iOS copy&mutableCopy理解

Copy&mutableCopy

通过copy方法可以创建可变或不可变对象的不可变副本，通过mutableCopy可以创建可变或不可变对象的可变副本。
拷贝分为浅拷贝和深拷贝：
- 浅拷贝：指针拷贝，对一个对象进行浅拷贝，相当于对指向该对象的指针进行复制，产生一个新的指向这个对象的指针。当一个对象销毁后，两个指针都应该置空。
- 深拷贝：内容拷贝，增加一个指针并且申请一个新的内存，使这个新增的指针指向这个新的内存。使用深拷贝不会出现浅拷贝时重复释放同一块内存的错误！

Not to say, show the code

一、NSArray

示例：不可变数组copy之后数组的地址没有变，是浅拷贝；mutableCopy之后数组的地址不同，但是里面的对象的地址相同，是深度为1的深拷贝。
- NSArray *array = @[[NSMutableString stringWithString:@"a"], @"b"];
  NSArray *arrCopy = [array copy];
  NSArray *arrMurableCopy = [array mutableCopy];
  
  NSLog(@"arr address: %p", array);
  NSLog(@"arrCopy address: %p",arrCopy);
  NSLog(@"arrMurableCopy address:%p", arrMurableCopy);
  
  NSLog(@"arr first address: %p", [array objectAtIndex:0]);
  NSLog(@"arrCopy first address: %p", [arrCopy objectAtIndex:0]);
  NSLog(@"arrMurableCopy first address:%p", [arrMurableCopy objectAtIndex:0]);
  
  [self myNslog:array];
  [self myNslog:arrCopy];
  [self myNslog:arrMurableCopy];
  
  [array[0] appendString:@"aaa"];
  
  NSLog(@"arr address: %p", array);
  NSLog(@"arrCopy address: %p",arrCopy);
  NSLog(@"arrMurableCopy address:%p", arrMurableCopy);
  
  NSLog(@"arr first address: %p", [array objectAtIndex:0]);
  NSLog(@"arrCopy first address: %p", [arrCopy objectAtIndex:0]);
  NSLog(@"arrMurableCopy first address:%p", [arrMurableCopy objectAtIndex:0]);
  
  [self myNslog:array];
  [self myNslog:arrCopy];
  [self myNslog:arrMurableCopy];
- arr address: 0x146e5a9f0
  arrCopy address: 0x146e5a9f0
  arrMurableCopy address: 0x146e3aa90
  arr first address: 0x146e5a9b0
  arrCopy first address: 0x146e5a9b0
  arrMurableCopy first address: 0x146e5a9b0
  (
      a,
      b
  )
  (
      a,
      b
  )
  (
      a,
      b
  )
  arr address: 0x146e5a9f0
  arrCopy address: 0x146e5a9f0
  arrMurableCopy address: 0x146e3aa90
  arr first address: 0x146e5a9b0
  arrCopy first address: 0x146e5a9b0
  arrMurableCopy first address: 0x146e5a9b0
  (
      aaaa,
      b
  )
  (
      aaaa,
      b
  )
  (
      aaaa,
      b
  )
不可变数组copy之后数组的地址没有变，是浅拷贝；mutableCopy之后数组的地址不同，但是里面的对象的地址相同，是深度为1的深拷贝。
从打印结果可以看出，打印的数组的第一个对象的地址相同，可见里面存放的是对象的内存地址, 并没有开辟内存空间存放对象。所以当为一个数组的第一个对象附加aaa后，所有数组的第一个对象值都变为aaaa

二、NSMutableArray

示例一：从结果可见，可变数组copy 和 mutableCopy之后数组的地址都不同，然而数组的第一个对象的地址都相同，说明没有开辟新的地址存放数组里面的对象，说明进行了深度为1的深拷贝，数组里面存的是 a , b 对象组成的数组的首地址。改变一个数组的第一个值，其他数组也发生变化。
- // 可变数组
  NSMutableArray *mutableArr = [NSMutableArray arrayWithArray:@[[NSMutableString stringWithString:@"a"], @"b"]];
  NSMutableArray *mutableArrCopy = [mutableArr copy];
  NSMutableArray *mutableArrMutableCopy = [mutableArr mutableCopy];
  
  NSLog(@"mutableArr address: %p", mutableArr);
  NSLog(@"mutableArrCopy address: %p", mutableArrCopy);
  NSLog(@"mutableArrMutableCopy address:%p", mutableArrMutableCopy);
  
