Trait async_std::prelude::StreamExt

pub trait StreamExt: Stream {
    // Provided methods
    fn next(&mut self) -> NextFuture<'_, Self>
       where Self: Unpin { ... }
    fn take(self, n: usize) -> Take<Self>
       where Self: Sized { ... }
    fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
       where Self: Sized,
             P: FnMut(&Self::Item) -> bool { ... }
    fn step_by(self, step: usize) -> StepBy<Self>
       where Self: Sized { ... }
    fn chain<U>(self, other: U) -> Chain<Self, U>
       where Self: Sized,
             U: Stream<Item = Self::Item> + Sized { ... }
    fn cloned<'a, T>(self) -> Cloned<Self>
       where Self: Sized + Stream<Item = &'a T>,
             T: Clone + 'a { ... }
    fn copied<'a, T>(self) -> Copied<Self>
       where Self: Sized + Stream<Item = &'a T>,
             T: Copy + 'a { ... }
    fn cycle(self) -> Cycle<Self>
       where Self: Clone + Sized { ... }
    fn enumerate(self) -> Enumerate<Self>
       where Self: Sized { ... }
    fn map<B, F>(self, f: F) -> Map<Self, F>
       where Self: Sized,
             F: FnMut(Self::Item) -> B { ... }
    fn inspect<F>(self, f: F) -> Inspect<Self, F>
       where Self: Sized,
             F: FnMut(&Self::Item) { ... }
    fn last(self) -> LastFuture<Self, Self::Item>
       where Self: Sized { ... }
    fn fuse(self) -> Fuse<Self>
       where Self: Sized { ... }
    fn filter<P>(self, predicate: P) -> Filter<Self, P>
       where Self: Sized,
             P: FnMut(&Self::Item) -> bool { ... }
    fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
       where Self: Sized,
             F: FnMut(Self::Item) -> Option<B> { ... }
    fn min_by_key<B, F>(self, key_by: F) -> MinByKeyFuture<Self, Self::Item, F>
       where Self: Sized,
             B: Ord,
             F: FnMut(&Self::Item) -> B { ... }
    fn max_by_key<B, F>(self, key_by: F) -> MaxByKeyFuture<Self, Self::Item, F>
       where Self: Sized,
             B: Ord,
             F: FnMut(&Self::Item) -> B { ... }
    fn min_by<F>(self, compare: F) -> MinByFuture<Self, F, Self::Item>
       where Self: Sized,
             F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
    fn max(self) -> MaxFuture<Self, Self::Item>
       where Self: Sized,
             Self::Item: Ord { ... }
    fn min(self) -> MinFuture<Self, Self::Item>
       where Self: Sized,
             Self::Item: Ord { ... }
    fn max_by<F>(self, compare: F) -> MaxByFuture<Self, F, Self::Item>
       where Self: Sized,
             F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
    fn nth(&mut self, n: usize) -> NthFuture<'_, Self>
       where Self: Unpin + Sized { ... }
    fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F, Self::Item>
       where Self: Unpin + Sized,
             F: FnMut(Self::Item) -> bool { ... }
    fn find<P>(&mut self, p: P) -> FindFuture<'_, Self, P>
       where Self: Unpin + Sized,
             P: FnMut(&Self::Item) -> bool { ... }
    fn find_map<F, B>(&mut self, f: F) -> FindMapFuture<'_, Self, F>
       where Self: Unpin + Sized,
             F: FnMut(Self::Item) -> Option<B> { ... }
    fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, F, B>
       where Self: Sized,
             F: FnMut(B, Self::Item) -> B { ... }
    fn for_each<F>(self, f: F) -> ForEachFuture<Self, F>
       where Self: Sized,
             F: FnMut(Self::Item) { ... }
    fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F, Self::Item>
       where Self: Unpin + Sized,
             F: FnMut(Self::Item) -> bool { ... }
    fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
       where Self: Sized,
             F: FnMut(&mut St, Self::Item) -> Option<B> { ... }
    fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
       where Self: Sized,
             P: FnMut(&Self::Item) -> bool { ... }
    fn skip(self, n: usize) -> Skip<Self>
       where Self: Sized { ... }
    fn try_fold<B, F, T, E>(
        &mut self,
        init: T,
        f: F,
    ) -> TryFoldFuture<'_, Self, F, T>
       where Self: Unpin + Sized,
             F: FnMut(B, Self::Item) -> Result<T, E> { ... }
    fn try_for_each<F, E>(&mut self, f: F) -> TryForEachFuture<'_, Self, F>
       where Self: Unpin + Sized,
             F: FnMut(Self::Item) -> Result<(), E> { ... }
    fn zip<U>(self, other: U) -> Zip<Self, U>
       where Self: Sized,
             U: Stream { ... }
    fn partial_cmp<S>(self, other: S) -> PartialCmpFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: PartialOrd<S::Item> { ... }
    fn position<P>(&mut self, predicate: P) -> PositionFuture<'_, Self, P>
       where Self: Unpin + Sized,
             P: FnMut(Self::Item) -> bool { ... }
    fn cmp<S>(self, other: S) -> CmpFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: Ord { ... }
    fn ne<S>(self, other: S) -> NeFuture<Self, S>
       where Self: Sized,
             S: Sized + Stream,
             <Self as Stream>::Item: PartialEq<S::Item> { ... }
    fn ge<S>(self, other: S) -> GeFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: PartialOrd<S::Item> { ... }
    fn eq<S>(self, other: S) -> EqFuture<Self, S>
       where Self: Sized + Stream,
             S: Sized + Stream,
             <Self as Stream>::Item: PartialEq<S::Item> { ... }
    fn gt<S>(self, other: S) -> GtFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: PartialOrd<S::Item> { ... }
    fn le<S>(self, other: S) -> LeFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: PartialOrd<S::Item> { ... }
    fn lt<S>(self, other: S) -> LtFuture<Self, S>
       where Self: Sized + Stream,
             S: Stream,
             <Self as Stream>::Item: PartialOrd<S::Item> { ... }
}

