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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 {} }