HH\Traversable
Represents an entity that can be iterated over using foreach, without
requiring a key
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.
Guides
Interface Synopsis
namespace HH;
interface Traversable {...}