[−][src]Trait futures::prelude::FutureExt

pub trait FutureExt: Future {
    fn map<U, F>(self, f: F) -> Map<Self, F>
    where
        F: FnOnce(Self::Output) -> U,
    { ... }

    fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
    where
        F: FnOnce(Self::Output) -> Fut,
        Fut: Future,
    { ... }

    fn left_future<B>(self) -> Either<Self, B>
    where
        B: Future<Output = Self::Output>,
    { ... }

    fn right_future<A>(self) -> Either<A, Self>
    where
        A: Future<Output = Self::Output>,
    { ... }

    fn into_stream(self) -> IntoStream<Self> { ... }

    fn flatten(self) -> Flatten<Self>
    where
        Self::Output: Future,
    { ... }

    fn flatten_stream(self) -> FlattenStream<Self>
    where
        Self::Output: Stream,
    { ... }

    fn fuse(self) -> Fuse<Self> { ... }

    fn inspect<F>(self, f: F) -> Inspect<Self, F>
    where
        F: FnOnce(&Self::Output),
    { ... }

    fn catch_unwind(self) -> CatchUnwind<Self>
    where
        Self: UnwindSafe,
    { ... }

    fn shared(self) -> Shared<Self>
    where
        Self::Output: Clone,
    { ... }

    fn remote_handle(self) -> (Remote<Self>, RemoteHandle<Self::Output>) { ... }

    fn boxed<'a>(
        self
    ) -> Pin<Box<dyn Future<Output = Self::Output> + 'a + Send>>
    where
        Self: Send + 'a,
    { ... }

    fn boxed_local<'a>(self) -> Pin<Box<dyn Future<Output = Self::Output> + 'a>>
    where
        Self: 'a,
    { ... }

    fn unit_error(self) -> UnitError<Self> { ... }

    fn never_error(self) -> NeverError<Self> { ... }

    fn poll_unpin(&mut self, cx: &mut Context) -> Poll<Self::Output>
    where
        Self: Unpin,
    { ... }
}

An extension trait for Futures that provides a variety of convenient adapters.

Provided methods

ⓘImportant traits for Map<Fut, F>
fn map<U, F>(self, f: F) -> Map<Self, F> where
    F: FnOnce(Self::Output) -> U, 

Map this future's output to a different type, returning a new future of the resulting type.

This function is similar to the Option::map or Iterator::map where it will change the type of the underlying future. This is useful to chain along a computation once a future has been resolved.

Note that this function consumes the receiving future and returns a wrapped version of it, similar to the existing map methods in the standard library.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let future = future::ready(1);
let new_future = future.map(|x| x + 3);
assert_eq!(new_future.await, 4);

ⓘImportant traits for Then<Fut1, Fut2, F>
fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where
    F: FnOnce(Self::Output) -> Fut,
    Fut: Future, 

Chain on a computation for when a future finished, passing the result of the future to the provided closure f.

The returned value of the closure must implement the Future trait and can represent some more work to be done before the composed future is finished.

The closure f is only run after successful completion of the self future.

Note that this function consumes the receiving future and returns a wrapped version of it.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let future_of_1 = future::ready(1);
let future_of_4 = future_of_1.then(|x| future::ready(x + 3));
assert_eq!(future_of_4.await, 4);

ⓘImportant traits for Either<A, B>
fn left_future<B>(self) -> Either<Self, B> where
    B: Future<Output = Self::Output>, 

Wrap this future in an Either future, making it the left-hand variant of that Either.

This can be used in combination with the right_future method to write if statements that evaluate to different futures in different branches.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let x = 6;
let future = if x < 10 {
    future::ready(true).left_future()
} else {
    future::ready(false).right_future()
};

assert_eq!(future.await, true);

ⓘImportant traits for Either<A, B>
fn right_future<A>(self) -> Either<A, Self> where
    A: Future<Output = Self::Output>, 

Wrap this future in an Either future, making it the right-hand variant of that Either.

This can be used in combination with the left_future method to write if statements that evaluate to different futures in different branches.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let x = 6;
let future = if x > 10 {
    future::ready(true).left_future()
} else {
    future::ready(false).right_future()
};

assert_eq!(future.await, false);

fn into_stream(self) -> IntoStream<Self>

Convert this future into a single element stream.

