class ParentWallet {
    var money: Int
    
    required init(money: Int) {
        self.money = money
    }
    
    func newWalletWithMoreMoney(_ moreMoney: Int) -> Self {
        let moneyForNewWallet = money + moreMoney
        return type(of:self).init(money: moneyForNewWallet )
    }
}

class ChildWallet: ParentWallet {
    required init(money: Int) {
        super.init(money: money)
    }
    
    override func newWalletWithMoreMoney(_ moreMoney: Int) -> Self {
        let newWallet = super.newWalletWithMoreMoney(moreMoney)    // newWallet has type ParentWallet instead of Self
        return newWallet    // Error: Cannot convert return expression of type 'ParentWallet' to return type 'Self'
    }
}

// wallet1 has type ParentWallet
let wallet1 = ParentWallet(money: 10).newWalletWithMoreMoney(5)
// wallet2 has type ChildWallet
let wallet2 = ChildWallet(money: 10).newWalletWithMoreMoney(5)