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Swift Optionals


What are Optionals ?

Consider Optionals as a kind of "parcel". Before you "unwrap" it you won't know if it contains something or not. Optionals in Swift are used to handle an optional values. Sometimes values may be present, sometimes not. The are indicated using ? (question) mark after optional name.

Syntax :-

Optionals are indicated using ? at the end of variable type.

  /* Optional Integer declaration */ 
 var age: Int?

 /* Optional String declaration */ 
 var name: String?

Now consider this, one with Optional string

var name: String? = "Jazz"

Another one with Non-Optional string

var name: String = "Jazz"

Though both versions Optional and Non-Optional looks same but they are not. An optional String is not a String with some "optional" setting turned on. It's not a special variety of String. A String and an optional String are completely different types.

What is forced unwrapping ?

Unwrapping of an optional value can be done by using ! (exclamation) mark at the end of variable type. Consider this example for better understanding of Forced Unwrapping

1) Before Unwrapping :-

import UIKit

var name:String?
name = "Manish"

if name != nil {
    print(name)
}else {
    print("Your Name has nil value")
}

Output :-

Optional("Manish")

2) After Unwrapping :-

import UIKit

var name:String?

name = "Manish"

if name != nil {
/* Exclamation mark is added at the end */
    print(name!)
}else {
    print("Your Name has nil value")
}

Output :-

Manish

Automatic Unwrapping

To avoid using '!' mark at every optional variable , you can do this instead ,

var name:String!

Instead of using ? just declare ! mark at the time of declaration of an Optional variable. Simple and easy :)

Example of Automatic unwrapping :-

import UIKit

/* Instead of writing ? mark, use ! mark for automatic unwrapping */
var name:String!
name = "Manish"
  if name != nil{
    print(name)
   }
  else 
   {
    print("Your Name has nil value")
   }

Output :-

Manish

Why Optionals ?

Optionals have two use cases:

1) Things that can fail (I was expecting something but I got nothing)

2) Things that are nothing now but might be something later (and vice-versa)

Some examples:

1) Trying to read a file's contents (which normally returns the file's data) but the file doesn't exist in library

2) Searching for a match in an array but it may or may not returns an data.

3) A property which can be there or not there, like middleName or spouse in a Person class