The returned stream contains single success if this future resolves to success or single error if this future resolves into error.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};
use futures::stream::StreamExt;

let future = future::ready(17);
let stream = future.into_stream();
let collected: Vec<_> = stream.collect().await;
assert_eq!(collected, vec![17]);

ⓘImportant traits for Flatten<Fut>
fn flatten(self) -> Flatten<Self> where
    Self::Output: Future, 

Flatten the execution of this future when the successful result of this future is itself another future.

This can be useful when combining futures together to flatten the computation out the final result. This method can only be called when the successful result of this future itself implements the IntoFuture trait and the error can be created from this future's error type.

This method is roughly equivalent to self.and_then(|x| x).

Note that this function consumes the receiving future and returns a wrapped version of it.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let nested_future = future::ready(future::ready(1));
let future = nested_future.flatten();
assert_eq!(future.await, 1);

fn flatten_stream(self) -> FlattenStream<Self> where
    Self::Output: Stream, 

Flatten the execution of this future when the successful result of this future is a stream.

This can be useful when stream initialization is deferred, and it is convenient to work with that stream as if stream was available at the call site.

Note that this function consumes this future and returns a wrapped version of it.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};
use futures::stream::{self, StreamExt};

let stream_items = vec![17, 18, 19];
let future_of_a_stream = future::ready(stream::iter(stream_items));

let stream = future_of_a_stream.flatten_stream();
let list: Vec<_> = stream.collect().await;
assert_eq!(list, vec![17, 18, 19]);

ⓘImportant traits for Fuse<Fut>
fn fuse(self) -> Fuse<Self>

Fuse a future such that poll will never again be called once it has completed. This method can be used to turn any Future into a FusedFuture.

Normally, once a future has returned Poll::Ready from poll, any further calls could exhibit bad behavior such as blocking forever, panicking, never returning, etc. If it is known that poll may be called too often then this method can be used to ensure that it has defined semantics.

If a fused future is polled after having returned Poll::Ready previously, it will return Poll::Pending, from poll again (and will continue to do so for all future calls to poll).

This combinator will drop the underlying future as soon as it has been completed to ensure resources are reclaimed as soon as possible.

ⓘImportant traits for Inspect<Fut, F>
fn inspect<F>(self, f: F) -> Inspect<Self, F> where
    F: FnOnce(&Self::Output), 

Do something with the output of a future before passing it on.

When using futures, you'll often chain several of them together. While working on such code, you might want to check out what's happening at various parts in the pipeline, without consuming the intermediate value. To do that, insert a call to inspect.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let future = future::ready(1);
let new_future = future.inspect(|&x| println!("about to resolve: {}", x));
assert_eq!(new_future.await, 1);

ⓘImportant traits for CatchUnwind<Fut>
fn catch_unwind(self) -> CatchUnwind<Self> where
    Self: UnwindSafe, 

Catches unwinding panics while polling the future.

In general, panics within a future can propagate all the way out to the task level. This combinator makes it possible to halt unwinding within the future itself. It's most commonly used within task executors. It's not recommended to use this for error handling.

Note that this method requires the UnwindSafe bound from the standard library. This isn't always applied automatically, and the standard library provides an AssertUnwindSafe wrapper type to apply it after-the fact. To assist using this method, the Future trait is also implemented for AssertUnwindSafe<F> where F implements Future.

This method is only available when the std feature of this library is activated, and it is activated by default.

Examples

ⓘThis example is not tested
#![feature(async_await)]
use futures::future::{self, FutureExt, Ready};

let future = future::ready(2);
assert!(future.catch_unwind().await.is_ok());

let future = future::lazy(|_| -> Ready<i32> {
    unimplemented!()
});
assert!(future.catch_unwind().await.is_err());

ⓘImportant traits for Shared<Fut>
fn shared(self) -> Shared<Self> where
    Self::Output: Clone, 

Create a cloneable handle to this future where all handles will resolve to the same result.

The shared combinator method provides a method to convert any future into a cloneable future. It enables a future to be polled by multiple threads.

This method is only available when the std feature of this library is activated, and it is activated by default.

Examples

#![feature(async_await)]
use futures::future::{self, FutureExt};

let future = future::ready(6);
let shared1 = future.shared();
let shared2 = shared1.clone();

assert_eq!(6, shared1.await);
assert_eq!(6, shared2.await);
// Note, unlike most examples this is written in the context of a
// synchronous function to better illustrate the cross-thread aspect of
// the `shared` combinator.

