Struct futures_util::stream::Peekable[][src]

pub struct Peekable<St: Stream> { /* fields omitted */ }
Expand description

A Stream that implements a peek method.

The peek method can be used to retrieve a reference to the next Stream::Item if available. A subsequent call to poll will return the owned item.

Implementations

Acquires a reference to the underlying sink or stream that this combinator is pulling from.

Acquires a mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

Acquires a pinned mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

Consumes this combinator, returning the underlying sink or stream.

Note that this may discard intermediate state of this combinator, so care should be taken to avoid losing resources when this is called.

Produces a future which retrieves a reference to the next item in the stream, or None if the underlying stream terminates.

Peek retrieves a reference to the next item in the stream.

This method polls the underlying stream and return either a reference to the next item if the stream is ready or passes through any errors.

Produces a future which retrieves a mutable reference to the next item in the stream, or None if the underlying stream terminates.

Examples
use futures::stream::{self, StreamExt};
use futures::pin_mut;

let stream = stream::iter(vec![1, 2, 3]).peekable();
pin_mut!(stream);

assert_eq!(stream.as_mut().peek_mut().await, Some(&mut 1));
assert_eq!(stream.as_mut().next().await, Some(1));

// Peek into the stream and modify the value which will be returned next
if let Some(p) = stream.as_mut().peek_mut().await {
    if *p == 2 {
        *p = 5;
    }
}

assert_eq!(stream.collect::<Vec<_>>().await, vec![5, 3]);

Peek retrieves a mutable reference to the next item in the stream.

Creates a future which will consume and return the next value of this stream if a condition is true.

If func returns true for the next value of this stream, consume and return it. Otherwise, return None.

Examples

Consume a number if it’s equal to 0.

use futures::stream::{self, StreamExt};
use futures::pin_mut;

let stream = stream::iter(0..5).peekable();
pin_mut!(stream);
// The first item of the stream is 0; consume it.
assert_eq!(stream.as_mut().next_if(|&x| x == 0).await, Some(0));
// The next item returned is now 1, so `consume` will return `false`.
assert_eq!(stream.as_mut().next_if(|&x| x == 0).await, None);
// `next_if` saves the value of the next item if it was not equal to `expected`.
assert_eq!(stream.next().await, Some(1));

Consume any number less than 10.

use futures::stream::{self, StreamExt};
use futures::pin_mut;

let stream = stream::iter(1..20).peekable();
pin_mut!(stream);
// Consume all numbers less than 10
while stream.as_mut().next_if(|&x| x < 10).await.is_some() {}
// The next value returned will be 10
assert_eq!(stream.next().await, Some(10));

Creates a future which will consume and return the next item if it is equal to expected.

Example

Consume a number if it’s equal to 0.

use futures::stream::{self, StreamExt};
use futures::pin_mut;

let stream = stream::iter(0..5).peekable();
pin_mut!(stream);
// The first item of the stream is 0; consume it.
assert_eq!(stream.as_mut().next_if_eq(&0).await, Some(0));
// The next item returned is now 1, so `consume` will return `false`.
assert_eq!(stream.as_mut().next_if_eq(&0).await, None);
// `next_if_eq` saves the value of the next item if it was not equal to `expected`.
assert_eq!(stream.next().await, Some(1));

Trait Implementations

Formats the value using the given formatter. Read more

Returns true if the stream should no longer be polled.

The type of value produced by the sink when an error occurs.

Attempts to prepare the Sink to receive a value. Read more

Begin the process of sending a value to the sink. Each call to this function must be preceded by a successful call to poll_ready which returned Poll::Ready(Ok(())). Read more

Flush any remaining output from this sink. Read more

Flush any remaining output and close this sink, if necessary. Read more

Values yielded by the stream.

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted. Read more

Returns the bounds on the remaining length of the stream. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

Composes a function in front of the sink. Read more

Composes a function in front of the sink. Read more

Transforms the error returned by the sink.

Map this sink’s error to a different error type using the Into trait. Read more

Adds a fixed-size buffer to the current sink. Read more

Close the sink.

Fanout items to multiple sinks. Read more

Flush the sink, processing all pending items. Read more

A future that completes after the given item has been fully processed into the sink, including flushing. Read more

A future that completes after the given item has been received by the sink. Read more

A future that completes after the given stream has been fully processed into the sink, including flushing. Read more

Wrap this sink in an Either sink, making it the left-hand variant of that Either. Read more

Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more

A convenience method for calling Sink::poll_ready on Unpin sink types. Read more

A convenience method for calling Sink::start_send on Unpin sink types. Read more

A convenience method for calling Sink::poll_flush on Unpin sink types. Read more

A convenience method for calling Sink::poll_close on Unpin sink types. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

The type of successful values yielded by this future

The type of failures yielded by this future

Poll this TryStream as if it were a Stream. Read more