In a fn
type, a lifetime appears only in the return type, and not in the arguments types.
Erroneous code example:
fn main() { // Here, `'a` appears only in the return type: let x: for<'a> fn() -> &'a i32; }
To fix this issue, either use the lifetime in the arguments, or use 'static
. Example:
fn main() { // Here, `'a` appears only in the return type: let x: for<'a> fn(&'a i32) -> &'a i32; let y: fn() -> &'static i32; }
Note: The examples above used to be (erroneously) accepted by the compiler, but this was since corrected. See issue #33685 for more details.