futures_util/future/mod.rs
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//! Futures
//!
//! This module contains a number of functions for working with `Future`s,
//! including the `FutureExt` trait which adds methods to `Future` types.
use core::result;
use futures_core::{Future, IntoFuture, Stream};
use futures_sink::Sink;
// Primitive futures
mod empty;
mod lazy;
mod poll_fn;
mod loop_fn;
pub use self::empty::{empty, Empty};
pub use self::lazy::{lazy, Lazy};
pub use self::poll_fn::{poll_fn, PollFn};
pub use self::loop_fn::{loop_fn, Loop, LoopFn};
// combinators
mod and_then;
mod flatten;
mod flatten_sink;
mod flatten_stream;
mod fuse;
mod into_stream;
mod join;
mod map;
mod map_err;
mod err_into;
mod or_else;
mod select;
mod then;
mod inspect;
mod inspect_err;
mod recover;
// impl details
mod chain;
pub use self::and_then::AndThen;
pub use self::flatten::Flatten;
pub use self::flatten_sink::FlattenSink;
pub use self::flatten_stream::FlattenStream;
pub use self::fuse::Fuse;
pub use self::into_stream::IntoStream;
pub use self::join::{Join, Join3, Join4, Join5};
pub use self::map::Map;
pub use self::map_err::MapErr;
pub use self::err_into::ErrInto;
pub use self::or_else::OrElse;
pub use self::select::Select;
pub use self::then::Then;
pub use self::inspect::Inspect;
pub use self::inspect_err::InspectErr;
pub use self::recover::Recover;
pub use either::Either;
if_std! {
mod catch_unwind;
mod join_all;
mod select_all;
mod select_ok;
mod shared;
mod with_executor;
pub use self::catch_unwind::CatchUnwind;
pub use self::join_all::{join_all, JoinAll};
pub use self::select_all::{SelectAll, SelectAllNext, select_all};
pub use self::select_ok::{SelectOk, select_ok};
pub use self::shared::{Shared, SharedItem, SharedError};
pub use self::with_executor::WithExecutor;
}
impl<T: ?Sized> FutureExt for T where T: Future {}
/// An extension trait for `Future`s that provides a variety of convenient
/// combinator functions.
pub trait FutureExt: Future {
/// Map this future's result 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.
///
/// The closure provided will only be called if this future is resolved
/// successfully. If this future returns an error, panics, or is dropped,
/// then the closure provided will never be invoked.
///
/// 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
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::ok::<u32, u32>(1);
/// let new_future = future.map(|x| x + 3);
/// assert_eq!(block_on(new_future), Ok(4));
/// # }
/// ```
///
/// Calling `map` on an errored `Future` has no effect:
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::err::<u32, u32>(1);
/// let new_future = future.map(|x| x + 3);
/// assert_eq!(block_on(new_future), Err(1));
/// # }
/// ```
fn map<U, F>(self, f: F) -> Map<Self, F>
where F: FnOnce(Self::Item) -> U,
Self: Sized,
{
assert_future::<U, Self::Error, _>(map::new(self, f))
}
/// Map this future's error to a different error, returning a new future.
///
/// This function is similar to the `Result::map_err` where it will change
/// the error type of the underlying future. This is useful for example to
/// ensure that futures have the same error type when used with combinators
/// like `select` and `join`.
///
/// The closure provided will only be called if this future is resolved
/// with an error. If this future returns a success, panics, or is
/// dropped, then the closure provided will never be invoked.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::future::err;
/// use futures::prelude::*;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = err::<u32, u32>(1);
/// let new_future = future.map_err(|x| x + 3);
/// assert_eq!(block_on(new_future), Err(4));
/// # }
/// ```
///
/// Calling `map_err` on a successful `Future` has no effect:
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::future::ok;
/// use futures::prelude::*;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = ok::<u32, u32>(1);
/// let new_future = future.map_err(|x| x + 3);
/// assert_eq!(block_on(new_future), Ok(1));
/// # }
/// ```
fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
where F: FnOnce(Self::Error) -> E,
Self: Sized,
{
assert_future::<Self::Item, E, _>(map_err::new(self, f))
}
/// Map this future's error to a new error type using the `Into` trait.
///
/// This function does for futures what `try!` does for `Result`,
/// by letting the compiler infer the type of the resulting error.
