Question

I understand why member template functions cannot be virtual, but I’m not sure what the best workaround is.

I have some code similar to this:

struct Entity
{
    template<typename It>
    virtual It GetChildren(It it) { return it; }
};

struct Person : public Entity
{
    template<typename It>
    virtual It GetChildren(It it) { *it++ = "Joe"; }
};

struct Node : public Entity
{
    Node left, right;
    const char *GetName() { return "dummy"; }

    template<typename It>
    virtual It GetChildren(It it)
    {
        *it++ = left.GetName();
        *it++ = right.GetName();
        return it;
    }
};

Clearly, I need dynamic dispatch. But given that the classes are actually pretty large, I don’t want to template the entire class. And I still want to support any kind of iterator.

What’s the best way to achieve this?

Answer 1

If supporting any kind of iterator is the only thing you want, you may use an iterator that uses type erasure. I think there is an any_iterator implemented somewhere in the Boost Sandbox/Vault or Adobe Labs or one of them. Here is the first result from Google:

http://thbecker.net/free_software_utilities/type_erasure_for_cpp_iterators/any_iterator.html