error: unsatisfied lifetime constraints --> $DIR/regions-creating-enums4.rs:17:5 | LL | fn mk_add_bad2<'a,'b>(x: &'a ast<'a>, y: &'a ast<'a>, z: &ast) -> ast<'b> { | -- -- lifetime `'b` defined here | | | lifetime `'a` defined here LL | ast::add(x, y) //~ ERROR cannot infer | ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'b` error: aborting due to previous error