Finding the actual type in macro - scala

Question

I am trying to write a macro that extracts the type information. Here is a minimized version.
class Extractor[E] {
def extract(entity: E): Unit = macro ExtractorImpl.extractImpl[E]
}
object ExtractorImpl {
def extractImpl[E: c.WeakTypeTag](c: Context)(entity: c.Expr[E]): c.Tree = {
import c.universe._
val actualType = implicitly[WeakTypeTag[E]].tpe
c.info(c.enclosingPosition, actualType.toString, true)
q"{}"
}
}
Here is a typical implementation of Extractor:
case class Person(name: String)
object PersonExtractor extends Extractor[Person]
If I use this class directly as in PersonExtractor.extract(new Person("test name")), I get Person printed as info. But, if I use it indirectly as follows, it prints only E:
class Mapper[E](extractor: Extractor[E]) {
def extract(e: E) = extractor.extract(e)
}
class PersonMapper extends Mapper[Person](new Extractor[Person])
class Test {
new PersonMapper().extract(new Person("test name"))
}
How do I go about getting the Person type available as actualType?

Answer 1

use implicit macro
trait Extractor[E] {
def extract(entity: E): Unit
}
object Extractor {
implicit def i[E] : Extractor[E] = macro ExtractorImpl.extractImpl[E]
}
object ExtractorImpl {
def extractImpl[E: c.WeakTypeTag](c: Context):c.Tree = {
import c.universe._
val actualType = c.weakTypeOf[E]
c.info(c.enclosingPosition, actualType.toString, false)
q"""
new Extractor[$actualType]{
def extract(entity: $actualType): Unit = println("hello world")
}
"""
}
}
// test
case class Person(name: String)
//object PersonExtractor extends Extractor[Person]
class Mapper[E] {
def extract(e: E)(implicit extractor: Extractor[E]) = extractor.extract(e)
}
class PersonMapper extends Mapper[Person]
class Test {
new PersonMapper().extract(new Person("test name")) // show info:Person
}
Edit:
//test2
class Mapper2[E](extractor: Extractor[E]) {
def extract(e: E) = extractor.extract(e)
}
object Mapper2 extends Mapper2[Person](Extractor.i[Person])//also show info:Person