♻️ refactor: Remove usage of class Leaf.

This avoids using multiple Hidden Classes and enables inline caching.

Fixes #107.

Author: make-github-pseudonymous-again

src/deletion/delete_case2.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import rotate_left from '../rotate/rotate_left.js';
 import rotate_right from '../rotate/rotate_right.js';
 import sibling from '../family/sibling.js';
@@ -17,10 +16,10 @@ import delete_case4 from './delete_case4.js';
  *   - all other root-leaf paths have a black height of b
  *   - n is not the root
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case2 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
 

src/deletion/delete_case3.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import sibling from '../family/sibling.js';
 
 import delete_case1 from './delete_case1.js';
@@ -16,10 +15,10 @@ import delete_case4 from './delete_case4.js';
  *   - n is not the root
  *   - n's sibling is black
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case3 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
 	const s = sibling(n);

src/deletion/delete_case4.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import sibling from '../family/sibling.js';
 
 import delete_case5 from './delete_case5.js';
@@ -16,10 +15,10 @@ import delete_case5 from './delete_case5.js';
  *   - n's sibling is black
  *   - n's parent and n's sibling's children cannot all be black
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case4 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
 	const s = sibling(n);

src/deletion/delete_case5.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import rotate_left from '../rotate/rotate_left.js';
 import rotate_right from '../rotate/rotate_right.js';
 import sibling from '../family/sibling.js';
@@ -18,10 +17,10 @@ import delete_case6 from './delete_case6.js';
  *   - n's sibling is black
  *   - at least one of n's sibling's children is red
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case5 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
 	const s = sibling(n);

src/deletion/delete_case6.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import rotate_left from '../rotate/rotate_left.js';
 import rotate_right from '../rotate/rotate_right.js';
 import sibling from '../family/sibling.js';
@@ -17,10 +16,10 @@ import sibling from '../family/sibling.js';
  *   - if n is a left child, the right child of n's sibling is red
  *   - if n is a right child, the left child of n's sibling is red
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case6 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
 	const s = sibling(n);

src/deletion/delete_no_child.js

@@ -2,7 +2,6 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 
 import replace_node from './replace_node.js';
 import delete_case2 from './delete_case2.js';
@@ -32,13 +31,15 @@ const delete_no_child = (n) => {
 	assert(n._color === BLACK);
 
 	// Mock leaf since there is no left child
-	const leaf = new Leaf(null);
+	// We use key = n.key to avoid mixing types, but this property is never
+	// accessed.
+	const leaf = new Node(BLACK, n.key);
 
 	// Replace n with the mocked leaf
 	replace_node(n, leaf);
 
 	// If n is black, deleting it reduces the black-height of every path going
-	// through it by 1. Leaf is black, so there are more things to fix.
+	// through it by 1. The leaf is black, so there are more things to fix.
 	delete_case2(leaf);
 
 	// Delete mocked leaf

src/deletion/prune.js

@@ -1,14 +1,13 @@
 import assert from 'assert';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 
 /**
  * Prune subtree rooted at input node.
  *
- * @param {Node|Leaf} root - The leaf to delete.
+ * @param {Node} root - The root of the subtree to prune.
  */
 const prune = (root) => {
-	assert(root instanceof Node || root instanceof Leaf);
+	assert(root instanceof Node);
 	assert(root.parent !== null);
 
 	if (root === root.parent.left) root.parent.left = null;

src/deletion/replace_node.js

@@ -1,16 +1,15 @@
 import assert from 'assert';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 
 /**
  * Replaces node <code>A</code> by node <code>B</code>.
  *
  * @param {Node} A - The node to replace.
- * @param {Node|Leaf} B - The replacement node.
+ * @param {Node} B - The replacement node.
  */
 const replace_node = (A, B) => {
 	assert(A instanceof Node);
-	assert(B instanceof Node || B instanceof Leaf);
+	assert(B instanceof Node);
 	// We never apply delete_one_child or delete_no_child on the root
 	assert(A.parent !== null);
 

src/family/sibling.js

@@ -1,15 +1,14 @@
 import assert from 'assert';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 
 /**
  * Computes the sibling of the input node.
  *
- * @param {Node|Leaf} node - The input node.
+ * @param {Node} node - The input node.
  * @returns {Node}
  */
 const sibling = (node) => {
-	assert(node instanceof Node || node instanceof Leaf);
+	assert(node instanceof Node);
 	// We only use this function when node HAS a non-leaf sibling.
 	assert(node.parent !== null);
 

src/index.js

@@ -28,6 +28,5 @@ export {default as rotate_right} from './rotate/rotate_right.js';
 export {default as search} from './search/search.js';
 export {default as inordertraversal} from './traversal/inordertraversal.js';
 export {default as rangetraversal} from './traversal/rangetraversal.js';
-export {default as Leaf} from './types/Leaf.js';
 export {default as Node} from './types/Node.js';
 export {default as RedBlackTree} from './types/RedBlackTree.js';