adds stream::skip combinator

pull/222/head
Fedor Sakharov 5 years ago
parent 55ea367415
commit 570329b176
No known key found for this signature in database
GPG Key ID: 93D436E666BF0FEE

@ -33,6 +33,7 @@ mod min_by;
mod next;
mod nth;
mod scan;
mod skip;
mod take;
mod zip;
@ -51,6 +52,7 @@ use fold::FoldFuture;
use min_by::MinByFuture;
use next::NextFuture;
use nth::NthFuture;
use skip::Skip;
use std::cmp::Ordering;
use std::marker::PhantomData;
@ -661,6 +663,31 @@ pub trait Stream {
Scan::new(self, initial_state, f)
}
/// Creates a combinator that skips the first `n` elements.
///
/// ## Examples
///
/// ```
/// # fn main() { async_std::task::block_on(async {
/// #
/// use std::collections::VecDeque;
/// use async_std::stream::Stream;
///
/// let s: VecDeque<usize> = vec![1, 2, 3].into_iter().collect();
/// let mut skipped = s.skip(2);
///
/// assert_eq!(skipped.next().await, Some(3));
/// assert_eq!(skipped.next().await, None);
/// #
/// # }) }
/// ```
fn skip(self, n: usize) -> Skip<Self>
where
Self: Sized,
{
Skip::new(self, n)
}
/// 'Zips up' two streams into a single stream of pairs.
///
/// `zip()` returns a new stream that will iterate over two other streams, returning a tuple

@ -0,0 +1,41 @@
use std::pin::Pin;
use std::task::{Context, Poll};
use crate::stream::Stream;
#[doc(hidden)]
#[allow(missing_debug_implementations)]
pub struct Skip<S> {
stream: S,
n: usize,
}
impl<S> Skip<S> {
pin_utils::unsafe_pinned!(stream: S);
pin_utils::unsafe_unpinned!(n: usize);
pub(crate) fn new(stream: S, n: usize) -> Self {
Skip { stream, n }
}
}
impl<S> Stream for Skip<S>
where
S: Stream,
{
type Item = S::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
match next {
Some(v) => match self.n {
0 => return Poll::Ready(Some(v)),
_ => *self.as_mut().n() -= 1,
},
None => return Poll::Ready(None),
}
}
}
}
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