Swift 2.0：推断闭包类型错误

我得到错误

无法在当前上下文中推断闭包类型

在可在Swift 1.2中运行的代码中

private lazy var _messagesVC =  { return MessagesViewController(nibName:"MessagesViewController",bundle:nil)}()

我收到此错误的整个View Controller

import UIKit
class FriendsViewController: UIViewController {

@IBOutlet weak var containerView: UIView!
@IBOutlet weak var segmentContainerView: UIView!
private lazy var _connectionVC  =  { return FriendsConnectionViewController(nibName:"FriendsConnectionViewController",bundle:nil)}()
private lazy var _messagesVC =  { return MessagesViewController(nibName:"MessagesViewController",bundle:nil)}()


override func viewDidLoad() {
    super.viewDidLoad()
    self.selectedControllerFrom(index: 0)
     // Do any additional setup after loading the view.
}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

}

func selectedControllerFrom(index index:UInt)
{
    var vc:UIViewController?
    switch index{
    case 0: vc = _connectionVC
    case 1: vc = _messagesVC
    default : vc = nil
    }
    if vc != nil{
         self.showViewController(vc!,containerView: containerView);
    }
}