Mastering Rust - Second Edition

Lifetimes in user defined types

If a struct definition has fields that are reference to any type, we need to explicitly specify how long those references will live. The syntax is similar to that of function signatures: we first declare the lifetime names on the struct line, and then use them in the fields.

Here's what the syntax looks like in its simplest form:

//  lifetime_struct.rsstruct Number<'a> {     num: &'a u8 }fn main() {    let _n = Number {num: &545}; }

The definition of Number lives as long as the reference for num.