computed property

contents.swift

     fileprivate var batchSum : Double!{
        willSet{
            if (newValue > 0 && newValue > batchSum){
                print("\((newValue - batchSum).format()) enqueud into the batch, the updated batch value is: \(newValue!.format())")
            }
            defaults.set(newValue, forKey: "batch_sum")
        }
    }