apartment.ts

type Apartment = {
	meterToStation: number;
	ageOfBuilding: number;
	options: string[];
};
type Optional<T> = [] | [T];

const apartment = {
	meterToStation: 400,
	ageOfBuilding: 4,
	options: ["ShoeLocker", "AutoLock"],
} satisfies Apartment;

const isNearStation = (apartment: Apartment) => apartment.meterToStation < 1000;
const isNewBuilding = (apartment: Apartment) => apartment.ageOfBuilding < 5;
const isAutoLock = (apartment: Apartment) =>
	apartment.options.includes("AutoLock");

const toOptional: <S, T>(
	predicate: (_: S) => boolean,
	value: T
) => (s: S) => Optional<T> = (predicate, value) => (s) =>
	predicate(s) ? [value] : [];

const tags: string[] = [
	toOptional(isNearStation, "駅近"),
	toOptional(isNewBuilding, "築浅"),
	toOptional(isAutoLock, "セキュリティ充実"),
].flatMap((f) => f(apartment));

original Tweet: https://twitter.com/t__keshi/status/1635267214008897537