第十八章 错误处理

enum VendingMachineError: Error {

    case invalidSelection

    case insufficientFunds(coinsNeeded: Int)

    case outOfStock

}

do {

    throw VendingMachineError.insufficientFunds(coinsNeeded: 5)

} catch VendingMachineError.insufficientFunds(let coinsNeeded) {

    print("Insufficient funds. Please insert \(coinsNeeded)")

}

struct Item {

    var price: Int

    var count: Int

}

class VendingMachine {

    var inventory = [

        "Candy Bar": Item(price: 12, count: 7),

        "Chips": Item(price: 10, count: 4),

        "Pretzels": Item(price: 7, count: 11)

    ]

    var coinsDeposited = 0

    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 > 0 else {

            throw VendingMachineError.outOfStock

        }

        guard item.price <= coinsDeposited else {

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

        }

        coinsDeposited -= item.price

        var newItem = item

        newItem.count -= 1

        inventory[name] = newItem

        print("Dispensing \(name)")

    }

}

let favoriteSnacks = [

    "Alice": "Chips",

    "Bob": "Licorice",

    "Eve": "Pretzels",

]

func buyFavoriteSnack(person: String, vendingMachine: VendingMachine) throws {

    let snackName = favoriteSnacks[person] ?? "Candy Bar"

    try vendingMachine.vend(itemNamed: snackName)

}

let vendintMachine = VendingMachine()

vendintMachine.coinsDeposited = 20

do {

    try buyFavoriteSnack(person: "Alice", vendingMachine: vendintMachine)

} catch VendingMachineError.invalidSelection {

    print("invalid selection")

} catch VendingMachineError.insufficientFunds(let coinsNeeded) {

    print("insufficient funds")

} catch VendingMachineError.outOfStock {

    print("out of stock")

}

print(vendintMachine.coinsDeposited)