As kibwen explains above, Rust is just switching the dominant iteration protocol to external iterators, i.e. the protocol privileged/understood by the `for` syn

As kibwen explains above, Rust is just switching the dominant iteration protocol to external iterators, i.e. the protocol privileged/understood by the `for` syntactic sugar. It will still perfectly possible to write do tree.visit_each_leaf |leaf| { // ... do things with leaf ... if some_continuation_condition { true } else { false } } (The last line is the replacement for what would be currently written `if !some_continuation_condition { break }` with the `for` sugar.)