[SPARK-8349] [SQL] Use expression constructors (rather than apply) in FunctionRegistry

Author: Reynold Xin <rxin@databricks.com>

Closes #6806 from rxin/gs and squashes the following commits:

ed1aebb [Reynold Xin] Fixed style.
c7fc3e6 [Reynold Xin] [SPARK-8349][SQL] Use expression constructors (rather than apply) in FunctionRegistry

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -158,27 +158,23 @@ object FunctionRegistry {
   /** See usage above. */
   private def expression[T <: Expression](name: String)
       (implicit tag: ClassTag[T]): (String, FunctionBuilder) = {
-    // Use the companion class to find apply methods.
-    val objectClass = Class.forName(tag.runtimeClass.getName + "$")
-    val companionObj = objectClass.getDeclaredField("MODULE$").get(null)
-
-    // See if we can find an apply that accepts Seq[Expression]
-    val varargApply = Try(objectClass.getDeclaredMethod("apply", classOf[Seq[_]])).toOption
 
+    // See if we can find a constructor that accepts Seq[Expression]
+    val varargCtor = Try(tag.runtimeClass.getDeclaredConstructor(classOf[Seq[_]])).toOption
     val builder = (expressions: Seq[Expression]) => {
-      if (varargApply.isDefined) {
+      if (varargCtor.isDefined) {
         // If there is an apply method that accepts Seq[Expression], use that one.
-        varargApply.get.invoke(companionObj, expressions).asInstanceOf[Expression]
+        varargCtor.get.newInstance(expressions).asInstanceOf[Expression]
       } else {
-        // Otherwise, find an apply method that matches the number of arguments, and use that.
+        // Otherwise, find an ctor method that matches the number of arguments, and use that.
         val params = Seq.fill(expressions.size)(classOf[Expression])
-        val f = Try(objectClass.getDeclaredMethod("apply", params : _*)) match {
+        val f = Try(tag.runtimeClass.getDeclaredConstructor(params : _*)) match {
           case Success(e) =>
             e
           case Failure(e) =>
             throw new AnalysisException(s"Invalid number of arguments for function $name")
         }
-        f.invoke(companionObj, expressions : _*).asInstanceOf[Expression]
+        f.newInstance(expressions : _*).asInstanceOf[Expression]
       }
     }
     (name, builder)

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala

@@ -27,8 +27,7 @@ import org.apache.spark.sql.types._
 /**
  * If an expression wants to be exposed in the function registry (so users can call it with
  * "name(arguments...)", the concrete implementation must be a case class whose constructor
- * arguments are all Expressions types. In addition, if it needs to support more than one
- * constructor, define those constructors explicitly as apply methods in the companion object.
+ * arguments are all Expressions types.
  *
  * See [[Substring]] for an example.
  */

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/random.scala

@@ -49,12 +49,10 @@ abstract class RDG(seed: Long) extends LeafExpression with Serializable {
 /** Generate a random column with i.i.d. uniformly distributed values in [0, 1). */
 case class Rand(seed: Long) extends RDG(seed) {
   override def eval(input: InternalRow): Double = rng.nextDouble()
-}
 
-object Rand {
-  def apply(): Rand = apply(Utils.random.nextLong())
+  def this() = this(Utils.random.nextLong())
 
-  def apply(seed: Expression): Rand = apply(seed match {
+  def this(seed: Expression) = this(seed match {
     case IntegerLiteral(s) => s
     case _ => throw new AnalysisException("Input argument to rand must be an integer literal.")
   })
@@ -63,12 +61,10 @@ object Rand {
 /** Generate a random column with i.i.d. gaussian random distribution. */
 case class Randn(seed: Long) extends RDG(seed) {
   override def eval(input: InternalRow): Double = rng.nextGaussian()
-}
 
-object Randn {
-  def apply(): Randn = apply(Utils.random.nextLong())
+  def this() = this(Utils.random.nextLong())
 
-  def apply(seed: Expression): Randn = apply(seed match {
+  def this(seed: Expression) = this(seed match {
     case IntegerLiteral(s) => s
     case _ => throw new AnalysisException("Input argument to rand must be an integer literal.")
   })

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala

@@ -20,6 +20,7 @@ package org.apache.spark.sql.catalyst.expressions
 import java.util.regex.Pattern
 
 import org.apache.spark.sql.catalyst.analysis.UnresolvedException
+import org.apache.spark.sql.catalyst.expressions.Substring
 import org.apache.spark.sql.catalyst.expressions.codegen._
 import org.apache.spark.sql.types._
 import org.apache.spark.unsafe.types.UTF8String
@@ -225,6 +226,10 @@ case class EndsWith(left: Expression, right: Expression)
 case class Substring(str: Expression, pos: Expression, len: Expression)
   extends Expression with ExpectsInputTypes {
 
+  def this(str: Expression, pos: Expression) = {
+    this(str, pos, Literal(Integer.MAX_VALUE))
+  }
+
   override def foldable: Boolean = str.foldable && pos.foldable && len.foldable
 
   override  def nullable: Boolean = str.nullable || pos.nullable || len.nullable
@@ -290,12 +295,6 @@ case class Substring(str: Expression, pos: Expression, len: Expression)
   }
 }
 
-object Substring {
-  def apply(str: Expression, pos: Expression): Substring = {
-    apply(str, pos, Literal(Integer.MAX_VALUE))
-  }
-}
-
 /**
  * A function that return the length of the given string expression.
  */

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -344,11 +344,11 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] {
    * @param newArgs the new product arguments.
    */
   def makeCopy(newArgs: Array[AnyRef]): this.type = attachTree(this, "makeCopy") {
-    val defaultCtor =
-      getClass.getConstructors
-        .find(_.getParameterTypes.size != 0)
-        .headOption
-        .getOrElse(sys.error(s"No valid constructor for $nodeName"))
+    val ctors = getClass.getConstructors.filter(_.getParameterTypes.size != 0)
+    if (ctors.isEmpty) {
+      sys.error(s"No valid constructor for $nodeName")
+    }
+    val defaultCtor = ctors.maxBy(_.getParameterTypes.size)
 
     try {
       CurrentOrigin.withOrigin(origin) {