pub fn iter(&self) -> Iter<'_, K, V> {
        if let Some(root) = &self.root {
            let full_range = root.reborrow().full_range();

            Iter { range: Range { inner: full_range }, length: self.length }
        } else {
            Iter { range: Range { inner: LeafRange::none() }, length: 0 }
        }
    }
Gets a mutable iterator over the values of the map, in order by key.

# Examples

Basic usage:

```
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, String::from("hello"));
a.insert(2, String::from("goodbye"));
benchmarks/haystacks/code/rust-library.rs