Github user markhamstra commented on a diff in the pull request:
https://github.com/apache/spark/pull/993#discussion_r14847035
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala
---
@@ -0,0 +1,421 @@
+/*
+ * 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.spark.sql.catalyst.expressions.codegen
+
+import scala.language.existentials
+
+import org.apache.spark.Logging
+import org.apache.spark.sql.catalyst.expressions
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.types._
+
+/**
+ * A base class for generators of byte code that performs expression
evaluation. Includes helpers
+ * for refering to Catalyst types and building trees that perform
evaluation of individual
+ * expressions.
+ */
+abstract class CodeGenerator extends Logging {
+ import scala.reflect.runtime.{universe => ru}
+ import scala.reflect.runtime.universe._
+
+ import scala.tools.reflect.ToolBox
+
+ val toolBox = runtimeMirror(getClass.getClassLoader).mkToolBox()
+
+ val rowType = typeOf[Row]
+ val mutableRowType = typeOf[MutableRow]
+ val genericRowType = typeOf[GenericRow]
+ val genericMutableRowType = typeOf[GenericMutableRow]
+
+ val projectionType = typeOf[Projection]
+ val mutableProjectionType = typeOf[MutableProjection]
+
+ private val curId = new java.util.concurrent.atomic.AtomicInteger()
+ private val javaSeperator = "$"
+
+ /**
+ * Returns a term name that is unique within this instance of a
`CodeGenerator`.
+ *
+ * (Since we aren't in a macro context we do not seem to have access to
the built in `freshName`
+ * function.)
+ */
+ protected def freshName(prefix: String): TermName = {
+ newTermName(s"$prefix$javaSeperator${curId.getAndIncrement}")
+ }
+
+ /**
+ * Scala ASTs for evaluating an [[Expression]] given a [[Row]] of input.
+ *
+ * @param code The sequence of statements required to evaluate the
expression.
+ * @param nullTerm A term that holds a boolean value representing
whether the expression evaluated
+ * to null.
+ * @param primitiveTerm A term for a possible primitive value of the
result of the evaluation. Not
+ * valid if `nullTerm` is set to `false`.
+ * @param objectTerm An possibly boxed version of the result of
evaluating this expression.
+ */
+ protected case class EvaluatedExpression(
+ code: Seq[Tree],
+ nullTerm: TermName,
+ primitiveTerm: TermName,
+ objectTerm: TermName)
+
+ /**
+ * Given an expression tree returns the code required to determine both
if the result is NULL
+ * as well as the code required to compute the value.
+ */
+ def expressionEvaluator(e: Expression): EvaluatedExpression = {
+ val primitiveTerm = freshName("primitiveTerm")
+ val nullTerm = freshName("nullTerm")
+ val objectTerm = freshName("objectTerm")
+
+ implicit class Evaluate1(e: Expression) {
+ def castOrNull(f: TermName => Tree, dataType: DataType): Seq[Tree] =
{
+ val eval = expressionEvaluator(e)
+ eval.code ++
+ q"""
+ val $nullTerm = ${eval.nullTerm}
+ val $primitiveTerm =
+ if($nullTerm)
+ ${defaultPrimitive(dataType)}
+ else
+ ${f(eval.primitiveTerm)}
+ """.children
--- End diff --
Is this really the way we want to format `q"""`? To my eye, it would be
much more readable as:
```scala
q"""
val $nullTerm = ${eval1.nullTerm} || ${eval2.nullTerm}
val $primitiveTerm: ${termForType(resultType)} =
if($nullTerm) {
${defaultPrimitive(resultType)}
} else {
$resultCode.asInstanceOf[${termForType(resultType)}]
}
""".children : Seq[Tree]
```
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