Inspired by travisbrown, I'm trying to use a macro to create some "smart constructors".
Given
package mypkg
sealed trait Hello[A]
case class Ohayo[A,B](a: (A,B)) extends Hello[A]
and
val smartConstructors = FreeMacros.liftConstructors[Hello]
The macro should find all the subclasses of Hello
, look at their constructors, and extract a few elements to populate this tree for the "smart constructor":
q"""
def $methodName[..$typeParams](...$paramLists): $baseType =
$companionSymbol[..$typeArgs](...$argLists)
"""
I hoped to get:
val smartConstructors = new {
def ohayo[A, B](a: (A, B)): Hello[A] = Ohayo[A, B](a)
}
but instead get:
error: type mismatch;
found : (A(in class Ohayo), B(in class Ohayo))
required: ((some other)A(in class Ohayo), (some other)B(in class Ohayo))
val liftedConstructors = FreeMacros.liftConstructors[Hello]
At a glance, the tree looks ok to me:
scala> q" new { ..$wellTyped }"
res1: u.Tree =
{
final class $anon extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
def ohayo[A, B](a: (A, B)): net.arya.constructors.Hello[A] = Ohayo[A, B](a)
};
new $anon()
}
but I guess it invisibly isn't. If I naively try to freshen up the typeParams with info.typeParams.map(p => TypeName(p.name.toString))
, I get "can't splice A as type parameter" when I do the quasiquoting.
Where am I going wrong? Thanks for taking a look.
-Arya
import scala.language.experimental.macros
import scala.reflect.api.Universe
import scala.reflect.macros.whitebox
class FreeMacros(val c: whitebox.Context) {
import c.universe._
import FreeMacros._
def liftedImpl[F[_]](implicit t: c.WeakTypeTag[F[_]]): Tree = {
val atc = t.tpe
val childSymbols: Set[ClassSymbol] = subCaseClassSymbols(c.universe)(atc.typeSymbol.asClass)
val wellTyped = childSymbols.map(ctorsForSymbol(c.universe)(atc)).unzip
q"new { ..${wellTyped} }"
}
}
object FreeMacros {
def liftConstructors[F[_]]: Any = macro FreeMacros.liftedImpl[F]
def smartName(name: String): String = (
name.toList match {
case h :: t => h.toLower :: t
case Nil => Nil
}
).mkString
def subCaseClassSymbols(u: Universe)(root: u.ClassSymbol): Set[u.ClassSymbol] = {
val subclasses = root.knownDirectSubclasses
val cast = subclasses.map(_.asInstanceOf[u.ClassSymbol])
val partitioned = mapped.partition(_.isCaseClass)
partitioned match {
case (caseClasses, regularClasses) => caseClasses ++ regularClasses.flatMap(r => subCaseClassSymbols(u)(r))
}
}
def ctorsForSymbol(u: Universe)(atc: u.Type)(caseClass: u.ClassSymbol): (u.DefDef, u.DefDef) = {
import u._
import internal._
// these didn't help
// def clearTypeSymbol(s: Symbol): TypeSymbol = internal.newTypeSymbol(NoSymbol, s.name.toTypeName, s.pos, if(s.isImplicit)Flag.IMPLICIT else NoFlags)
// def clearTypeSymbol2(s: Symbol): TypeSymbol = internal.newTypeSymbol(NoSymbol, s.name.toTypeName, NoPosition, if(s.isImplicit)Flag.IMPLICIT else NoFlags)
// def clearTypeDef(d: TypeDef): TypeDef = internal.typeDef(clearTypeSymbol(d.symbol))
val companionSymbol: Symbol = caseClass.companion
val info: Type = caseClass.info
val primaryCtor: Symbol = caseClass.primaryConstructor
val method = primaryCtor.asMethod
val typeParams = info.typeParams.map(internal.typeDef(_))
// val typeParams = info.typeParams.map(s => typeDef(newTypeSymbol(NoSymbol, s.name.toTypeName, NoPosition, NoFlags)))
// val typeParams = info.typeParams.map(s => internal.typeDef(clearTypeSymbol2(s)))
val typeArgs = info.typeParams.map(_.name)
val paramLists = method.paramLists.map(_.map(internal.valDef(_)))
val argLists = method.paramLists.map(_.map(_.asTerm.name))
val baseType = info.baseType(atc.typeSymbol)
val List(returnType) = baseType.typeArgs
val methodName = TermName(smartName(caseClass.name.toString))
val wellTyped =
q"""
def $methodName[..$typeParams](...$paramLists): $baseType =
$companionSymbol[..$typeArgs](...$argLists)
"""
wellTyped
}
}
P.S. I have been experimenting with toolbox.untypecheck / typecheck per this article but haven't found a working combination.
you need using
replace
info.typeParams.map(p => TypeName(p.name.toString))
it si my code
using like this