The Essential Tools Module provides several distinct methods for iterating over a collection class. Most collections offer an apply member function, which applies your supplied function to every element of a collection class before returning. Another form of iteration is provided by separate collaborating iterator classes associated with many of the collections. For example, an RWTPtrDlistIterator<T,A> can be used to visit each element of an RWTPtrDlist<T,A> in turn. Iterators are described in “Iterators in Collection Classes”.