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

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§

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Left(L)

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Right(R)

Trait Implementations§

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

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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. Read more
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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. Read more
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impl<L, R> AsyncRead for Either<L, R>where L: AsyncRead, R: AsyncRead,

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

Attempts to read from the AsyncRead into buf. Read more
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impl<L, R> AsyncSeek for Either<L, R>where L: AsyncSeek, R: AsyncSeek,

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

Attempts to seek to an offset, in bytes, in a stream. Read more
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fn poll_complete( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<u64>>

Waits for a seek operation to complete. Read more
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impl<L, R> AsyncWrite for Either<L, R>where L: AsyncWrite, R: AsyncWrite,

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

Attempt to write bytes from buf into the object. Read more
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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. Read more
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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. Read more
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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. Read more
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fn is_write_vectored(&self) -> bool

Determines if this writer has an efficient poll_write_vectored implementation. Read more
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impl<L: Clone, R: Clone> Clone for Either<L, R>

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

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<L: Debug, R: Debug> Debug for Either<L, R>

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

Formats the value using the given formatter. Read more
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impl<L, R, O> Future for Either<L, R>where L: Future<Output = O>, R: Future<Output = O>,

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type Output = O

The type of value produced on completion.
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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. Read more
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impl<L, R> Stream for Either<L, R>where L: Stream, R: Stream<Item = L::Item>,

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type Item = <L as Stream>::Item

Values yielded by the stream.
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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. Read more
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fn size_hint(&self) -> (usize, Option<usize>)

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

Auto Trait Implementations§

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impl<L, R> RefUnwindSafe for Either<L, R>where L: RefUnwindSafe, R: RefUnwindSafe,

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impl<L, R> Send for Either<L, R>where L: Send, R: Send,

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impl<L, R> Sync for Either<L, R>where L: Sync, R: Sync,

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impl<L, R> Unpin for Either<L, R>where L: Unpin, R: Unpin,

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impl<L, R> UnwindSafe for Either<L, R>where L: UnwindSafe, R: UnwindSafe,

Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<R> AsyncBufReadExt for Rwhere R: AsyncBufRead + ?Sized,

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fn read_until<'a>( &'a mut self, byte: u8, buf: &'a mut Vec<u8, Global> ) -> ReadUntil<'a, Self>where Self: Unpin,

Reads all bytes into buf until the delimiter byte or EOF is reached. Read more
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fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>where Self: Unpin,

Reads all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more
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fn split(self, byte: u8) -> Split<Self>where Self: Sized + Unpin,

Returns a stream of the contents of this reader split on the byte byte. Read more
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fn fill_buf(&mut self) -> FillBuf<'_, Self>where Self: Unpin,

Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty. Read more
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fn consume(&mut self, amt: usize)where Self: Unpin,

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read. Read more
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fn lines(self) -> Lines<Self>where Self: Sized,

Returns a stream over the lines of this reader. This method is the async equivalent to BufRead::lines. Read more
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impl<R> AsyncReadExt for Rwhere R: AsyncRead + ?Sized,

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fn chain<R>(self, next: R) -> Chain<Self, R>where Self: Sized, R: AsyncRead,

Creates a new AsyncRead instance that chains this stream with next. Read more
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fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>where Self: Unpin,

Pulls some bytes from this source into the specified buffer, returning how many bytes were read. Read more
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fn read_buf<B, 'a>(&'a mut self, buf: &'a mut B) -> ReadBuf<'a, Self, B>where Self: Sized + Unpin, B: BufMut,

Pulls some bytes from this source into the specified buffer, advancing the buffer’s internal cursor. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>where Self: Unpin,

Reads the exact number of bytes required to fill buf. Read more
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fn read_u8<'a>(&'a mut self) -> ReadU8<&'a mut Self>where Self: Unpin,

Reads an unsigned 8 bit integer from the underlying reader. Read more
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fn read_i8<'a>(&'a mut self) -> ReadI8<&'a mut Self>where Self: Unpin,

