You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: playground.rs
    path of file: ./repos/sled/examples
    
    the code of the file until where you have to start completion: extern crate sled;

use sled::{Config, Result};

fn basic() -> Result<()> {
    let config = Config::new().temporary(true);

    let db = config.open()?;

    let k = b"k".to_vec();
    let v1 = b"v1".to_vec();
    let v2 = b"v2".to_vec();

    // set and get
    db.insert(k.clone(), v1.clone())?;
    assert_eq!(db.get(&k).unwrap().unwrap(), (v1));

    // compare and swap
    match db.compare_and_swap(k.clone(), Some(&v1), Some(v2.clone()))? {
        Ok(()) => println!("it worked!"),
        Err(sled::CompareAndSwapError { current: cur, proposed: _ }) => {
            println!("the actual current value is {:?}", cur)
        }
    }

    // scan forward
    let mut iter = db.range(k.as_slice()..);
    let (k1, v1) = iter.next().unwrap().unwrap();
    assert_eq!(v1, v2);
    assert_eq!(k1, k);
    assert_eq!(iter.next(), None);

    // deletion
    db.remove(&k)?;

    Ok(())
}

fn merge_operator() -> Result<()> {
    fn concatenate_merge(
        _key: &[u8],              // the key being merged
        old_value: O
    
fn merge_operator() -> Result<()> {
    fn concatenate_merge(
        _key: &[u8],              // the key being merged
        old_value: Option<&[u8]>, // the previous value, if one existed
        merged_bytes: &[u8],      // the new bytes being merged in
    ) -> Option<Vec<u8>> {
        // set the new value, return None to delete
        let mut ret = old_value.map_or_else(Vec::new, |ov| ov.to_vec());

        ret.extend_from_slice(merged_bytes);

        Some(ret)
    }

    let config = Config::new().temporary(true);

    let db = config.open()?;
    db.set_merge_operator(concatenate_merge);

    let k = b"k".to_vec();

    db.insert(k.clone(), vec![0])?;
    db.merge(k.clone(), vec![1])?;
    db.merge(k.clone(), vec![2])?;
    assert_eq!(db.get(&*k).unwrap().unwrap(), (vec![0, 1, 2]));

    // sets replace previously merged data,
    // bypassing the merge function.
    db.insert(k.clone(), vec![3])?;
    assert_eq!(db.get(&*k).unwrap().unwrap(), (vec![3]));

    // merges on non-present values will add them
    db.remove(&*k)?;
    db.merge(k.clone(), vec![4])?;
    assert_eq!(db.get(&*k).unwrap().unwrap(), (vec![4]));

    Ok(())
}