mirror of
https://github.com/async-rs/async-std.git
synced 2025-01-31 17:55:35 +00:00
add stream::min_by method (#146)
* add stream::min_by method * Update src/stream/stream.rs Co-Authored-By: Yoshua Wuyts <yoshuawuyts+github@gmail.com>
This commit is contained in:
parent
bac74c2d7f
commit
7e3599a6a5
3 changed files with 90 additions and 0 deletions
54
src/stream/min_by.rs
Normal file
54
src/stream/min_by.rs
Normal file
|
@ -0,0 +1,54 @@
|
|||
use std::cmp::Ordering;
|
||||
use std::pin::Pin;
|
||||
|
||||
use super::stream::Stream;
|
||||
use crate::future::Future;
|
||||
use crate::task::{Context, Poll};
|
||||
|
||||
/// A future that yields the minimum item in a stream by a given comparison function.
|
||||
#[derive(Clone, Debug)]
|
||||
pub struct MinBy<S: Stream, F> {
|
||||
stream: S,
|
||||
compare: F,
|
||||
min: Option<S::Item>,
|
||||
}
|
||||
|
||||
impl<S: Stream + Unpin, F> Unpin for MinBy<S, F> {}
|
||||
|
||||
impl<S: Stream + Unpin, F> MinBy<S, F> {
|
||||
pub(super) fn new(stream: S, compare: F) -> Self {
|
||||
MinBy {
|
||||
stream,
|
||||
compare,
|
||||
min: None,
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
impl<S, F> Future for MinBy<S, F>
|
||||
where
|
||||
S: futures_core::stream::Stream + Unpin,
|
||||
S::Item: Copy,
|
||||
F: FnMut(&S::Item, &S::Item) -> Ordering,
|
||||
{
|
||||
type Output = Option<S::Item>;
|
||||
|
||||
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
|
||||
let next = futures_core::ready!(Pin::new(&mut self.stream).poll_next(cx));
|
||||
|
||||
match next {
|
||||
Some(new) => {
|
||||
cx.waker().wake_by_ref();
|
||||
match self.as_mut().min.take() {
|
||||
None => self.as_mut().min = Some(new),
|
||||
Some(old) => match (&mut self.as_mut().compare)(&new, &old) {
|
||||
Ordering::Less => self.as_mut().min = Some(new),
|
||||
_ => self.as_mut().min = Some(old),
|
||||
},
|
||||
}
|
||||
Poll::Pending
|
||||
}
|
||||
None => Poll::Ready(self.min),
|
||||
}
|
||||
}
|
||||
}
|
|
@ -27,6 +27,7 @@ pub use repeat::{repeat, Repeat};
|
|||
pub use stream::{Stream, Take};
|
||||
|
||||
mod empty;
|
||||
mod min_by;
|
||||
mod once;
|
||||
mod repeat;
|
||||
mod stream;
|
||||
|
|
|
@ -21,10 +21,12 @@
|
|||
//! # }) }
|
||||
//! ```
|
||||
|
||||
use std::cmp::Ordering;
|
||||
use std::pin::Pin;
|
||||
|
||||
use cfg_if::cfg_if;
|
||||
|
||||
use super::min_by::MinBy;
|
||||
use crate::future::Future;
|
||||
use crate::task::{Context, Poll};
|
||||
use std::marker::PhantomData;
|
||||
|
@ -118,6 +120,39 @@ pub trait Stream {
|
|||
}
|
||||
}
|
||||
|
||||
/// Returns the element that gives the minimum value with respect to the
|
||||
/// specified comparison function. If several elements are equally minimum,
|
||||
/// the first element is returned. If the stream is empty, `None` is returned.
|
||||
///
|
||||
/// # 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 min = Stream::min_by(s.clone(), |x, y| x.cmp(y)).await;
|
||||
/// assert_eq!(min, Some(1));
|
||||
///
|
||||
/// let min = Stream::min_by(s, |x, y| y.cmp(x)).await;
|
||||
/// assert_eq!(min, Some(3));
|
||||
///
|
||||
/// let min = Stream::min_by(VecDeque::<usize>::new(), |x, y| x.cmp(y)).await;
|
||||
/// assert_eq!(min, None);
|
||||
/// #
|
||||
/// # }) }
|
||||
/// ```
|
||||
fn min_by<F>(self, compare: F) -> MinBy<Self, F>
|
||||
where
|
||||
Self: Sized + Unpin,
|
||||
F: FnMut(&Self::Item, &Self::Item) -> Ordering,
|
||||
{
|
||||
MinBy::new(self, compare)
|
||||
}
|
||||
|
||||
/// Tests if every element of the stream matches a predicate.
|
||||
///
|
||||
/// `all()` takes a closure that returns `true` or `false`. It applies
|
||||
|
|
Loading…
Reference in a new issue