Deep and shallow copies in iOS

#import <Foundation/Foundation.h>intMainintargcConst Char*argv[]) {//A: The difference between copy and retain//who has the concept of reference counting://1. Heap space has a reference counting concept.//2. The heap area object will have a reference count. //%ld:-1%lu:18446744073709551615//retain: Always a shallow copy.    The reference count is added one at a time. //returns whether the object is mutable and consistent with the object being copied. //copy: For a deep copy of a mutable object, the reference count does not change; //for non-mutable objects is a shallow copy, the reference count is added one at a time. //always returns an immutable object. //NSString generally recommend that you use copy, so that changing the data does not affect the original assignment//mutablecopy: Always a deep copy, the reference count does not change. //always returns a Mutable object. //Two: The difference between a shallow copy and a deep copy//shallow copy definition: When copying the value of an object, no matter how much it is copied, the value points to the same object. //deep Copy definition: Add a pointer and request a new memory so that the added pointer points to the new memory. //a shallow copy is a pointer copy, and a deep copy is a copy of the content. //An example of a shallow copy: A person began to call Zhang San, later renamed John Doe, but still the same person. Mutual influence. //deep copy: A person began to call Zhang San, and later cloned individuals called John Doe, not the same person. Does not affect each other. //1. Of course not all objects in iOS support Copy,mutablecopy, classes that comply with the Nscopying protocol can send copy messages, and classes that follow the Nsmutablecopying protocol can send mutablecopy messages. //2. If you want to customize copy then you must obey Nscopying and implement Copywithzone: method, if you want to customize mutablecopy then you must obey Nsmutablecopying, and implement        Mutablecopywithzone: Method. //Three. iOS provides copy and Mutablecopy methods, copy is copying an immutable object, and Mutablecopy is copying a mutable object. //1. For copies of non-container class objects. (NSString, NSNumber, etc.)//for a copy of an immutable object://nsstring *str1 = [[NSString alloc] initwithformat:@ "bingbingbing"];//nsstring *str2 = [str1 copy];//nsmutablestring *STR3 = [str1 mutablecopy];//NSLog (@ "%p,%p,%p", str1, str2, STR3);//NSLog (@ "%lu,%lu,%lu", Str1.retaincount, Str2.retaincount, str3.retaincount);//[str1 release];//NSLog (@ "%p,%p,%p", str1, str2, STR3);//NSLog (@ "%lu,%lu,%lu", Str1.retaincount, Str2.retaincount, str3.retaincount);//If you copy a immutable object, copy is a shallow copy, and Mutablecopy is a deep copy. //for a copy of a mutable object://nsmutablestring *string1 = [[Nsmutablestring alloc] initwithformat:@ "Ice Ice"];//nsstring *string2 = [string1 mutablecopy];//nsmutablestring *string3 = [string1 mutablecopy];//nsmutablestring *string4 = [string1 copy];//NSLog (@ "%p,%p,%p,%p", string1, string2, String3, String4);//NSLog (@ "%lu,%lu,%lu,%lu", String1.retaincount, String2.retaincount, String3.retaincount, String4.retaincount); //if it is a copy of a mutable object, it is a deep copy, but the object returned by copy is immutable. //2. Copy of the container class object. (Nsarray, nsdictionary, etc.)//    //Nsarray *arr1 = [Nsarray arraywithobjects:@ "Bing", @ "Liang", nil];//Nsarray *arr2 = [arr1 copy];//Nsmutablearray *ARR3 = [arr1 mutablecopy];//NSLog (@ "%p,%p,%p", arr1, ARR2, ARR3);//NSLog (@ "%lu,%lu,%lu", Arr1.retaincount, Arr2.retaincount, Arr3.retaincount); //arr1 is pointing to the same object as ARR2, and the elements inside are pointing to the same pointer,//here arr2 is a shallow copy of arr1, ARR3 is a deep copy of arr1.//For (NSString *p in arr1) {//NSLog (@ "%p", p);//    }//NSLog (@ "_________________________________");//For (NSString *p in arr2) {//NSLog (@ "%p", p);//    }//NSLog (@ "_________________________________");//For (NSString *p in arr3) {//NSLog (@ "%p", p);//    }    //but the elements in the array are shallow copies.       /*nsmutablestring *mutabelstring1 = [nsmutablestring stringwithformat:@ "Bingbing"]; nsmutablestring *mutabelstring2 = [nsmutablestring stringwithformat:@ "Laingliang"];*/Nsmutablearray*array1 = [Nsmutablearray arraywithobjects:@"Bingbing",@"Laingliang", nil]; Nsarray*array2 =[array1 copy]; Nsmutablearray*array3 =[Array1 mutablecopy]; Nsmutablearray*array4 =[array1 copy]; NSLog (@"%p,%p,%p,%p", Array1, Array2, Array3, Array4); NSLog (@"%lu,%lu,%lu,%lu", Array1.retaincount, Array2.retaincount, Array3.retaincount, Array4.retaincount); //if an element of a container is immutable, the object remains unchanged after you copy it, so you only need the pointer to copy it. //For (NSString *p in array1) {//NSLog (@ "%p", p);//        }//NSLog (@ "_________________________________");//For (NSString *p in array2) {//NSLog (@ "%p", p);//        }//NSLog (@ "_________________________________");//For (NSString *p in array3) {//NSLog (@ "%p", p);//        }//NSLog (@ "_________________________________");//For (NSString *p in Array4) {//NSLog (@ "%p", p);//    }            //the difference between copy and retain://in the Foundation object, when copy is an immutable object, it acts as a retain and is a shallow copy. //when it is a mutable object, copy is a deep copy, and retain is a shallow copy. //the difference between copy and mutablecopy://in the Foundation object, copy is a shallow copy when the object is immutable. //when we use Copy a Mutable object, the deep copy, but the replica object is immutable. //when using mutablecopy, replicas are mutable regardless of whether the original object is mutable, and a deep copy is realized in real sense. //3. Custom copies of objects://The difference between a deep copy and a shallow copy is the implementation of the Copywithzone method (slightly)//A shallow copy of the copied object itself, the property in the object, the contained object does not copy//deep copy copy all, including object properties and other objects    return 0;}

Deep and shallow copies in iOS