| // Copyright (c) 2014, 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. |
| |
| library barback.transformer.declaring_aggregate_transformer; |
| |
| import 'declaring_aggregate_transform.dart'; |
| |
| /// An interface for [Transformer]s that can cheaply figure out which assets |
| /// they'll emit without doing the work of actually creating those assets. |
| /// |
| /// If a transformer implements this interface, that allows barback to perform |
| /// optimizations to make the asset graph work more smoothly. |
| abstract class DeclaringAggregateTransformer { |
| /// Declare which assets would be emitted for the primary input ids specified |
| /// by [transform]. |
| /// |
| /// This works a little like [AggregateTransformer.apply], with two main |
| /// differences. First, instead of having access to the primary inputs' |
| /// contents, it only has access to their ids. Second, instead of emitting |
| /// [Asset]s, it just emits [AssetId]s through [transform.addOutputId]. |
| /// |
| /// If this does asynchronous work, it should return a [Future] that completes |
| /// once it's finished. |
| /// |
| /// This may complete before [DeclaringAggregateTransform.primaryIds] stream |
| /// is closed. For example, it may know that each key will only have two |
| /// inputs associated with it, and so use `transform.primaryIds.take(2)` to |
| /// access only those inputs' ids. |
| declareOutputs(DeclaringAggregateTransform transform); |
| } |