```rust #![feature(universal_impl_trait)] #![feature(conservative_impl_trait)] fn qqq(lol: impl Iterator<Item=u32>) -> impl Iterator<Item=u64> { lol.map(|x|x as u64) } ``` ``` warning: type parameter `impl Iterator<Item = u32>` should have a camel case name such as `Impl iterator<item = u32>` ```