Iterator Lazy Evaluation and Chaining

Snippet

Iterator Lazy Evaluation and Chaining

Rust iterators are lazy - they perform no computation until consumed by a terminal operation like collect() or sum(). Each adaptor (filter, map, take) creates a new iterator wrapping the previous one, enabling efficient chaining without intermediate collections.

snippet.rs
rust
fn main() {
    let numbers = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    
    let result: Vec<i32> = numbers
        .iter()
        .filter(|&&x| x > 3)
        .map(|x| x * x)
        .take(3)
        .collect();
    
    println!("{:?}", result); // [16, 25, 36]
    
    let sum: i32 = (0..100)
        .filter(|&x| x % 2 == 0)
        .map(|x| x * x)
        .sum();
    
    println!("Sum of squares of evens: {}", sum); // 171700
}

Breakdown

.iter()

Creates an iterator reference - no computation yet

.filter(|&&x| x > 3)

Lazy adaptor - only runs when iterator is consumed

.take(3)

Limits output to first 3 matching elements, short-circuiting computation

.collect()

Terminal operation that triggers all lazy adaptors to execute

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Iterator Lazy Evaluation and Chaining

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