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//! Streams //! //! This module contains a number of functions for working with `Stream`s, //! including the `StreamExt` trait which adds methods to `Stream` types. use core::marker::Unpin; use core::pin::Pin; use either::Either; use futures_core::future::Future; use futures_core::stream::Stream; use futures_core::task::{LocalWaker, Poll}; use futures_sink::Sink; mod iter; pub use self::iter::{iter, Iter}; mod repeat; pub use self::repeat::{repeat, Repeat}; mod chain; pub use self::chain::Chain; mod concat; pub use self::concat::Concat; mod empty; pub use self::empty::{empty, Empty}; mod filter; pub use self::filter::Filter; mod filter_map; pub use self::filter_map::FilterMap; mod flatten; pub use self::flatten::Flatten; mod fold; pub use self::fold::Fold; mod forward; pub use self::forward::Forward; mod for_each; pub use self::for_each::ForEach; mod fuse; pub use self::fuse::Fuse; mod into_future; pub use self::into_future::StreamFuture; mod inspect; pub use self::inspect::Inspect; mod map; pub use self::map::Map; mod next; pub use self::next::Next; mod once; pub use self::once::{once, Once}; mod peek; pub use self::peek::Peekable; mod poll_fn; pub use self::poll_fn::{poll_fn, PollFn}; mod select; pub use self::select::Select; mod skip; pub use self::skip::Skip; mod skip_while; pub use self::skip_while::SkipWhile; mod take; pub use self::take::Take; mod take_while; pub use self::take_while::TakeWhile; mod then; pub use self::then::Then; mod unfold; pub use self::unfold::{unfold, Unfold}; mod zip; pub use self::zip::Zip; if_std! { use std; use std::iter::Extend; mod buffer_unordered; pub use self::buffer_unordered::BufferUnordered; mod buffered; pub use self::buffered::Buffered; mod catch_unwind; pub use self::catch_unwind::CatchUnwind; mod chunks; pub use self::chunks::Chunks; mod collect; pub use self::collect::Collect; mod for_each_concurrent; pub use self::for_each_concurrent::ForEachConcurrent; mod futures_ordered; pub use self::futures_ordered::{futures_ordered, FuturesOrdered}; mod futures_unordered; pub use self::futures_unordered::{futures_unordered, FuturesUnordered}; mod split; pub use self::split::{SplitStream, SplitSink, ReuniteError}; // ToDo // mod select_all; // pub use self::select_all::{select_all, SelectAll}; } impl<T: ?Sized> StreamExt for T where T: Stream {} /// An extension trait for `Stream`s that provides a variety of convenient /// combinator functions. pub trait StreamExt: Stream { /// Creates a future that resolves to the next item in the stream. /// /// Note that because `next` doesn't take ownership over the stream, /// the [`Stream`] type must be [`Unpin`]. If you want to use `next` with a /// [`!Unpin`](Unpin) stream, you'll first have to pin the stream. This can /// be done by boxing the stream using [`Box::pinned`] or /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils` /// crate. /// /// # Examples /// /// ``` /// #![feature(pin)] /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let mut stream = stream::iter(1..=3); /// /// assert_eq!(block_on(stream.next()), Some(1)); /// assert_eq!(block_on(stream.next()), Some(2)); /// assert_eq!(block_on(stream.next()), Some(3)); /// assert_eq!(block_on(stream.next()), None); /// ``` fn next(&mut self) -> Next<'_, Self> where Self: Sized + Unpin, { Next::new(self) } /// Converts this stream into a future of `(next_item, tail_of_stream)`. /// If the stream terminates, then the next item is [`None`]. /// /// The returned future can be used to compose streams and futures together /// by placing everything into the "world of futures". /// /// Note that because `into_future` moves the stream, the [`Stream`] type /// must be [`Unpin`]. If you want to use `into_future` with a /// [`!Unpin`](Unpin) stream, you'll first have to pin the stream. This can /// be done by boxing the stream using [`Box::pinned`] or /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils` /// crate. /// /// # Examples /// /// ``` /// #![feature(pin)] /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=3); /// /// let (item, stream) = block_on(stream.into_future()); /// assert_eq!(Some(1), item); /// /// let (item, stream) = block_on(stream.into_future()); /// assert_eq!