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);