# `Duration`

An exact length of time, to the millisecond: 90 minutes is `PT1H30M`.

Use it for timeouts and gaps between two instants. For a month, which has no fixed length, use [`CalendarPeriod`](/docs/types/type-calendar-period.md).

## Shape

One value, with no fields to fill in. As text it reads `PT26H`.

## Example

```jadpo
Duration(90m)
```

`text.parse(raw, as: Duration)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `5 minutes`, `P` or `PT`.

This operation gives one: `temporal.between`.

## Good to know

- In code, write a unit after the number: `500ms`, `30s`, `90m`, `2h`, `14d`. `m` is minutes, not metres.
- `temporal.between` gives the one between two instants.
- `==` 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
"PT5M"
"PT1H30M"
"PT26H"
```

## Details

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

`Duration` 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: `PT5M`, `PT1H30M` and `PT26H`.

### How it is stored

It is stored in one column named for the field, of type `bigint`. `PT1H30M` is stored as `5400000`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `PT5M` | `5 minutes` |
| `PT1H30M` | `1 hour, 30 minutes` |
| `PT26H` | `1 day, 2 hours` |

### Operations

- `temporal.between(start: Instant, end: Instant) -> Duration`: How long from `start` to `end`: `end - start`.

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>