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Preventing Derivation

Preventing Derivation

In general, disabling inheritance is a dubious idea. Yet under some circumstances it may be useful. To do this, declare the class in question (called A in our example) as a friend of another class (called Lock in our example). Locks constructor must be private:

 class A;class Lock { friend class A;private: Lock() {} };

Next, virtually derive the class in question from Lock:

 class A : virtual public Lock {  // ...public: A(); A(int);//.. additional ctors, dtors etc.};

Consequently, any attempt to derive from A will fail:

 A a; // OKclass Derived : public A { };Derived d;// error: Deriveds ctor cant access Locks ctor

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