13.ts

import { Expect, Equal } from "type-testing";

type Inc<N extends number> = [
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
  11,
  12,
  13,
  14,
  15,
  16,
  17,
  18,
  19,
  20,
  21,
  22,
  23,
  24,
  25,
][N];

type DayCounter<
  From extends number,
  To extends number,
  Counter extends number[] = [],
> = Counter["length"] extends To
  ? Counter[number]
  : DayCounter<From, To, [...Counter, Inc<Counter["length"]>]>;

type a = DayCounter<1, 5>;

type TwelveDaysOfChristmas = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12;
type test_0_actual = DayCounter<1, 12>;
//   ^?
type test_0_expected = TwelveDaysOfChristmas;
type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;

type DaysUntilChristmas =
  | 1
  | 2
  | 3
  | 4
  | 5
  | 6
  | 7
  | 8
  | 9
  | 10
  | 11
  | 12
  | 13
  | 14
  | 15
  | 16
  | 17
  | 18
  | 19
  | 20
  | 21
  | 22
  | 23
  | 24
  | 25;
type test_1_actual = DayCounter<1, 25>;
//   ^?
type test_1_expected = DaysUntilChristmas;
type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;