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