C ++使用纯虚方法覆盖纯虚方法 [英] C++ override pure virtual method with pure virtual method

问题描述

用另一个纯虚方法重写纯虚方法是否有意义？是否有任何功能差异或代码风格的理由，喜欢下面的选项之一比另一个？

Does it ever make sense to override a pure virtual method with another pure virtual method? Are there any functional differences or perhaps code style reasons to prefer one of the following options over the other?

class Interface {
 public:
  virtual int method() = 0;
};

class Abstract : public Interface {
 public:
  int method() override = 0;
};

class Implementation : public Abstract {
 public:
  int method() override { return 42; }
};

与

class Interface {
 public:
  virtual int method() = 0;
};

class Abstract : public Interface {};

class Implementation : public Abstract {
 public:
  int method() override { return 42; }
};

推荐答案

两个代码产生相同的效果：class 抽象是抽象的，你不能实例化它。

Both codes produce the same effect: class Abstract is abstract and you can't instantiate it.

但是这两种形式之间存在语义差异：

There is however a semantic difference between the two forms:

• 第一种形式清楚地提醒，类 Abstract 是抽象的它的名字不会自我分割足够 ;-)）。它不仅提醒它：它也确保它通过确保该方法是纯虚拟的。


• 第二种形式表示类 Abstract 完全继承 Interface 。它是抽象的，当且仅当它的基类是。

• The first form reminds clearly that the class Abstract is abstract (just in case it's name would not be self-sepaking enough ;-) ). Not only does it reminds it: it also ensures it by making sure that method is pure virtual.
• The second form means that the class Abstract inherits everything exactly from Interface. It's abstract if and only if its base class is.

这会对您的代码的未来发展造成影响。例如，如果有一天你改变主意，并希望界面具有 method（）的默认实现：

This has consequences on future evolutions of your code. For instance, if one day you change your mind and want interface to have a default implementation for method() :

• 在第一种形式 Absract 保持抽象，不会继承方法的默认实现。


• 第二种形式确保 Abstact 将继续继承并且行为与接口。

• In the first form Absract remains abstract and will not inherit the default implementation of the method.
• The second form ensures that Abstact would continue to inherit and behave exactly as Interface.

我发现第二种形式更直观，可以更好地分离关注点。但我可以想象，可能有一些情况下，第一种形式真的有意义。

Personnally I find that the second form is more intuitive and ensures better separation of concerns. But I can imagine that there could be some situations were the first form could really make sense.

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