Saboda TypeScript shine tsarin wacce aka rubuta ta hanya, UserId da OrderId waɗanda duka string ne suna iya juna maye gurbin — compiler ba ya iya tsaye ka daga haɗa su ba. Branded types suna yin allon typing ta hanyar haɗa musamman, albarkatun "brand" don haka nau'ikan da suke daidai tare sun zama daban-daban.
// the brand is a property that exists only in the type system, never at runtime
type Brand<T, B> = T & { readonly __brand: B };
type UserId = Brand<string, "UserId">;
type OrderId = Brand<string, "OrderId">;
function getUser(id: UserId) { return id; }
const uid = "u1" as UserId;
const oid = "o1" as OrderId;
getUser(uid); // ✅
getUser(oid); // ❌ Error: OrderId is not assignable to UserId
getUser("u1"); // ❌ Error: plain string is not a UserId
__brand property bai taɓa kasancewa a lokacin gudu ba (ƙimar shine kawai string), amma a cikin tsarin nau'i ya sa UserId da OrderId ba su dace ba — gare komawa daga jerin kurakurai na haɗawa.
function toUserId(s: string): UserId {
if (!s.startsWith("u")) throw new Error("invalid UserId");
return s as UserId; // validation happens here, once
}
Tabbatar da jiji a iyaka; sauran code na aminci ga nau'in branded.
IDs (UserId da OrderId), kurakuran da aka tabbatar/tsafi (Email, SafeHtml), raka'a (Meters da Feet), PositiveNumber — duk inda daraja biyu ya ba da nau'ikan primitive amma dole ne kada a haɗa su.
Branded types suna ƙara aminci na nominal inda aka saba da nau'i. Suna kama ita buɗa ita-ita ƙarfe-ƙarfe da "waɗanda ba a tabbata ba a gida tabbata" abubuwan rudani a lokacin haɗa, tare da sifili lokacin gudu - wata pattern mai iko ga yin yawa a cikin babbar, alamomi masu inganci.