futures_util/stream/mod.rs
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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 futures_core::{IntoFuture, Stream};
use futures_sink::Sink;
use super::future::Either;
mod iter_ok;
pub use self::iter_ok::{iter_ok, IterOk};
mod iter_result;
pub use self::iter_result::{iter_result, IterResult};
mod repeat;
pub use self::repeat::{repeat, Repeat};
mod and_then;
mod chain;
mod concat;
mod empty;
mod filter;
mod filter_map;
mod flatten;
mod fold;
mod for_each;
mod err_into;
mod fuse;
mod future;
mod inspect;
mod inspect_err;
mod map;
mod map_err;
mod once;
mod or_else;
mod peek;
mod poll_fn;
mod select;
mod skip;
mod skip_while;
mod take;
mod take_while;
mod then;
mod unfold;
mod zip;
mod forward;
mod recover;
pub use self::and_then::AndThen;
pub use self::chain::Chain;
pub use self::concat::Concat;
pub use self::empty::{Empty, empty};
pub use self::filter::Filter;
pub use self::filter_map::FilterMap;
pub use self::flatten::Flatten;
pub use self::fold::Fold;
pub use self::for_each::ForEach;
pub use self::err_into::ErrInto;
pub use self::fuse::Fuse;
pub use self::future::StreamFuture;
pub use self::inspect::Inspect;
pub use self::inspect_err::InspectErr;
pub use self::map::Map;
pub use self::map_err::MapErr;
pub use self::once::{Once, once};
pub use self::or_else::OrElse;
pub use self::peek::Peekable;
pub use self::poll_fn::{poll_fn, PollFn};
pub use self::select::Select;
pub use self::skip::Skip;
pub use self::skip_while::SkipWhile;
pub use self::take::Take;
pub use self::take_while::TakeWhile;
pub use self::then::Then;
pub use self::unfold::{Unfold, unfold};
pub use self::zip::Zip;
pub use self::forward::Forward;
pub use self::recover::Recover;
if_std! {
use std;
use std::iter::Extend;
mod buffered;
mod buffer_unordered;
mod catch_unwind;
mod chunks;
mod collect;
mod for_each_concurrent;
mod select_all;
mod split;
mod futures_unordered;
mod futures_ordered;
pub use self::buffered::Buffered;
pub use self::buffer_unordered::BufferUnordered;
pub use self::catch_unwind::CatchUnwind;
pub use self::chunks::Chunks;
pub use self::collect::Collect;
pub use self::select_all::{select_all, SelectAll};
pub use self::split::{SplitStream, SplitSink, ReuniteError};
pub use self::for_each_concurrent::ForEachConcurrent;
pub use self::futures_unordered::{futures_unordered, FuturesUnordered};
pub use self::futures_ordered::{futures_ordered, FuturesOrdered};
}
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 {
/// Converts this stream into a `Future`.
///
/// A stream can be viewed as a future which will resolve to a pair containing
/// the next element of the stream plus the remaining stream. If the stream
/// terminates, then the next element is `None` and the remaining stream is
/// still passed back, to allow reclamation of its resources.
///
/// The returned future can be used to compose streams and futures together by
/// placing everything into the "world of futures".
fn next(self) -> StreamFuture<Self>
where Self: Sized
{
future::new(self)
}
/// Converts a stream of type `T` to a stream of type `U`.
///
/// The provided closure is executed over all elements of this stream as
/// they are made available, and the callback will be executed inline with
/// calls to `poll`.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it, similar to the existing `map` methods in the
/// standard library.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
/// let rx = rx.map(|x| x + 3);
/// # }
/// ```
fn map<U, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> U,
Self: Sized
{
map::new(self, f)
}
/// Converts a stream of error type `T` to a stream of error type `U`.
///
/// The provided closure is executed over all errors of this stream as
/// they are made available, and the callback will be executed inline with
/// calls to `poll`.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it, similar to the existing `map_err` methods in the
/// standard library.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
/// let rx = rx.map_err(|_| 3);
/// # }
/// ```
fn map_err<U, F>(self, f: F) -> MapErr<Self, F>
where F: FnMut(Self::Error) -> U,
Self: Sized
{
map_err::new(self, f)
}
/// Filters the values produced by this stream according to the provided
/// predicate.
