How can I use Scala macros to create an object? - scala

Question

I am trying to create a Scala macro that will generate an object - something like
object SomeEnum {
sealed abstract class Enum(name: String)
case object Option1 extends Enum("option1")
case object Option2 extends Enum("option2")
private val elements: Seq[Enum] = Seq(Option1, Option2)
def apply(code: String): Enum = {
...
}
}
I thought I might be able to create a macro createEnum, so I could just put
createEnum("SomeEnum", "Option1", "Option2") into my code and have it generate. Seems like it's calling out for a macro.
But I must not be understanding macros. I am using Scala 2.11.6, and just to try to get something working, I created the following:
object createEnumObj {
def createEnumImpl(c: scala.reflect.macros.whitebox.Context)(ename: c.Expr[String]): c.universe.ModuleDef = {
import c.universe._
val Literal(Constant(s_ename: String)) = ename.tree
val oname = TermName(s_ename)
val barLine = q"val bar: Int = 5"
q"object $oname { $barLine }"
}
def createEnum(ename: String): Unit = macro createEnumImpl
}
This is in a separate project - everything seems to be compiling for it OK.
If I stick a call to createEnumObj.createEnum into some source and try to compile that, I get a billion lines (give or take a few) of exception output, which seems to repeat something like this:
[error] (main/compile:compile) java.lang.AssertionError: assertion failed:
[error] object foo extends scala.AnyRef {
[error] def <init>() = {
[error] super.<init>();
[error] ()
[error] };
[error] val bar: Int = 5
[error] }
[error] while compiling: /Users/bob/ICL/ironcore-id/src/main/scala/package.scala
[error] during phase: typer
[error] library version: version 2.11.6
[error] compiler version: version 2.11.6
[error] reconstructed args: -Xfuture ...
error]
[error] last tree to typer: term foo
[error] tree position: line 8 of /Users/bob/ICL/ironcore-id/src/main/scala/package.scala
[error] symbol: <none>
[error] symbol definition: <none> (a NoSymbol)
[error] symbol package: <none>
[error] symbol owners:
[error] call site: <none> in <none>
[error]
[error] == Source file context for tree position ==
[error]
[error] 5 type DateTime = Int
[error] 6
[error] 7 createEnumObj.createEnum("foo")
[error] 8
[error] 9 }
[error] Total time: 2 s, completed Jun 18, 2015 2:46:05 PM
What I am trying to do doesn't seem too dissimilar to this question, but I'm obviously missing something. Any ideas about how to accomplish this would be gratefully accepted.
Thanks,
Bob