今天在做网络状态监听的时候，用到了Reachability，但是在创建Reachability 的时候遇到了问题，Reachability是OC版本的，使用位置在swift中，

Reachability.h 中声明如下：

/*!
 * Use to check the reachability of a given host name.
 */
+ (instancetype)reachabilityWithHostName:(NSString *)hostName;

/*!
 * Use to check the reachability of a given IP address.
 */
+ (instancetype)reachabilityWithAddress:(const struct sockaddr *)hostAddress;

/*!
 * Checks whether the default route is available. Should be used by applications that do not connect to a particular host.
 */
+ (instancetype)reachabilityForInternetConnection;

使用时

    self.internetReachability = [Reachability reachabilityForInternetConnection];
    self.internetReachability = [Reachability reachabilityWithHostName:@"http://www.baidu.com"];

Swift 中，按照简单的转换应该是Reachability. reachabilityForInternetConnection 才对，
但是失败了，其使用方式是这样的：

internetReachability = Reachability(hostName: "")
internetReachability = Reachability(address: UnsafePointer(bitPattern: 0))
internetReachability = Reachability.forInternetConnection()

大概是因为*** instancetype***的方法与普通的类方法不一样吧，这里仅作为记录，具体原因就不探究了，毕竟比较少见，而且也是个规律的事儿