CODEWITHSUNDEEP
scalascala-reflect
siledh
siledh

Reputation: 3378

Scala equivalent of Java `Class` class?

In Java, there is a Class<T> class that represents, well, classes. It's useful when you need to do some class checks dynamically at runtime, for example, if some interface can accept varied number of arguments and it expects the arguments to have specific types: then the interface can return a list of Class objects to specify its requirements.

Apparently, it's available in Scala as well, but just as an alias to the Java class). Is it OK to use this in Scala (or in general, the Class class, in pure Scala code), or would there be a more idiomatic way to achieve the same thing there?

For more context, this is what I'm thinking of:

trait BuiltInFunction[Node] {
  def symbol: String
  def arity: Int
  def argumentTypes: List[Class[Node]]
  def apply(args: List[Node]): Node
}

BuiltInFunction represents functions that each can have different number of arguments and expect the arguments to be different subtypes of Node. If the system encounters a function, it will make sure that it's applied to arguments of proper types (as defined by argumentTypes) by calling the apply method with those arguments.

Is using Class the right way to do it in Scala?

Upvotes: 1

Views: 90

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170839

If you don't need Scala-specific details (differentiating between properties and methods, implicits, etc.) using Class is perfectly fine; if it wasn't, it wouldn't be available in scala.Predef as an alias!

If you do, there is Scala reflection but to be honest, in my experience it's harder to use than the Java Class-based reflection. If you can use both I'd prefer Class.

OTOH:

  1. List[Class[Node]] is not correct if you

    expect the arguments to be different subtypes of Node

    It should be List[Class[_ <: Node]] instead.

  2. Class only reflects classes after erasure, e.g. classOf[List[String]] and classOf[List[Int]] are the same. If you need to differentiate them Class won't be enough.

Upvotes: 4

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