src/main/java/net/hydromatic/linq4j/expressions/Expression.java

/*
// Licensed to Julian Hyde under one or more contributor license
// agreements. See the NOTICE file distributed with this work for
// additional information regarding copyright ownership.
//
// Julian Hyde 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 net.hydromatic.linq4j.expressions;

import java.lang.reflect.Type;

/**
 * <p>Analogous to LINQ's System.Linq.Expression.</p>
 */
public abstract class Expression extends AbstractNode {

  /**
   * Creates an Expression.
   *
   * <p>The type of the expression may, at the caller's discretion, be a
   * regular class (because {@link Class} implements {@link Type}) or it may
   * be a different implementation that retains information about type
   * parameters.</p>
   *
   * @param nodeType Node type
   * @param type Type of the expression
   */
  public Expression(ExpressionType nodeType, Type type) {
    super(nodeType, type);
    assert nodeType != null;
    assert type != null;
  }

  @Override
  public String toString() {
    ExpressionWriter writer = new ExpressionWriter(true);
    accept(writer, 0, 0);
    return writer.toString();
  }

  @Override
  // More specific return type.
  public abstract Expression accept(Visitor visitor);

  /**
   * Indicates that the node can be reduced to a simpler node. If this
   * returns true, Reduce() can be called to produce the reduced form.
   */
  public boolean canReduce() {
    return false;
  }
}

// End Expression.java