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.activemq.filter.function;
  
  import org.apache.activemq.filter.FunctionCallExpression;
  import org.apache.activemq.filter.MessageEvaluationContext;
  
  /**
   * Interface required for objects that will be registered as functions for use in selectors.  Handles parse-
   * time and evaluation-time operations.
   */
  public interface FilterFunction {
      /**
       * Check whether the function, as it is used, is valid.  Checking arguments here will return errors
       * to clients at the time invalid selectors are initially specified, rather than waiting until the selector is
       * applied to a message.
       *
       * @param expr - the full expression of the function call, as used.
       * @return true - if the function call is valid; false - otherwise.
       */
      public boolean isValid(FunctionCallExpression expr);
  
      /**
       * Determine whether the function, as it will be called, returns a boolean value.  Called during
       * expression parsing after the full expression for the function call, including its arguments, has
       * been parsed.  This allows functions with variable return types to function as boolean expressions in
       * selectors without sacrificing parse-time checking.
       *
       * @param expr - the full expression of the function call, as used.
       * @return true - if the function returns a boolean value for its use in the given expression;
       * false - otherwise.
       */
      public boolean returnsBoolean(FunctionCallExpression expr);
  
  
      /**
       * Evaluate the function call in the given context.  The arguments must be evaluated, as-needed, by the
       * function.  Note that boolean expressions must return Boolean objects.
       *
       * @param expr - the full expression of the function call, as used.
       * @param message - the context within which to evaluate the call.
       */
      public Object evaluate(FunctionCallExpression expr, MessageEvaluationContext message)
              throws jakarta.jms.JMSException;
  }
  
  