[GitHub] [beam] ibzib commented on a change in pull request #13593: [BEAM-10925] Convert ScalarFn to Method.

[GitBox <gi...@apache.org>]

ibzib commented on a change in pull request #13593:
URL: https://github.com/apache/beam/pull/13593#discussion_r547413377



##########
File path: sdks/java/extensions/sql/zetasql/src/main/java/org/apache/beam/sdk/extensions/sql/zetasql/translation/impl/ScalarFnImpl.java
##########
@@ -0,0 +1,78 @@
+/*
+ * 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.beam.sdk.extensions.sql.zetasql.translation.impl;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.util.Arrays;
+import java.util.Collection;
+import org.apache.beam.sdk.extensions.sql.udf.ScalarFn;
+import org.apache.beam.sdk.util.common.ReflectHelpers;
+
+/** Implementation logic for {@link ScalarFn}. */
+public class ScalarFnImpl {
+  /**
+   * Gets the method annotated with {@link
+   * org.apache.beam.sdk.extensions.sql.udf.ScalarFn.ApplyMethod} from {@code scalarFn}.
+   *
+   * <p>There must be exactly one method annotated with {@link
+   * org.apache.beam.sdk.extensions.sql.udf.ScalarFn.ApplyMethod}, and it must be public and
+   * non-static.
+   */
+  public static Method getApplyMethod(ScalarFn scalarFn) {
+    Class<? extends ScalarFn> clazz = scalarFn.getClass();
+    Collection<Method> matches =
+        ReflectHelpers.declaredMethodsWithAnnotation(
+            ScalarFn.ApplyMethod.class, clazz, ScalarFn.class);
+
+    if (matches.isEmpty()) {
+      throw new IllegalArgumentException(
+          String.format(
+              "No method annotated with @%s found in class %s.",
+              ScalarFn.ApplyMethod.class.getSimpleName(), clazz.getName()));
+    }
+
+    // If we have at least one match, then either it should be the only match
+    // or it should be an extension of the other matches (which came from parent
+    // classes).
+    Method first = matches.iterator().next();
+    for (Method other : matches) {

Review comment:
       This is standard inheritance, it shouldn't be any surprise to the user that a child class's implementation of a method overrides a parent class.




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