Iterator trait and combinators for zero-cost collection processing

Marcus Chen Jan 2026

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fn main() {
    let numbers = vec![1, 2, 3, 4, 5];

    let sum: i32 = numbers
        .iter()
        .filter(|&&x| x % 2 == 0)
        .map(|&x| x * 2)
        .sum();

    println!("Sum of doubled evens: {}", sum);
}

1 file · rust Explain with highlit

Rust's Iterator trait provides a rich set of combinators (.map(), .filter(), .fold(), etc.) that compose without allocating intermediate collections. Iterators are lazy: they don't do work until you consume them with .collect(), .for_each(), or similar. The compiler optimizes iterator chains into tight loops, often matching hand-written imperative code. I use iterators for data transformations, parsing, and anywhere I'd use loops in other languages. The key is that combinators are zero-cost abstractions: they're as fast as manual loops but more expressive and harder to get wrong. For parallel processing, rayon provides a drop-in replacement with .par_iter(). This functional style is idiomatic Rust and scales better than imperative loops.