Extension methods for Stream.

Provided Methods

fn next(&mut self) -> NextFuture<'_, Self>

where Self: Unpin,

Advances the stream and returns the next value.

Returns None when iteration is finished. Individual stream implementations may choose to resume iteration, and so calling next() again may or may not eventually start returning more values.

Examples

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::once(7);

assert_eq!(s.next().await, Some(7));
assert_eq!(s.next().await, None);

fn take(self, n: usize) -> Take<Self>

where Self: Sized,

Creates a stream that yields its first n elements.

Examples

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::repeat(9).take(3);

while let Some(v) = s.next().await {
    assert_eq!(v, 9);
}

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates a stream that yields elements based on a predicate.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1, 2, 3, 4]);
let mut s = s.take_while(|x| x < &3 );

assert_eq!(s.next().await, Some(1));
assert_eq!(s.next().await, Some(2));
assert_eq!(s.next().await, None);

fn step_by(self, step: usize) -> StepBy<Self>

where Self: Sized,

Creates a stream that yields each stepth element.

Panics

This method will panic if the given step is 0.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![0u8, 1, 2, 3, 4]);
let mut stepped = s.step_by(2);

assert_eq!(stepped.next().await, Some(0));
assert_eq!(stepped.next().await, Some(2));
assert_eq!(stepped.next().await, Some(4));
assert_eq!(stepped.next().await, None);

fn chain<U>(self, other: U) -> Chain<Self, U>

where Self: Sized, U: Stream<Item = Self::Item> + Sized,

Takes two streams and creates a new stream over both in sequence.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let first = stream::from_iter(vec![0u8, 1]);
let second = stream::from_iter(vec![2, 3]);
let mut c = first.chain(second);

assert_eq!(c.next().await, Some(0));
assert_eq!(c.next().await, Some(1));
assert_eq!(c.next().await, Some(2));
assert_eq!(c.next().await, Some(3));
assert_eq!(c.next().await, None);

fn cloned<'a, T>(self) -> Cloned<Self>

where Self: Sized + Stream<Item = &'a T>, T: Clone + 'a,

Creates an stream which copies all of its elements.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let v = stream::from_iter(vec![&1, &2, &3]);

let mut v_cloned = v.cloned();

