movie file on mac has long numbers for name

Movie file on mac has long numbers for name movie#

The result of item as? Movie is of type Movie?, or “optional Movie”.ĭowncasting to Movie fails when applied to the Song instances in the library array. Because of this uncertainty, the as? form of the type cast operator returns an optional value when attempting to downcast to a subclass type. Because item is a MediaItem instance, it’s possible that it might be a Movie equally, it’s also possible that it might be a Song, or even just a base MediaItem. The example starts by trying to downcast the current item as a Movie. // Song: Never Gonna Give You Up, by Rick Astley.

// Song: The One And Only, by Chesney Hawkes.// Song: Blue Suede Shoes, by Elvis Presley.You don’t know in advance which actual class to use for each item, and so it’s appropriate to use the conditional form of the type cast operator ( as?) to check the downcast each time through the loop: In this example, each item in the array might be a Movie, or it might be a Song. This is necessary in order for it to be able to access the director or artist property of a Movie or Song for use in the description. To do this, it needs to access each item as a true Movie or Song, and not just as a MediaItem. The example below iterates over each MediaItem in library, and prints an appropriate description for each item. This form of the operator will trigger a runtime error if you try to downcast to an incorrect class type. Use the forced form of the type cast operator ( as!) only when you are sure that the downcast will always succeed. This enables you to check for a successful downcast. This form of the operator will always return an optional value, and the value will be nil if the downcast was not possible. Use the conditional form of the type cast operator ( as?) when you aren’t sure if the downcast will succeed. The forced form, as!, attempts the downcast and force-unwraps the result as a single compound action. The conditional form, as?, returns an optional value of the type you are trying to downcast to. Where you believe this is the case, you can try to downcast to the subclass type with a type cast operator ( as? or as!).īecause downcasting can fail, the type cast operator comes in two different forms. A constant or variable of a certain class type may actually refer to an instance of a subclass behind the scenes.

Movie file on mac has long numbers for name