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
015package org.apache.tapestry5.plastic;
016
017/**
018 * A {@link FieldConduit} is an object that effectively <em>replaces</em> the field in the instantiated object.
019 * All reads and writes of the field are replaced with invocations on the conduit. Once a field's access is replaced
020 * with a conduit, the field itself is no longer used. The conduit will even see initializations of the field.
021 * <p>
022 * In Aspect Oriented Programming terms, a FieldConduit allows you to advise read and write access to the field.
023 * <p>
024 * If a field has both a FieldConduit and a {@link FieldHandle}, then the methods of the FieldHandle will be connected
025 * to the methods of the FieldConduit.
026 */
027public interface FieldConduit<T>
028{
029    /**
030     * Invoked when the field is read.
031     * 
032     * @param instance
033     *            the instance containing the field
034     * @param context
035     *            (see {@link ClassInstantiator#with(Class, Object)})
036     */
037    T get(Object instance, InstanceContext context);
038
039    /**
040     * Invoked when the field's value is updated.
041     * 
042     * @param instance
043     *            the instance containing the field
044     * @param context
045     *            (see {@link ClassInstantiator#with(Class, Object)})
046     * @param newValue
047     *            value assigned to the field
048     */
049    void set(Object instance, InstanceContext context, T newValue);
050}