Smart Array Arguments

I’m creating an application that ranks poker hands. To do this I’ve created a domain object called the PokerHandValue that consists of the following attributes: hand_rank, used_cards, kickers. The used_cards and kickers variables are arrays consisting of Card objects.

Sometimes a made Hand consists of just a high card and sometimes all five cards are used. Sometimes the kickers array can have zero cards. The point is, the PokerHandValue needs to account for the possibility of being passed a single object, an array, or even nil.

Consider for a moment:

class PokerHandValue
  def initialize(hand_rank, used_cards, kickers)
    @hand_rank  = hand_rank
    @used_cards = used_cards
    @kickers    = kickers
  end

  def hand
    @used_cards + @kickers
  end
end

The way I’ve structured PokerHandValue, it is expecting both used_cards and kickers to be arrays. If we somehow pass PokerHandValue nil, we’ll get a TypeError when trying to call the hand method.

To avoid this, we can utilize a little known method: Array.

class PokerHandValue
  def initialize(hand_rank, used_cards, kickers)
    @hand_rank  = hand_rank
    @used_cards = Array(used_cards)
    @kickers    = Array(kickers)
  end

  def hand
    @used_cards + @kickers
  end
end

Simple and elegant! Now our used_cards and kickers will always return an array no matter what sort of object sneaks into our arguments.

So let’s break down exactly what the Array method does for us:

irb> Array(nil)
---> []

irb> Array([])
---> []

irb> Array(%w(Ace Ten King))
---> ["Ace", "Ten", "King"]

With such a small change in our code, we increase it’s flexibility, and reduce the potential of bugs. That’s a great win with few, if any, side effects.