Error` type.
    ///
    /// This adaptor will buffer up to `n` futures and then return their
    /// outputs in the order in which they complete. If the underlying stream
    /// returns an error, it will be immediately propagated.
    ///
    /// The returned stream will be a stream of results, each containing either
    /// an error or a future's output. An error can be produced either by the
    /// underlying stream itself or by one of the futures it yielded.
    ///
    /// This method is only available when the `std` or `alloc` feature of this
    /// library is activated, and it is activated by default.
    ///
    /// # Examples
    ///
    /// Results are returned in the order of completion:
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::oneshot;
    /// use futures::stream::{self, StreamExt, TryStreamExt};
    ///
    /// let (send_one, recv_one) = oneshot::channel();
    /// let (send_two, recv_two) = oneshot::channel();
    ///
    /// let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]);
    ///
    /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
    ///
    /// send_two.send(2i32)?;
    /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
    ///
    /// send_one.send(1i32)?;
    /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
    ///
    /// assert_eq!(buffered.next().await, None);
    /// # Ok::<(), i32>(()) }).unwrap();
    /// ```
    ///
    /// Errors from the underlying stream itself are propagated:
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::channel::mpsc;
    /// use futures::stream::{StreamExt, TryStreamExt};
    ///
    /// let (sink, stream_of_futures) = mpsc::unbounded();
    /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
    ///
    /// sink.unbounded_send(Ok(async { Ok(7i32) }))?;
    /// assert_eq!(buffered.next().await, Some(Ok(7i32)));
    ///
    /// sink.unbounded_send(Err("error in the stream"))?;
    /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
    /// ```
    #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
    #[cfg(feature = "alloc")]
    fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
    where
        Self::Ok: TryFuture<Error = Self::Error>,
        Self: Sized,
    {
        TryBufferUnordered::new(self, n)
    }

    // TODO: false positive warning from rustdoc. Verify once #43466 settles
    //
    /// A convenience method for calling [`TryStream::try_poll_next`] on [`Unpin`]
    /// stream types.
    fn try_poll_next_unpin(
        &mut self,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Result<Self::Ok, Self::Error>>>
    where
        Self: Unpin,
    {
        Pin::new(self).try_poll_next(cx)
    }

    /// Wraps a [`TryStream`] into a stream compatible with libraries using
    /// futures 0.1 `Stream`. Requires the `compat` feature to be enabled.
    /// ```
    /// use futures::future::{FutureExt, TryFutureExt};
    /// # let (tx, rx) = futures::channel::oneshot::channel();
    ///
    /// let future03 = async {
    ///     println!("Running on the pool");
    ///     tx.send(42).unwrap();
    /// };
    ///
    /// let future01 = future03
    ///     .unit_error() // Make it a TryFuture
    ///     .boxed()  // Make it Unpin
    ///     .compat();
    ///
    /// tokio::run(future01);
    /// # assert_eq!(42, futures::executor::block_on(rx).unwrap());
    /// ```
    #[cfg(feature = "compat")]
    fn compat(self) -> Compat<Self>
    where
        Self: Sized + Unpin,
    {
        Compat::new(self)
    }

    /// Adapter that converts this stream into an [`AsyncRead`](crate::io::AsyncRead).
    ///
    /// Note that because `into_async_read` moves the stream, the [`Stream`](futures_core::stream::Stream) type must be
    /// [`Unpin`]. If you want to use `into_async_read` with a [`!Unpin`](Unpin) stream, you'll
    /// first have to pin the stream. This can be done by boxing the stream using [`Box::pin`]
    /// or pinning it to the stack using the `pin_mut!` macro from the `pin_utils` crate.
    ///
    /// This method is only available when the `std` feature of this
    /// library is activated, and it is activated by default.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::stream::{self, TryStreamExt};
    /// use futures::io::AsyncReadExt;
    ///
    /// let stream = stream::iter(vec![Ok(vec![1, 2, 3, 4, 5])]);
    /// let mut reader = stream.into_async_read();
    /// let mut buf = Vec::new();
    ///
    /// assert!(reader.read_to_end(&mut buf).await.is_ok());
    /// assert_eq!(buf, &[1, 2, 3, 4, 5]);
    /// # })
    /// ```
    #[cfg(feature = "io")]
    #[cfg(feature = "std")]
    fn into_async_read(self) -> IntoAsyncRead<Self>
    where
        Self: Sized + TryStreamExt<Error = std::io::Error> + Unpin,
        Self::Ok: AsRef<[u8]>,
    {
        IntoAsyncRead::new(self)
    }
}