[−][src]Trait futures::future::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 join<Fut2>(self, other: Fut2) -> Join<Self, Fut2>
    where
        Fut2: Future,
    { ... }

    fn join3<Fut2, Fut3>(
        self, 
        future2: Fut2, 
        future3: Fut3
    ) -> Join3<Self, Fut2, Fut3>
    where
        Fut2: Future,
        Fut3: Future,
    { ... }

    fn join4<Fut2, Fut3, Fut4>(
        self, 
        future2: Fut2, 
        future3: Fut3, 
        future4: Fut4
    ) -> Join4<Self, Fut2, Fut3, Fut4>
    where
        Fut2: Future,
        Fut3: Future + Future,
        Fut4: Future,
    { ... }

    fn join5<Fut2, Fut3, Fut4, Fut5>(
        self, 
        future2: Fut2, 
        future3: Fut3, 
        future4: Fut4, 
        future5: Fut5
    ) -> Join5<Self, Fut2, Fut3, Fut4, Fut5>
    where
        Fut2: Future,
        Fut3: Future + Future,
        Fut4: Future,
        Fut5: Future,
    { ... }

    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> { ... }

    fn boxed(self) -> PinBox<Self> { ... }

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

    fn with_spawner<Sp>(self, spawner: Sp) -> WithSpawner<Self, Sp>
    where
        Sp: Spawn,
    { ... }

    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

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, await_macro, futures_api)]
use futures::future::{self, FutureExt};

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

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, await_macro, futures_api)]
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!(await!(future_of_4), 4);

Joins the result of two futures, waiting for them both to complete.

This function will return a new future which awaits both this and the other future to complete. The returned future will finish with a tuple of both results.

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

Examples

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

let a = future::ready(1);
let b = future::ready(2);
let pair = a.join(b);

assert_eq!(await!(pair), (1, 2));

Same as join, but with more futures.

Examples

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

let a = future::ready(1);
let b = future::ready(2);
let c = future::ready(3);
let tuple = a.join3(b, c);

assert_eq!(await!(tuple), (1, 2, 3));

Same as join, but with more futures.

Examples

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

let a = future::ready(1);
let b = future::ready(2);
let c = future::ready(3);
let d = future::ready(4);
let tuple = a.join4(b, c, d);

assert_eq!(await!(tuple), (1, 2, 3, 4));

Same as join, but with more futures.

Examples

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

let a = future::ready(1);
let b = future::ready(2);
let c = future::ready(3);
let d = future::ready(4);
let e = future::ready(5);
let tuple = a.join5(b, c, d, e);

assert_eq!(await!(tuple), (1, 2, 3, 4, 5));

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, await_macro, futures_api)]
use futures::future::{self, FutureExt};
use futures::stream::StreamExt;

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

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, await_macro, futures_api)]
use futures::future::{self, FutureExt};

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

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, await_macro, futures_api)]
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<_> = await!(stream.collect());
assert_eq!(list, vec![17, 18, 19]);

Fuse a future such that poll will never again be called once it has completed.

Currently once a future has returned Ready or Err 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.

Once a future has been fused and it returns a completion from poll, then it will forever return Pending from poll again (never resolve). This, unlike the trait's poll method, is guaranteed.

This combinator will drop this future as soon as it's been completed to ensure resources are reclaimed as soon as possible.

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, await_macro, futures_api)]
use futures::future::{self, FutureExt};

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

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, await_macro, futures_api)]
use futures::future::{self, FutureExt, Ready};

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

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

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

The shared() 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, await_macro, futures_api)]
use futures::future::{self, FutureExt};

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

assert_eq!(6, await!(shared1));
assert_eq!(6, await!(shared2));
// 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.

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, block_on(shared1));
join_handle.join().unwrap();

Wrap the future in a Box, pinning it.

Turns a Future into a TryFuture with Error = ().

Assigns the provided Spawn to be used when spawning tasks from within the future.

Examples

#![feature(async_await, await_macro, futures_api)]
use futures::spawn;
use futures::executor::ThreadPool;
use futures::future::FutureExt;
use std::thread;

let pool = ThreadPool::builder()
    .name_prefix("my-pool-")
    .pool_size(1)
    .create().unwrap();

 let val = await!((async {
     assert_ne!(thread::current().name(), Some("my-pool-0"));

     // Spawned task runs on the executor specified via `with_spawner`
     spawn!(async {
         assert_eq!(thread::current().name(), Some("my-pool-0"));
     }).unwrap();
 }).with_spawner(pool));

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

Implementors