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为什么反射的setter不改变对象的字段值?

reflection scala

Greg · 技术社区 · 6 年前

我的示例类:

class Thing() {

  // Public vars
  var one: Int = 1
  var two: Int = 2

  // Scala-style getter/setter
  private var _age: Long = 3
  def age: Long = _age 
  def age_=(a: Long) = _age = a

  override def toString(): String = s"one: $one, two: $two, age: $age"
}

// A name -> setter holder class
case class Member(name:String, setter: MethodSymbol)

现在我的反射代码和setter调用程序:

  def analyze[T](classSymbol: ClassSymbol)(implicit tt:TypeTag[T]): List[Member] = {
    val tpe = tt.tpe
    val classMirror = currentMirror.reflectClass(classSymbol)

    tpe.members.filter(p => p.isPublic).collect {
      // Ignore the non-methods and methods we don't care about
      case (p) if (p.isMethod && tpe.member(TermName(p.name.toString + "_$eq")) != NoSymbol) =>
        val setter =
            // 1) Scala-stype getters/setters
            tpe.members.filter(f => f.name.toString == p.name.toString + "_" && f.isMethod).headOption.map(_.asMethod)
              // 2) Public var (no getter/setter)
              .orElse(tpe.members.filter(f => f.name.toString == p.name.toString).headOption.map(_.asMethod))
        Member(p.name.toString,setter.get)
    }.toList
  }

  def setValue[T](t:T, members: List[Member], field: String, value: Any)(implicit tt:TypeTag[T]) = {
    implicit val classTag = ClassTag[T](typeTag[T].mirror.runtimeClass(typeTag[T].tpe))
    members.find(_.name == field).map{ m =>
      println("--> Setting field "+m.name+" to "+value)
      currentMirror.reflect(t).reflectMethod(m.setter)(value)
    }
  }

最后我尝试使用:

  val obj = new Thing()
  println("Before: "+obj)

  val members = analyze[Thing](currentMirror.classSymbol(obj.getClass()))
  println(members.mkString("\n"))

  // Now set some value on a public var
  setValue[Thing](obj, members, "one", 99)
  println("After: "+obj)

输出显示:

Before: one: 1, two: 2, age: 3
Member(age,method age)
Member(two,variable two)
Member(one,variable one)
--> Setting field one to 99
After: one: 1, two: 2, age: 3

如您所见,反射正确地区分了getter/setter字段和公共var字段。在尝试设置时,它找到了字段并调用setter,但没有抛出异常,但是…对象中没有实际更改的值(getter/setter字段或var字段都是这样)。为什么我看不到价值观的改变?

0 回复 | 直到 6 年前

Greg 6 年前

找到它…以防帮助他人。

我在过滤错误的东西。scala中的setter的名称格式类似于“foo_u$eq”,因此我必须查找该模式。当调用这些方法时,实例类中的值将按预期更改。修订后的反射代码如下:

  def analyze[T](classSymbol: ClassSymbol, isGetterSetter:Boolean = false)(implicit tt:TypeTag[T]): List[Member] = {
    val tpe = tt.tpe
    val Pattern = """(.*)_\$eq""".r

    tpe.members.filter(p => p.isPublic).collect {
      case p if (p.isMethod && p.name.toString.endsWith("_$eq")) =>
        val Pattern(name) = p.name.toString
        val setter =
            // 1) Scala-stype getters/setters
            tpe.members.filter(f => f.name.toString == p.name.toString + "_" && f.isMethod).headOption.map(_.asMethod)
              // 2) Public var (no getter/setter)
              .orElse(tpe.members.filter(f => f.name.toString == p.name.toString).headOption.map(_.asMethod))
        Member(name,setter.get)
    }.toList
  }