Question

iOS App Development

10. (8 point) What are optionals? Why are optionals needed? Why must unwrapping be done? What can go wrong with optional unwrapping?

12. （6 Point）Name a swift / iOS type is a value type. Name a Swift/iOS type that is a reference type. Explain what happens when a value type variable is assigned a new value. Do not mention parameter passing in your answer.

Answer 1

10.

Optionals in Swift are can be having data or no-data

//for the user the input can be optional (he might give data or he can leave it blank)

if we dont use optional then every data input is mandatory

Syntax:

var name: String? or var name : Optional<String>

//above String? , variable name can be of type String or nothing

Unwrapping

Basically feel optionals as a container so until we open the container we dont know what is the data inside the container

to unwrap we use ! at the end of var name

eg : print("My name is \(name!)")

problem with optional is when we assign name=nil

it raises the runtime crash stating nil is unexpected

so,we have to be clear that the optional data is having a valid input

we can use if statements to handle this

eg : if (name != nil) {

print("My name is \(name!)")

}

only when there is data in var name print following statement

we can also use if let statement provided by swift

eg:

if let name: String = name {

   print("My name is \(name!)")

}