Document behavior of enum when casted to an integer

[jmi2k]

Consider the following example:

enum Foo {
    A,
    B,
    C
}

fn main() {
    println!("{}", Foo::A as usize);
    println!("{}", Foo::B as usize);
    println!("{}", Foo::C as usize);
}

The current behavior is that Foo members get casted to an increasing sequence starting from 0. Although that seems to be the most reasonable default, it should be documented to make clear that it won't be changed in the future.

[frewsxcv]

Somewhat related, the book has a section on casting semantics that maybe should be copied/moved into the reference:

https://doc.rust-lang.org/book/casting-between-types.html

Though, it doesn't look like there's much there on enum casting

[steveklabnik]

@aturon so, here's an interesting wrinkle. We were talking about getting the lang team and the docs team together to tackle issues like this one, but given this is in the nursery and not rust-lang, I can't cc @rust-lang/lang 😦

[aturon]

@steveklabnik Whelp! I guess there are basically two options here:

• Add in the teams to the nursery, which would probably be useful across the board.
• Move the reference to rust-lang.

I'm not sure what the status of the latter is. Was there some particular "graduation" point we had in mind?

[steveklabnik]

Was there some particular "graduation" point we had in mind?

I said "hey @alexcrichton ! Should this go in the nursery or rust-lang. I don't care." He shugged. So we asked @brson. He said "Eh given its level of polish let's put it in the nursery", to which alex and I said 🆒 .

So, it was basically a coinflip, and we didn't have any particular criteria set up.

[aturon]

@steveklabnik

Heh, alright! Let's keep this in mind when we set up the docs + lang team discussion soon.

[alercah]

This is now fixed: https://doc.rust-lang.org/nightly/reference/items/enumerations.html

[frewsxcv]

yep! looks like @Havvy took care of this in #156 🎉