[Swift]: extension

Extensions in Swift

• extions allows to add variables/functions to other classe/struct/enum even if you don't have the source
• You can also use extensions to Frameworks (i.e. UIKit, Int, UIButton, UIViewController, etc)

Restrictions

• Can't re-implement method/property that already exists
• Properties in extensions can only be computed
• Caveat: Do not add var/func that does not make sense to the class/struct/enum

Example in Concentration

Outside the Concentration class:

extension Int {
    var arc4random: Int {
        return Int(arc4random_uniform(UInt32(self)))
    }
}

• self is the Int that's sent

Changes made after creating extension

Before

let randomIndex = Int(arc4random_uniform(UInt32(emojiChoices.count)))
emoji[card.identifier] = emojiChoices.remove(at: randomIndex)

After

emoji[card.identifier] = emojiChoices.remove(at: emojiChoices.count.arc4random)

Check for invalid inputs

extension Int {
    var arc4random: Int {
        if self > 0 {
            return Int(arc4random_uniform(UInt32(self)))
        } else if self < 0 {
            return -Int(arc4random_uniform(UInt32(self)))
        } else {
            return 0
        }
    }
}