C was my first language, and I actually have the opposite opinion - I suspect that calling them 'enums' helps adoption. My reasoning is that phrases like 'tagged unions' and 'algebraic datatypes' strike some developers as sounding very academic/ivory tower and so somewhat intimidating. I think this is really unfortunate (and is definitely not universal among developers).

Being able to say 'Rust enums can carry arguments' - for some reason - sounds less intimidating and conveys the core feature.

I agree that something like 'sum type' sounds a bit too esoteric, but IMHO 'tagged union' is very descriptive. It's the same thing as a C union plus a tag indicating the currently active content (and that's also what the memory layout looks like under the hood).

(but yeah, 'enum with arguments' also describes it very well)

They do point them out as tagged unions many times in the documentation. But the syntax `tagged_union Whatever {}` doesn't exactly have me jumping out of my seat.

It’s not like “enum” and “mut” are complete English words either, so maybe an abbreviation like “tun” could have worked.

But honestly I think enum was a better choice.

I personally think enum was basically the only reasonable choice, as normal enums really are just a subset of tagged unions. They just happen to support tagged unions on top of them.

All C and C++ peasants should refer this: https://cheats.rs/#memory-layout . It will probably accelerate your initiation ritual.

That would still be technically misleading, since enums don't necessarily have tags due to niche optimization. Eg `Option` is an enum but `Option<Box<Foo>>` does not have any tags; it uses the content being zero to represent None since `Box<Foo>` cannot be zero.

Also, Rust does have actual tagged unions for C interop that you have to define yourself as a `struct` with an int field and a `union` field, just like in C.

Rust enums always have a discriminant: https://doc.rust-lang.org/std/mem/fn.discriminant.html

Their representation in memory may not use it, but it's still defined.

They do, but IIRC this mostly to compare enum variants when it can't implement `Eq` and/or `PartialEq`. For example, in tests.

There are also zero variants enums that don't have any discriminant, but still could be used.

I'm not sure what's the point of comparing it to C because enums in C only carry tags and no data, while unions only carry data and no tag. Enums in rust could do both.

Discriminated Records is The Way.