Implementing an interface's function using member function templates

Question

I'm wondering whether it's possible to implement an "interface"'s function via member function templates like so:

struct VisitorI
{
    virtual void Visit(int) = 0;
    virtual void Visit(float) = 0;
};

struct VisitorC : public VisitorI
{
    template<class T>
    void Visit(T) { /*Assume Visit(T) has syntatically the same implemenation for each relevant T */}
};


template void VisitorC::Visit(int);
template void VisitorC::Visit(float);


int main()
{
    VisitorC Visitor;

    return 0;
}

The above code doesn't compile because foo(int) and foo(float) are considered pure virtual in VisitorC, so I'm thinking it's not possible. I don't really see any particular reason why it shouldn't though...?

Cheers, Damian

I guess that falls into the "virtual member function templates cannot be made virtual" category. Even though in this particular I think it wouldn't be too hard for the compiler to work it out. — Damian Birchler, Mar 18 '16 at 09:11
related: http://stackoverflow.com/questions/2354210/can-a-member-function-template-be-virtual (in particular: the most upvoted answer) — YSC, Mar 18 '16 at 09:12

score 3 · Accepted Answer · answered Mar 18 '16 at 09:20

3

As a workaround, you could:

struct VisitorC : public VisitorI
{
    virtual void Visit(int a)   { Visit_impl(a); }
    virtual void Visit(float a) { Visit_impl(a); }
private:
    template<class T>
    void Visit_impl(T) { /* ... */ }
};

answered Mar 18 '16 at 09:20

YSC

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Implementing an interface's function using member function templates

1 Answers1