Error code E0643

This error indicates that there is a mismatch between generic parameters and impl Trait parameters in a trait declaration versus its impl.

#![allow(unused)]
fn main() {
trait Foo {
    fn foo(&self, _: &impl Iterator);
}
impl Foo for () {
    fn foo<U: Iterator>(&self, _: &U) { } // error method `foo` has incompatible
                                          // signature for trait
}
}
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