assert_eq!(v_cloned.next().await, Some(1));
assert_eq!(v_cloned.next().await, Some(2));
assert_eq!(v_cloned.next().await, Some(3));
assert_eq!(v_cloned.next().await, None);

fn copied<'a, T>(self) -> Copied<Self>

where Self: Sized + Stream<Item = &'a T>, T: Copy + 'a,

Creates an stream which copies all of its elements.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![&1, &2, &3]);
let mut s_copied  = s.copied();

assert_eq!(s_copied.next().await, Some(1));
assert_eq!(s_copied.next().await, Some(2));
assert_eq!(s_copied.next().await, Some(3));
assert_eq!(s_copied.next().await, None);

fn cycle(self) -> Cycle<Self>

where Self: Clone + Sized,

Creates a stream that yields the provided values infinitely and in order.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::once(7).cycle();

assert_eq!(s.next().await, Some(7));
assert_eq!(s.next().await, Some(7));
assert_eq!(s.next().await, Some(7));
assert_eq!(s.next().await, Some(7));
assert_eq!(s.next().await, Some(7));

fn enumerate(self) -> Enumerate<Self>

where Self: Sized,

Creates a stream that gives the current element’s count as well as the next value.

Overflow behaviour.

This combinator does no guarding against overflows.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec!['a', 'b', 'c']);
let mut s = s.enumerate();

assert_eq!(s.next().await, Some((0, 'a')));
assert_eq!(s.next().await, Some((1, 'b')));
assert_eq!(s.next().await, Some((2, 'c')));
assert_eq!(s.next().await, None);

fn map<B, F>(self, f: F) -> Map<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates a stream that calls that closure on every element of this stream.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1, 2, 3]);
let mut s = s.map(|x| 2 * x);

assert_eq!(s.next().await, Some(2));
assert_eq!(s.next().await, Some(4));
assert_eq!(s.next().await, Some(6));
assert_eq!(s.next().await, None);

fn inspect<F>(self, f: F) -> Inspect<Self, F>

where Self: Sized, F: FnMut(&Self::Item),

A combinator that does something with each element in the stream, passing the value on.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1, 2, 3, 4, 5]);

let sum = s
   .inspect(|x| println!("about to filter {}", x))
   .filter(|x| x % 2 == 0)
   .inspect(|x| println!("made it through filter: {}", x))
   .fold(0, |sum, i| sum + i)
   .await;

assert_eq!(sum, 6);

fn last(self) -> LastFuture<Self, Self::Item>

where Self: Sized,

Returns the last element of the stream.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1, 2, 3]);

let last  = s.last().await;
assert_eq!(last, Some(3));

An empty stream will return None:

use async_std::stream;
use crate::async_std::prelude::*;

let s = stream::empty::<()>();

let last  = s.last().await;
assert_eq!(last, None);

fn fuse(self) -> Fuse<Self>

where Self: Sized,

Creates a stream which ends after the first None.

After a stream returns None, future calls may or may not yield Some(T) again. fuse() adapts an iterator, ensuring that after a None is given, it will always return None forever.

Examples

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::once(1).fuse();
assert_eq!(s.next().await, Some(1));
assert_eq!(s.next().await, None);
assert_eq!(s.next().await, None);

fn filter<P>(self, predicate: P) -> Filter<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates a stream that uses a predicate to determine if an element should be yielded.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1, 2, 3, 4]);
let mut s = s.filter(|i| i % 2 == 0);

assert_eq!(s.next().await, Some(2));
assert_eq!(s.next().await, Some(4));
assert_eq!(s.next().await, None);

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Both filters and maps a stream.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec!["1", "lol", "3", "NaN", "5"]);

let mut parsed = s.filter_map(|a| a.parse::<u32>().ok());

let one = parsed.next().await;
assert_eq!(one, Some(1));

let three = parsed.next().await;
assert_eq!(three, Some(3));

let five = parsed.next().await;
assert_eq!(five, Some(5));

let end = parsed.next().await;
assert_eq!(end, None);

fn min_by_key<B, F>(self, key_by: F) -> MinByKeyFuture<Self, Self::Item, F>

where Self: Sized, B: Ord, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value with respect to the specified key function. If several elements are equally minimum, the first element is returned. If the stream is empty, None is returned.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![-1isize, 2, -3]);

