CODEWITHSUNDEEP
scalaclassconstructor
St.Antario
St.Antario

Reputation: 27375

Classes with ValueType parameters

I wrote the following simple program:

object Main extends App {
  println(s"${classOf[MyValueClass].getSimpleName}")
  val pt = classOf[MyClass].getDeclaredConstructors.asInstanceOf[Array[Constructor[MyClass]]].iterator.next.getParameterTypes
  pt.asInstanceOf[Array[Class[_]]] foreach { c =>
    println (c.getSimpleName)
  }
}

case class MyValueClass(v: Int) extends AnyVal

class MyClass(v: MyValueClass)

DEMO

The program prints:

MyValueClass
int

But I expected it would print

MyValueClass
MyValueClass

Why is the parameters of the constructor int, not MyValueClass?

Upvotes: 0

Views: 39

Answers (1)

chengpohi
chengpohi

Reputation: 14217

because MyValueClass is extending AnyVal with only one val Int parameter.

The type at compile time is Wrapper, but at runtime, the representation is an Int http://docs.scala-lang.org/overviews/core/value-classes.html

ByteCode:

scala> :javap -c MyClass
Compiled from "<console>"
public class $line4.$read$$iw$$iw$MyClass {
  public $line4.$read$$iw$$iw$MyClass(int);
    Code:
       0: aload_0
       1: invokespecial #19                 // Method java/lang/Object."<init>":()V
       4: return
}

as you can see the bytecode, the MyClass constructor parameter has been dealt as int primitive type after compiling.

Upvotes: 3

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