Iterators in Storm's standard library are fairly similar to iterators in C++.

An iterator is a pointer into some position of a container. To get iterators to a container, call that container's begin and end function. The begin iterator points to the first element in the container, while the end iterator points one element past the last element in the container.

When an iterator has been created, the iterator assumes the referred container is not changed during the iterator's lifetime. Modifying the container (other than altering any contained elements) make the associated iterators behave in an undefined way.

Iterators do not inherit from a base class, they only have to support the following operations:

As can be seen, iterators to containers like Map work differently in Storm compared to C++. In Storm, the iterator allows you to access the key and the value separately, rather than returning a pair with both the key and the value. The reason for this is that Storm has no natural dereference operation, and therefore k and v are easier to read and write. This also allows containers to provide optional keys for their values. For example, Array provides the index of the current element as the key, which can be used if desired. Basic Storm implements a range-based for loop that uses this.

A second type of iterators are provided by the WeakSet<T> class. This type has a single operation:

This type is also supported by the for loop in storm. This type does, however, not support keys.