Best syntax for a diagonal and vertical slice

[kerdemdemir via Digitalmars-d-learn]

We have awesome way for creating slices like:

     a = new int[5];
     int[] b = a[0..2];

But what about if I have 2D array and I don't want to go 
vertical. Something like :

int[3][3] matrix = [
     [ 1, 2, 3 ],
     [ 4, 5, 6 ],
     [ 7, 8, 9 ]
];

I believe I can use std.range function "RoundRobin"(or maybe it 
won't work with 2D array directly) for having a good looking 
vertical slice which will have 1,4,7 or 2,5,8 or 3,6,9 in my 
example above.

And what if I want to go diagonal like 1,5,9 or 3,5,7 in the 
example above. Is there a good solution in std without using for 
loops?

I have one more requirement for fulfilling the task that I 
working on. This slices do not have to be the same size as the 
array. For example in the example above slice size could have 2 
instead of 3. In this case I need to have slices like 
1,5;2,6;4,8;5,9 ... and so on for diagonal case.

Erdem

Ps: Converting the 2D array to 1D array is possible in my case.