Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0199: implementing the trait `Bar` is not unsafe
What it meansA trait implementation was marked as unsafe while the trait is safe.
What rustc prints
error[E0199]: implementing the trait `Bar` is not unsafe --> main.rs:5:1 | 5 | unsafe impl Bar for Foo { } // error! | ^^^^^^^^^^^^^^^^^^^^^^^ | help: remove `unsafe` from this trait implementation | 5 - unsafe impl Bar for Foo { } // error! 5 + impl Bar for Foo { } // error! |
Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
The compiler team's explanation
A trait implementation was marked as unsafe while the trait is safe.
Erroneous code example:
struct Foo;
trait Bar { }
unsafe impl Bar for Foo { } // error!Safe traits should not have unsafe implementations, therefore marking an implementation for a safe trait unsafe will cause a compiler error. Removing the unsafe marker on the trait noted in the error will resolve this problem:
struct Foo;
trait Bar { }
impl Bar for Foo { } // ok!From rustc --explain E0199 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0308mismatched types
- E0277the trait bound is not satisfied
- E0599no method named X found in the current scope
- E0433failed to resolve
- E0197inherent impls cannot be unsafe
- E0198negative impls cannot be unsafe
- E0200the trait `Bar` requires an `unsafe impl` declaration
- E0201duplicate definitions with name `baz`:
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?