Rust lifetime rules

Elision rules are as follows:


Each elided lifetime in input position becomes a distinct lifetime parameter.

pub fn do_something<'a: 'b, 'b>(input: &'a str, other_input: &'b str) -> &'a str {


If there is exactly one input lifetime position (elided or not), that lifetime is assigned to all elided output lifetimes.

pub fn first_do_something(input: &str) -> (&str, &str) {
    (input, input)


If there are multiple input lifetime positions, but one of them is &self or &mut self, the lifetime of self is assigned to all elided output lifetimes.

struct Config { 
    name: String

impl Config {
    fn name(&self, other_useless_val: &str) -> &str {
        &self.name // <- same lifetime as &self


Otherwise, it is an error to elide an output lifetime.

Given the following:

fn lifetimes<'a: 'b, 'b>(a: &'a str, b: &'b str) {}

Read this as "'a will live for at least as long as 'b, rather than 'a has to outlive 'b. It's a small distinction but a relevant one.

See: lifetime coercion