Optional Types

Wednesday, 19 September 2018

Optional Types

Optional represents either wrapped value or nil.
Optionals are generic enum type that works as wrapper.

Basically wrapper allow variable have 2 states:

  1. User define type
  2. nil (that represent no value)
In swift nil value must be optional.
Optional can be created by appending either "?" or "!".

example :

var name : String? = nil
var lname : String! = nil

"?" must be explicitly unwrapped where as "!" automatically unwrapped.
Conditionally unwrapped use "?" optional binding where as force unwrapped use "!" operator. If you force unwrapped variable and value is nil then program will throw exception and crash so be careful.

example :

var lname : String! = nil
print(lname!)

Output :

fatal error: unexpectedly found nil while unwrapping an Optional value

Safe unwrapping :

Using if-let statement safe unwrap

example :

func safeUnwrap(withName name : String?){
    if let userName = name{
        print(userName)
    }else{
        print("name value is nil")
    }
}

safeUnwrap(withName: "Pratik")

Output :

Pratik

safeUnwrap(withName: nil)


Output :

name value is nil

Using guard-let statement safe unwrap

example :

func safeUnwrap(withName name : String?){
    guard let userName = name else{
        print("user name not found")
        return
    }
    print(userName)
}

safeUnwrap(withName: "Pratik")

Output :

Pratik

safeUnwrap(withName: nil)


Output :

user name not found

Using Coalescing operator safe unwrap

example :

var name : String? = nil
print(name ?? "name value is nil")


Output :

name value is nil

var name : String? = nil
name = "Pratik"
print(name ?? "name value is nil")


Output :

Pratik

You can also use Optional chaining in order to call method,property or subscript.

example : 

struct Family{
    func printName() {
        print("Hello friends")
    }
}

var objFamily : Family?
objFamily?.printName()

Output :

no print 

var objFamily : Family? = Family()
objFamily?.printName()

Output :

Hello friends



unwrapped using optional type in swift
Optional types unwrapped

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