///
/// As values of this stream are made available, the provided predicate 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.
///
/// All errors are passed through without filtering in this combinator.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it, similar to the existing `filter` methods in the
/// standard library.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
/// let evens = rx.filter(|x| Ok(x % 2 == 0));
/// # }
/// ```
fn filter<R, P>(self, pred: P) -> Filter<Self, R, P>
where P: FnMut(&Self::Item) -> R,
R: IntoFuture<Item=bool, Error=Self::Error>,
Self: Sized,
{
filter::new(self, pred)
}
/// Filters the values produced by this stream while simultaneously mapping
/// them to a different type.
///
/// As values of this stream are made available, the provided function will
/// be run on them. If the predicate returns `Some(e)` then the stream will
/// yield the value `e`, but if the predicate returns `None` then the next
/// value will be produced.
///
/// All errors are passed through without filtering in this combinator.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it, similar to the existing `filter_map` methods in the
/// standard library.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
/// let evens_plus_one = rx.filter_map(|x| {
/// Ok(
/// if x % 0 == 2 {
/// Some(x + 1)
/// } else {
/// None
/// }
/// )
/// });
/// # }
/// ```
fn filter_map<R, B, F>(self, f: F) -> FilterMap<Self, R, F>
where F: FnMut(Self::Item) -> R,
R: IntoFuture<Item=Option<B>, Error=Self::Error>,
Self: Sized,
{
filter_map::new(self, f)
}
/// Chain on a computation for when a value is ready, passing the resulting
/// item to the provided closure `f`.
///
/// This function can be used to ensure a computation runs regardless of
/// the next value on the stream. The closure provided will be yielded a
/// `Result` once a value is ready, and the returned future will then be run
/// to completion to produce the next value on this stream.
///
/// The returned value of the closure must implement the `IntoFuture` trait
/// and can represent some more work to be done before the composed stream
/// is finished. Note that the `Result` type implements the `IntoFuture`
/// trait so it is possible to simply alter the `Result` yielded to the
/// closure and return it.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
///
/// let rx = rx.then(|result| {
/// match result {
/// Ok(e) => Ok(e + 3),
/// Err(_) => Err(4),
/// }
/// });
/// # }
/// ```
fn then<U, F>(self, f: F) -> Then<Self, U, F>
where F: FnMut(Result<Self::Item, Self::Error>) -> U,
U: IntoFuture,
Self: Sized
{
then::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 `IntoFuture` trait
/// and can represent some more work to be done before the composed stream
/// is finished. Note that the `Result` type implements the `IntoFuture`
/// trait so it is possible to simply alter the `Result` yielded to the
/// closure and return it.
///
/// 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 `for_each` instead.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// use futures::prelude::*;
/// use futures_channel::mpsc;
///
/// # fn main() {
/// let (_tx, rx) = mpsc::channel::<i32>(1);
///
/// let rx = rx.and_then(|result| {
/// if result % 2 == 0 {
/// Ok(Some(result))
/// } else {
/// Ok(None)
/// }
/// });
/// # }
/// ```
fn and_then<U, F>(self, f: F) -> AndThen<Self, U, F>
where F: FnMut(Self::Item) -> U,
U: IntoFuture<Error = Self::Error>,
Self: Sized
{
and_then::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 `IntoFuture` trait
/// and can represent some more work to be done before the composed stream
/// is finished. Note that the `Result` type implements the `IntoFuture`
/// trait so it is possible to simply alter the `Result` yielded to the
/// closure and return it.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it.
fn or_else<U, F>(self, f: F) -> OrElse<Self, U, F>
where F: FnMut(Self::Error) -> U,
U: IntoFuture<Item = Self::Item>,
Self: Sized
{
or_else::new(self, f)
}
/// Collect all of the values of this stream into a vector, returning a
/// future representing the result of that computation.
