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.mutable;
  
  import org.apache.calcite.rel.type.RelDataType;
  
  /** Implementation of {@link MutableRel} whose only purpose is to have a
   * child. Used as the root of a tree. */
  public class Holder extends MutableSingleRel {
    private Holder(RelDataType rowType, MutableRel input) {
      super(MutableRelType.HOLDER, rowType, input);
    }
  
    /**
     * Creates a Holder.
     *
     * @param input Input relational expression
     */
    public static Holder of(MutableRel input) {
      return new Holder(input.rowType, input);
    }
  
    @Override public StringBuilder digest(StringBuilder buf) {
      return buf.append("Holder");
    }
  
    @Override public MutableRel clone() {
      return Holder.of(input.clone());
    }
  }
  