Closed
Description
I was just going through my FizzBuzz article as I do every year or so to update compiler error messages and make any related changes necessary, and came across a regression in error output for Figure 3.
Given the following code:
fn main() {
for i in 1..101 {
let result = if i % 15 == 0 {
"FizzBuzz"
} else if i % 5 == 0 {
"Buzz"
} else if i % 3 == 0 {
"Fizz"
} else {
i.to_string()
};
println!("{}", result);
}
}This is the output in 1.57.0 (and it’s been just the one error that we now call E0308 right from the outset):
$ rustc +1.57.0 x.rs
error[E0308]: `if` and `else` have incompatible types
--> x.rs:10:9
|
7 | } else if i % 3 == 0 {
| ____________-
8 | | "Fizz"
| | ------ expected because of this
9 | | } else {
10 | | i.to_string()
| | ^^^^^^^^^^^^^ expected `&str`, found struct `String`
11 | | };
| |_____- `if` and `else` have incompatible types
error: aborting due to previous error
For more information about this error, try `rustc --explain E0308`.
But the output in 1.58.0 and in currently nightly adds another error, E0283:
$ rustc +1.58.0 x.rs
error[E0308]: `if` and `else` have incompatible types
--> x.rs:10:9
|
7 | } else if i % 3 == 0 {
| ____________-
8 | | "Fizz"
| | ------ expected because of this
9 | | } else {
10 | | i.to_string()
| | ^^^^^^^^^^^^^ expected `&str`, found struct `String`
11 | | };
| |_____- `if` and `else` have incompatible types
error[E0283]: type annotations needed for `{integer}`
--> x.rs:10:11
|
2 | for i in 1..101 {
| ------ the element type for this iterator is not specified
...
10 | i.to_string()
| ^^^^^^^^^ cannot infer type for type `{integer}`
|
= note: multiple `impl`s satisfying `{integer}: ToString` found in the `alloc` crate:
- impl ToString for i8;
- impl ToString for u8;
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0283, E0308.
For more information about an error, try `rustc --explain E0283`.
The integer type inference error is spurious, because if you resolve the if/else type mismatch (e.g. tack on .to_string() on the other branches), it also vanishes (resolved to the default of i32, I presume).