Make isEmpty a getter.

lib/compiler/implementation/universe/selector_map.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.
 
 class SelectorMap<T> extends PartialTypeTree {
 
   SelectorMap(Compiler compiler) : super(compiler);
 
   SelectorMapNode<T> newSpecializedNode(ClassElement type)
       => new SelectorMapNode<T>(type);
 
   T operator [](Selector selector) {
     SelectorMapNode<T> node = findNode(selectorType(selector), false);
     if (node == null) return null;
     Link<SelectorValue<T>> selectors = node.selectorsByName[selector.name];
     if (selectors == null) return null;
-    for (Link link = selectors; !link.isEmpty(); link = link.tail) {
+    for (Link link = selectors; !link.isEmpty; link = link.tail) {
       SelectorValue<T> existing = link.head;
       if (existing.selector.equalsUntyped(selector)) return existing.value;
     }
     return null;
   }
 
   void operator []=(Selector selector, T value) {
     SelectorMapNode<T> node = findNode(selectorType(selector), true);
     Link<SelectorValue<T>> selectors = node.selectorsByName[selector.name];
     if (selectors == null) {
       // No existing selectors with the given name. Create a new
       // linked list.
       SelectorValue<T> head = new SelectorValue<T>(selector, value);
       node.selectorsByName[selector.name] =
           new Link<SelectorValue<T>>().prepend(head);
     } else {
       // Run through the linked list of selectors with the same name. If
       // we find one that matches, we update the value in the mapping.
-      for (Link link = selectors; !link.isEmpty(); link = link.tail) {
+      for (Link link = selectors; !link.isEmpty; link = link.tail) {
         SelectorValue<T> existing = link.head;
         // It is safe to ignore the type here, because all selector
         // mappings that are stored in a single node have the same type.
         if (existing.selector.equalsUntyped(selector)) {
           existing.value = value;
           return;
         }
       }
       // We could not find an existing mapping for the selector, so
       // we add a new one to the existing linked list.
       SelectorValue<T> head = new SelectorValue<T>(selector, value);
       node.selectorsByName[selector.name] = selectors.prepend(head);
     }
   }
 
   // TODO(kasperl): Share code with the [] operator?
   bool containsKey(Selector selector) {
     SelectorMapNode<T> node = findNode(selectorType(selector), false);
     if (node == null) return false;
     Link<SelectorValue<T>> selectors = node.selectorsByName[selector.name];
     if (selectors == null) return false;
-    for (Link link = selectors; !link.isEmpty(); link = link.tail) {
+    for (Link link = selectors; !link.isEmpty; link = link.tail) {
       SelectorValue<T> existing = link.head;
       if (existing.selector.equalsUntyped(selector)) return true;
     }
     return false;
   }
 
   /**
    * Visits all mappings for selectors that may be used to invoke the
    * given [member] element. If the [visit] function ever returns false,
    * we abort the traversal early.
    */
   void visitMatching(Element member, bool visit(Selector selector, T value)) {
     assert(member.isMember());
     if (root == null) return;
     // TODO(kasperl): For now, we use a different implementation for
     // visiting if the tree contains interface subtypes.
     if (containsInterfaceSubtypes) {
       visitAllMatching(member, visit);
     } else {
       visitHierarchyMatching(member, visit);
     }
   }
 
   void visitAllMatching(Element member, bool visit(selector, value)) {
     root.visitRecursively((SelectorMapNode<T> node) {
       Link<SelectorValue<T>> selectors = node.selectorsByName[member.name];
       if (selectors == null) return true;
-      for (Link link = selectors; !link.isEmpty(); link = link.tail) {
+      for (Link link = selectors; !link.isEmpty; link = link.tail) {
         SelectorValue<T> existing = link.head;
         Selector selector = existing.selector;
         // Since we're running through the entire tree we have to use
         // the applies method that takes types into account.
         if (selector.applies(member, compiler)) {
           if (!visit(selector, existing.value)) return false;
         }
       }
       return true;
     });
   }
 
   void visitHierarchyMatching(Element member, bool visit(selector, value)) {
     visitHierarchy(member.getEnclosingClass(), (SelectorMapNode<T> node) {
       Link<SelectorValue<T>> selectors = node.selectorsByName[member.name];
       if (selectors == null) return true;
-      for (Link link = selectors; !link.isEmpty(); link = link.tail) {
+      for (Link link = selectors; !link.isEmpty; link = link.tail) {
         SelectorValue<T> existing = link.head;
         Selector selector = existing.selector;
         if (selector.appliesUntyped(member, compiler)) {
           if (!visit(selector, existing.value)) return false;
         }
       }
       return true;
     });
   }
 
 }
 
 class SelectorMapNode<T> extends PartialTypeTreeNode {
 
   final Map<SourceString, Link<SelectorValue<T>>> selectorsByName;
 
   SelectorMapNode(ClassElement type) : super(type),
       selectorsByName = new Map<SourceString, Link<SelectorValue<T>>>();
 
 }
 
 class SelectorValue<T> {
   final Selector selector;
   T value;
   SelectorValue(this.selector, this.value);
   toString() => "$selector -> $value";
 }