# E4063

Type does not implement trait, although an `impl` is defined.

This error can be further divided into 5 cases:

- Method is missing
- Implementation is private
- Method type mismatch
- Constraints are not satisfied
- Method contains unresolved type parameters

## Erroneous example

### Method is missing

```{literalinclude} /sources/error_codes/E4063_error/top.mbt
:language: moonbit
```

## Suggestion

Modify the code according to the hint provided along with the error message. For
the example above, you can add the missing method `to_float` to type `A`.

```{literalinclude} /sources/error_codes/E4063_fixed/top.mbt
:language: moonbit
```