///
/// This combinator will collect all successful results of this stream and
/// collect them into a `Vec<Self::Item>`. If an error happens then all
/// collected elements will be dropped and the error will be returned.
///
/// The returned future will be resolved whenever an error happens or when
/// the stream returns `Ok(None)`.
///
/// This method is only available when the `std` feature of this
/// library is activated, and it is activated by default.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// # extern crate futures_channel;
/// use std::thread;
///
/// use futures::prelude::*;
/// use futures_channel::mpsc;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let (mut tx, rx) = mpsc::unbounded();
///
/// thread::spawn(move || {
/// for i in (0..5).rev() {
/// tx.unbounded_send(i + 1).unwrap();
/// }
/// });
///
/// let result = block_on(rx.collect());
/// assert_eq!(result, Ok(vec![5, 4, 3, 2, 1]));
/// # }
/// ```
#[cfg(feature = "std")]
fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C>
where Self: Sized
{
collect::new(self)
}
/// Concatenate all results 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 successful results of the stream. If the stream is
/// empty, the default value will be returned. If an error occurs,
/// all the results will be dropped and the error will be returned.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// # extern crate futures_channel;
/// use std::thread;
///
/// use futures::prelude::*;
/// use futures_channel::mpsc;
/// use futures_executor::block_on;
///
/// # fn main() {
/// 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, Ok(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 computation over a stream, collecting all the
/// values into one final result.
///
/// This combinator will collect all successful results of 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.
///
/// If an error happens then collected state will be dropped and the error
/// will be returned.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::stream;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let number_stream = stream::iter_ok::<_, ()>(0..6);
/// let sum = number_stream.fold(0, |acc, x| future::ok(acc + x));
/// assert_eq!(block_on(sum), Ok(15));
/// # }
/// ```
fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F>
where F: FnMut(T, Self::Item) -> Fut,
Fut: IntoFuture<Item = T, Error = Self::Error>,
Self: Sized
{
fold::new(self, f, init)
}
/// 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.
///
/// ```
/// # extern crate futures;
/// # extern crate futures_channel;
/// # extern crate futures_executor;
/// use std::thread;
///
/// use futures::prelude::*;
/// use futures_channel::mpsc;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let (tx1, rx1) = mpsc::unbounded::<i32>();
/// let (tx2, rx2) = mpsc::unbounded::<i32>();
/// 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 result = block_on(rx3.flatten().collect());
/// assert_eq!(result, Ok(vec![1, 2, 3, 4]));
/// # }
/// ```
fn flatten(self) -> Flatten<Self>
where Self::Item: Stream<Error = Self::Error>,
Self: Sized
{
flatten::new(self)
}
/// Skip elements on this stream while the predicate provided resolves to
/// `true`.
///
/// This function, like `Iterator::skip_while`, will skip elements on the
/// stream until the `predicate` resolves to `false`. Once one element
/// returns false all future elements will be returned from the underlying
/// stream.
fn skip_while<R, P>(self, pred: P) -> SkipWhile<Self, R, P>
where P: FnMut(&Self::Item) -> R,
R: IntoFuture<Item=bool, Error=Self::Error>,
Self: Sized
{
skip_while::new(self, pred)
}
/// Take elements from this stream while the predicate provided resolves to
/// `true`.
///
/// This function, like `Iterator::take_while`, will take elements from the
/// stream until the `predicate` resolves to `false`. Once one element
/// returns false it will always return that the stream is done.
fn take_while<R, P>(self, pred: P) -> TakeWhile<Self, R, P>
where P: FnMut(&Self::Item) -> R,
R: IntoFuture<Item=bool, Error=Self::Error>,
Self: Sized
{
take_while::new(self, pred)
}
/// Runs this stream to completion, executing the provided closure for each
/// element on the stream.
///
/// The closure provided will be called for each item this stream resolves
/// to successfully, producing 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 `Item` type is the completed
/// stream, and errors are otherwise threaded through. Any error on the
/// stream or in the provided future will cause iteration to be halted
/// immediately and the future will resolve to that error.
