What are C# Extension 💻Methods? Use Cases and Examples 🚀

R M Shahidul Islam Shahed
3 min readFeb 11, 2024

The concept of extension methods in C# introduces a valuable mechanism for enhancing the capabilities of existing types without directly modifying their source code. C# Extension Methods allow developers to add new methods to existing types without modifying the original type’s code. These methods enable the augmentation of functionality for classes, structs, interfaces, or enums without altering their source code. Extension methods are static methods that are called as if they were instance methods of the extended type.

What are C# Extension Methods? Use Cases and Examples

They are defined in static classes and must be in the same namespace as the type they extend or imported through a using directive.

Use Cases

  1. Augmenting functionality of third-party or built-in types: Extension methods enable developers to add new methods to types without access to their source code. For example, extending the String class with a method to convert a string to a title case.
  2. Providing syntactic sugar: Extension methods can improve code readability and maintainability by offering intuitive methods for common operations. For instance, adding a method to the IEnumerable<T> interface to easily perform a custom filter operation.
  3. Facilitating fluent interfaces: Extension methods are often used to create fluent interfaces, allowing method chaining for improved code expressiveness. This approach is common in libraries like LINQ, where methods are chained to perform various operations on collections.

Example:

What are C# Extension Methods? Use Cases and Examples

In this example, the ToTitleCaseNew extension method is added to the String class. It capitalizes the first letter of the string and converts the rest to lowercase, effectively converting the string to a title case. The method is invoked on a string object as if it were an instance method of the String class.

Program Output:

What are C# Extension Methods? Use Cases and Examples

--

--