Advent of Typescript 2023

aot-day8.ts

// Filter out key-value pairs in an object that start with 'naughty'

type RemoveNaughtyChildren<T extends {}> = {
	[key in keyof T as key extends `naughty_${string}` ? never : key] : T[key]
}
  
// Test cases

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

type SantasList = {
  naughty_tom: { address: '1 candy cane lane' };
  good_timmy: { address: '43 chocolate dr' };
  naughty_trash: { address: '637 starlight way' };
  naughty_candace: { address: '12 aurora' };
};
type test_wellBehaved_actual = RemoveNaughtyChildren<SantasList>;
//   ^?
type test_wellBehaved_expected = {
  good_timmy: { address: '43 chocolate dr' };
};
type test_wellBehaved = Expect<Equal<test_wellBehaved_expected, test_wellBehaved_actual>>;

type Unrelated = {
  dont: 'cheat';
  naughty_play: 'fair';
};
type test_Unrelated_actual = RemoveNaughtyChildren<Unrelated>;
//   ^?
type test_Unrelated_expected = {
  dont: 'cheat';
};
type test_Unrelated = Expect<Equal<test_Unrelated_expected, test_Unrelated_actual>>;

aot-day9.ts

// Reverse a string

type Reverse<S extends string> =
  S extends `${infer First}${infer Rest}`
    ? `${Reverse<Rest>}${First}`
    : '';
  
// Test cases

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

type test_0_actual = Reverse<'rehsaD'>;
//   ^?
type test_0_expected = 'Dasher';
type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;

type test_1_actual = Reverse<'recnaD'>;
//   ^?
type test_1_expected = 'Dancer';
type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;

type test_2_actual = Reverse<'recnarP'>;
//   ^?
type test_2_expected = 'Prancer';
type test_2 = Expect<Equal<test_2_expected, test_2_actual>>;

type test_3_actual = Reverse<'nexiV'>;
//   ^?
type test_3_expected = 'Vixen';
type test_3 = Expect<Equal<test_3_expected, test_3_actual>>;

type test_4_actual = Reverse<'temoC'>;
//   ^?
type test_4_expected = 'Comet';
type test_4 = Expect<Equal<test_4_expected, test_4_actual>>;

type test_5_actual = Reverse<'dipuC'>;
//   ^?
type test_5_expected = 'Cupid';
type test_5 = Expect<Equal<test_5_expected, test_5_actual>>;

type test_6_actual = Reverse<'rennoD'>;
//   ^?
type test_6_expected = 'Donner';
type test_6 = Expect<Equal<test_6_expected, test_6_actual>>;

type test_7_actual = Reverse<'neztilB'>;
//   ^?
type test_7_expected = 'Blitzen';
type test_7 = Expect<Equal<test_7_expected, test_7_actual>>;

type test_8_actual = Reverse<'hploduR'>;
//   ^?
type test_8_expected = 'Rudolph';
type test_8 = Expect<Equal<test_8_expected, test_8_actual>>;