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Visitor mode is to encapsulate some operations applied to a certain data structure. Once these operations need to be modified, the data structure that accepts this operation can be saved unchanged. Visitor mode is suitable for systems with relatively stable data structures. It reduces the coupling degree between data structures and operations acting on data structures, making the set of operations relatively free to change. The specific structure diagram is as follows:Update 2017/2/9该剧改编自烽火戏诸侯原著小说《老子是癞蛤蟆》，讲述了在时代变迁中，三代人的成长和选择，以及青春少年披荆斩棘守护家庭与爱情的故事。谁知道这小子命大，竟然回来去定陶救援。蛮荒时代，一只名叫“小脚板”的雷龙，因大地震而与家人失散，他必须独自前往传说中的恐龙乐园“大林”，才能与家人团聚。在旅途中，他结交了四个并不同类的伙伴。他们不仅在冒险的绑架体验到了大自然的奥秘，更重要的是，通过大家的互爱互助，他们学会了理解、关怀、负责和接纳，懂得了什么是友谊、幸福和真爱。Endothermic theory: When the flame retardant is heated, endothermic reactions occur, such as decomposition, melting, sublimation, phase change, etc., which make the fiber dissipate heat rapidly and fail to reach the combustion temperature.