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//@ check-fail
//@ known-bug: unknown
// This should pass, but we need an extension of implied bounds (probably).
pub trait AsRef2 {
type Output<'a> where Self: 'a;
fn as_ref2<'a>(&'a self) -> Self::Output<'a>;
}
impl<T> AsRef2 for Vec<T> {
type Output<'a> = &'a [T] where Self: 'a;
fn as_ref2<'a>(&'a self) -> Self::Output<'a> {
&self[..]
}
}
#[derive(Debug)]
struct Foo<T>(T);
#[derive(Debug)]
struct FooRef<'a, U>(&'a [U]);
impl<'b, T, U> AsRef2 for Foo<T>
where
// * `for<'b, 'c> T: AsRef2<Output<'b> = &'c [U]>>` does not work
//
// * `U` is unconstrained but should be allowed in this context because `Output` is
// an associated type
T: AsRef2<Output<'b> = &'b [U]>,
U: 'b
{
type Output<'a> = FooRef<'a, U> where Self: 'a;
fn as_ref2<'a>(&'a self) -> Self::Output<'a> {
FooRef(self.0.as_ref2())
}
}
fn main() {
let foo = Foo(vec![1, 2, 3]);
dbg!(foo.as_ref2());
}
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