TypeScript - Opaque Types

opaque-types.ts

type Opaque<V> = V & { readonly __opq__: unique symbol };

type AccountNumber = Opaque<number>;
type AccountBalance = Opaque<number>;

function createAccountNumber (): AccountNumber {
    return 2 as AccountNumber;
}

function getMoneyForAccount (accountNumber: AccountNumber): AccountBalance {
    return 4 as AccountBalance;
}