ClassTag

A ClassTag[T] stores the erased class of a given type T, accessible via the runtimeClass field. This is particularly useful for instantiating Arrays whose element types are unknown at compile time.

ClassTags are a weaker special case of scala.reflect.api.TypeTags.TypeTags, in that they wrap only the runtime class of a given type, whereas a TypeTag contains all static type information. That is, ClassTags are constructed from knowing only the top-level class of a type, without necessarily knowing all of its argument types. This runtime information is enough for runtime Array creation.

For example:

scala> def mkArray[T : ClassTag](elems: T*) = Array[T](elems: _*)
mkArray: [T](elems: T*)(implicit evidence$1: scala.reflect.ClassTag[T])Array[T]

scala> mkArray(42, 13)
res0: Array[Int] = Array(42, 13)

scala> mkArray("Japan","Brazil","Germany")
res1: Array[String] = Array(Japan, Brazil, Germany)

See scala.reflect.api.TypeTags for more examples, or the Reflection Guide: TypeTags for more details.