Create singleton in swift 4 in a class having public init - ios

Question

I am having a public class in a different code like this -
public class Person {
public required init() {}
}
This class is in a framework and cannot be modified.
Now the problem is I have been told to inherit from this class and create a singleton object of the new class
public class Jon: Person {
public static var shared: Jon = Jon()
required init() {}
}
But the required init is letting users create multiple instances of the class Jon.
Can anybody suggest on how to do this in swift 4.

Answer 1

I found a solution to achieve this. Look into my solution hopefully it will serve your purpose.
public class ParentClass {
public required init() {}
}
class SubClass: ParentClass {
static let sharedInstance = SubClass(foo: "")
#available(*, unavailable)
required init() { }
//You can change the init parameter as per your requirement
private init(foo: String) {
super.init()
//Write your initialization code
}
}
If you dont want to pass any argument to the init you can do something like this.
private init(_ foo: String? = nil) {
super.init()
//Write your initialization code
}
Now you initialize your object without passing any argument like
static let sharedInstance = SubClass()

Answer 2

One solution is to use Composition rather than Inheritance as the design solution. Since the Person object is supposed to be singleton as well we make it immutable and initialise it in the private init method using the required init
public class Jon {
static let instance = Jon()
private init() {
person = Person()
}
public let person: Person
}
And it can be used like this (with a name property for instance)
var jon = Jon.instance
jon.person.name = "John"
or Person could be made private and computed properties added to the singleton class
public class Jon {
static let instance = Jon()
private init() {
person = Person()
}
private let person: Person
var name: String? {
get { return person.name }
set { person.name = newValue}
}
}
and then the name property is accessed directly
var jon = Jon.instance
jon.name = "John"