| // edition:2018 |
| |
| #![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 need something outlived by `'a` *and* outlived by `'b`, but |
| // we can only name `'a` and `'b` (and neither suits). So we get an |
| // error. Somewhat unfortunate, though, since the caller would have to |
| // consider the loans for both `'a` and `'b` alive. |
| |
| fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> |
| //~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds |
| { |
| // We return a value: |
| // |
| // ``` |
| // 'a: '0 |
| // 'b: '1 |
| // '0 in ['a, 'b] |
| // ``` |
| // |
| // but we don't have it. |
| // |
| // We are forced to pick that '0 = 'e, because only 'e is outlived by *both* 'a and 'b. |
| if condition() { a } else { b } |
| } |
| |
| fn condition() -> bool { |
| true |
| } |
| |
| fn main() {} |
