Enum futures_util::future::Either

pub enum Either<A, B> {
    Left(A),
    Right(B),
}

Combines two different futures, streams, or sinks having the same associated types into a single type.

This is useful when conditionally choosing between two distinct future types:

use futures::future::Either;

let cond = true;

let fut = if cond {
    Either::Left(async move { 12 })
} else {
    Either::Right(async move { 44 })
};

assert_eq!(fut.await, 12);

Variants

Left(A)

First branch of the type

Right(B)

Second branch of the type

Implementations

impl<A, B> Either<A, B>

pub fn as_pin_ref(self: Pin<&Self>) -> Either<Pin<&A>, Pin<&B>>

Convert Pin<&Either<A, B>> to Either<Pin<&A>, Pin<&B>>, pinned projections of the inner variants.

pub fn as_pin_mut(self: Pin<&mut Self>) -> Either<Pin<&mut A>, Pin<&mut B>>

Convert Pin<&mut Either<A, B>> to Either<Pin<&mut A>, Pin<&mut B>>, pinned projections of the inner variants.

impl<A, B, T> Either<(T, A), (T, B)>

pub fn factor_first(self) -> (T, Either<A, B>)

Factor out a homogeneous type from an either of pairs.

Here, the homogeneous type is the first element of the pairs.

impl<A, B, T> Either<(A, T), (B, T)>

pub fn factor_second(self) -> (Either<A, B>, T)

Factor out a homogeneous type from an either of pairs.

Here, the homogeneous type is the second element of the pairs.

impl<T> Either<T, T>

pub fn into_inner(self) -> T

Extract the value of an either over two equivalent types.

Trait Implementations

impl<A, B> AsyncBufRead for Either<A, B>

where A: AsyncBufRead, B: AsyncBufRead,

fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

Attempt to return the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

fn consume(self: Pin<&mut Self>, amt: usize)

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to poll_read.

impl<A, B> AsyncRead for Either<A, B>

where A: AsyncRead, B: AsyncRead,

fn poll_read( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut [u8] ) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into buf.

fn poll_read_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &mut [IoSliceMut<'_>] ) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into bufs using vectored IO operations.

impl<A, B> AsyncSeek for Either<A, B>

where A: AsyncSeek, B: AsyncSeek,

fn poll_seek( self: Pin<&mut Self>, cx: &mut Context<'_>, pos: SeekFrom ) -> Poll<Result<u64>>

Attempt to seek to an offset, in bytes, in a stream.

impl<A, B> AsyncWrite for Either<A, B>

where A: AsyncWrite, B: AsyncWrite,

fn poll_write( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8] ) -> Poll<Result<usize>>

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>] ) -> Poll<Result<usize>>

Attempt to write bytes from bufs into the object using vectored IO operations.

fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object.

impl<A: Clone, B: Clone> Clone for Either<A, B>

fn clone(&self) -> Either<A, B>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<A: Debug, B: Debug> Debug for Either<A, B>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<A, B> FusedFuture for Either<A, B>

where A: FusedFuture, B: FusedFuture<Output = A::Output>,

fn is_terminated(&self) -> bool

Returns true if the underlying future should no longer be polled.

impl<A, B> FusedStream for Either<A, B>

where A: FusedStream, B: FusedStream<Item = A::Item>,

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.

impl<A, B> Future for Either<A, B>

where A: Future, B: Future<Output = A::Output>,

type Output = <A as Future>::Output

The type of value produced on completion.

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

impl<A, B, Item> Sink<Item> for Either<A, B>

where A: Sink<Item>, B: Sink<Item, Error = A::Error>,

type Error = <A as Sink<Item>>::Error

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

fn poll_ready( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<(), Self::Error>>

Attempts to prepare the Sink to receive a value.

fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>

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(())).

fn poll_flush( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<(), Self::Error>>

Flush any remaining output from this sink.

fn poll_close( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<(), Self::Error>>

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

impl<A, B> Stream for Either<A, B>

where A: Stream, B: Stream<Item = A::Item>,

type Item = <A as Stream>::Item

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Self::Item>>

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.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.