# `TraceId`

A whole trace's id: 32 lower-case hexadecimal digits, not all zero.

Use it to link logs across services. For one step in it, use [`SpanId`](/docs/types/type-span-id.md). For the header that carries both, use [`TraceParent`](/docs/types/type-trace-parent.md).

## Shape

One value, held as text in one set form, with no parts: `0af7651916cd43dd8448eb211c80319c`.

## Example

```jadpo
TraceId("4bf92f3577b34da6a3ce929d0e0e4736")
```

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

`text.parse(raw, as: TraceId)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `00000000000000000000000000000000`, `4BF92F3577B34DA6A3CE929D0E0E4736` or `4bf92f3577b34da6a3ce929d0e0e473`.

## Good to know

- `==` 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
"4bf92f3577b34da6a3ce929d0e0e4736"
"0af7651916cd43dd8448eb211c80319c"
```

## Details

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

`TraceId` is in the group Software, 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: `4bf92f3577b34da6a3ce929d0e0e4736` and `0af7651916cd43dd8448eb211c80319c`.

### How it is stored

It is stored in one column named for the field, of type `text`. `0af7651916cd43dd8448eb211c80319c` is stored as `'0af7651916cd43dd8448eb211c80319c'`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `4bf92f3577b34da6a3ce929d0e0e4736` | `4bf92f3577b34da6a3ce929d0e0e4736` |
| `0af7651916cd43dd8448eb211c80319c` | `0af7651916cd43dd8448eb211c80319c` |

### 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>