说明问题的示例:
import scala.language.experimental.macros
import scala.reflect.macros.blackbox
object Test {
def foo1[A, B]: Unit = macro impl[A, B]
def foo2[A]: Unit = macro impl[A, Option[Int]]
def impl[A: c.WeakTypeTag, B: c.WeakTypeTag](c: blackbox.Context): c.Expr[Unit] = {
import c.universe._
c.echo(c.enclosingPosition, s"A=${weakTypeOf[A]}, B=${weakTypeOf[B]}")
reify(())
}
}
/*
scala> Test.foo1[Int, Option[Int]]
<console>:12: A=Int, B=Option[Int]
Test.foo1[Int, Option[Int]]
^
scala> Test.foo2[Int]
<console>:12: A=Int, B=Option[A] // <--- Expected: A=Int, B=Option[Int]
Test.foo2[Int]
*/
为什么我们丢失了foo2
中的具体类型?它看起来与foo1
非常相似。
PS:我找到了一个可能不是最好的解决方案:
import scala.language.experimental.macros
import scala.reflect.macros.blackbox
import scala.reflect.runtime.universe.TypeTag
object Test {
def foo1[A, B](implicit bTag: TypeTag[B]): Unit = macro impl[A, B]
def foo2[A](implicit bTag: TypeTag[Option[Int]]): Unit = macro impl[A, Option[Int]]
def impl[A: c.WeakTypeTag, B](c: blackbox.Context)(bTag: c.Expr[TypeTag[B]]): c.Expr[Unit] = {
import c.universe._
c.echo(c.enclosingPosition, s"A=${weakTypeOf[A]}, B=${bTag.actualType.typeArgs.head}")
reify(())
}
}
/*
scala> Test.foo1[Int, Option[Int]]
<console>:12: A=Int, B=Option[Int]
Test.foo1[Int, Option[Int]]
^
scala> Test.foo2[Int]
<console>:12: A=Int, B=Option[Int]
Test.foo2[Int]
*/
但问题的答案对我来说仍然很有趣。
答案 0 :(得分:0)
输入Lambda
def foo2[A]: Unit = macro impl[A, {type A = Option[Int]}]
def impl[A: c.WeakTypeTag, B: c.WeakTypeTag](c: blackbox.Context): c.Expr[Unit] = {
import c.universe._
//Option[Int]
println(c.weakTypeOf[B].members.find(_.isType).get.typeSignature)
reify(())
}