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//@ edition:2018
//@ check-pass
trait Trait<'a, 'b> {}
impl<T> Trait<'_, '_> for T {}
// `Invert<'a> <: Invert<'b>` if `'b: 'a`, unlike 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 Invert<'a>(fn(&'a u8));
fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Invert<'a>, b: Invert<'b>) -> impl Trait<'d, 'e>
where
'c: 'a,
'c: 'b,
'd: 'c,
{
// Representing the where clauses as a graph, where `A: B` is an
// edge `B -> A`:
//
// ```
// 'a -> 'c -> 'd
// ^
// |
// 'b
// ```
//
// Meanwhile we return a value &'0 u8 where we have the constraints:
//
// ```
// '0: 'a
// '0: 'b
// '0 in ['d, 'e]
// ```
//
// Here, ignoring the "in" constraint, the minimal choice for `'0`
// is `'c`, but that is not in the "in set". Still, that reduces
// the range of options in the "in set" to just `'d` (`'e: 'c`
// does not hold).
let p = if condition() { a } else { b };
p
}
fn condition() -> bool {
true
}
fn main() {}
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