[Objective-C] Copy 和 MutableCopy

看了几篇文章，因为文章很新手向，所以内容很繁琐。故整理一下重点，写了测试程序去了解几个知识点，不讨论基本概念。

非集合类对象的copy与mutableCopy

      //NSString & NSMutableString
      NSString *strA = @"origin";
      NSLog(@"strA        pointer: %p content: %@", strA, strA);

      NSString *strACopy = [strA copy];
      NSLog(@"strCopy     pointer: %p content: %@", strACopy, strACopy);

      NSMutableString *strAMCopy = [strA mutableCopy];
      NSLog(@"strMCopy    pointer: %p content: %@", strAMCopy, strAMCopy);


      NSMutableString *strB = [NSMutableString stringWithString:@"mutable string"];
      NSLog(@"strB        pointer: %p content: %@", strB, strB);

      NSMutableString *strBCopy = [strB copy];
      NSLog(@"strBCopy    pointer: %p content: %@", strBCopy, strBCopy);

      NSMutableString *strBMCopy = [strB mutableCopy];
      NSLog(@"strBMCopy   pointer: %p content: %@", strBMCopy, strBMCopy);

//输出
strA        pointer: 0x100003180 content: origin
strCopy     pointer: 0x100003180 content: origin
strMCopy    pointer: 0x100102e90 content: origin
strB        pointer: 0x100700510 content: mutable string
strBCopy    pointer: 0x100700570 content: mutable string
strBMCopy   pointer: 0x1006002c0 content: mutable string

在非集合类对象中：对immutable对象进行copy操作，是指针复制，mutableCopy操作时内容复制；对mutable对象进行copy和mutableCopy都是内容复制。

结论

• [immutableObject copy] // 浅复制
• [immutableObject mutableCopy] //深复制
• [mutableObject copy] //深复制
• [mutableObject mutableCopy] //深复制

集合类对象的copy与mutableCopy

      NSArray *arrayA = @[@[@"A", @"B"], @[@"C", @"D"]];
      NSLog(@"arrayA      pointer:%p  contentA:%p contentB:%p", arrayA, arrayA[0], arrayA[1]);

      NSArray *arrCopyA = [arrayA copy];
      NSLog(@"arrCopyA    pointer:%p  contentA:%p contentB:%p", arrCopyA, arrCopyA[0], arrCopyA[1]);

      NSMutableArray *arrMCopyA = [arrayA mutableCopy];
      NSLog(@"arrMCopyA   pointer:%p  contentA:%p contentB:%p", arrMCopyA,arrMCopyA[0], arrMCopyA[1]);


      NSMutableArray *arrayB = [NSMutableArray arrayWithObjects:@[@"A", @"B"], @[@"C", @"D"], nil];
      NSLog(@"arrayB      pointer:%p  contentA:%p contentB:%p", arrayB, arrayB[0], arrayB[1]);

      NSArray *arrCopyB = [arrayB copy];
      NSLog(@"arrCopyB    pointer:%p  contentA:%p contentB:%p", arrCopyB, arrCopyB[0], arrCopyB[1]);

      NSMutableArray *arrMCopyB = [arrayB mutableCopy];
      NSLog(@"arrMCopyB   pointer:%p  contentA:%p contentB:%p", arrMCopyB,arrMCopyB[0], arrMCopyB[1]);

//输出
arrayA      pointer:0x100700860  contentA:0x100700840 contentB:0x1007007c0
arrCopyA    pointer:0x100700860  contentA:0x100700840 contentB:0x1007007c0
arrMCopyA   pointer:0x100700990  contentA:0x100700840 contentB:0x1007007c0

arrayB      pointer:0x100701970  contentA:0x100700880 contentB:0x100701730
arrCopyB    pointer:0x100102080  contentA:0x100700880 contentB:0x100701730
arrMCopyB   pointer:0x100701ab0  contentA:0x100700880 contentB:0x100701730

可以看到拷贝过程和非集合类大体相同。注意一点，就是拷贝过程只是针对对象本身，而对象内部的元素还是指针复制，从上面打印的输出就可以看出来。

示例

看如下代码，有一个mutable数组，赋值给immutable数组

 @property (nonatomic, copy) NSArray *array;
  NSMutableArray *mArray = [NSMutableArray array];
  [mArray addObject:@"AA"];
  _array = mArray;
  NSLog(@"mArray: %p, _array: %p", mArray, _array);
  [mArray addObject:@"BB"];
  NSLog(@"mArray = %@, _array = %@", mArray, _array);

其中，直接对array属性赋值，这样，_array和mArray便是指向同一对象的指针，因为NSMutableArray是NSArray的子类，故_array能够接受mArray的值。

应该说是 _array 是一个指针，通过 _array = mArray 使两个指针指向同一个地方。

输出结果：

mArray: 0x126ec3e00, _array: 0x126ec3e00
mArray = (
    AA,
    BB
), _array = (
    AA,
    BB
)

下面做个修改，把

_array = mArray;

改为

_array = [mArray copy];

想想结果如何？

mArray是mutable对象，拷贝属于（不完全）深拷贝，所以可以想到_array的指针和mArray并不相同，所以后面mArray改变内容也与_array无关。

输出：

mArray: 0x154dc8070, _array: 0x154dcf4e0
mArray = (
    AA,
    BB
), _array = (
    AA
)

Reference
小结 iOS 中的 copy
iOS 集合的深复制与浅复制