| // 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() {} |
