Internal structure of the iOS class

1. Definition of Class and Object

/a opaque type that represents an Objective-c class.typedef struct objc_class *class;
// represents an instance of a class.struct objc_Object { Class Isa; };/ A pointer to an instance of a class.typedef struct objc_object *id;

The class is a pointer to the Objc_class struct, and the ID is a pointer to the Objc_object struct, whose member Isa is a pointer to the Objec_class struct body.

2. Definition of Objc_class

struct objc_class { Class Isa; //point to Metaclass          class Super_class ; //point to its parent class Const char *name ; //class name Long version ; //class version information, initialization defaults to 0, can be modified by the runtime function class_setversion and class_getversion, read
long info; ///Some identifying information, such as Cls_class (0X1L), indicates that the class is a normal class which contains object methods and member variables ; Cls_meta (0x2l) indicates that the class is Metaclass, which contains class methods ; Long instance_size ; //The instance variable size of the class (including instance variables inherited from the parent class); struct objc_ivar_list *ivars; //address for storing each member variable struct objc_method_list **methodlists ; //related to some flag bits of info, Such ascls_class (0x1l), the method of storing objects, such as Cls_meta (0x2l), is the storage class method ; struct objc_cache *cache; //Pointer to the nearest method used to improve efficiency; struct objc_protocol_list *protocols; //Storage of the agreements to which such class complies     }The class structure pointed to by the ISA pointer in Isa:objec_object (object) is called Class (that is, the class to which the object belongs), which holds the normal member variable and the method of the object method ("-"), but here the class structure pointed to by the ISA pointer is called Metaclass, A method that holds a member variable of type static and a method of static type ("+").

Super_class: A pointer to the parent class of the class, and if the class is a root class (such as NSObject or Nsproxy), then Super_class is null.

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Internal structure of the iOS class