The key to using optionals is to always verify that they contain a valid value prior to accessing them. We use the term unwrapping to refer to the process of retrieving a value from an optional.
Using optionals
Forced unwrapping of an optional
To unwrap or retrieve the value of an optional, we place an exclamation mark (!) after the variable name. This is called forced unwrapping. Forced unwrapping, in this manner, is very dangerous and should be used only if we are certain that the variable contains a non- nil value. Otherwise, if it does contain a nil value, we will get a runtime error and the application will crash.
When we use the exclamation point to unwrap an optional, we are telling the compiler that we know the optional...