AssociationObject

// 关系伪代码
class AssociationsManager {
	static AssociationsHashMap *_map;
};
class AssociationsHashMap: public unordered_map<disguised_ptr_t, ObjectAssociationMap>
class ObjectAssociationMap: public std::map<void *, ObjcAssociationMap>
class ObjcAssociationMap {
	uintptr_t _policy;
	id _value;
};

void objc_setAssociatedObject(id object, const void * key, id value, objc_AssociationPolicy policy)

id objc_getAssociatedObject(id object, const void * key)

void objc_removeAssociatedObjects(id object)

static void *MyKey = &MyKey;
objc_setAssociatedObject(obj, MyKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, MyKey)

static char MyKey;
objc_setAssociatedObject(obj, &MyKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, &MyKey)

// 使用属性名作为key
objc_setAssociatedObject(obj, @"property", value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
objc_getAssociatedObject(obj, @"property");

// 使用get方法的@selecor作为key（推荐）
objc_setAssociatedObject(obj, @selector(getter), value, OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj, @selector(getter))

#import "Person+Test.h"
#import <objc/runtime.h>

@implementation Person(Test)
- (void)setAge:(int)age {
	objc_setAssociatedObject(self, 
							 @selector(age), 
							 @(age), 
							 OBJC_ASSOCIATION_COPY_NONATOMIC);
}
- (int)age {
	return [objc_getAssociatedObject(self, _cmd) intValue];
}
@end