Struct async_std::io::Cursor

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pub struct Cursor<T> { /* private fields */ }
Expand description

A Cursor wraps an in-memory buffer and provides it with a Seek implementation.

Cursors are used with in-memory buffers, anything implementing AsRef<[u8]>, to allow them to implement Read and/or Write, allowing these buffers to be used anywhere you might use a reader or writer that does actual I/O.

The standard library implements some I/O traits on various types which are commonly used as a buffer, like Cursor<Vec<u8>> and Cursor<&[u8]>.

Implementations§

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impl<T> Cursor<T>

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pub fn new(inner: T) -> Cursor<T>

Creates a new cursor wrapping the provided underlying in-memory buffer.

Cursor initial position is 0 even if underlying buffer (e.g., Vec) is not empty. So writing to cursor starts with overwriting Vec content, not with appending to it.

Examples
use async_std::io::Cursor;

let buff = Cursor::new(Vec::new());
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pub fn into_inner(self) -> T

Consumes this cursor, returning the underlying value.

Examples
use async_std::io::Cursor;

let buff = Cursor::new(Vec::new());

let vec = buff.into_inner();
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pub fn get_ref(&self) -> &T

Gets a reference to the underlying value in this cursor.

Examples
use async_std::io::Cursor;

let buff = Cursor::new(Vec::new());

let reference = buff.get_ref();
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pub fn get_mut(&mut self) -> &mut T

Gets a mutable reference to the underlying value in this cursor.

Care should be taken to avoid modifying the internal I/O state of the underlying value as it may corrupt this cursor’s position.

Examples
use async_std::io::Cursor;

let mut buff = Cursor::new(Vec::new());

let reference = buff.get_mut();
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pub fn position(&self) -> u64

Returns the current position of this cursor.

Examples
use async_std::io::Cursor;
use async_std::io::prelude::*;
use async_std::io::SeekFrom;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.seek(SeekFrom::Current(2)).await?;
assert_eq!(buff.position(), 2);

buff.seek(SeekFrom::Current(-1)).await?;
assert_eq!(buff.position(), 1);
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pub fn set_position(&mut self, pos: u64)

Sets the position of this cursor.

Examples
use async_std::io::Cursor;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.set_position(2);
assert_eq!(buff.position(), 2);

buff.set_position(4);
assert_eq!(buff.position(), 4);

Trait Implementations§

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impl<T> AsyncBufRead for Cursor<T>
where T: AsRef<[u8]> + Unpin,

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fn poll_fill_buf( self: Pin<&mut Self>, _: &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. 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<T> AsyncRead for Cursor<T>
where T: AsRef<[u8]> + Unpin,

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

Attempt to read from the AsyncRead into buf. Read more
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fn poll_read_vectored( self: Pin<&mut Self>, _: &mut Context<'_>, bufs: &mut [IoSliceMut<'_>] ) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into bufs using vectored IO operations. Read more
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impl<T> AsyncSeek for Cursor<T>
where T: AsRef<[u8]> + Unpin,

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

Attempt to seek to an offset, in bytes, in a stream. Read more
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impl AsyncWrite for Cursor<&mut [u8]>

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

Attempt to write bytes from buf into the object. Read more
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fn poll_write_vectored( self: Pin<&mut Self>, _: &mut Context<'_>, bufs: &[IoSlice<'_>] ) -> Poll<Result<usize>>

Attempt to write bytes from bufs into the object using vectored IO operations. Read more
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fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Attempt to flush the object, ensuring that any buffered data reach their destination. Read more
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fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object. Read more
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impl AsyncWrite for Cursor<&mut Vec<u8>>

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

Attempt to write bytes from buf into the object. Read more
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fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object. Read more
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fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Attempt to flush the object, ensuring that any buffered data reach their destination. Read more
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fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>] ) -> Poll<Result<usize, Error>>

Attempt to write bytes from bufs into the object using vectored IO operations. Read more
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impl AsyncWrite for Cursor<Vec<u8>>

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

Attempt to write bytes from buf into the object. Read more
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fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object. Read more
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fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Attempt to flush the object, ensuring that any buffered data reach their destination. Read more
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fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>] ) -> Poll<Result<usize, Error>>

Attempt to write bytes from bufs into the object using vectored IO operations. Read more
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impl<T: Clone> Clone for Cursor<T>

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fn clone(&self) -> Cursor<T>

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<T: Debug> Debug for Cursor<T>

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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<T: Default> Default for Cursor<T>

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fn default() -> Cursor<T>

Returns the “default value” for a type. Read more

Auto Trait Implementations§

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impl<T> RefUnwindSafe for Cursor<T>
where T: RefUnwindSafe,

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impl<T> Send for Cursor<T>
where T: Send,

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impl<T> Sync for Cursor<T>
where T: Sync,

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impl<T> Unpin for Cursor<T>
where T: Unpin,

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impl<T> UnwindSafe for Cursor<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where 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 R
where R: AsyncBufRead + ?Sized,

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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 if empty. Read more
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fn consume(&mut self, amt: usize)
where Self: Unpin,

Consumes amt buffered bytes. Read more
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fn read_until<'a>( &'a mut self, byte: u8, buf: &'a mut Vec<u8> ) -> ReadUntilFuture<'a, Self>
where Self: Unpin,

