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.rel.type.RelDataTypeField;
  import org.apache.calcite.runtime.PairList;
  import org.apache.calcite.sql.SqlKind;
  import org.apache.calcite.util.Pair;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  /**
   * Variable which references a field of an input relational expression.
   *
   * <p>Fields of the input are 0-based. If there is more than one input, they are
   * numbered consecutively. For example, if the inputs to a join are
   *
   * <ul>
   * <li>Input #0: EMP(EMPNO, ENAME, DEPTNO) and</li>
   * <li>Input #1: DEPT(DEPTNO AS DEPTNO2, DNAME)</li>
   * </ul>
   *
   * <p>then the fields are:
   *
   * <ul>
   * <li>Field #0: EMPNO</li>
   * <li>Field #1: ENAME</li>
   * <li>Field #2: DEPTNO (from EMP)</li>
   * <li>Field #3: DEPTNO2 (from DEPT)</li>
   * <li>Field #4: DNAME</li>
   * </ul>
   *
   * <p>So <code>RexInputRef(3, Integer)</code> is the correct reference for the
   * field DEPTNO2.
   */
  public class RexInputRef extends RexSlot {
    //~ Static fields/initializers ---------------------------------------------
  
    // list of common names, to reduce memory allocations
    @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
    private static final List<String> NAMES = new SelfPopulatingList("$", 30);
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates an input variable.
     *
     * @param index Index of the field in the underlying row-type
     * @param type  Type of the column
     */
    public RexInputRef(int index, RelDataType type) {
      super(createName(index), index, type);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof RexInputRef
          && index == ((RexInputRef) obj).index;
    }
  
    @Override public int hashCode() {
      return index;
    }
  
    /**
     * Creates a reference to a given field in a row type.
     */
    public static RexInputRef of(int index, RelDataType rowType) {
      return of(index, rowType.getFieldList());
    }
  
    /**
     * Creates a reference to a given field in a list of fields.
     */
    public static RexInputRef of(int index, List<RelDataTypeField> fields) {
      return new RexInputRef(index, fields.get(index).getType());
    }
  
    /**
     * Creates a reference to a given field in a list of fields.
     */
    public static Pair<RexNode, String> of2(
        int index,
        List<RelDataTypeField> fields) {
      final RelDataTypeField field = fields.get(index);
      return Pair.of(new RexInputRef(index, field.getType()),
          field.getName());
    }
  
    /**
     * Adds to a PairList a reference to a given field in a list of fields.
     */
    public static void add2(PairList<RexNode, String> list,
        int index,
        List<RelDataTypeField> fields) {
      final RelDataTypeField field = fields.get(index);
      list.add(new RexInputRef(index, field.getType()),
          field.getName());
    }
  
    @Override public SqlKind getKind() {
      return SqlKind.INPUT_REF;
    }
  
    @Override public <R> R accept(RexVisitor<R> visitor) {
      return visitor.visitInputRef(this);
    }
  
    @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
      return visitor.visitInputRef(this, arg);
    }
  
    /**
     * Creates a name for an input reference, of the form "$index". If the index
     * is low, uses a cache of common names, to reduce gc.
     */
    public static String createName(int index) {
      return NAMES.get(index);
    }
  }
  