# `IsoWeek`

A numbered week of a year, as ISO 8601 counts them: `2026-W43`.

Use it for weekly reports and rotas. A week's number doesn't always belong to the year of its days, so for a span of dates, use [`DateRange`](/docs/types/type-date-range.md).

## Shape

| Field | Type | Required? |
|---|---|---|
| `year` | `Int` | Yes |
| `week` | `Int` | Yes |

Its parts keep these rules, and a value that breaks one fails with the rule's name:

- `week_in_year`: week is 53 only in a year with 53 ISO weeks

## Example

```jadpo
IsoWeek { year: 2026 week: 43 }
```

`text.parse(raw, as: IsoWeek)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `2027-W53`, `2026-W54` or `2026-W00`.

## Good to know

- Week 53 exists only in some years, so `2027-W53` is refused and `2026-W53` is not.
- `==` tells you whether two are the same, and `<` and `list.sort_by` compare and sort them.

## In JSON

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

```json
"2026-W01"
"2026-W53"
```

## Details

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

`IsoWeek` is in the group Time and calendar, 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: `2026-W01` and `2026-W53`.

### How it is stored

It is stored in 2 columns, each named for the field, `_` and its suffix. This is `2026-W53`:

| Column | Type | Holds |
|---|---|---|
| `<field>_year` | `smallint` | `2026` |
| `<field>_week` | `smallint` | `53` |

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `2026-W01` | `2026-W01` |
| `2026-W53` | `2026-W53` |

### 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>