[图解]实现领域驱动设计译文暴露的问题03

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前面我们讲了

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第①句话的

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第（1）个问题和第（2）个问题

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共享父类的对象，对象树

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这样的说法是有问题的

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第二个，关联

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这个不对

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上一期视频我们也说到了

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这里面有个反转

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那我们来看这个反转是什么

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如果没有共享父类这样的文字

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那这里的对象树，原文是图

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它就有可能误打误撞

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就变成是对的

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为什么呢

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你看

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如果我们一个聚合组合的关联的整体的一端

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它的

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多重性上限是1

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它可以是0

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因为可能最顶上那个，像这个

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它就没有上级嘛

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没有老大

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那么这个整体部分的对象的链接结构

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它确实是一棵有向的树

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像这样

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你看，左边是类图

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右边是对象链接

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的形状构造

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包括上面这个ABC也行

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下面这个A的自反关联

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自反的聚合

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类图上面只有一个类A

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但是A的

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实例本身

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它也可能构成一个什么

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构成一个

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对象的一棵树

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就像

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商品的类别一样嘛

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对不对

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大类别下面有小类别

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小类别下面有小小类别

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如果说

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我这里面只有一个类，叫类别

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那么类别和类别之间的这种

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关系，它就变成了递归的关联

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如果这个递归关联本身是一个

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一对多的，就是说

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一个下级只能有一个上级

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一个上级可以有多个下级

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它确实就是一棵这样的树

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那如果不是一对多

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整体这一端

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它可以是多的

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就是一个部分对象

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可以属于多个整体对象

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当然这个时候，所谓的整体部分

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就已经没有

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严谨的含义了

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含义已经模糊了

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对不对

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你既然是部分

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你还能够同时属于别人，不行的

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你应该是什么

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在同一个时间内，啪

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拍一张快照

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应该是什么样，只能够拍到

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它只属于

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一个整体

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当然你可以把它转移

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比如说，你本来是他的小弟

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是属于他的

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现在你被他抛弃了

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他把你解除了

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扔到一边去了

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另外一个老大把你捡起来，这可以

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对吧

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但是同一时间，你不可能拍到，啪

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同一个

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部分属于两个或多个

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不同的整体，那就不对了

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如果说一个部分对象

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可以同时属于多个的话

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那就可以是这样了

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就变成一张有向无环图

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变成一张图了

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对不对

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但这个时候这个含义已经模糊了

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所以呢，这个我们只是说

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如果是这样的情况

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但不代表这样的情况是提倡的

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那就无所谓什么整体部分关系

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变成普通关联就行了

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对吧

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那为什么是有向

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因为这个

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组合聚合关系

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它是非对称的

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实际上，我们的继承关系

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或者泛化关系也是非对称的

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只不过这个非对称是什么

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它是在集合的层面上非对称

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不能说

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A是B的一种

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B是C的一种

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然后C又是A的一种

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那不行的

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不可能是这样

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对吧

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泛化，集合的包含嘛

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而聚合组合关系

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也是非对称的

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如果B对象是A对象的一部分的话

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那么A

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就不可能直接或间接成为B的部分

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所以呢，在对象级别上不可能有这样的

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A组合B

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B是A的一部分

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然后C又是B的一部分

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然后C反过来又

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组合A，那不行的

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就像汽车有轮子

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轮子上面呢，有个轴承

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有个轮子的芯

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ABC嘛

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然后这个芯反过来组装了这个汽车

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怎么可能呢

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对吧

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要注意，我们这里说的是对象级别

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有的同学这里搞不清楚，说

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可以呀

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我这个轮子里面

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可以再组装一个汽车对象

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汽车组装轮子

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轮子也组装汽车

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可不可以，可以的

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但是，那个汽车对象跟

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这个汽车对象不是同一个汽车对象

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搞清楚

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就像我们这个

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你看

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A自己组装A，可不可以，可以呀

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对吧

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部门里面有小部门

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两个都是部门

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但是大部门里面有小部门

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但这里经常很多人在这里糊涂的

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特别是很多现在的程序员

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缺少基本的训练

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基本的抽象能力都没有

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经常这个就把他打晕掉了

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这是类级别上的

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但是展开到对象级别上

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它是不同的对象

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对不对

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很多同学这里经常就出问题的

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类似这样的观点

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我前面已经说过很多遍了

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比如说，一个人

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他说我觉得

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很多搞迷信的

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这些是对的

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我就信那个

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这是他的自由

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但如果说这个人

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他说

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我的迷信这一套就比科学强

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我要证明给你看

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你科学没什么了不起的

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他就认真去学科学

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学物理

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学化学，等等

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还去参加高考，结果呢

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高考

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物理、化学考了很高的分

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你想想

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如果一个人他能够

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考到这么高的分的话

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他有可能回去信之前的那一套吗

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他不可能的

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对不对

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我们之所以很多时候信那些东西

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就是因为什么，我们没有认真去学习过

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比较严谨的一些思维

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这是第（3）点

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第（4）点就是

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确实为什么有这样的误解

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跟译者本身的知识的缺陷有关

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但是呢，原文的parent这个词确实用得不好

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因为这个往往是用在类上面

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应该是整体

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整体对象，这样用更好一点

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那建议的译文

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就这样

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聚合只是把共同父对象之下的

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%……&&￥￥

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我们就忠实地

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根据原文来译

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这里父对象，这个我们依然留下来

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不改成整体

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好

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这是第①句了

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那我们来看第②句

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第②句

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这是原文和译文

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那问题呢，有这么几个

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比较大的

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这个

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（1）（2）这是比较大的了

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你看这里

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它说“遍历”

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但这里并没有说遍历

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只是说什么

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导航

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没有说遍历

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只是说导航

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第（2）个

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这里有个深度的递归

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这里面

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有一个深地

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这个有，没有说递归

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那为什么会有这样的一个译文出来

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背后有什么样的思想上的根源

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可能有什么样的思想上的根源

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这个我们

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下期

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我们再来探讨

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