1 use super::assert_sink;
2 use crate::never::Never;
3 use core::marker::PhantomData;
4 use core::pin::Pin;
5 use futures_core::task::{Context, Poll};
6 use futures_sink::Sink;
7
8 /// Sink for the [`drain`] function.
9 #[derive(Debug)]
10 #[must_use = "sinks do nothing unless polled"]
11 pub struct Drain<T> {
12 marker: PhantomData<T>,
13 }
14
15 /// Create a sink that will just discard all items given to it.
16 ///
17 /// Similar to [`io::Sink`](::std::io::Sink).
18 ///
19 /// # Examples
20 ///
21 /// ```
22 /// # futures::executor::block_on(async {
23 /// use futures::sink::{self, SinkExt};
24 ///
25 /// let mut drain = sink::drain();
26 /// drain.send(5).await?;
27 /// # Ok::<(), futures::never::Never>(()) }).unwrap();
28 /// ```
drain<T>() -> Drain<T>29 pub fn drain<T>() -> Drain<T> {
30 assert_sink::<T, Never, _>(Drain { marker: PhantomData })
31 }
32
33 impl<T> Unpin for Drain<T> {}
34
35 impl<T> Clone for Drain<T> {
clone(&self) -> Self36 fn clone(&self) -> Self {
37 drain()
38 }
39 }
40
41 impl<T> Sink<T> for Drain<T> {
42 type Error = Never;
43
poll_ready(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>44 fn poll_ready(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
45 Poll::Ready(Ok(()))
46 }
47
start_send(self: Pin<&mut Self>, _item: T) -> Result<(), Self::Error>48 fn start_send(self: Pin<&mut Self>, _item: T) -> Result<(), Self::Error> {
49 Ok(())
50 }
51
poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>52 fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
53 Poll::Ready(Ok(()))
54 }
55
poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>56 fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
57 Poll::Ready(Ok(()))
58 }
59 }
60