Slab-based B-Tree implementation

This crate provides an alternative implementation to the standard BTreeMap and BTreeSet data structures based on a slab data-structure. In principle, this implementation is more flexible and more memory efficient. It is more flexible by providing an extended set of low-level operations on B-Trees through the BTreeExt trait which can be used to further extend the functionalities of the BTreeMap collection. In addition, the underlying node allocation scheme is abstracted by a type parameter that can be instantiated by any data structure implementing slab-like operations. By default, the Slab type (from the slab crate) is used, which means that every node of the tree are allocated in a contiguous memory region, reducing the number of allocations needed. In theory, another type could be used to store the entire B-Tree on the stack.

Usage

From the user point of view, the collection provided by this crate can be used just like the standard BTreeMap and BTreeSet collections.

use btree_slab::BTreeMap;

// type inference lets us omit an explicit type signature (which
// would be `BTreeMap<&str, &str>` in this example).
let mut movie_reviews = BTreeMap::new();

// review some movies.
movie_reviews.insert("Office Space",       "Deals with real issues in the workplace.");
movie_reviews.insert("Pulp Fiction",       "Masterpiece.");
movie_reviews.insert("The Godfather",      "Very enjoyable.");
movie_reviews.insert("The Blues Brothers", "Eye lyked it a lot.");

// check for a specific one.
if !movie_reviews.contains_key("Les Misérables") {
    println!("We've got {} reviews, but Les Misérables ain't one.",
             movie_reviews.len());
}

// oops, this review has a lot of spelling mistakes, let's delete it.
movie_reviews.remove("The Blues Brothers");

// look up the values associated with some keys.
let to_find = ["Up!", "Office Space"];
for movie in &to_find {
    match movie_reviews.get(movie) {
       Some(review) => println!("{}: {}", movie, review),
       None => println!("{} is unreviewed.", movie)
    }
}

// Look up the value for a key (will panic if the key is not found).
println!("Movie review: {}", movie_reviews["Office Space"]);

// iterate over everything.
for (movie, review) in &movie_reviews {
    println!("{}: \"{}\"", movie, review);
}

Custom node allocation

One can use btree_slab::generic::BTreeMap to use a custom slab type to handle nodes allocation.

use slab::Slab;
use btree_slab::generic::BTreeMap;

let mut map: BTreeMap<K, V, Slab<Node<K, V>>> = BTreeMap::new();

In this example, the Slab<Node<_, _>> type is a slab-like data structure responsible for the nodes allocation. It must implement all the traits defining the cc_traits::Slab trait alias.

Extended API & Addressing

In this implementation of B-Trees, each node of a tree is addressed by the Address type. The extended API, visible through the BTreeExt trait, allows the caller to explore, access and modify the internal structure of the tree using this addressing system. This can be used to further extend the functionalities of the BTreeMap collection, for example in the btree-range-map crate.

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution