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Const closure weirdness #55272
Description
The following compiles just fine:
#![feature(impl_trait_in_bindings)]
fn main() {
let func: impl Fn(&str) -> usize = |s| s.parse().unwrap();
}However this does not:
#![feature(impl_trait_in_bindings)]
fn main() {
const func: impl Fn(&str) -> usize = |s| s.parse().unwrap();
}It gives the following error message:
error: non-defining existential type use in defining scope
--> src/main.rs:4:42
|
4 | const func: impl Fn(&str) -> usize = |s| s.parse().unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^ lifetime `` is part of concrete type but not used in parameter list of existential type
error: aborting due to previous error
error: Could not compile `playground`.
Why is this an error? The closure does not capture anything, so it's lifetime is 'static, and const requires 'static.
Activity
ExpHP commentedon Oct 22, 2018
Note also that the following works:
so it has something to do with the
&strtype parameter. But the trick that often fixes problems like this in other places in rust does not help here:ilyvion commentedon Oct 1, 2022
Seems this feature doesn't even exist anymore.
traviscross commentedon Apr 28, 2025
We can close this as the feature was pulled out in #86729 and what was added back in #134185 only supports local bindings.