Elision rules are as follows:
🔗1.
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 {
input
}
🔗2.
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)
}
🔗3.
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
}
}
🔗4.
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