Why can't I use `&Iterator` as an iterator?

Question

I have the following function that\'s supposed to find and return the longest length of a String given an Iterator:

fn max_width(st         


        

Answer 1

Your code fails because Iterator is not the same as &Iterator. You can fix this if you pass Iterator to your function, but since Iterator is a trait, the size cannot be determined (You can't know, what Iterator you are passing). The solution is to pass anything that implements Iterator:

fn max_width<'a>(strings: impl Iterator) -> usize

playground

---

For more experienced Rust users:

The most generic way is probably this:

fn max_width>(strings: impl IntoIterator) -> usize {
    let mut max_width = 0;
    for string in strings {
        let string = string.as_ref();
        if string.len() > max_width {
            max_width = string.len();
        }
    }
    max_width
}

playground

However, you can also use

fn max_width>(strings: impl IntoIterator) -> usize {
    strings
        .into_iter()
        .map(|s| s.as_ref().len())
        .max()
        .unwrap_or(0)
}

playground