iOS关联对象objc_setAssociatedObject探讨
主要函数为:
//为给定的对象设置一个关联值
public func objc_setAssociatedObject(_ object: Any, _ key: UnsafeRawPointer, _ value: Any?, _ policy: objc_AssociationPolicy)
//返回与给定键的给定对象关联的值
public func objc_getAssociatedObj