(Some(2), item); /// ``` fn into_future(self) -> StreamFuture<Self> where Self: Sized + Unpin, { StreamFuture::new(self) } /// Maps this stream's items to a different type, returning a new stream of /// the resulting type. /// /// The provided closure is executed over all elements of this stream as /// they are made available. It is executed inline with calls to /// [`poll_next`](Stream::poll_next). /// /// Note that this function consumes the stream passed into it and returns a /// wrapped version of it, similar to the existing `map` methods in the /// standard library. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=3); /// let stream = stream.map(|x| x + 3); /// /// assert_eq!(vec![4, 5, 6], block_on(stream.collect::<Vec<_>>())); /// ``` fn map<T, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> T, Self: Sized { Map::new(self, f) } /// Filters the values produced by this stream according to the provided /// asynchronous predicate. /// /// As values of this stream are made available, the provided predicate `f` /// will be run against them. If the predicate returns a `Future` which /// resolves to `true`, then the stream will yield the value, but if the /// predicate returns a `Future` which resolves to `false`, then the value /// will be discarded and the next value will be produced. /// /// 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 /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10); /// let evens = stream.filter(|x| future::ready(x % 2 == 0)); /// /// assert_eq!(vec![2, 4, 6, 8, 10], block_on(evens.collect::<Vec<_>>())); /// ``` fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F> where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized, { Filter::new(self, f) } /// Filters 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. /// /// 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 /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10); /// let evens = stream.filter_map(|x| { /// let ret = if x % 2 == 0 { Some(x + 1) } else { None }; /// future::ready(ret) /// }); /// /// assert_eq!(vec![3, 5, 7, 9, 11], block_on(evens.collect::<Vec<_>>())); /// ``` fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F> where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = Option<T>>, Self: Sized, { FilterMap::new(self, f) } /// Computes from this stream's items new items of a different type using /// an asynchronous closure. /// /// The provided closure `f` will be called with an `Item` once a value is /// ready, it returns a future which will then be run to completion /// to produce the next value on this stream. /// /// Note that this function consumes the stream passed into it and returns a /// wrapped version of it. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=3); /// let stream = stream.then(|x| future::ready(x + 3)); /// /// assert_eq!(vec![4, 5, 6], block_on(stream.collect::<Vec<_>>())); /// ``` fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where F: FnMut(Self::Item) -> Fut, Fut: Future, Self: Sized { Then::new(self, f) } /// Collect all of the values of this stream into a vector, returning a /// future representing the result of that computation. /// /// The returned future will be resolved when the stream terminates. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. /// /// # Examples /// /// ``` /// use futures::channel::mpsc; /// use futures::executor::block_on; /// use futures::stream::StreamExt; /// use std::thread; /// /// let (mut tx, rx) = mpsc::unbounded(); /// /// thread::spawn(move || { /// for i in (1..=5) { /// tx.unbounded_send(i).unwrap(); /// } /// }); /// /// let output = block_on(rx.collect::<Vec<i32>>()); /// assert_eq!(output, vec![1, 2, 3, 4, 5]); /// ``` #[cfg(feature = "std")] fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C> where Self: Sized { Collect::new(self) } /// 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 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. /// /// # Examples /// /// ``` /// use futures::channel::mpsc; /// use futures::executor::block_on; /// use futures::stream::StreamExt; /// use std::thread; /// /// let (mut tx, rx) = mpsc::unbounded(); /// /// thread::spawn(move || { /// for i in (0..3).rev() { /// let n = i * 3; /// tx.unbounded_send(vec![n + 1, n + 2, n + 3]).unwrap(); /// } /// }); /// /// let result = block_on(rx.concat()); /// /// assert_eq!