typescript type-level example: check keys match

check_keys_match.ts

import { Equals } from 'typelevel-ts';

export const __KEYS_MATCH_OK_STRING = 'Keys Match!'
export type isMatch<TType> = TType extends 'T' ?
  typeof __KEYS_MATCH_OK_STRING : never;

export type RequireSameKeys<
  A extends object,
  B extends object
> = {
  isMatch: isMatch<Equals<keyof A, keyof B>>;
  A?: keyof A;
  B?: keyof B;
}

export type Example1 = {
  a: string;
  b: number;
}
export type Example2 = {
  a: boolean;
  b: boolean;
}

export type Example3 = {
  a: boolean;
}

export const KeyTest1: RequireSameKeys<Example1, Example2> = {
  isMatch: 'Keys Match!',
}

export const KeyTest2: RequireSameKeys<Example2, Example3> = {
  // @ts-expect-error
  isMatch: 'Keys Match!',
}