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import UIKit
class ViewController: UIViewController {
enum VendingMachineError : ErrorType {
case InvalidSelection
case InsufficientFunds(coinsNeeded:Int)
case OutOfStock
}
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("dispensine \(snack)")
}
func vend(itemNamed name:String) throws {
guard var 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
--item.count
inventory[name] = item
dispenseSnack(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)
}
func someThrowingFunction(value : Int) throws -> Int {
// ...
return value*3
}
override func viewDidLoad() {
super.viewDidLoad()
let vendingMachine = VendingMachine()
vendingMachine.coinsDeposited = 8
// 标准用法
do {
try buyFavoriteSnack("Alice", vendingMachine: vendingMachine)
} catch VendingMachineError.InvalidSelection {
print("Invalid Selection.")
} catch VendingMachineError.OutOfStock {
print("Out of Stock.")
} catch VendingMachineError.InsufficientFunds(let coinsNeeded) {
print("Insufficient funds.Please insert an addtional \(coinsNeeded) coins.")
} catch is ErrorType {
print("其他异常.")
}
// try?
let x = try? someThrowingFunction(100)
// 相当于
let y :Int?
do {
y = try someThrowingFunction(100)
} catch {
y = nil
}
// TODO: try!
// TODO: defer 关键字
}
}
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