no #[repr(...)] for rust crate

Question

I'm trying to solve a trivially simple exercism task on using external crates.

use int_enum::IntEnum;

#[derive(Debug, PartialEq, Eq, IntEnum)]

pub enum ResistorColor {
    Black = 0,
    Brown = 1,
    Red = 2,
    Orange = 3,
    Yellow = 4,
    Green = 5,
    Blue = 6,
    Violet = 7,
    Grey = 8,
    White = 9,
}

pub fn value_to_color_string(value: u32) -> String {
    match ResistorColor::from_int(value) {
        Ok(r) => format!("{:?}", r),
        Err(r) => "value out of range".to_string(),
    }
}

which gives me an error stating that no #[repr(...)] found

And further when using methods from the package:

pub fn value_to_color_string(value: u32) -> String {
    match ResistorColor::from_int(value) {
        Ok(r) => format!("{:?}", r),
        Err(r) => "value out of range".to_string(),
    }
}

I get an error when using the method from_int(value)

items from traits can only be used if the trait is implemented and in scope
the following trait defines an item 'from_int', perhaps you need to implement it:
candidate #1: 'IntEnum'

When checking similar solutions, they are implemented in the exact same way as mine. Any tips?

Could you share a reproducible example (https://stackoverflow.com/help/mcve)? I guess what might be the problem, but it's impossible to be sure without full context. — Cerberus, Sep 15 '22 at 08:50
Yes, what @Cerberus said. Your `#derive`, for example, makes no sense without an item attached to it. — Finomnis, Sep 15 '22 at 08:51
I've added the full context now. It's my second day learning Rust and second question on stack, so still fairly new! — Fabian Thorsen, Sep 15 '22 at 13:50

score 0 · Accepted Answer · answered Sep 15 '22 at 09:04

0

This is not documented, but apparently #[derive(IntEnum)] requires the enum to have a #[repr(integer)], for each variant to have an explicit integer value (Name = value), and in addition the IntEnum trait requires the type to be Copy.

answered Sep 15 '22 at 09:04

Chayim Friedman

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Thank you, this seemed to solve it! – Fabian Thorsen Sep 15 '22 at 13:55

no #[repr(...)] for rust crate

1 Answers1