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//@ build-pass
#![feature(type_alias_impl_trait)]
use std::marker::PhantomData;
/* copied Index and TryFrom for convenience (and simplicity) */
trait MyIndex<T> {
type O;
fn my_index(self) -> Self::O;
}
trait MyFrom<T>: Sized {
type Error;
fn my_from(value: T) -> Result<Self, Self::Error>;
}
/* MCVE starts here */
mod f {
pub trait F {}
impl F for () {}
pub type DummyT<T> = impl F;
fn _dummy_t<T>() -> DummyT<T> {}
}
use f::DummyT;
struct Phantom1<T>(PhantomData<T>);
struct Phantom2<T>(PhantomData<T>);
struct Scope<T>(Phantom2<DummyT<T>>);
impl<T> Scope<T> {
fn new() -> Self {
unimplemented!()
}
}
impl<T> MyFrom<Phantom2<T>> for Phantom1<T> {
type Error = ();
fn my_from(_: Phantom2<T>) -> Result<Self, Self::Error> {
unimplemented!()
}
}
impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<Phantom1<T>> for Scope<U> {
type O = T;
fn my_index(self) -> Self::O {
MyFrom::my_from(self.0).ok().unwrap()
}
}
fn main() {
let _pos: Phantom1<DummyT<()>> = Scope::new().my_index();
}
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