Isn’t it funny how the “easiest” concepts can be the most complicated?  A reader sent me the following quiz to help us appreciate the subtlies of equality in the system.  Luckily he gave me the answers as well… ;-)          

Consider the following program:

object x = new object();

object y = new object();

/*Question 1*/ Console.WriteLine(x == y && !x.Equals(y));

/*Question 2*/ Console.WriteLine(x != y && x.Equals(y));

/*Question 3*/ Console.WriteLine(x == y);

/*Question 4*/ Console.WriteLine(x == y && (object)x != (object)y);

They should all print “false” right?

For each question, find a way to declare and initialize x and y such that:

            Question 1: prints true

            Question 2: prints true

            Question 3: does not even compile

            Question 4: prints true

Notice, we are not asking for a solution that works for all 4, one solution for each will be fine…

All answers should be of the form:

         public static void Question<<question number>>()

        {

            <<type>> x = <<intialize instance>>;

            <<type>> y = <<intialize instance>>;

            Console.WriteLine(<<question>>);

        }

So for example, a legal (but incorrect) answer to question1 would be:

         public static void Question1()

        {

            string x = "1";

            object y = new Object() ;

            Console.WriteLine(x == y && !x.Equals(y));

        }

The rules of the game:

1. You can only use “base” data types: object, string, Int32, double, Type, etc
2. No more than two lines of plainly formatted code (before the Console.WriteLine)
3. You can’t change anything about the question line, it has to appear exactly as I show above
4. Extra credit for getting solutions no one else thinks of and for pointing out differences between versions of the CLR