# `SerialNumber`

An item's serial number (GS1 AI 21), up to 20 of GS1's characters: `SN-0042a`.

[Commerce and logistics](types.md#commerce-and-logistics); not ordered; since Jadpo 0.1.0.

## Make one

Build one from its text, `SerialNumber("12345678")`, which checks it: text that isn't one breaks `format`.

`text.parse(raw, as: SerialNumber)` reads one from its text; text that isn't one at all fails `malformed`, such as `SN 0042`, `SN#0042` or `123456789012345678901`.

## 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 |
|---|---|
| `12345678` | `"12345678"` |
| `SN-0042a` | `"SN-0042a"` |

It is stored in one column named for the field, of type `text`. `SN-0042a` is stored as `'SN-0042a'`.

## Shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `12345678` | `12345678` |
| `SN-0042a` | `SN-0042a` |

## Operations

It 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.