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Lavare
2017-05-23 17:21:49 +08:00
committed by 安正超
parent c04b28ba60
commit b91f75b529
1 changed files with 10 additions and 10 deletions
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20
source/chapter2/18_Error_Handling.md
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@ -7,7 +7,7 @@
> >
> 2.2 > 2.2
> 翻译+校对：[SketchK](https://github.com/SketchK) 2016-05-15 > 翻译+校对：[SketchK](https://github.com/SketchK) 2016-05-15
> >
> 3.0 > 3.0
> 翻译+校对：[shanks](http://codebuild.me) 2016-09-24 > 翻译+校对：[shanks](http://codebuild.me) 2016-09-24
> 3.0.1，shanks，2016-11-13 > 3.0.1，shanks，2016-11-13
@ -93,22 +93,22 @@ class VendingMachine {
func dispenseSnack(snack: String) { func dispenseSnack(snack: String) {
print("Dispensing \(snack)") print("Dispensing \(snack)")
} }
func vend(itemNamed name: String) throws { func vend(itemNamed name: String) throws {
guard let item = inventory[name] else { guard let item = inventory[name] else {
throw VendingMachineError.InvalidSelection throw VendingMachineError.InvalidSelection
} }
guard item.count > 0 else { guard item.count > 0 else {
throw VendingMachineError.OutOfStock throw VendingMachineError.OutOfStock
} }
guard item.price <= coinsDeposited else { guard item.price <= coinsDeposited else {
throw VendingMachineError.InsufficientFunds(coinsNeeded: item.price - coinsDeposited) throw VendingMachineError.InsufficientFunds(coinsNeeded: item.price - coinsDeposited)
} }
coinsDeposited -= item.price coinsDeposited -= item.price
var newItem = item var newItem = item
newItem.count -= 1 newItem.count -= 1
inventory[name] = newItem inventory[name] = newItem
@ -120,7 +120,7 @@ class VendingMachine {
在`vend(itemNamed:)`方法的实现中使用了`guard`语句来提前退出方法，确保在购买某个物品所需的条件中，有任一条件不满足时，能提前退出方法并抛出相应的错误。由于`throw`语句会立即退出方法，所以物品只有在所有条件都满足时才会被售出。 在`vend(itemNamed:)`方法的实现中使用了`guard`语句来提前退出方法，确保在购买某个物品所需的条件中，有任一条件不满足时，能提前退出方法并抛出相应的错误。由于`throw`语句会立即退出方法，所以物品只有在所有条件都满足时才会被售出。
因为`vend(itemNamed:)`方法会传递出它抛出的任何错误，在你的代码中调用此方法的地方，必须要么直接处理这些错误——使用`do-catch`语句，`try?`或`try!`；要么继续将这些错误传递下去。例如下面例子中，`buyFavoriteSnack(_:vendingMachine:)`同样是一个 throwing 函数，任何由`vend(itemNamed:)`方法抛出的错误会一直被传递到`buyFavoriteSnack(person:vendingMachine:) `函数被调用的地方。 因为`vend(itemNamed:)`方法会传递出它抛出的任何错误，在你的代码中调用此方法的地方，必须要么直接处理这些错误——使用`do-catch`语句，`try?`或`try!`；要么继续将这些错误传递下去。例如下面例子中，`buyFavoriteSnack(person:vendingMachine:)`同样是一个 throwing 函数，任何由`vend(itemNamed:)`方法抛出的错误会一直被传递到`buyFavoriteSnack(person:vendingMachine:) `函数被调用的地方。
```swift ```swift
let favoriteSnacks = [ let favoriteSnacks = [
@ -174,7 +174,7 @@ do {
var vendingMachine = VendingMachine() var vendingMachine = VendingMachine()
vendingMachine.coinsDeposited = 8 vendingMachine.coinsDeposited = 8
do { do {
try buyFavoriteSnack("Alice", vendingMachine: vendingMachine) try buyFavoriteSnack(person: "Alice", vendingMachine: vendingMachine)
} catch VendingMachineError.InvalidSelection { } catch VendingMachineError.InvalidSelection {
print("Invalid Selection.") print("Invalid Selection.")
} catch VendingMachineError.OutOfStock { } catch VendingMachineError.OutOfStock {
@ -195,9 +195,9 @@ do {
func someThrowingFunction() throws -> Int { func someThrowingFunction() throws -> Int {
// ... // ...
} }
let x = try? someThrowingFunction() let x = try? someThrowingFunction()
let y: Int? let y: Int?
do { do {
y = try someThrowingFunction() y = try someThrowingFunction()