Description
Code
pub enum Error {
NotFound,
PreconditionFailed {
description: String,
}
}
pub fn demonstration(error: Error) {
match error {
Error::NotFound => println!("gone fishin"),
Error::PreconditionFailed => println!("you're missing something"),
_ => println!("i literally have no idea"),
}
}Current output
error[E0533]: expected unit struct, unit variant or constant, found struct variant `Error::PreconditionFailed`
--> src/lib.rs:12:9
|
12 | Error::PreconditionFailed => println!("you're missing something"),
| ^^^^^^^^^^^^^^^^^^^^^^^^^ not a unit struct, unit variant or constantDesired output
error[E0533]: expected unit struct, unit variant or constant, found struct variant `Error::PreconditionFailed`
--> src/lib.rs:12:9
|
12 | Error::PreconditionFailed => println!("you're missing something"),
| ^^^^^^^^^^^^^^^^^^^^^^^^^ not a unit struct, unit variant or constant
help: if you don't care about the variant's fields, ignore them with `{ .. }`
|
12 | Error::PreconditionFailed { .. } => println!("you're missing something"),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Rationale and extra context
I wrote code that looked like this while not having my brain turned on 100%. Due to said brain not functioning, it took me a while to understand what rustc was trying to tell me with the message pointing to the Error::PreconditionFailed pattern with the text not a unit struct, unit variant or constant. Error::PreconditionFailed sure looked like a unit variant to me!
What rustc was trying to tell me was that the definition of the Error::PreconditionFailed variant was a struct variant ("found struct variant") and my pattern wasn't matching the definition ("this pattern you specified looks like it's trying to match a variant that is not a unit struct, unit variant or constant").
The change I needed to make was adding { .. } to my pattern, because I was trying to distinguish different variants from each other, not use pieces within the variants. Suggesting { .. } seems like a decent starting point to me, but there could definitely be cases I'm not considering here and I'm totally open to hearing that ❤️
Other cases
No response
Rust Version
$ rustc --version --verbose
rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: aarch64-apple-darwin
release: 1.78.0
LLVM version: 18.1.2Anything else?
No response