# `JsonPointer`

A pointer into a JSON document: `/foo/0`.

Use it to name a value in a document, such as in an error. Empty text means the whole document.

## Shape

One value, held as text in one set form, with no parts: `""`.

## Example

```jadpo
JsonPointer("/foo/0")
```

`JsonPointer(raw)` checks the text, and text that isn't one breaks the `format` rule.

`text.parse(raw, as: JsonPointer)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `foo`, `/a~2b` or `/a~`.

## Good to know

- `~1` stands for `/` in a name, and `~0` for `~`. A pointer that doesn't start with `/` is refused.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.

## In JSON

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

```json
"/foo/0"
"/a~1b"
"/m~0n"
```

## Details

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

`JsonPointer` is in the group Web and network, 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: `/foo/0`, `/a~1b` and `/m~0n`.

### How it is stored

It is stored in one column named for the field, of type `text`. `/m~0n` is stored as `'/m~0n'`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `/foo/0` | `/foo/0` |
| `/a~1b` | `/a~1b` |
| `/m~0n` | `/m~0n` |
| `""` | `""` |

### 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>