Reads a signed 8 bit integer from the underlying reader. Read more
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fn read_u16<'a>(&'a mut self) -> ReadU16<&'a mut Self>where Self: Unpin,

Reads an unsigned 16-bit integer in big-endian order from the underlying reader. Read more
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fn read_i16<'a>(&'a mut self) -> ReadI16<&'a mut Self>where Self: Unpin,

Reads a signed 16-bit integer in big-endian order from the underlying reader. Read more
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fn read_u32<'a>(&'a mut self) -> ReadU32<&'a mut Self>where Self: Unpin,

Reads an unsigned 32-bit integer in big-endian order from the underlying reader. Read more
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fn read_i32<'a>(&'a mut self) -> ReadI32<&'a mut Self>where Self: Unpin,

Reads a signed 32-bit integer in big-endian order from the underlying reader. Read more
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fn read_u64<'a>(&'a mut self) -> ReadU64<&'a mut Self>where Self: Unpin,

Reads an unsigned 64-bit integer in big-endian order from the underlying reader. Read more
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fn read_i64<'a>(&'a mut self) -> ReadI64<&'a mut Self>where Self: Unpin,

Reads an signed 64-bit integer in big-endian order from the underlying reader. Read more
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fn read_u128<'a>(&'a mut self) -> ReadU128<&'a mut Self>where Self: Unpin,

Reads an unsigned 128-bit integer in big-endian order from the underlying reader. Read more
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fn read_i128<'a>(&'a mut self) -> ReadI128<&'a mut Self>where Self: Unpin,

Reads an signed 128-bit integer in big-endian order from the underlying reader. Read more
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fn read_f32<'a>(&'a mut self) -> ReadF32<&'a mut Self>where Self: Unpin,

Reads an 32-bit floating point type in big-endian order from the underlying reader. Read more
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fn read_f64<'a>(&'a mut self) -> ReadF64<&'a mut Self>where Self: Unpin,

Reads an 64-bit floating point type in big-endian order from the underlying reader. Read more
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fn read_u16_le<'a>(&'a mut self) -> ReadU16Le<&'a mut Self>where Self: Unpin,

Reads an unsigned 16-bit integer in little-endian order from the underlying reader. Read more
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fn read_i16_le<'a>(&'a mut self) -> ReadI16Le<&'a mut Self>where Self: Unpin,

Reads a signed 16-bit integer in little-endian order from the underlying reader. Read more
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fn read_u32_le<'a>(&'a mut self) -> ReadU32Le<&'a mut Self>where Self: Unpin,

Reads an unsigned 32-bit integer in little-endian order from the underlying reader. Read more
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fn read_i32_le<'a>(&'a mut self) -> ReadI32Le<&'a mut Self>where Self: Unpin,

Reads a signed 32-bit integer in little-endian order from the underlying reader. Read more
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fn read_u64_le<'a>(&'a mut self) -> ReadU64Le<&'a mut Self>where Self: Unpin,

Reads an unsigned 64-bit integer in little-endian order from the underlying reader. Read more
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fn read_i64_le<'a>(&'a mut self) -> ReadI64Le<&'a mut Self>where Self: Unpin,

Reads an signed 64-bit integer in little-endian order from the underlying reader. Read more
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fn read_u128_le<'a>(&'a mut self) -> ReadU128Le<&'a mut Self>where Self: Unpin,

Reads an unsigned 128-bit integer in little-endian order from the underlying reader. Read more
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fn read_i128_le<'a>(&'a mut self) -> ReadI128Le<&'a mut Self>where Self: Unpin,

Reads an signed 128-bit integer in little-endian order from the underlying reader. Read more
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fn read_f32_le<'a>(&'a mut self) -> ReadF32Le<&'a mut Self>where Self: Unpin,

Reads an 32-bit floating point type in little-endian order from the underlying reader. Read more
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fn read_f64_le<'a>(&'a mut self) -> ReadF64Le<&'a mut Self>where Self: Unpin,

Reads an 64-bit floating point type in little-endian order from the underlying reader. Read more
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fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8, Global> ) -> ReadToEnd<'a, Self>where Self: Unpin,

