I have this code base
pub struct Foo<V> {
pub data: HashMap<u64, V>
}
impl<V> Foo<V> {
pub fn keys(&self) -> HashMap<u64, V>::Keys { self.data.keys() }
}
```
I get compile error:
```
|
11 | pub fn keys(&self) -> HashMap<u64, V>::Keys { self.data.keys() }
| ^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<std::collections::HashMap<u64, V> as Trait>::Keys`
```
What is the right return type of keys?