How do I convert an enum reference to a number?

Question

I have an enum:

enum Foo {     Bar = 1, } 

How do I convert a reference to this enum into an integer to be used in math?

fn f(foo: &Foo) {     let f = foo as u8;  // error[E0606]: casting `&Foo` as `u8` is invalid     let f = foo as &u8; // error[E0605]: non-primitive cast: `&Foo` as `&u8`     let f = *foo as u8; // error[E0507]: cannot move out of borrowed content } 

Answer 1

*foo as u8 is correct, but you have to implement Copy because otherwise you would leave behind an invalid reference.

#[derive(Copy, Clone)] enum Foo {     Bar = 1, }  fn f(foo: &Foo) -> u8 {     *foo as u8 } 

Since your enum will be a very lightweight object you should pass it around by value anyway, for which you would need Copy as well.