Chequer

import mir.ndslice.allocation: slice;
auto s = [5, 4].slice!int;

Chequer.black.each!"a = 1"(s);
assert(s == [
    [1, 0, 1, 0],
    [0, 1, 0, 1],
    [1, 0, 1, 0],
    [0, 1, 0, 1],
    [1, 0, 1, 0],
]);

Chequer.red.each!((ref b) => b = 2)(s);
assert(s == [
    [1, 2, 1, 2],
    [2, 1, 2, 1],
    [1, 2, 1, 2],
    [2, 1, 2, 1],
    [1, 2, 1, 2],
]);