Extract _ListTaskInputMixin and allow chaining.

pkg/analyzer/lib/src/task/inputs.dart

Index: pkg/analyzer/lib/src/task/inputs.dart
diff --git a/pkg/analyzer/lib/src/task/inputs.dart b/pkg/analyzer/lib/src/task/inputs.dart
index 72532e738939890a8fc5da4eb2b00399c2edaed5..221861bfd14e905009075dd18298442b6258b012 100644
--- a/pkg/analyzer/lib/src/task/inputs.dart
+++ b/pkg/analyzer/lib/src/task/inputs.dart
@@ -20,35 +20,13 @@ typedef TaskInput<E> GenerateTaskInputs<B, E>(B object);
  * defined on a single target.
  */
 class ListTaskInputImpl<E> extends SimpleTaskInput<List<E>>
-    implements ListTaskInput<E> {
+    with _ListTaskInputMixin<E> implements ListTaskInput<E> {
   /**
    * Initialize a newly created task input that computes the input by accessing
    * the given [result] associated with the given [target].
    */
   ListTaskInputImpl(AnalysisTarget target, ResultDescriptor<List<E>> result)
       : super(target, result);
-
-  @override
-  TaskInput<List /*<V>*/ > toList(UnaryFunction<E, dynamic /*<V>*/ > mapper) {
-    return new ListToListTaskInput<E, dynamic /*V*/ >(this, mapper);
-  }
-
-  @override
-  TaskInput<List /*<V>*/ > toListOf(ResultDescriptor /*<V>*/ valueResult) {
-    return (this as ListTaskInputImpl<AnalysisTarget>).toList(valueResult.of);
-  }
-
-  @override
-  TaskInput<Map<E, dynamic /*V*/ >> toMap(
-      UnaryFunction<E, dynamic /*<V>*/ > mapper) {
-    return new ListToMapTaskInput<E, dynamic /*V*/ >(this, mapper);
-  }
-
-  @override
-  TaskInput<Map<AnalysisTarget, dynamic /*V*/ >> toMapOf(
-      ResultDescriptor /*<V>*/ valueResult) {
-    return (this as ListTaskInputImpl<AnalysisTarget>).toMap(valueResult.of);
-  }
 }
 
 /**
@@ -59,7 +37,8 @@ class ListTaskInputImpl<E> extends SimpleTaskInput<List<E>>
  * and the list of the analysis results is used as the input to the task.
  */
 class ListToListTaskInput<B, E>
-    extends _ListToCollectionTaskInput<B, E, List<E>> {
+    extends _ListToCollectionTaskInput<B, E, List<E>>
+    with _ListTaskInputMixin<E> {
   /**
    * Initialize a result accessor to use the given [baseAccessor] to access a
    * list of values that can be passed to the given [generateTaskInputs] to
@@ -380,6 +359,29 @@ class TopLevelTaskInputBuilder
 }
 
 /**
+ * A mixin-ready class implementing [ListTaskInput].
+ */
+abstract class _ListTaskInputMixin<E> implements ListTaskInput<E> {

[Brian Wilkerson, 2015/03/25 21:20:58]

Is there any reason to make this a private class (given that it's in an internal
library)?

+  ListTaskInput /*<V>*/ toList(UnaryFunction<E, dynamic /*<V>*/ > mapper) {
+    return new ListToListTaskInput<E, dynamic /*V*/ >(this, mapper);
+  }
+
+  ListTaskInput /*<V>*/ toListOf(ResultDescriptor /*<V>*/ valueResult) {
+    return (this as ListTaskInputImpl<AnalysisTarget>).toList(valueResult.of);
+  }
+
+  TaskInput<Map<E, dynamic /*V*/ >> toMap(
+      UnaryFunction<E, dynamic /*<V>*/ > mapper) {
+    return new ListToMapTaskInput<E, dynamic /*V*/ >(this, mapper);
+  }
+
+  TaskInput<Map<AnalysisTarget, dynamic /*V*/ >> toMapOf(
+      ResultDescriptor /*<V>*/ valueResult) {
+    return (this as ListTaskInputImpl<AnalysisTarget>).toMap(valueResult.of);
+  }
+}
+
+/**
  * An input to an [AnalysisTask] that is computed by the following steps. First
  * another (base) task input is used to compute a [List]-valued result. An input
  * generator function is then used to map each element of that list to a task