src/main/java/freemarker/template/GeneralPurposeNothing.java

/*
 * Copyright (c) 2003 The Visigoth Software Society. All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Visigoth Software Society (http://www.visigoths.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
 * 4. Neither the name "FreeMarker", "Visigoth", nor any of the names of the 
 *    project contributors may be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact visigoths@visigoths.org.
 *
 * 5. Products derived from this software may not be called "FreeMarker" or "Visigoth"
 *    nor may "FreeMarker" or "Visigoth" appear in their names
 *    without prior written permission of the Visigoth Software Society.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE VISIGOTH SOFTWARE SOCIETY OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Visigoth Software Society. For more
 * information on the Visigoth Software Society, please see
 * http://www.visigoths.org/
 */

package freemarker.template;

import java.util.ArrayList;
import java.util.List;

/**
 * Singleton object representing nothing, used by ?if_exists built-in.
 * It is meant to be interpreted in the most sensible way possible in various contexts.
 * This can be returned to avoid exceptions.
 *
 * @author <a href="mailto:jon@revusky.com">Jonathan Revusky</a>
 */

final class GeneralPurposeNothing
implements TemplateBooleanModel, TemplateScalarModel, TemplateSequenceModel, TemplateHashModelEx, TemplateMethodModelEx {

    private static final TemplateModel instance = new GeneralPurposeNothing();
      
    private static final TemplateCollectionModel EMPTY_COLLECTION = new SimpleCollection(new ArrayList(0));

    private GeneralPurposeNothing() {
    }

    static TemplateModel getInstance()  {
        return instance;
    }

    public String getAsString() {
        return "";
    }

    public boolean getAsBoolean() {
        return false;
    }

    public boolean isEmpty() {
        return true;
    }

    public int size() {
        return 0;
    }

    public TemplateModel get(int i) throws TemplateModelException {
        throw new TemplateModelException("Empty list");
    }

    public TemplateModel get(String key) {
        return null;
    }

    public Object exec(List args) {
        return null;
    }
    
    public TemplateCollectionModel keys() {
        return EMPTY_COLLECTION;
    }

    public TemplateCollectionModel values() {
        return EMPTY_COLLECTION;
    }
}