error: lifetime may not live long enough --> $DIR/match-ref-mut-invariance.rs:10:9 | LL | impl<'b> S<'b> { | -- lifetime `'b` defined here LL | fn bar<'a>(&'a mut self) -> &'a mut &'a i32 { | -- lifetime `'a` defined here LL | match self.0 { ref mut x => x } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ associated function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a` | = help: consider adding the following bound: `'a: 'b` = note: requirement occurs because of a mutable reference to `&i32` = note: mutable references are invariant over their type parameter = help: see for more information about variance error: aborting due to previous error