What is the best way to replace or substitute if..else if..else trees in programs?

Question

This question is motivated by something I\'ve lately started to see a bit too often, the if..else if..else structure. While it\'s simple and has its uses, somet

Answer 1

The example given in the question is trivial enough to work with a simple switch. The problem comes when the if-elses are nested deeper and deeper. They are no longer "clear or easy to read," (as someone else argued) and adding new code or fixing bugs in them becomes more and more difficult and harder to be sure about because you might not end up where you expected if the logic is complex.

I've seen this happen lots of times (switches nested 4 levels deep and hundreds of lines long--impossible to maintain), especially inside of factory classes that are trying to do too much for too many different unrelated types.

If the values you're comparing against are not meaningless integers, but some kind of unique identifier (i.e. using enums as a poor man's polymorphism), then you want to use classes to solve the problem. If they really are just numeric values, then I would rather use separate functions to replace the contents of the if and else blocks, and not design some kind of artificial class hierarchy to represent them. In the end that can result in messier code than the original spaghetti.