let min = s.clone().min_by_key(|x| x.abs()).await;
assert_eq!(min, Some(-1));

let min = stream::empty::<isize>().min_by_key(|x| x.abs()).await;
assert_eq!(min, None);

fn max_by_key<B, F>(self, key_by: F) -> MaxByKeyFuture<Self, Self::Item, F>

where Self: Sized, B: Ord, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value with respect to the specified key function. If several elements are equally maximum, the first element is returned. If the stream is empty, None is returned.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![-3_i32, 0, 1, 5, -10]);

let max = s.clone().max_by_key(|x| x.abs()).await;
assert_eq!(max, Some(-10));

let max = stream::empty::<isize>().max_by_key(|x| x.abs()).await;
assert_eq!(max, None);

fn min_by<F>(self, compare: F) -> MinByFuture<Self, F, Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

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

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1u8, 2, 3]);

let min = s.clone().min_by(|x, y| x.cmp(y)).await;
assert_eq!(min, Some(1));

let min = s.min_by(|x, y| y.cmp(x)).await;
assert_eq!(min, Some(3));

let min = stream::empty::<u8>().min_by(|x, y| x.cmp(y)).await;
assert_eq!(min, None);

fn max(self) -> MaxFuture<Self, Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the element that gives the maximum value. If several elements are equally maximum, the first element is returned. If the stream is empty, None is returned.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1usize, 2, 3]);

let max = s.clone().max().await;
assert_eq!(max, Some(3));

let max = stream::empty::<usize>().max().await;
assert_eq!(max, None);

fn min(self) -> MinFuture<Self, Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the element that gives the minimum value. If several elements are equally minimum, the first element is returned. If the stream is empty, None is returned.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1usize, 2, 3]);

let min = s.clone().min().await;
assert_eq!(min, Some(1));

let min = stream::empty::<usize>().min().await;
assert_eq!(min, None);

fn max_by<F>(self, compare: F) -> MaxByFuture<Self, F, Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function. If several elements are equally maximum, the first element is returned. If the stream is empty, None is returned.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1u8, 2, 3]);

let max = s.clone().max_by(|x, y| x.cmp(y)).await;
assert_eq!(max, Some(3));

let max = s.max_by(|x, y| y.cmp(x)).await;
assert_eq!(max, Some(1));

let max = stream::empty::<usize>().max_by(|x, y| x.cmp(y)).await;
assert_eq!(max, None);

fn nth(&mut self, n: usize) -> NthFuture<'_, Self>

where Self: Unpin + Sized,

Returns the nth element of the stream.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::from_iter(vec![1u8, 2, 3]);

let second = s.nth(1).await;
assert_eq!(second, Some(2));

Calling nth() multiple times:

use async_std::stream;
use async_std::prelude::*;

let mut s = stream::from_iter(vec![1u8, 2, 3]);

let second = s.nth(0).await;
assert_eq!(second, Some(1));

let second = s.nth(0).await;
assert_eq!(second, Some(2));

Returning None if the stream finished before returning n elements:

use async_std::prelude::*;
use async_std::stream;

let mut s  = stream::from_iter(vec![1u8, 2, 3]);

let fourth = s.nth(4).await;
assert_eq!(fourth, None);

fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F, Self::Item>

where Self: Unpin + Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the stream matches a predicate.

all() takes a closure that returns true or false. It applies this closure to each element of the stream, and if they all return true, then so does all(). If any of them return false, it returns false.

all() is short-circuiting; in other words, it will stop processing as soon as it finds a false, given that no matter what else happens, the result will also be false.

An empty stream returns true.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::repeat::<u32>(42).take(3);
assert!(s.all(|x| x ==  42).await);

Empty stream:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::empty::<u32>();
assert!(s.all(|_| false).await);

fn find<P>(&mut self, p: P) -> FindFuture<'_, Self, P>

where Self: Unpin + Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element in a stream that satisfies a predicate.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::from_iter(vec![1u8, 2, 3]);
let res = s.find(|x| *x == 2).await;
assert_eq!(res, Some(2));

Resuming after a first find:

use async_std::prelude::*;
use async_std::stream;

let mut s= stream::from_iter(vec![1, 2, 3]);
let res = s.find(|x| *x == 2).await;
assert_eq!(res, Some(2));

let next = s.next().await;
assert_eq!(next, Some(3));

fn find_map<F, B>(&mut self, f: F) -> FindMapFuture<'_, Self, F>

where Self: Unpin + Sized, F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of stream and returns the first non-none result.

