Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0185: method `foo` has a `&self` declaration in the impl, but not in the trait
What it meansAn associated function for a trait was defined to be static, but an implementation of the trait declared the same function to be a method (i.e., to take a self parameter).
What rustc prints
error[E0185]: method `foo` has a `&self` declaration in the impl, but not in the trait
--> main.rs:10:5
|
2 | fn foo();
| --------- trait method declared without `&self`
...
10 | fn foo(&self) {}
| ^^^^^^^^^^^^^ `&self` used 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 static, but an implementation of the trait declared the same function to be a method (i.e., to take a self parameter).
Erroneous code example:
trait Foo {
fn foo();
}
struct Bar;
impl Foo for Bar {
// error, method `foo` has a `&self` declaration in the impl, but not in
// the trait
fn foo(&self) {}
}When a type implements a trait's associated function, it has to use the same signature. So in this case, since Foo::foo does not take any argument and does not return anything, its implementation on Bar should be the same:
trait Foo {
fn foo();
}
struct Bar;
impl Foo for Bar {
fn foo() {} // ok!
}From rustc --explain E0185 (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
- E0183manual implementations of `FnOnce` are experimental
- E0184the trait `Copy` cannot be implemented for this type; the type has a destructor
- E0186method `foo` has a `&self` declaration in the trait, but not in the impl
- E0191the value of the associated type `Bar` in `Trait` must be specified
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?