How to avoid conditionals in your code

A couple of weeks ago I was asked to share how I avoided if in my code at the Global Day of Coderetreat 2017.

DISCLAIMER: this solution was produced during a kata where we forced ourselves to code under certain conditions (no if in this case). It is not the only solution (you can use polymorphism for example) and is probably not a good pattern to solve this specific case in a real project.

In my implementation of Conway's Game of Life, I have the following method to know if a cell will be DEAD or ALIVE in the next iteration.

public Status newStatusFor(int neighborsCount) {
  if (neighborsCount < 2 || neighborsCount > 3) {
    return Status.DEAD;
  }
  return Status.ALIVE;
}

Because we have a small finite number of possibilities (a cell has up to 8 neighbors), I did as follows:

private static ImmutableMap<Integer, Status> neighborsRules = ImmutableMap.<Integer, Status>builder()
  .put(0, Status.DEAD)
  .put(1, Status.DEAD)
  .put(2, Status.ALIVE)
  .put(3, Status.ALIVE)
  .put(4, Status.DEAD)
  .put(5, Status.DEAD)
  .put(6, Status.DEAD)
  .put(7, Status.DEAD)
  .put(8, Status.DEAD)
  .build();

public Status newStatusFor(int neighborsCount) {
  return neighborsRules.get(neighborsCount);
}

In this case, I just return the value of the enum but I could have returned a Function and done something more complicated.

Conclusion

• When to use: you have a small finite number of possibilities
• Benefit: if you put a Function in the value it's easy to modify it without changing the existing code (open/closed principle)