GenericViewStates.swift

import UIKit

protocol ViewStateType {
    var title: String { get set }
    
    init()
}

protocol BaseViewDelegate: class {
    associatedtype BaseViewType
    
    func baseViewDidSomeAction(_ view: BaseViewType)
}

class BaseView<T: ViewStateType> {
    var viewState: T = T(){
        didSet {
            update()
        }
    }
    
//    weak var delegate: BaseViewDelegate? This does not work. If it did, everyone would be happy.
    
    func update() {
        print("BaesView<T> update()")
    }
}

struct SubclassViewState: ViewStateType {
    var title: String
    var subtitle: String
    
    init() {
        title = "Default Title"
        subtitle = "Default Subtitle"
    }
}

class SubclassView: BaseView<SubclassViewState> {
    
    override func update() {
        super.update()
        
        // viewState is a SubclassViewState
    }
}

class SomeViewController: BaseViewDelegate {
    
    func baseViewDidSomeAction(_ view: SubclassView) {
        print("view is a SubclassView!")
    }
}