Group Group Group Group Group Group Group Group Group

Difference between "as? NSError" and "as NSError?"

In some chapters of the book there’s lines like this:

if let error = error as NSError?

whereas in Swift I usually see optional binding like this:

if let something = something as? Type

Can someone explain the difference and why we’re using “as Type?” instead of “as? Type”, I don’t get it.

Thank you!

1 Like

@ritsz The first line of code uses as to typecast error to NSError? because you are sure that error is of type NSError? in this case.

The second line of code uses as? to downcast something to Type since this definitely fails if something isn’t of type Type.

Please do let me know if you have any other questions or issues about the whole thing when you get a chance. Thank you!

To me it looks weird to use if let when typecasting to an optional, I’m used to see it for optional binding (to unwrap the optional) instead, but I understand. Thank you.

@ritsz You use if let in the first case to unwrap error because it may be nil since it is of type NSError?.

You use if let in the second case to unwrap something because it is nil if the downcast to Type fails.

Please do let me know if you have any other questions or issues about the whole thing when you get a chance. Thank you!

This topic was automatically closed after 166 days. New replies are no longer allowed.