Rust Iter

Core Concepts

Rust iterators are used for processing collections of data in a functional way. They're lazy, meaning they do not consume their values until they are needed.

Iterator Trait

An iterator is any type that implements the Iterator trait, which requires defining a single method: next.

pub trait Iterator {
    type Item;
    fn next(&mut self) -> Option<Self::Item>;
}

Adapter Methods

Adapter methods are methods that take an iterator and return a new iterator with modified behavior. These adapters can be chained together to create complex processing pipelines. Common adapter methods include map, filter, and take.

Transformation & Filtering

let numbers = vec![1, 2, 3, 4, 5];
let even_squares = numbers.iter()
    .map(|x| x * x)         // Transform each number to its square
    .filter(|x| x % 2 == 0) // Keep only even numbers
    .collect();             // Collect results into a vector

|x| x * x is a closure, which in other languages is called an anonymous function or lambda.

Limiting Results

let first_three_evens = numbers.iter()
    .map(|x| x * x)
    .filter(|x| x % 2 == 0)
    .take(3)
    .collect();

Links to Related Notes

• borrow-checker - Understanding how iter() vs into_iter() interacts with ownership.
• chaining-methods - How method chaining syntax makes iterators readable.
• AoC Day 02 - Example of using custom types with iterators.