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#![feature(type_alias_impl_trait)]
use std::marker::PhantomData;
trait ProofForConversion<'a, 'b> {
fn convert<T: ?Sized>(_: PhantomData<Self>, r: &'a T) -> &'b T;
}
impl<'a, 'b> ProofForConversion<'a, 'b> for &'b &'a () {
fn convert<T: ?Sized>(_: PhantomData<Self>, r: &'a T) -> &'b T {
r
}
}
type Converter<'a, 'b> = impl ProofForConversion<'a, 'b>;
//~^ ERROR reference has a longer lifetime than the data it references
// Even _defining_use with an explicit `'a: 'b` compiles fine, too.
fn _defining_use<'a, 'b>(x: &'b &'a ()) -> Converter<'a, 'b> {
x
}
fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
Converter::<'a, 'b>::convert(PhantomData, x)
}
fn main() {
let d;
{
let x = "Hello World".to_string();
d = extend_lifetime(&x);
}
println!("{}", d);
}
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