Macro code to build a enum Just a simple prototype, but maybe useful for future. Learn how to build the AST, I first using the reify and the c.universe.showRaw, and using the scalac -Xprint:4 to show how the compiler generate the reifly code. It is nesseary to learn the reflect API in more deep.

EnumsMacro.scala

package wangzx.macros

import scala.language.experimental.macros
import scala.reflect.macros.Context
import java.lang.String
import scala.reflect.api.Symbols

object EnumsMacro {

  def docs[A](obj: A): Map[Int, String] = macro docsMacro[A]

  def docsMacro[A](c: Context)(obj: c.Expr[A]): c.Expr[Map[Int, String]] = {
    import c.universe._
    val m = rootMirror

    val typ = obj.actualType
    
    val fields: Map[String, String] = typ.declarations.filter{ it =>
      (it.typeSignature <:< typeOf[AnyVal]) && it.asTerm.isVal 
    }.toList.map { decl: Symbol =>
      val docs = decl.annotations.filter { ant => 
        ant.tpe.typeSymbol.name.toString == "doc"
      }.map { ant => 
        val Literal(Constant(doc: String)) :: Nil = ant.scalaArgs
        doc
      }
      println(s"${decl.name} ${docs}")
      (decl.name.toString.trim, docs(0))
    }.toMap

    // elem.valField -> elem.doc
    // val expr = reify {
    //   scala.collection.immutable.Map[Int, String](Tuple2(1, "hello"), Tuple2(2, "world"))
    // }

    val mapSymbol = m.staticModule("scala.collection.immutable.Map")
    
    val fieldsAsArgs = fields.map { case (name, doc) =>
      Apply(
          Select(Ident(m.staticModule("scala.Tuple2")), newTermName("apply")),
          List(
            Select(Select(obj.tree, newTermName(name)), newTermName("v")),
            Literal(Constant(doc))))
    }

    //val x = Select(obj.tree, newTermName("Normal"))
    val body = Apply(
      TypeApply(
        Select(build.Ident(mapSymbol), newTermName("apply")),
        List(Ident(m.staticClass("scala.Int")), Ident(m.staticClass("java.lang.String")))),
      fieldsAsArgs.toList)
    val expr2 = c.Expr[scala.collection.immutable.Map[Int, String]](body)

    expr2
  }
}

SpuState.scala

  /**
   * Spu状态
   */
  object SpuState {
    @doc("正常") val Normal  = new SpuState(0)
    @doc("预删除") val PreDelete  = new SpuState(1)
    @doc("删除/废弃") val Abandon  = new SpuState(2)
    
    val docs: Map[Int, String] = EnumsMacro.docs(CommodityModel.SpuState)
  }
  class SpuState(val v: Byte) extends AnyVal