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adds stream::skip combinator
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2 changed files with 68 additions and 0 deletions
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@ -33,6 +33,7 @@ mod min_by;
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mod next;
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mod nth;
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mod scan;
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mod skip;
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mod take;
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mod zip;
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@ -51,6 +52,7 @@ use fold::FoldFuture;
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use min_by::MinByFuture;
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use next::NextFuture;
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use nth::NthFuture;
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use skip::Skip;
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use std::cmp::Ordering;
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use std::marker::PhantomData;
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@ -661,6 +663,31 @@ pub trait Stream {
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Scan::new(self, initial_state, f)
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}
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/// Creates a combinator that skips the first `n` elements.
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///
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/// ## Examples
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///
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/// ```
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/// # fn main() { async_std::task::block_on(async {
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/// #
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/// use std::collections::VecDeque;
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/// use async_std::stream::Stream;
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///
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/// let s: VecDeque<usize> = vec![1, 2, 3].into_iter().collect();
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/// let mut skipped = s.skip(2);
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///
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/// assert_eq!(skipped.next().await, Some(3));
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/// assert_eq!(skipped.next().await, None);
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/// #
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/// # }) }
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/// ```
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fn skip(self, n: usize) -> Skip<Self>
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where
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Self: Sized,
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{
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Skip::new(self, n)
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}
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/// 'Zips up' two streams into a single stream of pairs.
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///
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/// `zip()` returns a new stream that will iterate over two other streams, returning a tuple
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41
src/stream/stream/skip.rs
Normal file
41
src/stream/stream/skip.rs
Normal file
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@ -0,0 +1,41 @@
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use std::pin::Pin;
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use std::task::{Context, Poll};
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use crate::stream::Stream;
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#[doc(hidden)]
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#[allow(missing_debug_implementations)]
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pub struct Skip<S> {
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stream: S,
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n: usize,
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}
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impl<S> Skip<S> {
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pin_utils::unsafe_pinned!(stream: S);
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pin_utils::unsafe_unpinned!(n: usize);
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pub(crate) fn new(stream: S, n: usize) -> Self {
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Skip { stream, n }
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}
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}
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impl<S> Stream for Skip<S>
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where
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S: Stream,
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{
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type Item = S::Item;
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fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
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loop {
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let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
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match next {
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Some(v) => match self.n {
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0 => return Poll::Ready(Some(v)),
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_ => *self.as_mut().n() -= 1,
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},
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None => return Poll::Ready(None),
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}
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}
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}
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}
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