Extension methods C# 2.0 allowed you to decorate existing classes with additional instance methods.
C# 14 brings a new syntax that also allows for extension properties and methods as well as static properties and methods using the new extension keyword.
Code
C#
Console.WriteLine(customer.GetFullName()); // Method
Console.WriteLine(customer.FullName); // Property
static class CustomerHelper
{
extension(Customer c)
{
// Extension method
public string GetFullName() => c.FirstName + " " + c.LastName;
// Extension property
string FullName => c.FirstName + " " + c.LastName;
}
}C#
Console.WriteLine(CustomerHelper.GetFullName(customer)); // Method
static class CustomerHelper
{
public static string GetFullName(Customer c) => c.FirstName + " " + c.LastName;
}