Generics & Lifetimes in Rust

From the Rust cheat sheet · Generics & Lifetimes · verified Jul 2026

Generics & Lifetimes

Generic functions, structs, and lifetime annotations.

rust

// Generic function
fn largest<T: PartialOrd>(list: &[T]) -> &T {
    let mut max = &list[0];
    for item in list { if item > max { max = item; } }
    max
}

// Generic struct
struct Wrapper<T> { value: T }

// Lifetime annotation — tells Rust how long references live
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() { x } else { y }
}

💡 Lifetimes don't change how long data lives — they help the compiler verify references are valid

⚡ Most lifetimes are inferred (elision rules) — you only annotate when the compiler asks

📌 'static means the reference can live for the entire program — string literals are 'static

🟢 Rule: if a function returns a reference, it must come from an input — not from local data

genericslifetimesbounds

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