Mastering Rust - Second Edition

Lifetime elision and the rules

Any time there's a reference in a function or a type definition, there's a lifetime involved. Most of the time, you don't need to use explicit lifetime annotation is you code as the compiler is smart to infer them for you as a lot of information is already available at compile time about references.

In other words, these two function signatures are identical:

fn func_one(x: &u8) → &u8 { .. }fn func_two<'a>(x: &'a u8) → &'a u8 { .. }

In the usual case, the compiler has elided the lifetime parameter for func_one and we don't need to write it as func_two.

But the compiler can elide lifetimes only in restricted places and there are rules for elision. Before we talk about these rules, we need to talk about input ...