Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0186: method `foo` has a `&self` declaration in the trait, but not in the impl
What it meansAn associated function for a trait was defined to be a method (i.e., to take a self parameter), but an implementation of the trait declared the same function to be static.
What rustc prints
error[E0186]: method `foo` has a `&self` declaration in the trait, but not in the impl
--> main.rs:10:5
|
2 | fn foo(&self);
| -------------- `&self` used in trait
...
10 | fn foo() {}
| ^^^^^^^^ expected `&self` in implReal 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
An associated function for a trait was defined to be a method (i.e., to take a self parameter), but an implementation of the trait declared the same function to be static.
Erroneous code example:
trait Foo {
fn foo(&self);
}
struct Bar;
impl Foo for Bar {
// error, method `foo` has a `&self` declaration in the trait, but not in
// the impl
fn foo() {}
}When a type implements a trait's associated function, it has to use the same signature. So in this case, since Foo::foo takes self as argument and does not return anything, its implementation on Bar should be the same:
trait Foo {
fn foo(&self);
}
struct Bar;
impl Foo for Bar {
fn foo(&self) {} // ok!
}From rustc --explain E0186 (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
- E0184the trait `Copy` cannot be implemented for this type; the type has a destructor
- E0185method `foo` has a `&self` declaration in the impl, but not in the trait
- E0191the value of the associated type `Bar` in `Trait` must be specified
- E0197inherent impls cannot be unsafe
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?