72 lines
1.7 KiB
Rust
72 lines
1.7 KiB
Rust
// edition: 2021
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// known-bug: #108309
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#![feature(async_fn_in_trait)]
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#![feature(min_specialization)]
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struct MyStruct;
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trait MyTrait<T> {
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async fn foo(_: T) -> &'static str;
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}
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impl<T> MyTrait<T> for MyStruct {
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default async fn foo(_: T) -> &'static str {
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"default"
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}
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}
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impl MyTrait<i32> for MyStruct {
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async fn foo(_: i32) -> &'static str {
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"specialized"
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}
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}
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async fn async_main() {
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assert_eq!(MyStruct::foo(42).await, "specialized");
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assert_eq!(indirection(42).await, "specialized");
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}
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async fn indirection<T>(x: T) -> &'static str {
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//explicit type coercion is currently necessary
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// because of https://github.com/rust-lang/rust/issues/67918
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<MyStruct as MyTrait<T>>::foo(x).await
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}
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// ------------------------------------------------------------------------- //
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// Implementation Details Below...
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use std::future::Future;
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use std::pin::Pin;
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use std::task::*;
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pub fn noop_waker() -> Waker {
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let raw = RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE);
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// SAFETY: the contracts for RawWaker and RawWakerVTable are upheld
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unsafe { Waker::from_raw(raw) }
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}
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const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
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unsafe fn noop_clone(_p: *const ()) -> RawWaker {
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RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE)
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}
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unsafe fn noop(_p: *const ()) {}
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fn main() {
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let mut fut = async_main();
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// Poll loop, just to test the future...
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let waker = noop_waker();
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let ctx = &mut Context::from_waker(&waker);
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loop {
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match unsafe { Pin::new_unchecked(&mut fut).poll(ctx) } {
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Poll::Pending => {}
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Poll::Ready(()) => break,
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}
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}
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}
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