What is the difference between Iterator and IntoIterator

Iterator is a trait that defines how to produce a sequence of items one by one, while IntoIterator is a trait that converts a collection into an Iterator.

use std::iter::{Iterator, IntoIterator};

fn main() {
    let v = vec![1, 2, 3];
    
    // IntoIterator: Converts the vector into an iterator (consumes v)
    let iter: impl Iterator<Item = i32> = v.into_iter();
    
    // Iterator: Consumes the iterator to get the next item
    if let Some(first) = iter.next() {
        println!("First item: {}", first);
    }
}

Think of Iterator as the machine that hands you items one at a time, and IntoIterator as the adapter that turns a box of items into that machine. You use IntoIterator when you have a collection like a vector and want to start looping through it. You use Iterator when you are already inside the loop and need to get the next item.