枚举类型

enum GCDAsyncSocketConfig
{
	kIPv4Disabled              = 1 << 0,  // If set, IPv4 is disabled
	kIPv6Disabled              = 1 << 1,  // If set, IPv6 is disabled
	kPreferIPv6                = 1 << 2,  // If set, IPv6 is preferred over IPv4
	kAllowHalfDuplexConnection = 1 << 3,  // If set, the socket will stay open even if the read stream closes
};

 以上是GCDAsyncSocket的一个枚举类型，这种枚举类型的好处是可以通过按位与(&)来进行包含判断。

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