[−][src]Crate pin_project
An attribute that would create a projection struct covering all the fields.
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: Unpin, U> Unpin for Foo<T, U> {} // Conditional Unpin impl
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, } } } } impl<T, U> Unpin for Foo<T, U> where T: Unpin {} 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 } }
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:
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), } } } } impl<T, U> Unpin for Foo<T, U> where T: Unpin {} impl<T, U> Foo<T, U> { fn baz(mut self: Pin<&mut Self>) { match self.project() { __FooProjection::Future(future) => { let _: Pin<&mut T> = future; } __FooProjection::Done(value) => { let _: &mut U = value; } } } }
See unsafe_project
and project
for more details.
Attribute Macros
project | An attribute to support pattern matching. |
unsafe_fields | An attribute that would create projections for each struct fields. |
unsafe_project | An attribute that would create a projection struct covering all the fields. |
unsafe_variants | An attribute that would create projections for each enum variants. |