Scala Macros: Accessing members with quasiquotes - scala

Question

I'm trying to implement an implicit materializer as described here: http://docs.scala-lang.org/overviews/macros/implicits.html
I decided to create a macro that converts a case class from and to a String using quasiquotes for prototyping purposes. For example:
case class User(id: String, name: String)
val foo = User("testid", "foo")
Converting foo to text should result in "testid foo" and vice versa.
Here is the simple trait and its companion object I have created:
trait TextConvertible[T] {
def convertTo(obj: T): String
def convertFrom(text: String): T
}
object TextConvertible {
import language.experimental.macros
import QuasiTest.materializeTextConvertible_impl
implicit def materializeTextConvertible[T]: TextConvertible[T] = macro materializeTextConvertible_impl[T]
}
and here is the macro:
object QuasiTest {
import reflect.macros._
def materializeTextConvertible_impl[T: c.WeakTypeTag](c: Context): c.Expr[TextConvertible[T]] = {
import c.universe._
val tpe = weakTypeOf[T]
val fields = tpe.declarations.collect {
case field if field.isMethod && field.asMethod.isCaseAccessor => field.asMethod.accessed
}
val strConvertTo = fields.map {
field => q"obj.$field"
}.reduce[Tree] {
case (acc, elem) => q"""$acc + " " + $elem"""
}
val strConvertFrom = fields.zipWithIndex map {
case (field, index) => q"splitted($index)"
}
val quasi = q"""
new TextConvertible[$tpe] {
def convertTo(obj: $tpe) = $strConvertTo
def convertFrom(text: String) = {
val splitted = text.split(" ")
new $tpe(..$strConvertFrom)
}
}
"""
c.Expr[TextConvertible[T]](quasi)
}
}
which generates
{
final class $anon extends TextConvertible[User] {
def <init>() = {
super.<init>();
()
};
def convertTo(obj: User) = obj.id.$plus(" ").$plus(obj.name);
def convertFrom(text: String) = {
val splitted = text.split(" ");
new User(splitted(0), splitted(1))
}
};
new $anon()
}
The generated code looks fine, but yet I get the error value id in class User cannot be accessed in User in compilation while trying to use the macro.
I suspect I am using a wrong type for fields. I tried field.asMethod.accessed.name, but it results in def convertTo(obj: User) = obj.id .$plus(" ").$plus(obj.name ); (note the extra spaces after id and name), which naturally results in the error value id is not a member of User.
What am I doing wrong?

Answer 1

Ah, figured it out almost immediately after sending my question.
I changed the lines
val fields = tpe.declarations.collect {
case field if field.isMethod && field.asMethod.isCaseAccessor => field.asMethod.accessed
}
to
val fields = tpe.declarations.collect {
case field if field.isMethod && field.asMethod.isCaseAccessor => field.name
}
which solved the problem.

Answer 2

The field you get with accessed.name has a special suffix attached to it, to avoid naming conflicts.
The special suffix is scala.reflect.api.StandardNames$TermNamesApi.LOCAL_SUFFIX_STRING, which has the value, you guessed it, a space char.
This is quite evil, of course.