[Swift]: Learning 2

Common usage for optional

The following two code blocks are equivalent

if emoji[card.identifier] != nill {
    return emoji[card.identifier]!
} else {
    return "?"
}

return emoji[card.identifier] ?? "?"

• nill means "the absence of a valid object."
• this only works for objects, not fur structures, basic C types, or enumeration values
• Swift's optionals let you indicate the absence of a value for any type at all, without the need for special constants.

Use of Dictionary

var emojiChoices = ["🦇", "😱", "🙀", "😈","🎃", "👻", "🍭", "🍬", "🍎"]
var emoji = [Int:String]()

func emoji(for card: Card) -> String {
    if emoji[card.identifier] == nil, emojiChoices.count > 0 {
    let randIndex = Int (arc4random_uniform(UInt32(emojiChoices.count)))
    emoji[card.identifier] = emojiChoices.remove(at: randIndex)
    }

    return emoji[card.identifier] ?? "?"
 }

The following codes are equivalent, but first one is preferred

var emoji = [Int:String]()

var emoji = Dictionary<Int, String>()

• Dictionary is an implementation of Map like HashMap in java
• arc4random_uniform is a useful in generating random Int. But uses unsigned integer. Swift doesn't support automatic conversion, so casting is needed manually