Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/819#discussion_r113835921
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/DrillStringCastFuncHolder.java
---
@@ -0,0 +1,56 @@
+/*
+ * 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.expr.fn;
+
+import com.google.common.primitives.Ints;
+import org.apache.drill.common.expression.LogicalExpression;
+import org.apache.drill.common.expression.ValueExpressions;
+import org.apache.drill.common.types.TypeProtos;
+
+import java.util.List;
+
+/**
+ * Function holder for functions with function scope set as
+ * {@link
org.apache.drill.exec.expr.annotations.FunctionTemplate.FunctionScope#STRING_CAST}.
+ */
+public class DrillStringCastFuncHolder extends DrillSimpleFuncHolder {
+
+ public DrillStringCastFuncHolder(FunctionAttributes functionAttributes,
FunctionInitializer initializer) {
+ super(functionAttributes, initializer);
+ }
+
+ /**
+ * Defines function return type and sets cast length as type precision
+ * if cast length is simple long expression.
--- End diff --
Why just long?
In general, if we know the input type, we know the maximum output string
width for that type (for all types except, say, Map, List, Repeated,
VarBinary.) In many cases, the actual string won't be the maximum, but at least
we set an upper bound far less than the default of 64K.
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