C++ Extending Class Forcing some methods private

Question

My question is simple: ~Given two classes, I want to one of them to extend the other one, but turning some methods to be private:

Class B
public Method a();
public Method b();
public Method c();

Class A extends B
private Method a();
private Method b();
public Method c();

Is this possible and how? Thanks!

score 1 · Answer 1 · edited May 23 '17 at 12:05

1

Use private inheritance, all the function in base class B will become private.

  class A:   private B
  {
  }

Difference between private, public, and protected inheritance in C++ are explained here.

edited May 23 '17 at 12:05

Community

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1

answered Dec 12 '14 at 15:30

Matt

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Minor issues: `class` is lowercase, not Pascal-case. Classes end with a semi-colon (`;`). – abelenky Dec 12 '14 at 15:33
@Piotr S. you are correct. But what is missing from the response is that now OP has control of what methods to expose if wished. – MatiasFG Dec 12 '14 at 17:45
@MatiasFG OP has the same ability to control access with any other inheritance as well – Piotr Skotnicki Dec 12 '14 at 17:59

score 1 · Accepted Answer · answered Dec 12 '14 at 15:32

1

This is what Private Inheritance is for.

class A:   private B
{
    // All methods of class B are now private.
    // To make some "public" again:
    public:
        Method c()  { return B::c(); } // Call the private c-method from class B.
};

answered Dec 12 '14 at 15:32

abelenky

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Can't you also use `public: using B::c;` to expose a method? – Fred Larson Dec 12 '14 at 15:34
1

@FredLarson: That also works [reference](http://en.cppreference.com/w/cpp/language/using_declaration) – abelenky Dec 12 '14 at 15:36

score 0 · Answer 3 · answered Dec 12 '14 at 15:37

You could change the inheritance type from public to private, when you declare class B.

class B : public A {
   private:
      baseMethod();
};
or
class B : private A {
   public:
      baseMethod();
};

The use appropriate override that you want for each method.

Looks like you don't want all of the methods to turn private. Choose the type of inheritance based on the fraction of methods changing their visibility.

C++ Extending Class Forcing some methods private

3 Answers3