    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005// http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.plastic;
    014
    015/**
    016 * A {@link FieldConduit} is an object that effectively <em>replaces</em> the field in the instantiated object.
    017 * All reads and writes of the field are replaced with invocations on the conduit. Once a field's access is replaced
    018 * with a conduit, the field itself is no longer used. The conduit will even see initializations of the field.
    019 *
    020 * In Aspect Oriented Programming terms, a FieldConduit allows you to advise read and write access to the field.
    021 *
    022 * If a field has both a FieldConduit and a {@link FieldHandle}, then the methods of the FieldHandle will be connected
    023 * to the methods of the FieldConduit.
    024 */
    025public interface FieldConduit<T>
    026{
    027    /**
    028     * Invoked when the field is read.
    029     *
    030     * @param instance
    031     *            the instance containing the field
    032     * @param context
    033     *            (see {@link ClassInstantiator#with(Class, Object)})
    034     */
    035    T get(Object instance, InstanceContext context);
    036
    037    /**
    038     * Invoked when the field's value is updated.
    039     *
    040     * @param instance
    041     *            the instance containing the field
    042     * @param context
    043     *            (see {@link ClassInstantiator#with(Class, Object)})
    044     * @param newValue
    045     *            value assigned to the field
    046     */
    047    void set(Object instance, InstanceContext context, T newValue);
    048}