ICE C++ question

mcrystal

Please forgive my C++ ignorance, but I am really a Java programmer attempting to write a C++ test and am hoping that someone can point me in the right direction. I have a slice file which essentially defines a bunch of interfaces and classes. The basic structure is I have a base class which is extended by a bunch of subclasses and I have a base service interface which is extended by subinterfaces:

ClassA
ClassB : ClassA

ServiceX {
virtual ClassA getA();
}

ServiceY : ServiceX {
getA() {
return ClassB();
}
}

In C++ the interface generates something like:
ClassAPtr getA();

where ClassAPtr is the rerference counted pointer (IceInternal::Handle) which is typedefed in the generated header file. My question is, how does one properly downcast this to the actual implementation class. In Java one would do something like:

ClassB val = (ClassB)ServiceY.getA();

How do I accomplish this same functionality in C++?


Thanks again,
Mayer

mes

Hi,

In C++, we usually recommend that you create a smart pointer type for implementation classes. For example:

// C++
class ClassAI : public ClassA { ... };
typedef IceUtil::Handle<ClassAI> ClassAIPtr;

Having done that, you can downcast quite easily:

ClassAPtr a = ...
ClassAIPtr ai = ClassAIPtr::dynamicCast(a);
if(ai) {
    // dynamicCast may return nil!
}

In the absence of a typedef for your implementation class, you can use the normal C++ mechanism:

ClassAPtr a = ...
ClassAI* ai = dynamic_cast<ClassAI*>(a.get());
if(ai) {
    ...
}

Hope that helps,
- Mark

mes

After re-reading your post, it sounds like you simply want to downcast to another Slice-defined type. In this case you would use the same technique I described above:

ClassAPtr a = ...
ClassBPtr b = ClassBPtr::dynamicCast(a);
if(b) {
    ...
}

- Mark