# Error code E0437

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

Erroneous code example:

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

    impl Foo for i32 {
        type Bar = bool;
    }
    }

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

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

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

    impl Foo for i32 {}
    }