---
title: Rust Lifetimes
editedAt:
  - 2025-12-01T19:58:38.251Z
---

- lifetimes = how long references are valid
- prevent dangling references (memory safety)
- every reference has a lifetime (compiler tracks it)
- most lifetimes are inferred automatically
- explicit lifetimes use `'a`, `'b`, etc
- needed when returning references or storing refs in structs
- ```rust
    fn longest<'a>(x: &'a str, y: &'a str) -> &'a str
    ```
- - expl: return ref will be valid as long as x & y are valid
- structs with refs need lifetime annotations:
- - ```rust
    struct foo<'a> { part: &'a str }
    ```
- lifetimes only exist at compile time
- they describe validity; they don’t extend object life