iOS ARC 下的单例模式

#import <Foundation/Foundation.h>

@interface RYSingleExample : NSObject<NSCopying>

+(instancetype)singleExample;

@end

#import "RYSingleExample.h"

static id _single;

@implementation RYSingleExample

+(instancetype)singleExample

{

if(_single==nil)

{

@synchronized(self)

{

if (_single==nil) {

_single=[[self alloc]init];

}

}

}

return _single;

}

+(instancetype)allocWithZone:(struct _NSZone *)zone

{

if(_single==nil)

{

@synchronized(self)

{

if (_single==nil) {

_single=[super allocWithZone:zone];

}

}

}

return _single;

}

-(id)copyWithZone:(NSZone *)zone

{

return _single;

}

@end