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Learn Rust Coding · Lesson

Lifetimes in Structs

Borrowed fields.

Structs Can Borrow

Most structs own their data. But a struct can also hold a reference to data it does not own. When it does, the struct needs a lifetime parameter.

This guarantees the struct never outlives the borrowed data.

Declaring a Lifetime on a Struct

Add the lifetime in angle brackets after the struct name, then use it on the reference field. This says the struct cannot outlive that reference.

struct Excerpt<'a> {
    text: &'a str,
}

fn main() {
    let novel = String::from("Call me Ishmael. Some years ago...");
    let first = novel.split('.').next().unwrap();
    let e = Excerpt { text: first };
    println!("{}", e.text);
}

All lessons in this course

  1. Why Lifetimes
  2. Lifetime Annotations
  3. Lifetimes in Structs
  4. Elision Rules
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