【iOS】淺拷貝和深拷貝

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淺拷貝和深拷貝

• 淺拷貝即指標拷貝，可以認為是給一隻狗加了一條繩子；深拷貝不但拷貝了對象的指標，還在系統中在分配了一塊記憶體用來存放拷貝對象的內容，可以認為是產生了一條帶繩子的新狗。即淺拷貝是兩根繩子一條狗，深拷貝是兩根繩子兩條狗且每隻狗對應各自的繩子。
• 圖示：
  

• 深淺拷貝取決於拷貝後的對象是不是和被拷貝對象的地址相同，如果不同，則產生了新的對象，即為深拷貝。如果不同，則只是指標拷貝，相當於retain一次原對象，即為淺拷貝。

  copy與mutableCopy

• copy複製後的對象是不可變對象，mutableCopy複製後的對象是可變對象，與原始對象是否可變無關。

  非集合類的copy與mutableCopy
• 對不可變對象執行copy操作，是指標複製（淺拷貝），執行mutableCopy操作是內容複寫（深拷貝）。
• 對可變對象執行copy操作和mutableCopy操作都是內容複寫（深拷貝）。

• 代碼錶示如下：

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

  容器類的淺複製和深複製
• 容器物件和非容器物件類似，可變對象複製的都是一個新對象，不可變對象copy的是淺複製，mutableCopy是深複製
• 對於容器而言，元素對象始終是指標複製。

• 驗證代碼：

  NSMutableArray *array01 = [NSMutableArray arrayWithObjects:@"a",@"b",@"c", nil];NSArray *copyArray01 = [array01 copy];NSMutableArray *mutableCopyArray01 = [array01 mutableCopy];NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);NSLog(@"==================================================================");[array01 addObject:@"d"];NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01);NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p,array01[3] = %p",array01[0],array01[1],array01[2],array01[3]);NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]);NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2]);NSLog(@"==================================================================");[mutableCopyArray01 addObject:@"e"];NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01);NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p",array01[0],array01[1],array01[2]);NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]);NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p,mutableCopyArray01[3] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2],mutableCopyArray01[3]);

• 列印結果：

  2018-06-14 11:16:43.117758+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd02018-06-14 11:16:43.117887+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a802018-06-14 11:16:43.118014+0800 copy_demo[1988:95724] ==================================================================2018-06-14 11:16:43.118108+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd02018-06-14 11:16:43.118323+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a802018-06-14 11:16:43.118485+0800 copy_demo[1988:95724] array01 =(a,b,c,d) copyArray01 =(a,b,c) mutableCopyArray01 =(a,b,c)2018-06-14 11:16:43.118559+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf06168,array01[3] = 0x10bf061e82018-06-14 11:16:43.118661+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf061682018-06-14 11:16:43.118758+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf061682018-06-14 11:16:43.118891+0800 copy_demo[1988:95724] ==================================================================2018-06-14 11:16:43.119034+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd02018-06-14 11:16:43.119095+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a802018-06-14 11:16:43.119185+0800 copy_demo[1988:95724] array01 =(a,b,c,d) copyArray01 =(a,b,c) mutableCopyArray01 =(a,b,c,e)2018-06-14 11:16:43.119346+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf061682018-06-14 11:16:43.119527+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf061682018-06-14 11:16:43.119595+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf06168,mutableCopyArray01[3] = 0x10bf06288

  深拷貝淺拷貝面試中也經常問到，這隻是一個簡單的理解和總結，除了這些，還有很多比較複雜的以及自訂對象的深複製和淺複製。
  推薦一篇講得比較詳細和深刻的文章：https://github.com/pro648/tips/wiki/%E6%B7%B1%E5%A4%8D%E5%88%B6%E3%80%81%E6%B5%85%E5%A4%8D%E5%88%B6%E3%80%81copy%E3%80%81mutableCopy。我在整理這篇文章的時候也參考了這篇文章，感謝作者的分享。

【iOS】淺拷貝和深拷貝