本文介绍了如何在C ++中定义密封类?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

如何停止其他类继承的类。

解决方案

C ++ 11解决方案



在C ++ 11中,可以通过在定义中使用 final 关键字来封装类:



class A final //注释在类名后面使用final关键字
{
// ...
} ;

class B:public A //错误 - 因为类A被标记为final(sealed)。
{//所以A不能派生自。
// ...
};

要知道final的其他用法,请参见我的回答:










C ++ 03解决方案



可以

  class Usable; 
类Usable_lock {
friend class Usable;
private:
Usable_lock(){}
Usable_lock(const Usable_lock&){}
};

类可用:public virtual Usable_lock {
public:
Usable();
Usable(char *);
};
可用a;

class DD:public Usable {};

DD dd; //错误:DD :: DD()无法访问
// Usable_lock :: Usable_lock():private member


b $ b




Generic_lock



所以我们可以使用模板来使 Usable_lock 通用以封闭任何类:

 模板< class T& 
class Generic_lock
{
friend T;
Generic_lock(){} // private
Generic_lock(const Generic_lock&){} // private
};

class可用:public virtual Generic_lock< Usable>
{
public:
Usable(){}
};

可用a; // Okay
class DD:public Usable {};

DD dd; //不行!


How to stop the class to be inherited by other class.

解决方案

C++11 solution

In C++11, you can seal a class by using final keyword in the definition as:

class A final  //note final keyword is used after the class name
{
   //...
};

class B : public A  //error - because class A is marked final (sealed).
{                   //        so A cannot be derived from.
   //...
};

To know the other uses of final, see my answer here:


C++03 solution

Bjarne Stroustrup's code : Can I stop people deriving from my class?

class Usable;
class Usable_lock {
    friend class Usable;
private:
    Usable_lock() {}
    Usable_lock(const Usable_lock&) {}
};

class Usable : public virtual Usable_lock {
public:
    Usable();
    Usable(char*);
};
Usable a;

class DD : public Usable { };

DD dd;  // error: DD::DD() cannot access
        // Usable_lock::Usable_lock(): private  member


Generic_lock

So we can make use of template to make the Usable_lock generic enough to seal any class:

template<class T>
class  Generic_lock
{
    friend T;
    Generic_lock() {}                     //private
    Generic_lock(const Generic_lock&) {}  //private
};

class Usable : public virtual Generic_lock<Usable>
{
public:
    Usable() {}
};

Usable a; //Okay
class DD : public Usable { };

DD dd; //Not okay!

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09-05 09:15