Example
fn foo<'a>(x: &'a u32) {
// ...
}
This specifies that foo has lifetime 'a, and the parameter x must have a lifetime of at least 'a. Function lifetimes are usually omitted through lifetime elision:
fn foo(x: &u32) {
// ...
}
In the case that a function takes multiple references as parameters and returns a reference, the compiler cannot infer the lifetime of result through lifetime elision.
error[E0106]: missing lifetime specifier
1 | fn foo(bar: &str, baz: &str) -> &i32 {
| ^ expected lifetime parameter
Instead, the lifetime parameters should be explicitly specified.
// Return value of `foo` is valid as long as `bar` and `baz` are alive.
fn foo<'a>(bar: &'a str, baz: &'a str) -> &'a i32 {
Functions can take multiple lifetime parameters too.
// Return value is valid for the scope of `bar`
fn foo<'a, 'b>(bar: &'a str, baz: &'b str) -> &'a i32 {
