pin-project

An attribute that would create a projection struct covering all the fields.

Documentation

Usage

Add this to your Cargo.toml:

[dependencies]
pin-project = "0.2.1"

Now, you can use pin-project:

use pin_project::unsafe_project;

The current version of pin-project requires Rust 1.33 or later.

Examples

Structs and enums are supported.

Structs

use pin_project::unsafe_project;
use std::pin::Pin;

#[unsafe_project(Unpin)]
struct Foo<T, U> {
    #[pin]
    future: T,
    field: U,
}

impl<T, U> Foo<T, U> {
    fn baz(mut self: Pin<&mut Self>) {
        let this = self.project();
        let _: Pin<&mut T> = this.future; // Pinned reference to the field
        let _: &mut U = this.field; // Normal reference to the field
    }
}

// Automatically create the appropriate conditional Unpin implementation.
// impl<T, U> Unpin for Foo<T, U> where T: Unpin {} // Conditional Unpin impl

Code like this will be generated

Enums

use pin_project::{project, unsafe_project};
use std::pin::Pin;

#[unsafe_project(Unpin)]
enum Foo<T, U> {
    Future(#[pin] T),
    Done(U),
}

impl<T, U> Foo<T, U> {
    #[project] // Nightly does not need a dummy attribute to the function.
    fn baz(mut self: Pin<&mut Self>) {
        #[project]
        match self.project() {
            Foo::Future(future) => {
                let _: Pin<&mut T> = future;
            }
            Foo::Done(value) => {
                let _: &mut U = value;
            }
        }
    }
}

// Automatically create the appropriate conditional Unpin implementation.
// impl<T, U> Unpin for Foo<T, U> where T: Unpin {} // Conditional Unpin impl

Code like this will be generated

See the documentation for more details.

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.