Github user hsuanyi commented on a diff in the pull request: https://github.com/apache/drill/pull/397#discussion_r54955232 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/DrillCalciteSqlWrapper.java --- @@ -0,0 +1,33 @@ +/** + * 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.drill.exec.planner.sql; + +import org.apache.calcite.sql.SqlOperator; +/** + * This interface is meant for the users of the wrappers, {@link DrillCalciteSqlOperatorWrapper}, + * {@link DrillCalciteSqlFunctionWrapper} and {@link DrillCalciteSqlAggFunctionWrapper}, to access the wrapped Calcite + * {@link SqlOperator} without knowing exactly which wrapper it is. + */ +public interface DrillCalciteSqlWrapper { --- End diff -- This is unfortunately not possible. Take DrillCalciteSqlAggFunctionWrapper as an example: In order to let Calcite believe this is a SqlAggFunction, we have to claim DrillCalciteSqlAggFunctionWrapper is "extended" from SqlAggFunction. Not being able to do multi-inherentence in JAVA prevents code sharing from another base implementation
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