Question

错误发生在班级VendingMachine: VendingMachineType{}

上

我似乎无法找到造成问题的差异。我错过了什么，还是我在错误的地方？

如果我正确理解协议，它基本上确定了要遵循的类的蓝图，据我所知，我无法找到该函数不遵循协议设置的蓝图的位置。

协议：

protocol VendingMachineType {
    var selection: [VendingSelection] { get }
    var inventory: [VendingSelection: ItemType] { get set }
    var amountDeposited: Double { get set }

    init(inventory: [VendingSelection: ItemType])
    func vend(selection: VendingSelection, quantity: Double) throws
    func deposit(amount: Double)
    func itemForCurrentSelection(selection: VendingSelection) -> ItemType?
}

类别：

class VendingMachine: VendingMachineType {
    let selection: [VendingSelection] = [.Soda, .DietSoda, .Chips, .Cookie, .Sandwich, .Wrap, .CandyBar, .PopTart, .Water, .FruitJuice, .SportsDrink, .Gum]

    var inventory: [VendingSelection: ItemType]
    var amountDesposited: Double = 10.0

    required init(inventory: [VendingSelection : ItemType]) {
        self.inventory = inventory
    }

    func vend(selection: VendingSelection, quantity: Double) throws {
        guard var item = inventory[selection] else {
            throw VendingMachineError.InvalidSelection
        }

        guard item.quantity > 0 else {
            throw VendingMachineError.OutOfStock
        }
        //at this point we have an item and a quantity implement a cancel button as homework here. 

        //time to reduce quantity by amount purchased

        item.quantity -= quantity
        inventory.updateValue(item, forKey: selection)


        //here we are checking to see if we have enough money and throwing an error if they do not
        let totalPrice = item.price * quantity
        if amountDesposited >= totalPrice {
            amountDesposited -= totalPrice
        } else {
            let amountRequired = totalPrice - amountDesposited
            throw VendingMachineError.InsufficientFunds(required: amountRequired)
        }
    }

    func itemForCurrentSelection(selection: VendingSelection) -> ItemType? {
        return inventory[selection]
    }

    func deposit(amount: Double) {
        amountDesposited += amount
    }
}

赞赏任何正确方向的帮助或指示。

Answer 1

我将您的代码复制到IBM Sandbox中，因为您没有粘贴所有代码，所以必须进行一些简化。不过，我得到了同样的第一个错误。第二个错误是解释问题的原因：

protocol requires property 'amountDeposited' with type 'Double'

您在课程定义中错误拼写了该属性。

Answer 2

您的VendingMachine amountDeposited是一个存储的属性。但协议只能声明计算属性。

Swift Type不符合协议

2 个答案: