# async_trait_proto

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[![docs.rs](https://img.shields.io/docsrs/async_trait_proto)](https://docs.rs/async_trait_proto/latest/async_trait_proto/)
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Async trait prototype using the desugarization described in [RFC 3185 Static Async Fn in Traits](https://rust-lang.github.io/rfcs/3185-static-async-fn-in-trait.html#equivalent-desugaring).

It should be faster than [async-trait](https://crates.io/crates/async-trait) because it doesn't use allocations on every invocation and type erasure.

[Benchmark](https://umgefahren.github.io/async-trait-proto/dev/bench/)

Requires these feature flags and a **nightly compiler**:
- `#![feature(generic_associated_types)]`
- `#![feature(type_alias_impl_trait)]`

### Example
```rust
#![feature(generic_associated_types)]
#![feature(type_alias_impl_trait)]
use async_trait_proto::async_trait_proto;
struct Foo;

#[async_trait_proto]
trait Bar {
    async fn wait(&self);
}

#[async_trait_proto]
impl Bar for Foo {
    async fn wait(&self) {
        sleep(Duration::from_secs(10)).await;
    }
}
```

##### Send + Sync
The trait definition can include attributes that indicate, that the resulting Future has to be
Send and/or Sync. This is important when using the traits with work stealing schedulers like tokio.
```rust
#![feature(generic_associated_types)]
#![feature(type_alias_impl_trait)]
use async_trait_proto::async_trait_proto;
struct Foo;

#[async_trait_proto]
trait Bar {
    #[send]
    async fn wait(&self);
}

#[async_trait_proto]
impl Bar for Foo {
    async fn wait(&self) {
        todo!()
    }
}

// this trait can now be used with tokio::spawn
async fn spawn_trait<T: Bar + Sync + Send + 'static>(foo: T) {
    let handle = tokio::spawn(async move {
        foo.wait().await;
    });
    handle.await;
}
```

On the other hand this will not compile:
```compile_fail
# #![feature(generic_associated_types)]
# #![feature(type_alias_impl_trait)]
# use async_trait_proto::async_trait_proto;
# struct Foo;

#[async_trait_proto]
trait Bar {
    async fn wait(&self);
}

# #[async_trait_proto]
# impl Bar for Foo {
#     async fn wait(&self) {
#         todo!()
#     }
# }
// this trait can not now be used with tokio::spawn
async fn spawn_trait<T: Bar + Sync + Send + 'static>(foo: T) {
    let handle = tokio::spawn(async move {
        foo.wait().await;
    });
    handle.await;
}
```

License: Unlicense