Understanding IEnumerable, ICollection, and IList in C#

By mulzatech.comBlog

Introduction

Developers frequently bump into different c# collection interfaces, which can sometimes be a head-scratcher. The big three in this mix are IEnumerable, ICollection, and IList. Today, we’ll break down these interfaces, making them easy to understand. In addition to this, I’ll highlight the key differences between using IEnumerable and List. Let’s get started!

Interface hierarchy

1. IEnumerable

Definition: IEnumerable is the most basic interface that represents a forward-only cursor of T. Any collection that can be iterated using a foreach loop in C# implements this interface.

Example:

IEnumerable<string> names = new List<string>() { "Alice", "Bob", "Charlie" };
foreach (var name in names)
{
    Console.WriteLine(name);
}

Key Points:

  • It provides a basic iteration capability.
  • It doesn’t support adding or removing items.
  • It doesn’t provide random access to items.

2. ICollection

Definition: ICollection is a step up from IEnumerable. It includes all the capabilities of IEnumerable and adds functionalities like adding, removing, and checking the existence of items.

Example:

ICollection<string> names = new List<string>() { "Alice", "Bob" };
names.Add("Charlie");
names.Remove("Alice");
Console.WriteLine(names.Contains("Bob"));  // Outputs: True

Key Points:

  • It extends IEnumerable.
  • Provides methods to add and remove items.
  • Can check the number of items and if a particular item exists.

3. IList

Definition: IList is an extension of ICollection that provides capabilities to access elements by index, check the index of a particular item, and insert or remove items at a specific position.

Example:

IList<string> names = new List<string>() { "Alice", "Charlie" };
names.Insert(1, "Bob");
Console.WriteLine(names[1]);  // Outputs: Bob

Key Points:

  • It extends both IEnumerable and ICollection.
  • Supports indexed access.
  • Can insert or remove items at a specific position.

IEnumerable vs. List

While IEnumerable is an interface that provides basic iteration capabilities, List is a concrete implementation that offers a set of functionalities, including adding, removing, and accessing items by index.

Key Differences:

  • IEnumerable is read-only, while List allows modification.
  • List provides faster access to items by index.
  • IEnumerable is more suitable for scenarios where only iteration is required, whereas List is versatile and can be used in a wider range of scenarios.

Example:

List<string> myList = new List<string>() { "Alice", "Bob", "Charlie" };
myList.Add("David");
IEnumerable<string> myEnumerable = myList;

Conclusion

Understanding the nuances between IEnumerable, ICollection, and IList is very important for us C# developers. While they might seem similar, each serves a unique purpose. By grasping their differences and when to use each, we can write more efficient and cleaner code.

I hope this article provides a clear understanding of the differences between IEnumerable, ICollection, and IList, as well as the distinction between IEnumerable and List.

If you have further questions or need more examples, feel free to ask!

Happy coding!