Error code E0665

Note: this error code is no longer emitted by the compiler.

The Default trait was derived on an enum.

Erroneous code example:

#![allow(unused)] fn main() { #[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":

#![allow(unused)] fn main() { enum Food { Sweet, Salty, } impl Default for Food { fn default() -> Food { Food::Sweet } } }