# `JsonPointer`

A pointer into a JSON document (RFC 6901): `/foo/0`, with `~0` for `~` and `~1` for `/`, and empty for the whole document.

[Web and network](types.md#web-and-network); not ordered; since Jadpo 0.1.0.

## Make one

Build one from its text, `JsonPointer("/foo/0")`, which checks it: text that isn't one breaks `format`.

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

## Text, JSON and storage

`text.from` writes its canonical text, the one form `text.parse` reads back. JSON sends its canonical text as a string.

| Text | JSON |
|---|---|
| `/foo/0` | `"/foo/0"` |
| `/a~1b` | `"/a~1b"` |
| `/m~0n` | `"/m~0n"` |
| `""` | `""` |

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

## 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 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.