  NSLog(@"mutableArr first address: %p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address: %p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
  
  // 可变数组改变第一个值
  [mutableArr[0] appendString:@"aaa"];
  
  NSLog(@"mutableArr first address: %p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address: %p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
- mutableArr address: 0x135e2e040
  mutableArrCopy address: 0x135e19880
  mutableArrMutableCopy address: 0x135d0f0a0
  mutableArr first address: 0x135d49580
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
      a,
      b
  )
  (
      a,
      b
  )
  (
      a,
      b
  )
  mutableArr first address: 0x135d49580
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
      aaaa,
      b
  )
  (
      aaaa,
      b
  )
  (
      aaaa,
      b
  )
从结果可见，可变数组copy 和 mutableCopy之后数组的地址都不同，然而数组的第一个对象的地址都相同，说明没有开辟新的地址存放数组里面的对象，说明进行了深度为1的深拷贝，数组里面存的是 a , b 对象组成的数组的首地址。改变一个数组的第一个值，其他数组也发生变化。

示例二：这里创建一个新的可变字符串对象，并赋值给 mutableArr[0]，而其他数组指针指向的对象不变，所以输出时其他数组值不变。
- // 设置新值
  mutableArr[0] = [NSMutableString stringWithString:@"A"];
  
  NSLog(@"mutableArr first address:%p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address:%p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
- 设置新值之后的打印；
- mutableArr first address: 0x12f625590
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
  A,
      b
  )
  (
  A,
      b
  )
  (
  A,
      b
  )
这里创建一个新的可变字符串对象，并赋值给 mutableArr[0]，而其他数组指针指向的对象不变，所以输出时其他数组值不变。

示例三：这里创建了一个新的可变字符串对象，并将其内存地址保存到指针mutableArr[3]中。而其他几个数组指针的引用不受影响。
- // 添加新值
  [mutableArr addObject:[NSMutableString stringWithString:@"c"]];
  
  NSLog(@"mutableArr first address: %p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address: %p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
- mutableArr first address:   0x135d49580
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
  a,
      b,
      c
  )
  (
  a,
      b
  )
  (
  a,
      b
  )
这里创建了一个新的可变字符串对象，并将其内存地址保存到指针mutableArr[3]中。而其他几个数组指针的引用不受影响

示例四：操作的是mutableArr对对象的引用，所以不会影响到其他数组
- // 操作数组的引用
  NSMutableString *mutableString = [NSMutableString stringWithString:mutableArr[0]];
  [mutableString appendString:@"aaa"];
  [mutableArr replaceObjectAtIndex:0 withObject:mutableString];
  
  NSLog(@"mutableArr first address: %p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address: %p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
- mutableArr first address:   0x135d49570
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
  aaaa,
      b,
      c
  )
  (
  a,
      b
  )
  (
  a,
      b
  )
- // 操作数组的引用
  [mutableArr removeObjectAtIndex:1];
  
  NSLog(@"mutableArr first address: %p", [mutableArr objectAtIndex:0]);
  NSLog(@"mutableArrCopy first address: %p", [mutableArrCopy objectAtIndex:0]);
  NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);
  
  [self myNslog:mutableArr];
  [self myNslog:mutableArrCopy];
  [self myNslog:mutableArrMutableCopy];
- mutableArr first address:   0x135d49580
  mutableArrCopy first address: 0x135d49580
  mutableArrMutableCopy first address:0x135d49580
  (
  a
  )
  (
  a,
      b
  )
  (
  a,
      b
  )
操作的是mutableArr对对象的引用，所以不会影响到其他数组

三、NSString

示例：copy 之后地址没有变，mutableCopy之后地址发生了变化，当改变了stringMutableCopy字符串之后，其他连个字符串没有发生变化，说明NSString copy 是浅拷贝，mutableCopy是深拷贝
- NSString *string = @"abc";
  NSString *stringCopy = [string copy];
  NSMutableString *stringMutableCopy = [string mutableCopy];
  
  NSLog(@"string = %p", string);
  NSLog(@"stringCopy = %p", stringCopy);
  NSLog(@"stringMutableCopy = %p", stringMutableCopy);
  
  [stringMutableCopy appendString:@"def"];
  
  NSLog(@"string = %p", string);
  NSLog(@"stringCopy = %p", stringCopy);
  NSLog(@"stringMutableCopy = %p", stringMutableCopy);
  
