Scala: Declaring method with generic type parameter

Question

What is the equivalent of the following Java method declaration in Scala:

public <T>  T readValue(java.lang.String s, java.lang.Class<T> tClass)

In other words, I'd like to declare a method that takes a class of type T, and returns an instance of that type.

Answer 1

• I. Very close to what you want:

   def readValue[T:ClassTag](s:String):T = { val tClass = implicitly[ClassTag[T]].runtimeClass //implementation for different classes. } 

  usage is a bit clearer than in Java:

   val myDouble = readValue[Double]("1.0") 

Answer 2

• II. Another, more involved way, is to externalize implementation of readValue to some user-provided object (type class):

   trait ValueReader[T] { def readValue(s: String): T } def readValue[T: ValueReader](s: String): T = { val reader = implicitly[ValueReader[T]] reader.readValue(s) } implicit val doubleReader = new ValueReader[Double] { def readValue(s:String) = // implementation for Double }