struct InventoryList< T > {
    var items: [T]

    mutating func add(item: T) {
        items.append(item)
    }

    mutating func remove() -> T {
        return items.removeLast()
    }

    func isCapacityLow() -> Bool {
        return items.count < 3
    }

    func numberOfItems() -> Int {
        return items.count
    }
}