pub trait HashExt {
    // Provided methods
    fn hash_value(self, h: u64) -> HashWrapper<Self>
       where Self: Sized { ... }
    fn hash_empty(self) -> EmptyHashWrapper<Self>
       where Self: Sized { ... }
}pub trait HashExt {
    // Provided methods
    fn hash_value(self, h: u64) -> HashWrapper<Self>
       where Self: Sized { ... }
    fn hash_empty(self) -> EmptyHashWrapper<Self>
       where Self: Sized { ... }
}