Should I choose optionals or implicitly unwrapped optionals

Question

Suppose that you need to write function that takes closure as one of the parameters to call it as a callback. The user of this function should be able to pass nil instead of closure. Will you use optionals or implicitly unwrapped optionals in this case?

Thanks in advance.

Answer 1

As a complement to Nate's answer (which is imo the solution ), my suggestion is to never use implicitly unwrapped optionals, unless you have a good reason. Deferred initialization is a good reason.

• If you are not sure, don't use it

• If the optional can be nil during its post-initialization life cycle, don't use it

• If you want to avoid typing an extra ? , don't use it

• If a 3rd party function, method or closure passes an optional, don't turn it into an implicitly unwrapped

• If a 3rd party function, method or closure provides an implicitly unwrapped... judge by yourself whether to explicitly check for not nil (ie whether to trust that optional will always be not nil)

• More generally, if you have doubts about how an implicitly unwrapped works, it's always better to always avoid

Answer 2

Definitely use an optional here, since the expectation is that it could be nil . When implicitly unwrapped optionals are used, the intention is that they'll never be nil by the time they're used - the typical example is @IBOutlet properties that can't be created in the initializer but will be created via the storyboard before they're used in viewDidLoad .