---
name: value-object
description: Add a validated input type (postcode, email, hours, id number, …) as a branded value object with a parser — "parse, don't validate". Use whenever a form field or API value has format rules.
---

# Value object (parse, don't validate)

Raw input becomes a branded type only via a parser returning `Result`. Once you hold
the type, never re-check it. Never model validity as a boolean flag next to a string.

## Skeleton

`<context>/domain/value-objects/<name>.ts` (pure TS, no Angular):

```ts
import { Brand, Result, ok, err } from '@shared/kernel/fp';

export type Postcode = Brand<string, 'Postcode'>;

export function parsePostcode(raw: string): Result<string, Postcode> {
  const t = raw.trim().toUpperCase();
  if (!/^[1-9]\d{3}\s?[A-Z]{2}$/.test(t)) {
    return err($localize`:@@validation.postcode:Voer een geldige postcode in, bijv. 1234 AB.`);
  }
  // The parser also normalises — callers always hold the canonical form.
  return ok(t.replace(/^(\d{4})\s?([A-Z]{2})$/, '$1 $2') as Postcode);
}
```

Rules:

- The `as Brand` cast appears **only** inside the parser — the type is mintable nowhere else.
- Error message is user-facing → `$localize` with a stable `@@validation.<name>` id.
- Trim/normalise before testing; return the cleaned value.
- This is **format** feedback only. The server re-validates as authority (ADR-0001) — never encode business rules (existence, eligibility) here.

## Spec (required)

Co-located `<name>.spec.ts`: happy path, normalisation, each rejection case. Call the
parser directly — no TestBed.

## Wiring into a form

The machine's `validate(draft)` calls the parsers and collects errors into
`StepErrors`; the `Valid` type holds the branded values (see **form-machine** skill).

## Worked examples

`src/app/registratie/domain/value-objects/` — `postcode.ts`, `email.ts`, `uren.ts`,
`big-nummer.ts`, each with a co-located spec.

## Verify

```bash
npm test && npm run lint
```