  NSLog(@"string = %@", string);
  NSLog(@"stringCopy = %@", stringCopy);
  NSLog(@"stringMutableCopy = %@", stringMutableCopy);
- string = 0x1000f0310
  stringCopy = 0x1000f0310
  stringMutableCopy = 0x14752fcf0
  string = 0x1000f0310
  stringCopy = 0x1000f0310
  stringMutableCopy = 0x14752fcf0
  string = abc
  stringCopy = abc
  stringMutableCopy = abcdef
copy 之后地址没有变，mutableCopy之后地址发生了变化，当改变了stringMutableCopy字符串之后，其他连个字符串没有发生变化，说明NSString copy 是浅拷贝，mutableCopy是深拷贝

四、NSMutableString

示例：
- NSMutableString *mutaleString = [NSMutableString stringWithString:@"a"];
  NSMutableString *mutaleStringcopy = [mutaleString copy];
  NSMutableString *mutaleStringmutableCopy = [mutaleString mutableCopy];
  
  NSLog(@"mutaleString = %p", mutaleString);
  NSLog(@"mutaleStringcopy = %p", mutaleStringcopy);
  NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);
  
  [mutaleString appendString:@"bcd"];
  
  NSLog(@"mutaleString = %p", mutaleString);
  NSLog(@"mutaleStringcopy = %p", mutaleStringcopy);
  NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);
  
  NSLog(@"mutaleString = %@", mutaleString);
  NSLog(@"mutaleStringcopy = %@", mutaleStringcopy);
  NSLog(@"mutaleStringmutableCopy = %@", mutaleStringmutableCopy);
- mutaleString = 0x14e637470
  mutaleStringcopy = 0xa000000000000611
  mutaleStringmutableCopy = 0x14e6374b0
  mutaleString = 0x14e637470
  mutaleStringcopy = 0xa000000000000611
  mutaleStringmutableCopy = 0x14e6374b0
  mutaleString = abcd
  mutaleStringcopy = a
  mutaleStringmutableCopy = a
- mutaleString = [NSMutableStringstringWithString:@"A"];
  
  NSLog(@"mutaleString = %p", mutaleString);
  NSLog(@"mutaleStringcopy = %p", mutaleStringcopy);
  NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);
  
  NSLog(@"mutaleString = %@", mutaleString);
  NSLog(@"mutaleStringcopy = %@", mutaleStringcopy);
  NSLog(@"mutaleStringmutableCopy = %@", mutaleStringmutableCopy);
- mutaleString = 0x14e637470
  mutaleStringcopy = 0xa000000000000611
  mutaleStringmutableCopy = 0x14e6374b0
  mutaleString = 0x13c657000
  mutaleStringcopy = 0xa000000000000611
  mutaleStringmutableCopy = 0x14e6374b0
  mutaleString = A
  mutaleStringcopy = a
  mutaleStringmutableCopy = a
- copy 和 mutableCopy都进行了深拷贝，开辟了新的地址空间存储拷贝后的变量；
- 注意：copy 后的地址 0xa000000000000611 跟其他的不一样，copy后的对象是不可变的，强行修改会导致程序崩溃。
- -[NSTaggedPointerString appendString:]: unrecognized selector sent to instance 0xa000000000000611
  *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSTaggedPointerString appendString:]: unrecognized selector sent to instance 0xa000000000000611'

五、NSMutableDictionary

示例一：mutableDict 的索引key1, key2, key3 分别对应对象 mutableStr1， mutableStr2， mutableStr3 的内存地址，copy 后所有的字典第一个对象的地址都相同，对字典拷贝也是浅拷贝。
- NSMutableString *mutableStr1 = [NSMutableString stringWithString:@"a"];
  NSMutableString *mutableStr2 = [NSMutableString stringWithString:@"b"];
  NSMutableString *mutableStr3 = [NSMutableString stringWithString:@"c"];
  NSMutableDictionary *mutableDict = [NSMutableDictionary dictionaryWithObjects:@[mutableStr1, mutableStr2, mutableStr3] forKeys:@[@"key1", @"key2", @"key3"]];
  NSMutableDictionary *mutableDictCopy = [mutableDict copy];
  NSMutableDictionary *mutableDictMutableCopy = [mutableDict mutableCopy];
  
  NSLog(@"mutableDict = %p", mutableDict);
  NSLog(@"mutableDictCopy = %p", mutableDictCopy);
  NSLog(@"mutableDictMutableCopy = %p", mutableDictMutableCopy);
  
