Lifetimes in Rust

Previous: Rust

Lifetimes in Rust are a type of generic for validating references. Lifetimes are inextricably linked to references and the concept of borrowing.

Lifetimes are a crucial aspect of Rust’s memory management model that ties into borrowing. A lifetime specifies the scope for which a reference to a resource is valid. In Rust, the compiler uses lifetimes to ensure that references do not outlive the data they refer to, thus preventing dangling references. Lifetimes help the compiler understand how long a reference should be considered valid, and they need to be specified when the compiler cannot automatically infer the duration itself. This makes lifetimes a powerful—though sometimes challenging, tool for managing memory safely and efficiently.

The Borrow Checker

The Rust compiler has a borrow checker that compares scopes to determine whether all borrows are valid.

fn main() {
    let r;                // ---------+-- 'a
    {                     //          |
        let x = 5;        // -+-- 'b  |
        r = &x;           //  |       |
    }                     // -+       |
    println!("r: {r}");   //          |
}                         // ---------+

The example above will not compile because the reference to x in r has a shorter lifetime ‘b than the variable r. Therefore the reference is invalid.