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//@ check-pass
trait Yokeable<'a>: 'static {
type Output: 'a;
}
trait IsCovariant<'a> {}
struct Yoke<Y: for<'a> Yokeable<'a>> {
data: Y,
}
// impl<Y: for<'a> Yokeable<'a>> Yoke<Y> {
// fn project<Y2: for<'a> Yokeable<'a>>(
// &self,
// f: for<'a> fn(<Y as Yokeable<'a>>::Output, &'a (),
// ) -> <Y2 as Yokeable<'a>>::Output) -> Yoke<Y2> {
// unimplemented!()
// }
// }
fn upcast<Y>(x: Yoke<Y>) -> Yoke<Box<dyn IsCovariant<'static> + 'static>> where
Y: for<'a> Yokeable<'a>,
for<'a> <Y as Yokeable<'a>>::Output: IsCovariant<'a>
{
// x.project(|data, _| {
// Box::new(data)
// })
unimplemented!()
}
impl<'a> Yokeable<'a> for Box<dyn IsCovariant<'static> + 'static> {
type Output = Box<dyn IsCovariant<'a> + 'a>;
}
// this impl is mostly an example and unnecessary for the pure repro
use std::borrow::*;
impl<'a, T: ToOwned + ?Sized> Yokeable<'a> for Cow<'static, T> {
type Output = Cow<'a, T>;
}
impl<'a, T: ToOwned + ?Sized> IsCovariant<'a> for Cow<'a, T> {}
fn upcast_yoke(y: Yoke<Cow<'static, str>>) -> Yoke<Box<dyn IsCovariant<'static> + 'static>> {
upcast(y)
}
fn main() {}
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