Question

some minutes ago “Jon Skeet” found something. see this

this issue and many issues like this made me to think about something about Undefined Operation or Undefined Result.

should these kind of things that may cause different result in different implementation of libraries like .net or mono results in an Undefined Operation or Undefined Result? maybe throwing an exception or setting a field in it’s struct or class?!
what are cons and pros of having Undefined Operation or Undefined Result?

also look at this
I think some of them mentioned there makes unexpected results which should be handled or make the programmer be aware of them.

I mean some how it is getting a big amount of knowing “X is doing something in this way” and “how X implemented another thing”! is this really help programming and developers?

Answer 1

Do you mean like throwing a NotSupportedException? By tautology, if you define that your operation will throw an exception or return a special value, your behavior was defined. If the specification says that behavior is undefined, then the implementation is free to do anything that the implementer wishes – enforcing that they throw an UndefinedOperation (or similar behavior) means your operation is now defined!

For the case you linked:

It’s already specified that comparing a number to NaN returns false ( 1<NaN, 1>NaN, and 1==NaN are all false)? Given that information, when asked “what’s biggest – 1 or NaN?” I would answer “there is no maximum , hence the answer is not a number” (like Math.Max does). But if you phrase it like “given these values – 1,2, NaN – which is the biggest number?” I would have to say “2” – because it’s the biggest number (NaN is not a number!)

So in this case the issue isn’t that the operation is undefined at all – the problem is that the specification is confusing! I agree that there are confusing issues with NaN (and countless other things), but those are places to argue that the specification needs cleaning or changing. In my opinion, you should petition for a spec change, or possibly a compiler warning – not an exception or special return value.