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

Reads all bytes and appends them into buf until a newline (the 0xA byte) or EOF is found. Read more
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fn lines(self) -> Lines<Self>
where Self: Unpin + Sized,

Returns a stream over the lines of this byte stream. Read more
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fn split(self, byte: u8) -> Split<Self>
where Self: Sized,

Returns a stream over the contents of this reader split on the specified byte. Read more
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impl<R> AsyncReadExt for R
where R: AsyncRead + ?Sized,

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fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadFuture<'a, Self>
where Self: Unpin,

Reads some bytes from the byte stream. Read more
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fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>] ) -> ReadVectoredFuture<'a, Self>
where Self: Unpin,

Like read(), except it reads into a slice of buffers. Read more
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fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8> ) -> ReadToEndFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a Vec. Read more
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fn read_to_string<'a>( &'a mut self, buf: &'a mut String ) -> ReadToStringFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a String. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExactFuture<'a, Self>
where Self: Unpin,

Reads the exact number of bytes required to fill buf. Read more
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fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an adapter which will read at most limit bytes from it. Read more
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fn bytes(self) -> Bytes<Self>
where Self: Sized,

Converts this AsyncRead into a Stream of bytes. Read more
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fn chain<R>(self, next: R) -> Chain<Self, R>
where R: AsyncRead, Self: Sized,

Creates an adapter which will chain this stream with another. Read more
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fn boxed_reader<'a>(self) -> Pin<Box<dyn AsyncRead + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the reader and changes its type to dyn AsyncRead + Send + 'a. Read more
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impl<S> AsyncSeekExt for S
where S: AsyncSeek + ?Sized,

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

Seeks to a new position in a byte stream. Read more
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impl<W> AsyncWriteExt for W
where W: AsyncWrite + ?Sized,

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

Writes some bytes into the byte stream. Read more
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fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>] ) -> WriteVectoredFuture<'a, Self>
where Self: Unpin,

Like write(), except that it writes a slice of buffers. Read more
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fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAllFuture<'a, Self>
where Self: Unpin,

Writes an entire buffer into the byte stream. Read more
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fn flush(&mut self) -> FlushFuture<'_, Self>
where Self: Unpin,

Flushes the stream to ensure that all buffered contents reach their destination. Read more
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fn close(&mut self) -> CloseFuture<'_, Self>
where Self: Unpin,

Closes the writer. Read more
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fn boxed_writer<'a>(self) -> Pin<Box<dyn AsyncWrite + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the writer and changes its type to dyn AsyncWrite + Send + 'a. Read more
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impl<T> Borrow<T> for T
where 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 T
where 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> BufReadExt for T
where T: AsyncBufRead + ?Sized,

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

Reads all bytes and appends them into buf until a newline (the 0xA byte) is reached. Read more
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fn lines(self) -> Lines<Self>
where Self: Unpin + Sized,

Returns a stream over the lines of this byte stream. Read more
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fn split(self, byte: u8) -> Split<Self>
where Self: Sized,

Returns a stream over the contents of this reader split on the byte byte. 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, U> Into<U> for T
where 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<T> ReadExt for T
where T: AsyncRead + ?Sized,

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fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadFuture<'a, Self>
where Self: Unpin,

Reads some bytes from the byte stream. Read more
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fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>] ) -> ReadVectoredFuture<'a, Self>
where Self: Unpin,

Like read, except that it reads into a slice of buffers. Read more
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fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8> ) -> ReadToEndFuture<'a, Self>
where Self: Unpin,

Reads all bytes from the byte stream. Read more
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fn read_to_string<'a>( &'a mut self, buf: &'a mut String ) -> ReadToStringFuture<'a, Self>
where Self: Unpin,

Reads all bytes from the byte stream and appends them into a string. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExactFuture<'a, Self>
where Self: Unpin,

Reads the exact number of bytes required to fill buf. Read more
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fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an adaptor which will read at most limit bytes from it. Read more
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fn by_ref(&mut self) -> &mut Self
where Self: Sized,

Creates a “by reference” adaptor for this instance of Read. Read more
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fn bytes(self) -> Bytes<Self>
where Self: Sized,

Transforms this Read instance to a Stream over its bytes. Read more
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fn chain<R: Read>(self, next: R) -> Chain<Self, R>
where Self: Sized,

Creates an adaptor which will chain this stream with another. Read more
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impl<T> SeekExt for T
where T: AsyncSeek + ?Sized,

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

Seeks to a new position in a byte stream. Read more
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impl<T> ToOwned for T
where 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 T
where 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<T, U> TryInto<U> for T
where 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<T> WriteExt for T
where T: AsyncWrite + ?Sized,

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

Writes some bytes into the byte stream. Read more
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fn flush(&mut self) -> FlushFuture<'_, Self>
where Self: Unpin,

Flushes the stream to ensure that all buffered contents reach their destination. Read more
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fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>] ) -> WriteVectoredFuture<'a, Self>
where Self: Unpin,

Like write, except that it writes from a slice of buffers. Read more
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fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAllFuture<'a, Self>
where Self: Unpin,

Writes an entire buffer into the byte stream. Read more
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fn write_fmt<'a>(&'a mut self, fmt: Arguments<'_>) -> WriteFmtFuture<'a, Self>
where Self: Unpin,

Writes a formatted string into this writer, returning any error encountered. Read more