note: external requirements --> $DIR/ty-param-closure-approximate-lower-bound.rs:24:24 | LL | twice(cell, value, |a, b| invoke(a, b)); | ^^^^^^ | = note: defining type: generic::::{closure#0} with closure args [ i16, for extern "rust-call" fn((std::option::Option>, &ReBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrAnon }) T)), (), ] = note: number of external vids: 2 = note: where T: '?1 note: no external requirements --> $DIR/ty-param-closure-approximate-lower-bound.rs:22:1 | LL | fn generic(value: T) { | ^^^^^^^^^^^^^^^^^^^^^^^ | = note: defining type: generic:: note: external requirements --> $DIR/ty-param-closure-approximate-lower-bound.rs:29:24 | LL | twice(cell, value, |a, b| invoke(a, b)); | ^^^^^^ | = note: defining type: generic_fail::::{closure#0} with closure args [ i16, for extern "rust-call" fn((std::option::Option>, &ReBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrAnon }) T)), (), ] = note: late-bound region is '?2 = note: number of external vids: 3 = note: where T: '?1 note: no external requirements --> $DIR/ty-param-closure-approximate-lower-bound.rs:28:1 | LL | fn generic_fail<'a, T>(cell: Cell<&'a ()>, value: T) { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: defining type: generic_fail:: error[E0309]: the parameter type `T` may not live long enough --> $DIR/ty-param-closure-approximate-lower-bound.rs:29:31 | LL | fn generic_fail<'a, T>(cell: Cell<&'a ()>, value: T) { | -- the parameter type `T` must be valid for the lifetime `'a` as defined here... LL | twice(cell, value, |a, b| invoke(a, b)); | ^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds | help: consider adding an explicit lifetime bound | LL | fn generic_fail<'a, T: 'a>(cell: Cell<&'a ()>, value: T) { | ++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0309`.