auto d = Date(2020, 1, 1);
d += 2;
assert(d == Date(2020, 1, 3));
d -= 1;
assert(d == Date(2020, 1, 2));

import mir.ndslice.topology: iota, map;

static immutable result1 = [Date(2020, Month.mar, 1), Date(2020, Month.mar, 2), Date(2020, Month.mar, 3), Date(2020, Month.mar, 4)];
static immutable result2 = [Date(2020, Month.mar, 1), Date(2020, Month.mar, 3), Date(2020, Month.mar, 5), Date(2020, Month.mar, 7)];
static immutable result3 = [Date(2020, Month.mar, 1), Date(2020, Month.apr, 1), Date(2020, Month.may, 1), Date(2020, Month.jun, 1)];
static immutable result4 = [Date(2020, Month.mar, 1), Date(2020, Month.jun, 1), Date(2020, Month.sep, 1), Date(2020, Month.dec, 1)];
static immutable result5 = [Date(2020, Month.mar, 1), Date(2021, Month.mar, 1), Date(2022, Month.mar, 1), Date(2023, Month.mar, 1)];

auto d = Date(2020, Month.mar, 1);

auto x = d + 4.iota!uint;
assert(x == result1);

// every other date
auto y = d + iota!uint([4], 0, 2);
assert(y == result2);

// every month
auto z = (d.YearMonth + 4.iota!uint).map!Date;
assert(z == result3);

// every quarter
auto a = (d.YearQuarter + 4.iota!uint).map!(a => a.Date(AssumePeriod.end, AssumePeriod.begin));
assert(a == result4);

// every year
auto b = (d.year + 4.iota!uint).map!(a => YearMonthDay(cast(short) a, Month.mar, 1).Date);
assert(b == result5);