oc copy属性赋值不可变对象 地址为什么是一样的

Question

刚学习oc,发现一个很难理解的问题
假设我在某一个类里面定义如下几个实例属性

@property (nonatomic, strong) NSString *strongString;
@property (nonatomic, strong) NSMutableString *strongMutableString;
@property (nonatomic, copy) NSString *copyedString;
@property (nonatomic, copy) NSMutableString *copyedMutableString;

调用实例方法，实现的功能如下，就是简单的赋值

1. 将不可变字符串赋值给属性

       NSString *string = [NSString stringWithFormat:@"abc"];
       self.strongString = string;
       self.strongMutableString = string;
       self.copyedMutableString = string;
       self.copyedString = string;
       
       string = [string stringByAppendingString:@"123"];
       // 打印输出实例属性的地址
       NSLog(@"\n origin string: %p, %p  %@", string, &string, string);
       NSLog(@"\n strong string: %p, %p  %@", _strongString, &_strongString, _strongString);
       NSLog(@"\n strongMutable string: %p, %p  %@", _strongMutableString, &_strongMutableString, _strongMutableString);
       NSLog(@"\n copy string: %p, %p  %@", _copyedString, &_copyedString, _copyedString);
       NSLog(@"\n copyMutable: %p, %p  %@", _copyedMutableString, &_copyedMutableString, _copyedMutableString);

   输出如下

    origin string: 0x100534da0, 0x7ffeefbff4c8  abc123
    strong string: 0x21bd4156d4fa7111, 0x100534c88  abc
    strongMutable string: 0x21bd4156d4fa7111, 0x100534c90  abc
    copy string: 0x21bd4156d4fa7111, 0x100534c98  abc
    copyMutable: 0x21bd4156d4fa7111, 0x100534ca0  abc

   这个大概能理解 都是浅拷贝 地址没有变化

2. 然而将可变字符串赋值给属性时，我就搞不懂了

       NSMutableString *multableString = [NSMutableString stringWithFormat:@"def"];
       self.strongString = multableString;
       self.strongMutableString = multableString;
       self.copyedMutableString = multableString;
       self.copyedString = multableString;
       
       [multableString appendString:@"123"];
       // 打印输出实例属性的地址
       NSLog(@"\n origin string: %p, %p  %@", multableString, &multableString, multableString);
       NSLog(@"\n strong string: %p, %p  %@", _strongString, &_strongString, _strongString);
       NSLog(@"\n strongMutable string: %p, %p  %@", _strongMutableString, &_strongMutableString, _strongMutableString);
       NSLog(@"\n copy string: %p, %p  %@", _copyedString, &_copyedString, _copyedString);
       NSLog(@"\n copyMutable: %p, %p  %@", _copyedMutableString, &_copyedMutableString, _copyedMutableString);

   输出结果

    origin string: 0x100651af0, 0x7ffeefbff4c8  def123
    strong string: 0x100651af0, 0x100651a28  def123
    strongMutable string: 0x100651af0, 0x100651a30  def123
    copy string: 0x64fd82cbad71056f, 0x100651a38  def
    copyMutable: 0x64fd82cbad71056f, 0x100651a40  def

   用strong修饰的属性是浅拷贝，地址一样我能理解但是！！
   为什么copy的属性，地址是一样的？？？？

Answer 1

浅拷贝和深拷贝的理解
copy 相对于指针复制，内存地址一致的

Answer 2

https://www.jianshu.com/p/4c1...
这么复杂