派生对象的模板是基类型模板的子类吗 [英] Is Template of derived object a subclass of template of base type

问题描述

如果 'apple' 是 'fruit' 的子类，那么 List 是 List 的子类，这样对吗?

If 'apple' is a subclass of 'fruit' , then List<apple> is a subclass of List<fruit> is this correct ?

推荐答案

没有.List 和 List 不相关.这两个类可能有完全不同的实现，并且无法将一个转换为另一个.例如，List<> 模板可以以某种方式专门用于 apple 与一般 List 具有完全不同的结构> 模板.

No. List<apple> and List<fruit> are not related. These both classes could have totally different implementations and there is no way to convert one into the other. For example the List<> template could be specialized in some way for apples that has a totally different structure than the general List<T> template.

即使实现是兼容的，将 List 视为 List 仍然是一个坏主意，因为人们会开始把所有种类的水果都放在应该包含苹果的列表中.另请参阅C++ FAQ Lite 中的条目，说到苹果和香蕉...

And even if the implementations were compatible, it would still be a bad idea to treat a List<apple> as a List<fruit> since then people would start to put all kinds of fruits into that list that was just supposed to contain apples. See also this entry in the C++ FAQ Lite, that talks about apples and bananas...

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