Question

我有一个工具正在尝试构建各种scala集合的子类实例，例如scala.collection.Seq。我事先不知道应该构建什么特定的类，所以我尝试使用反射来获取伴随对象中的apply方法，如下所示（类似于声明List[Int](1, 2, 3)）。

import scala.reflect.runtime.{universe => ru}
import scala.reflect.runtime.universe._

def makeNewInstance[T <: scala.collection.Seq[_]](clazz: Class[T], args: List[_]): T = {
  val clazzMirror: ru.Mirror = ru.runtimeMirror(clazz.getClassLoader)
  val clazzSymbol = clazzMirror.classSymbol(clazz) 
  val companionObject = clazzSymbol.companion.asModule
  val instanceMirror = clazzMirror reflect (clazzMirror reflectModule companionObject).instance
  val typeSignature = instanceMirror.symbol.typeSignature
  val name = "apply"
  val ctor = typeSignature.member(TermName(name)).asMethod
  instanceMirror.reflectMethod(ctor)(args:_*).asInstanceOf[T]
}
makeNewInstance(clazz = classOf[scala.collection.mutable.ListBuffer[Int]], args = List[Int](1,2,3))

尽管如此，我得到以下例外情况。我无法弄清楚我应该传递给apply方法的内容。

java.lang.IllegalArgumentException: argument type mismatch
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaVanillaMethodMirror1.jinvokeraw(JavaMirrors.scala:373)
at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaMethodMirror.jinvoke(JavaMirrors.scala:339)
at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaVanillaMethodMirror.apply(JavaMirrors.scala:355)
at Main$$anon$1.makeNewInstance(test.scala:12)
at Main$$anon$1.<init>(test.scala:15)
at Main$.main(test.scala:1)
at Main.main(test.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:101)
at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:70)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
at scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$$runCompiled(ScriptRunner.scala:175)
at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun$apply$mcZ$sp$1.apply(ScriptRunner.scala:161)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply$mcZ$sp(ScriptRunner.scala:161)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
at scala.tools.nsc.util.package$.trackingThreads(package.scala:43)
at scala.tools.nsc.util.package$.waitingForThreads(package.scala:27)
at scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala:128)
at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:192)
at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:205)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:67)
at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

感谢您提前提供的任何帮助。

Answer 1

我将回答我自己的问题，检查构造函数是否接受varargs：

if (ctor.isVarargs) instanceMirror.reflectMethod(ctor)(args.toList).asInstanceOf[T] else instanceMirror.reflectMethod(ctor)(args:_*).asInstanceOf[T]

感谢一位朋友指出了我正确的方向。

使用scala反射通过apply方法实例化scala集合

1 个答案: