# `Range`

The values of one ordered type from `start` up to but not including `end`, either of them `none` for an open end, written `2026-10-01/..`. `T` is the type in `< >`: `Range<Grams>`.

[Maths and data](types.md#maths-and-data); not ordered; since Jadpo 0.1.0.

## Make one

Build one from its fields, `Range<CalendarDate> { start: ...  end: ... }`.

`text.parse(raw, as: Range<CalendarDate>)` reads one from its text; text that isn't one at all fails `malformed`, such as `2026-10-01`, `2026-11-01/2026-10-01` or `2026-10-01/tomorrow`.

This operation gives one: `range.intersection`.

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

- `start_not_after_end`: `start <= end`

## Fields

| Field | Type |
|---|---|
| `start` | `T?` |
| `end` | `T?` |

## Text, JSON and storage

`text.from` writes its canonical text, the one form `text.parse` reads back. JSON sends an object of its parts.

| Text | JSON |
|---|---|
| `2026-10-01/2026-11-01` | `{"start":"2026-10-01","end":"2026-11-01"}` |
| `2026-10-01/..` | `{"start":"2026-10-01","end":null}` |
| `../2026-11-01` | `{"start":null,"end":"2026-11-01"}` |
| `../..` | `{"start":null,"end":null}` |

It is stored in one column named for the field, of type `daterange`. `../2026-11-01` is stored as `daterange(NULL::date, '2026-11-01'::date, '[)')`.

## Shown to people

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

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

| Value | Shown |
|---|---|
| `2026-10-01/2026-11-01` | `1 Oct 2026 – 1 Nov 2026` |
| `2026-10-01/..` | `1 Oct 2026 – …` |
| `../2026-11-01` | `… – 1 Nov 2026` |
| `../..` | `… – …` |

## Operations

- `range.contains(range: Range<T>, value: T) -> Bool`: Whether `value` is inside `range`.
- `range.intersection(a: Range<T>, b: Range<T>) -> Range<T>?`: The part `a` and `b` share; `none` when they don't overlap.
- `range.overlaps(a: Range<T>, b: Range<T>) -> Bool`: Whether `a` and `b` share at least one value.

Like every standard type, it also 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.