exception handler.swift

// src from:https://www.cnswift.org/error-handling
struct Item {
    var price: Int
    var count: Int
}
//定义异常-枚举是典型的为一组相关错误条件建模的完美配适类型，关联值还允许错误错误通讯携带额外的信息。比如说，这是你可能会想到的游戏里自动售货机会遇到的错误条件：
enum VendingMachineError: Error {
    case invalidSelection
    case insufficientFunds(coinsNeeded: Int)
    case outOfStock
}
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
    // 使用抛出函数传递错误
    func vend(_ name: String) throws {
        guard let item = inventory[name] else {
            // 抛出异常
            throw VendingMachineError.invalidSelection
        }

        guard item.count > 0 else {
            // 抛出异常
            throw VendingMachineError.outOfStock
        }

        guard item.price <= coinsDeposited else {
            //// 抛出带参数异常
            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",
]
//为了明确一个函数或者方法可以抛出错误，你要在它的声明当中的形式参数后边写上 throws关键字
func buyFavoriteSnack(person: String, vendingMachine: VendingMachine) throws {
    let snackName = favoriteSnacks[person] ?? "Candy Bar"
    try vendingMachine.vend(snackName)
}
let v = VendingMachine()
v.coinsDeposited = 888
//使用 Do-Catch 处理错误
do{
//    try v.vend("noexists")
    try v.vend("Pretzels")
    try v.vend("Pretzels")
    try buyFavoriteSnack(person: "Alice", vendingMachine: v)
} catch VendingMachineError.invalidSelection {
    print("Invalid Selection.")
} catch VendingMachineError.outOfStock {
    print("Out of Stock.")
} catch VendingMachineError.insufficientFunds(let coinsNeeded) {
    print("Insufficient funds. Please insert an additional \(coinsNeeded) coins.")
} catch {
    print("Unexpected error: \(error).")
}