Iterators

https://doc.rust-lang.org/book/ch13-02-iterators.html

Iterators in rust let you iterate over a vector/array/strings.

When you write

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

    for i in v {
        println!("{}", i);
    }

}

This under the hood gets converted to

fn main() {
    let v = vec![1, 2, 3];
    let mut v_iter = v.into_iter();

    while let Some(i) = v_iter.next() {
        print!("{}", i);
    }
}

Iter

Iter doesn’t consume the original variable and it can be used afterwards

fn main() {
    let v = vec![1, 2, 3];
    let mut v_iter = v.iter();

    while let Some(i) = v_iter.next() {
        print!("{}", i);
    }

    println!("{:?}", v);
}

IntoIter

IntoIter consumes the original variable and it cant be used after the intoiter is used.

fn main() {
    let v = vec![1, 2, 3];
    let mut v_iter = v.into_iter();

    while let Some(i) = v_iter.next() {
        print!("{}", i);
    }

    println!("{:?}", v);
}

Consuming adapters

Methods that call next are called consuming adapters, because calling them uses up the iterator (not the original variable but the iterator). For example - sum or count

fn main() {
    let v = vec![1, 2, 3];
    let v_iter = v.into_iter();
    let sum: i32 = v_iter.sum();
    println!("{}", sum);
    // try using the iterator again here.
}

Iterator adapter

Iterator adapters are methods defined on the Iterator trait that don’t consume the iterator.Instead, they produce different iterators by changing some aspect of the original iterator.

fn main() {
    let v = vec![1, 2, 3];
    let v_iter = v.into_iter();
    let v2: Vec<i32> = v_iter.map(|x| x + 1).collect();
    println!("{:?}", v2);
}