Enabling Foreach Functionality in C# Classes

Enabling Foreach Functionality in C# Classes


The foreach loop in C# provides a simple, clean way to iterate over collections. To make a custom class compatible with the foreach loop, the class needs to implement the IEnumerable interface.

This article explores how to enable foreach functionality in a custom C# class.

Implementing IEnumerable

The IEnumerable interface requires that your class implements the GetEnumerator method, which returns an IEnumerator. The IEnumerator iterates over the collection, maintaining the state of the iteration.

Basic Implementation Steps

  1. Implementing IEnumerable:
    • Add IEnumerable to your class.
    • Implement the GetEnumerator method.
  2. Creating an Enumerator:
    • You can either return the enumerator of an internal collection or implement a custom enumerator.

Example: Custom Collection Class

Here’s an example of a custom collection class that implements IEnumerable:

public class CustomCollection<T> : IEnumerable<T> 

    private readonly List<T> _itemsnew List<T>(); 
    public void Add(T item

    public IEnumerator<TGetEnumerator() 

        return _items.GetEnumerator(); 
    IEnumerator IEnumerable.GetEnumerator() 

        return GetEnumerator(); 

In this example, CustomCollection<T> is a generic collection class that stores its elements in a List<T>. By implementing IEnumerable<T>, it can be used with a foreach loop.

Usage with Foreach

You can now iterate over instances of CustomCollection<T> using a foreach loop:

var collectionnew CustomCollection<string>(); 
collection.Add("Item 1"); 
collection.Add("Item 2"); 

foreach (var item in collection) 

Advanced Implementation: Custom Enumerator

In some cases, you might need a custom enumerator. This is particularly useful when the collection structure is not based on existing .NET collection types.

public class CustomCollection<T> : IEnumerable<T> 

    // ... other members ... 

        for (int i0; i < _items.Count; i++) 

            // Custom logic for yielding items 
            yield return _items[i]; 
    IEnumerator IEnumerable.GetEnumerator() 

        return GetEnumerator(); 

Best Practices

  1. Thread Safety: Be aware of thread safety issues if the collection can be accessed by multiple threads.
  2. Performance Considerations: For large collections, consider the performance implications of your enumerator logic.
  3. Consistency: Ensure that the state of the collection remains consistent during enumeration.


Enabling foreach functionality in a custom C# class involves implementing the IEnumerable (or IEnumerable<T>) interface and providing an appropriate enumerator.

This not only allows your class to be used with the foreach loop but also makes it compatible with many other features of the .NET framework that work with collections.

Whether you use an enumerator of an internal collection or implement a custom enumerator, the key is to provide a mechanism for iterating over the elements of your class in a sequential manner.


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.