# `UsSsn`

A US Social Security number: nine digits.

Use it only where US law asks for one. For a US company, use [`UsEin`](/docs/types/type-us-ein.md). For tax numbers from any country, use [`TaxId`](/docs/types/type-tax-id.md).

## Shape

One value, held as text in one set form, with no parts: `001010001`.

## Example

```jadpo
UsSsn("123456789")
```

`UsSsn(raw)` checks the text, and text that isn't one breaks the `format` rule.

`text.parse(raw, as: UsSsn)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `000123456`, `666123456` or `900123456`.

## Good to know

- Write it with no dashes. `text.format` shows only the last four: `•••-••-6789`.
- It refuses numbers that were never issued, such as those starting `000` or `666`.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.
- A field that holds one counts as personal data (`government_id`), so you don't mark it yourself.

## In JSON

A string, in a request, a response or `json.write`:

```json
"123456789"
"001010001"
```

## Details

<details>
<summary>Text form, storage, how it is shown, and operations</summary>

`UsSsn` is in the group Tax and identity numbers, and has been in Jadpo since 0.1.0.

### Text form

`text.from` writes one standard text form, the same form `text.parse` reads back: `123456789` and `001010001`.

### How it is stored

It is stored in one column named for the field, of type `text`. `001010001` is stored as `'001010001'`.

### How it is shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `123456789` | `•••-••-6789` |
| `001010001` | `•••-••-0001` |

### Operations

It also takes `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. [How every standard type behaves](/docs/every-standard-type-meets-one-contract.md) says how they work.

</details>