001    // Copyright 2011 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.plastic;
016    
017    /**
018     * Provides an indirect, or computed, value. This is used for certain
019     * kinds of injection, where the exact value to be injected must be computed
020     * for each <em>instance</em> being instantiated, rather than for the
021     * class as a whole.
022     * 
023     * @see PlasticField#injectComputed(ComputedValue)
024     */
025    public interface ComputedValue<T>
026    {
027        /**
028         * Computes or otherwise provides the value, given the instance's context.
029         */
030        T get(InstanceContext context);
031    }