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Trait async_std::stream::FromStream

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pub trait FromStream<T: Send> {
    fn from_stream<'a, S: IntoStream<Item = T> + 'a>(
        stream: S
    ) -> Pin<Box<dyn Future<Output = Self> + Send + 'a>>ⓘNotable traits for Pin<P>impl<P> Future for Pin<P> where
    P: DerefMut,
    <P as Deref>::Target: Future,     type Output = <<P as Deref>::Target as Future>::Output;
    where
        <S as IntoStream>::IntoStream: Send;
}
Expand description

Conversion from a Stream.

By implementing FromStream for a type, you define how it will be created from a stream. This is common for types which describe a collection of some kind.

See also: IntoStream.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream::{self, FromStream};

let five_fives = stream::repeat(5).take(5);

let v = Vec::from_stream(five_fives).await;

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Using collect to implicitly use FromStream

use async_std::prelude::*;
use async_std::stream;
let five_fives = stream::repeat(5).take(5);

let v: Vec<i32> = five_fives.collect().await;

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Implementing FromStream for your type:

use async_std::prelude::*;
use async_std::stream::{self, FromStream, IntoStream};
use std::pin::Pin;

// A sample collection, that's just a wrapper over Vec<T>
#[derive(Debug)]
struct MyCollection(Vec<i32>);

// Let's give it some methods so we can create one and add things
// to it.
impl MyCollection {
    fn new() -> MyCollection {
        MyCollection(Vec::new())
    }

    fn add(&mut self, elem: i32) {
        self.0.push(elem);
    }
}

// and we'll implement FromIterator
impl FromStream<i32> for MyCollection {
    fn from_stream<'a, S: IntoStream<Item = i32> + 'a>(
        stream: S,
    ) -> Pin<Box<dyn Future<Output = Self> + 'a + Send>>
   where
       <S as IntoStream>::IntoStream: Send,
   {
        let stream = stream.into_stream();

        Box::pin(async move {
            let mut c = MyCollection::new();

            let mut v = vec![];
            stream::extend(&mut v, stream).await;

            for i in v {
                c.add(i);
            }
            c
        })
    }
}

// Now we can make a new stream...
let stream = stream::repeat(5).take(5);

// ...and make a MyCollection out of it
let c = MyCollection::from_stream(stream).await;

assert_eq!(c.0, vec![5, 5, 5, 5, 5]);

// collect works too!

let stream = stream::repeat(5).take(5);
let c: MyCollection = stream.collect().await;

assert_eq!(c.0, vec![5, 5, 5, 5, 5]);

Required methods

Creates a value from a stream.

Examples

Basic usage:

use async_std::prelude::*;
use async_std::stream::{self, FromStream};

let five_fives = stream::repeat(5).take(5);

let v = Vec::from_stream(five_fives).await;

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Implementations on Foreign Types

Takes each element in the stream: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, a container with the values of each Result is returned.

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

let v = stream::from_iter(vec![1, 2]);
let res: Result<Vec<u32>, &'static str> = v.map(|x: u32|
    x.checked_add(1).ok_or("Overflow!")
).collect().await;
assert_eq!(res, Ok(vec![2, 3]));

Takes each element in the stream: if it is None, no further elements are taken, and None is returned. Should no None occur, a container with the values of each Option is returned.

Implementors