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Comment by tialaramex | Hacker News Reader

Also they probably have their understanding upside down. What's going on here isn't that either Swift or Rust treats the enum types as "more than just types" but that they are indeed first class types, whereas in C and C++ what you get isn't a type at all, it's just a strange way to spell an integer.

I don't think Swift has union types, but Rust does and so does C++ and in both languages the unions, just like their main product type (C++ class, Rust struct) can have methods defined on them. The enumeration "types" in the C-like languages are special and it's because they really aren't proper types at all, they're just integers wearing a funny hat.

One of Rust's most important post 1.0 types MaybeUninit<T> is actually a union, lots of Rust's important types, in 1.0 and since, are enums.

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C++'s scoped enums are strict types.

They are still a long way from the features of enums in Swift.

Scoped enums ("enum class") are a very small improvement on the previous enum, the main thing they deliver is that they don't pollute your namespace as badly thanks to the scoping.

Their notional status as "strict types" means nothing in a language which doesn't really care anyway, that's why memory_order::relaxed < cv_status::timeout is true

In Rust if you write nonsense like that it doesn't compile, these aren't comparable things. In C++ they're just integers, so of course you can see that relaxed (the integer zero) is less than timeout (the integer one) ...

They are just integers wearing funny hats.

> memory_order::relaxed < cv_status::timeout is true

No it isn't. https://godbolt.org/z/bz7EhMhMT

I knew I should have checked that in Godbolt before posting it. You're correct, the types don't coerce and so this actually doesn't work.

Oh come on now, everyone who programs in C++ knows operators don't work like that. Operators are tied to types, those enums don't have operator < defined.

You also can't add them, or subtract them.

Yes behind the scenes their integers, but almost certainly this is the case in Rust too. You can SOMETIMES coerce an enum class instance back to an int if you do unsafe casts (on purpose).

Both those scoped enums do in fact have operator< but, as your sibling comment points out, they insist on type matching and so my example won't actually compile because it uses dissimilar types. The analogous Rust types implement only Eq not PartialOrd, so we can't make this error.

However whether you can add or subtract them is harder to guess than you seem to have assumed

https://godbolt.org/z/3vdazcr7E

Of course the bit pattern representation is the same in Rust. The point isn't the representation or we'd be talking about machine code. The point is the ergonomics.

These types aren't (shouldn't be) integers, but in C and C++ they are anyway.

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