(result, vec![7, 8, 9, 4, 5, 6, 1, 2, 3]); /// ``` fn concat(self) -> Concat<Self> where Self: Sized, Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default, { Concat::new(self) } /// 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. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let number_stream = stream::iter(0..6); /// let sum = number_stream.fold(0, |acc, x| future::ready(acc + x)); /// assert_eq!(block_on(sum), 15); /// ``` fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> where F: FnMut(T, Self::Item) -> Fut, Fut: Future<Output = T>, Self: Sized { Fold::new(self, f, init) } /// Flattens a stream of streams into just one continuous stream. /// /// # Examples /// /// ``` /// use futures::channel::mpsc; /// use futures::executor::block_on; /// use futures::stream::StreamExt; /// use std::thread; /// /// let (tx1, rx1) = mpsc::unbounded(); /// let (tx2, rx2) = mpsc::unbounded(); /// let (tx3, rx3) = mpsc::unbounded(); /// /// thread::spawn(move || { /// tx1.unbounded_send(1).unwrap(); /// tx1.unbounded_send(2).unwrap(); /// }); /// thread::spawn(move || { /// tx2.unbounded_send(3).unwrap(); /// tx2.unbounded_send(4).unwrap(); /// }); /// thread::spawn(move || { /// tx3.unbounded_send(rx1).unwrap(); /// tx3.unbounded_send(rx2).unwrap(); /// }); /// /// let output = block_on(rx3.flatten().collect::<Vec<i32>>()); /// assert_eq!(output, vec![1, 2, 3, 4]); /// ``` fn flatten(self) -> Flatten<Self> where Self::Item: Stream, Self: Sized { Flatten::new(self) } /// Skip elements on this stream while the provided asynchronous predicate /// resolves to `true`. /// /// This function, like `Iterator::skip_while`, will skip elements on the /// stream until the predicate `f` resolves to `false`. Once one element /// returns false all future elements will be returned from the underlying /// stream. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10); /// /// let stream = stream.skip_while(|x| future::ready(*x <= 5)); /// /// assert_eq!(vec![6, 7, 8, 9, 10], block_on(stream.collect::<Vec<_>>())); /// ``` fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F> where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized { SkipWhile::new(self, f) } /// Take elements from this stream while the provided asynchronous predicate /// resolves to `true`. /// /// This function, like `Iterator::take_while`, will take elements from the /// stream until the predicate `f` resolves to `false`. Once one element /// returns false it will always return that the stream is done. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10); /// /// let stream = stream.take_while(|x| future::ready(*x <= 5)); /// /// assert_eq!(vec![1, 2, 3, 4, 5], block_on(stream.collect::<Vec<_>>())); /// ``` fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F> where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized { TakeWhile::new(self, f) } /// Runs this stream to completion, executing the provided asynchronous /// closure for each element on the stream. /// /// The closure provided 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` where the `Output` type is `()`; it is /// executed entirely for its side effects. /// /// To process each item in the stream and produce another stream instead /// of a single future, use `then` instead. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let mut x = 0; /// /// { /// let fut = stream::repeat(1).take(3).for_each(|item| { /// x += item; /// future::ready(()) /// }); /// block_on(fut); /// } /// /// assert_eq!(x, 3); /// ``` fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized { ForEach::new(self, f) } /// Runs this stream to completion, executing the provided asynchronous /// closure for each element on the stream concurrently as elements become /// available. /// /// This is similar to [`StreamExt::for_each`], but the futures /// produced by the closure are run concurrently (but not in parallel-- /// this combinator does not introduce any threads). /// /// The closure provided will be called for each item this stream produces, /// yielding a future. That future will then be executed to completion /// concurrently with the other futures produced by the closure. /// /// The first argument is an optional limit on the number of concurrent /// futures. If this limit is not `None`, no more than `limit` futures /// will be run concurrently. The `limit` argument is of type /// `Into<Option<usize>>`, and so can be provided as either `None`, /// `Some(10)`, or just `10`. Note: a limit of zero is interpreted as /// no limit at all, and will have the same result as passing in `None`. