The `Default` trait was derived on an enum.
Erroneous code example:
```compile_fail,E0665
#[derive(Default)]
enum Food {
Sweet,
Salty,
}
```
The `Default` cannot be derived on an enum for the simple reason that the
compiler doesn't know which value to pick by default whereas it can for a
struct as long as all its fields implement the `Default` trait as well.
If you still want to implement `Default` on your enum, you'll have to do it "by
hand":
```
enum Food {
Sweet,
Salty,
}
impl Default for Food {
fn default() -> Food {
Food::Sweet
}
}
```