foreach( i, e; a) vs ndslice

[Jay Norwood via Digitalmars-d-learn]

I'm playing with the example below.  I noticed a few things.
1. The ndslice didn't support the extra index, i, in the foreach, 
so had to add extra i,j.
2. I couldn't figure out a way to use sliced on the original 'a' 
array.  Is slicing only available on 1 dim arrays?
3. Sliced parameter order is different than multi-dimension array 
dimension declaration.

import std.stdio;
import std.experimental.ndslice.slice;

void main() {
    int[4][5] a = new int[20];
    foreach(i,ref r; a){
        foreach(j,ref c; r){
            c= i+j;
            writefln("a(%d,%d)=%s",i,j,c);
        }
    }
    writefln("a=%s",a);

    auto b = new int[20].sliced(5,4);

    int i=0;
    foreach( ref r; b){
        int j=0;
        foreach( ref c; r){
            c= i+j;
            writefln("b(%d,%d)=%s",i,j,c);
            j++;
        }
        i++;
    }
    writefln("b=%s",b);

}