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. /// /// # Examples /// /// ``` /// #![feature(async_await, await_macro)] /// # futures::executor::block_on(async { /// use futures::channel::oneshot; /// use futures::stream::{self, StreamExt}; /// /// let (tx1, rx1) = oneshot::channel(); /// let (tx2, rx2) = oneshot::channel(); /// let (tx3, rx3) = oneshot::channel(); /// /// let fut = stream::iter(vec![rx1, rx2, rx3]).for_each_concurrent( /// /* limit */ 2, /// async move |rx| { /// await!(rx).unwrap(); /// } /// ); /// tx1.send(()).unwrap(); /// tx2.send(()).unwrap(); /// tx3.send(()).unwrap(); /// await!(fut); /// # }) /// ``` #[cfg(feature = "std")] fn for_each_concurrent<Fut, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> ForEachConcurrent<Self, Fut, F> where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized, { ForEachConcurrent::new(self, limit.into(), f) } /// Creates a new stream of at most `n` items of the underlying stream. /// /// Once `n` items have been yielded from this stream then it will always /// return that the stream is done. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10).take(3); /// /// assert_eq!(vec![1, 2, 3], block_on(stream.collect::<Vec<_>>())); /// ``` fn take(self, n: u64) -> Take<Self> where Self: Sized { Take::new(self, n) } /// Creates a new stream which skips `n` items of the underlying stream. /// /// Once `n` items have been skipped from this stream then it will always /// return the remaining items on this stream. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(1..=10).skip(5); /// /// assert_eq!(vec![6, 7, 8, 9, 10], block_on(stream.collect::<Vec<_>>())); /// ``` fn skip(self, n: u64) -> Skip<Self> where Self: Sized { Skip::new(self, n) } /// Fuse a stream such that [`poll_next`](Stream::poll_next) will never /// again be called once it has finished. /// /// Normally, once a stream has returned [`None`] from /// [`poll_next`](Stream::poll_next) any further calls could exhibit bad /// behavior such as block forever, panic, never return, etc. If it is known /// that [`poll_next`](Stream::poll_next) may be called after stream /// has already finished, then this method can be used to ensure that it has /// defined semantics. /// /// The [`poll_next`](Stream::poll_next) method of a `fuse`d stream /// is guaranteed to return [`None`] after the underlying stream has /// finished. /// /// # Examples /// /// ``` /// #![feature(futures_api)] /// use futures::executor::block_on_stream; /// use futures::stream::{self, StreamExt}; /// use futures::task::Poll; /// /// let mut x = 0; /// let stream = stream::poll_fn(|_| { /// x += 1; /// match x { /// 0..=2 => Poll::Ready(Some(x)), /// 3 => Poll::Ready(None), /// _ => panic!("should not happen") /// } /// }).fuse(); /// /// let mut iter = block_on_stream(stream); /// assert_eq!(Some(1), iter.next()); /// assert_eq!(Some(2), iter.next()); /// assert_eq!(None, iter.next()); /// assert_eq!(None, iter.next()); /// // ... /// ``` fn fuse(self) -> Fuse<Self> where Self: Sized { Fuse::new(self) } /// Borrows a stream, rather than consuming it. /// /// This is useful to allow applying stream adaptors while still retaining /// ownership of the original stream. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::future; /// use futures::stream::{self, StreamExt}; /// /// let mut stream = stream::iter(1..5); /// /// let sum = block_on(stream.by_ref() /// .take(2) /// .fold(0, |a, b| future::ready(a + b))); /// assert_eq!(sum, 3); /// /// // You can use the stream again /// let sum = block_on(stream.take(2).fold(0, |a, b| future::ready(a + b))); /// assert_eq!(sum, 7); /// ``` fn by_ref(&mut self) -> &mut Self where Self: Sized { self } /// Catches unwinding panics while polling the stream. /// /// Caught panic (if any) will be the last element of the resulting stream. /// /// In general, panics within a stream can propagate all the way out to the /// task level. This combinator makes it possible to halt unwinding within /// the stream itself. It's most commonly used within task executors. This /// method should not be used for error handling. /// /// Note that this method requires the `UnwindSafe` bound from the standard /// library. This isn't always applied automatically, and the standard /// library provides an `AssertUnwindSafe` wrapper type to apply it /// after-the fact. To assist using this method, the [`Stream`] trait is /// also implemented for `AssertUnwindSafe<St>` where `St` implements /// [`Stream`]. