Instantiating scala collections via their apply method with scala reflection - scala

Question

I have a tool that is trying to build instances of sub-classes of various scala collections, for example scala.collection.Seq. I don't know in advance what specific class should be built, so I am trying to use reflection to get the apply method in the companion object as follows (similar to declaring 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))
Nonetheless, I am getting the following exception. I am unable to figure out what I should be passing into the apply method.
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)
Thank-you for any help you can offer in advance.

Answer 1

I will answer my own question, check if the constructor accepts varargs or not:
if (ctor.isVarargs) instanceMirror.reflectMethod(ctor)(args.toList).asInstanceOf[T]
else instanceMirror.reflectMethod(ctor)(args:_*).asInstanceOf[T]
Thanks to a friend who pointed me in the right direction.