# `Carrier`

A shipping company by its two-to-four-letter code: `UPSN`, `MAEU`.

Use it to name a carrier, as part of a [`TrackingNumber`](/docs/types/type-tracking-number.md) or alone. Codes are the Standard Carrier Alpha Codes.

## Shape

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

## Example

```jadpo
Carrier("UPSN")
```

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

`text.parse(raw, as: Carrier)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `upsn`, `UP5N` or `U`.

## Good to know

- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.

## In JSON

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

```json
"UPSN"
"MAEU"
```

## Details

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

`Carrier` is in the group Commerce and logistics, 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: `UPSN` and `MAEU`.

### How it is stored

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

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `UPSN` | `UPSN` |
| `MAEU` | `MAEU` |

### 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>