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.rex;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.SqlKind;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  import java.util.Objects;
  
  import static com.google.common.base.Preconditions.checkArgument;
  
  /**
   * Local variable.
   *
   * <p>Identity is based upon type and index. We want multiple references to the
   * same slot in the same context to be equal. A side effect is that references
   * to slots in different contexts which happen to have the same index and type
   * will be considered equal; this is not desired, but not too damaging, because
   * of the immutability.
   *
   * <p>Variables are immutable.
   */
  public class RexLocalRef extends RexSlot {
    //~ Static fields/initializers ---------------------------------------------
  
    // array of common names, to reduce memory allocations
    @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
    private static final List<String> NAMES = new SelfPopulatingList("$t", 30);
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a local variable.
     *
     * @param index Index of the field in the underlying row type
     * @param type  Type of the column
     */
    public RexLocalRef(int index, RelDataType type) {
      super(createName(index), index, type);
      checkArgument(index >= 0);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public SqlKind getKind() {
      return SqlKind.LOCAL_REF;
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof RexLocalRef
          && Objects.equals(this.type, ((RexLocalRef) obj).type)
          && this.index == ((RexLocalRef) obj).index;
    }
  
    @Override public int hashCode() {
      return Objects.hash(type, index);
    }
  
    @Override public <R> R accept(RexVisitor<R> visitor) {
      return visitor.visitLocalRef(this);
    }
  
    @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
      return visitor.visitLocalRef(this, arg);
    }
  
    private static String createName(int index) {
      return NAMES.get(index);
    }
  }
  