Automatically obtaining the address of another member of the same object

[Lindley]

There must be a simpler way of doing this.

Sure----just implement the copy constructor. I'm just playing around with ideas for alternatives in the case when *most* of the object doesn't need special copy treatment.

I'm still not clear what exactly are you trying to achieve, can you show us an actual example?

vector<double> actualvals;

struct CmpInds
{
    vector<double> *vals;
    CmpInds(vector<double> &vals_): vals(&vals_) {}
    bool operator<(int i1, int i2) const
    {    return (*vals)[i1] < (*vals)[i2];    }
};

struct Sorted
{
    vector<int> inds;
    CmpInds cmp;
    Sorted(vector<double> &actualvals):
        inds(boost::counting_iterator(0),boost::counting_iterator(actualvals.size())),
        cmp(CmpInds(actualvals))
    {
        sort(inds.begin(), inds.end(), cmp);
    }
};

This is the basic idea, except with a simple sort rather than a KDTree, and only 1-D data (doubles). Now, put the Sorted object into another object alongside the actualvals:

struct Object
{
    vector<double> vals;
    Sorted srt;
    Object(): srt(vals) {}
}

Now, what do you do to make sure srt remains valid when an Object is copied?

Assume that Sorted has some additional query functions which require the use of cmp.