在Swift 1.2（Xcode 6.3 beta 2）中，你可以覆盖的哈希属性
> NSObject 作为计算属性：

In Swift 1.2 (Xcode 6.3 beta 2) you can override the hash property of NSObject as a computed property:

class Object: NSObject {
    override var hash: Int {
        return 0
    }
}