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.plan;
  
  import org.apache.calcite.rel.RelNode;
  
  import org.apiguardian.api.API;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.stream.Stream;
  
  /**
   * A registry of common relational expressions for a given query.
   *
   * <p>The registry is only meant to hold common expressions for a single query.
   *
   * <p>The class is not thread-safe.
   */
  @API(since = "1.41.0", status = API.Status.INTERNAL)
  public final class CommonRelExpressionRegistry {
    /**
     * A unique collection of common expressions.
     *
     * <p>The expressions may contain internal planning concepts such as {@link org.apache.calcite.plan.hep.HepRelVertex}.
     */
    private final Map<RelDigest, RelNode> rels = new HashMap<>();
  
    /**
     * Adds the specified expression to this registry.
     *
     * @param rel a relational expression to be added to the registry.
     */
    public void add(RelNode rel) {
      this.rels.put(rel.getRelDigest(), rel);
    }
  
    /**
     * Returns a stream with all expression entries.
     *
     * @return a stream with all expression entries
     */
    public Stream<RelNode> entries() {
      return rels.values().stream().map(RelOptUtil::stripAll);
    }
  }
  