斯卡拉 "reflective toolbox failed due to unresolved free type"

Question

第一次尝试使用准引号来生成新的案例类:

val universe: scala.reflect.runtime.universe.type = scala.reflect.runtime.universe
import universe._
import scala.reflect.runtime.{currentMirror => m}
import scala.tools.reflect.ToolBox
val toolbox = m.mkToolBox()

trait Father
class A extends Father {
  println("I'm A")
  val a = 0
}
class B extends Father {
  println("I'm B")
  val b = 0
}

object Produce {
  def A(): A = {
    val weakT = weakTypeOf[A]
    val genTree = q"""
      case class Son() extends $weakT {
        println("I'm alive")
      }
      Son()
      """
    val compiledCode = toolbox.eval(genTree)
    compiledCode.asInstanceOf[A]
  }
  def apply[T <: Father](): T = {
    val weakT = weakTypeOf[T]
    val genTree = q"""
      case class Son() extends $weakT {
        println("I'm alive")
      }
      Son()
      """
    val compiledCode = toolbox.eval(genTree)
    compiledCode.asInstanceOf[T]
  }
}

Produce.A()

Produce[A]()

Produce.A() 的结果：

I'm A

I'm alive

res0: A = Son()

Produce[A]() 的结果：

scala.tools.reflect.ToolBoxError: reflective toolbox failed due to unresolved free type variables: T defined by apply in :32:13 have you forgotten to use TypeTag annotations for type parameters external to a reifee? if you have troubles tracking free type variables, consider using -Xlog-free-types at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.verify(ToolBoxFactory.scala:82) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.compile(ToolBoxFactory.scala:208) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$compile.apply(ToolBoxFactory.scala:429) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$compile.apply(ToolBoxFactory.scala:422) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.liftedTree2(ToolBoxFactory.scala:355) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.apply(ToolBoxFactory.scala:355) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.compile(ToolBoxFactory.scala:422) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.eval(ToolBoxFactory.scala:444) at Produce$.apply(:40) ... 34 elided

Answer 1

根据@Andreas Jim-Hartmann 的建议，添加了“: TypeTag”（请参阅下面的评论），现在此代码适用于通用和特定：

val universe: scala.reflect.runtime.universe.type = scala.reflect.runtime.universe
import universe._
import scala.reflect.runtime.{currentMirror => m}
import scala.tools.reflect.ToolBox
val toolbox = m.mkToolBox()

trait Father
class A extends Father {
  println("I'm A")
  val a = 0
}
class B extends Father {
  println("I'm B")
  val b = 0
}

object Produce {
  def A(): A = {
    val weakT = weakTypeOf[A]
    val genTree = q"""
      case class Son() extends $weakT {
        println("I'm alive")
      }
      Son()
      """
    val compiledCode = toolbox.eval(genTree)
    compiledCode.asInstanceOf[A]
  }
  def apply[T <: Father : TypeTag](): T = { //Fixed here
    val weakT = weakTypeOf[T]
    val genTree = q"""
      case class Son() extends $weakT {
        println("I'm alive")
      }
      Son()
      """
    val compiledCode = toolbox.eval(genTree)
    compiledCode.asInstanceOf[T]
  }
}

Produce.A()

Produce[A]()

Produce[B]()

斯卡拉 "reflective toolbox failed due to unresolved free type"

Scala "reflective toolbox failed due to unresolved free type"

scala

scala-quasiquotes