C++ : implementation of derived (extended) interfaces

sidney

Hi all,

We have a question regarding the proper way of implementing, in C++, the following interface:

module example {

    interface Base {
        void sayHi();
    };

    interface Derived extends Base {
        void sayHello();
    };
};

What we want to do is give an implementation for Base::sayHi() that is inherited in all derived classes from Base. What we do to achieve this is use multiple inheritance:

class BaseI : public virtual public virtual example::Base
{
    virtual void sayHi(const Ice::Current &) {}
}

class DerivedI: public virtual example:Derived, public virtual BaseI
{
    virtual void sayHello(const Ice::Current &) {}
}

In the Ice user manual, we couldn't find any explicit guidelines on implementing extended interfaces in the C++ language mapping section. Given the fact that we cannot use multiple inheritance in c++ to implement multiple interfaces in a single class, we were wondering if the solution given here is, in fact, the proper way.

Any comments would be appreciated.

Best regards, Sidney

mes

Hi Sidney,

Your example is the correct approach. The C++ classes generated from Slice interfaces always use virtual inheritance, so you can reuse the implementation of a base class in a derived class like you have shown.

Note that Slice classes have different default semantics. A Slice class does not inherit virtually from Ice::Object by default; you would need to use the cpp:virtual metadata tag to enable the use of virtual inheritance.

Regards,
Mark

sidney

Ok, it's good to know we're on the right track here.

Cheers, Sidney