HH\Traversable

The HH\Traversable<Tv> interface

The iteration variable will have a type of T.

In addition to Hack collections, PHP arrays and anything that implement Iterator are Traversable.

In general, if you are implementing your own Hack class, you will want to implement Iterable instead of Traversable since Traversable is more of a bridge for PHP arrays to work well with Hack collections.

Interface synopsis

interface Traversable  {...}