ChainIterator.swift

ChainIterator.swift

import UIKit

protocol PA {}
protocol PB {}
protocol PC {}
protocol PD {}

class A : PA {}
class B : A, PB {}
class C : B, PC {}
class D : C, PD {}

let mirror = Mirror(reflecting: D())

// helper function
func chainIterator<T>(_ value: T, _ f: @escaping (T?) -> (T?)) -> AnyIterator<T> {
    var next: T? = value
    return AnyIterator {
        defer { next = f(next) }
        return next
    }
}

// chain superclass
let superclasses = chainIterator(mirror) { $0?.superclassMirror }
superclasses.forEach { print($0) }
/*
 Mirror for D
 Mirror for C
 Mirror for B
 Mirror for A
 */

// also can use UIView
let v1 = UIView(); v1.tag = 1;
let v2 = UIView(); v2.tag = 2; v1.addSubview(v2)
let v3 = UIView(); v3.tag = 3; v2.addSubview(v3)
let v4 = UIView(); v4.tag = 4; v3.addSubview(v4)

let superviews = chainIterator(v4) { $0?.superview }
superviews.forEach { print($0.tag) }
/*
 4
 3
 2
 1
 */