c++核心准则C.137: 使用虚基类避免过于一般的基类‍

C.137: Use virtual bases to avoid overly general base classes

C.137: 使用虚基类避免过于一般的基类‍

Reason(原因）

Allow separation of shared data and interface. To avoid all shared data to being put into an ultimate base class.

允许共享数据和接口的分离。避免将所有的共享数据放进一个终极基类中。

Example(示例）

struct Interface {
    virtual void f();
    virtual int g();
    // ... no data here ...
};

class Utility {  // with data
    void utility1();
    virtual void utility2();    // customization point
public:
    int x;
    int y;
};

class Derive1 : public Interface, virtual protected Utility {
    // override Interface functions
    // Maybe override Utility virtual functions
    // ...
};

class Derive2 : public Interface, virtual protected Utility {
    // override Interface functions
    // Maybe override Utility virtual functions
    // ...
};

Factoring out Utility makes sense if many derived classes share significant "implementation details."

如果很多派生类之间分享特别有用的共通的"实现细节"，从中分离出共通功能就是有意义的。

Note(注意)

Obviously, the example is too "theoretical", but it is hard to find a small realistic example. Interface is the root of an interface hierarchy and Utility is the root of an implementation hierarchy. Here is a slightly more realistic example with an explanation.

很显然，示例过于理论化了，但是找到一个接近现实的小例子太难了。接口是接口体系的起点，而公用程序是实现体系的起点。这里有一个带有说明的，略微更接近实际的例子。

链接：https://www.quora.com/What-are-the-uses-and-advantages-of-virtual-base-class-in-C%2B%2B/answer/Lance-Diduck

Note(注意）

Often, linearization of a hierarchy is a better solution.

通常，线性的继承体系是较好的解决方案。

Enforcement(实施建议)

Flag mixed interface and implementation hierarchies.

提示接口继承和实现继承体系混合的情况。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c137-use-virtual-bases-to-avoid-overly-general-base-classes

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