/// Just as `map_err` above, this is useful for example to ensure
/// that futures have the same error type when used with
/// combinators like `select` and `join`.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future;
///
/// # fn main() {
/// let future_with_err_u8 = future::err::<(), u8>(1);
/// let future_with_err_u32 = future_with_err_u8.err_into::<u32>();
/// # }
/// ```
fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized,
Self::Error: Into<E>
{
assert_future::<Self::Item, E, _>(err_into::new(self))
}
/// Chain on a computation for when a future finished, passing the result of
/// the future to the provided closure `f`.
///
/// This function can be used to ensure a computation runs regardless of
/// the conclusion of the future. The closure provided will be yielded a
/// `Result` once the future is complete.
///
/// The returned value of the closure must implement the `IntoFuture` trait
/// and can represent some more work to be done before the composed future
/// is finished. Note that the `Result` type implements the `IntoFuture`
/// trait so it is possible to simply alter the `Result` yielded to the
/// closure and return it.
///
/// If this future is dropped or panics then the closure `f` will not be
/// run.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future;
///
/// # fn main() {
/// let future_of_1 = future::ok::<u32, u32>(1);
/// let future_of_4 = future_of_1.then(|x| {
/// x.map(|y| y + 3)
/// });
///
/// let future_of_err_1 = future::err::<u32, u32>(1);
/// let future_of_4 = future_of_err_1.then(|x| {
/// match x {
/// Ok(_) => panic!("expected an error"),
/// Err(y) => future::ok::<u32, u32>(y + 3),
/// }
/// });
/// # }
/// ```
fn then<B, F>(self, f: F) -> Then<Self, B, F>
where F: FnOnce(result::Result<Self::Item, Self::Error>) -> B,
B: IntoFuture,
Self: Sized,
{
assert_future::<B::Item, B::Error, _>(then::new(self, f))
}
/// Execute another future after this one has resolved successfully.
///
/// This function can be used to chain two futures together and ensure that
/// the final future isn't resolved until both have finished. The closure
/// provided is yielded the successful result of this future and returns
/// another value which can be converted into a future.
///
/// Note that because `Result` implements the `IntoFuture` trait this method
/// can also be useful for chaining fallible and serial computations onto
/// the end of one future.
///
/// If this future is dropped, panics, or completes with an error then the
/// provided closure `f` is never called.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future::{self, FutureResult};
///
/// # fn main() {
/// let future_of_1 = future::ok::<u32, u32>(1);
/// let future_of_4 = future_of_1.and_then(|x| {
/// Ok(x + 3)
/// });
///
/// let future_of_err_1 = future::err::<u32, u32>(1);
/// future_of_err_1.and_then(|_| -> FutureResult<u32, u32> {
/// panic!("should not be called in case of an error");
/// });
/// # }
/// ```
fn and_then<B, F>(self, f: F) -> AndThen<Self, B, F>
where F: FnOnce(Self::Item) -> B,
B: IntoFuture<Error = Self::Error>,
Self: Sized,
{
assert_future::<B::Item, Self::Error, _>(and_then::new(self, f))
}
/// Execute another future if this one resolves with an error.
///
/// Return a future that passes along this future's value if it succeeds,
/// and otherwise passes the error to the closure `f` and waits for the
/// future it returns. The closure may also simply return a value that can
/// be converted into a future.
///
/// Note that because `Result` implements the `IntoFuture` trait this method
/// can also be useful for chaining together fallback computations, where
/// when one fails, the next is attempted.
///
/// If this future is dropped, panics, or completes successfully then the
/// provided closure `f` is never called.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future::{self, FutureResult};
///
/// # fn main() {
/// let future_of_err_1 = future::err::<u32, u32>(1);
/// let future_of_4 = future_of_err_1.or_else(|x| -> Result<u32, u32> {
/// Ok(x + 3)
/// });
///
/// let future_of_1 = future::ok::<u32, u32>(1);
/// future_of_1.or_else(|_| -> FutureResult<u32, u32> {
/// panic!("should not be called in case of success");
/// });
/// # }
/// ```
fn or_else<B, F>(self, f: F) -> OrElse<Self, B, F>
where F: FnOnce(Self::Error) -> B,
B: IntoFuture<Item = Self::Item>,
Self: Sized,
{
assert_future::<Self::Item, B::Error, _>(or_else::new(self, f))
}
/// Waits for either one of two differently-typed futures to complete.
///
/// This function will return a new future which awaits for either this or
/// the `other` future to complete. The returned future will finish with
/// both the value resolved and a future representing the completion of the
/// other work.
///
/// Note that this function consumes the receiving futures and returns a
/// wrapped version of them.
///
/// Also note that if both this and the second future have the same
/// success/error type you can use the `Either::split` method to
/// conveniently extract out the value at the end.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future::{self, Either};
///
/// // A poor-man's join implemented on top of select
///
/// fn join<A, B, E>(a: A, b: B) -> Box<Future<Item=(A::Item, B::Item), Error=E>>
/// where A: Future<Error = E> + 'static,
/// B: Future<Error = E> + 'static,
/// E: 'static,
/// {
/// Box::new(a.select(b).then(|res| -> Box<Future<Item=_, Error=_>> {
/// match res {
/// Ok(Either::Left((x, b))) => Box::new(b.map(move |y| (x, y))),
/// Ok(Either::Right((y, a))) => Box::new(a.map(move |x| (x, y))),
/// Err(Either::Left((e, _))) => Box::new(future::err(e)),
/// Err(Either::Right((e, _))) => Box::new(future::err(e)),
/// }
/// }))
/// }
/// # fn main() {}
/// ```
fn select<B>(self, other: B) -> Select<Self, B::Future>
where B: IntoFuture, Self: Sized
{
select::new(self, other.into_future())
}
/// 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.
///
/// Both futures must have the same error type, and if either finishes with
/// an error then the other will be dropped and that error will be
/// returned.
///
/// Note that this function consumes the receiving future and returns a
/// wrapped version of it.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let a = future::ok::<u32, u32>(1);
/// let b = future::ok::<u32, u32>(2);
/// let pair = a.join(b);
///
/// assert_eq!(block_on(pair), Ok((1, 2)));
/// # }
/// ```
///
/// If one or both of the joined `Future`s is errored, the resulting
/// `Future` will be errored:
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let a = future::ok::<u32, u32>(1);
/// let b = future::err::<u32, u32>(2);
/// let pair = a.join(b);
///
/// assert_eq!(block_on(pair), Err(2));
/// # }
/// ```
fn join<B>(self, other: B) -> Join<Self, B::Future>
where B: IntoFuture<Error=Self::Error>,
Self: Sized,
{
let f = join::new(self, other.into_future());
assert_future::<(Self::Item, B::Item), Self::Error, _>(f)
}
/// Same as `join`, but with more futures.
fn join3<B, C>(self, b: B, c: C) -> Join3<Self, B::Future, C::Future>
where B: IntoFuture<Error=Self::Error>,
C: IntoFuture<Error=Self::Error>,
Self: Sized,
{
join::new3(self, b.into_future(), c.into_future())
}
/// Same as `join`, but with more futures.
fn join4<B, C, D>(self, b: B, c: C, d: D)
-> Join4<Self, B::Future, C::Future, D::Future>
where B: IntoFuture<Error=Self::Error>,
C: IntoFuture<Error=Self::Error>,
D: IntoFuture<Error=Self::Error>,
Self: Sized,
{
join::new4(self, b.into_future(), c.into_future(), d.into_future())
}
/// Same as `join`, but with more futures.
