dynamic版 ?演算子 (なぜかimplicit conversionされないのと、dynamicでフィールド名を可変にしても {def value: B}という構造的部分型の部分が可変にならないので詰んだ・・・(◞‸◟)

build.sbt

name := "OptionValueAccessor"

version := "1.0"

scalaVersion := "2.11.6"

libraryDependencies += "org.scala-lang" % "scala-reflect" % scalaVersion.value
scalacOptions += "-language:dynamics"

OptionValueAccessor.scala

package OptionValueAccessor

import scala.language.experimental.macros
import scala.reflect.macros.whitebox

object OptionValueAccessor {

  implicit class OptValue[A, B](val self: Option[A])(implicit ev: A <:< {def value: B}) extends Dynamic {
    def selectDynamic(name: String): Option[B] = macro Impl.Opt.selectDynamicImpl[B]
  }

  implicit class OptOpt[A, B](val self: Option[Option[A]])(implicit ev: A <:< {def value: B}) {
    def selectDynamic(name: String): Option[B] = macro Impl.OptOpt.selectDynamicImpl[B]
  }

  object Impl {
    object Opt {
      def selectDynamicImpl[B: c.WeakTypeTag](c: whitebox.Context)(name: c.Expr[String]): c.Expr[Option[B]] = {
        import c.universe._

        val nameStr: String = name.tree match {
          case pq"${n: String}" if n.startsWith("_") => n.drop(1)
          case _                                     => c.abort(c.enclosingPosition, s"#$name not found.")
        }
        c.Expr[Option[B]](q"${c.prefix}.self.map {_.${TermName(nameStr)}}")
      }
    }

    object OptOpt {
      def selectDynamicImpl[B: c.WeakTypeTag](c: whitebox.Context)(name: c.Expr[String]): c.Expr[Option[B]] = {
        import c.universe._
        val nameStr: String = name.tree match {
          case pq"${n: String}" if n.startsWith("_") => n.drop(1)
          case _                                     => c.abort(c.enclosingPosition, s"#$name not found.")
        }
        c.Expr[Option[B]](q"${c.prefix}.self.flatten.map {_.${TermName(nameStr)}}")
      }
    }
  }
}

OptionValueAccessorTest.scala

package OptionValueAccessor

import OptionValueAccessor._

object OptionValueAccessorTest {

  case class A(value: Int)
  case class B(value: Option[A])
  case class C(value: Option[B])
  case class D(value: Option[C])
  case class E(value: D)

  def main(args: Array[String]): Unit = {
    val edcba: Option[E] = Some(E(D(Some(C(Some(B(Some(A(1)))))))))
    println(
      edcba
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
    )

    val edcbnone = Some(E(D(None)))
    println(
      edcbnone
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
        .selectDynamic("_value")
    )
  }
}