Multicast delegate in swift

multicast.swift

import Foundation

internal final class MulticastDelegate<T> {
	private var delegates = [Weak]()
	
	func add(_ delegate: T) {
		if Mirror(reflecting: delegate).subjectType is AnyClass {
			let weakValue = Weak(value: delegate as AnyObject)
			guard delegates.index(of: weakValue) == nil else {
				return
			}
			delegates.append(weakValue)
		} else {
			fatalError("Multicast delegates do not support value types")
		}
	}
	
	func remove(_ delegate: T) {
		if Mirror(reflecting: delegate).subjectType is AnyClass {
			let weakValue = Weak(value: delegate as AnyObject)
			guard let index = delegates.index(of: weakValue) else {
				return
			}
			delegates.remove(at: index)
		}
	}
	
	func invoke(_ invocation: (T) -> Void) {
		var indices = IndexSet()
		for (index, delegate) in delegates.enumerated() {
			if let delegate = delegate.value as? T {
				invocation(delegate)
			} else {
				indices.insert(index)
			}
		}
		
		self.removeObjects(atIndices: indices)
	}
	
	private func removeObjects(atIndices indices: IndexSet) {
		let indexArray = Array(indices).sorted(by: >)
		for index in indexArray {
			delegates.remove(at: index)
		}
	}
	
	internal func numberOfDelegates() -> Int {
		return delegates.count
	}
}

private final class Weak: Equatable {
	weak var value: AnyObject?
	
	init(value: AnyObject) {
		self.value = value
	}
	
	static func == (lhs: Weak, rhs: Weak) -> Bool {
		return lhs.value === rhs.value
	}
}