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A federation engine for virtually integrating SPARQL endpoints

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/*******************************************************************************
 * Copyright (c) 2024 Eclipse RDF4J contributors.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *******************************************************************************/
package org.eclipse.rdf4j.federated.algebra;

import org.eclipse.rdf4j.query.algebra.AbstractQueryModelNode;
import org.eclipse.rdf4j.query.algebra.QueryModelNode;
import org.eclipse.rdf4j.query.algebra.QueryModelVisitor;

/**
 * An artificial holder node serving as parent holder to allow replacement.
 */
public class HolderNode extends AbstractQueryModelNode {

	private static final long serialVersionUID = -4689963986499825771L;
	private QueryModelNode child;

	public HolderNode(QueryModelNode child) {
		super();
		setChild(child);
	}

	public void setChild(QueryModelNode child) {
		this.child = child;
		this.child.setParentNode(this);
	}

	@Override
	public  void visitChildren(QueryModelVisitor visitor) throws X {
		child.visit(visitor);
	}

	@Override
	public  void visit(QueryModelVisitor visitor) throws X {
		visitor.meetOther(this);
	}

	@Override
	public void replaceChildNode(QueryModelNode current, QueryModelNode replacement) {
		if (child.equals(current)) {
			setChild(replacement);

		}
	}
}