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Update 17_Optional_Chaining.md

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alsotang
2014-10-18 01:32:14 +08:00
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@ -200,7 +200,7 @@ func printNumberOfRooms(){
如果你利用可选链调用此方法，这个方法的返回值类型将是`Void?`，而不是`Void`，因为当通过可选链调用方法时返回值总是可选类型（optional type）。即使这个方法本身没有定义返回值，你也可以使用`if`语句来检查是否能成功调用`printNumberOfRooms`方法：如果方法通过可选链调用成功，`printNumberOfRooms`的隐式返回值将会是`Void`，如果没有成功，将返回`nil`： 如果你利用可选链调用此方法，这个方法的返回值类型将是`Void?`，而不是`Void`，因为当通过可选链调用方法时返回值总是可选类型（optional type）。即使这个方法本身没有定义返回值，你也可以使用`if`语句来检查是否能成功调用`printNumberOfRooms`方法：如果方法通过可选链调用成功，`printNumberOfRooms`的隐式返回值将会是`Void`，如果没有成功，将返回`nil`：
```swift ```swift
if john.residence?.printNumberOfRooms() { if john.residence?.printNumberOfRooms?() {
println("It was possible to print the number of rooms.") println("It was possible to print the number of rooms.")
} else { } else {
println("It was not possible to print the number of rooms.") println("It was not possible to print the number of rooms.")