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 {} }