关联对象的原理

实现关联对象技术的核心对象有
AssociationsManager
AssociationsHasMap
objectAssociationMap
objcAssociation

class AssociationsManager {
    static AssociationsHashMap *_map;
};
class AssociationsHashMap : public unordered_map<disguised_ptr_t,ObjectAssociationMap>
 class ObjectAssociationMap : public std::map<void *, ObjcAssociation> 
class ObjcAssociation {
        uintptr_t _policy;
        id _value;
};

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🌟关联对象并不是存储在被关联对象本身内存中
🌟关联对象存储在全局的统一的一个AssociationsManager中
🌟设置关联对象为nil，就相当于是移除关联对象