Question about interface method and implementation

Hi All,

I'm trying the Visual Studio 2005 Beta 2, especially for C++/CLI implementation
in VC++. I was wondering if someone could please help me with a question
that I have. Any suggestions would be greatly appreciated.

I've defined an interface like this:

public interface class IMyInterface
{
    void TryAndTry();
};

and a class implementing this interface

ref class MyClass: IMyInterface
{
public:
void TryAndTry()
    {
        Console::WriteLine("DONE");
    }

};

I've a test program that simply creates an instance of this class. When I compile this
project, I get following compilation error:

"error C3766: 'MyClass' must provide an implementation for the interface method 'void IMyInterface::TryAndTry(void)'   "

I'm surely missing something here as I clearly have provided the implementation
for the interface's method and still the compiler is complaining. Any ideas

Thanks,
Bhavin

Answer this question

Question about interface method and implementation

etncc
Thanks Jonathan, that solves the problem.. However, I'm not quite
sure about the need for using virtual in method implementation. If we
go by pure C++ way, shouldn't virtual be used in the interface definition
rather in the classes that implement it That is the way I'd have done
it by creating an abstract class in C++ by declaring a pure virtual
method in the class and providing implementation down in the
hieararchy..Sorry if this is too naive.

Best,
Bhavin
KevinBurton

In your interface defininition you're requesting that base classes implement a private method named "TryAndTry" that returns void and takes no parameters.

In your base class you are defining a public method named "TryAndTry" that returns void and takes no parameters.
PavanM

Peter: interfaces are like structs: all the members are public by default. The problem here is that in C++/CLI there is not such thing as an implicitly virtual method. The fix, I suspect, is to change the definition of the ref class to:

ref class MyClass : IMyInterface
{
public:
virtual void TryAndTry()
    {
        Console::WriteLine("DONE");
    }
};
Stevo Guy
In regular C++ the method in the class is virtual even though you haven't marked it as virtual. Consider the following case:

struct IDoSomething {
   virtual void vmf() = 0;
};

class A : public IDoSomething {
public:
   void vmf() {
   }
};

In this case as A::vmf overrides IDoSomething::vmf() it is implicitly marked as virtual. The definition of class A above is identical to:

class A : public IDoSomething {
public:
   virtual void vmf() {
   }
};

The C++/CLR rules are stricter: mostly because the CLR allows (but Visual C++ does not support - mostly because it is too weird) the following:

ref interface IDoSomething {
   void vmf();
};

ref class A : IDoSomething {
public:
   void vmf() {
   }
};

In this case the non-virtual method A::vmf could be used to implement the interface method IDoSomething::vmf: but as I said don't try this at home.

So for this reason and for the reasons I mention in my earlier posts C++/CLI does not support implicitly virtual methods. Doing so, even though it requires slightly more typing, does lead to much clearer code. I hate having to walk up a class hierarchy just to check if a method is virtual or not .
Question about interface method and implementation

Answer this question