Copy不可变字符串

   NSString *name = @"xiaoshuai";
   NSString *copyName = [name copy];
   NSLog(@"name = %p,copyName = %p",name,copyName);
   NSLog(@"指针地址:name = %p,copyName = %p",&name,&copyName);
   2019-03-08 00:26:19.143276+0800 CopyAndMutableCopy[65754:3650641] name = 0x100001070,copyName = 0x100001070
   2019-03-08 00:26:19.143338+0800 CopyAndMutableCopy[65754:3650641] 指针地址:name = 0x7ffeefbff588,copyName = 0x7ffeefbff580

不可变字符串的Copy,对象的内存地址没有改变，指针的地址改变了。

Copy可变字符串

        NSMutableString *behave = [NSMutableString stringWithFormat:@"general"];
        NSString *copyBehave = [behave copy];
        NSLog(@"behave = %p copyBehave = %p",behave,copyBehave);
        NSLog(@"behave = %p copyBehave= %p",&behave,&copyBehave);
        2019-03-08 00:54:27.021365+0800 CopyAndMutableCopy[66226:3670386] behave = 0x100604710 copyBehave = 0x6c6172656e656775
        2019-03-08 00:54:27.021408+0800 CopyAndMutableCopy[66226:3670386] 指针地址:behave = 0x7ffeefbff588 copyBehave= 0x7ffeefbff580

可变字符串的Copy,直接拷贝了对象。

MutableCopy不可变字符串

        NSString *responsibility = @"responsible";
        NSMutableString *mutableResponsibility = [responsibility mutableCopy];
        NSLog(@"responsibility = %p,mutableResponsibility = %p",responsibility,mutableResponsibility);
        NSLog(@"指针地址:responsibility = %p,mutableResponsibility = %p",&responsibility,&mutableResponsibility);
        2019-03-08 21:59:54.829128+0800 CopyAndMutableCopy[82805:4463966] responsibility = 0x100001070,mutableResponsibility = 0x1033003a0
        2019-03-08 21:59:54.829435+0800 CopyAndMutableCopy[82805:4463966] 指针地址:responsibility = 0x7ffeefbff588,mutableResponsibility = 0x7ffeefbff580

不可变字符串的mutableCopy默认进行了深拷贝。

MutableCopy可变字符串

        NSString *obligation = @"obligation";
        NSMutableString *mutableObligation = [obligation mutableCopy];
        NSLog(@"obligation = %p,mutableObligation = %p",obligation,mutableObligation);
        NSLog(@"指针地址:obligation = %p,mutableObligation = %p",&obligation,&mutableObligation);
        2019-03-08 22:08:47.297261+0800 CopyAndMutableCopy[82999:4475527] obligation = 0x100001070,mutableObligation = 0x100609bf0
        2019-03-08 22:08:47.297325+0800 CopyAndMutableCopy[82999:4475527] 指针地址:obligation = 0x7ffeefbff588,mutableObligation = 0x7ffeefbff580

可变字符串的mutableCopy默认进行了深拷贝。

集合对象Copy 和 MutableCopy

        NSArray *array = @[@"shenteng",@"mali",@"ailun"];
        NSMutableArray *mutableArray = [array mutableCopy];
        NSArray *copyArray = [array copy];
        
        NSMutableArray *newMutableArray = [NSMutableArray arrayWithObjects:@"xuzheng",@"huangbo",@"wangbaoqiang",nil];
        NSArray *newCopyArray = [newMutableArray copy];
        NSMutableArray *newMutableCopyArray = [newMutableArray mutableCopy];
        
        NSString *name = [array firstObject];
        NSString *copyName = [copyArray firstObject];
        NSString *mutableName = [mutableArray firstObject];
        
        NSString *compellation = [newMutableArray firstObject];
        NSString *copyCompellation = [newCopyArray firstObject];
        NSString *mutableCompellation = [newMutableCopyArray firstObject];
        
(lldb) p array
(__NSArrayI *) $1 = 0x0000000102c055d0 @"3 elements"
(lldb) p mutableArray
(__NSArrayM *) $2 = 0x0000000102c05c60 @"3 elements"
(lldb) p copyArray
(__NSArrayI *) $3 = 0x0000000102c055d0 @"3 elements"
(lldb) p newMutableArray
(__NSArrayM *) $4 = 0x00000001029013f0 @"3 elements"
(lldb) p newCopyArray
(__NSArrayI *) $5 = 0x00000001029000d0 @"3 elements"
(lldb) p newMutableCopyArray
(__NSArrayM *) $6 = 0x0000000102901880 @"3 elements"

(lldb) p name
(__NSCFConstantString *) $7 = 0x0000000100002080 @"shenteng"
(lldb) p copyName
(__NSCFConstantString *) $8 = 0x0000000100002080 @"shenteng"
(lldb) p mutableName
(__NSCFConstantString *) $9 = 0x0000000100002080 @"shenteng"

(lldb) p compellation
(__NSCFConstantString *) $10 = 0x00000001000020e0 @"xuzheng"
(lldb) p copyCompellation
(__NSCFConstantString *) $11 = 0x00000001000020e0 @"xuzheng"
(lldb) p mutableCompellation
(__NSCFConstantString *) $12 = 0x00000001000020e0 @"xuzheng"

通过打印1 可以见到，对于不可变的 arr 如果进行 copy 的话会进行浅拷贝，如果 mutableCopy 会进行内容拷贝。但是，通过打印2 打印出的地址信息，这里的内容拷贝仅仅是拷贝 array 这个对象，array 集合内的元素仍然是指针拷贝。所以可以定义为是单层深拷贝。通过打印3可以看出，对于可变的集合元素的 copy 与 mutableCopy 都是单层深复制。

结论

对于非集合对象

• copy：因为copy默认返回的是不可变的，所以当我们对一个不可变的字符串进行copy的时候，我们只是拷贝了它的指针（浅拷贝）。当我们对一个可变的字符串进行拷贝的时候，因为类型转变了，我们需对其进行深拷贝。

• mutableCopy：默认返回的是一个可变的对象，适用于可变的对象，例如NSMutableString，NSMutableArray，NSMutableDictionary、etc。 无论对于可变的字符串还是不可变的字符串进行mutableCopy，系统都默认进行深拷贝，那么为什么对于相同类型的进行mutableCopy返回的仍然是新的对象呢，因为在这里系统要保证，旧的对象和新的对象都是可变的，且他们之前不会相互影响。

对于集合对象

• 对于不可变的集合对象，copy 是浅拷贝，mutableCopy 是单层深拷贝。
• 对于可变的集合对象，无论 copy 或者 mutableCopy 都是单层深拷贝。