DelegateMulticaster.swift

/// delegateなどを配列などに持ちたいときに使う
private final class WeakObject<T: AnyObject> {
    weak var object: T?
    
    init(_ object: T?) {
        self.object = object
    }
}

final class PageViewControllerDelegateMulticaster: NSObject, UIPageViewControllerDelegate {
    private var targets: [WeakObject<UIPageViewControllerDelegate>] = []
    
    func add(_ delegate: UIPageViewControllerDelegate) {
        targets.append(WeakObject(delegate))
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        targets.forEach { target in
            guard let targetUnwrapped = target.object else {
                return
            }
            targetUnwrapped.pageViewController?(pageViewController, didFinishAnimating: finished, previousViewControllers: previousViewControllers, transitionCompleted: completed)
        }
    }
}