Optional chaining

Optional chaining is a process to query and call properties, methods, and subscripts on an optional that may currently be nil. Optional chaining in Swift is similar to messaging nil in Objective-C but in a way that works for any type and can be checked for success or failure.

The following example presents two different classes. One of the classes, Person, has a property of type of Optional (residence), which wraps the other class type Residence:

class Residence { 
    var numberOfRooms = 1 
} 

class Person { 
    var residence: Residence? 
} 

We will create an instance of the Person class, sangeeth:

let residence = Residence() 
residence.numberOfRooms = 5 

let sangeeth = Person() 
sangeeth.residence = residence 

To check for numberOfRooms, we need to use the residence property of the Person class, which is an optional. Optional chaining enables us to go through Optionals as follows:

if let roomCount = sangeeth.residence?.numberOfRooms { 
    // Use the roomCount 
    print...