ios – 无法声明具有内部要求的公共协议扩展

我正在编写媒体播放器应用程序,并创建了自己的框架来管理所有播放器功能.在这个框架中,我有一个名为PlayerControllerType的公共协议和一个内部协议_PlayerControllerType.在PlayerControllerType中,我已经声明了所有方法和属性,这些方法和属性应该可以从框架外部访问.在_PlayerControllerType中,我定义了几个属性,这些属性由在框架内实现PlayerControllerType的具体类型使用.其中一种类型是PlayerController.其声明如下：

public class PlayerController<Item: Equatable>: NSObject,PlayerControllerType,_PlayerControllerType,QueueDelegate

现在我想为我的框架中的类提供一些默认实现,它们符合PlayerControllerType和内部_PlayerControllerType,例如：

import Foundation  
import MediaPlayer  

public extension PlayerControllerType where Self: _PlayerControllerType,Item == MPMediaItem,Self.QueueT == Queue<Item>,Self: QueueDelegate {  

    public func setQueue(query query: MPMediaQuery) {  
        queue.items = query.items ?? []  
    }  

}

这在Xcode 7 Beta 4中按预期工作.昨天我更新到Beta 6并收到此错误：
“扩展不能公开,因为它的通用要求使用内部类型”(另见截图).

我发现这个错误很刺激.当然,我的框架之外的类型没有这个扩展的好处,因为它无法访问内部协议_PlayerControllerType,但它对我的框架中实现PlayerControllerType和_PlayerControllerType的类型非常有用.

这只是Swift编译器中的一个错误,还是预期的行为？
非常不幸的是,这不再适用了,因为现在我必须将这些方法放入一个新创建的基类中,用于所有的PlayerControllers.

任何帮助或反馈将非常感谢.

凯

编辑：
以下是协议及其扩展的缩写示例：

public protocol PlayerControllerType {
    typealias Item
    var nowPlayingItem: Item {get}
    func play()
}

protocol _PlayerControllerType {
    var nowPlayingItem: Item {get set}
}

public extension PlayerControllerType where Self: _PlayerControllerType {

    /* 
    I want to provide a default implementation of play() for
    all my PlayerControllers in my framework (there is more than one).
    This method needs to be declared public,because it implements a
    requirement of the public protocol PlayerControllerType. 
    But it cannot be implemented here,because this extension 
    has the requirement _PlayerControllerType. It needs this requirement,because otherwise it cannot set the nowPlayingItem. I don't want to
    expose the setter of nowPlayingItem.
    I could make a base class for all PlayerControllers,but then I'm
    restricted to this base class because Swift does not support
    multiple inheritance.
    */
    public func play() {
        if nowPlayingItem == nil {
            nowPlayingItem = queue.first
        }
        // Other stuff
    }

}

public protocol _PlayerControllerType {
   // some code
}