What are extension methods? When do you use them?

• Extension methods help extending types without altering them
• They're particularly useful for extending classes which are sealed
• They're created as static methods inside static classes
• The first parameter of the extension methods is the type for which the method is to extend.
• If the return type of the extension method is the type they're extending, then the methods can be chained together.

public class MyClass {
  /// 
}

public static MyClassExtensions {
  public static MyClass DoExtended(this MyClass obj, int someparam1, int someparam2.. )
  {
      // do something
      return obj;
  }
}


MyClass obj = new MyClass();
obj.DoExtended(); // this works although DoExtended is not a part of MyClass