Force unwrapping

Optionals represent data that may or may not be there, but sometimes you know for sure that a value isn’t nil. In these cases, Swift lets you force unwrap the optional: convert it from an optional type to a non-optional type.

For example, if you have a string that contains a number, you can convert it to an Int like this:

let str = "5"
let num = Int(str)

That makes num an optional Int because you might have tried to convert a string like “Fish” rather than “5”.

Even though Swift isn’t sure the conversion will work, you can see the code is safe so you can force unwrap the result by writing ! after Int(str), like this:

let num = Int(str)!

Swift will immediately unwrap the optional and make num a regular Int rather than an Int?. But if you’re wrong – if str was something that couldn’t be converted to an integer – your code will crash.

As a result, you should force unwrap only when you’re sure it’s safe – there’s a reason it’s often called the crash operator.