在学习 Swift 错误处理的时候，官方给出的 do-catch 例子如下：
...
...
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)
}
var vendingMachine = VendingMachine()
vendingMachine.coinsDeposited = 8
do {
try buyFavoriteSnack(person: "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 additional \(coinsNeeded) coins.")
}
// Prints "Insufficient funds. Please insert an additional 2 coins."
但是亲自上手敲代码的时候，却总是在 "do" 闭包中 try 语句上报错：
"Errors thrown from here are not handled because the enclosing catch is not exhaustive"
1.png
大体意思是说这个 do-catch 是不完整的。这时候需要再加上一个空的 catch 语句用于关闭 catch。
do {
try buyFavoriteSnack(person: "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 additional \(coinsNeeded) coins.")
} catch { // 加入一个空的catch，用于关闭catch。否则会报错：Errors thrown from here are not handled because the enclosing catch is not exhaustive
}
