/*
 * ElementMapUnion.java March 2011
 *
 * Copyright (C) 2011, Niall Gallagher <niallg@users.sf.net>
 *
 * 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 org.simpleframework.xml;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * The <code>ElementMapUnion</code> annotation is used to describe a 
 * field or method that can dynamically match a schema class. Each union
 * can have a number of different XML class schemas matched based on
 * an XML element name or the instance type. Here a map of element 
 * map annotations can be declared. Each annotation expresses the types
 * the map can accept. Taking the declaration below, if the annotation 
 * is inline, the map can take a number of varying types all determined
 * from the XML element name.
 * <pre>
 * 
 *    &#64;ElementMapUnion({
 *       &#64;ElementMap(entry="x", inline=true, valueType=X.class),
 *       &#64;ElementMap(entry="y", inline=true, valueType=Y.class),
 *       &#64;ElementMap(entry="z", inline=true, valueType=Z.class)               
 *    })
 *    private Map&lt;String, Code&gt; codes;
 *    
 * </pre>
 * For the above definition the map field can take any of the declared
 * types. On deserialization the name of the element will determine the
 * type that is instantiated and inserted in to the map. When the map
 * is serialized the list entry instance type will determine the name 
 * of the element the instance will serialized as. This provides a 
 * useful means of consume more complicated sources. 
 * 
 * @author Niall Gallagher
 * 
 * @see org.simpleframework.xml.ElementMap
 */
@Retention(RetentionPolicy.RUNTIME)
public @interface ElementMapUnion {
   
   /**
    * This provides the <code>ElementMap</code> annotations that have 
    * been defined for this union. Each element map describes the 
    * XML class schema to use and the name of the XML element. This 
    * allows the serialization process to determine which elements
    * map to the defined types. Also, the types define how the XML
    * is generated for a given instance.     
    * 
    * @return the element maps defined for the union declaration
    */ 
   public ElementMap[] value();
}
