One way to let a subclass inherit a method referencing its own type in Swift (slightly improved)

static-class-method-that-references-subclass-type-try-2.swift

// Mason 2019-09-29: This is one way to allow subclasses to inherit a
// method with a parameter whose type refers to the actual subclass type
// (and not the parent class's type).
//
// One purpose here is to define a base class, that can have various
// subclasses, and enable all of the subclasses to inherit a class method
// named configure(), which creates an instance of the subclass and then
// configures the instance and its various subclass-specific properties.
//
// The improvements are based on feedback in this thread on the Swift forum:
//
// https://forums.swift.org/t/how-to-let-subclass-inherit-a-method-referencing-its-own-type/29350
//
// This is a simplified and improved revision to my first attempt:
//
// https://gist.github.com/masonmark/9036c1767ffef24c15e450478861cdde


protocol Configurable: AnyObject {
    init()
}

extension Configurable {
    static func configure( _ configurator: (Self) -> Void) -> Self {
        let result = Self.init()
        configurator(result)
        return result
    }
}


/// Classes which conform to `Configurable` must also implement (or
/// inherit from another class that implements) a `required init()`
/// initializer to satisfy the compiler.
class Person: Configurable {
    
    /// This required initializer must be present to satisfy the compiler.
    required init() {}
    
    var name = "Alice"
    var age  = 0
    
    var bio: String {
        "My name is \(name), and I am a \(Self.self). I am \(age) years old."
    }
}

class FireFighter: Person {
    var helmetSize: Int?
    var hasLicenseToDriveFireEngine = false
}

class PoliceOfficer: Person {
    var badgeNumber: String = "0000000"
}

let rand = Person.configure { rand in
    rand.age = 117
    rand.name = "Rand"
}

let jane = PoliceOfficer.configure() { jane in
    jane.name = "Jane"
    jane.age = 42
    jane.badgeNumber = "8675309"
}

func configureBiff(biff: FireFighter) {
    biff.hasLicenseToDriveFireEngine = true;
    biff.helmetSize = 15
    biff.age = 21
    biff.name = "Biff Wigginberger Jr."
}

// Pass a function to `configure()` instead of doing it inline:
let biff = FireFighter.configure(configureBiff)

print(rand.bio)
print(jane.bio)
print(biff.bio)

// prints:
//    My name is Rand, and I am a Person. I am 117 years old.
//    My name is Jane, and I am a PoliceOfficer. I am 42 years old.
//    My name is Biff Wigginberger Jr., and I am a FireFighter. I am 21 years old.