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Make specifying repr optional for fieldless enums #88203
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I don't believe we should allow enums with struct or tuple variants (even if they don't have fields) to omit the repr. (Ideally, I'd also prefer if such enums couldn't be Personally, I'm hoping that #81642 helps improve this substantially, so that using |
@fee1-dead Do you think you'd be able to prepare a PR that rejected casting enums with 0-field tuple/struct variants? (Per the discussion at https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/arbitrary.20enum.20discriminants/near/251899236) I can maybe give it a try myself if you'd like. |
I'm busy with other stuff. You can do it if you'd like. |
☔ The latest upstream changes (presumably #89884) made this pull request unmergeable. Please resolve the merge conflicts. |
merge conflicts |
Hello. This was discussed at the lang team meeting today.
|
Actually, the answer is "yes". https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f38e9d525cd1ca67ea8836aa65d6f7b9 #[repr(u8)]
pub enum Foo {
A,
B(),
C{},
}
pub fn a(foo: Foo) -> u8 {
foo as u8
} |
This makes it consistent for another behavior, which is casting an enum to its discriminant.
We can currently cast "fieldless" enums to its discriminants, but only "c-like" (only unit variants) enums are allowed to leave the repr unspecified. See rust-lang/reference#1055 (comment) for previous discussion.