import UIKit

enum VendingMachineError: Error {

    case invalidSelection //选择无效

    case insufficientFunds(coinsNeeded: Int) //金额不足

    case outOfStock //缺货

}

struct Item {

    var price: Int

    var count: Int

}

class VendingMachine {

    var inventory = [

        "Candy Bar": Item(price: , count: ),

        "Chips": Item(price: , count: ),

        "Pretzels": Item(price: , count: )

    ]

    //货币沉淀

    var coinsDeposited =

    func dispenseSnack(snack: String) {

        print("Dispensing \(snack)")

    }

    func vend(itemNamed name: String) throws {

        guard let item = inventory[name] else {

            throw VendingMachineError.invalidSelection

        }

        guard item.count >  else {

            throw VendingMachineError.outOfStock

        }

        guard item.price <= coinsDeposited else {

            throw VendingMachineError.insufficientFunds(coinsNeeded: item.price - coinsDeposited)

        }

        coinsDeposited -= item.price

        var newItem = item

        newItem.count -=

        inventory[name] = newItem

        print("Dispensing \(name)")

    }

}

class First_Demo3: UIViewController {

    override func viewDidLoad() {

        super.viewDidLoad()

        self.navigationItem.title = "throws异常抛出"

        self.view.backgroundColor = UIColor.white

        let vend = VendingMachine()

        //货币沉淀

        vend.coinsDeposited = 

        /*

         try抓取异常，如果执行成功，那么执行 vend.vend(itemNamed: "Pretzels")。cathch 完枚举的三个错误以后，要把catch关闭，即：

注意：最后加入一个空的catch，否则则会报错 Error throw from are not handled because the enclosing catch is not exhaustive  意思就是catch没有关闭。

         */

        do {

            try  vend.vend(itemNamed: "Pretzels")

            // 没有错误抛出

        }catch VendingMachineError.invalidSelection{

            print("选择无效")

            // 有错误抛出

        }catch VendingMachineError.outOfStock{

            print("缺货")

        }catch VendingMachineError.insufficientFunds(let coinsNeeded){

            print("还差\(coinsNeeded)货币")

        }catch {

        }

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

}