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//! [](https://docs.rs/async-fuse) //! [](https://crates.io/crates/async-fuse) //! [](https://github.com/udoprog/async-fuse/actions) //! //! Helpers for "fusing" asynchronous computations. //! //! A fused operation has a well-defined behavior once the operation has //! completed. For [Fuse] it means that an operation that has completed will //! *block forever* by returning [Poll::Pending]. //! //! This is similar to the [Fuse][futures-fs-fuse] type provided in futures-rs, //! but provides more utility allowing it to interact with types which does not //! implement [FusedFuture] or [FusedStream] as is now the case with all Tokio //! types since 1.0. //! //! We also use [Fuse] to represent optional values, just like [Option]. But //! [Fuse] provides implementations and functions which allow us to safely //! perform operations over the value when it's pinned. Like what's needed to //! poll a future. //! //! So we can take code that looks like this: //! //! ```rust,ignore //! let mut maybe_future = Some(future); //! //! tokio::select! { //! // NB: The async block is necessary because the future is polled eagerly //! // regardless of the condition, which could cause the `unwrap` to panic. //! value = async { maybe_future.as_mut().unwrap().await }, if maybe_future.is_some() => { //! /* do something */ //! } //! } //! ``` //! //! And rewrite it into: //! //! ```rust,ignore //! let mut maybe_future = Fuse::new(future); //! //! tokio::select! { //! value = &mut maybe_future, if !maybe_future.is_empty() => { //! /* do something */ //! } //! } //! ``` //! //! If we don't need the [else branch] to evalute, we can skip the [branch //! precondition]. Allowing us to further reduce it to: //! //! ```rust,ignore //! let mut maybe_future = Fuse::new(future); //! //! tokio::select! { //! value = &mut maybe_future => { //! /* do something */ //! } //! } //! ``` //! //! # Features //! //! * `stream` - Makes the [Fuse] implement the [Stream] trait if it contains a //! stream. //! //! # Fusing on the stack //! //! For the first example we'll be fusing the value *on the stack* using //! [tokio::pin]. We'll also be updating the fuse as it completes with another //! sleep with a configurable delay. Mimicking the behavior of [Interval]. //! //! > This is available as the `stack_ticker` example: //! > ```sh //! > cargo run --example stack_ticker //! > ``` //! //! ```rust //! use async_fuse::Fuse; //! use std::time::Duration; //! use tokio::time; //! //! # #[tokio::main] //! # async fn main() { //! let mut duration = Duration::from_millis(500); //! //! let sleep = Fuse::new(time::sleep(duration)); //! tokio::pin!(sleep); //! //! let update_duration = Fuse::new(time::sleep(Duration::from_secs(2))); //! tokio::pin!(update_duration); //! //! for _ in 0..10usize { //! tokio::select! { //! _ = &mut sleep => { //! println!("Tick"); //! sleep.set(Fuse::new(time::sleep(duration))); //! } //! _ = &mut update_duration => { //! println!("Tick faster!"); //! duration = Duration::from_millis(250); //! } //! } //! } //! # } //! ``` //! //! # Fusing on the heap //! //! For some types it might be easier to fuse the value on the heap. To make //! this easier, we provide the [Fuse::pin] constructor which provides a fused //! value which is pinned on the heap. //! //! As a result, it looks pretty similar to the above example. //! //! > This is available as the `heap_ticker` example: //! > ```sh //! > cargo run --example heap_ticker //! > ``` //! //! ```rust //! use async_fuse::Fuse; //! use std::time::Duration; //! use tokio::time; //! //! # #[tokio::main] //! # async fn main() { //! let mut duration = Duration::from_millis(500); //! //! let mut sleep = Fuse::pin(time::sleep(duration)); //! let mut update_duration = Fuse::pin(time::sleep(Duration::from_secs(2))); //! //! for _ in 0..10usize { //! tokio::select! { //! _ = &mut sleep => { //! println!("Tick"); //! sleep.set(Box::pin(time::sleep(duration))); //! } //! _ = &mut update_duration => { //! println!("Tick faster!"); //! duration = Duration::from_millis(250); //! } //! } //! } //! # } //! ``` //! //! # Fusing trait objects //! //! The following showcases how we can fuse a trait object. Trait objects are //! useful since they allow the fused value to change between distinct //! implementations. The price is that we perform dynamic dispatch which has a //! small cost. //! //! Also note that because [CoerceUnsized] is not yet stable, we cannot use //! [Fuse::pin] for convenience and have to pass a pinned box through //! [Fuse::new]. //! //! > This is available as the `trait_object_ticker` example: //! > ```sh //! > cargo run --example trait_object_ticker //! > ``` //! //! ```rust //! use async_fuse::Fuse; //! use std::future::Future; //! use std::pin::Pin; //! use std::time::Duration; //! use tokio::time; //! //! # #[tokio::main] //! # async fn main() { //! let mut duration = Duration::from_millis(500); //! //! let mut sleep: Fuse<Pin<Box<dyn Future<Output = ()>>>> = //! Fuse::new(Box::pin(time::sleep(duration))); //! //! let mut update_duration: Fuse<Pin<Box<dyn Future<Output = ()>>>> = //! Fuse::new(Box::pin(time::sleep(Duration::from_secs(2)))); //! //! for _ in 0..10usize { //! tokio::select! { //! _ = &mut sleep => { //! println!("Tick"); //! sleep.set(Box::pin(time::sleep(duration))); //! } //! _ = &mut update_duration => { //! println!("Tick faster!"); //! duration = Duration::from_millis(250); //! } //! } //! } //! # } //! ``` //! //! [branch precondition]: https://docs.rs/tokio/1.0.1/tokio/macro.select.html#avoid-racy-if-preconditions //! [CoerceUnsized]: https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html //! [else branch]: https://docs.rs/tokio/1.0.1/tokio/macro.select.html //! [Fuse::new]: https://docs.rs/async-fuse/0/async_fuse/struct.Fuse.html#method.new //! [Fuse::pin]: https://docs.rs/async-fuse/0/async_fuse/struct.Fuse.html#method.pin //! [Fuse]: https://docs.rs/async-fuse/0/async_fuse/struct.Fuse.html //! [Fuse]: https://docs.rs/async-fuse/0/async_fuse/struct.Fuse.html //! [FusedFuture]: https://docs.rs/futures/0/futures/future/trait.FusedFuture.html //! [FusedStream]: https://docs.rs/futures/0/futures/stream/trait.FusedStream.html //! [futures-fs-fuse]: https://docs.rs/futures/0/futures/future/struct.Fuse.html //! [Interval]: https://docs.rs/tokio/1/tokio/time/struct.Interval.html //! [Poll::Pending]: https://doc.rust-lang.org/std/task/enum.Poll.html#variant.Pending //! [Stream]: https://docs.rs/futures-core/0/futures_core/stream/trait.Stream.html //! [tokio::pin]: https://docs.rs/tokio/1/tokio/macro.pin.html //! [tokio::select]: https://docs.rs/tokio/1/tokio/macro.select.html #![deny(missing_docs)] mod fuse; mod poll; pub use self::fuse::Fuse; #[cfg(feature = "stream")] pub use futures_core::Stream;