///
/// To process each item in the stream and produce another stream instead
/// of a single future, use `and_then` instead.
fn for_each<U, F>(self, f: F) -> ForEach<Self, U, F>
where F: FnMut(Self::Item) -> U,
U: IntoFuture<Item=(), Error = Self::Error>,
Self: Sized
{
for_each::new(self, f)
}
/// Runs this stream to completion, executing the provided closure for each
/// element on the stream. This is similar to `for_each` but may begin
/// processing an element while previous elements are still being processed.
///
/// When this stream successfully resolves to an item, the closure will be
/// called to produce a future. That future will then be added to
/// the set of futures to resolve.
///
/// The returned value is a `Future` where the `Item` type is the completed
/// stream, and errors are otherwise threaded through. Any error on the
/// stream or in the provided future will cause iteration to be halted
/// immediately and the future will resolve to that error.
///
/// To process each item in the stream and produce another stream instead
/// of a single future, use `and_then` instead.
#[cfg(feature = "std")]
fn for_each_concurrent<U, F>(self, f: F) -> ForEachConcurrent<Self, U, F>
where F: FnMut(Self::Item) -> U,
U: IntoFuture<Item=(), Error = Self::Error>,
Self: Sized
{
for_each_concurrent::new(self, f)
}
/// Map this stream's error to a different type using the `Into` trait.
///
/// This function does for streams what `try!` does for `Result`,
/// by letting the compiler infer the type of the resulting error.
/// Just as `map_err` above, this is useful for example to ensure
/// that streams have the same error type when used with
/// combinators.
///
/// Note that this function consumes the receiving stream and returns a
/// wrapped version of it.
fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized,
Self::Error: Into<E>,
{
err_into::new(self)
}
/// Creates a new stream of at most `amt` items of the underlying stream.
///
/// Once `amt` items have been yielded from this stream then it will always
/// return that the stream is done.
///
/// # Errors
///
/// Any errors yielded from underlying stream, before the desired amount of
/// items is reached, are passed through and do not affect the total number
/// of items taken.
fn take(self, amt: u64) -> Take<Self>
where Self: Sized
{
take::new(self, amt)
}
/// Creates a new stream which skips `amt` items of the underlying stream.
///
/// Once `amt` items have been skipped from this stream then it will always
/// return the remaining items on this stream.
///
/// # Errors
///
/// All errors yielded from underlying stream are passed through and do not
/// affect the total number of items skipped.
fn skip(self, amt: u64) -> Skip<Self>
where Self: Sized
{
skip::new(self, amt)
}
/// Fuse a stream such that `poll` will never again be called once it has
/// finished.
///
/// Currently once a stream has returned `None` from `poll` any further
/// calls could exhibit bad behavior such as block forever, panic, never
/// return, etc. If it is known that `poll` may be called after stream has
/// already finished, then this method can be used to ensure that it has
/// defined semantics.
///
/// Once a stream has been `fuse`d and it finishes, then it will forever
/// return `None` from `poll`. This, unlike for the traits `poll` method,
/// is guaranteed.
///
/// Also note that as soon as this stream returns `None` it will be dropped
/// to reclaim resources associated with it.
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.
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::stream;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let mut stream = stream::iter_ok::<_, ()>(1..5);
///
/// let sum = block_on(stream.by_ref().take(2).fold(0, |a, b| future::ok(a + b)));
/// assert_eq!(sum, Ok(3));
///
/// // You can use the stream again
/// let sum = block_on(stream.take(2).fold(0, |a, b| future::ok(a + b)));
/// assert_eq!(sum, Ok(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<S>` where `S` implements `Stream`.
///
/// This method is only available when the `std` feature of this
/// library is activated, and it is activated by default.
///
/// # Examples
///
/// ```rust
/// # extern crate futures;
/// # extern crate futures_executor;
///
/// use futures::prelude::*;
/// use futures::stream;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let stream = stream::iter_ok::<_, bool>(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().then(|r| Ok::<_, ()>(r));
///
/// let results: Vec<_> = block_on(stream.collect()).unwrap();
/// match results[0] {
/// Ok(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
{
catch_unwind::new(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 `amt` futures and then return results in the
/// same order as the underlying stream. No more than `amt` futures will be
/// buffered at any point in time, and less than `amt` may also be buffered
/// depending on the state of each future.
