C# Feature – Extension methods

Overview

Extension methods add static methods callable as if they were instance methods on the target type.

Introduced In

C# 3 (2007)

Before

var text = ToTitleCase("hello world");

After

var text = "hello world".ToTitleCase();

Annotated Example

public static class StringExtensions
{
  public static string ToTitleCase(this string s) =>
    System.Globalization.CultureInfo.CurrentCulture.TextInfo.ToTitleCase(s);
}

Gotchas & Best Practices

• Don’t overuse; avoid polluting IntelliSense. Prefer domain-relevant extensions.

Related Features

• Lambda expressions
• Generics & LINQ

Version Notes

• Works across assemblies with using.