Fabulous Adventures In Coding : Representation and Identity

Questions about the C# cast operator, the most frequent question I get is: short sss = 123; object ooo = sss; // Box the short. int iii = (int) sss; // Perfectly legal. int jjj = (int) (short) ooo; // Perfectly legal int kkk = (int) ooo; // Invalid cast exception?! Why? Why? Because a boxed T can only be unboxed to T. (*) Once it is unboxed, it’s just a value that can be cast as usual, so the double cast works just fine. Many people find this restriction grating; they expect to be able to cast a boxed thing to anything that the unboxed thing could have been cast to. There are ways to do that, as we’ll see, but there are good reasons why the cast operator does what it does.