import UIKit

protocol CellType {
    associatedtype Model
}

class DataSource<Item, Cell where Cell: CellType, Item == Cell.Model>: NSObject {
    var items: [Item] = []
    
    init(items: [Item], cellType: Cell.Type) {
        self.items = items
    }
}

struct A {
    var flag: Bool = false
}

class CellA: CellType {
    typealias Model = A
}

class MyViewController {
    var dataSource = DataSource(items: [A()], cellType: CellA.self)
}


@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        
        let vc = MyViewController()
        
        return true
    }
}

* thread #​1: tid = 0x3ec3, 0x00283d38 libswiftCore.dylib`swift_initClassMetadata_UniversalStrategy + 440, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x79de8)
  * frame #​0: 0x00283d38 libswiftCore.dylib`swift_initClassMetadata_UniversalStrategy + 440
    frame #​1: 0x00075bd8 SwiftCrashCode`___lldb_unnamed_function3$$SwiftCrashCode + 196
    frame #&#8203;2: 0x00285052 libswiftCore.dylib`(anonymous namespace)::GenericCacheEntry* llvm::function_ref<(anonymous namespace)::GenericCacheEntry* ()>::callback_fn<swift_getGenericMetadata::$_1>(long) + 18
    frame #&#8203;3: 0x00284f46 libswiftCore.dylib`swift::MetadataCache<(anonymous namespace)::GenericCacheEntry>::addMetadataEntry(swift::EntryRef<(anonymous namespace)::GenericCacheEntry>, ConcurrentList<swift::MetadataCache<(anonymous namespace)::GenericCacheEntry>::EntryPair>&, llvm::function_ref<(anonymous namespace)::GenericCacheEntry* ()>) + 80
    frame #&#8203;4: 0x00282efc libswiftCore.dylib`swift::MetadataCache<(anonymous namespace)::GenericCacheEntry>::findOrAdd(void const* const*, unsigned long, llvm::function_ref<(anonymous namespace)::GenericCacheEntry* ()>) + 308
    frame #&#8203;5: 0x00283054 libswiftCore.dylib`swift_getGenericMetadata3 + 68
    frame #&#8203;6: 0x00075ff4 SwiftCrashCode`type metadata accessor for DataSource<A, CellA> + 116 at AppDelegate.swift:0
    frame #&#8203;7: 0x0007524c SwiftCrashCode`MyViewController.init() -> MyViewController + 24 at AppDelegate.swift:32
    frame #&#8203;8: 0x000752f4 SwiftCrashCode`MyViewController.__allocating_init() -> MyViewController + 36 at AppDelegate.swift:0
    frame #&#8203;9: 0x000754fc SwiftCrashCode`AppDelegate.application(application=0x15e285f0, launchOptions=nil, self=0x15d29ff0) -> Bool + 52 at AppDelegate.swift:44
    frame #&#8203;10: 0x000756c0 SwiftCrashCode`@objc AppDelegate.application(UIApplication, didFinishLaunchingWithOptions : [NSObject : AnyObject]?) -> Bool + 260 at AppDelegate.swift:0
    frame #&#8203;11: 0x32224586 UIKit`-[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 274
    frame #&#8203;12: 0x32223eda UIKit`-[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1610
    frame #&#8203;13: 0x3221e56a UIKit`-[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 714
    frame #&#8203;14: 0x321ba6e8 UIKit`-[UIApplication handleEvent:withNewEvent:] + 3540
    frame #&#8203;15: 0x321b9850 UIKit`-[UIApplication sendEvent:] + 72
    frame #&#8203;16: 0x3221dca8 UIKit`_UIApplicationHandleEvent + 616
    frame #&#8203;17: 0x34826aec GraphicsServices`_PurpleEventCallback + 608
    frame #&#8203;18: 0x348266d6 GraphicsServices`PurpleEventCallback + 34
    frame #&#8203;19: 0x2f962a66 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 34
    frame #&#8203;20: 0x2f962a02 CoreFoundation`__CFRunLoopDoSource1 + 346
    frame #&#8203;21: 0x2f9611d6 CoreFoundation`__CFRunLoopRun + 1398
    frame #&#8203;22: 0x2f8cbebe CoreFoundation`CFRunLoopRunSpecific + 522
    frame #&#8203;23: 0x2f8cbca2 CoreFoundation`CFRunLoopRunInMode + 106
    frame #&#8203;24: 0x3221ced0 UIKit`-[UIApplication _run] + 760
    frame #&#8203;25: 0x3221814c UIKit`UIApplicationMain + 1136
    frame #&#8203;26: 0x000759c8 SwiftCrashCode`main + 172 at AppDelegate.swift:37
    frame #&#8203;27: 0x3a71fab6 libdyld.dylib`start + 2