Error code E0438

An associated constant whose name does not match any of the associated constants in the trait was used when implementing the trait.

Erroneous code example:

#![allow(unused)]
fn main() {
trait Foo {}

impl Foo for i32 {
    const BAR: bool = true;
}
}
ⓘ

Trait implementations can only implement associated constants that are members of the trait in question.

The solution to this problem is to remove the extraneous associated constant:

#![allow(unused)]
fn main() {
trait Foo {}

impl Foo for i32 {}
}