What is a good way to get a value in a Scala macro?

Question

I have this code:

object M {
  implicit class Obj(str: List[_]) {
    def mm(other: String) = macro Test.impl
  }
}

//macro
//in macro i would get a `str` argument with actual value which pass into Obj
//
object Test {
  def impl(c: Context)(other: c.Expr[String]) = { 
    import c.universe._
    ???
    reify{}
  }
} 

At the moment, I use

c.prefix.tree {
  case ....
}

But is there a better choice available? Because at compile time, I have a full tree for the class and there may be available something like this:

c.prefix.actualType.someMethodForInitialize.str //get `str` from object

Is this possible or are there others?

Example:

List("a", "b", "c") mm "z"

in macro i got a tree:

Apply(Select(Ident(M), newTermName("Obj")),  List(Apply(TypeApply(Select(Select(This(newTypeName("immutable")), scala.collection.immutable.List), newTermName("apply")), List(TypeTree())), List(Literal(Constant("a")), Literal(Constant("b")), Literal(Constant("c"))))))

and an actual type M.Obj is it possible without tree traversal extract a List?

Answer 1

Although this might not answer your question directly but in soon to be released 2.11 you'll be able to use quasiquotes to do all the hard work for you:

 val q"${s: String}" = other.tree

Answer 2

If you're trying to extract the String from other, use

val otherStr: String = other.tree match {
  case Literal(Constant(str: String)) => str
}