import std.algorithm.comparison : equal;
int[][] ror = [
    [1, 2, 3],
    [4, 5, 6]
];
auto xp = transposed(ror);
assert(equal!"a.equal(b)"(xp, [
    [1, 4],
    [2, 5],
    [3, 6]
]));

int[][] x = new int[][2];
x[0] = [1, 2];
x[1] = [3, 4];
auto tr = transposed(x);
int[][] witness = [ [ 1, 3 ], [ 2, 4 ] ];
uint i;

foreach (e; tr)
{
    assert(array(e) == witness[i++]);
}