Question

Lets say I have a linked list with a bunch of different data in it.

class Node
{
public:
    Node* next;
    AAA dataA;
    BBB dataB;
    CCC dataC;
};

Is there a way I make one iterator that would iterate over whatever variable I specify (rather than making three separate ones for each variable). I understand that the iterator could use templates to make it iterate over types AAA, BBB or CCC, but I don’t know how I could specify which variable to return.

Answer 1

I think I’ve found a way to do pretty much what I want based on rstevens’ suggestion. I looked up some stuff on class member pointers and was able to skip the middleman accessor class by doing this:

template <typename T>
class iterator
{
private:
    Node *current;
    T Node::*var;

public:
    iterator()
        : current(NULL), var(NULL) {}

    iterator(Node *start, T Node::*var)
        : current(start), var(var)
    {
    }

    typename T &operator *() const
    {
        return current->*var;
    }

    bool end() const
    {
        return (current == NULL);
    }

    iterator &operator++()
    {
        if (current)
            current = current->next;
        return *this;
    }
};

And then I modified Node to have convenience functions to make the iterators:

class Node
{
public:    
    Node* next;
    AAA dataA;
    BBB dataB;
    CCC dataC;

    typedef iterator<AAA> AIter;
    typedef iterator<BBB> BIter;
    typedef iterator<CCC> CIter;

    AIter getAIter()
    {
        return AIter(this, &Node::dataA);
    }

    BIter getBIter()
    {
        return BIter(this, &Node::dataB);
    }

    CIter getCIter()
    {
        return CIter(this, &Node::dataC);
    }
};

So now I can do this to easily iterate over each data member of my class:

for (Node::CIter iter = n1.getCIter(); !iter.end(); ++iter)
{
    // tada!
}