multidispatch.ts

multidispatch.ts

export const multidispatch = <T>() => {
  const routes = new Map<
    (...args: unknown[]) => boolean,
    (...args: unknown[]) => T
  >();

  const call = (...args: unknown[]) => {
    for (const [isMatch, handler] of routes.entries()) {
      if (isMatch(...args)) {
        return handler(...args);
      }
    }
    throw new TypeError(`No handler for ${args}`);
  };

  call.register = <Args extends unknown[]>(
    isMatch: (...args: unknown[]) => boolean,
    handler: (...args: Args) => T,
  ) => {
    routes.set(isMatch, handler as (...args: unknown[]) => T);
    return call;
  };

  return call;
};