Delegate Forwarding in Swift. Useful for choosing some methods of a delegate to handle yourself and others to pass to a different delegate. Inspired by WebKit's Objective-C implementation of the same for UIScrollViewDelegate: https://github.com/WebKit/WebKit/blob/20586209d4e623ecaf489c9913a5732d80ba6e39/Source/WebKit/UIProcess/ios/WKScrollView.m…

DelegateForwarder.swift

class DelegateForwarder<T: NSObjectProtocol>: NSObject {

	//	MARK: - Properties
	
	weak var internalDelegate: T?
	
	weak var externalDelegate: T?
	
	
	var asConforming: T {
		return unsafeBitCast(self, to: T.self)
	}
	
	
	//	MARK: - Init
	
	init(internalDelegate: T? = nil, externalDelegate: T? = nil) {
		self.internalDelegate = internalDelegate
		self.externalDelegate = externalDelegate
	}
	
	
	//	MARK: - Forwarding
	
	override func responds(to sel: Selector!) -> Bool {
		return
			self.internalDelegate?.responds(to: sel) ?? false ||
			self.externalDelegate?.responds(to: sel) ?? false
	}
	
	override func forwardingTarget(for sel: Selector!) -> Any? {
		if self.internalDelegate?.responds(to: sel) == true {
			return self.internalDelegate
		}
		
		return self.externalDelegate
	}
	
}