Initial B-tree interface.

lib/cretonne/src/btree.rs

@@ -0,0 +1,98 @@
+use std::marker::PhantomData;
+
+// A Node reference is a direct index to an element of the pool.
+type NodeRef = u32;
+
+/// A B-tree data structure which nodes are allocated from a pool.
+pub struct BTree<K, V> {
+    index: NodeRef,
+    unused1: PhantomData<K>,
+    unused2: PhantomData<V>,
+}
+
+/// An enum representing a B-tree node.
+/// Keys and values are required to implement Default.
+enum Node<K, V> {
+    Inner {
+        size: u8,
+        keys: [K; 7],
+        nodes: [NodeRef; 8],
+    },
+    Leaf {
+        size: u8,
+        keys: [K; 7],
+        values: [V; 7],
+    },
+}
+
+/// Memory pool for nodes.
+struct NodePool<K, V> {
+    // The array containing the nodes.
+    data: Vec<Node<K, V>>,
+
+    // A free list
+    freelist: Vec<NodeRef>,
+}
+
+impl<K: Default, V: Default> NodePool<K, V> {
+    /// Create a new NodePool.
+    pub fn new() -> NodePool<K, V> {
+        NodePool {
+            data: Vec::new(),
+            freelist: Vec::new(),
+        }
+    }
+
+    /// Get a B-tree node.
+    pub fn get(&self, index: u32) -> Option<&Node<K, V>> {
+        unimplemented!()
+    }
+}
+
+impl<K: Default, V: Default> BTree<K, V> {
+    /// Search for `key` and return a `Cursor` that either points at `key` or the position where it would be inserted.
+    pub fn search(&mut self, key: K) -> Cursor<K, V> {
+        unimplemented!()
+    }
+}
+
+pub struct Cursor<'a, K: 'a, V: 'a> {
+    pool: &'a mut NodePool<K, V>,
+    height: usize,
+    path: [(NodeRef, u8); 16],
+}
+
+impl<'a, K: Default, V: Default> Cursor<'a, K, V> {
+    /// The key at the cursor position. Returns `None` when the cursor points off the end.
+    pub fn key(&self) -> Option<K> {
+        unimplemented!()
+    }
+
+    /// The value at the cursor position. Returns `None` when the cursor points off the end.
+    pub fn value(&self) -> Option<&V> {
+        unimplemented!()
+    }
+
+    /// Move to the next element.
+    /// Returns `false` if that moves the cursor off the end.
+    pub fn next(&mut self) -> bool {
+        unimplemented!()
+    }
+
+    /// Move to the previous element.
+    /// Returns `false` if this moves the cursor before the beginning.
+    pub fn prev(&mut self) -> bool {
+        unimplemented!()
+    }
+
+    /// Insert a `(key, value)` pair at the cursor position.
+    /// It is an error to insert a key that would be out of order at this position.
+    pub fn insert(&mut self, key: K, value: V) {
+        unimplemented!()
+    }
+
+    /// Remove the current element.
+    pub fn remove(&mut self) {
+        unimplemented!()
+    }
+}