suggestion to use generic parameter in case of "error[E0782]: trait objects must include the dyn keyword"

Code

trait StateTrait {
  fn handle_state(&self);
}

trait StateView: Sized {
  fn view(_: &StateTrait) -> Vec<Self>;
}

fn main() {}

Current output

error[E0782]: trait objects must include the `dyn` keyword
 --> src/lib.rs:7:15
  |
7 |   fn view(_: &StateTrait) -> Vec<Self>;
  |               ^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
7 |   fn view(_: &dyn StateTrait) -> Vec<Self>;
  |               +++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0782`.

Desired output

error[E0782]: trait objects must include the `dyn` keyword for dynamic dispatch
 --> src/lib.rs:7:15
  |
7 |   fn view(_: &StateTrait) -> Vec<Self>;
  |               ^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
7 |   fn view(_: &dyn StateTrait) -> Vec<Self>;
  |               +++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0782`.


error[????]: use a generic parameter for the trait objects for static dispatch
 --> src/lib.rs:7:15
  |
7 |   fn view(_: &StateTrait) -> Vec<Self>;
  |               ^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
7 |   fn view<S: StateTrait>(_: &S) -> Vec<Self>;
  |               +++

error: aborting due to previous error

For more information about this error, try `rustc --explain ????`.

Rationale and extra context

The issue was created with regard to the suggestion made in the thread https://users.rust-lang.org/t/how-can-i-avoid-dynamic-dispatch/111395
The content of Current output is the result of rustc --crate-name foo --edition=2021 src/lib.rs

Other cases

No response

Rust Version

$ rustc --version --verbose
rustc 1.74.1 (a28077b28 2023-12-04)
binary: rustc
commit-hash: a28077b28a02b92985b3a3faecf92813155f1ea1
commit-date: 2023-12-04
host: x86_64-unknown-linux-gnu
release: 1.74.1
LLVM version: 17.0.4

Anything else?

No response

Help text could be combined instead of throwing a separate error to increase readability and show association between suggestions.

error[E0782]: trait objects must include the `dyn` keyword for dynamic dispatch
 --> src/lib.rs:7:15
  |
7 |   fn view(_: &StateTrait) -> Vec<Self>;
  |               ^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
7 |   fn view(_: &dyn StateTrait) -> Vec<Self>;
  |               +++
help: or use a generic parameter for static dispatch
  |
7 |   fn view<S: StateTrait>(_: &S) -> Vec<Self>;
  |          +++++++++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0782`.

Huh, I think we did suggest that at some point (well, at least suggesting adding impl next to existing dyn suggestion).

@rustbot

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Rollup merge of rust-lang#127692 - veera-sivarajan:bugfix-125139, r=e…

Unrolled build for rust-lang#127692

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suggestion to use generic parameter in case of "error[E0782]: trait objects must include the `dyn` keyword" #125139

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suggestion to use generic parameter in case of "error[E0782]: trait objects must include the dyn keyword" #125139

Description

Code

Current output

Desired output

Rationale and extra context

Other cases

Rust Version

Anything else?

Activity

HaydenAtFoxHaven commented on May 15, 2024

fmease commented on May 15, 2024

veera-sivarajan commented on Jul 9, 2024

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suggestion to use generic parameter in case of "error[E0782]: trait objects must include the `dyn` keyword" #125139