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The `Default` trait was derived on an enum without specifying the default
variant.
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.
For the case where the desired default variant has no payload, you can
annotate it with `#[default]` to derive it:
```
#[derive(Default)]
enum Food {
#[default]
Sweet,
Salty,
}
```
In the case where the default variant does have a payload, you will have to
implement `Default` on your enum manually:
```
enum Food {
Sweet(i32),
Salty,
}
impl Default for Food {
fn default() -> Food {
Food::Sweet(1)
}
}
```
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