Errata: makes no sense to force-cast to optional

Under “Decoding” (p480 in iBooks on the Mac) the init(coder:) method uses

which makes absolutely no sense. This will crash when the cast to an optional String fails.
The correct way to do it I’d say would be

as this will never crash and correctly just assign nil to the name property in case anything doesn’t match up.

[quote]name = aDecoder.decodeObjectForKey("name") as! String?
This will crash when the cast to an optional String fails.[/quote]

As I mentioned at the end of this post:


in the examples the authors seem to have taken the position, “We want this code to fail immediately if the value is nil.” In other words, they seem to always use the unsafe ! rather than adding error handling code. That makes some sense to me because I rarely see programming books that include exception handling-- the thought being that adding exception handling just lengthens the code examples and can confuse the main concepts. However, it would have been nice if the authors had stated they were going to use the unsafe ! after they explained the safe and unsafe way to do things.

D’oh, missed it again :wink:

May I suggest that you create separate concise posts for things you’d consider an error in the book?
You have great and very informative long posts but I usually look for a post-title to determine if anyone has found some mistake already.

Sorry, I wasn’t saying that you shouldn’t have posted about that line of code, I was just trying to join both our posts with a link. When I was copying the code in the book, I tried to do it from memory, and I wrote the code in my program as:

Then I spent a little while trying to determine why the book used:

Early on in the book, I couldn’t understand the optionals used in the examples, and I posted about them, but I eventually came to realize that the book just uses the unsafe ! whenever there is an optional, which I interpret to mean, “We want the program to fail here if the value is nil”.

The name variable was declared as type String?, so it seems reasonable to cast the right hand side of the assignment to the type String?. But when I write this:

[code]func doStuff(x: Int) -> AnyObject? {
if x==2 {
return “Jim”
else {
return nil

var name: String?
name = doStuff(2) as? String?

…in the assignment statement, I think I am saying, “Cast the return value of doStuff(2) to the type String? and if that cast can’t be done, then return nil.” But Xcode immediately flags that with the error:

What?? You mean String?? is a type? What the?! Let’s try it:

var name: String??
name = doStuff(2) as? String?


Oh, boy.

In any case, the reason for the ! in the original example may be as simple as: "The authors tried as? but Xcode indicated that was an error and asked the authors if they wanted to change it to as!.