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// As per http://meta.plasm.us/posts/2013/08/31/feeding-our-vampires/
import scala.annotation.StaticAnnotation
import scala.reflect.macros.whitebox.Context
import scala.language.experimental.macros
class body(tree: Any) extends StaticAnnotation
object Macros {
def selFieldImpl(c: Context) = {
import c.universe._
val field = c.macroApplication.symbol
val bodyAnn = field.annotations.filter(_.tree.tpe <:< typeOf[body]).head
c.Expr[Any](bodyAnn.tree.children(1))
}
def mkObjectImpl(c: Context)(xs: c.Expr[Any]*) = {
import c.universe._
import Flag._
// val kvps = xs.toList map { case q"${_}(${Literal(Constant(name: String))}).->[${_}]($value)" => name -> value }
val kvps = xs.map(_.tree).toList map { case Apply(TypeApply(Select(Apply(_, List(Literal(Constant(name: String)))), _), _), List(value)) => name -> value }
// val fields = kvps map { case (k, v) => q"@body($v) def ${TermName(k)} = macro Macros.selFieldImpl" }
val fields = kvps map { case (k, v) => DefDef(
Modifiers(MACRO, typeNames.EMPTY, List(Apply(Select(New(Ident(TypeName("body"))), termNames.CONSTRUCTOR), List(v)))),
TermName(k), Nil, Nil, Ident(TypeName("Any")), Select(Ident(TermName("Macros")), TermName("selFieldImpl"))) }
// q"import scala.language.experimental.macros; class Workaround { ..$fields }; new Workaround{}"
c.Expr[Any](Block(
List(
Import(Select(Select(Ident(TermName("scala")), TermName("language")), TermName("experimental")), List(ImportSelector(TermName("macros"), 51, TermName("macros"), 51))),
ClassDef(
NoMods, TypeName("Workaround"), Nil,
Template(
List(Select(Ident(TermName("scala")), TypeName("AnyRef"))), noSelfType,
DefDef(
NoMods, termNames.CONSTRUCTOR, Nil, List(Nil), TypeTree(),
Block(List(Apply(Select(Super(This(typeNames.EMPTY), typeNames.EMPTY), termNames.CONSTRUCTOR), List())), Literal(Constant(()))))
+: fields)),
ClassDef(
Modifiers(FINAL), TypeName("$anon"), Nil,
Template(
List(Ident(TypeName("Workaround"))), noSelfType,
List(
DefDef(
NoMods, termNames.CONSTRUCTOR, Nil, List(Nil), TypeTree(),
Block(List(Apply(Select(Super(This(typeNames.EMPTY), typeNames.EMPTY), termNames.CONSTRUCTOR), List())), Literal(Constant(())))))))),
Apply(Select(New(Ident(TypeName("$anon"))), termNames.CONSTRUCTOR), List())))
}
}
object mkObject {
def apply(xs: Any*): Any = macro Macros.mkObjectImpl
}
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