This forum has been archived. Please start a new discussion on GitHub.

C++ : implementation of derived (extended) interfaces

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
    mes California
    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.

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

    Cheers, Sidney