[][src]Crate pin_project

An attribute that creates a projection struct covering all the fields.

Examples

unsafe_project attribute creates a projection struct covering all the fields.

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

#[unsafe_project(Unpin)] // `(Unpin)` is optional (create the appropriate conditional Unpin implementation)
struct Foo<T, U> {
    #[pin]
    future: T,
    field: U,
}

impl<T, U> Foo<T, U> {
    fn baz(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 (optional).
// impl<T: Unpin, U> Unpin for Foo<T, U> {}
Code like this will be generated:
struct Foo<T, U> {
    future: T,
    field: U,
}

struct __FooProjection<'__a, T, U> {
    future: ::core::pin::Pin<&'__a mut T>,
    field: &'__a mut U,
}

impl<T, U> Foo<T, U> {
    fn project<'__a>(self: ::core::pin::Pin<&'__a mut Self>) -> __FooProjection<'__a, T, U> {
        unsafe {
            let this = ::core::pin::Pin::get_unchecked_mut(self);
            __FooProjection {
                future: ::core::pin::Pin::new_unchecked(&mut this.future),
                field: &mut this.field,
            }
        }
    }
}

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

unsafe_project also supports enums, but to use it ergonomically, you need to use the project attribute.

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

#[unsafe_project(Unpin)] // `(Unpin)` is optional (create the appropriate conditional Unpin implementation)
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(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 (optional).
// impl<T, U> Unpin for Foo<T, U> where T: Unpin {}
Code like this will be generated:
enum Foo<T, U> {
    Future(T),
    Done(U),
}

enum __FooProjection<'__a, T, U> {
    Future(::core::pin::Pin<&'__a mut T>),
    Done(&'__a mut U),
}

impl<T, U> Foo<T, U> {
    fn project<'__a>(self: ::core::pin::Pin<&'__a mut Self>) -> __FooProjection<'__a, T, U> {
        unsafe {
            match ::core::pin::Pin::get_unchecked_mut(self) {
                Foo::Future(_x0) => __FooProjection::Future(::core::pin::Pin::new_unchecked(_x0)),
                Foo::Done(_x0) => __FooProjection::Done(_x0),
            }
        }
    }
}

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

See unsafe_project and project for more details.

Attribute Macros

project

An attribute to support pattern matching.

unsafe_project

An attribute that creates a projection struct covering all the fields.