fn join5<B, C, D, E>(self, b: B, c: C, d: D, e: E)
-> Join5<Self, B::Future, C::Future, D::Future, E::Future>
where B: IntoFuture<Error=Self::Error>,
C: IntoFuture<Error=Self::Error>,
D: IntoFuture<Error=Self::Error>,
E: IntoFuture<Error=Self::Error>,
Self: Sized,
{
join::new5(self, b.into_future(), c.into_future(), d.into_future(),
e.into_future())
}
/// 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` method to write `if`
/// statements that evaluate to different futures in different branches.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::executor::block_on;
/// use futures::future::*;
///
/// # fn main() {
/// let x = 6;
/// let future = if x < 10 {
/// ok::<_, bool>(x).left()
/// } else {
/// empty().right()
/// };
///
/// assert_eq!(x, block_on(future).unwrap());
/// # }
/// ```
#[deprecated(note = "use `left_future` instead")]
fn left<B>(self) -> Either<Self, B>
where B: Future<Item = Self::Item, Error = Self::Error>,
Self: Sized
{
Either::Left(self)
}
/// 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
///
/// ```
/// # extern crate futures;
/// use futures::executor::block_on;
/// use futures::future::*;
///
/// # fn main() {
/// let x = 6;
/// let future = if x < 10 {
/// ok::<_, bool>(x).left_future()
/// } else {
/// empty().right_future()
/// };
///
/// assert_eq!(x, block_on(future).unwrap());
/// # }
/// ```
fn left_future<B>(self) -> Either<Self, B>
where B: Future<Item = Self::Item, Error = Self::Error>,
Self: Sized
{
Either::Left(self)
}
/// 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
///
/// ```
/// # extern crate futures;
/// use futures::executor::block_on;
/// use futures::future::*;
///
/// # fn main() {
/// let x = 6;
/// let future = if x < 10 {
/// ok::<_, bool>(x).left()
/// } else {
/// empty().right()
/// };
///
/// assert_eq!(x, block_on(future).unwrap());
/// # }
/// ```
#[deprecated(note = "use `right_future` instead")]
fn right<A>(self) -> Either<A, Self>
where A: Future<Item = Self::Item, Error = Self::Error>,
Self: Sized,
{
Either::Right(self)
}
/// 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
///
/// ```
/// # extern crate futures;
/// use futures::executor::block_on;
/// use futures::future::*;
///
/// # fn main() {
/// let x = 6;
/// let future = if x < 10 {
/// ok::<_, bool>(x).left_future()
/// } else {
/// empty().right_future()
/// };
///
/// assert_eq!(x, block_on(future).unwrap());
/// # }
/// ```
fn right_future<A>(self) -> Either<A, Self>
where A: Future<Item = Self::Item, Error = Self::Error>,
Self: Sized,
{
Either::Right(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
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::ok::<_, bool>(17);
/// let stream = future.into_stream();
/// let collected: Vec<_> = block_on(stream.collect()).unwrap();
/// assert_eq!(collected, vec![17]);
///
/// let future = future::err::<bool, _>(19);
/// let stream = future.into_stream();
/// let collected: Result<Vec<_>, _> = block_on(stream.collect());
/// assert_eq!(collected, Err(19));
/// # }
/// ```
fn into_stream(self) -> IntoStream<Self>
where Self: Sized
{
into_stream::new(self)
}
/// 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
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let nested_future = future::ok::<_, u32>(future::ok::<u32, u32>(1));
/// let future = nested_future.flatten();
/// assert_eq!(block_on(future), Ok(1));
/// # }
/// ```
///
/// Calling `flatten` on an errored `Future`, or if the inner `Future` is
/// errored, will result in an errored `Future`:
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let nested_future = future::ok::<_, u32>(future::err::<u32, u32>(1));
/// let future = nested_future.flatten();
/// assert_eq!(block_on(future), Err(1));
/// # }
/// ```
fn flatten(self) -> Flatten<Self>
where Self::Item: IntoFuture<Error = <Self as Future>::Error>,
Self: Sized
{
let f = flatten::new(self);
assert_future::<<<Self as Future>::Item as IntoFuture>::Item,
<<Self as Future>::Item as IntoFuture>::Error,
_>(f)
}
/// Flatten the execution of this future when the successful result of this
/// future is a sink.
///
/// This can be useful when sink initialization is deferred, and it is
/// convenient to work with that sink as if sink was available at the
/// call site.
///
/// Note that this function consumes this future and returns a wrapped
/// version of it.
fn flatten_sink(self) -> FlattenSink<Self>
where <Self as Future>::Item: Sink<SinkError=Self::Error>,
Self: Sized
{
flatten_sink::new(self)
}
/// 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
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures::stream;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let stream_items = vec![17, 18, 19];
/// let future_of_a_stream = future::ok::<_, bool>(stream::iter_ok(stream_items));
///
/// let stream = future_of_a_stream.flatten_stream();
/// let list: Vec<_> = block_on(stream.collect()).unwrap();
/// assert_eq!(list, vec![17, 18, 19]);
/// # }
/// ```
fn flatten_stream(self) -> FlattenStream<Self>
where <Self as Future>::Item: Stream<Error=Self::Error>,
Self: Sized
{
flatten_stream::new(self)
}
/// 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 `fuse`d 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.
