Extending borrowed lifetime for String slice

Question

I have a function that reads in a file, and for each line adds it to a HashSet of type &str, but I can\'t work out how to tell the borrow check

Answer 1

reader.lines() returns an iterator over owned Strings. But then in your for loop you cast these to borrowed references to &str. So when the iterator goes out of scope all your borrowed references become invalid. Consider using a HashSet instead, which also is zero cost, because the Strings get moved into the HashSet and therefore aren't copied.

Working example

fn build_collection_set(reader: &mut BufReader) -> HashSet {
    let mut collection_set: HashSet = HashSet::new();

    for line in reader.lines() {
        let line = line.unwrap();
        if line.len() > 0 {
            collection_set.insert(line);
        }
    }
    collection_set
}