    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}