Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
47 lines (39 sloc) 1.08 KB
// edition:2018
// build-pass (FIXME(62277): could be check-pass?)
// revisions: migrate mir
//[mir]compile-flags: -Z borrowck=mir
#![feature(member_constraints)]
trait Trait<'a, 'b> {}
impl<T> Trait<'_, '_> for T {}
// `Ordinary<'a> <: Ordinary<'b>` if `'a: 'b`, as with most types.
//
// I am purposefully avoiding the terms co- and contra-variant because
// their application to regions depends on how you interpreted Rust
// regions. -nikomatsakis
struct Ordinary<'a>(&'a u8);
// Here we wind up selecting `'e` in the hidden type because
// we need something outlived by both `'a` and `'b` and only `'e` applies.
fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
where
'a: 'e,
'b: 'e,
'a: 'd,
{
// We return a value:
//
// ```
// 'a: '0
// 'b: '1
// '0 in ['d, 'e]
// ```
//
// but we don't have it.
//
// We are forced to pick that '0 = 'e, because only 'e is outlived by *both* 'a and 'b.
let p = if condition() { a } else { b };
p
}
fn condition() -> bool {
true
}
fn main() {}
You can’t perform that action at this time.