fn extend_one(&mut self, (k, v): (K, V)) {
        self.insert(k, v);
    }
Gets an iterator over the entries of the map, sorted by key.

# Examples

Basic usage:

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

let mut map = BTreeMap::new();
map.insert(3, "c");
map.insert(2, "b");
map.insert(1, "a");

for (key, value) in map.iter() {
println!("{}: {}", key, value);
}
benchmarks/haystacks/code/rust-library.rs