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use super::assert_stream;
use core::marker::PhantomData;
use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
/// Stream for the [`empty`] function.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Empty<T> {
_phantom: PhantomData<T>,
}
/// Creates a stream which contains no elements.
///
/// The returned stream will always return `Ready(None)` when polled.
pub fn empty<T>() -> Empty<T> {
assert_stream::<T, _>(Empty { _phantom: PhantomData })
}
impl<T> Unpin for Empty<T> {}
impl<T> FusedStream for Empty<T> {
fn is_terminated(&self) -> bool {
true
}
}
impl<T> Stream for Empty<T> {
type Item = T;
fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
Poll::Ready(None)
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(0))
}
}
impl<T> Clone for Empty<T> {
fn clone(&self) -> Self {
empty()
}
}