Rust for C-Programmers

13.5 Performance Considerations

13.5.1 Iterator Laziness

Lazy Evaluation delays computation until necessary.

Example:

fn main() {
    let numbers = vec![1, 2, 3, 4, 5];
    let mut iter = numbers.iter().map(|x| x * 2).filter(|x| *x > 5); // no action
    assert_eq!(iter.next(), Some(6)); // processing starts here!
    assert_eq!(iter.next(), Some(8));
    assert_eq!(iter.next(), Some(10));
    assert_eq!(iter.next(), None);
}

13.5.2 Zero-Cost Abstractions

Rust's iterators are designed to have no runtime overhead compared to manual implementations.

Iterator vs. Loop:

Using Iterators:

fn main() {
    let numbers = vec![1, 2, 3, 4, 5];
    let total: i32 = numbers.iter().map(|x| x * 2).sum();
    println!("Total: {}", total); // Output: Total: 30
}

Using a Loop:

fn main() {
    let numbers = vec![1, 2, 3, 4, 5];
    let mut total = 0;
    for x in &numbers {
        total += x * 2;
    }
    println!("Total: {}", total); // Output: Total: 30
}