Objective-C deep replication and protocols

1. Simple replication can only implement shallow copy: assign values to the pointer, so that the two pointers point to the same memory space, and the operation is not safe.

2. The foundation class complies with the <nscopying> and <nsmutablecopying> protocols to implement the copy and mutablecopy methods. Therefore, foundation objects can use these methods to create copies or mutable copies of objects.

@ Protocol nscopying

-(ID) copywithzone :( nszone *) zone;

@ End

@ Protocol nsmutablecopying

-(ID) mutablecopywithzone :( nszone *) zone;

@ End

3. If the user-defined class complies with the <nscopying> protocol and <nsmutablecopying> protocol, the copywithzone method and the mutablecopywithzone method must be implemented. Otherwise, the Class Object cannot respond to the copy and mutablecopy messages.

4. Implement the copywithzone method, for example:

-(ID) copywithzone :( nszone *) Zone

{

Student * Stu = [[STUDENT allocwithzone: Zone] initwithname: Self. Name age: Self. Age];

Return Stu;

}

Corresponding to the main function: Suppose there is already a student object stu1;

Then: Student stu2 = [stu1 copy];

Stu2 is a copy of stu1, where deep replication is implemented. stu1 and stu2 correspond to different memory.

 

5. If your class produces a subclass, The copywithzone: method will also

Inherited

Student * Stu = [[STUDENT allocwithzone: Zone] init];

This method should be changed to: Student * Stu = [[[Self class]
Allocwithzone: Zone] init];

If you compile a copywithzone: Method of a class, the subclass method should first call the copy method of the parent class to copy the inherited copy instance variable.