Let's Scope & Optionals -- Huh?

== Scope ==

let isMorning = true

var greeting = ""

if isMorning { greeting = "Good Morning" }

else { greeting = "Good Afternoon" }

print( greeting)

== Optional Value ==

- Think of it as a bag with value or empty (nil)

Example: var teacherName: String?

- Need to unwrap optional value before using it

print("Next year, my teacher is Ms. \(futureTeacher)")

print("Next year, my teacher is Ms. \(futureTeacher!)")

NOTE: force-unwrapping an optional with no value will cause error.

=======

Better way:

var futureTeacher: String?

print(futureTeacher!)

/*if futureTeacher != nil {

let unknownTeacher = futureTeacher!

print("next year my teacher is \(futureTeacher!)")

} else {

print("I don't know who is my teacher")

=====

if-let = to see if optional has a value

**

if let knownTeacher = futureTeacher {

print("Your next year teacher is \(knownTeacher)")

} else {

print("I don't know who is my teacher")

}

==

if let knownTeacher = futureTeacher { print(" Next year \( knownTeacher) will be my teacher.") }

==

if futureTeacher != nil { let knownTeacher = futureTeacher! print(" Next year \( knownTeacher) will be my teacher.")

==

nil coalescing operator ?? HUH ??

When the optional has a value, the value will be used as usual, but when the optional is nil, the nil coalescing operator will use the default value instead.

optionalThing ?? defaultThing

==

let defaultLunch = "Pizza"

var specialLunch: String?

var myLunch = specialLunch ?? defaultLunch

print("On Monday, I had \(myLunch) for lunch")

specialLunch = "Pie"

myLunch = specialLunch ?? defaultLunch

print("On Monday, I had \(myLunch) for lunch")

==

Homework:

- Review this class and the previous classes of Swift

- Make sure you understand the optional variables

- Remember that you need to unwrap the optional variables before using it. But, how?