The Iterator Pattern

The Iterator Pattern


The Iterator Pattern is a tool for traversing and accessing the elements of aggregate objects without exposing their internal implementation details.

This pattern promotes encapsulation and flexibility, allowing for the iteration of collections without modifying their structure.

Understanding the Iterator Pattern

The Iterator Pattern revolves around the concept of an iterator object, which serves as a bridge between the client code and the underlying collection.

The iterator object provides a standardised way to traverse and access the elements of a collection, hiding the complexities of the collection’s internal structure.

Benefits of the Iterator Pattern

The Iterator Pattern offers several advantages, including:

  • Encapsulation: It promotes encapsulation by hiding the internal structure of the collection from the client code.
  • Flexibility: It allows for multiple traversal algorithms without modifying the collection’s structure.
  • Code Reusability: It facilitates code reuse by providing a common interface for iterating through collections.
  • Maintainability: It enhances maintainability by simplifying the code that interacts with collections.
  • Efficiency: It can be optimized for specific traversal needs, such as sequential, random, or reverse traversal.

Types of Iterator Patterns

The Iterator Pattern encompasses several variations, each with its specific characteristics:

  • Concrete Iterator: This pattern uses nested loops to traverse the collection.
  • Polymorphic Iterator: This pattern allows for multiple iteration styles, such as forward, backward, or hierarchical.
  • Lazy Iterator: This pattern defers the actual computation of the iterator’s elements until they are actually needed.

Implementing the Iterator Pattern in C#

To illustrate the implementation of the Iterator Pattern in C#, consider a simplified scenario of iterating over a list of strings:

List Class:

The list class represents a collection of strings and provides methods for adding, removing, and accessing its elements.

public class List<T>
    private List<T> items = new List<T>();

    public void Add(T item)

    public void Remove(T item)

    public T GetItem(int index)
        return items[index];

Iterator Class:

The iterator class provides methods for traversing the list of items and accessing each element.

public class Iterator<T>
    private List<T> list;
    private int currentIndex = 0;

    public Iterator(List<T> list)
        this.list = list;

    public bool HasNext()
        return currentIndex < list.Count;

    public T GetNext()
        return list[currentIndex++];

Using the Iterator Pattern:

To use the iterator pattern for iterating over a list of strings:

List<string> strings = new List<string>();

Iterator<string> iterator = new Iterator<string>(strings);

while (iterator.HasNext())

This example demonstrates a basic implementation of the Iterator Pattern in C# for iterating over a list of strings.

The iterator pattern can be extended to handle more complex collections and traversal needs.


The Iterator Pattern is a tool for navigating and accessing the elements of collections in a reusable and flexible manner.

It promotes encapsulation, code readability, and maintainability, making it a valuable addition to the C# developer’s toolkit.


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.