Brand primitive IDs to prevent mix-ups | BeforeMerge Rules | BeforeMerge

Brand primitive IDs to prevent mix-ups | BeforeMerge Rules | BeforeMerge

Why this matters

Branding distinguishes otherwise-identical primitives, so the compiler stops you from passing the wrong kind of id even though both are strings.

// Bad
function getOrder(orderId: string) {}
getOrder(userId); // compiles — wrong id, no warning
 
// Good
type Brand<T, B> = T & { readonly __brand: B };
type UserId = Brand<string, "UserId">;
type OrderId = Brand<string, "OrderId">;
function getOrder(orderId: OrderId) {}
getOrder(userId); // compile error