C++核心準(zhǔn)則C.121:如果基類被用來定義接口,保證它是一個純虛類?

綠色碧璽

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

C.121:如果基類被用來定義接口，保證它是一個純虛類?

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.

不包含數(shù)據(jù)的類會更穩(wěn)定(更少脆弱性)。接口通常應(yīng)該由公開的純虛函數(shù)和默認/空的純虛析構(gòu)函數(shù)組成。

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.

派生類通過它的Goof接口被銷毀，(但是由于Goof的析構(gòu)函數(shù)不是虛函數(shù)，導(dǎo)致Derived的析構(gòu)函數(shù)不會被調(diào)用，譯者注)因此它的string成員會發(fā)生泄露。為Goof設(shè)計一個虛析構(gòu)函數(shù)就所有都OK了。

Enforcement(實施建議)

• 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.

• 對于所有同時包含數(shù)據(jù)成員和并非繼承自基類的可覆蓋(非最終)虛函數(shù)的類發(fā)出警告。

原文鏈接：

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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