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.linq4j.tree;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Represents a constant null of unknown type
   * Java allows type inference for such nulls, thus "null" cannot always be
   * replaced to (Object)null and vise versa.
   *
   * <p>{@code ConstantExpression(null, Object.class)} is not equal to
   * {@code ConstantUntypedNull} However, optimizers might treat all the nulls
   * equal (e.g. in case of comparison).
   */
  public class ConstantUntypedNull extends ConstantExpression {
    public static final ConstantExpression INSTANCE = new ConstantUntypedNull();
  
    private ConstantUntypedNull() {
      super(Object.class, null);
    }
  
    @Override void accept(ExpressionWriter writer, int lprec, int rprec) {
      writer.append("null");
    }
  
    @Override public boolean equals(@Nullable Object o) {
      return o == INSTANCE;
    }
  
    @Override public int hashCode() {
      return ConstantUntypedNull.class.hashCode();
    }
  }
  