What is the cost of bounds checking

Rust's bounds checking has zero runtime cost in optimized builds when the compiler can prove safety, otherwise it incurs a minimal constant overhead to prevent panics.

The cost of bounds checking in Rust is zero at runtime for safe code because the compiler optimizes away redundant checks, but it may incur a small, constant overhead for necessary checks to prevent panics on invalid access. Rust achieves this through its ownership system and strict compile-time guarantees, ensuring memory safety without the performance penalty typical of garbage-collected languages.

let v = vec![1, 2, 3];
let third = v.get(2); // Safe, returns Option<&i32>
let third = &v[2];    // Safe, panics if index is out of bounds

In debug builds, the compiler includes these checks to help catch bugs early, but in release builds (cargo build --release), aggressive optimizations often eliminate them entirely when the compiler can prove the index is valid.

Bounds checking ensures you don't access data outside a list's limits, preventing crashes. In Rust, this safety check usually costs nothing extra because the compiler is smart enough to remove unnecessary checks or prove they aren't needed. Think of it like a security guard who only checks your ID if they can't already see your face; if they know you, they let you pass instantly.