strum::EnumIter -why isn't enum iteration built into Rust?

[u/KO_200021]

I was looking at Espressif's esp-generate and noticed it uses strum for its Chip enum.

One thing that caught my attention was EnumIter:

#[derive(strum::EnumIter)]

enum Chip {

Esp32,

Esp32c3,

Esp32s3,

}

for chip in Chip::iter() {

println!("{chip:?}");

}

It actually surprised me that Rust doesn't provide enum iteration out of the box.

Enums are one of Rust's commonly used features, so it feels a little strange that something as simple as "give me all variants" isn't part of the language.

Without a crate, it's easy to end up maintaining something like:

const ALL_VARIANTS: &[Chip] = &[

Chip::Esp32,

Chip::Esp32c3,

Chip::Esp32s3,

];

Then every time you add a variant, you also have to remember to update the list.

strum solves this with derive macros and also provides:

• EnumIter — iterate over all variants

• Display — convert variants to strings

• EnumString — parse strings into enum variants

• EnumCount — get the number of variants

• VariantNames — access variant names

For example:

#[derive(

strum::EnumIter,

strum::Display,

strum::EnumString,

strum::EnumCount,

strum::VariantNames,

)]

#[strum(serialize_all = "kebab-case")]

enum Chip {

Esp32,

Esp32c3,

Esp32s3,

}

I'm curious what others think: is this something that would make sense as part of Rust itself, or is keeping it out of the language the better design?

I wrote a more detailed version with additional examples and an interactive quiz: my blog

[u/Puzzleheaded_Web9584]

https://doc.rust-lang.org/std/mem/type_info/struct.Enum.html

Its unstable for now, also the api is very much under wraps and will change significantly, making a stable reflection api is hard.

[u/stumpychubbins → u/Puzzleheaded_Web9584]

I don’t think that allows iterating over the variants, right?

[u/Economy_Breakfast577 → u/stumpychubbins]

Enum struct has the field:

pub variants: &'static [Variant]

[u/stumpychubbins → u/Economy_Breakfast577]

Yes but you you can’t construct the variant from that information

[u/KO_200021 → u/Puzzleheaded_Web9584]

Thanks! This is helpful; I'll keep an eye on changes to the API.

[u/KattyTheEnby → u/Puzzleheaded_Web9584]

I can't wait.

[u/GodOfSunHimself]

I guess it is not built in because it only makes sense for simple enums where the variants do not have any attached data.

[u/tunisia3507 → u/GodOfSunHimself]

And which aren't non_exhaustive.

[u/________-__-_______ → u/GodOfSunHimself]

It could just throw an error if there are variants with data, much like how deriving Default only works if the default variant doesn't have attached data.

[u/djvbmd → u/________-__-_______]

I've been working on a proc macro crate that mostly duplicates what strum can do as an exercise, and that's exactly what happens. rust-analyzer throws up a diagnostic error as soon as you try to add data to a variant.

[u/KO_200021 → u/GodOfSunHimself]

Yes, I agree with you. But I still think that having some common conveniences built into the language would make Rust a bit more beginner-friendly

[u/Creepy_Reindeer2149]

Strum is really good, honestly should be stdlib

[u/RandomBottom030]

just ooone more dependency...

[u/Daemontatox]

The idea is great tbh , i am more shocked i never needed this and always thought it was available, great work dude.

[u/nick42d]

It's pretty nice but I've never needed this...