How to list annotations (custom java ones and others) on field members of Scala case class - scala

Question

So I'm trying to list fields with specific annotation in a Scala case class and I'm not able to get it working... Let's see come code right away
The case class (it's a simplified version of it, mine extends another class and is also nested in my test class where I use it for unit testing only):
case class Foo(#Unique var str: String) {}
The custom Java annotation:
#Retention(RetentionPolicy.RUNTIME)
#Target({ElementType.FIELD, ElementType.PARAMETER})
public #interface Unique {}
And my class (simplified again) where I'm trying to do some stuffs with fields marked as unique
class SomeClass[T] (implicit typeTag: TypeTag[T]) {
val fields: Iterable[universe.TermSymbol] = typeOf(typeTag).members.collect { case s: TermSymbol => s }.
filter(s => s.isVal || s.isVar)
val list = fields.flatMap(f => f.annotations.find(_.tpe =:= TypeOf[Unique]).((f, _))).toList
}
But the val list in the last peace of code is always empty... fields has str listed in but without the annotation.
What am I missing?
The code listing the annotations is from the following answer:
How to list all fields with a custom annotation using Scala's reflection at runtime?

Answer 1

Seems the reference post is Scala 2.10 is old and is not compatible with the newest Scala version.
There is an example for how to get the specify annotation by type.
def listProperties[T: TypeTag]: List[universe.Annotation] = {
typeOf[T].typeSymbol.asClass
.asClass
.primaryConstructor
.typeSignature
.paramLists.flatten.flatMap(_.annotations)
}
val annotations = listProperties[Foo].filter(_.tree.tpe =:= typeOf[Unique])
println(annotations)
and there is way to get the annotation's field value:
case class Foo(#Unique(field = "bar") val str: String) {}
import scala.reflect.runtime.currentMirror
import scala.tools.reflect.ToolBox
val tb = currentMirror.mkToolBox()
val result = tb.eval(tb.untypecheck(head.tree)).asInstanceOf[Unique]
and need to call out your annotation class is implemented by using Java style, In Scala maybe you want to use StaticAnnotation for creating Annotation, like:
class Unique extends StaticAnnotation