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// edition: 2021
// known-bug: #108309
#![feature(async_fn_in_trait)]
#![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,
}
}
}
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