NSString *a = [[NSString alloc]initWithString:@"hello"];
    NSString *b = [a copy];
    NSLog(@"%d   %d",a.retainCount, b.retainCount);// 2，2
    
    NSMutableString *f = [a mutableCopy];
    
     NSLog(@"%d   %d",a.retainCount, f.retainCount);// 2，1
    
    [f appendString:@"dd"];
    NSLog(@"%@,%@",a,f);// hello,hellodd
    // 对于一个不可变对象来说 copy 是浅copy 只是指针复制 其retainCount 1
    // mutablecopy 是深copy 是对象复制
    
    NSMutableString *c = [[NSMutableString alloc]initWithString:@"hello"];
    NSMutableString *d = [c copy];
    NSLog(@"%d  %d",c.retainCount,d.retainCount);// 1,1
    //  [d appendString:@"ddd"]; //error 因为copy返回一个不可改变对象
    NSMutableString *e = [c mutableCopy];
     NSLog(@"%d  %d",c.retainCount,e.retainCount);// 1,1
    [e appendString:@"dddd"];
    NSLog(@"%@,%@",c,e);// hello,hellodddd
    // 对于可变对象来说 copy 和mutablecopy 都是深copy  都是拷贝对象  不过copy返回的对象是一个不可变对象
    //------------------------------------------------------------//
//    对于系统容器类对象
    
     NSArray *array1 = [NSArray arrayWithObjects:@"a",@"b",@"c",nil];
    NSArray *array1Copy = [array1 copy];
    NSLog(@"%d, %d",array1.retainCount,array1Copy.retainCount);//2,2
    NSMutableArray *arrayMcopy = [array1 mutableCopy];
     NSLog(@"%d, %d",array1.retainCount,arrayMcopy.retainCount);//2,1
    [arrayMcopy removeObjectAtIndex:0];
    [arrayMcopy addObject:@"d"];
    NSLog(@"%@-----%@",array1,arrayMcopy);//a,b,c  -----b,c,d
     NSArray *mArray1 = [NSArray arrayWithObjects:[NSMutableString stringWithString:@"a"],@"b",@"c",nil];
    NSArray *mArray1copy = [mArray1 copy];
    NSLog(@"%d,%d",mArray1.retainCount,mArray1copy.retainCount);//2,2
    NSMutableArray *mArrayMcopy = [mArray1 mutableCopy];
    NSLog(@"%d,%d",mArray1.retainCount,mArrayMcopy.retainCount);//2,1
    NSMutableString *temp = [mArray1 objectAtIndex:0];
    NSLog(@"%@",temp);//a
    [temp appendString:@"aa"];
    NSLog(@"%@",mArray1);//aaa b c
    NSLog(@"%@",mArray1copy); //aaa b c
    NSLog(@"%@",mArrayMcopy);// aaa b c
    //对于容器而言，其元素对象始终是指针复制。如果需要元素对象也是对象复制，就需要实现深拷贝。
    NSArray* trueDeepCopyArray = [NSKeyedUnarchiver unarchiveObjectWithData:
                                  [NSKeyedArchiver archivedDataWithRootObject: mArray1]];
    NSMutableString *temp2 = [trueDeepCopyArray objectAtIndex:0];
    [temp2 appendString:@"aa"];
    
    NSLog(@"%@",mArray1);//aaa b c
    NSLog(@"%@",trueDeepCopyArray);//aaaaa b c
    //trueDeepCopyArray是完全意义上的深拷贝