  NSLog(@"mutableDict first address = %p", mutableDict[@"key1"]);
  NSLog(@"mutableDictCopy first address = %p", mutableDictCopy[@"key1"]);
  NSLog(@"mutableDictMutableCopy first address = %p", mutableDictMutableCopy[@"key1"]);
  
  [mutableDict[@"key1"] appendString:@"aaa"];
  
  NSLog(@"mutableDict = %@", mutableDict);
  NSLog(@"mutableDictCopy = %@", mutableDictCopy);
  NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);
  
  NSLog(@"mutableDict first address = %p", mutableDict[@"key1"]);
  NSLog(@"mutableDictCopy first address = %p", mutableDictCopy[@"key1"]);
  NSLog(@"mutableDictMutableCopy first address = %p", mutableDictMutableCopy[@"key1"]);
- mutableDict = 0x15f62f7d0
  mutableDictCopy = 0x15f62f800
  mutableDictMutableCopy = 0x15f62f570
  mutableDict first address = 0x15f62f530
  mutableDictCopy first address = 0x15f62f530
  mutableDictMutableCopy first address = 0x15f62f530
  mutableDict            = {
      key1 = aaaa;
      key2 = b;
      key3 = c;
  }
  mutableDictCopy        = {
      key1 = aaaa;
      key2 = b;
      key3 = c;
  }
  mutableDictMutableCopy = {
      key1 = aaaa;
      key2 = b;
      key3 = c;
  }
  mutableDict first address = 0x15f62f530
  mutableDictCopy first address = 0x15f62f530
  mutableDictMutableCopy first address = 0x15f62f530
mutableDict 的索引key1, key2, key3 分别对应对象 mutableStr1， mutableStr2， mutableStr3 的内存地址，copy 后所有的字典第一个对象的地址都相同，对字典拷贝也是浅拷贝。
对key1对应的对象mutableStr1进行修改后，由于指向同一个字典，所以输出相同，第一个对象的地址也相同。

示例二：
- [mutableDict setObject:@"A" forKey:@"key1"];
  
  NSLog(@"mutableDict = %@", mutableDict);
  NSLog(@"mutableDictCopy = %@", mutableDictCopy);
  NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);
  
  NSLog(@"mutableDict first address = %p", mutableDict[@"key1"]);
  NSLog(@"mutableDictCopy first address = %p", mutableDictCopy[@"key1"]);
  NSLog(@"mutableDictMutableCopy first address = %p", mutableDictMutableCopy[@"key1"]);
- mutableDict            = {
      key1 = A;
      key2 = b;
      key3 = c;
  }
  mutableDictCopy        = {
      key1 = a;
      key2 = b;
      key3 = c;
  }
  mutableDictMutableCopy = {
      key1 = a;
      key2 = b;
      key3 = c;
  }
  mutableDict first address = 0x1000fc390
  mutableDictCopy first address = 0x15f62f530
  mutableDictMutableCopy first address = 0x15f62f530

mutableDict中key1存放的是第一个对象的内存地址，[mutableDict setObject:@"A" forKey:@"key1”]; 将key1中的内存地址修改为 @"A"的内存地址，不会影响到其他引用所指向的对象。

示例三：为 mutableDict 添加先得键值对，没有影响到其他字典指针，所以只有mutableDict发生变化。
- [mutableDict setObject:@"d" forKey:@"key4"];
  
  NSLog(@"mutableDict = %@", mutableDict);
  NSLog(@"mutableDictCopy = %@", mutableDictCopy);
  NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);
  
  NSLog(@"mutableDict first address = %p", mutableDict[@"key1"]);
  NSLog(@"mutableDictCopy first address = %p", mutableDictCopy[@"key1"]);
  NSLog(@"mutableDictMutableCopy first address = %p", mutableDictMutableCopy[@"key1"]);
- mutableDict            = {
      key1 = A;
      key2 = b;
  key3 = c;
      key4 = d;
  }
  mutableDictCopy        = {
      key1 = a;
      key2 = b;
      key3 = c;
  }
  mutableDictMutableCopy = {
      key1 = a;
      key2 = b;
      key3 = c;
  }
  mutableDict first address = 0x15f62f530
  mutableDictCopy first address = 0x15f62f530
  mutableDictMutableCopy first address = 0x15f62f530
为 mutableDict 添加先得键值对，没有影响到其他字典指针，所以只有mutableDict发生变化。

总结：NSMutableArray和NSMutableDictionary的复制是浅复制，NSMutableString的复制是深复制。由于数组或字典中对象数目或大小可能非常大，所以对对象的复制可能引起大量开销，因此这里只复制引用可以节省开销。