pub fn iter(&self) -> ValueIter<'_, VE> {
        ValueIter {
            inner: Some(self.inner.iter()),
            phantom: PhantomData,
        }
    }
Returns an iterator visiting all values associated with the entry.

Values are iterated in insertion order.

# Examples

```
# use tonic::metadata::*;
let mut map = MetadataMap::new();
map.insert("host", "world".parse().unwrap());
map.append("host", "earth".parse().unwrap());

if let Entry::Occupied(e) = map.entry("host").unwrap() {
let mut iter = e.iter();
assert_eq!(&"world", iter.next().unwrap());
assert_eq!(&"earth", iter.next().unwrap());
assert!(iter.next().is_none());
}
```
tonic/src/metadata/map.rs