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.rel;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.runtime.FlatLists;
  
  import java.util.List;
  
  /**
   * Abstract base class for relational expressions with a two inputs.
   *
   * <p>It is not required that two-input relational expressions use this
   * class as a base class. However, default implementations of methods make life
   * easier.
   */
  public abstract class BiRel extends AbstractRelNode {
    protected RelNode left;
    protected RelNode right;
  
    protected BiRel(
        RelOptCluster cluster, RelTraitSet traitSet, RelNode left,
        RelNode right) {
      super(cluster, traitSet);
      this.left = left;
      this.right = right;
    }
  
    @Override public void childrenAccept(RelVisitor visitor) {
      visitor.visit(left, 0, this);
      visitor.visit(right, 1, this);
    }
  
    @Override public List<RelNode> getInputs() {
      return FlatLists.of(left, right);
    }
  
    public RelNode getLeft() {
      return left;
    }
  
    public RelNode getRight() {
      return right;
    }
  
    @Override public void replaceInput(
        int ordinalInParent,
        RelNode p) {
      switch (ordinalInParent) {
      case 0:
        this.left = p;
        break;
      case 1:
        this.right = p;
        break;
      default:
        throw new IndexOutOfBoundsException("Input " + ordinalInParent);
      }
      recomputeDigest();
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .input("left", left)
          .input("right", right);
    }
  }
  