How do you write code whose logic is protected against future additional enumerations?

Question

I\'m having a hard time describing this problem. Maybe that\'s why I\'m having a hard time finding a good solution (the words just aren\'t cooperating). Let me explain via cod

Answer 1

A lot of people have good suggestions, but let me add one other that doesn't require a complete redesign of code or the support of objects/classes in places (like sql) that obviously have no support for such things.

You stated:

Fruit fruit = acquireFruit();
if (fruit != Fruit.Orange && fruit != Fruit.Banana)
    coreFruit();
else
    pealFruit();
eatFruit();

Which will absolutely break in unexpected ways if Grapes are introduced. I think a better approach would be:

Fruit fruit = acquireFruit();
Boolean fruitPrepared = false;

if (fruit == Fruit.Orange || fruit == Fruit.Banana) {
    pealFruit();
    fruitPrepared = true;
}

if (fruit == Fruit.Apple) {
    coreFruit();
    fruitPrepared = true;
}

if (!fruitPrepared) 
  throw new exception();

eatFruit();

A third approach is very similar:

Fruit fruit = acquireFruit();

switch(fruit) {
  case Fruit.Orange:
  case Fruit.Banana:
    pealFruit();
    break;    
  case Fruit.Apple:
    coreFruit();
    break;
  default:
    throw new exception('unknown fruit detected');
    break;
}

Each of the above breaks in well defined ways when you've gone outside of what you've explicitly coded for. The main thing to take away is that you are explicitly doing something for a known condition as opposed to defaulting to something on an unknown condition. There's probably a better way of phrasing that.