How do I reuse the SplitWhitespace iterator?

Question

I've got a piece of code which is supposed to check if two sentences are "too similar", as defined by a heuristic made clearest by the code.

fn too_similar(thing1: &String, thing2: &String) -> bool {
    let split1 = thing1.split_whitespace();
    let split2 = thing2.split_whitespace();

    let mut matches = 0;
    for s1 in split1 {
        for s2 in split2 {
            if s1.eq(s2) {
                matches = matches + 1;
                break;
            }
        }
    }

    let longer_length =
        if thing1.len() > thing2.len() {
            thing1.len()
        } else {
            thing2.len()
        };

    matches > longer_length / 2
}

However, I'm getting the following compilation error:

error[E0382]: use of moved value: `split2`
 --> src/main.rs:7:19
  |
7 |         for s2 in split2 {
  |                   ^^^^^^ value moved here in previous iteration of loop
  |
  = note: move occurs because `split2` has type `std::str::SplitWhitespace<'_>`, which does not implement the `Copy` trait

I'm not sure why split2 is getting moved in the first place, but what's the Rust way of writing this function?

Answer 1

split2 is getting moved because iterating with for consumes the iterator and since the type does not implement Copy, Rust isn't copying it implicitly.

You can fix this by creating a new iterator inside the first for:

let split1 = thing1.split_whitespace();

let mut matches = 0;
for s1 in split1 {
    for s2 in thing2.split_whitespace() {
        if s1.eq(s2) {
            matches = matches + 1;
            break;
        }
    }
}
...

You can also rewrite the matches counting loop using some higher order functions available in the Iterator trait:

let matches = thing1.split_whitespace()
    .flat_map(|c1| thing2.split_whitespace().filter(move |&c2| c1 == c2))
    .count();

longer_length can also be written as:

let longer_length = std::cmp::max(thing1.len(), thing2.len());