How does borrowing work with iterators

Iterators borrow collections to process items safely without taking ownership, using .iter() for reading, .iter_mut() for writing, or .into_iter() to consume.

Iterators borrow the collection they iterate over, allowing you to process items without taking ownership or mutating the data unless explicitly requested. Use .iter() to borrow immutably, .iter_mut() to borrow mutably, or .into_iter() to take ownership.

let numbers = vec![1, 2, 3];

// Immutable borrow (read-only)
for n in numbers.iter() {
    println!("{}", n);
}

// Mutable borrow (read-write)
for n in numbers.iter_mut() {
    *n += 1;
}

// Consumes the vector (takes ownership)
for n in numbers.into_iter() {
    println!("{}", n);
}

Borrowing with iterators lets you look at or change items in a list without stealing the list itself. Think of it like checking out a book from a library: you can read it (immutable borrow) or write notes in it (mutable borrow), but you must return it when you are done. You only take the book home permanently if you specifically ask to own it.