[][src]Crate pin_project

A crate for safe and ergonomic pin-projection.

This crate provides the following attribute macros:

  • pin_project - An attribute that creates a projection struct covering all the fields.
  • pinned_drop - An attribute for annotating a function that implements Drop.
  • project - An attribute to support pattern matching.

Examples

pin_project attribute creates a projection struct covering all the fields.

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

#[pin_project]
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
    }
}
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 Drop implementation.
impl<T, U> Drop for Foo<T, U> {
    fn drop(&mut self) {
        // Do nothing. The precense of this Drop
        // impl ensures that the user can't provide one of their own
    }
}

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

See pin_project attribute for more details.

Traits

UnsafeUnpin

A trait used for custom implementations of Unpin. This trait is used in conjunction with the UnsafeUnpin argument to pin_project