Make Assets know their ID.

pkg/barback/lib/src/transform.dart

Index: pkg/barback/lib/src/transform.dart
diff --git a/pkg/barback/lib/src/transform.dart b/pkg/barback/lib/src/transform.dart
index 8023d0edb65818296f6200a214ea9f163af3bf0d..751973ec621ca5c74b4365f0961ae206bf97789c 100644
--- a/pkg/barback/lib/src/transform.dart
+++ b/pkg/barback/lib/src/transform.dart
@@ -18,7 +18,7 @@ import 'transform_node.dart';
 /// itself a public constructor, which would be visible to external users.
 /// Unlike the [Transform] class, this function is not exported by barback.dart.
 Transform createTransform(TransformNode node, Set<AssetNode> inputs,
-                          Map<AssetId, Asset> outputs) =>
+                          Set<Asset> outputs) =>
     new Transform._(node, inputs, outputs);
 
 /// While a [Transformer] represents a *kind* of transformation, this defines
@@ -32,7 +32,7 @@ class Transform {
   final TransformNode _node;
 
   final Set<AssetNode> _inputs;
-  final Map<AssetId, Asset> _outputs;
+  final Set<Asset> _outputs;
 
   /// Gets the ID of the primary input for this transformation.
   ///
@@ -71,9 +71,10 @@ class Transform {
     });
   }
 
-  /// Stores [output] as the output created by this transformation for asset
-  /// [id]. A transformation can output as many assets as it wants.
-  void addOutput(AssetId id, Asset output) {
-    _outputs[id] = output;
+  /// Stores [output] as the output created by this transformation.
+  ///
+  /// A transformation can output as many assets as it wants.
+  void addOutput(Asset output) {

[nweiz, 2013/07/03 20:08:25]

This should throw an error if the transformer outputs the same asset id multiple
times. A TODO is fine.

[Bob Nystrom, 2013/07/03 22:32:11]

Done.

+    _outputs.add(output);
   }
 }