seen_set

A HashSet that doesn't store values, but instead only stores hashes.

This is useful when you only need to tell if you've seen a value before and you don't want to clone the value for performance reasons.

let mut seen = SeenSet::new();
for path in some_func_that_may_return_duplicate_paths() {
  if !seen.insert(&path) {
    continue;
  }
  // we haven't seen this path before
}

Note: This will be slower for values like numbers. Just use a regular HashSet for that.