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C.121: If a base class is used as an interface, make it a pure abstract class

C.121:如果基类被用来定义接口，保证它是一个纯虚类‍

Reason(原因)

A class is more stable (less brittle) if it does not contain data. Interfaces should normally be composed entirely of public pure virtual functions and a default/empty virtual destructor.

不包含数据的类会更稳定(更少脆弱性)。接口通常应该由公开的纯虚函数和默认/空的纯虚析构函数组成。

Example(示例)

class My_interface {public:    // ...only pure virtual functions here ...    virtual ~My_interface() {}   // or =default};

Example, bad(反面示例)

class Goof {public:    // ...only pure virtual functions here ...    // no virtual destructor};class Derived : public Goof {    string s;    // ...};void use(){    unique_ptr
   
     p {new Derived{"here we go"}};    f(p.get()); // use Derived through the Goof interface    g(p.get()); // use Derived through the Goof interface} // leak
   

The Derived is deleted through its Goof interface, so its string is leaked. Give Goof a virtual destructor and all is well.

派生类通过它的Goof接口被销毁，(但是由于Goof的析构函数不是虚函数，导致Derived的析构函数不会被调用，译者注)因此它的string成员会发生泄露。为Goof设计一个虚析构函数就所有都OK了。

Enforcement(实施建议)

• Warn on any class that contains data members and also has an overridable (non-final) virtual function that wasn't inherited from a base class.

• 对于所有同时包含数据成员和并非继承自基类的可覆盖(非最终)虚函数的类发出警告。

   

  原文链接：

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c121-if-a-base-class-is-used-as-an-interface-make-it-a-pure-abstract-class

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