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Google App Engine compliant variation of FreeMarker. FreeMarker is a "template engine"; a generic tool to generate text output based on templates.

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/*
 * Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
 * 
 * Licensed 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.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.
 */

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;
    }
}