Playground
I tried this code:
fn main() {
let a = if true {
((), todo!())
} else {
((), ())
};
}I expected to see this happen:
Code compiles, runs, and panics.
a has type ((), ()).
Instead, this happened:
Compiling example v0.1.0 (/tmp/exmaple)
warning: unreachable expression
--> src/main.rs:3:9
|
3 | ((), todo!())
| ^^^^^-------^
| | |
| | any code following this expression is unreachable
| unreachable expression
|
= note: `#[warn(unreachable_code)]` on by default
error[E0308]: `if` and `else` have incompatible types
--> src/main.rs:5:9
|
2 | let a = if true {
| _____________-
3 | | ((), todo!())
| | ------------- expected because of this
4 | | } else {
5 | | ((), ())
| | ^^^^^^^^ expected `((), !)`, found `((), ())`
6 | | };
| |_____- `if` and `else` have incompatible types
|
= note: expected tuple `((), !)`
found tuple `((), ())`
For more information about this error, try `rustc --explain E0308`.
warning: `example` (bin "example") generated 1 warning
error: could not compile `example` (bin "example") due to previous error; 1 warning emitted
The following changes have no effect:
- Removing
let a = .
- Changing
true to some runtime-only condition.
- Swapping the two branches.
- Replacing
if-else with match.
- Swapping
todo!() and () inside of the tuple.
- Replacing
todo!() with loop{} or std::process::exit(0).
- Replacing
todo!() with a call to a function returning std::convert::Infallible (though this makes the warning about the unreachable code go away).
- Using
u8 or any other "normal" type instead of ().
The following changes make the error go away.
-
-
fn foo() -> () { todo!() }
((), foo())
-
let foo = || todo!();
((), foo())
-
Meta
rustc --version --verbose:
binary: rustc
commit-hash: 90c541806f23a127002de5b4038be731ba1458ca
commit-date: 2023-05-31
host: x86_64-unknown-linux-gnu
release: 1.70.0
LLVM version: 16.0.2
Same on nightly and beta.
Must be related to #35121.
Playground
I tried this code:
I expected to see this happen:
Code compiles, runs, and panics.
ahas type((), ()).Instead, this happened:
The following changes have no effect:
let a =.trueto some runtime-only condition.if-elsewithmatch.todo!()and()inside of the tuple.todo!()withloop{}orstd::process::exit(0).todo!()with a call to a function returningstd::convert::Infallible(though this makes the warning about the unreachable code go away).u8or any other "normal" type instead of().The following changes make the error go away.
Meta
rustc --version --verbose:Same on nightly and beta.
Must be related to #35121.