CODEWITHSUNDEEP
scalareflection
Huzhenyu
Huzhenyu

Reputation: 97

How to Reflect Construction Method Based on Method Signature In Scala

class Test(a: String, b: Array[String], c: Array[String]){
  def this(b: Array[String], c: Array[String]) {
    this("1", b, c)
  }

  def this() = {
    this(null, null, null)
  }
}

I have a class Test like above, and I would like use scala reflection to invoke one of them

I try to use the follow code

import scala.reflect.runtime.{universe => ru}
val clsTest = ru.typeOf[Test].typeSymbol.asClass
val cm = m.reflectClass(clsTest)
val ctor =  ru.typeOf[Test].decl(ru.termNames.CONSTRUCTOR).asTerm.alternatives.map(_.asMethod)

but I don't know how to select the method based on method signature. Is there any approach to select the method based on the type signature like java reflect code? Thanks!

I have read the scala doc about reflect, but it don't solve my problem. it has only one constructor method. scala reflect doc

Upvotes: 1

Views: 257

Answers (2)

余杰水
余杰水

Reputation: 1384

// the method as List(list(a,b,c))
// and this is PrimaryConstructor
class Test(a: String, b: Array[String], c: Array[String]) {
  // the method as List(list(b,c))
  def this(b: Array[String], c: Array[String]) {
    this("1", b, c)
  }

  // the method as List(list())
  def this() = {
    this(null, null, null)
  }

  // the method as List(list(a),list(b,c)
  def this(a:String )(b:String,c:String ){
    this(null,null,null)
  }
}

val constructor = typeOf[Test].members
  // filter all constructor
  .filter(e => e.isConstructor).map(e => e.asMethod)
  // find which are you want 
  // edit 1
  .find( e =>{
    val methodParamsType =  e.paramLists.head.map(e =>e.typeSignature)
    // what params  type are you 
    val expectParamsType = List(typeOf[Array[String]],typeOf[Array[String]])

    methodParamsType.length == expectParamsType.length && 
      methodParamsType.zip(expectParamsType).forall{case (l,r)=>l =:= r }
  })
  //   or
  //  .find(e=>e.isPrimaryConstructor)
  //  .find(e=>e.paramLists.head.length == 2)
  .get

Upvotes: 1

Huzhenyu
Huzhenyu

Reputation: 97

I have found a approach to filter by parameter types

  1. methodName: means which method you want to reflect
  2. allScope: true means find from this and super, false means find only from this
  3. types: is the parameter types, you can use Seq(typeOf[T1], typeOf[T2]):_*
  4. x: is the instance which will be reflected

the key is we can get method parameter types by methodSymbol.paramLists.head.map(_.info)

  val ru: scala.reflect.runtime.universe.type = scala.reflect.runtime.universe

  def m: ru.Mirror = {
    ru.runtimeMirror(Thread.currentThread().getContextClassLoader)
  }
//reflect method, method can't be curry
  def reflectMethod[T: ru.TypeTag : ClassTag](methodName: String, allScope: Boolean, types: ru.Type*)(x: T): ru.MethodMirror = {
    val instanceMirror = m.reflect(x)
    val methodSymbols = if (allScope) {
      val members = getTypeTag(x).tpe.member(ru.TermName(methodName))
      if (members.equals(ru.NoSymbol)) {
        throw new NoSuchMethodException(noSuchMethodException(methodName, allScope, types: _*)(x))
      }
      members
        .asTerm
        .alternatives
        .map(_.asMethod)
    } else {
      val decls = getTypeTag(x).tpe.decl(ru.TermName(methodName))
      if (decls.equals(ru.NoSymbol)) {
        throw new NoSuchMethodException(noSuchMethodException(methodName, allScope, types: _*)(x))
      }
      decls
        .asTerm
        .alternatives
        .map(_.asMethod)
    }
    methodSymbols.foreach(item => assert(item.paramLists.size < 2, "we don't support curry method yet"))
    val methodSymbol = methodSymbols.find(item =>
      if (item.paramLists.head.isEmpty) {
        types.isEmpty
      } else {
        if (types.isEmpty) {
          item.paramLists.head.isEmpty
        } else {
          // empty forall is true
          item.paramLists.head.zip(types).forall(pair => pair._1.info =:= pair._2)
        }
      }).getOrElse(throw new NoSuchMethodException(noSuchMethodException(methodName, allScope, types: _*)(x)))

    val methodMirror = instanceMirror.reflectMethod(methodSymbol)
    methodMirror
  }

private def noSuchMethodException[T: ru.TypeTag : ClassTag](methodName: String, allScope: Boolean, types: ru.Type*)(x: T): String = {
    s"no such method: $methodName, allScope: $allScope type: $types in ${getRuntimeClass(x)}"
  }

Upvotes: 1

Related Questions