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::from_iter(vec!["lol", "NaN", "2", "5"]);
let first_number = s.find_map(|s| s.parse().ok()).await;

assert_eq!(first_number, Some(2));

fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, F, B>

where Self: Sized, F: FnMut(B, Self::Item) -> B,

A combinator that applies a function to every element in a stream producing a single, final value.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1u8, 2, 3]);
let sum = s.fold(0, |acc, x| acc + x).await;

assert_eq!(sum, 6);

fn for_each<F>(self, f: F) -> ForEachFuture<Self, F>

where Self: Sized, F: FnMut(Self::Item),

Call a closure on each element of the stream.

Examples

use async_std::prelude::*;
use async_std::stream;
use std::sync::mpsc::channel;

let (tx, rx) = channel();

let s = stream::from_iter(vec![1usize, 2, 3]);
let sum = s.for_each(move |x| tx.clone().send(x).unwrap()).await;

let v: Vec<_> = rx.iter().collect();

assert_eq!(v, vec![1, 2, 3]);

fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F, Self::Item>

where Self: Unpin + Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the stream matches a predicate.

any() takes a closure that returns true or false. It applies this closure to each element of the stream, and if any of them return true, then so does any(). If they all return false, it returns false.

any() is short-circuiting; in other words, it will stop processing as soon as it finds a true, given that no matter what else happens, the result will also be true.

An empty stream returns false.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::repeat::<u32>(42).take(3);
assert!(s.any(|x| x ==  42).await);

Empty stream:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::empty::<u32>();
assert!(!s.any(|_| false).await);

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>

where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

A stream adaptor similar to fold that holds internal state and produces a new stream.

scan() takes two arguments: an initial value which seeds the internal state, and a closure with two arguments, the first being a mutable reference to the internal state and the second a stream element. The closure can assign to the internal state to share state between iterations.

On iteration, the closure will be applied to each element of the stream and the return value from the closure, an Option, is yielded by the stream.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1isize, 2, 3]);
let mut s = s.scan(1, |state, x| {
    *state = *state * x;
    Some(-*state)
});

assert_eq!(s.next().await, Some(-1));
assert_eq!(s.next().await, Some(-2));
assert_eq!(s.next().await, Some(-6));
assert_eq!(s.next().await, None);

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Combinator that skips elements based on a predicate.

Takes a closure argument. It will call this closure on every element in the stream and ignore elements until it returns false.

After false is returned, SkipWhile’s job is over and all further elements in the stream are yielded.

Examples

use async_std::prelude::*;
use async_std::stream;

let a = stream::from_iter(vec![-1i32, 0, 1]);
let mut s = a.skip_while(|x| x.is_negative());

assert_eq!(s.next().await, Some(0));
assert_eq!(s.next().await, Some(1));
assert_eq!(s.next().await, None);

fn skip(self, n: usize) -> Skip<Self>

where Self: Sized,

Creates a combinator that skips the first n elements.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1u8, 2, 3]);
let mut skipped = s.skip(2);

assert_eq!(skipped.next().await, Some(3));
assert_eq!(skipped.next().await, None);

fn try_fold<B, F, T, E>( &mut self, init: T, f: F, ) -> TryFoldFuture<'_, Self, F, T>

where Self: Unpin + Sized, F: FnMut(B, Self::Item) -> Result<T, E>,

A combinator that applies a function as long as it returns successfully, producing a single, final value. Immediately returns the error when the function returns unsuccessfully.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream;

let mut s = stream::from_iter(vec![1usize, 2, 3]);
let sum = s.try_fold(0, |acc, v| {
    if (acc+v) % 2 == 1 {
        Ok(v+3)
    } else {
        Err("fail")
    }
}).await;

assert_eq!(sum, Err("fail"));

fn try_for_each<F, E>(&mut self, f: F) -> TryForEachFuture<'_, Self, F>

where Self: Unpin + Sized, F: FnMut(Self::Item) -> Result<(), E>,

Applies a falliable function to each element in a stream, stopping at first error and returning it.

