> For the complete documentation index, see [llms.txt](https://draekien-industries.wpei.me/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://draekien-industries.wpei.me/reference/source-generation/code-format.md).

# Code format language

Shape the generated strings with {enum} and {member}, an optional casing, and one default for the whole assembly.

## Choosing the code format

`OrderErrorCode.NotFound` is the default, not the only option. Set `Format` on the attribute and the generated codes follow it:

```csharp
[ErrorCodeCatalog(Format = "order.{member:kebab}")]
public enum OrderErrorCode
{
    NotFound,
    AlreadyShipped,
}
```

```csharp
OrderErrorCodeCatalog.Names.NotFound       // "order.not-found"
OrderErrorCodeCatalog.Names.AlreadyShipped // "order.already-shipped"
```

Everything the format does happens at build time, so what you get out is still a `const string`.

## The format language

Two placeholders, and everything else is literal text:

| Placeholder | Substitutes                       |
| ----------- | --------------------------------- |
| `{enum}`    | The enum's name, `OrderErrorCode` |
| `{member}`  | The member's name, `NotFound`     |

Either one takes an optional casing after a colon — `{member:kebab}`:

| Casing   | `NotFound`  | `HTTPNotFound`   | `Error404`  |
| -------- | ----------- | ---------------- | ----------- |
| *(none)* | `NotFound`  | `HTTPNotFound`   | `Error404`  |
| `kebab`  | `not-found` | `http-not-found` | `error-404` |
| `snake`  | `not_found` | `http_not_found` | `error_404` |
| `lower`  | `notfound`  | `httpnotfound`   | `error404`  |
| `upper`  | `NOTFOUND`  | `HTTPNOTFOUND`   | `ERROR404`  |

`kebab` and `snake` split the identifier into words; `lower` and `upper` only change case. A word boundary falls where a lowercase or a digit meets an uppercase, before the last uppercase of a run that runs into a lowercase, and between letters and digits. An underscore already in the name counts as a boundary rather than doubling up, so `Already_Shipped` gives `already-shipped`.

Write a literal brace by doubling it: `{{` and `}}`.

The default is `{enum}.{member}`, which is what an enum that sets nothing gets.

## One format for the whole assembly

Put the attribute on the assembly and every attributed enum in the project uses it:

```csharp
[assembly: ErrorCodeFormat("{enum:kebab}/{member:kebab}")]
```

An enum's own `Format` wins over the assembly's, so the assembly attribute sets the house style and an individual enum departs from it where it needs to.

## The format is your contract, not your factory

The generated strings come from the format and nothing else. In particular:

{% hint style="warning" %}
**A generated member never consults your `ErrorCodeFactory`.** The generator runs at build time and cannot run a factory you install at run time. A factory installed through `MonadOptions.UseErrorCodeFactory` still shapes the codes it derives from an exception; it has no say over an attributed enum.

That holds for every generated member, including the fallback for an undeclared value. If you were using a custom factory in 6.x to shape the codes an enum produces, say the same thing with `Format` instead — you get the same strings as constants, and one answer rather than two.
{% endhint %}

Shaping enum codes is the part of `ErrorCodeFactory` the format replaces, and 7.0.0 removes that part. `ErrorCodeFactory.FromEnum` and `ErrorCode.FromEnum` reported `CS0618` from 6.2.0 and are gone now — the override produces `CS0115`. See [Deprecations](/upgrading/deprecations.md). `FromException` is not affected.