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casting variable with type &Unsized to &dyn Trait incorrectly says that the variable is unsized. #111406
Description
Code
use std::fmt::Debug;
fn f(x: &dyn Debug) {
println!("{:?}", x)
}
fn main() {
let x: &[u8] = &[1, 2, 3];
f(x);
}Current output
Compiling playground v0.0.1 (/playground)
error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
--> src/lib.rs:9:7
|
9 | f(x);
| ^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `[u8]`
= note: required for the cast from `[u8]` to the object type `dyn Debug`
help: consider borrowing the value, since `&[u8]` can be coerced into `dyn Debug`
|
9 | f(&x);
| +
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to previous errorDesired output
No response
Rationale and extra context
This error confused me as it was in a context that I thought the type of x is actually [u8], but it was &[u8] and the problem was about dyn cast.
Other cases
No response
Anything else?
No response
Activity
Rollup merge of rust-lang#111451 - compiler-errors:note-cast-origin, …
Rollup merge of rust-lang#111451 - compiler-errors:note-cast-origin, …
Rollup merge of rust-lang#111451 - compiler-errors:note-cast-origin, …
Rollup merge of rust-lang#111451 - compiler-errors:note-cast-origin, …
Rollup merge of rust-lang#111451 - compiler-errors:note-cast-origin, …
Zoybean commentedon May 17, 2024
I can see how this pointer could have been especially misleading, given
xis&[u8]and thereforeSized:Maybe if it instead said:
but that might risk being too much repetition of similar-but-distinct terms (
[u8],&[u8],dyn Debug,&dyn Debug) in the context of the full error