[−][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(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 (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(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 (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. |