Delegate-pattern without a weak delegate object creates retain cycle

retain-cycle.swift

class Parent {
  var child: Child? {
    didSet {
      child.callback = delegateCallback // Fix: child.callback = weakify(self, Parent.delegateCallback) using https://github.com/klundberg/Weakify/blob/master/Weakify/Weakify.swift#L15-L21
    }
  }
  
  func delegateCallback() {
    // ...
  }
}

class Child {
  var callback: (Void -> Void)?
  
  private func triggerCallback() {
    callback?()
  }
}