fn fuse(self) -> Fuse<Self>
where Self: Sized
{
let f = fuse::new(self);
assert_future::<Self::Item, Self::Error, _>(f)
}
/// Do something with the item of a future, 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. To do that, insert a call to `inspect`.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::ok::<u32, u32>(1);
/// let new_future = future.inspect(|&x| println!("about to resolve: {}", x));
/// assert_eq!(block_on(new_future), Ok(1));
/// # }
/// ```
fn inspect<F>(self, f: F) -> Inspect<Self, F>
where F: FnOnce(&Self::Item) -> (),
Self: Sized,
{
assert_future::<Self::Item, Self::Error, _>(inspect::new(self, f))
}
/// Do something with the error of a future, 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
/// to the errors at various parts in the pipeline. To do that, insert a
/// call to `inspect_err`.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future;
/// use futures::executor::block_on;
///
/// # fn main() {
/// let future = future::err::<u32, u32>(1);
/// let new_future = future.inspect_err(|&x| println!("about to error: {}", x));
/// assert_eq!(block_on(new_future), Err(1));
/// # }
/// ```
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
where F: FnOnce(&Self::Error) -> (),
Self: Sized,
{
assert_future::<Self::Item, Self::Error, _>(inspect_err::new(self, f))
}
/// 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
///
/// ```rust
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future::{self, FutureResult};
/// use futures_executor::block_on;
///
/// # fn main() {
/// let mut future = future::ok::<i32, u32>(2);
/// assert!(block_on(future.catch_unwind()).is_ok());
///
/// let mut future = future::lazy(|_| -> FutureResult<i32, u32> {
/// panic!();
/// future::ok::<i32, u32>(2)
/// });
/// assert!(block_on(future.catch_unwind()).is_err());
/// # }
/// ```
#[cfg(feature = "std")]
fn catch_unwind(self) -> CatchUnwind<Self>
where Self: Sized + ::std::panic::UnwindSafe
{
catch_unwind::new(self)
}
/// 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.
///
/// The returned `Shared` future resolves successfully with
/// `SharedItem<Self::Item>` or erroneously with `SharedError<Self::Error>`.
/// Both `SharedItem` and `SharedError` implements `Deref` to allow shared
/// access to the underlying result. Ownership of `Self::Item` and
/// `Self::Error` cannot currently be reclaimed.
///
/// This method is only available when the `std` feature of this
/// library is activated, and it is activated by default.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::ok::<_, bool>(6);
/// let shared1 = future.shared();
/// let shared2 = shared1.clone();
///
/// assert_eq!(6, *block_on(shared1).unwrap());
/// assert_eq!(6, *block_on(shared2).unwrap());
/// # }
/// ```
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use std::thread;
///
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::ok::<_, bool>(6);
/// let shared1 = future.shared();
/// let shared2 = shared1.clone();
/// let join_handle = thread::spawn(move || {
/// assert_eq!(6, *block_on(shared2).unwrap());
/// });
/// assert_eq!(6, *block_on(shared1).unwrap());
/// join_handle.join().unwrap();
/// # }
/// ```
#[cfg(feature = "std")]
fn shared(self) -> Shared<Self>
where Self: Sized
{
shared::new(self)
}
/// Handle errors generated by this future by converting them into
/// `Self::Item`.
///
/// Because it can never produce an error, the returned `Recover` future can
/// conform to any specific `Error` type, including `Never`.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::block_on;
///
/// # fn main() {
/// let future = future::err::<(), &str>("something went wrong");
/// let new_future = future.recover::<Never, _>(|_| ());
/// assert_eq!(block_on(new_future), Ok(()));
/// # }
/// ```
fn recover<E, F>(self, f: F) -> Recover<Self, E, F>
where Self: Sized,
F: FnOnce(Self::Error) -> Self::Item
{
recover::new(self, f)
}
/// Assigns the provided `Executor` to be used when spawning tasks
/// from within the future.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// # extern crate futures_executor;
/// use futures::prelude::*;
/// use futures::future;
/// use futures_executor::{block_on, spawn, ThreadPool};
///
/// # fn main() {
/// let pool = ThreadPool::new().expect("unable to create threadpool");
/// let future = future::ok::<(), _>(());
/// let spawn_future = spawn(future).with_executor(pool);
/// assert_eq!(block_on(spawn_future), Ok(()));
/// # }
/// ```
#[cfg(feature = "std")]
fn with_executor<E>(self, executor: E) -> WithExecutor<Self, E>
where Self: Sized,
E: ::futures_core::executor::Executor
{
with_executor::new(self, executor)
}
}
// Just a helper function to ensure the futures we're returning all have the
// right implementations.
fn assert_future<A, B, F>(t: F) -> F
where F: Future<Item=A, Error=B>,
{
t
}