| // 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.impala.rewrite; |
| |
| import org.apache.impala.analysis.Analyzer; |
| import org.apache.impala.analysis.Expr; |
| import org.apache.impala.common.AnalysisException; |
| |
| /** |
| * Base class for all Expr rewrite rules. A rule is free to modify Exprs in place, |
| * but must return a different Expr object if any modifications were made. |
| * An ExprRewriteRule is intended to apply its transformation on a single Expr and not |
| * recursively on all its children. The recursive and repeated application of |
| * ExprRewriteRules is driven by an ExprRewriter. |
| * An ExprRewriteRule should preserve the type of the transformed expression to avoid |
| * having to re-analyze its parent (if any). This behavior guarantees that the Expr |
| * tree remains valid even if arbitrary subexpressions are transformed. It also means |
| * that the transformed expression may have a wider type than necessary. Callers are |
| * free to reset() and analyze() the result if they desire the minimal type. |
| */ |
| public interface ExprRewriteRule { |
| /** |
| * Applies this rewrite rule to the given analyzed Expr. Returns the transformed and |
| * analyzed Expr or the original unmodified Expr if no changes were made. If any |
| * changes were made, the transformed Expr is guaranteed to be a different Expr object, |
| * so callers can rely on object reference comparison for change detection. |
| */ |
| public abstract Expr apply(Expr expr, Analyzer analyzer) throws AnalysisException; |
| } |