objective-c中的深、淺拷貝

淺複製：只複製指向對象的指針，而不複製引用對象本身。計數器+1 ,就像比如retain

深層複製：複製引用對象本身。計數器不變，產生新對象 

retain：始終是淺複製。引用計數每次加一。返回對象是否可變與被覆制的對象保持一致。

copy：對於可變對象為深複製，引用計數不改變;對於不可變對象是淺複製，引用計數每次加一。始終返回一個不可變對象。

mutableCopy：始終是深複製，引用計數不改變。始終返回一個可變對象。

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {


    NSMutableArray *array1=[NSMutableArray arrayWithObjects:@"two day", nil];
    NSMutableArray *array2=[array1 copy];
    NSArray *array3=[array2 copy];
    NSArray *array4=[array2 retain];
    NSMutableArray *array5=[array1 retain];
    NSMutableArray *array6=[array1 mutableCopy];
    NSArray *array7=[array2 mutableCopy];
    NSLog(@"-------------");
    NSLog(@"array1:%@ %p",array1, array1);
    NSLog(@"array2:%@ %p",array2, array2);
    NSLog(@"array3:%@ %p",array3, array3);
    NSLog(@"array4:%@ %p",array4, array4);
    NSLog(@"array5:%@ %p",array5, array5);
    NSLog(@"array6:%@ %p",array6, array6);
    NSLog(@"array7:%@ %p",array7, array7);
    NSLog(@"-------------");
    return 0;
}

2015-04-01 20:46:23.131 04-01-person[2204:165655] -------------
2015-04-01 20:46:23.132 04-01-person[2204:165655] array1:(
    "two day"
) 0x100114570
2015-04-01 20:46:23.133 04-01-person[2204:165655] array2:(
    "two day"
) 0x100114700
2015-04-01 20:46:23.133 04-01-person[2204:165655] array3:(
    "two day"
) 0x100114700
2015-04-01 20:46:23.133 04-01-person[2204:165655] array4:(
    "two day"
) 0x100114700
2015-04-01 20:46:23.133 04-01-person[2204:165655] array5:(
    "two day"
) 0x100114570
2015-04-01 20:46:23.133 04-01-person[2204:165655] array6:(
    "two day"
) 0x1001150d0
2015-04-01 20:46:23.134 04-01-person[2204:165655] array7:(
    "two day"
) 0x100115b00
2015-04-01 20:46:23.134 04-01-person[2204:165655] -------------
Program ended with exit code: 0

數組類型轉換：

1、不可變對象→可變對象的轉換：       

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    NSArray *array01=[NSArray arrayWithObjects:@"zhang",@"wang",@"li", nil];
    
    NSMutableArray  *array02=[array01 mutableCopy]; //mutableCopy始終返回一個可變對象
    
    NSLog(@"array01: %@  %p",array01,array01);
    NSLog(@"array02: %@  %p",array02,array02);
    return 0;
}

2015-04-01 21:00:28.218 04-01-person[2252:170414] array01: (
    zhang,
    wang,
    li
)  0x100106c80
2015-04-01 21:00:28.220 04-01-person[2252:170414] array02: (
    zhang,
    wang,
    li
)  0x1001076d0
Program ended with exit code: 0

2、可變對象→不可變對象的轉換：

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    NSMutableArray *array1   = [NSMutableArray arrayWithObjects:@"zhang",@"wang",@"li", nil];
    NSArray *array2=[array1   copy];//copy對於可變對象為深複製，引用計數不改變;對於不可變對象是淺複製，引用計數每次加一。始終返回一個不可變對象
    NSLog(@"array1: %@  %p",array1,array1);
    NSLog(@"array2: %@  %p",array2,array2);
    return 0;
}

2015-04-01 21:03:45.349 04-01-person[2263:171615] array1: (
    zhang,
    wang,
    li
)  0x100112900
2015-04-01 21:03:45.350 04-01-person[2263:171615] array2: (
    zhang,
    wang,
    li
)  0x1001133b0

3、可變對象→可變對象的轉換（不同指針變數指向不同的記憶體地址）：

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {

    NSMutableArray *array1= [NSMutableArray arrayWithObjects:@"zhang",@"wang",@"li", nil];
    
    NSMutableArray *array2=[array1 mutableCopy];
    NSLog(@"array1: %@  %p",array1,array1);
    NSLog(@"array2: %@  %p",array2,array2);
    return 0;
}

2015-04-01 20:57:41.732 04-01-person[2243:169571] array1: (
    zhang,
    wang,
    li
)  0x100114570
2015-04-01 20:57:41.734 04-01-person[2243:169571] array2: (
    zhang,
    wang,
    li
)  0x100115020
Program ended with exit code: 0

4、同類型對象之間的指針複製（不同指針變數指向同一塊記憶體地址）：

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {


    NSArray *array1=[NSArray arrayWithObjects:@"one",@"two",@"three", nil];
    NSArray *array2=[array1 copy];
    NSLog(@"array1: %@  %p",array1,array1);
    NSLog(@"array2: %@  %p",array2,array2);
    return 0;
}

2015-04-01 20:53:07.398 04-01-person[2217:167996] array1: (
    one,
    two,
    three
)  0x1006069a0
2015-04-01 20:53:07.399 04-01-person[2217:167996] array2: (
    one,
    two,
    three
)  0x1006069a0
Program ended with exit code: 0

當多個指針同時指向同一塊記憶體區域，那麼這些個指針同時擁有對該記憶體區的所有權。所有權的瓜分過程，這時候就要用到淺拷貝了。