#![feature(async_await)]
use futures::future::{self, FutureExt};
use futures::executor::block_on;
use std::thread;

let future = future::ready(6);
let shared1 = future.shared();
let shared2 = shared1.clone();
let join_handle = thread::spawn(move || {
    assert_eq!(6, block_on(shared2));
});
assert_eq!(6, shared1.await);
join_handle.join().unwrap();

fn remote_handle(self) -> (Remote<Self>, RemoteHandle<Self::Output>)

Turn this future into a future that yields () on completion and sends its output to another future on a separate task.

This can be used with spawning executors to easily retrieve the result of a future executing on a separate task or thread.

ⓘImportant traits for Pin<P>
fn boxed<'a>(self) -> Pin<Box<dyn Future<Output = Self::Output> + 'a + Send>> where
    Self: Send + 'a, 

Wrap the future in a Box, pinning it.

ⓘImportant traits for Pin<P>
fn boxed_local<'a>(self) -> Pin<Box<dyn Future<Output = Self::Output> + 'a>> where
    Self: 'a, 

Wrap the future in a Box, pinning it.

Similar to boxed, but without the Send requirement.

ⓘImportant traits for UnitError<Fut>
fn unit_error(self) -> UnitError<Self>

Turns a Future<Output = T> into a TryFuture<Ok = T, Error = ()>.

ⓘImportant traits for NeverError<Fut>
fn never_error(self) -> NeverError<Self>

Turns a Future<Output = T> into a TryFuture<Ok = T, Error = !>.

fn poll_unpin(&mut self, cx: &mut Context) -> Poll<Self::Output> where
    Self: Unpin, 

A convenience for calling Future::poll on Unpin future types.

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Implementors

impl<T> FutureExt for T where
    T: Future + ?Sized, [src]

ⓘImportant traits for Map<Fut, F>
fn map<U, F>(self, f: F) -> Map<Self, F> where
    F: FnOnce(Self::Output) -> U, [src]

ⓘImportant traits for Then<Fut1, Fut2, F>
fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where
    F: FnOnce(Self::Output) -> Fut,
    Fut: Future, [src]

ⓘImportant traits for Either<A, B>
fn left_future<B>(self) -> Either<Self, B> where
    B: Future<Output = Self::Output>, [src]

ⓘImportant traits for Either<A, B>
fn right_future<A>(self) -> Either<A, Self> where
    A: Future<Output = Self::Output>, [src]

fn into_stream(self) -> IntoStream<Self>[src]

ⓘImportant traits for Flatten<Fut>
fn flatten(self) -> Flatten<Self> where
    Self::Output: Future, [src]

fn flatten_stream(self) -> FlattenStream<Self> where
    Self::Output: Stream, [src]

ⓘImportant traits for Fuse<Fut>
fn fuse(self) -> Fuse<Self>[src]

ⓘImportant traits for Inspect<Fut, F>
fn inspect<F>(self, f: F) -> Inspect<Self, F> where
    F: FnOnce(&Self::Output), [src]

ⓘImportant traits for CatchUnwind<Fut>
fn catch_unwind(self) -> CatchUnwind<Self> where
    Self: UnwindSafe, [src]

ⓘImportant traits for Shared<Fut>
fn shared(self) -> Shared<Self> where
    Self::Output: Clone, [src]

fn remote_handle(self) -> (Remote<Self>, RemoteHandle<Self::Output>)[src]

ⓘImportant traits for Pin<P>
fn boxed<'a>(self) -> Pin<Box<dyn Future<Output = Self::Output> + 'a + Send>> where
    Self: Send + 'a, [src]

ⓘImportant traits for Pin<P>
fn boxed_local<'a>(self) -> Pin<Box<dyn Future<Output = Self::Output> + 'a>> where
    Self: 'a, [src]

ⓘImportant traits for UnitError<Fut>
fn unit_error(self) -> UnitError<Self>[src]

ⓘImportant traits for NeverError<Fut>
fn never_error(self) -> NeverError<Self>[src]

fn poll_unpin(&mut self, cx: &mut Context) -> Poll<Self::Output> where
    Self: Unpin, [src]

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