using System;

using System.Reflection;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var method = typeof(Program).GetMethod("MyFn");

        var first = (MyAttribute)method.GetCustomAttributes(typeof(MyAttribute), true)[0] ;

        // Should print A

        Console.WriteLine(first.ErrorMessage);

        first.ChangeMe();

        // Should print B

        Console.WriteLine(first.ErrorMessage);

        var second = (MyAttribute)method.GetCustomAttributes(typeof(MyAttribute), true)[0] ;

        // Should print A

        Console.WriteLine(second.ErrorMessage);

        // If we cached the first retrieval though... it'll print B

        // In ASP.NET MVC; validation attributes are cached; so changing state in the attribute

        // will persist over form calls.

        Console.WriteLine(first.ErrorMessage);

    }

    [My(ErrorMessage = "A")]

    public void MyFn()

    {

        Console.WriteLine("Hello World");

    }

    public class MyAttribute : Attribute

    {

        public string ErrorMessage {get;set;}

        public void ChangeMe()

        {

            this.ErrorMessage = "B";

        }

    }

}