# `Hash`

A SHA-256 digest (FIPS 180-4): the 32 bytes `hash.sha256` gives, so `Hash(hash.sha256(body))` builds one. Sent and read back as its Base64, compared in constant time.

[Security](types.md#security); not ordered; since Jadpo 0.1.0.

## Make one

Build one from `Bytes`, `Hash(bytes)`, which checks them: bytes that aren't one break `format`.

`text.parse(raw, as: Hash)` reads one from its text; text that isn't one at all fails `malformed`, such as `""`.

## 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 |
|---|---|
| `47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=` | `"47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU="` |
| `ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=` | `"ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0="` |

It is stored in one column named for the field, of type `bytea`. `ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=` is stored as `E'\\xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad'::bytea`.

## Shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=` | `47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=` |
| `ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=` | `ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=` |

## 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.