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream = stream::iter(vec![Some(10), None, Some(11)]); /// // Panic on second element /// let stream_panicking = stream.map(|o| o.unwrap()); /// // Collect all the results /// let stream = stream_panicking.catch_unwind(); /// /// let results: Vec<Result<i32, _>> = block_on(stream.collect()); /// match results[0] { /// Ok(10) => {} /// _ => panic!("unexpected result!"), /// } /// assert!(results[1].is_err()); /// assert_eq!(results.len(), 2); /// ``` #[cfg(feature = "std")] fn catch_unwind(self) -> CatchUnwind<Self> where Self: Sized + std::panic::UnwindSafe { CatchUnwind::new(self) } /// Wrap the stream in a Box, pinning it. #[cfg(feature = "std")] fn boxed(self) -> Pin<Box<Self>> where Self: Sized { Box::pinned(self) } /// An adaptor for creating a buffered list of pending futures. /// /// If this stream's item can be converted into a future, then this adaptor /// will buffer up to at most `n` futures and then return the outputs in the /// same order as the underlying stream. No more than `n` futures will be /// buffered at any point in time, and less than `n` may also be buffered /// depending on the state of each future. /// /// The returned stream will be a stream of each future's output. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. #[cfg(feature = "std")] fn buffered(self, n: usize) -> Buffered<Self> where Self::Item: Future, Self: Sized { Buffered::new(self, n) } /// An adaptor for creating a buffered list of pending futures (unordered). /// /// If this stream's item can be converted into a future, then this adaptor /// will buffer up to `n` futures and then return the outputs in the order /// in which they complete. No more than `n` futures will be buffered at /// any point in time, and less than `n` may also be buffered depending on /// the state of each future. /// /// The returned stream will be a stream of each future's output. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. /// /// # Examples /// /// ``` /// #![feature(async_await, await_macro)] /// # futures::executor::block_on(async { /// use futures::channel::oneshot; /// use futures::stream::{self, StreamExt}; /// /// let (send_one, recv_one) = oneshot::channel(); /// let (send_two, recv_two) = oneshot::channel(); /// /// let stream_of_futures = stream::iter(vec![recv_one, recv_two]); /// let mut buffered = stream_of_futures.buffer_unordered(10); /// /// send_two.send(2i32); /// assert_eq!(await!(buffered.next()), Some(Ok(2i32))); /// /// send_one.send(1i32); /// assert_eq!(await!(buffered.next()), Some(Ok(1i32))); /// /// assert_eq!(await!(buffered.next()), None); /// # }) /// ``` #[cfg(feature = "std")] fn buffer_unordered(self, n: usize) -> BufferUnordered<Self> where Self::Item: Future, Self: Sized { BufferUnordered::new(self, n) } /// An adapter for zipping two streams together. /// /// The zipped stream waits for both streams to produce an item, and then /// returns that pair. If either stream ends then the zipped stream will /// also end. /// /// # Examples /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let mut stream1 = stream::iter(1..=3); /// let mut stream2 = stream::iter(5..=10); /// /// let vec = block_on(stream1.zip(stream2) /// .collect::<Vec<_>>()); /// assert_eq!(vec![(1, 5), (2, 6), (3, 7)], vec); /// ``` /// fn zip<St>(self, other: St) -> Zip<Self, St> where St: Stream, Self: Sized, { Zip::new(self, other) } /// Adapter for chaining two stream. /// /// The resulting stream emits elements from the first stream, and when /// first stream reaches the end, emits the elements from the second stream. /// /// ``` /// use futures::executor::block_on; /// use futures::stream::{self, StreamExt}; /// /// let stream1 = stream::iter(vec![Ok(10), Err(false)]); /// let stream2 = stream::iter(vec![Err(true), Ok(20)]); /// /// let stream = stream1.chain(stream2); /// /// let result: Vec<_> = block_on(stream.collect()); /// assert_eq!