Question

I have an issue where I have an interface that has parts that make sense as templated, and parts that make sense as not-templated. I’m in the middle of a refactor where I’m splitting that out into two different interfaces where the more specific (the templated one) inherits from the other one. E.g., say I have an interface IArray, this would contain functions like Size() since it doesn’t care about the data type. But I’d have another interface ITArray<DataType> that would have something like DataType GetElement(...). (This is just for illustration, don’t yell at me to use std::vector). The reason I’m doing this refactor is that there are a lot of consumers of the non-templated interface and they’d like to not have to write templated functions that accept a templated interface if they don’t need the templated type (generally extern "C" stuff)

The problem is that I have overloaded functions that appear in both interfaces, but for some reason I can’t resolve the base class functions. Here’s a simple example that I put together that’s not compiling in MSVC:

#include <iostream>

class IA
{
public:
        virtual void X()=0;
};

template <class DataType>
class ITA : public IA
{
public:
        //If I uncomment this line, it all works!
        //virtual void X()=0;
        virtual void X(DataType d)=0;
};

template <class DataType>
class A : public ITA<DataType>
{
public:
    void X()
    {
        std::cout << "In X" << std::endl;
    }

    void X(DataType d)
    {
        std::cout << "In X, d=" << d << std::endl;
    }
};

template <class DataType>
void DoSomething(ITA<DataType>& I, DataType d)
{
    I.X(); //MSVC can't resolve this since it's in IA, not ITA
    I.X(d);
}

int main(int argc, char* argv[])
{
    A<int> I;
    DoSomething(I,10);
}

Is there some way that I can make IA’s functions appear in ITA<> without manually putting them there? I see a maintenance nightmare ahead of me.

Answer 1

Have you tried adding a using directive? IA::X is a hidden by A::X.

class A : ...
{
public:
    using IA::X;
    virtual void X(DataType d) = 0; 
};