Private Virtual Functions

The way private virtual functions are handled in derived classes has changed from Managed Extensions for C++ to Visual C++ 2005.

In Managed Extensions, the access level of a virtual function does not constrain its ability to be overridden within a derived class. This has changed. In the new syntax, a virtual function cannot override a base class virtual function that it cannot access. For example:

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__gc class Foo { // inaccessible to a derived class вЂ¦ virtual void g(); }; __gc class Bar : public Foo { public: // in Managed Extensions, ok: g() overrides Foo::g() // in new syntax, error: cannot override: Foo::g() is inaccessible вЂ¦ void g(); };

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__gc class Foo {
   // inaccessible to a derived class вЂ¦
   virtual void g();
};

__gc class Bar : public Foo {
public:
   // in Managed Extensions, ok: g() overrides Foo::g()
   // in new syntax, error: cannot override: Foo::g() is inaccessible вЂ¦
   void g();
};

There is no real mapping of this sort of design onto the new syntax. One simply has to make the base class members accessible вЂ“ that is, non-private. The inherited methods do not have to bear the same access. In this example, the least invasive change is to make the Foo member protected. This way the general program's access to the method through Foo is still prohibited,

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ref class Foo { protected: virtual void g(); }; ref class Bar : Foo { public: virtual void g() override; };

Note that the absence of the explicit virtual keyword in the base class, under the new syntax, generates a warning message.

See Also

Reference

Concepts