make case-class⇄csv-row conversion robust to public fields

build.sbt

@@ -1,2 +1,4 @@
 name := "string-utils"
-version := "1.0.0"
+version := "1.1.0"
+
+libraryDependencies += "org.scala-lang" % "scala-reflect" % scalaVersion.value

src/main/scala/org/hammerlab/csv/CaseClassUtil.scala

@@ -0,0 +1,11 @@
+package org.hammerlab.csv
+
+import scala.reflect.runtime.universe._
+
+object CaseClassUtil {
+  // cf. http://stackoverflow.com/a/16079804/544236
+  def methodNames[T <: Product: TypeTag]: List[String] =
+    typeOf[T].members.sorted.collect {
+      case m: MethodSymbol if m.isCaseAccessor => m
+    } map(_.name.toString)
+}

src/main/scala/org/hammerlab/csv/ProductsToCSV.scala

@@ -1,37 +1,24 @@
 package org.hammerlab.csv
 
+import org.hammerlab.csv.CaseClassUtil.methodNames
 import org.hammerlab.csv.ProductToCSVRow._
 
-import scala.reflect.ClassTag
+import scala.reflect.runtime.universe.TypeTag
+
+class ProductsToCSV[T <: Product: TypeTag](products: Iterator[T]) {
 
-class ProductsToCSV[T <: Product: ClassTag](products: Iterator[T]) {
   def toCSV(includeHeaderLine: Boolean = true): Iterator[String] =
     if (includeHeaderLine) {
-      val (clazz, firstOpt) =
-        if (products.hasNext) {
-          val first = products.next()
-          (first.getClass, Some(first))
-        } else {
-          val ctag = implicitly[reflect.ClassTag[T]]
-          (ctag.runtimeClass.asInstanceOf[Class[T]], None)
-        }
 
-      val headerLine =
-        clazz
-          .getDeclaredFields
-          .map(_.getName)
-          .filterNot(_ == "$outer")  // Field added on case classes nested inside another class.
-          .mkString(",")
+      val headerLine = methodNames[T].mkString(",")
 
-      Iterator(headerLine) ++
-        firstOpt.map(_.toCSV).iterator ++
-        toCSV(includeHeaderLine = false)
+      Iterator(headerLine) ++ toCSV(includeHeaderLine = false)
     } else
       products.map(_.toCSV)
 }
 
 object ProductsToCSV {
-  implicit def apply[T <: Product: ClassTag](products: Iterator[T]): ProductsToCSV[T] = new ProductsToCSV(products)
-  implicit def apply[T <: Product: ClassTag](products: Iterable[T]): ProductsToCSV[T] = new ProductsToCSV(products.iterator)
-  implicit def apply[T <: Product: ClassTag](products: Array[T]): ProductsToCSV[T] = new ProductsToCSV(products.iterator)
+  implicit def apply[T <: Product: TypeTag](products: Iterator[T]): ProductsToCSV[T] = new ProductsToCSV(products)
+  implicit def apply[T <: Product: TypeTag](products: Iterable[T]): ProductsToCSV[T] = new ProductsToCSV(products.iterator)
+  implicit def apply[T <: Product: TypeTag](products: Array[T]): ProductsToCSV[T] = new ProductsToCSV(products.iterator)
 }

src/test/scala/org/hammerlab/csv/ProductsToCSVTest.scala

@@ -9,7 +9,9 @@ class ProductsToCSVTest
     with Matchers {
 
   // cf. http://stackoverflow.com/questions/30271823/converting-a-case-class-to-csv-in-scala
-  case class Person(name: String, age: Int, address: Option[String])
+  case class Person(name: String, age: Int, address: Option[String]) {
+    val foo: Int = age * age
+  }
 
   test("people") {
     val ppl =