iOS快速单例宏

// 单例
#define DECLARE_SHARED_INSTANCE(className)  + (className *)sharedInstance;


#define IMPLEMENT_SHARED_INSTANCE(className)  + (className *)sharedInstance { static className *sharedInstance = nil; @synchronized(self) { if (!sharedInstance) { sharedInstance = [[[self class] alloc] init]; } } return sharedInstance; }