# E4230

Invalid use of the `#builtin` attribute.

`#builtin` is reserved for the standard library's built-in type declarations;
it cannot be used to mark a type in an ordinary application or library package
as built-in.

## Erroneous example

```{literalinclude} /sources/error_codes/4230_error/top.mbt
:language: moonbit
```

## Suggestion

Remove `#builtin` and declare the type normally. To use an existing built-in
type, refer to that type directly rather than trying to redeclare it.

```{literalinclude} /sources/error_codes/4230_fixed/top.mbt
:language: moonbit
```