# `IdempotencyKey`

A request's idempotency key (the IETF's `Idempotency-Key`): 1 to 255 printable ASCII characters, no `"` or `\`.

[Software](types.md#software); not ordered; since Jadpo 0.1.0.

## Make one

Build one from its text, `IdempotencyKey("8e03978e-40d5-43e8-bc93-6894a57f9324")`, which checks it: text that isn't one breaks `format`.

`text.parse(raw, as: IdempotencyKey)` reads one from its text; text that isn't one at all fails `malformed`, such as ` key`, `key ` or `say "hi"`.

## 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 |
|---|---|
| `8e03978e-40d5-43e8-bc93-6894a57f9324` | `"8e03978e-40d5-43e8-bc93-6894a57f9324"` |
| `order-1042-attempt` | `"order-1042-attempt"` |
| `a` | `"a"` |

It is stored in one column named for the field, of type `text`. `order-1042-attempt` is stored as `'order-1042-attempt'`.

## Shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `8e03978e-40d5-43e8-bc93-6894a57f9324` | `8e03978e-40d5-43e8-bc93-6894a57f9324` |
| `order-1042-attempt` | `order-1042-attempt` |
| `a` | `a` |

## 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.