Remove AbstractUnaryMathExpression and let BIN inherit UnaryExpression.

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

@@ -54,28 +54,16 @@ abstract class LeafMathExpression(c: Double, name: String)
  * @param f The math function.
  * @param name The short name of the function
  */
-abstract class AbstractUnaryMathExpression[T, U](name: String)
+abstract class UnaryMathExpression(f: Double => Double, name: String)
   extends UnaryExpression with Serializable with ExpectsInputTypes {
   self: Product =>
 
+  override def expectedChildTypes: Seq[DataType] = Seq(DoubleType)
+  override def dataType: DataType = DoubleType
   override def foldable: Boolean = child.foldable
   override def nullable: Boolean = true
   override def toString: String = s"$name($child)"
 
-  // name of function in java.lang.Math
-  def funcName: String = name.toLowerCase
-}
-
-/**
- * Base for [[AbstractUnaryMathExpression]] that accepts a Double and returns a Double.
- */
-abstract class UnaryMathExpression(f: Double => Double, name: String)
-  extends AbstractUnaryMathExpression[Double, Double](name) {
-  self: Product =>
-
-  override def expectedChildTypes: Seq[DataType] = Seq(DoubleType)
-  override def dataType: DataType = DoubleType
-
   override def eval(input: InternalRow): Any = {
     val evalE = child.eval(input)
     if (evalE == null) {
@@ -86,6 +74,9 @@ abstract class UnaryMathExpression(f: Double => Double, name: String)
     }
   }
 
+  // name of function in java.lang.Math
+  def funcName: String = name.toLowerCase
+
   override def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode): String = {
     val eval = child.gen(ctx)
     eval.code + s"""
@@ -218,11 +209,19 @@ case class ToRadians(child: Expression) extends UnaryMathExpression(math.toRadia
 }
 
 case class Bin(child: Expression)
-  extends AbstractUnaryMathExpression[Long, String]("BIN") {
+  extends UnaryExpression with Serializable with ExpectsInputTypes {
+
+  val name: String = "BIN"
+
+  override def foldable: Boolean = child.foldable
+  override def nullable: Boolean = true
+  override def toString: String = s"$name($child)"
 
   override def expectedChildTypes: Seq[DataType] = Seq(LongType)
   override def dataType: DataType = StringType
 
+  def funcName: String = name.toLowerCase
+
   override def eval(input: catalyst.InternalRow): Any = {
     val evalE = child.eval(input)
     if (evalE == null) {