Reads all bytes until EOF in this source, placing them into buf. Read more
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fn read_to_string<'a>( &'a mut self, dst: &'a mut String ) -> ReadToString<'a, Self>where Self: Unpin,

Reads all bytes until EOF in this source, appending them to buf. Read more
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fn take(self, limit: u64) -> Take<Self>where Self: Sized,

Creates an adaptor which reads at most limit bytes from it. Read more
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impl<S> AsyncSeekExt for Swhere S: AsyncSeek + ?Sized,

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fn seek(&mut self, pos: SeekFrom) -> Seek<'_, Self>where Self: Unpin,

Creates a future which will seek an IO object, and then yield the new position in the object and the object itself. Read more
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fn rewind(&mut self) -> Seek<'_, Self>where Self: Unpin,

Creates a future which will rewind to the beginning of the stream. Read more
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fn stream_position(&mut self) -> Seek<'_, Self>where Self: Unpin,

Creates a future which will return the current seek position from the start of the stream. Read more
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impl<W> AsyncWriteExt for Wwhere W: AsyncWrite + ?Sized,

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fn write<'a>(&'a mut self, src: &'a [u8]) -> Write<'a, Self>where Self: Unpin,

Writes a buffer into this writer, returning how many bytes were written. Read more
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fn write_vectored<'a, 'b>( &'a mut self, bufs: &'a [IoSlice<'b>] ) -> WriteVectored<'a, 'b, Self>where Self: Unpin,

Like write, except that it writes from a slice of buffers. Read more
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fn write_buf<B, 'a>(&'a mut self, src: &'a mut B) -> WriteBuf<'a, Self, B>where Self: Sized + Unpin, B: Buf,

Writes a buffer into this writer, advancing the buffer’s internal cursor. Read more
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fn write_all_buf<B, 'a>( &'a mut self, src: &'a mut B ) -> WriteAllBuf<'a, Self, B>where Self: Sized + Unpin, B: Buf,

Attempts to write an entire buffer into this writer. Read more
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fn write_all<'a>(&'a mut self, src: &'a [u8]) -> WriteAll<'a, Self>where Self: Unpin,

Attempts to write an entire buffer into this writer. Read more
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fn write_u8<'a>(&'a mut self, n: u8) -> WriteU8<&'a mut Self>where Self: Unpin,

Writes an unsigned 8-bit integer to the underlying writer. Read more
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fn write_i8<'a>(&'a mut self, n: i8) -> WriteI8<&'a mut Self>where Self: Unpin,

Writes a signed 8-bit integer to the underlying writer. Read more
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fn write_u16<'a>(&'a mut self, n: u16) -> WriteU16<&'a mut Self>where Self: Unpin,

Writes an unsigned 16-bit integer in big-endian order to the underlying writer. Read more
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fn write_i16<'a>(&'a mut self, n: i16) -> WriteI16<&'a mut Self>where Self: Unpin,

Writes a signed 16-bit integer in big-endian order to the underlying writer. Read more
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fn write_u32<'a>(&'a mut self, n: u32) -> WriteU32<&'a mut Self>where Self: Unpin,

Writes an unsigned 32-bit integer in big-endian order to the underlying writer. Read more
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fn write_i32<'a>(&'a mut self, n: i32) -> WriteI32<&'a mut Self>where Self: Unpin,

Writes a signed 32-bit integer in big-endian order to the underlying writer. Read more
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fn write_u64<'a>(&'a mut self, n: u64) -> WriteU64<&'a mut Self>where Self: Unpin,

Writes an unsigned 64-bit integer in big-endian order to the underlying writer. Read more
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fn write_i64<'a>(&'a mut self, n: i64) -> WriteI64<&'a mut Self>where Self: Unpin,

Writes an signed 64-bit integer in big-endian order to the underlying writer. Read more
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fn write_u128<'a>(&'a mut self, n: u128) -> WriteU128<&'a mut Self>where Self: Unpin,

Writes an unsigned 128-bit integer in big-endian order to the underlying writer. Read more
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fn write_i128<'a>(&'a mut self, n: i128) -> WriteI128<&'a mut Self>where Self: Unpin,

