Object-based interface for a range of ranges

[Luís Marques via Digitalmars-d]

This works:

     int[][] a;
     RandomAccessFinite!(int[]) r = inputRangeObject(a);

What would be a good way to achieve something equivalent to this?:

     int[][] a;
     RandomAccessFinite!(RandomAccessFinite!int) r = 
inputRangeObject(a);