[Objective-C] Copy 和 MutableCopy

看了幾篇文章，因為文章很新手向，所以內容很繁瑣。故整理一下重點，寫了測試程式去瞭解幾個知識點，不討論基本概念。新博客wossoneri.com傳送門

非集合類對象的copy與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);

//輸出
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

在非集合類對象中：對immutable對象進行copy操作，是指針複製，mutableCopy操作時內容複製；對mutable對象進行copy和mutableCopy都是內容複製。

結論

• [immutableObject copy] // 淺複製
• [immutableObject mutableCopy] //深複製
• [mutableObject copy] //深複製
• [mutableObject mutableCopy] //深複製

集合類對象的copy與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]);
      
//輸出
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

可以看到拷貝過程和非集合類大體相同。註意一點，就是拷貝過程只是針對對象本身，而對象內部的元素還是指針複製，從上面列印的輸出就可以看出來。

示例

看如下代碼，有一個mutable數組，賦值給immutable數組

@property (nonatomic, strong) 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，直接對array屬性賦值，這樣，_array和mArray便是指向同一對象的指針，因為NSMutableArray是NSArray的子類，故_array能夠接受mArray的值。

輸出結果：

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

下麵做個修改，把

_array = mArray;

改為

_array = [mArray copy];

想想結果如何？

mArray是mutable對象，拷貝屬於（不完全）深拷貝，所以可以想到_array的指針和mArray並不相同，所以後面mArray改變內容也與_array無關。

輸出：

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

小結

Reference
小結 iOS 中的 copy
iOS 集合的深複製與淺複製