Swift Functional Programming - Second Edition

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 ...