Typescript nominal typing scratch

Nominal.ts

/**
 * Inspired by [Drew Colthorp's blog post, Flavoring: Flexible Nominal Typing for TypeScript](https://spin.atomicobject.com/2018/01/15/typescript-flexible-nominal-typing)
 */

/**
 * Last form of an attempt to define a generic constrained to `unique symbol` for
 * the property symbol (`NominalIdentifierSymbol` in this case).
 *
 *                'NominalIdentifierSymbol' is declared but its value is never read.(6133)
 *                                      VVVVVVVVVVVVVVVVVVVVVV
 */
interface NominalSchema<NominalLiteral, NominalIdentifierSymbol>
{
    [NominalIdentifierSymbol]?: NominalLiteral
}

/**
 * (Original plan was to use a generic similar to above to define
 * NominalPattern / Nominal as a partial application using
 * newly defined unique symbol `NominalSymbol`)
 */
const NominalSymbol: unique symbol = Symbol.for('NominalProperty');

interface NominalPattern<NominalLiteral>
{
    [NominalSymbol]?: NominalLiteral
}

type Nominal<BaseType, NominalLiteral>
    = BaseType & NominalPattern<NominalLiteral> // { [NominalSymbol]: NominalLiteral }

type AbsoluteNominal<BaseType, NominalLiteral>
    = BaseType & { [NominalSymbol]: NominalLiteral }

/**
 * @todo
 * Shape of function that validates a defined Nominal type
 */
type NominalValidation<Base, NominalKind extends Base> = (obj: Base) => obj is NominalKind;

type Real = Nominal<number, "Number#Real">

/**
 * Original definition
 *
 * ```` ts
 *
 * type Nominal<K, T> = K & { __brand?: T }
 *
 * ````
 */

//#region Test

type USD = Nominal<number, "USD">
type EUR = Nominal<number, "EUR">

const amoney = 10;
const usd = 10 as USD;
const eur = 10 as EUR;

// @ts-expect-error ts(2367) This condition will always return 'false' since the types 'Nominal<number, "USD">' and 'Nominal<number, "EUR">' have no overlap
let notSame = usd === eur;
// @ts-expect-error ts(2322) Type 'boolean' is not assignable to type 'number'
let badAssign: number = notSame

function gross(net: USD, tax: USD): USD { return net + tax }

gross(usd, usd);    // ok
// @ts-expect-error ts(2345) Type '"EUR"' is not assignable to type '"USD"'
gross(eur, usd);
gross(amoney, usd); // ok

//#endregion Test