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 java.util.AbstractList;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  /**
   * Abstract base class for {@link RexInputRef}, {@link RexLocalRef} and {@link RexLambdaRef}.
   */
  public abstract class RexSlot extends RexVariable {
    //~ Instance fields --------------------------------------------------------
  
    protected final int index;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a slot.
     *
     * @param index Index of the field in the underlying rowtype
     * @param type  Type of the column
     */
    protected RexSlot(
        String name,
        int index,
        RelDataType type) {
      super(name, type);
      assert index >= 0;
      this.index = index;
    }
  
    //~ Methods ----------------------------------------------------------------
  
    public int getIndex() {
      return index;
    }
  
    /**
     * Thread-safe list that populates itself if you make a reference beyond
     * the end of the list. Useful if you are using the same entries repeatedly.
     * Once populated, accesses are very efficient.
     */
    protected static class SelfPopulatingList
        extends CopyOnWriteArrayList<String> {
      private final String prefix;
  
      SelfPopulatingList(final String prefix, final int initialSize) {
        super(fromTo(prefix, 0, initialSize));
        this.prefix = prefix;
      }
  
      private static AbstractList<String> fromTo(
          final String prefix,
          final int start,
          final int end) {
        return new AbstractList<String>() {
          @Override public String get(int index) {
            return prefix + (index + start);
          }
  
          @Override public int size() {
            return end - start;
          }
        };
      }
  
      @Override public String get(int index) {
        for (;;) {
          try {
            return super.get(index);
          } catch (IndexOutOfBoundsException e) {
            if (index < 0) {
              throw new IllegalArgumentException();
            }
            // Double-checked locking, but safe because CopyOnWriteArrayList.array
            // is marked volatile, and size() uses array.length.
            synchronized (this) {
              final int size = size();
              if (index >= size) {
                addAll(fromTo(prefix, size, Math.max(index + 1, size * 2)));
              }
            }
          }
        }
      }
    }
  }
  