Scala 宏注解 - case class with type parameters

Question

我正在尝试为案例 classes 编写一个简单的宏注释，它向伴随对象添加一个方法。问题是新方法必须考虑带注释的案例 class.

上的类型参数

这是我需要通过的测试

package my.macros

import org.scalatest._

class DefaultApplyTest extends FlatSpec with Matchers {

  @defaultApply case class Generic[A, B](a: A, b: B)

  it should "define defaultApply method in companion object" in {
    assert(Generic.defaultApply("str", 1) == Generic("str", 1))
  }
}

这是我为实现此目的而编写的代码

package my.macros

import scala.reflect.macros._
import scala.language.experimental.macros
import scala.annotation.StaticAnnotation

class defaultApply extends StaticAnnotation {
  def macroTransform(annottees: Any*): Any = macro DefaultApply.impl
}

object DefaultApply {

  def impl(c: blackbox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
    import c.universe._

    def defaultApplyCompanion(classDecl: ClassDef) = {
      val (name, typeParams, valueParams) = try {
        val q"case class ${name: TypeName}[..${typeParams: Seq[TypeDef]}](..${valueParams: Seq[ValDef]}) extends ..$bases { ..$body }" = classDecl
        (name, typeParams, valueParams)
      } catch {
        case e: MatchError =>
          c.warning(c.enclosingPosition, e.toString)
          c.abort(c.enclosingPosition, "Annotation is only supported on case class")
      }

      val applyDef = q"""${name.toTermName}.apply[..$typeParams]"""
      c.warning(c.enclosingPosition, showRaw(applyDef))

      q"""
        object ${name.toTermName} {
          def defaultApply: (..${valueParams.map(_.tpt)}) => $name[..$typeParams] = $applyDef
        }
      """
    }

    def modifiedDeclaration(classDecl: ClassDef) = {
      val compDecl = defaultApplyCompanion(classDecl)

      c.Expr(q"""
        $classDecl
        $compDecl
      """)
    }

    annottees.map(_.tree) match {
      case (classDecl: ClassDef) :: Nil => modifiedDeclaration(classDecl)
      case _ => c.abort(c.enclosingPosition, "Invalid annottee")
    }
  }
}

据我了解，问题是当我尝试将类型参数列表 lift 放入生成的语法树中时，它们不会被识别为与原始树相同的类型参数。

所以我关注的是宏的这一部分

  val applyDef = q"""${name.toTermName}.apply[..$typeParams]"""
  c.warning(c.enclosingPosition, showRaw(applyDef))

原始语法树作为

发出

TypeApply(Select(Ident(TermName("Generic")), TermName("apply")), List(TypeDef(Modifiers(PARAM), TypeName("A"), List(), TypeBoundsTree(EmptyTree, EmptyTree)), TypeDef(Modifiers(PARAM), TypeName("B"), List(), TypeBoundsTree(EmptyTree, EmptyTree))))

但编译器对此不满意

type arguments [<notype>,<notype>] do not conform to method apply's type parameter bounds [A,B]

最终用例是生成可缓存类型的实例 class，它涉及超过 1k 行代码。非参数化版本已经可以工作了，这只是锦上添花。在 scalac 的幕后有一些我不了解但很想了解的东西。非常感谢您花时间阅读本文。

我在 macro paradise 2.1.0

中使用 Scala 2.11.8

Answer 1

问题似乎是您在类型参数的位置使用了类型参数。这似乎可行（我还必须将类型参数添加到 defaultApply 方法声明中）：

  val typeArgs = typeParams.map(_.name)
  val applyDef = q"""${name.toTermName}.apply[..$typeArgs]"""
  c.warning(c.enclosingPosition, showRaw(applyDef))

  q"""
    object ${name.toTermName} {
      def defaultApply[..$typeParams]:
          (..${valueParams.map(_.tpt)}) => $name[..$typeArgs] = $applyDef
    }
  """

Scala 宏注解 - case class with type parameters

Scala macro annotation - case class with type parameters

macros

scala

scala-quasiquotes

scala-2.11

scala-macro-paradise