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.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataType;
  
  import com.google.common.collect.ImmutableList;
  
  import java.util.List;
  
  /**
   * Abstract base class for relational expressions with a single input.
   *
   * <p>It is not required that single-input relational expressions use this
   * class as a base class. However, default implementations of methods make life
   * easier.
   */
  public abstract class SingleRel extends AbstractRelNode {
    //~ Instance fields --------------------------------------------------------
  
    protected RelNode input;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a <code>SingleRel</code>.
     *
     * @param cluster Cluster this relational expression belongs to
     * @param input   Input relational expression
     */
    protected SingleRel(
        RelOptCluster cluster,
        RelTraitSet traits,
        RelNode input) {
      super(cluster, traits);
      this.input = input;
    }
  
    //~ Methods ----------------------------------------------------------------
  
    public RelNode getInput() {
      return input;
    }
  
    @Override public List<RelNode> getInputs() {
      return ImmutableList.of(input);
    }
  
    @Override public double estimateRowCount(RelMetadataQuery mq) {
      // Not necessarily correct, but a better default than AbstractRelNode's 1.0
      return mq.getRowCount(input);
    }
  
    @Override public void childrenAccept(RelVisitor visitor) {
      visitor.visit(input, 0, this);
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .input("input", getInput());
    }
  
    @Override public void replaceInput(
        int ordinalInParent,
        RelNode rel) {
      assert ordinalInParent == 0;
      this.input = rel;
      recomputeDigest();
    }
  
    @Override protected RelDataType deriveRowType() {
      return input.getRowType();
    }
  }
  