Downcasting

class BaseClass {
    var baseClassVariable: String = "I am the baseClassVariable"
}
class ChildClass: BaseClass {
    var childClassVariable: String = "I am the childClassVariable"
}
class ChildOfChildClass: ChildClass { // this is also a descendant of BaseClass, because ChildClass is a descendent if BaseClass (think family trees)
    var childOfChildClassVariable: String = "I am the childOfChildClassVariable"
}
class RandomClass {
    var randomClassVariable: String = "I am the randomClassVariable"
}

let baseClassObject = BaseClass()
let childClassObject = ChildClass()
let grandchildClassObject = ChildOfChildClass()
let randomClassObject = RandomClass()

// you can test making variables that upcast or downcast the above objects.
var testBaseToChildDowncast = baseClassObject as? ChildClass // this will be 'nil' because baseClassObject never was any more specific than 'BaseClass'... so you cannot downcast it.

var testGrandchildToBaseUpcast = grandchildClassObject as BaseClass // this will NOT be nil, ChildOfChildClass is related to BaseClass and is more specific than BaseClass, so you can make it less specific by labeling it as a 'BaseClass' object.
// xcode will tell you to remove the optional operator (?) from after the 'as' because you can always upcast to a related class (you can describe it as something less specific), whereas you cannot always make something more specific (downcasting)

var testOtherBaseToChildDowncast = testGrandchildToBaseUpcast as? ChildClass // this will NOT be nil.
// Even though testGrandchildToBaseUpcast is a BaseClass object, it was originally a ChildOfChildClass object therefore you CAN downcast it into being a ChildClass object (ChildClass is in between BaseClass and ChildOfChildClass on the family tree!)

// take a look at what printing these objects to the console does!
println(testBaseToChildDowncast) // "nil", as expected
println(testGrandchildToBaseUpcast) // ""__lldb_expr_2.ChildOfChildClass""
println(testOtherBaseToChildDowncast)


// xcode will have issues if you try to cast an object to something that it isn't even remotely related to
// for instance, if you cast randomClassObject to a ChildOfChildClassObject, any playground file will begin giving you a nasty error
// e.g.: var randomToGrandchild = randomClassObject as? ChildOfChildClassObject

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "showPlaylistDetail" {
        let buttonTitle: String? = (sender as? UIButton)?.titleLabel?.text
        if buttonTitle == "Button1" {
            playlistDetailController.segueLabelText = "Yay you pressed Button1!"
        } else if buttonTitle == "Button2" {
            playlistDetailController.segueLabelText = "Yay you pressed Button2!"
        } else {
        // this else block is executed if buttonTitle is nil or some String value we weren't expecting.
        }
    }
}
// also notice how the 'sender' needed to be downcast from 'AnyObject' to 'UIButton'.
// this is because the 'sender' is one of those buttons
// if sender is not a 'UIButton' then the label text would not be set because 'buttonTitle: String?' would have a value of 'nil'