RetainCount.swift

import Foundation

class A: NSObject {
    weak var delegate: B?
}

class B: NSObject {
    weak var delegate: A?
}

var a: A?
var b: B?

func configure() {
    a = A()
    b = B()

    a?.delegate = b
    b?.delegate = a
}
configure()

print(a)
print(b)
print(a?.delegate)
print(b?.delegate)