/*
 * @(#)$Id: ElementExp.java,v 1.8 2001/06/15 03:24:21 Bear Exp $
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */
package com.sun.msv.grammar;

/**
 * Element declaration.
 * 
 * For RELAX, this is a base implementation of 'elementRule' declaration.
 * For TREX, this is a base implementation of 'element' pattern.
 * 
 * Each grammar must/can provide only one concrete implementation.
 * Therefore, they cannot override visit method.
 * 
 * <p>
 * This class can be extended.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public abstract class ElementExp extends Expression implements NameClassAndExpression {
	/** content model of this element declaration. */
	public Expression contentModel;
	public final Expression getContentModel() { return contentModel; }
	
	/** a flag that indicates undeclared attributes should be ignored. */
	public boolean ignoreUndeclaredAttributes;
	
	/** obtains a constraint over tag name.
	 * 
	 * ElementExp is cannot be shared because NameClass has to be mutable
	 * to absorb the difference of RELAX and TREX.
	 * 
	 * In case of TREX, name class will be determined when parsing ElementExp itself.
	 * Thus effectively it's immutable.
	 * 
	 * In case of RELAX, name class will be determined when its corresponding Clause
	 * object is parsed. 
	 */
	abstract public NameClass getNameClass();
	
	public ElementExp( Expression contentModel, boolean ignoreUndeclaredAttributes ) {
		// since ElementExp is not unified, no two ElementExp objects are considered equal.
		// therefore essentially any value can be used as hash code.
		// that's why this code works even when content model may be changed later.
		super( hashCode( contentModel, HASHCODE_ELEMENT ) );
		this.contentModel = contentModel;
		this.ignoreUndeclaredAttributes = ignoreUndeclaredAttributes;
	}

	public final boolean equals( Object o ) {
		return this==o;
	}

	public final Object visit( ExpressionVisitor visitor )					{ return visitor.onElement(this); }
	public final Expression visit( ExpressionVisitorExpression visitor )	{ return visitor.onElement(this); }
	public final boolean visit( ExpressionVisitorBoolean visitor )			{ return visitor.onElement(this); }
	public final void visit( ExpressionVisitorVoid visitor )				{ visitor.onElement(this); }
	
	protected final boolean calcEpsilonReducibility()
	{ return false; }
}