content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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.apache.calcite.materialize;
  
  import org.apache.calcite.util.mapping.IntPair;
  
  import com.google.common.collect.ImmutableList;
  
  import java.util.List;
  
  import static java.util.Objects.requireNonNull;
  
  /** Non-root node in a {@link Lattice}. */
  public class LatticeChildNode extends LatticeNode {
    public final LatticeNode parent;
    public final ImmutableList<IntPair> link;
  
    LatticeChildNode(LatticeSpace space, LatticeNode parent,
        MutableNode mutableNode) {
      super(space, parent, mutableNode);
      this.parent = requireNonNull(parent, "parent");
      this.link = ImmutableList.copyOf(requireNonNull(mutableNode.step, "step").keys);
    }
  
    @Override void use(List<LatticeNode> usedNodes) {
      if (!usedNodes.contains(this)) {
        parent.use(usedNodes);
        usedNodes.add(this);
      }
    }
  }
  