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import language.experimental.macros
import scala.reflect.macros.Context
object Macros {
implicit class ContextExtensions(c: StringContext) {
object q {
def unapply(x: Any): Option[Any] = macro impl
}
}
def impl(c: Context)(x: c.Expr[Any]): c.Expr[Option[Any]] = {
import c.universe._
import Flag._
// parts here will be string literals - static parts of the string interpolation
// e.g. for q"$x, $y" parts will be Literal(Constant("")), Literal(Constant(", ")) and Literal(Constant(""))
val Apply(Select(Select(Apply(_, List(Apply(_, parts))), _), _), _) = c.macroApplication
val nresults = parts.length - 1
def results() =
((1 to (nresults - 1)).toList map (i => Literal(Constant(i)))) :+ // (n - 1) results of type Int
Apply(Ident(TermName("List")), List(Literal(Constant(nresults)))) // and also one result of a different type
def extractorBody() =
if (nresults == 0) Literal(Constant(true))
else if (nresults == 1) Apply(Ident(TermName("Some")), results())
else Apply(Ident(TermName("Some")), List(Apply(Ident(TermName("Tuple" + nresults)), results())))
val name = TermName(java.util.UUID.randomUUID().toString.replace("-", ""))
val mdef = ModuleDef(NoMods, name, Template(List(Select(Ident(TermName("scala")), TypeName("AnyRef"))), emptyValDef, List(
DefDef(Modifiers(), nme.CONSTRUCTOR, List(), List(List()), TypeTree(),
Block(List(pendingSuperCall), Literal(Constant(())))),
DefDef(Modifiers(), TermName("unapply"), List(), List(List(ValDef(Modifiers(PARAM), TermName("x"), Ident(TypeName("Any")), EmptyTree))), TypeTree(),
extractorBody()))))
c.introduceTopLevel(nme.EMPTY_PACKAGE_NAME.toString, mdef)
c.Expr[Option[Any]](Apply(Select(Ident(name), TermName("unapply")), List(x.tree)))
}
}
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