使用方法:

1. 聲明了兩個宏 SingleH(name) 和 SingleM(name) 兩個宏
2. 創(chuàng)建一個想要實現(xiàn)單例模式的類.在.h文件中包含單例宏文件
   #import<single.h>
3. 在.h文件中使用SingleH(name)宏
   #import <Foundation/Foundation.h>
   #import <Single.h>
   @interface CustomClass : NSObject
   SingleH();
   @end
4. 在.m文件中使用SingleM(name)宏
   #import "CustomClass.h"
   @implementation CustomClass
   SingleM(customClass);
   @end

Single.h 文件

#define SingleH(name) +(instancetype)share##name;

#if __has_feature(objc_arc)
//條件滿足 ARC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}

#else
//MRC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
-(oneway void)release\
{\
}\
\
-(instancetype)retain\
{\
    return _instance;\
}\
\
-(NSUInteger)retainCount\
{\
    return MAXFLOAT;\
}
#endif