단일 사례 - 매크로를 통한 단일 사례

#ifdef __has_feature(objc_arc) // ARC   

//.h  
#define singleton_h(name) +(instancetype)sharad##name;
//.m  
#define singleton_m(name) static id _instanceType = nil;\
+(instancetype)sharad##name\
{\
    static dispatch_once_t onceToken;\
    dispatch_once(&onceToken, ^{\
        _instanceType = [[self alloc]init];\
    });\
    return _instanceType;\
}\
+ (instancetype)allocWithZone:(struct _NSZone *)zone\
{\
    static dispatch_once_t onceToken;\
    dispatch_once(&onceToken, ^{\
        _instanceType = [super allocWithZone:zone];\
    });\
    return _instanceType;\
}\
-(id)copyWithZone:(NSZone *)zone\
{\
    return _instanceType;\
}

#else //MRC   

//.h       ##
#define singleton_h(name) +(instancetype)sharad##name;

//.m      
#define singleton_m(name) static id _instanceType = nil;\
+(instancetype)sharad##name\
{\
    static dispatch_once_t onceToken;\
    dispatch_once(&onceToken, ^{\
        _instanceType = [[self alloc]init];\
    });\
    return _instanceType;\
}\
+ (instancetype)allocWithZone:(struct _NSZone *)zone\
{\
    static dispatch_once_t onceToken;\
    dispatch_once(&onceToken, ^{\
        _instanceType = [super allocWithZone:zone];\
    });\
    return _instanceType;\
}\
-(id)copyWithZone:(NSZone *)zone\
{\
    return _instanceType;\
}\
-(oneway void)release\
{\
\
}\
-(instancetype)retain\
{\
    return _instanceType;\
}\
-(instancetype)autorelease\
{\
    return _instanceType;\
}\
- (NSUInteger)retainCount\
{\
    return 1;\
}

#endif

#import "singleton.h"
@interface DBTools : NSObject
singleton_h(     )
@end

@implementation DBTools
singleton_m(     )
@end