(result, vec![ /// Ok(10), /// Err(false), /// Err(true), /// Ok(20), /// ]); /// ``` fn chain<St>(self, other: St) -> Chain<Self, St> where St: Stream<Item = Self::Item>, Self: Sized { Chain::new(self, other) } /// Creates a new stream which exposes a `peek` method. /// /// Calling `peek` returns a reference to the next item in the stream. fn peekable(self) -> Peekable<Self> where Self: Sized { Peekable::new(self) } /// An adaptor for chunking up items of the stream inside a vector. /// /// This combinator will attempt to pull items from this stream and buffer /// them into a local vector. At most `capacity` items will get buffered /// before they're yielded from the returned stream. /// /// Note that the vectors returned from this iterator may not always have /// `capacity` elements. If the underlying stream ended and only a partial /// vector was created, it'll be returned. Additionally if an error happens /// from the underlying stream then the currently buffered items will be /// yielded. /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. /// /// # Panics /// /// This method will panic of `capacity` is zero. #[cfg(feature = "std")] fn chunks(self, capacity: usize) -> Chunks<Self> where Self: Sized { Chunks::new(self, capacity) } /// This combinator will attempt to pull items from both streams. Each /// stream will be polled in a round-robin fashion, and whenever a stream is /// ready to yield an item that item is yielded. /// /// After one of the two input stream completes, the remaining one will be /// polled exclusively. The returned stream completes when both input /// streams have completed. /// /// Note that this method consumes both streams and returns a wrapped /// version of them. fn select<St>(self, other: St) -> Select<Self, St> where St: Stream<Item = Self::Item>, Self: Sized, { Select::new(self, other) } /// A future that completes after the given stream has been fully processed /// into the sink, including flushing. /// /// This future will drive the stream to keep producing items until it is /// exhausted, sending each item to the sink. It will complete once both the /// stream is exhausted and the sink has received and flushed all items. /// Note that the sink is **not** closed. /// /// On completion, the sink is returned. /// /// Note that this combinator is only usable with `Unpin` sinks. /// Sinks that are not `Unpin` will need to be pinned in order to be used /// with `forward`. fn forward<S>(self, sink: S) -> Forward<Self, S> where S: Sink + Unpin, Self: Stream<Item = Result<S::SinkItem, S::SinkError>> + Sized, { Forward::new(self, sink) } /// Splits this `Stream + Sink` object into separate `Stream` and `Sink` /// objects. /// /// This can be useful when you want to split ownership between tasks, or /// allow direct interaction between the two objects (e.g. via /// `Sink::send_all`). /// /// This method is only available when the `std` feature of this /// library is activated, and it is activated by default. #[cfg(feature = "std")] fn split(self) -> (SplitSink<Self>, SplitStream<Self>) where Self: Sink + Sized { split::split(self) } /// Do something with each item of this stream, afterwards passing it on. /// /// This is similar to the `Iterator::inspect` method in the standard /// library where it allows easily inspecting each value as it passes /// through the stream, for example to debug what's going on. fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item), Self: Sized, { Inspect::new(self, f) } /// Wrap this stream in an `Either` stream, making it the left-hand variant /// of that `Either`. /// /// This can be used in combination with the `right_stream` method to write `if` /// statements that evaluate to different streams in different branches. fn left_stream<B>(self) -> Either<Self, B> where B: Stream<Item = Self::Item>, Self: Sized { Either::Left(self) } /// Wrap this stream in an `Either` stream, making it the right-hand variant /// of that `Either`. /// /// This can be used in combination with the `left_stream` method to write `if` /// statements that evaluate to different streams in different branches. fn right_stream<B>(self) -> Either<B, Self> where B: Stream<Item = Self::Item>, Self: Sized { Either::Right(self) } /// A convenience method for calling [`Stream::poll_next`] on [`Unpin`] /// stream types. fn poll_next_unpin( &mut self, lw: &LocalWaker ) -> Poll<Option<Self::Item>> where Self: Unpin + Sized { Pin::new(self).poll_next(lw) } }