mirror of https://github.com/rust-lang/rust
47 lines
1.5 KiB
Rust
47 lines
1.5 KiB
Rust
//@ check-pass
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#![feature(coroutine_trait, negative_impls)]
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use std::ops::{Coroutine, CoroutineState};
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use std::task::{Poll, Context};
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use std::future::{Future};
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use std::ptr::NonNull;
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use std::pin::Pin;
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fn main() {}
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#[derive(Debug, Copy, Clone)]
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pub struct ResumeTy(NonNull<Context<'static>>);
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unsafe impl Send for ResumeTy {}
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unsafe impl Sync for ResumeTy {}
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pub const fn from_coroutine<T>(gen: T) -> impl Future<Output = T::Return>
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where
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T: Coroutine<ResumeTy, Yield = ()>,
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{
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struct GenFuture<T: Coroutine<ResumeTy, Yield = ()>>(T);
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// We rely on the fact that async/await futures are immovable in order to create
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// self-referential borrows in the underlying coroutine.
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impl<T: Coroutine<ResumeTy, Yield = ()>> !Unpin for GenFuture<T> {}
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impl<T: Coroutine<ResumeTy, Yield = ()>> Future for GenFuture<T> {
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type Output = T::Return;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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// SAFETY: Safe because we're !Unpin + !Drop, and this is just a field projection.
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let gen = unsafe { Pin::map_unchecked_mut(self, |s| &mut s.0) };
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// Resume the coroutine, turning the `&mut Context` into a `NonNull` raw pointer. The
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// `.await` lowering will safely cast that back to a `&mut Context`.
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match gen.resume(ResumeTy(NonNull::from(cx).cast::<Context<'static>>())) {
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CoroutineState::Yielded(()) => Poll::Pending,
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CoroutineState::Complete(x) => Poll::Ready(x),
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}
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}
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}
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GenFuture(gen)
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}
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