Writes an signed 128-bit integer in big-endian order to the underlying writer. Read more
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fn write_f32<'a>(&'a mut self, n: f32) -> WriteF32<&'a mut Self>where Self: Unpin,

Writes an 32-bit floating point type in big-endian order to the underlying writer. Read more
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fn write_f64<'a>(&'a mut self, n: f64) -> WriteF64<&'a mut Self>where Self: Unpin,

Writes an 64-bit floating point type in big-endian order to the underlying writer. Read more
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fn write_u16_le<'a>(&'a mut self, n: u16) -> WriteU16Le<&'a mut Self>where Self: Unpin,

Writes an unsigned 16-bit integer in little-endian order to the underlying writer. Read more
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fn write_i16_le<'a>(&'a mut self, n: i16) -> WriteI16Le<&'a mut Self>where Self: Unpin,

Writes a signed 16-bit integer in little-endian order to the underlying writer. Read more
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fn write_u32_le<'a>(&'a mut self, n: u32) -> WriteU32Le<&'a mut Self>where Self: Unpin,

Writes an unsigned 32-bit integer in little-endian order to the underlying writer. Read more
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fn write_i32_le<'a>(&'a mut self, n: i32) -> WriteI32Le<&'a mut Self>where Self: Unpin,

Writes a signed 32-bit integer in little-endian order to the underlying writer. Read more
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fn write_u64_le<'a>(&'a mut self, n: u64) -> WriteU64Le<&'a mut Self>where Self: Unpin,

Writes an unsigned 64-bit integer in little-endian order to the underlying writer. Read more
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fn write_i64_le<'a>(&'a mut self, n: i64) -> WriteI64Le<&'a mut Self>where Self: Unpin,

Writes an signed 64-bit integer in little-endian order to the underlying writer. Read more
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fn write_u128_le<'a>(&'a mut self, n: u128) -> WriteU128Le<&'a mut Self>where Self: Unpin,

Writes an unsigned 128-bit integer in little-endian order to the underlying writer. Read more
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fn write_i128_le<'a>(&'a mut self, n: i128) -> WriteI128Le<&'a mut Self>where Self: Unpin,

Writes an signed 128-bit integer in little-endian order to the underlying writer. Read more
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fn write_f32_le<'a>(&'a mut self, n: f32) -> WriteF32Le<&'a mut Self>where Self: Unpin,

Writes an 32-bit floating point type in little-endian order to the underlying writer. Read more
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fn write_f64_le<'a>(&'a mut self, n: f64) -> WriteF64Le<&'a mut Self>where Self: Unpin,

Writes an 64-bit floating point type in little-endian order to the underlying writer. Read more
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fn flush(&mut self) -> Flush<'_, Self>where Self: Unpin,

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
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fn shutdown(&mut self) -> Shutdown<'_, Self>where Self: Unpin,

Shuts down the output stream, ensuring that the value can be dropped cleanly. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for Twhere U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<F> IntoFuture for Fwhere F: Future,

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type Output = <F as Future>::Output

The output that the future will produce on completion.
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type IntoFuture = F

Which kind of future are we turning this into?
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fn into_future(self) -> <F as IntoFuture>::IntoFuture

Creates a future from a value. Read more
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impl<T> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<F, T, E> TryFuture for Fwhere F: Future<Output = Result<T, E>> + ?Sized,

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type Ok = T

The type of successful values yielded by this future
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type Error = E

The type of failures yielded by this future
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fn try_poll( self: Pin<&mut F>, cx: &mut Context<'_> ) -> Poll<<F as Future>::Output>

Poll this TryFuture as if it were a Future. Read more
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<S, T, E> TryStream for Swhere S: Stream<Item = Result<T, E>> + ?Sized,

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type Ok = T

The type of successful values yielded by this future
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type Error = E

The type of failures yielded by this future
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fn try_poll_next( self: Pin<&mut S>, cx: &mut Context<'_> ) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

Poll this TryStream as if it were a Stream. Read more
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more