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)
