scala - 使用 Scala 宏在树中查找所有可能的序列创建

Question

我想使用 Scala 宏在树中找到所有可能的序列创建。

val l = List(1, 2)
val v = Vector(1, 2)
val ab = ArrayBuffer(1, 2)
val s = Seq(1, 2)

但是以下匹配不起作用:

case Apply(TypeApply(Select(path, Name("apply")), _), args) if path.tpe <:< weakTypeOf[SeqFactory[Any]] => ...

类似地，我需要按序列上的索引查找所有访问:

val v = Vector(1, 2)
val one = v(0)

或路径上的所有“apply”方法调用，其中 path.tpe <:< ????[Seq[_]

这张支票怎么写？这无法编译:

case Apply(Select(path, Name("apply")), List(idx)) if path.tpe <:< typeOf[Seq[_]]

Answer 1

我不确定您到底尝试过什么，但乍一看，您似乎缺少至少两部分:您需要使用 Traverser要遍历树的所有后代，您需要对每个候选树进行类型检查，以确保它被脱糖到您可以知道您已经有了一个 SeqFactory 的应用程序。

例如，下面是一个快速实现，它在编译时打印类中的所有序列创建树:

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

object SeqSearch {
  def printCreatesInClass = macro printCreatesInClass_impl

  def printCreatesInClass_impl(c: Context) = {
    import c.universe._
    import scala.collection.generic.SeqFactory

    val factorySym = c.typeOf[SeqFactory[Seq]].typeSymbol

    def isCreation(tree: Tree) = c.typeCheck(tree) match {
      case Apply(TypeApply(Select(factory, name), _), _) if
        factory.tpe.baseClasses.contains(factorySym) &&
        name == newTermName("apply") => true
      case _ => false
    }

    object printCreates extends Traverser {
      override def traverse(tree: Tree) = tree match {
        case application @ Apply(_, args) if isCreation(application) =>
          println("Matched create: " + application)
          super.traverseTrees(args)
        case _ => super.traverse(tree)
      }
    }

    printCreates(c.enclosingClass)

    c.literalUnit
  }
}

它的工作原理如下:

scala> class Foo {
     |   SeqSearch.printCreatesInClass
     |   val l = List(1, 2)
     |   val v = Vector(1, 2)
     |   val ab = collection.mutable.ArrayBuffer(1, 2)
     |   val s = Seq(1, 2)
     | }
Matched create: List(1, 2)
Matched create: Vector(1, 2)
Matched create: collection.mutable.ArrayBuffer(1, 2)
Matched create: Seq(1, 2)
defined class Foo

查找访问类似 - 只需将以下方法添加到上面的对象即可:

  def printAccessesInClass = macro printAccessesInClass_impl

  def printAccessesInClass_impl(c: Context) = {
    import c.universe._

    def isAccess(tree: Tree) = c.typeCheck(tree) match {
      case Apply(Select(seq, name), _) if
        seq.tpe <:< typeOf[Seq[Any]] &&
        name == newTermName("apply") => true
      case _ => false
    }

    object printAccesses extends Traverser {
      override def traverse(tree: Tree) = tree match {
        case application @ Apply(_, args) if isAccess(application) =>
          println("Matched access: " + application)
          super.traverseTrees(args)
        case _ => super.traverse(tree)
      }
    }

    printAccesses(c.enclosingClass)

    c.literalUnit
  }

然后:

scala> class Foo {
     |   SeqSearch.printCreatesInClass
     |   SeqSearch.printAccessesInClass
     |   val xs = List(1, 2, 3)
     |   val xh = xs(0)
     | }
Matched create: List(1, 2, 3)
Matched access: xs(0)
defined class Foo

调整 Traverser 的副作用来捕获您感兴趣的任何信息应该非常容易，而不仅仅是在编译时打印树。