Examples

use std::sync::mpsc::channel;
use async_std::prelude::*;
use async_std::stream;

let (tx, rx) = channel();

let mut s = stream::from_iter(vec![1u8, 2, 3]);
let s = s.try_for_each(|v| {
    if v % 2 == 1 {
        tx.clone().send(v).unwrap();
        Ok(())
    } else {
        Err("even")
    }
});

let res = s.await;
drop(tx);
let values: Vec<_> = rx.iter().collect();

assert_eq!(values, vec![1]);
assert_eq!(res, Err("even"));

fn zip<U>(self, other: U) -> Zip<Self, U>

where Self: Sized, U: Stream,

‘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 where the first element comes from the first stream, and the second element comes from the second stream.

In other words, it zips two streams together, into a single one.

If either stream returns None, poll_next from the zipped stream will return None. If the first stream returns None, zip will short-circuit and poll_next will not be called on the second stream.

Examples

use async_std::prelude::*;
use async_std::stream;

let l = stream::from_iter(vec![1u8, 2, 3]);
let r = stream::from_iter(vec![4u8, 5, 6, 7]);
let mut s = l.zip(r);

assert_eq!(s.next().await, Some((1, 4)));
assert_eq!(s.next().await, Some((2, 5)));
assert_eq!(s.next().await, Some((3, 6)));
assert_eq!(s.next().await, None);

fn partial_cmp<S>(self, other: S) -> PartialCmpFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: PartialOrd<S::Item>,

Lexicographically compares the elements of this Stream with those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

use std::cmp::Ordering;

let s1 = stream::from_iter(vec![1]);
let s2 = stream::from_iter(vec![1, 2]);
let s3 = stream::from_iter(vec![1, 2, 3]);
let s4 = stream::from_iter(vec![1, 2, 4]);
assert_eq!(s1.clone().partial_cmp(s1.clone()).await, Some(Ordering::Equal));
assert_eq!(s1.clone().partial_cmp(s2.clone()).await, Some(Ordering::Less));
assert_eq!(s2.clone().partial_cmp(s1.clone()).await, Some(Ordering::Greater));
assert_eq!(s3.clone().partial_cmp(s4.clone()).await, Some(Ordering::Less));
assert_eq!(s4.clone().partial_cmp(s3.clone()).await, Some(Ordering::Greater));

fn position<P>(&mut self, predicate: P) -> PositionFuture<'_, Self, P>

where Self: Unpin + Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in a Stream that satisfies a predicate, returning its index.

Examples

use async_std::prelude::*;
use async_std::stream;

let s = stream::from_iter(vec![1usize, 2, 3]);
let res = s.clone().position(|x| x == 1).await;
assert_eq!(res, Some(0));

let res = s.clone().position(|x| x == 2).await;
assert_eq!(res, Some(1));

let res = s.clone().position(|x| x == 3).await;
assert_eq!(res, Some(2));

let res = s.clone().position(|x| x == 4).await;
assert_eq!(res, None);

fn cmp<S>(self, other: S) -> CmpFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: Ord,

Lexicographically compares the elements of this Stream with those of another using ‘Ord’.

Examples

use async_std::prelude::*;
use async_std::stream;
use std::cmp::Ordering;

let s1 = stream::from_iter(vec![1]);
let s2 = stream::from_iter(vec![1, 2]);
let s3 = stream::from_iter(vec![1, 2, 3]);
let s4 = stream::from_iter(vec![1, 2, 4]);

assert_eq!(s1.clone().cmp(s1.clone()).await, Ordering::Equal);
assert_eq!(s1.clone().cmp(s2.clone()).await, Ordering::Less);
assert_eq!(s2.clone().cmp(s1.clone()).await, Ordering::Greater);
assert_eq!(s3.clone().cmp(s4.clone()).await, Ordering::Less);
assert_eq!(s4.clone().cmp(s3.clone()).await, Ordering::Greater);

fn ne<S>(self, other: S) -> NeFuture<Self, S>

where Self: Sized, S: Sized + Stream, <Self as Stream>::Item: PartialEq<S::Item>,

