#define singleton_interface(className) \

+ (className *)shared##className;

// @implementation

#define singleton_implementation(className) \

static className *_instance; \

+ (id)allocWithZone:(NSZone *)zone \

{ \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instance = [super allocWithZone:zone]; \

}); \

return _instance; \

} \

+ (className *)shared##className \

{ \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instance = [[self alloc] init]; \

}); \

return _instance; \

}

@interface AccountTool : NSObject

singleton_interface(AccountTool)

@end

@implementation AccountTool

singleton_implementation(AccountTool)

@end