Error code E0666
impl Trait types cannot appear nested in the generic arguments of other
impl Trait types.
Erroneous code example:
#![allow(unused)] fn main() { trait MyGenericTrait<T> {} trait MyInnerTrait {} fn foo( bar: impl MyGenericTrait<impl MyInnerTrait>, // error! ) {} }
Type parameters for impl Trait types must be explicitly defined as named
generic parameters:
#![allow(unused)] fn main() { trait MyGenericTrait<T> {} trait MyInnerTrait {} fn foo<T: MyInnerTrait>( bar: impl MyGenericTrait<T>, // ok! ) {} }