///
/// The returned stream will be a stream of each future's result, with
/// errors passed through whenever they occur.
///
/// 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, amt: usize) -> Buffered<Self>
where Self::Item: IntoFuture<Error = <Self as Stream>::Error>,
Self: Sized
{
buffered::new(self, amt)
}
/// 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 `amt` futures and then return results in the order
/// in which they complete. No more than `amt` futures will be buffered at
/// any point in time, and less than `amt` may also be buffered depending on
/// the state of each future.
///
/// The returned stream will be a stream of each future's result, with
/// errors passed through whenever they occur.
///
/// This method is only available when the `std` feature of this
/// library is activated, and it is activated by default.
#[cfg(feature = "std")]
fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self>
where Self::Item: IntoFuture<Error = <Self as Stream>::Error>,
Self: Sized
{
buffer_unordered::new(self, amt)
}
/// An adapter for zipping two streams together.
///
/// The zipped stream waits for both streams to produce an item, and then
/// returns that pair. If an error happens, then that error will be returned
/// immediately. If either stream ends then the zipped stream will also end.
fn zip<S>(self, other: S) -> Zip<Self, S>
where S: Stream<Error = Self::Error>,
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.
///
/// ```rust
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::stream;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let stream1 = stream::iter_result(vec![Ok(10), Err(false)]);
/// let stream2 = stream::iter_result(vec![Err(true), Ok(20)]);
///
/// let stream = stream1.chain(stream2)
/// .then(|result| Ok::<_, ()>(result));
///
/// let result: Vec<_> = block_on(stream.collect()).unwrap();
/// assert_eq!(result, vec![
/// Ok(10),
/// Err(false),
/// Err(true),
/// Ok(20),
/// ]);
/// # }
/// ```
fn chain<S>(self, other: S) -> Chain<Self, S>
where S: Stream<Item = Self::Item, Error = Self::Error>,
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
{
peek::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.
///
/// Errors are passed through the stream unbuffered.
///
/// 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)
}
/// Creates a stream that selects the next element from either this stream
/// or the provided one, whichever is ready first.
///
/// 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.
///
/// Error are passed through from either stream.
fn select<S>(self, other: S) -> Select<Self, S>
where S: Stream<Item = Self::Item, Error = Self::Error>,
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.
///
/// Doing `stream.forward(sink)` is roughly equivalent to
/// `sink.send_all(stream)`. The returned future will exhaust all items from
/// `self`, sending them all to `sink`.
///
/// On completion, the pair `(stream, sink)` is returned.
fn forward<S>(self, sink: S) -> Forward<Self, S>
where S: Sink<SinkItem = Self::Item>,
Self::Error: From<S::SinkError>,
Self: 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)
}
/// Do something with the error of this stream, afterwards passing it on.
///
/// This is similar to the `Stream::inspect` method where it allows
/// easily inspecting the error 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,
{
inspect_err::new(self, f)
}
/// Handle errors generated by this stream by converting them into
/// `Option<Self::Item>`, such that a `None` value terminates the stream.
///
/// Because it can never produce an error, the returned `Recover` stream can
/// conform to any specific `Error` type, including `Never`.
fn recover<E, F>(self, f: F) -> Recover<Self, E, F>
where F: FnMut(Self::Error) -> Option<Self::Item>,
Self: Sized,
{
recover::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` method to write `if`
/// statements that evaluate to different streams in different branches.
#[deprecated(note = "use `left_stream` instead")]
fn left<B>(self) -> Either<Self, B>
where B: Stream<Item = Self::Item, Error = Self::Error>,
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` method to write `if`
/// statements that evaluate to different streams in different branches.
#[deprecated(note = "use `right_stream` instead")]
fn right<B>(self) -> Either<B, Self>
where B: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized
{
Either::Right(self)
}
/// 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, Error = Self::Error>,
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, Error = Self::Error>,
Self: Sized
{
Either::Right(self)
}
}