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.tools;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptRule;
  import org.apache.calcite.plan.RelOptSchema;
  import org.apache.calcite.rel.core.RelFactories;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** A partially-created RelBuilder.
   *
   * <p>Add a cluster, and optionally a schema,
   * when you want to create a builder.
   *
   * <p>A {@code ProtoRelBuilder} can be shared among queries, and thus can
   * be inside a {@link RelOptRule}. It is a nice way to encapsulate the policy
   * that this particular rule instance should create {@code DrillFilter}
   * and {@code DrillProject} versus {@code HiveFilter} and {@code HiveProject}.
   *
   * @see RelFactories#LOGICAL_BUILDER
   */
  public interface RelBuilderFactory {
    /** Creates a RelBuilder. */
    RelBuilder create(RelOptCluster cluster, @Nullable RelOptSchema schema);
  }
  