Getting object instance by string name in scala - reflection

Question

I need the object (or "singleton object" or "companion object"... anything but the class) defined by a string name. In other words, if I have:
package myPackage
object myObject
...then is there anything like this:
GetSingletonObjectByName("myPackage.myObject") match {
case instance: myPackage.myObject => "instance is what I wanted"
}

Answer 1

In scala 2.10 we can do like this
import scala.reflect.runtime.universe
val runtimeMirror = universe.runtimeMirror(getClass.getClassLoader)
val module = runtimeMirror.staticModule("package.ObjectName")
val obj = runtimeMirror.reflectModule(module)
println(obj.instance)

Answer 2

Scala is still missing a reflection API. You can get the an instance of the companion object by loading the companion object class:
import scala.reflect._
def companion[T](implicit man: Manifest[T]) : T =
man.erasure.getField("MODULE$").get(man.erasure).asInstanceOf[T]
scala> companion[List$].make(3, "s")
res0: List[Any] = List(s, s, s)
To get the untyped companion object you can use the class directly:
import scala.reflect.Manifest
def companionObj[T](implicit man: Manifest[T]) = {
val c = Class.forName(man.erasure.getName + "$")
c.getField("MODULE$").get(c)
}
scala> companionObj[List[Int]].asInstanceOf[List$].make(3, "s")
res0: List[Any] = List(s, s, s)
This depends on the way scala is mapped to java classes.

Answer 3

Adjustment to Thomas Jung's answer above: you would do better to say companion[List.type] because a) this should be a stable way to refer to it, not dependant on the name mangling scheme and b) you get the unerased types.
def singleton[T](implicit man: reflect.Manifest[T]) = {
val name = man.erasure.getName()
assert(name endsWith "$", "Not an object: " + name)
val clazz = java.lang.Class.forName(name)
clazz.getField("MODULE$").get(clazz).asInstanceOf[T]
}
scala> singleton[List.type].make(3, "a")
res0: List[java.lang.String] = List(a, a, a)

Answer 4

Barring reflection tricks, you can't. Note, for instance, how the method companion is defined on Scala 2.8 collections -- it is there so an instance of a class can get the companion object, which is otherwise not possible.

Answer 5

Scala 2:
val runtimeMirror = universe.runtimeMirror(this.getClass.getClassLoader)
val objectClass = Class.forName("org.test.MyObject$")
val moduleSymbol = runtimeMirror.staticModule(objectClass.getName)
val moduleMirror = runtimeMirror.reflectModule(moduleSymbol)
val instance = moduleMirror.instance
Or just use Java API to get the value from the static field:
val instance = objectClass.getField("MODULE$").get(null)
Mind the $ in the object name.