Scala Macros: Getting a List of TypeSymbols to be used at runtime

Question

Is there a way to return a `List` of `TypeSymbol`s for each class under a package using macros? What I am trying to achieve is to write a macro that gives out something equivalent to this list: ``` scala> import scala.reflect.runtime.universe._ import scala.reflect.runtime.universe._ scala> case class MyClass1() defined class MyClass1 scala> case class MyClass2() defined class MyClass2 scala> val typeSymbols = List(typeOf[MyClass1].typeSymbol, typeOf[MyClass2].typeSymbol) typeSymbols: List[reflect.runtime.universe.Symbol] = List(class MyClass1, class MyClass2) ``` Here's my setup: I have a package named `foo`, under which these are defined: ``` trait FooTrait case class Bar() extends FooTrait case class Bar() extends FooTrait ``` Here's my macro that gets all type symbols for the classes under foo that extend `FooTrait`: ``` def allTypeSymbols_impl[T: c.WeakTypeTag](c: Context)(packageName: c.Expr[String]) = { import c.universe._ // Get package name from the expression tree val Litera…

Accepted Answer

You have to use `reifyType` to create reflection artifacts in the runtime universe:

```
import scala.language.experimental.macros
import scala.reflect.macros.Context

object PackageMacros {
  def allTypeSymbols[T](packageName: String) = macro allTypeSymbols_impl[T]

def allTypeSymbols_impl[T: c.WeakTypeTag](c: Context)(
    packageName: c.Expr[String]
  ) = {
    import c.universe._

val pkg = packageName.tree match {
      case Literal(Constant(name: String)) => c.mirror.staticPackage(name)
    }

val types = pkg.typeSignature.members.collect {
      case sym: ClassSymbol =>
        c.reifyType(treeBuild.mkRuntimeUniverseRef, EmptyTree, sym.toType)
    }.toList

val listApply = Select(reify(List).tree, newTermName("apply"))

c.Expr[List[Any]](Apply(listApply, types))
  }
}
```

This will give you a list of type tags, not symbols, but you can pretty easily get the symbols, either like this:

```
scala> PackageMacros.allTypeSymbols("foo").map(_.tpe.typeSymbol) foreach println
class Baz$
class Bar
class Baz
trait FooTrait
class Bar$
```

Or in the macro itself.

Scala Macros: Getting a List of TypeSymbols to be used at runtime

Solution

Problem