Singleton.h
// .h #define singleton_interface(class) + (instancetype)shared##class; // .m #define singleton_implementation(class) \ static class *_instance; \ \ + (id)allocWithZone:(struct _NSZone *)zone \ { \ static dispatch_once_t onceToken; \ dispatch_once(&onceToken, ^{ \ _instance = [super allocWithZone:zone]; \ }); \ \ return _instance; \ } \ \ + (instancetype)shared##class \ { \ if (_instance == nil) { \ _instance = [[class alloc] init]; \ } \ \ return _instance; \ }