Iterator Adapters

Adapters transform iterators lazily: map, filter, take, skip, zip, flat_map, enumerate, peekable.

Recipe

fn main() {
    let out: Vec<i32> = (0..10)
        .filter(|n| n % 2 == 0)
        .map(|n| n * 2)
        .collect();
    println!("{:?}", out);
}

When to reach for this: Functional-style transforms without intermediate Vec unless needed.

Working Example

fn parse_lines(lines: &str) -> Result<Vec<i32>, std::num::ParseIntError> {
    lines.lines()
        .map(|l| l.trim().parse())
        .collect()
}
 
fn main() {
    let data = "1\n2\n3\n";
    println!("{:?}", parse_lines(data));
}

What this demonstrates:

• lines() adapter on &str
• map + collect into Result<Vec<_>, _>
• Lazy until collect

Deep Dive

Chain order matters: filter before map avoids useless work. flat_map flattens Iterator<Item=impl Iterator>.

Gotchas

• Multiple passes on cold iterator - Consumed after first pass. Fix: collect then reuse vec.
• Closures capturing references - Lifetime limits. Fix: move closure or owned data.
• Infinite zip shorter - Zip ends on shortest. Fix: zip_longest crates if needed.
• filter_map vs map+filter - Single pass with filter_map.
• Collect type inference - Turbofish needed sometimes.

Alternatives

FAQs

Related

• The Iterator Trait
• Consuming Iterators
• Iterator + Closure Patterns
• Fallible Iterators & collect()

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.