Enum Either

pub enum Either<L, R> {
    Left(L),
    Right(R),
}

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

This type implements common asynchronous traits such as Future and those in Tokio.

Example

The following code will not work:

#[tokio::main]
async fn main() {
    let result = if some_condition() {
        some_async_function()
    } else {
        other_async_function() // <- Will print: "`if` and `else` have incompatible types"
    };

    println!("Result is {}", result.await);
}

When the output type is the same, we can wrap each future in Either to avoid the issue:

use tokio_util::either::Either;

#[tokio::main]
async fn main() {
    let result = if some_condition() {
        Either::Left(some_async_function())
    } else {
        Either::Right(other_async_function())
    };

    let value = result.await;
    println!("Result is {}", value);
}

Variants

Left(L)

Right(R)

Trait Implementations

impl<L, R> AsyncBufRead for Either<L, R>

where L: AsyncBufRead, R: AsyncBufRead,

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

Attempts 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<L, R> AsyncRead for Either<L, R>

where L: AsyncRead, R: AsyncRead,

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

Attempts to read from the AsyncRead into buf.

impl<L, R> AsyncSeek for Either<L, R>

where L: AsyncSeek, R: AsyncSeek,

fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> Result<()>

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

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

Waits for a seek operation to complete.

impl<L, R> AsyncWrite for Either<L, R>

where L: AsyncWrite, R: 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_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

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

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

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

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

Like poll_write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

Determines if this writer has an efficient poll_write_vectored implementation.

impl<L: Clone, R: Clone> Clone for Either<L, R>

fn clone(&self) -> Either<L, R>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<L: Debug, R: Debug> Debug for Either<L, R>

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

Formats the value using the given formatter.

impl<L, R, O> Future for Either<L, R>

where L: Future<Output = O>, R: Future<Output = O>,

type Output = O

The type of value produced on completion.

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

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

impl<L, R, Item, Error> Sink<Item> for Either<L, R>

where L: Sink<Item, Error = Error>, R: Sink<Item, Error = Error>,

type Error = 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<L, R> Stream for Either<L, R>

where L: Stream, R: Stream<Item = L::Item>,

type Item = <L 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.