Description
Because I naturally write ellipsises as three dots rather than two, I found myself writing the following:
#[derive(Debug, Clone)]
enum Stuff {
Blank,
Holder{
thing: u64,
},
}
impl Stuff {
fn is_blank(&self) -> bool {
match self {
&Stuff::Blank => true,
&Stuff::Holder{...} => false,
}
}
}
fn main(){
println!("{}", Stuff::Blank.is_blank());
}This is wrong because it should be Stuff::Holder{..}: wrong number of dots in the match.
But the error message I got is this:
error: expected identifier, found `...`
--> ellipsis.rs:14:22
|
14 | &Stuff::Holder{...} => false,
| ^^^
error[E0027]: pattern does not mention field `thing`
--> ellipsis.rs:14:8
|
14 | &Stuff::Holder{...} => false,
| ^^^^^^^^^^^^^^^^^^ missing field `thing`
error: aborting due to 2 previous errors
This isn't an intrinsically unreasonable error message or anything, but it totally mislead me: I did not parse "expected identifier, found ..." as meaning "You have the wrong number of dots and three dots is not valid syntax here", I just figured that I was misunderstanding something and that e.g. you had to mention at least one field or something and the ellipsis syntax was only for then ignoring the other fields.
This was I think compounded by the fact that it provided a second error message "pattern does not mention field thing" because it meant that I didn't read it as "You have a syntax error" but "You have a syntactically valid pattern match that happens not to be semantically valid due to some requirement you don't understand".
Meta
rustc --version --verbose:
rustc 1.21.0 (3b72af97e 2017-10-09)
binary: rustc
commit-hash: 3b72af97e42989b2fe104d8edbaee123cdf7c58f
commit-date: 2017-10-09
host: x86_64-unknown-linux-gnu
release: 1.21.0
LLVM version: 4.0