# `PaymentCardNumber`

A payment card's number (ISO/IEC 7812), 12 to 19 digits with a Luhn check digit: `4242424242424242`. Shown to people as its last four only, `•••• 4242`. Personal data.

[Money and banking](types.md#money-and-banking); not ordered; personal data (financial); since Jadpo 0.1.0.

## Make one

Build one from its text, `PaymentCardNumber("4242424242424242")`, which checks it: text that isn't one breaks `format`.

`text.parse(raw, as: PaymentCardNumber)` reads one from its text; text that isn't one at all fails `malformed`, such as `4242424242424241`, `4242 4242 4242 4242` or `42424242424`.

## Text, JSON and storage

`text.from` writes its canonical text, the one form `text.parse` reads back. JSON sends its canonical text as a string.

| Text | JSON |
|---|---|
| `4242424242424242` | `"4242424242424242"` |
| `378282246310005` | `"378282246310005"` |
| `5555555555554444` | `"5555555555554444"` |

It is stored in one column named for the field, of type `text`. `378282246310005` is stored as `'378282246310005'`.

## Shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `4242424242424242` | `•••• 4242` |
| `378282246310005` | `•••• 0005` |
| `5555555555554444` | `•••• 4444` |

## Operations

- `money.mask(card: PaymentCardNumber) -> MaskedCardNumber`: What may be kept of `card` once its number is gone: its brand, told by its first digits from the ranges each scheme publishes (`none` for a range no listed scheme issues), and its last four digits.

Like every standard type, it also has the contract's own operations: `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. It isn't ordered, so `<` and sorting don't take it. [Every standard type meets one contract](../topics/every-standard-type-meets-one-contract.md) says how they work.