# `CalendarDate`

A day on the calendar, with no time or zone: `2026-10-25`.

Use it for birthdays, due dates and anything else that is a day wherever you are. For a moment in time, use [`Instant`](/docs/types/type-instant.md). For a span of days, use [`DateRange`](/docs/types/type-date-range.md).

## Shape

One value, with no fields to fill in. As text it reads `2026-10-25`.

## Example

```jadpo
CalendarDate("2026-10-25")
```

`text.parse(raw, as: CalendarDate)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `2026-02-30` or `25/10/2026`.

These operations give one: `temporal.add_days`, `temporal.add_months`, `temporal.add_years` and `temporal.date`.

## Good to know

- `temporal.add_days`, `temporal.add_months` and `temporal.add_years` give another.
- It checks the date is real, so `2026-02-30` is refused.
- `==` 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
"2026-02-28"
"2026-10-25"
```

## Details

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

`CalendarDate` 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: `2026-02-28` and `2026-10-25`.

### How it is stored

It is stored in one column named for the field, of type `date`. `2026-10-25` is stored as `'2026-10-25'::date`.

### How it is shown to people

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

With `locale: Locale.en_gb` and `format: TimeFormat.date_medium`:

| Value | Shown |
|---|---|
| `2026-02-28` | `28 Feb 2026` |
| `2026-10-25` | `25 Oct 2026` |

### Operations

- `temporal.add_days(value: T, days: Int, dst: Dst?) -> T`: `value` moved by whole calendar days, the clock time kept.
- `temporal.add_months(value: T, months: Int, invalid_day: InvalidDay?, dst: Dst?) -> T`: `value` moved by whole calendar months, the day and clock time kept.
- `temporal.add_years(value: T, years: Int, invalid_day: InvalidDay?, dst: Dst?) -> T`: `value` moved by whole calendar years, the day and clock time kept.
- `temporal.date(value: ZonedTime) -> CalendarDate`: A local time's date.
- `temporal.day(value: T) -> Int`: The day of the month, from 1.
- `temporal.day_bounds(date: CalendarDate, zone: Zone) -> InstantRange`: The instants `date` runs between in `zone`: 23, 24 or 25 hours.
- `temporal.month(value: T) -> Int`: The month, from 1 for January.
- `temporal.month_bounds(date: CalendarDate, zone: Zone) -> InstantRange`: The month holding `date` in `zone`.
- `temporal.occurrences(rule: RecurrenceRule, from: T, count: Int) -> List<ZonedTime>`: The next `count` occurrences of `rule` at or after `from`, in its zone (RFC 5545): fewer when the rule ends first; `count` is from 1 to 1000, so an unbounded rule is never expanded without a bound. From a date, the days they fall on, `List<CalendarDate>`, which a rule on dates gives; from an `Instant`, a timed rule's local times.
- `temporal.period_between(start: CalendarDate, end: CalendarDate) -> CalendarPeriod`: Whole years, months and days from `start` to `end`, so `start` plus the period is `end`; each part negative when `end` is earlier.
- `temporal.week_bounds(date: CalendarDate, zone: Zone, starts_on: Weekday) -> InstantRange`: The week holding `date` in `zone`, starting on `starts_on`.
- `temporal.weekday(value: T) -> Weekday`: The day of the week.
- `temporal.year(value: T) -> Int`: The year of a date or of a local time's date.
- `temporal.year_bounds(date: CalendarDate, zone: Zone) -> InstantRange`: The year holding `date` in `zone`.

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>