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openedon May 20, 2024
I tried this code:
fn foo() -> Option<Box<u8>> {
todo!()
}
fn bar(_: Option<&u8>) {}
fn main() {
let mut v = vec![];
bar(v.last().map(|x| &**x));
v.push(foo());
}I would expect v to have a knowable type but it's failing with this error:
error[E0282]: type annotations needed for `&T`
--> src/main.rs:11:27
|
11 | bar(v.last().map(|x| &**x));
| ^ --- type must be known at this point
|
help: consider giving this closure parameter an explicit type, where the type for type parameter `T` is specified
|
11 | bar(v.last().map(|x: &T| &**x));
| ++++
For more information about this error, try `rustc --explain E0282`.
error: could not compile `tests` (bin "tests") due to 1 previous error
It's able to infer it if we swap the lines
v.push(foo());
bar(v.last().map(|x| &**x));Meta
Tried on nightly and stable
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Area: Type inferenceArea: Type inferenceCategory: This is a bug.Category: This is a bug.Relevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.