/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package freemarker.ext.beans;

import freemarker.template.ObjectWrapper;

Marker interface useful when used together with MethodAppearanceFineTuner and such customizer objects, to indicate that it doesn't contain reference to the ObjectWrapper (so beware with non-static inner
classes) and can be and should be used in call introspection cache keys. This also implies that you won't
create many instances of the class, rather just reuse the same (or same few) instances over and over. Furthermore,
the instances must be thread-safe. The typical pattern in which this instance should be used is like this:
static class MyMethodAppearanceFineTuner implements MethodAppearanceFineTuner, SingletonCustomizer {
     
   // This is the singleton:
   static final MyMethodAppearanceFineTuner INSTANCE = new MyMethodAppearanceFineTuner();
    
   // Private, so it can't be constructed from outside this class.
   private MyMethodAppearanceFineTuner() { }
   @Override
   public void fineTuneMethodAppearance(...) {
      // Do something here, only using the parameters and maybe some other singletons. 
      ...
   }
    
}
Since:
2.3.21/**
 * Marker interface useful when used together with {@link MethodAppearanceFineTuner} and such customizer objects, to
 * indicate that it <b>doesn't contain reference to the {@link ObjectWrapper}</b> (so beware with non-static inner
 * classes) and can be and should be used in call introspection cache keys. This also implies that you won't
 * create many instances of the class, rather just reuse the same (or same few) instances over and over. Furthermore,
 * the instances must be thread-safe. The typical pattern in which this instance should be used is like this:
 * 
 * <pre>static class MyMethodAppearanceFineTuner implements MethodAppearanceFineTuner, SingletonCustomizer {
 *      
 *    // This is the singleton:
 *    static final MyMethodAppearanceFineTuner INSTANCE = new MyMethodAppearanceFineTuner();
 *     
 *    // Private, so it can't be constructed from outside this class.
 *    private MyMethodAppearanceFineTuner() { }
 *
 *    &#64;Override
 *    public void fineTuneMethodAppearance(...) {
 *       // Do something here, only using the parameters and maybe some other singletons. 
 *       ...
 *    }
 *     
 * }</pre>
 *
 * @since 2.3.21
 */
public interface SingletonCustomizer {

}