Swift 2.0: use of self in method call before stored properties are initialised

Question

Just started looking at Swift this weekend. I'm creating an id for my class to quickly compare objects. I want an immutable id, so should use let.

Using var and initialising id to "" will fix "use of self in method call before stored properties are initialised" but then of course it's mutable. Every other question i've seen similar to this is regarding a super class / calling super.init, which I don't have. It's very frustrating, I don't know why it's not straightforward.

class MagicCard {

    let id:String
    let name: String
    let manaCost: Int
    let description: String
    let attack: Int
    let defence: Int

    init (name: String, manaCost: Int, description: String, attack: Int, defence: Int) {
        self.name = name
        self.manaCost = manaCost
        self.description = description
        self.attack = attack
        self.defence = defence
        id = generateRandomID()
    }

    private func generateRandomID() -> String {
        let charSet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        let charSetArray = Array(charSet.characters)
        var id:String = ""
        for _ in (0..<10) {
            id.append(charSetArray[Int(arc4random()) % charSetArray.count])
        }
        return id
    }
}

func == (lhs: MagicCard, rhs: MagicCard) -> Bool {
    return lhs.id == rhs.id
}

Answer 1

A hot-fix I can suggest is to make generateRandomID a class func. So make it like so :

private class func generateRandomID() -> String {

And call like this :

id = MagicCard.generateRandomID()

Answer 2

The generateRandomID() method does not use or modify any properties of the instance, so one possible solution would be to make it a type (class) method:

private class func generateRandomID() -> String {
    // ...
    return id
}

and use it like

id = MagicCard.generateRandomID()

(as also written in the other answer while I was writing this).

You could also drop the method and use an "immediately evaluated closure":

id = { () -> String in
    // ...
    return id
}()

But if the intention of the id property is to make the objects Equatable then you don't need it at all. Classes are reference types and instances can be compared with the "identical to" operator:

func == (lhs: MagicCard, rhs: MagicCard) -> Bool {
    return lhs === rhs
}

which makes the id and the generateRandomID() method obsolete.