How to iterate all k-subsets of a range in a specific order?

[Tommi]

Uh... never mind. I guess this one was kind of like a magic 
trick; the solution was so obvious and simple I neglected it:


void fun(R)(R r)
     if (isForwardRange!R)
{
     writeln("idx x y");

     auto idx = 0;
     auto rsaved = r.save;

     for (size_t n = 0; !r.empty; r.popFront(), ++n)
     {
         size_t n2 = 0;

         for (auto r2 = rsaved; n2 < n; r2.popFront(), ++n2)
         {
             writefln("%s : %s %s", idx, r2.front, r.front);
             ++idx;
         }
     }
}