Make isEmpty a getter.

lib/coreimpl/splay_tree.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * A node in a splay tree. It holds the key, the value and the left
  * and right children in the tree.
  */
 class SplayTreeNode<K, V> {
   SplayTreeNode(K this.key, V this.value);
@@ skipping 33 matching lines @@
   }
 
   /**
    * Perform the splay operation for the given key. Moves the node with
    * the given key to the top of the tree.  If no node has the given
    * key, the last node on the search path is moved to the top of the
    * tree. This is the simplified top-down splaying algorithm from:
    * "Self-adjusting Binary Search Trees" by Sleator and Tarjan.
    */
   void splay_(K key) {
-    if (isEmpty()) return;
+    if (isEmpty) return;
 
     // The right child of the dummy node will hold
     // the L tree of the algorithm.  The left child of the dummy node
     // will hold the R tree of the algorithm.  Using a dummy node, left
     // and right will always be nodes and we avoid special cases.
     SplayTreeNode<K, V> left = _dummy;
     SplayTreeNode<K, V> right = _dummy;
     SplayTreeNode<K, V> current = _root;
     while (true) {
       int comp = key.compareTo(current.key);
@@ skipping 34 matching lines @@
     right.left = current.right;
     current.left = _dummy.right;
     current.right = _dummy.left;
     _root = current;
 
     _dummy.right = null;
     _dummy.left = null;
   }
 
   V operator [](K key) {
-    if (!isEmpty()) {
+    if (!isEmpty) {
       splay_(key);
       if (_root.key.compareTo(key) == 0) return _root.value;
     }
     return null;
   }
 
   V remove(K key) {
-    if (isEmpty()) return null;
+    if (isEmpty) return null;
     splay_(key);
     if (_root.key.compareTo(key) != 0) return null;
     V value = _root.value;
 
     _count--;
     // assert(_count >= 0);
     if (_root.left === null) {
       _root = _root.right;
     } else {
       SplayTreeNode<K, V> right = _root.right;
       _root = _root.left;
       // Splay to make sure that the new root has an empty right child.
       splay_(key);
       // Insert the original right child as the right child of the new
       // root.
       _root.right = right;
     }
     return value;
   }
 
   void operator []=(K key, V value) {
-    if (isEmpty()) {
+    if (isEmpty) {
       _count++;
       _root = new SplayTreeNode(key, value);
       return;
     }
     // Splay on the key to move the last node on the search path for
     // the key to the root of the tree.
     splay_(key);
     if (_root.key.compareTo(key) == 0) {
       _root.value = value;
       return;
@@ skipping 13 matching lines @@
     _root = node;
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
     if (containsKey(key)) return this[key];
     V value = ifAbsent();
     this[key] = value;
     return value;
   }
 
-  bool isEmpty() {
+  bool get isEmpty {
     // assert(!((_root === null) && (_count != 0)));
     // assert(!((_count == 0) && (_root !== null)));
     return (_root === null);
   }
 
   void forEach(void f(K key, V value)) {
     List<SplayTreeNode<K, V>> list = new List<SplayTreeNode<K, V>>();
     SplayTreeNode<K, V> current = _root;
     while (current !== null) {
       if (current.left !== null) {
         list.add(current);
         current = current.left;
       } else {
         f(current.key, current.value);
         while (current.right === null) {
-          if (list.isEmpty()) return;
+          if (list.isEmpty) return;
           current = list.removeLast();
           f(current.key, current.value);
         }
         current = current.right;
       }
     }
   }
 
   int get length {
     return _count;
   }
 
   void clear() {
     _root = null;
     _count = 0;
   }
 
   bool containsKey(K key) {
-    if (!isEmpty()) {
+    if (!isEmpty) {
       splay_(key);
       if (_root.key.compareTo(key) == 0) return true;
     }
     return false;
   }
 
   bool containsValue(V value) {
     bool found = false;
     bool visit(SplayTreeNode node) {
       if (node === null) return false;
@@ skipping 78 matching lines @@
       if (node.key.compareTo(key) > 0) {
         return visit(node.left, node.key);
       }
       if (node.key.compareTo(key) <= 0) {
         return visit(node.right, ifEmpty);
       }
     }
     return visit(_root, null);
   }
 }