Source code
Revision control
Copy as Markdown
Other Tools
use futures_core::task::{Context, Poll};
use futures_io::{AsyncBufRead, AsyncRead};
use std::fmt;
use std::io;
use std::pin::Pin;
/// Reader for the [`empty()`] function.
#[must_use = "readers do nothing unless polled"]
pub struct Empty {
_priv: (),
}
/// Constructs a new handle to an empty reader.
///
/// All reads from the returned reader will return `Poll::Ready(Ok(0))`.
///
/// # Examples
///
/// A slightly sad example of not reading anything into a buffer:
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::io::{self, AsyncReadExt};
///
/// let mut buffer = String::new();
/// let mut reader = io::empty();
/// reader.read_to_string(&mut buffer).await?;
/// assert!(buffer.is_empty());
/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
/// ```
pub fn empty() -> Empty {
Empty { _priv: () }
}
impl AsyncRead for Empty {
#[inline]
fn poll_read(
self: Pin<&mut Self>,
_: &mut Context<'_>,
_: &mut [u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(Ok(0))
}
}
impl AsyncBufRead for Empty {
#[inline]
fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
Poll::Ready(Ok(&[]))
}
#[inline]
fn consume(self: Pin<&mut Self>, _: usize) {}
}
impl fmt::Debug for Empty {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Empty { .. }")
}
}