type Brand<T, B> = T & { __brand: B };
type KM = Brand<number, 'km'>;
type Mile = Brand<number, 'mile'>;

function kmToMile(km: KM) {
    return km * 0.62 as Mile;
}

const km = 3 as KM;
const mile = kmToMile(km);
// const mile: Mile
const mile2 = 5 as Mile;
// Argument of type 'Mile' is not assignable to parameter of type 'KM'.
kmToMile(mile2);