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Merge pull request #388 from felipesere/cycle
Implement stream::cycle(..)
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commit
d0f1996759
2 changed files with 107 additions and 0 deletions
73
src/stream/stream/cycle.rs
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73
src/stream/stream/cycle.rs
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@ -0,0 +1,73 @@
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use std::pin::Pin;
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use pin_project_lite::pin_project;
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use crate::stream::Stream;
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use crate::task::{Context, Poll};
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pin_project! {
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/// A stream that will repeatedly yield the same list of elements
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pub struct Cycle<S, T> {
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#[pin]
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source: S,
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index: usize,
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buffer: Vec<T>,
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state: CycleState,
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}
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}
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#[derive(Eq, PartialEq)]
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enum CycleState {
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FromStream,
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FromBuffer,
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}
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impl<S> Cycle<S, S::Item>
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where
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S: Stream,
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S::Item: Clone,
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{
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pub fn new(source: S) -> Cycle<S, S::Item> {
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Cycle {
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source,
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index: 0,
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buffer: Vec::new(),
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state: CycleState::FromStream,
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}
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}
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}
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impl<S> Stream for Cycle<S, S::Item>
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where
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S: Stream,
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S::Item: Clone,
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{
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type Item = S::Item;
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fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
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let this = self.project();
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let mut next;
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if *this.state == CycleState::FromStream {
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next = futures_core::ready!(this.source.poll_next(cx));
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if let Some(val) = next {
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this.buffer.push(val.clone());
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next = Some(val)
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} else {
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*this.state = CycleState::FromBuffer;
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next = this.buffer.get(*this.index).cloned();
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}
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} else {
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let mut index = *this.index;
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if index == this.buffer.len() {
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index = 0
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}
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next = Some(this.buffer[index].clone());
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*this.index = index + 1;
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}
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Poll::Ready(next)
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}
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}
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@ -27,6 +27,7 @@ mod chain;
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mod cloned;
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mod cmp;
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mod copied;
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mod cycle;
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mod enumerate;
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mod eq;
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mod filter;
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@ -66,6 +67,7 @@ mod zip;
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use all::AllFuture;
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use any::AnyFuture;
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use cmp::CmpFuture;
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use cycle::Cycle;
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use enumerate::Enumerate;
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use eq::EqFuture;
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use filter_map::FilterMap;
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@ -448,6 +450,38 @@ extension_trait! {
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Copied::new(self)
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}
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#[doc = r#"
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Creates a stream that yields the provided values infinitely and in order.
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# Examples
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Basic usage:
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```
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# async_std::task::block_on(async {
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#
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use async_std::prelude::*;
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use async_std::stream;
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let mut s = stream::once(7).cycle();
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assert_eq!(s.next().await, Some(7));
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assert_eq!(s.next().await, Some(7));
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assert_eq!(s.next().await, Some(7));
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assert_eq!(s.next().await, Some(7));
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assert_eq!(s.next().await, Some(7));
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#
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# })
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```
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"#]
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fn cycle(self) -> Cycle<Self, Self::Item>
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where
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Self: Sized,
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Self::Item: Clone,
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{
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Cycle::new(self)
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}
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#[doc = r#"
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Creates a stream that gives the current element's count as well as the next value.
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