What is the point of a private pure virtual function?

user_182448 0
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I came across the following code in a header file:

class Engine
{
public:
    void SetState( int var, bool val );
    {   SetStateBool( int var, bool val ); }

    void SetState( int var, int val );
    {   SetStateInt( int var, int val ); }
private:
    virtual void SetStateBool(int var, bool val ) = 0;    
    virtual void SetStateInt(int var, int val ) = 0;    
};

To me, this implies that either the Engine class or a class derived from it, has to provide the implementation for those pure virtual functions. But I didn't think derived classes could have access to those private functions in order to reimplement them - so why make them virtual?

non-virtual-interface inheritance oop c++
6 Answers

TL;DR answer:

You can treat it like another level of encapsulation - somewhere between protected and private: you can't call it from child class, but you can override it.

It is useful when implementing Template Method design pattern. You could use protected, but private together with virtual may be considered as better choice, because of better encapsulation.

user_41316730
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