move selectNested to FlattenedDataFrame

core/src/main/scala/ste/selector.scala

@@ -212,9 +212,9 @@ trait SelectorImplicits {
 }
 
 object DFUtils {
-  def selectNested[A](df: DataFrame)(implicit s: StructTypeSelector[A]): DataFrame = s.select(df, None)
-
   implicit class FlattenedDataFrame(df: DataFrame) {
-    def asNested[A : Encoder : StructTypeSelector]: Dataset[A] = selectNested(df).as[A]
+    def asNested[A : Encoder : StructTypeSelector]: Dataset[A] = selectNested.as[A]
+
+    def selectNested[A](implicit s: StructTypeSelector[A]): DataFrame = s.select(df, None)
   }
 }

core/src/test/scala/ste/StructTypeSelectorSpec.scala

@@ -37,7 +37,7 @@ class StructSelectorSpec extends FlatSpec with Matchers {
     import spark.implicits._
     val values = List((1, "a", 2, "b", 3), (4, "c", 5, "d", 6))
     val df = values.toDF(StructTypeEncoder[Bar].encode.fields.map(_.name) :_*)
-    val result = selectNested[Bar](df)
+    val result = df.selectNested[Bar]
     val expected = Array(
       Bar(Map("asd" -> Foo(1, "a"), "qwe" -> Foo(2, "b")), 3),
       Bar(Map("asd" -> Foo(4, "c"), "qwe" -> Foo(5, "d")), 6)