rust - 如何将枚举引用转换为数字？

Question

我有一个枚举:

enum Foo {
    Bar = 1,
}

如何将对此枚举的引用转换为用于数学的整数？

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 是正确的，但您必须实现 Copy，否则您会留下无效的引用。

#[derive(Copy, Clone)]
enum Foo {
    Bar = 1,
}

fn f(foo: &Foo) -> u8 {
    *foo as u8
}

由于您的枚举将是一个非常轻量级的对象，您无论如何都应该按值传递它，为此您还需要Copy。