Determines if the elements of this Stream are lexicographically not equal to those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single     = stream::from_iter(vec![1usize]);
let single_ne  = stream::from_iter(vec![10usize]);
let multi      = stream::from_iter(vec![1usize,2]);
let multi_ne   = stream::from_iter(vec![1usize,5]);

assert_eq!(single.clone().ne(single.clone()).await, false);
assert_eq!(single_ne.clone().ne(single.clone()).await, true);
assert_eq!(multi.clone().ne(single_ne.clone()).await, true);
assert_eq!(multi_ne.clone().ne(multi.clone()).await, true);

fn ge<S>(self, other: S) -> GeFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: PartialOrd<S::Item>,

Determines if the elements of this Stream are lexicographically greater than or equal to those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single    = stream::from_iter(vec![1]);
let single_gt = stream::from_iter(vec![10]);
let multi     = stream::from_iter(vec![1,2]);
let multi_gt  = stream::from_iter(vec![1,5]);

assert_eq!(single.clone().ge(single.clone()).await, true);
assert_eq!(single_gt.clone().ge(single.clone()).await, true);
assert_eq!(multi.clone().ge(single_gt.clone()).await, false);
assert_eq!(multi_gt.clone().ge(multi.clone()).await, true);

fn eq<S>(self, other: S) -> EqFuture<Self, S>

where Self: Sized + Stream, S: Sized + Stream, <Self as Stream>::Item: PartialEq<S::Item>,

Determines if the elements of this Stream are lexicographically equal to those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single     = stream::from_iter(vec![1]);
let single_eq  = stream::from_iter(vec![10]);
let multi      = stream::from_iter(vec![1,2]);
let multi_eq   = stream::from_iter(vec![1,5]);

assert_eq!(single.clone().eq(single.clone()).await, true);
assert_eq!(single_eq.clone().eq(single.clone()).await, false);
assert_eq!(multi.clone().eq(single_eq.clone()).await, false);
assert_eq!(multi_eq.clone().eq(multi.clone()).await, false);

fn gt<S>(self, other: S) -> GtFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: PartialOrd<S::Item>,

Determines if the elements of this Stream are lexicographically greater than those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single = stream::from_iter(vec![1]);
let single_gt = stream::from_iter(vec![10]);
let multi = stream::from_iter(vec![1,2]);
let multi_gt = stream::from_iter(vec![1,5]);

assert_eq!(single.clone().gt(single.clone()).await, false);
assert_eq!(single_gt.clone().gt(single.clone()).await, true);
assert_eq!(multi.clone().gt(single_gt.clone()).await, false);
assert_eq!(multi_gt.clone().gt(multi.clone()).await, true);

fn le<S>(self, other: S) -> LeFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: PartialOrd<S::Item>,

Determines if the elements of this Stream are lexicographically less or equal to those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single = stream::from_iter(vec![1]);
let single_gt = stream::from_iter(vec![10]);
let multi = stream::from_iter(vec![1,2]);
let multi_gt = stream::from_iter(vec![1,5]);

assert_eq!(single.clone().le(single.clone()).await, true);
assert_eq!(single.clone().le(single_gt.clone()).await, true);
assert_eq!(multi.clone().le(single_gt.clone()).await, true);
assert_eq!(multi_gt.clone().le(multi.clone()).await, false);

fn lt<S>(self, other: S) -> LtFuture<Self, S>

where Self: Sized + Stream, S: Stream, <Self as Stream>::Item: PartialOrd<S::Item>,

Determines if the elements of this Stream are lexicographically less than those of another.

Examples

use async_std::prelude::*;
use async_std::stream;

let single = stream::from_iter(vec![1]);
let single_gt = stream::from_iter(vec![10]);
let multi = stream::from_iter(vec![1,2]);
let multi_gt = stream::from_iter(vec![1,5]);

assert_eq!(single.clone().lt(single.clone()).await, false);
assert_eq!(single.clone().lt(single_gt.clone()).await, true);
assert_eq!(multi.clone().lt(single_gt.clone()).await, true);
assert_eq!(multi_gt.clone().lt(multi.clone()).await, false);

Object Safety

This trait is not object safe.

Implementors

impl<T: Stream + ?Sized> StreamExt for T