Cannot infer type using `as _` while indexing
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A-coercions
A-inference
C-enhancement
T-types
- Dominant language
- Rust
- Stars
- 119k
- Forks
- 16.1k
- PR merge metrics
- PR metrics pending
Description
When trying to index an array with another type that is not usize that can be converted to it using as _ inference fails.
Example code:
fn main() {
let array = [0, 1, 1, 2, 3, 5];
let index: u32 = 1;
array[index as _];
}
Error:
error[E0282]: type annotations needed
--> src/main.rs:4:20
|
4 | array[index as _];
| ^ cannot infer type
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the example in src/main.rs and inspect how the compiler handles as _ during array indexing and type inference. Confirm the intended inference behavior, then add regression coverage and verify that the example no longer produces E0282.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100