Refactor Future constructors.

utils/pub/version_solver.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.
 
 /// Attempts to resolve a set of version constraints for a package dependency
 /// graph and select an appropriate set of best specific versions for all
 /// dependent packages. It works iteratively and tries to reach a stable
 /// solution where the constraints of all dependencies are met. If it fails to
 /// reach a solution after a certain number of iterations, it assumes the
 /// dependency graph is unstable and reports and error.
@@ skipping 79 matching lines @@
   Future<List<PackageId>> solve() {
     // Kick off the work by adding the root package at its concrete version to
     // the dependency graph.
     var ref = new PackageRef.root(_root);
     enqueue(new AddConstraint('(entrypoint)', ref));
     _pubspecs.cache(ref.atVersion(_root.version), _root.pubspec);
 
     Future processNextWorkItem(_) {
       while (true) {
         // Stop if we are done.
-        if (_work.isEmpty) return new Future.immediate(buildResults());
+        if (_work.isEmpty) return new Future.value(buildResults());
 
         // If we appear to be stuck in a loop, then we probably have an unstable
         // graph, bail. We guess this based on a rough heuristic that it should
         // only take a certain number of steps to solve a graph with a given
         // number of connections.
         // TODO(rnystrom): These numbers here are magic and arbitrary. Tune
         // when we have a better picture of real-world package topologies.
         _numIterations++;
         if (_numIterations > max(50, _packages.length * 5)) {
           throw new CouldNotSolveException();
@@ skipping 166 matching lines @@
         solver.enqueue(new AddConstraint(package, newRef));
       }
     });
   }
 
   /// Get the dependencies at [version] of the package being changed.
   Future<Map<String, PackageRef>> getDependencyRefs(VersionSolver solver,
       Version version) {
     // If there is no version, it means no package, so no dependencies.
     if (version == null) {
-      return new Future<Map<String, PackageRef>>.immediate(
-          <String, PackageRef>{});
+      return new Future<Map<String, PackageRef>>.value(<String, PackageRef>{});
     }
 
     var id = new PackageId(package, source, version, description);
     return solver._pubspecs.load(id).then((pubspec) {
       var dependencies = <String, PackageRef>{};
       for (var dependency in pubspec.dependencies) {
         dependencies[dependency.name] = dependency;
       }
 
       // Include dev dependencies only from the root package.
@@ skipping 169 matching lines @@
 
   /// Caches [pubspec] as the [Pubspec] for the package identified by [id].
   void cache(PackageId id, Pubspec pubspec) {
     _pubspecs[id] = pubspec;
   }
 
   /// Loads the pubspec for the package identified by [id].
   Future<Pubspec> load(PackageId id) {
     // Complete immediately if it's already cached.
     if (_pubspecs.containsKey(id)) {
-      return new Future<Pubspec>.immediate(_pubspecs[id]);
+      return new Future<Pubspec>.value(_pubspecs[id]);
     }
 
     return id.describe().then((pubspec) {
       // Cache it.
       _pubspecs[id] = pubspec;
       return pubspec;
     });
   }
 }
 
@@ skipping 217 matching lines @@
 
   String toString() {
     // TODO(nweiz): Dump descriptions to YAML when that's supported.
     return "Incompatible dependencies on '$package':\n"
         "- '$depender1' depends on it with description "
         "${json.stringify(description1)}\n"
         "- '$depender2' depends on it with description "
         "${json.stringify(description2)}";
   }
 }