Code
struct T(i32);
impl PartialEq<i32> for T {
fn eq(&self, other: &i32) -> bool {
&self.0 == other
}
}
fn main() {
println!("{:?}", 4i32 == T(4))
}Current output
error[E0308]: mismatched types
--> src/main.rs:10:30
|
10 | println!("{:?}", 4i32 == T(4))
| ---- ^^^^ expected `i32`, found `T`
| |
| expected because this is `i32`
For more information about this error, try `rustc --explain E0308`.Desired output
error[E0308]: mismatched types
--> src/main.rs:10:30
|
10 | println!("{:?}", 4i32 == T(4))
| ---- ^^^^ expected `i32`, found `T`
| |
| expected because this is `i32`
help: `T` implements `PartialEq<i32>` consider swapping the LHS and RHS of the equality
For more information about this error, try `rustc --explain E0308`.For more information about this error, try rustc --explain E0308.
Rationale and extra context
Because PartialEq<Rhs> is asymmetric, t == s and s == t are semantically different if s and t are different types. Because most people view == as being a symmetric operation, this could lead to confusion if T implements PartialEq<S> but S does not implement PartialEq<T>. Thus, providing a hint that swapping the LHS and RHS of the equality operator could elucidate why the error is occurring.
Other cases
No response
Rust Version
rustc 1.81.0 (eeb90cd 2024-09-04)
binary: rustc
commit-hash: eeb90cd
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7
Anything else?
No response
Code
Current output
Desired output
For more information about this error, try
rustc --explain E0308.Rationale and extra context
Because
PartialEq<Rhs>is asymmetric,t == sands == tare semantically different ifsandtare different types. Because most people view==as being a symmetric operation, this could lead to confusion ifTimplementsPartialEq<S>butSdoes not implementPartialEq<T>. Thus, providing a hint that swapping the LHS and RHS of the equality operator could elucidate why the error is occurring.Other cases
No response
Rust Version
rustc 1.81.0 (eeb90cd 2024-09-04)
binary: rustc
commit-hash: eeb90cd
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7
Anything else?
No response